Record each file's size on disk and print it in trees (closes #147)

The files table gets a disk_size column: the file's allocated blocks,
st_blocks × 512, from the lstat the walk already does. scan writes it
with every record it writes. When a rescan finds a file with its size
and mtime unchanged but a different disk_size, it updates disk_size
alone, without reading the file. trees adds disk_size up per directory
and prints it as a column after size. On a compressed or sparse file it
is less than size, so two copies of one tree can differ.

Judgement calls: each row's disk_size is the dupe copy's, not the
first's. A file whose record gets only a new disk_size counts as
unchanged.

Model: opus-5-5

README.md

@@ -33,14 +33,14 @@ export SFDUPES_DATABASE="$HOME/.local/share/sfdupes/db.sqlite"
 ```
 
 `scan` walks one or more filesystem trees and maintains one database record per
-regular file (path, size, mtime, head hash, tail hash, content hash). The
-database persists between runs. A rescan hashes only the files that are new or
-changed, and removes the records of files that no longer exist. `report` reads
-the database and prints the file-level duplicates report. `trees` reads the same
-database and prints the duplicate-tree report. `info` prints the database's
-details: its path, the sizes of its files and the number of its records. A
-missing/invalid subcommand — or a `scan` invocation with no `PATH` operand —
-prints a usage message and exits 2.
+regular file (path, size, size on disk, mtime, head hash, tail hash, content
+hash). The database persists between runs. A rescan hashes only the files that
+are new or changed, and removes the records of files that no longer exist.
+`report` reads the database and prints the file-level duplicates report. `trees`
+reads the same database and prints the duplicate-tree report. `info` prints the
+database's details: its path, the sizes of its files and the number of its
+records. A missing/invalid subcommand — or a `scan` invocation with no `PATH`
+operand — prints a usage message and exits 2.
 
 The database defaults to `/var/lib/sfdupes/db.sqlite` and can be placed anywhere
 by setting `SFDUPES_DATABASE`. The intended deployment is a daily `sfdupes scan`
@@ -226,12 +226,12 @@ Goals, in order:
     its ends and at 1 MiB per gigabyte (see "Duplicate detection" below).
     Therefore no file of 100 MiB or more is read in full. Scale target: tens of
     millions of files, ~150 TB filesystem, possibly slow or busy disks (ZFS pool
-    under resilver). Holding one small record (path, size, mtime) per file in
-    memory during a scan is acceptable; holding every file's hashes is not (they
-    stay in the database). The reporting commands do not hold every file's
-    hashes either: `report` reads the records in signature order and holds the
-    duplicate paths of one size at a time, so its memory grows with the
-    duplicates of the size that has the most of them, and `trees` reads the
+    under resilver). Holding one small record (path, size, size on disk, mtime)
+    per file in memory during a scan is acceptable; holding every file's hashes
+    is not (they stay in the database). The reporting commands do not hold every
+    file's hashes either: `report` reads the records in signature order and
+    holds the duplicate paths of one size at a time, so its memory grows with
+    the duplicates of the size that has the most of them, and `trees` reads the
     records in path order and keeps each directory's path, digest and totals,
     plus the hashes of only the files in the directories holding the record
     being read, so its memory grows with the number of directories and with the
@@ -368,7 +368,8 @@ All four subcommands operate on a single SQLite database file:
     - While it loads the existing records (`load`) and walks: no records. A
       first scan's database holds none, however long its walk has run.
     - During the hash phase: the first records, committed 10,000 at a time.
-    - In the update phase: the rest of the hashed records, and the deletions.
+    - In the update phase: the rest of the hashed records, the new `disk_size`
+      of unchanged files whose size on disk changed, and the deletions.
     - At the end, as it closes the database: the `-wal` and `-shm` files go
       away, unless a report still has the database open (see above).
 - `report`, `trees` and `info` open the database read-only and need only read
@@ -386,6 +387,7 @@ All four subcommands operate on a single SQLite database file:
     CREATE TABLE files (
         path       BLOB PRIMARY KEY,  -- absolute path, raw bytes
         size       INTEGER NOT NULL,  -- bytes, from lstat
+        disk_size  INTEGER NOT NULL,  -- bytes allocated on disk (st_blocks × 512), from lstat
         mtime      INTEGER NOT NULL,  -- whole Unix seconds of the mtime, from lstat
         mtime_nsec INTEGER NOT NULL,  -- nanoseconds within that second, 0 to 999999999
         head       BLOB NOT NULL,     -- raw 32-byte SHA-256 of the first 64 KiB
@@ -393,6 +395,20 @@ All four subcommands operate on a single SQLite database file:
         content    BLOB NOT NULL      -- raw 32-byte SHA-256; whole file under 100 MiB, else samples
     ) WITHOUT ROWID;
     CREATE INDEX files_signature ON files (size, head, tail, content);
+    CREATE TABLE totals (
+        records INTEGER NOT NULL,  -- number of records in files
+        size    INTEGER NOT NULL   -- sizes of all records in files added up
+    );
+    INSERT INTO totals (records, size) VALUES (0, 0);
+    CREATE TRIGGER totals_after_insert AFTER INSERT ON files BEGIN
+        UPDATE totals SET records = records + 1, size = size + NEW.size;
+    END;
+    CREATE TRIGGER totals_after_delete AFTER DELETE ON files BEGIN
+        UPDATE totals SET records = records - 1, size = size - OLD.size;
+    END;
+    CREATE TRIGGER totals_after_update AFTER UPDATE OF size ON files BEGIN
+        UPDATE totals SET size = size + NEW.size - OLD.size;
+    END;
     ```
 
     Paths are stored as BLOBs because Unix paths are raw bytes, not guaranteed
@@ -406,6 +422,17 @@ All four subcommands operate on a single SQLite database file:
     `files_signature` index lets `report` read the records in signature order
     without sorting the table.
 
+    `totals` holds one row: the number of records in `files` and the sum of
+    their sizes. Three triggers on `files` keep that row current. Each runs in
+    the transaction of the change to `files` that fires it, so the row and the
+    records always agree. `info` reads both numbers from this row. `scan`,
+    `report` and `trees` read the number of records from it as the total of
+    their progress displays. Counting the records in `files` would read every
+    record, which takes minutes on a database of tens of millions. The triggers
+    make each write to `files` slower, so a first scan of many small files takes
+    about two fifths longer. On large files, where reading them takes most of
+    the time, the difference is small.
+
 ### Duplicate detection
 
 Two files are duplicates when they have the same size and the same three hashes.
@@ -461,17 +488,26 @@ exclude, is not on a persistent filesystem (see "Rules for the walk"), or, with
 `-x`, is on a different filesystem than that operand, because that operand's
 walk does not enter such a directory and so does not reach it.
 
-An operand that is a symlink (never followed, not even as an operand), socket,
-FIFO, or device node, or a directory named `.zfs`, is not scanned. `scan` prints
-a one-line warning naming the path and what it is, counts it as skipped, and
-drops it from the scanned operands before reading the database. Another operand
-beneath it is still scanned. The records stored beneath it are not deleted: they
-are treated like any other record outside the scanned operands. If it lies under
-another operand, they are under that operand instead, and are treated like any
-other record there. This is not an error: a scan whose every operand is dropped
-walks nothing and exits 0. An operand that is not on a persistent filesystem
-(see "Rules for the walk") is dropped the same way. The line `scan` prints for
-it is not a warning, though, and it is not counted as skipped.
+An operand is not scanned when it is:
+
+- a symlink, which `scan` never follows, not even as an operand;
+- a socket, FIFO or device node;
+- at or inside a directory named `.zfs`.
+
+An operand reached through a symlink into a `.zfs` directory is not scanned
+either.
+
+This holds even when the operand lies under another operand. `scan` prints a
+one-line warning naming the path and what it is, counts it as skipped, and drops
+it from the scanned operands before reading the database. An operand beneath a
+symlink operand is still scanned. The records stored beneath the dropped operand
+are not deleted: they are treated like any other record outside the scanned
+operands. If it lies under another operand, they are under that operand instead,
+and are treated like any other record there. This is not an error: a scan whose
+every operand is dropped walks nothing and exits 0. An operand that is not on a
+persistent filesystem (see "Rules for the walk") is dropped the same way. The
+line `scan` prints for it is not a warning, though, and it is not counted as
+skipped.
 
 `scan` synchronizes the database with the filesystem state under the scanned
 operands:
@@ -480,6 +516,11 @@ operands:
 - A file already in the database is **skipped without reading its contents**
   when its lstat size equals the recorded size and its lstat mtime is not newer
   than the recorded mtime. This is what makes a daily rescan cheap.
+- When such a file's size on disk differs from the recorded `disk_size`, the
+  scan updates `disk_size` alone. It still does not read the file, and counts it
+  as unchanged. ZFS, for example, counts a new file's blocks only seconds after
+  the write. A file scanned within those seconds gets its real `disk_size` at
+  the next scan.
 - A file whose mtime is newer than recorded, or whose size differs, is hashed
   again. Change detection compares the mtime to the nanosecond, as finely as the
   filesystem records it, so a same-size rewrite counts as a change whenever the
@@ -507,8 +548,8 @@ inside the walk and hash phases, and batched database writes begin during the
 hash phase:
 
 1.  **load** — read the existing records. Each record under the operands is kept
-    in memory, by path, with its size and its mtime, for the walk to compare
-    each file with.
+    in memory, by path, with its size, its size on disk and its mtime, for the
+    walk to compare each file with.
 2.  **walk + stat** — enumerate the trees under all `PATH` operands concurrently
     with the walk worker pool: every operand seeds the shared queue, and each
     worker reads one directory at a time, handing discovered subdirectories back
@@ -516,9 +557,10 @@ hash phase:
     (while the directory's metadata is still hot). Sequential directory
     enumeration is metadata-latency-bound and takes hours at tens of millions of
     files; per-directory parallelism is what makes the walk tractable on large
-    or busy pools. The walk compares each file with its record as it goes, and
-    an unchanged file needs nothing more. Every new or changed file is carried
-    to the hash phase as a (path, size, mtime) record.
+    or busy pools. The walk compares each file with its record as it goes. An
+    unchanged file is not read again. When its size on disk has changed, the
+    update phase writes its new `disk_size`. Every new or changed file is
+    carried to the hash phase as a (path, size, size on disk, mtime) record.
 3.  **hash** — the worker pool hashes every carried file as described in
     "Duplicate detection" above, which gives the file its `head`, `tail` and
     `content`. Zero-length files have constant hashes and are never opened.
@@ -530,7 +572,8 @@ hash phase:
     committed in batched transactions **while hashing runs**. A scan interrupted
     after hours therefore keeps everything hashed so far, and the next scan
     resumes cheaply, skipping records already written.
-4.  **update** — commit the final partial batch of hashed records. Then delete
+4.  **update** — commit the final partial batch of hashed records, and the new
+    `disk_size` of each unchanged file whose size on disk changed. Then delete
     the records the scan did not verify: those of vanished files, and of paths
     that failed to stat or hash.
 
@@ -679,14 +722,18 @@ Processing:
   database state.
 
 `report` runs in two phases, each with its own progress display on stderr (see
-"Progress"): `open` opens the database; `read` counts the records, then reads
-them in signature order, largest size first. That is the order of the
-`files_signature` index read backwards, so SQLite sorts nothing and returns the
-first record at once. The records sharing a signature come together, and so do
-the records of one size, so `report` holds only the duplicate groups of the size
-it is reading, and writes them, ordered by `first` path, once it reaches a
-smaller size. Its memory holds at most the duplicate paths of one size at a
-time, never every record.
+"Progress"):
+
+- `open` opens the database.
+- `read` gets the number of records from `totals`, then reads the records in
+  signature order, largest size first.
+
+Signature order, largest size first, is the `files_signature` index read
+backwards, so SQLite sorts nothing and returns the first record at once. The
+records sharing a signature come together, and so do the records of one size, so
+`report` holds only the duplicate groups of the size it is reading, and writes
+them, ordered by `first` path, once it reaches a smaller size. Its memory holds
+at most the duplicate paths of one size at a time, never every record.
 
 #### Report output format
 
@@ -760,22 +807,37 @@ Processing:
   ascending. Output must be fully deterministic for a given input.
 
 `trees` runs in four phases, each with its own progress display on stderr (see
-"Progress"): `open` opens the database; `read` counts the records, then reads
-them in path order, building the hierarchy and computing the digests as it goes;
-`group` groups the directories by digest and picks the maximal groups; `write`
-writes the groups to stdout.
+"Progress"):
+
+- `open` opens the database.
+- `read` gets the number of records from `totals`, then reads the records in
+  path order, building the hierarchy and computing the digests as it goes.
+- `group` groups the directories by digest and picks the maximal groups.
+- `write` writes the groups to stdout.
 
 #### Trees output format
 
 TSV on stdout: a header line, then one row per duplicate tree (N-1 rows for a
-group of N). `files` is the recursive regular-file count of one copy of the
-tree; `size` is the recursive total byte size of one copy:
+group of N). After the `first` and `dupe` paths come three numbers:
+
+- `files`, the number of regular files in one copy of the tree, counted
+  recursively;
+- `size`, the bytes of one copy, its files' sizes added up;
+- `disk_size`, the bytes the `dupe` copy takes on disk, its files' `disk_size`
+  added up.
 
 ```
-first	dupe	files	size
-/srv/a/project	/srv/backup/project	3417	104857600
+first	dupe	files	size	disk_size
+/srv/a/project	/srv/backup/project	3417	104857600	61865984
 ```
 
+A file's `disk_size` is the space its blocks take on disk. It can be more than
+the file's size, because space is allocated in whole blocks. It is less than the
+file's size on a compressed or sparse file, so two copies of one tree can differ
+in `disk_size`. When a file in one copy is a hard link to one in the other, both
+copies count its blocks in full. Removing it from one copy then frees nothing,
+as the known limitation under "`trees` mode" says.
+
 The `first` and `dupe` paths are escaped as described under "Report output
 format". The root directory's path is `/`.
 
@@ -810,15 +872,19 @@ size of recorded files	150000000000000 (136.4 TiB)
   database is in WAL mode, the newest changes may be in the `-wal` file alone.
 - `schema version` is the database's `PRAGMA user_version`. A database with
   another version than this build's is refused, as by `report`.
-- `records` is the number of records. `size of recorded files` adds up the sizes
-  of all records, in bytes, then in human units.
+- `records` is the number of records. `size of recorded files` is the sum of the
+  sizes of all records, in bytes, then in human units.
 
 `info` runs in two phases, each with its own progress display on stderr (see
-"Progress"): `open` opens the database; `count` reads the schema version and
-counts the records with one query, a single pass over the table, both in one
-read-only transaction, so the numbers agree with each other while a scan is
-committing. `info` writes its lines once the `count` display has ended, so on a
-terminal they come after the displays.
+"Progress"):
+
+- `open` opens the database.
+- `count` reads the schema version and the row of `totals` (see "Database").
+  Both reads run in one read-only transaction, so the numbers agree with each
+  other while a scan is committing.
+
+`info` writes its lines once the `count` display has ended, so on a terminal
+they come after the displays.
 
 ### Progress
 
@@ -834,8 +900,9 @@ progress, its elapsed time and its time remaining.
 A scan has four phases (`[1/4] load`, `[2/4] walk`, `[3/4] hash`,
 `[4/4] update`):
 
-- `load` counts the records first, then reads them against that count. While the
-  count runs, the display says it is counting the records.
+- `load` gets the number of records from `totals` first, then reads the records
+  against that number. Until it has the number, the display says it is counting
+  the records.
 - `walk` has no exact total. Its estimate is the number of records the last scan
   left under the operands, known once `load` is done and shown with a `~`. The
   time remaining is unknown once the walk passes the estimate, and when there
@@ -848,8 +915,9 @@ A scan has four phases (`[1/4] load`, `[2/4] walk`, `[3/4] hash`,
 
 - `open` has no total. While it opens the database, waiting on a busy one
   included, the display says it is opening the database.
-- `read` counts the records first, then reads them against that count. While the
-  count runs, the display says it is counting the records.
+- `read` gets the number of records from `totals` first, then reads the records
+  against that number. Until it has the number, the display says it is counting
+  the records.
 - `group` has the directories `read` found as its total, and `write` the
   duplicate-tree groups.
 
@@ -857,17 +925,16 @@ A scan has four phases (`[1/4] load`, `[2/4] walk`, `[3/4] hash`,
 
 - `open` has no total. While it opens the database, waiting on a busy one
   included, the display says it is opening the database.
-- `read` counts the records first, then reads them against that count, writing
-  the rows to stdout as it goes. While the count runs, the display says it is
-  counting the records.
+- `read` gets the number of records from `totals` first, then reads the records
+  against that number, writing the rows to stdout as it goes. Until it has the
+  number, the display says it is counting the records.
 
 `info` has two phases (`[1/2] open`, `[2/2] count`, see "`info` mode"):
 
 - `open` has no total. While it opens the database, waiting on a busy one
   included, the display says it is opening the database.
-- `count` has no total either, because one query counts everything: the display
-  says it is counting the records until the query returns, and its time
-  remaining is unknown.
+- `count` has no total either, because it reads one row: the display says it is
+  counting the records until it has the row, and its time remaining is unknown.
 
 Each display is one line holding:
 
@@ -1154,9 +1221,9 @@ All of the following, run in this directory, must pass:
     ordered by size descending.
 
     Expected from `trees`: exactly one row — `first` `$d/t1`, `dupe` `$d/t2`, 2
-    files, 3100 bytes. `$d/t1/sub` vs `$d/t2/sub` is suppressed as non-maximal
-    (implied by the `t1`/`t2` group), and `t3` appears nowhere (its file set
-    differs by name).
+    files, 3100 bytes, and a `disk_size` that depends on the filesystem.
+    `$d/t1/sub` vs `$d/t2/sub` is suppressed as non-maximal (implied by the
+    `t1`/`t2` group), and `t3` appears nowhere (its file set differs by name).
 
     Expected from the second `report` (after the modify/delete rescan):
     `one.bin` has left its group (its content changed), so

TODO.md

@@ -1,47 +1,55 @@
 # Workflow
 
-- Take an issue from the `1.0.0` milestone on the tracker. Work that is not on
-  the tracker yet is filed as an issue first.
-- Branch from `next`.
-- Do the work, with tests, in small focused commits.
-- Record the step at the top of Completed Steps, in the same commit as the work.
-- Push the branch and open a PR against `next`. Its title ends with
-  ` (closes #N)`.
-- An independent review gates each merge to `next`. Every finding is addressed
-  or rebutted on the PR.
-- Only the owner merges `next` into `main`.
+- take an issue from the `1.0.0` milestone on the tracker; work not yet on the
+  tracker gets filed as an issue first
+- branch from `next`
+- do the work, with tests, in small focused commits
+- record it at the top of Completed Steps (`TODO.md` changes in the same commit
+  as the work)
+- push the branch and open a PR against `next` whose title ends with
+  ` (closes #N)`
+- an independent review gates each merge to `next`; every finding is addressed
+  or explicitly rebutted on the PR
+- only the owner merges `next` to `main`
 
 # Status
 
-- Pre-1.0.
-- The tracker is authoritative for the pre-1.0 backlog. The open issues under
-  the `1.0.0` milestone are what remains before the tag. This file records
-  history and process, not the queue.
+- pre-1.0
+- the Gitea tracker is authoritative for the pre-1.0 backlog: the open issues
+  under the `1.0.0` milestone are what remains before the tag, and this file
+  records history and process, not the queue
 
 # Next Step
 
-- Take the next issue from the `1.0.0` milestone:
-  https://git.eeqj.de/sneak/sfdupes/milestone/17. The issues are not restated
-  here, because a copy drifts as soon as the tracker moves.
+- take the next issue from the `1.0.0` milestone on the tracker:
+  https://git.eeqj.de/sneak/sfdupes/milestone/17 — the milestone is the source
+  of truth for what is left before 1.0.0. Individual issues are deliberately not
+  restated here; a copy in this file drifts out of date the moment the tracker
+  moves
 
 # Completed Steps
 
-Newest first. An entry ends with its date and its issue or branch, where those
-are known.
+- each record holds `disk_size`, the bytes the file takes on disk: its allocated
+  blocks, `st_blocks` × 512, from the lstat the walk already does. `trees`
+  prints a `disk_size` column after `size`, the sum over the `dupe` copy's
+  files; on a compressed or sparse file it differs from `size`. A rescan updates
+  the `disk_size` of an unchanged file whose size on disk changed, without
+  reading the file (2026-10-27, https://git.eeqj.de/sneak/sfdupes/issues/147)
 
-- `TODO.md` rewritten from scratch by the same rules as `README.md`: short
-  sentences, lists as bullets, nothing a newcomer reads twice. Every completed
-  step is kept, with its date and its issue or branch. The policy-compliance
-  checklist of 2026-07-22 is folded into its step (2026-10-26,
-  https://git.eeqj.de/sneak/sfdupes/issues/135)
+- the database keeps the number of records and the sum of their sizes in the one
+  row of a `totals` table, which three triggers on `files` keep current. `info`
+  reads that row, and so do `scan`'s `load` phase and the `read` phases of
+  `report` and `trees` for their totals; no count reads every record any more.
+  The triggers make each write to `files` slower. `scan` keeps SQLite's
+  temporary data in memory, which wins back part of that time (2026-10-27,
+  https://git.eeqj.de/sneak/sfdupes/issues/146)
 
-- `README.md` rewritten from scratch, sentence by sentence, as a newcomer reads
-  it. It leads with what the program is and how to use it. A reference section
-  covers the settings, the database, the output formats and the exit codes;
-  development and testing come last. Every statement was checked against the
-  code on `next` (2026-10-26, https://git.eeqj.de/sneak/sfdupes/issues/135)
+- an operand at or inside a directory named `.zfs` is never scanned, whether
+  given alone or under another operand. `scan` warns about it, counts it as
+  skipped and does not walk it (2026-10-26,
+  https://git.eeqj.de/sneak/sfdupes/issues/142)
 
-- A file or directory removed while the scan runs is not an error, in the walk
+- a file or directory removed while the scan runs is not an error, in the walk
   or in the hash phase. The scan prints no line for it and does not count it as
   skipped. When the first of several hard links to a file is gone, the hash
   phase reads the next one instead. On a terminal every progress display starts
@@ -51,236 +59,218 @@ are known.
   terminal now loses its rate before its bar. The time remaining is labelled
   `remain`, not `eta` (2026-10-26, https://git.eeqj.de/sneak/sfdupes/issues/133)
 
-- The `head`, `tail` and `content` columns are BLOBs, each holding the raw 32
+- the `head`, `tail` and `content` columns are BLOBs, each holding the raw 32
   bytes of a SHA-256, half the size of the hex text they held. The hashes stay
   raw from the hash phase through the database to `report` and `trees`. Reading
   a record whose hash is not 32 bytes is an error (2026-10-26,
   https://git.eeqj.de/sneak/sfdupes/issues/134)
 
-- Every file the walk records gets three hashes in the hash phase. `head` and
-  `tail` are the SHA-256 of its first and last 64 KiB. `content` is the SHA-256
-  of the whole file under 100 MiB, and of 1 MiB at each gigabyte from 100 MiB
-  up. Gone are:
-    - the 10 MiB and 50 MiB thresholds;
-    - the size census;
-    - the records without hashes;
-    - the content phase.
+- the hash phase gives every file the walk records three hashes: `head` and
+  `tail`, the SHA-256 of its first and last 64 KiB, and `content`, the SHA-256
+  of the whole file under 100 MiB and of 1 MiB at each gigabyte from 100 MiB up.
+  The 10 MiB and 50 MiB thresholds, the size census, the records stored without
+  hashes and the content phase are gone, so a scan has four phases and a rescan
+  reads only new and changed files. `info` no longer counts the records with
+  hashes, since every record has them (2026-10-25,
+  https://git.eeqj.de/sneak/sfdupes/issues/132)
 
-    A scan has four phases, and a rescan reads only new and changed files.
-    `info` no longer counts the records with `head` and `tail` hashes, nor those
-    with a content hash, since every record has all three (2026-10-25,
-    https://git.eeqj.de/sneak/sfdupes/issues/132)
-
-- `REPO_POLICIES.md` and the four scripts that pass `CACHEBUST` re-vendored from
-  `sneak/prompts` `next` at `0653579`. Two steps now come before
-  `ARG CACHEBUST`: the module download in the `lint`, `test` and `builder`
-  stages of the `Dockerfile`, and the package install in `builder`. Docker keeps
-  them until the base image, the install line, `go.mod` or `go.sum` changes.
-  Every step that lints, tests or compiles still comes after it.
-  `golangci-lint run` also keeps the linter's own cache. README says the same
+- re-vendor `REPO_POLICIES.md` and the four scripts that pass `CACHEBUST` from
+  `sneak/prompts` `next` at `0653579`: in the `lint`, `test` and `builder`
+  stages of the `Dockerfile` the module download, and in `builder` the
+  system-package install, now come before `ARG CACHEBUST`, so Docker keeps them
+  until the base image, the install line, `go.mod` or `go.sum` changes, and
+  every step that lints, tests or compiles still comes after it;
+  `golangci-lint run` also keeps golangci-lint's cache. README says the same
   (2026-10-18, https://git.eeqj.de/sneak/sfdupes/issues/109)
 
-- Release rule set: until 1.0, each tip of `main` that passes the build gets the
-  next `v0.0.N` tag, so `go install sneak.berlin/go/sfdupes@latest` installs it.
-  `go.mod` retracts `v0.0.1`, the early build without a database. When the
-  linker set no version, `sfdupes --version` prints the version Go recorded in
-  the binary: the tag, or the pseudo-version of a `go install` build. It prints
-  `dev` only when neither is known. README "Install" documented the rule, what
-  `@main` and `v0.0.1` give, and how to check an installed binary (2026-10-17,
+- releases until 1.0 are `v0.0.N` tags on `main`'s tip, so
+  `go install sneak.berlin/go/sfdupes@latest` installs `main`'s tip once it has
+  passed the build; README "Install" says so, says what `@main` and `v0.0.1`
+  give, and how to check an installed binary. `go.mod` retracts `v0.0.1`, the
+  early build without a database. When the linker set no version,
+  `sfdupes --version` prints the main module's version that Go recorded in the
+  binary, the tag or the pseudo-version of a `go install` build, and `dev` only
+  when neither is known (2026-10-17,
   https://git.eeqj.de/sneak/sfdupes/issues/116)
 
-- `scan` creates the database's directory where the database path leads. The
-  directory is the path with its last element cut off as text, never cleaned. A
-  `..` after a symlinked directory therefore goes through the symlink, as it
-  does when the file is opened. With
-  `SFDUPES_DATABASE=/srv/link/../new/db.sqlite` and `/srv/link` a symlink to
-  `/data/x`, it now creates `/data/new` and the database in it. It used to
-  create `/srv/new` and then fail (2026-10-17,
+- `scan` creates the database's directory where the database path leads: the
+  path with its last element cut off as text, never cleaned, so a `..` after a
+  symlinked directory is followed through the symlink, as when the file is
+  opened. With `SFDUPES_DATABASE=/srv/link/../new/db.sqlite` and `/srv/link` a
+  symlink to `/data/x`, it creates `/data/new` and the database in it, where it
+  used to create `/srv/new` and then fail (2026-10-17,
   https://git.eeqj.de/sneak/sfdupes/issues/119)
 
-- `scan` never records its own database. Once the database and its `.lock` file
+- `scan` never records its own database: once the database and its `.lock` file
   are open, it notes the device and inode of the database file, its `-wal` and
-  `-shm` files and the `.lock` file. The walk passes over a file with one of
-  them wherever it reaches it, through a symlinked directory included, printing
-  no line and counting nothing. A record an earlier scan left for one of them is
-  deleted (2026-10-17, https://git.eeqj.de/sneak/sfdupes/issues/115)
+  `-shm` files and its `.lock` file, and the walk passes over a file with one of
+  them wherever the operands reach it, through a symlinked directory included,
+  printing no line and counting nothing. A record an earlier scan left for one
+  of them is deleted (2026-10-17, https://git.eeqj.de/sneak/sfdupes/issues/115)
 
-- `scan` never records or reads anything on a filesystem that is not persistent:
-  `tmpfs`, `proc`, `sysfs` and the other kernel or memory-backed types. It
-  matches them by device ID. As the scan starts, it lists the mounted
-  filesystems of those types, from `/proc/self/mountinfo` on Linux and from the
-  mount list on macOS. No flag turns that off. Below an operand, the walk does
-  not enter the default excludes either, so `sfdupes scan /` skips the kernel's
-  view of the running system and the temporary directories. On Linux those are
-  `/proc`, `/sys`, `/dev`, `/run`, `/tmp` and `/var/tmp`. On macOS they are
-  `/dev`, `/private/tmp`, `/private/var/tmp`, `/private/var/vm`,
-  `/System/Volumes/VM` and `/System/Volumes/Data`. A Windows list exists in the
-  code but is not used. An operand at or inside a default exclude is still
+- `scan` never records or reads anything that is not on a persistent filesystem
+  (`tmpfs`, `proc`, `sysfs` and the other kernel or memory-backed types),
+  matched by the device ID of each such filesystem, listed as the scan starts
+  from `/proc/self/mountinfo` on Linux and the mounted-filesystem list on macOS,
+  however the walk or the content phase reaches it; no flag turns that off.
+  Below an operand, its walk does not enter the default excludes either, so
+  `sfdupes scan /` skips the kernel's view of the running system and the
+  temporary directories: on Linux `/proc`, `/sys`, `/dev`, `/run`, `/tmp` and
+  `/var/tmp`, on macOS `/dev`, `/private/tmp`, `/private/var/tmp`,
+  `/private/var/vm`, `/System/Volumes/VM` and `/System/Volumes/Data`, and a
+  Windows list, not used yet. An operand at or inside a default exclude is still
   walked. The scan prints a line for each path it leaves out, without counting
   it as skipped, and the records there count as outside the scanned operands, as
   for `-x`. `--no-default-excludes` turns off the default excludes only, and
   `scan --help` lists them (2026-10-17,
   https://git.eeqj.de/sneak/sfdupes/issues/124)
 
-- The rate a progress display shows covers the items completed over the last 5
-  seconds, or since the line before when stderr is not a terminal. It falls to 0
-  while nothing completes, and a burst after a wait no longer reads as a steady
-  rate of over 1,000 files a second. The time remaining still comes from the
-  phase's average. Once no item has completed for 10 seconds, the word `stalled`
-  and where the phase waits take the rate's place, as `stalled disk/db`. The
-  places are `disk`, `db`, `out` for stdout and `cpu`, or two of them for a
-  phase that may wait on either. Each phase gives its word where it is defined.
-  A line too wide for the terminal loses its bar first, then its rate or those
-  words, so the phase, progress, elapsed time and ETA stay whole. On an
-  80-column terminal, at counts like those of README's example, the content
-  phase's checks and reads lose those words at most times in minutes. Every
-  other phase keeps them whenever the elapsed time and the ETA are both in
-  minutes. The content phase's last partial batch is written under a display of
-  its own (2026-10-16, https://git.eeqj.de/sneak/sfdupes/issues/125)
+- the rate a progress display shows covers the items completed over the last 5
+  seconds, or since the line before when stderr is not a terminal, so it falls
+  to 0 while nothing completes, and a burst after a wait no longer reads as a
+  steady rate of over 1,000 files a second; the ETA still comes from the phase's
+  average. Once no item has completed for 10 seconds, the word `stalled` and
+  where the phase waits take the rate's place, as `stalled disk/db`: `disk`,
+  `db`, `out` for stdout or `cpu`, or two of them for a phase that may wait on
+  either, each phase giving its word where it is defined. A line too wide for
+  the terminal loses its bar first, then its rate or those words, so the phase,
+  progress, elapsed time and ETA stay whole. On an 80-column terminal, at counts
+  like those of README's example, the content phase's checks and reads lose
+  those words at most times in minutes, and every other phase keeps them
+  whenever the elapsed time and the ETA are both in minutes. The content phase's
+  last partial batch is now written under a display of its own (2026-10-16,
+  https://git.eeqj.de/sneak/sfdupes/issues/125)
 
-- New subcommand `info` prints the database's details on stdout, one per line as
-  a name, a tab and the value:
-    - the path and where it came from;
-    - the sizes of the database file and of its `-wal` file, when there is one;
-    - when the database file was last changed;
-    - the schema version;
-    - the number of records, how many have `head` and `tail` hashes, and how
-      many have a content hash;
-    - the sizes of all records added up.
-
-    It opens the database as `report` does and shows two phases on stderr,
-    `[1/2] open` and `[2/2] count`. The schema version and the counts come from
-    one read-only transaction, the counts from one query (2026-10-16,
-    https://git.eeqj.de/sneak/sfdupes/issues/117)
+- new subcommand `info` prints the database's details on stdout, one per line as
+  a name, a tab and the value: its path and where it came from, the sizes of the
+  database file and of its `-wal` file when there is one, when the database file
+  was last changed, the schema version, the number of records, how many have
+  head and tail hashes and how many a content hash, and the sizes of all records
+  added up. It opens the database as `report` does, and shows two phases on
+  stderr, `[1/2] open` and `[2/2] count`; the schema version and the counts come
+  from one read-only transaction, the counts from one query (2026-10-16,
+  https://git.eeqj.de/sneak/sfdupes/issues/117)
 
 - `report` shows its work on stderr in two phases, `[1/2] open` and
-  `[2/2] read`, with the progress display `scan` and `trees` use. The display
-  runs from the moment `report` starts until the summary line. `open` says it is
-  opening the database, also while it waits on a busy one. `read` counts the
-  records, then reads them against that count in signature order. SQLite takes
-  that order from the `files_signature` index without sorting, so the first
-  record comes at once. `report` forms the duplicate groups itself, holding only
-  those of the size it is reading, and writes them ordered by first path before
-  it reads the next size. stdout and the summary line are unchanged, and SQLite
-  no longer needs a temporary file to sort in (2026-10-16,
+  `[2/2] read`, with the progress display `scan` and `trees` use, from the
+  moment it starts until the summary line: `open` says it is opening the
+  database, also while it waits on a busy one; `read` counts the records, then
+  reads them against that count in signature order, which SQLite takes from the
+  `files_signature` index without sorting, so the first record comes at once.
+  `report` forms the duplicate groups itself, holding only those of the size it
+  is reading, and writes them ordered by first path before it reads the next
+  size. stdout and the summary line are unchanged, and SQLite no longer needs a
+  temporary file to sort in (2026-10-16,
   https://git.eeqj.de/sneak/sfdupes/issues/114)
 
 - `trees` shows its work on stderr in four phases, `[1/4] open`, `[2/4] read`,
-  `[3/4] group` and `[4/4] write`, each with the progress display `scan` uses.
-  The display runs from the moment `trees` starts until the summary line. `open`
-  says it is opening the database, also while it waits on a busy one. `read`
-  counts the records, then reads them against that count. `group` counts the
-  directories it groups, and `write` the groups it writes. A display's rate
-  names what its phase counts: files, records, directories or groups. stdout and
-  the summary line are unchanged. When stdout and stderr are the same file, as
-  one terminal is, no line of stdout shares a line with the display. When they
-  are not, the display keeps being drawn while stdout waits on a slow reader
-  (2026-10-16, https://git.eeqj.de/sneak/sfdupes/issues/113)
+  `[3/4] group` and `[4/4] write`, each with the progress display `scan` uses,
+  from the moment it starts until the summary line: `open` says it is opening
+  the database, also while it waits on a busy one; `read` counts the records,
+  then reads them against that count; `group` counts the directories it groups,
+  and `write` the groups it writes. A display's rate names what its phase
+  counts: files, records, directories or groups. stdout and the summary line are
+  unchanged. When stdout and stderr are the same file, as one terminal is, none
+  of stdout's lines shares a line with the display; when they are not, the
+  display keeps being drawn while stdout waits on a slow reader (2026-10-16,
+  https://git.eeqj.de/sneak/sfdupes/issues/113)
 
-- Each `scan` phase's progress display names the phase and its place among the
-  five, as `[2/5] walk`. It runs from the moment the phase starts and shows its
-  progress, elapsed time and ETA. `load` counts the records first. The walk's
-  total is estimated from the records under the operands. The content phase
-  counts the records it checks from SQLite's grouping alone, then says it is
-  searching the database until the first one is returned. On a terminal a phase
-  with an exact total draws its line followed by the library's bar. Any other
-  phase draws a spinner followed by the line. Every display is drawn again
-  several times a second. No line reaches the terminal's last column, however
-  narrow, also after the terminal is made narrower during a phase. A line too
-  wide leaves out its rate, then its bar, keeping the phase, progress, elapsed
-  time and ETA whole. It is cut short only when those alone do not fit, as below
-  about 70 columns late in a large scan. In plain mode the line is printed every
-  5 seconds whether or not an item completed (2026-10-16,
-  https://git.eeqj.de/sneak/sfdupes/issues/112)
+- each `scan` phase's progress display names the phase and its place among the
+  five, as `[2/5] walk`, from the moment it starts, with its progress, elapsed
+  time and ETA: `load` counts the records first, the walk's total is estimated
+  from the records under the operands, and the content phase counts the records
+  it checks from SQLite's grouping alone, then says it is searching the database
+  until the first one is returned. On a terminal a phase with an exact total
+  draws its line followed by the library's bar, and any other a spinner followed
+  by the line; every display is drawn again several times a second. No line
+  reaches the terminal's last column, however narrow, also after the terminal is
+  made narrower during a phase: a line too wide leaves out its rate, then its
+  bar, keeping the phase, progress, elapsed time and ETA whole, and is cut short
+  only when those alone do not fit, as below about 70 columns late in a large
+  scan. In plain mode the line is printed every 5 seconds whether or not an item
+  completed (2026-10-16, https://git.eeqj.de/sneak/sfdupes/issues/112)
 
 - `scan`, `report` and `trees` first print a line on stderr naming the database
   they use, as an absolute path, and whether that path is the default or comes
-  from `SFDUPES_DATABASE`. `scan` says when the database is new. README
+  from `SFDUPES_DATABASE`; `scan` says when the database is new. README
   "Database" says when `scan` writes each file (2026-10-16,
   https://git.eeqj.de/sneak/sfdupes/issues/111)
 
-- The canonical files and model scripts re-vendored from `sneak/prompts` `next`
-  at `e3f79c4`:
-    - `golangci-lint` v2.14.0;
-    - lint and test are phases of the `Dockerfile` that write no image, and
-      `make test` runs the suite under the race detector. `Dockerfile.lint`,
-      `script/verify-lint-image-pin` and `make test-race` are gone;
-    - every `docker build` in `script/` passes a new `CACHEBUST` value, which
-      every stage of the `Dockerfile` declares first, so every `RUN` step runs
-      on every build. The steps that compile keep Go's build cache, and the
-      tests run with `-count=1`;
-    - `prettier` runs on the host, from the `node` and `yarn` that
-      `script/bootstrap` installs, so the `prettier` and `markdown` stages are
-      gone and the build stage installs `git` and `make` itself;
-    - a new push cancels the workflow's older run on the same branch, and a run
-      stops after 20 minutes;
-    - `.claude/settings.json` is deleted.
+- re-vendor the canonical files and model scripts from `sneak/prompts` `next` at
+  `e3f79c4`: golangci-lint v2.14.0; lint and test are phases of the `Dockerfile`
+  that write no image, and `make test` runs the suite under the race detector,
+  so `Dockerfile.lint`, `script/verify-lint-image-pin` and `make test-race` are
+  gone; every `docker build` in `script/` passes a new `CACHEBUST` value, which
+  every stage of the `Dockerfile` declares first, so every `RUN` step runs on
+  every build, while the steps that compile keep Go's build cache and the tests
+  run with `-count=1`; prettier runs on the host, from the node and yarn
+  `script/bootstrap` installs, so the `prettier` and `markdown` stages are gone
+  and the build stage installs `git` and `make` itself; a new push cancels the
+  workflow's older run on the same branch, and a run stops after 20 minutes;
+  `.claude/settings.json` is deleted (2026-10-15,
+  https://git.eeqj.de/sneak/sfdupes/issues/95). Since
+  https://git.eeqj.de/sneak/sfdupes/issues/109 the module download in `lint`,
+  `test` and the build stage, and the install of `git` and `make` in the build
+  stage, come before `ARG CACHEBUST`, and Docker keeps them between builds;
+  every step that lints, tests or compiles still runs on every build
 
-    Since https://git.eeqj.de/sneak/sfdupes/issues/109 two steps come before
-    `ARG CACHEBUST`: the module download in `lint`, `test` and the build stage,
-    and the install of `git` and `make` in the build stage. Docker keeps them
-    between builds, and every step that lints, tests or compiles still runs on
-    every build (2026-10-15, https://git.eeqj.de/sneak/sfdupes/issues/95)
-
-- With `-x`, an operand under another operand is no longer dropped when the
-  outer operand's walk cannot reach it. That is the case when a directory from
-  the inner operand up to, but not including, the outer one is on a different
-  filesystem than the outer one. The inner operand is then walked on its own.
-  For a regular-file operand the directories checked start at its directory. The
-  records of files gone from below it are deleted (2026-10-14,
+- with `-x`, an operand under another operand is walked on its own instead of
+  being dropped when a directory from it (from its directory, for a regular
+  file) up to but not including that operand is on a different filesystem than
+  that operand, whose walk then cannot reach it, and the records of files gone
+  from below it are deleted (2026-10-14,
   https://git.eeqj.de/sneak/sfdupes/issues/106)
 
-- With `-x`, `scan` keeps the records below a directory on another filesystem
+- with `-x`, `scan` keeps the records below a directory on another filesystem
   under its operand, and counts their sizes in the size census, instead of
   deleting them (2026-10-14, https://git.eeqj.de/sneak/sfdupes/issues/99)
 
-- The hash and content phases open each file without blocking and check that it
-  is still a regular file. A file replaced by a FIFO or device node after it was
+- the hash and content phases open each file without blocking and check that it
+  is still a regular file, so one replaced by a FIFO or device node after it was
   statted is warned about and skipped instead of hanging the scan (2026-10-14,
   https://git.eeqj.de/sneak/sfdupes/issues/100)
 
-- The scan lock file is named from the database's path with symlinks resolved,
-  after `scan` creates the database file if it is missing. A scan through a
-  symlink to the database therefore fails while another scan holds the lock
-  (2026-10-14, https://git.eeqj.de/sneak/sfdupes/issues/101)
+- the scan lock file is named from the database's path with symlinks resolved,
+  after `scan` creates the database file if it is missing, so a scan through a
+  symlink to the database fails while another scan holds the lock (2026-10-14,
+  https://git.eeqj.de/sneak/sfdupes/issues/101)
 
-- On a terminal, a warning for the last file of a phase no longer erases the
-  phase's finished bar. The bar is drawn again below the warning (2026-10-14,
+- on a terminal, a warning for the last file of a phase no longer erases the
+  phase's finished bar: the bar is drawn again below the warning (2026-10-14,
   https://git.eeqj.de/sneak/sfdupes/issues/102)
 
-- `scan` records the mtime to the nanosecond, as whole seconds in `mtime` plus
-  `mtime_nsec`, and compares it at that resolution. A same-size rewrite within
-  the same second is hashed again (2026-10-07,
+- `scan` records mtime to the nanosecond, as whole seconds in `mtime` plus
+  `mtime_nsec`, and compares it at that resolution, so a same-size rewrite
+  within the same second is re-hashed (2026-10-07,
   https://git.eeqj.de/sneak/sfdupes/issues/12)
 
-- The narration was cut from `TODO.md` Completed Steps and from the comments in
+- cut the narration from `TODO.md` Completed Steps and from the comments in
   `script/`, `Dockerfile` and `Dockerfile.lint` (gone since
-  https://git.eeqj.de/sneak/sfdupes/issues/95). The Workflow section now
-  branches from and merges to `next` (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/49)
+  https://git.eeqj.de/sneak/sfdupes/issues/95); §Workflow now branches from and
+  merges to `next` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/49)
 
 - `make test-race` ran the test suite under the race detector in a cgo-enabled
-  container, outside `make check`. Since
+  container, outside `make check` (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/18). Since
   https://git.eeqj.de/sneak/sfdupes/issues/95 `make test` itself runs the suite
   under the race detector, in the `Dockerfile`'s Debian-based `test` phase, and
-  `make test-race` is gone (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/18)
+  `make test-race` is gone
 
-- A bare `docker build .` failed, naming `script/cibuild` and `script/docker`,
-  rather than serve the gates from cache. Since
+- a bare `docker build .` failed, naming `script/cibuild` and `script/docker`,
+  rather than serve the gates from cache (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/39). Since
   https://git.eeqj.de/sneak/sfdupes/issues/95 a bare build succeeds, as
-  `REPO_POLICIES.md` requires, and may serve the gates from cache. The builds in
-  `script/` pass a new `CACHEBUST` value, so theirs always run (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/39)
+  `REPO_POLICIES.md` requires, and may serve the gates from cache; the builds in
+  `script/` pass a new `CACHEBUST` value, so theirs always run
 
-- `make fmt` and `make fmt-check` run `prettier` over all Markdown, and CI
-  checks it. All Markdown was reformatted (2026-10-04,
+- `make fmt` and `make fmt-check` run prettier over all Markdown, and CI checks
+  it; all Markdown reformatted (2026-10-04,
   https://git.eeqj.de/sneak/sfdupes/issues/19)
 
 - `script/lint` writes no image, so a run no longer leaves an untagged one
   behind (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/48)
 
-- Tests cover a missing database, `scan` keeping stdout empty, its skip warning,
+- tests cover a missing database, `scan` keeping stdout empty, its skip warning,
   the `report` and `trees` summary lines, and every subcommand going through
   `runE` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/16)
 
@@ -288,307 +278,296 @@ are known.
   `gomodguard_v2`, so lint no longer prints a deprecation warning (2026-10-04,
   https://git.eeqj.de/sneak/sfdupes/issues/26)
 
-- A test fails when either `hashWorker` cancellation check in `scan.go` is
+- a test fails when either `hashWorker` cancellation check in `scan.go` is
   removed (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/83)
 
-- A database path holding `?`, `#` or `%` opens exactly the file it names
+- a database path holding `?`, `#` or `%` opens exactly the file it names
   (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/55)
 
 - `scan` rejects `--workers` below 1 as a usage error instead of running
   single-threaded (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/10)
 
-- A test fails when either walk cancellation check in `scan.go` is removed
+- a test fails when either walk cancellation check in `scan.go` is removed
   (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/81)
 
-- A test checks that `scan` refuses a database with another schema version
-  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/64)
+- test that `scan` refuses a database with another schema version (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/64)
 
-- Four inaccurate comments in `cancel_test.go` corrected, and
-  `walkCancelInFlightDirs` renamed to `walkCancelInFlightFiles` (2026-10-04,
+- correct four inaccurate comments in `cancel_test.go` and rename
+  `walkCancelInFlightDirs` to `walkCancelInFlightFiles` (2026-10-04,
   https://git.eeqj.de/sneak/sfdupes/issues/33)
 
-- The `-x` filesystem-boundary rules in `subdirJob` are tested (2026-10-04,
+- test the `-x` filesystem-boundary rules in `subdirJob` (2026-10-04,
   https://git.eeqj.de/sneak/sfdupes/issues/17)
 
-- `scan` creates the schema in one transaction. A version-0 database with a
+- `scan` creates the schema in one transaction; a version-0 database with a
   `files` table is refused with a clear schema-version error (2026-10-04,
   https://git.eeqj.de/sneak/sfdupes/issues/11)
 
 - README documents install, Docker, a daily cron scan and how to read and check
   the reports (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/54)
 
-- The `Dockerfile` build stage kept the Go module cache out of `builder`'s home
-  and copied the sources with `--chown`, so no `chown -R` walked them. Since
+- the `Dockerfile` build stage kept the Go module cache out of `builder`'s home
+  and copied the sources with `--chown`, so no `chown -R` walked them
+  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/43). Since
   https://git.eeqj.de/sneak/sfdupes/issues/95 there is no `builder` user and
   nothing changes owner: the build stage only compiles, as root, and the tests
-  run as `nobody` in the `test` phase (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/43)
+  run as `nobody` in the `test` phase
 
-- `--version` prints `sfdupes VERSION` to stdout. README documents it and
+- `--version` prints `sfdupes VERSION` to stdout; README documents it and
   `--help` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/15)
 
-- `scan` stops cleanly on `SIGINT` or `SIGTERM`: it commits what it has hashed,
-  deletes nothing more, and exits 1 (2026-10-04,
+- `scan` stops cleanly on `SIGINT` or `SIGTERM`: commits what it has hashed,
+  deletes nothing more, exits 1 (2026-10-04,
   https://git.eeqj.de/sneak/sfdupes/issues/5)
 
-- `report` and `trees` stream the records instead of holding them all in memory.
-  The schema gains the `files_signature` index (2026-10-04,
+- `report` and `trees` stream the records instead of holding them all in memory;
+  the schema gains the `files_signature` index (2026-10-04,
   https://git.eeqj.de/sneak/sfdupes/issues/14)
 
-- Progress prints at once on a non-terminal, uses a real terminal test, and
+- progress prints at once on a non-terminal, uses a real terminal test, and
   prints warnings through a spinner instead of racing its redraw (2026-10-03,
   https://git.eeqj.de/sneak/sfdupes/issues/13)
 
-- Symlink, socket, FIFO, device and `.zfs` operands are warned about and
-  skipped, and the records beneath them are kept (2026-10-03,
+- warn about and skip symlink, socket, FIFO, device and `.zfs` operands, keeping
+  the records beneath them (2026-10-03,
   https://git.eeqj.de/sneak/sfdupes/issues/9)
 
 - `scan` holds a lock on a lock file beside the database for its whole run, so a
   second `scan` fails at once with exit 1 (2026-10-03,
   https://git.eeqj.de/sneak/sfdupes/issues/53)
 
-- Tests cover stdout write failures in `report` and `trees`. README states that
-  `| head` ends `sfdupes` by `SIGPIPE` and that `>&-` writes to `/dev/null`
+- test stdout write failures in `report` and `trees`; README states that
+  `| head` ends sfdupes by `SIGPIPE` and `>&-` writes to `/dev/null`
   (2026-10-03, https://git.eeqj.de/sneak/sfdupes/issues/30)
 
 - `report` and `trees` open the database read-only, and `scan` leaves it out of
-  WAL mode, so reading needs only read access (2026-10-03,
+  WAL mode, so reading needs only read access (2026-10-03, closes
   https://git.eeqj.de/sneak/sfdupes/issues/8)
 
-- Tabs, newlines, carriage returns and backslashes are escaped in report, trees
-  and warning paths. The root directory's path is `/` (2026-10-03,
+- escape tabs, newlines, carriage returns and backslashes in report, trees and
+  warning paths; the root directory's path is `/` (2026-10-03,
   https://git.eeqj.de/sneak/sfdupes/issues/7)
 
-- A plain `docker build .` stamps the git tag or short commit instead of `dev`.
-  `.dockerignore` sends `.git` without `.git/config`. The build stage stamps the
-  `VERSION` build argument, else `git describe --tags --always`. It fails if the
-  context carries `.git` and the version is still empty, `dev` or `unknown`. CI
-  checks out the full history (`fetch-depth: 0`), so it stamps the same value as
-  `make build` (2026-10-02, branch `next`,
-  https://git.eeqj.de/sneak/sfdupes/issues/67)
+- stamp the git tag or short commit in a plain `docker build .` instead of `dev`
+  (2026-10-02, branch `next`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/67): `.dockerignore` sends `.git`
+  without `.git/config`; the build stage stamps the `VERSION` build argument,
+  else `git describe --tags --always`, and fails if the context carries `.git`
+  and the version is still empty, `dev` or `unknown`. CI checks out the full
+  history (`fetch-depth: 0`) so it stamps the same value as `make build`.
 
-- The 1 KiB end-window sampling was replaced with the hashes chosen by file
-  size, and README "Duplicate detection" documented every size threshold. A file
-  under 10 MiB was hashed in full, and its `head`, `tail` and `content` all held
-  that hash. A larger file got only its 64 KiB `head` and `tail` in the hash
-  phase. The content phase, after the update phase, read it for `content` only
-  when its size, `head` and `tail` matched another record's, from this scan or
-  an earlier one. `content` was the whole file below 50 MiB, and gigabyte-spaced
-  1 MiB samples at or above. A file gone or changed since its record was written
-  was never read. `report` and `trees` left out any record without a `content`
-  hash. The `content` column is part of the version 1 schema. Superseded by
-  https://git.eeqj.de/sneak/sfdupes/issues/132 (2026-09-22, branch `next`,
-  https://git.eeqj.de/sneak/sfdupes/issues/61)
+- replace the 1 KiB end-window sampling with the head/tail plus content-hash
+  ladder (2026-09-22, branch `next`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/61); README "Duplicate detection"
+  documents every rung. A file under 10 MiB is hashed in full, and its `head`,
+  `tail` and `content` all hold that hash. A larger file gets only its 64 KiB
+  `head` and `tail` in the hash phase; the content phase, after the update
+  phase, reads it for `content` (the whole file below 50 MiB, gigabyte-spaced 1
+  MiB samples at or above) only when its size, `head` and `tail` match another
+  record's from this scan or an earlier one, and never reads a file gone or
+  changed since its record was written. `report` and `trees` leave out any
+  record without a `content` hash. The `content` column is part of the version 1
+  schema.
 
-- The dead `files.dat` references removed from `Makefile`, `.gitignore` and
-  `.dockerignore` (2026-09-21, branch `next`,
+- remove the dead `files.dat` references from `Makefile`, `.gitignore` and
+  `.dockerignore` (2026-09-21, branch `next`, closes
   https://git.eeqj.de/sneak/sfdupes/issues/22)
 
-- The lint-image pin comments and `FROM` form in `Dockerfile` and
-  `Dockerfile.lint` fixed. Both pins became the policy
+- fix the lint-image pin comments and `FROM` form in `Dockerfile` and
+  `Dockerfile.lint` (2026-08-10, branch `next`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/25): both pins became the policy
   `# image:vX.Y.Z, YYYY-MM-DD` comment over a bare `FROM image@sha256:...`,
   without the false `(Debian-based)` note or the tag. Since
   https://git.eeqj.de/sneak/sfdupes/issues/95 the `Dockerfile`'s `lint` phase
-  holds the only `golangci-lint` pin, in that form. `Dockerfile.lint` and
-  `script/verify-lint-image-pin`, which compared the two pins, are gone
-  (2026-08-10, branch `next`, https://git.eeqj.de/sneak/sfdupes/issues/25)
+  holds the only golangci-lint pin, in that form, so `Dockerfile.lint` and
+  `script/verify-lint-image-pin`, which compared the two pins, are gone.
 
-- All linting ran in Docker, via `Dockerfile.lint` and `script/lint`. Per the
+- run all linting in Docker via `Dockerfile.lint` and `script/lint` (2026-08-10,
+  branch `next`, closes https://git.eeqj.de/sneak/sfdupes/issues/46): per the
   owner ruling the linter is never installed on a host, and
   `golangci-lint config verify` runs before `golangci-lint run`.
   `script/bootstrap` stopped installing or pinning the linter, and
   `script/verify-linter-pin` was retired. Since
   https://git.eeqj.de/sneak/sfdupes/issues/95 both commands run in the
   `Dockerfile`'s `lint` phase, which `script/lint` builds alone and the build
-  stage depends on through `COPY --from=lint /src/go.sum /dev/null`.
+  stage depends on through `COPY --from=lint /src/go.sum /dev/null`;
   `Dockerfile.lint` and `script/verify-lint-image-pin` are gone. Nothing inside
-  an image build may run `docker`, so the phase calls `golangci-lint` directly
-  (2026-08-10, branch `next`, https://git.eeqj.de/sneak/sfdupes/issues/46)
+  an image build may run docker, so the phase calls `golangci-lint` directly.
 
-- The Docker build stage's prerequisites were installed by running
-  `script/bootstrap` instead of `apk add --no-cache make` inline.
-  `script/verify-linter-pin` failed the build unless the linter copied from the
-  lint stage was the version `script/bootstrap` pinned. Builds then took up to
-  5m14s cold, mostly in a `chown -R` of the module cache, filed as
+- install the Docker build stage's prerequisites by running `script/bootstrap`
+  instead of `apk add --no-cache make` inline (2026-08-09, branch
+  `dockerfile-bootstrap`, closes https://git.eeqj.de/sneak/sfdupes/issues/42),
+  with `script/verify-linter-pin` failing the build unless the linter copied
+  from the lint stage was the version `script/bootstrap` pinned. Builds then
+  took up to 5m14s cold, mostly in a `chown -R` of the module cache, filed as
   https://git.eeqj.de/sneak/sfdupes/issues/43. Since
   https://git.eeqj.de/sneak/sfdupes/issues/95 the build stage installs `git` and
   `make` with `apk add --no-cache` and only compiles; the `lint` and `test`
-  phases are the gates (2026-08-09, branch `dockerfile-bootstrap`,
-  https://git.eeqj.de/sneak/sfdupes/issues/42)
-
-- The Docker layer cache is busted for the gate steps, so `script/cibuild` and
-  `script/docker` cannot report a green they did not earn. The `Dockerfile`
-  copies the tree before its gates, so on an unchanged tree Docker served them
-  from cache and the build exited 0 having run nothing. The fix was a
-  `CHECK_EPOCH` build argument. Since
+  phases are the gates
+- bust the Docker layer cache for the gate steps, so `script/cibuild` and
+  `script/docker` cannot report a green they did not earn (2026-08-09, branch
+  `cibuild-cache-bust`, closes https://git.eeqj.de/sneak/sfdupes/issues/32): the
+  `Dockerfile` copies the tree before its gates, so on an unchanged tree Docker
+  served them from cache and the build exited 0 having run nothing. The fix was
+  a `CHECK_EPOCH` build argument; since
   https://git.eeqj.de/sneak/sfdupes/issues/95 every `docker build` in `script/`
   passes a new `CACHEBUST` value instead, which every stage of the `Dockerfile`
   declares before every step that lints, tests or compiles. Run as root, the
   tests fail `TestScanHardlinkRunFailsTogether`, because root reads through the
   `chmod(0)` the test relies on, so the `test` phase runs them as `nobody`
-  (2026-08-09, branch `cibuild-cache-bust`,
-  https://git.eeqj.de/sneak/sfdupes/issues/32)
+- check the installed golangci-lint version in `script/bootstrap` instead of
+  only its presence (2026-08-09, branch `bootstrap-version-check`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/24): the version lives only in
+  `GOLANGCI_LINT_VERSION`, with the `go install` module ref derived from it, and
+  any installed version that is not the pin — older, newer, absent or
+  unparseable — is reinstalled. `go install` writes into `GOBIN` (or
+  `GOPATH/bin`) while `make lint` runs the first `golangci-lint` on `PATH`, so
+  bootstrap re-reads the effective version after installing and, on a mismatch,
+  prints both paths and both versions and exits non-zero; it does not reorder
+  `PATH` or delete anyone's binary. The `--version` call keeps its stderr and is
+  bounded by `timeout(1)` where that exists. `git`, `make` and `go` keep
+  presence-only checks. Verified by bootstrapping this host from v2.10.1 to
+  v2.12.2 and again to a no-op, and by stub runs of the script under `dash`
+  covering a thirteen-input version-parse matrix, a shadowed install that must
+  exit non-zero, an install destination not on `PATH`, `GOBIN` set, and a wedged
+  binary that must hit the timeout; `make check` and `make lint` are clean at
+  v2.12.2, so v2.10.1 was not hiding any findings on `main`
+- unwind the hash worker pool on the error path (2026-08-09, branch
+  `hash-pool-cleanup`, closes https://git.eeqj.de/sneak/sfdupes/issues/6): the
+  pool is now an owned, context-aware `hashPool`: every blocking send in the
+  feeder and the workers selects on `ctx.Done()`, `jobs` is closed on every path
+  out, and `hashPhase` defers `pool.stop()`, which cancels and then drains
+  `results` until the last goroutine has exited — draining is what frees a
+  worker already parked on a send. `ctx` is threaded from `cmd.Context()`
+  through `runScan`, `syncScan`, both worker pools and the whole database layer,
+  as the first parameter everywhere. The walk pool gets the same treatment plus
+  a `ctx.Err()` guard after the walk: a cancelled walk yields a partial size
+  census, and every file it never reached looks vanished to the update phase.
+  That phase's own `BeginTx` also fails on the cancelled context before deleting
+  anything, but the guard is the barrier that still holds once an interrupted
+  scan may commit what it has. Tests drive `run(scan)` against a database whose
+  insert trigger aborts and assert that the scan fails instead of hanging and
+  that `runtime.NumGoroutine()` polls back to its pre-scan baseline; others
+  cancel a scan part-way through the walk, deterministically, by counting its
+  own consultations of `ctx.Done()`, and assert that it stops at the guard
+  holding a partial census and a still-populated record index, with every record
+  intact. Direct tests of `sendEvent`, the walk workers, `dispatchDirs`,
+  `feedHashJobs`, `hashWorker` and `hashPhase` cover the remaining cancellation
+  branches of both pools
+- guarantee the database is closed on every fatal exit path (2026-08-09, branch
+  `db-close-on-fatal`, closes https://git.eeqj.de/sneak/sfdupes/issues/4):
+  `fatalf` and its `os.Exit(1)` are gone, so the deferred `db.Close()` — and
+  with it the SQLite WAL checkpoint — now actually runs when a subcommand fails;
+  `runScan`, `runReport`, `runTrees`, `loadRecords` and `resolveRoots` return
+  errors instead. The single exit point is `run` in `main.go`: it maps a
+  `fatalError` (anything a subcommand returned) to exit 1 and cobra's own
+  argument and flag errors to exit 2, which keeps a runtime failure from being
+  reported as a usage error or printing the usage text. New `main_test.go`
+  drives the CLI in-process and asserts the exit codes from README §Error
+  handling plus the stdout/stderr split, including that a fatal error raised
+  after the database is open leaves no `-wal`/`-shm` sidecar behind for `scan`,
+  `report` or `trees`
+- update golangci-lint to v2.12.2 with the canonical config (2026-08-09, branch
+  `golangci-v2.12.2`, merged as `38a01bd`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/3): bumped the pinned linter in the
+  `Dockerfile` lint stage and `script/bootstrap` from v2.12.1 to v2.12.2, and
+  replaced `.golangci.yml` with the canonical file — the linter settings (`lll`,
+  `funlen`, `cyclop`, `dupl` thresholds) now live under `linters.settings` per
+  the v2 schema, so they are actually applied; no new lint findings surfaced
+- convert Makefile targets to scripts-to-rule-them-all `script/` entrypoints
+  like the other managed repos (2026-07-26, commit `3abeacf`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/1): all 12 `script/` entrypoints
+  exist (`bootstrap`, `setup`, `projectname`, `test`, `lint`, `fmt`,
+  `fmt-check`, `check`, `docker`, `cibuild`, `precommit`, `install-precommit`)
+  and every Makefile target is now a thin shim over them
+- make the binary the default Make target (2026-07-24, branch
+  `make-default-target`): plain `make` now builds `sfdupes` (previously it ran
+  `check` plus `build`); `make build` remains as an alias
+- scan-wide phases, concurrent operands, batched updates (2026-07-24, branch
+  `scan-wide-phases`): all operands seed the shared walk pool and every pass
+  runs once over the whole scan, so totals and ETAs are scan-global; the
+  per-operand walk/hash/update cycles and their stderr announcements are gone;
+  the update pass commits in batched transactions — the filesystem is
+  authoritative and the database an eventually-consistent reflection, so
+  scan-level atomicity is not required
+- split the stat pass back out of the walk (2026-07-24, branch
+  `parallel-phases`): phases are strictly sequential again — walk, stat, hash,
+  update per operand — with parallelism only inside each phase; the walk
+  enumerates paths with per-directory workers and the stat pass lstats them with
+  per-file workers, restoring the exact total/ETA stat bar
+- announce each operand on stderr before its passes (2026-07-24, branch
+  `scan-operand-progress`): with per-operand walk/hash/update cycles, a
+  multi-operand run (e.g. `scan /srv/*`) showed pass totals that looked like the
+  whole run's
+- parallel walk (2026-07-24, branch `parallel-walk`): the walk pass was a single
+  goroutine and took hours at ~20M files on a busy pool (observed: 22M files in
+  4h on a ZFS server); it is now a per-directory worker-pool traversal that
+  records size/mtime during the walk (folding away the separate stat pass,
+  halving metadata I/O), and each `PATH` operand commits in its own transaction
+  so an interrupted scan keeps completed operands
 
-- `script/bootstrap` checked the installed `golangci-lint` version instead of
-  only its presence. The version lived only in `GOLANGCI_LINT_VERSION`, with the
-  `go install` module ref derived from it. Any installed version that was not
-  the pin was reinstalled: older, newer, absent or unparseable. `go install`
-  writes into `GOBIN` (or `GOPATH/bin`) while `make lint` ran the first
-  `golangci-lint` on `PATH`, so bootstrap re-read the effective version after
-  installing. On a mismatch it printed both paths and both versions and exited
-  non-zero; it did not reorder `PATH` or delete anyone's binary. The `--version`
-  call kept its stderr and was bounded by `timeout(1)` where that exists. `git`,
-  `make` and `go` kept presence-only checks. `make check` and `make lint` were
-  clean at v2.12.2, so v2.10.1 had not been hiding findings on `main`.
-  Superseded by https://git.eeqj.de/sneak/sfdupes/issues/46: the linter is no
-  longer installed on a host (2026-08-09, branch `bootstrap-version-check`,
-  https://git.eeqj.de/sneak/sfdupes/issues/24)
-
-- The hash worker pool unwinds on the error path. The pool is an owned,
-  context-aware `hashPool`. Every blocking send in the feeder and the workers
-  selects on `ctx.Done()`, and `jobs` is closed on every path out. `hashPhase`
-  defers `pool.stop()`, which cancels and then drains `results` until the last
-  goroutine has exited; draining is what frees a worker parked on a send. `ctx`
-  is threaded from `cmd.Context()` through `runScan`, `syncScan`, both worker
-  pools and the whole database layer, as the first parameter everywhere. The
-  walk pool gets the same treatment, plus a `ctx.Err()` guard after the walk. A
-  cancelled walk yields a partial size census, and every file it never reached
-  looks vanished to the update phase. That phase's own `BeginTx` also fails on
-  the cancelled context before deleting anything, but the guard is the barrier
-  that still holds once an interrupted scan may commit what it has. Tests drive
-  `run(scan)` against a database whose insert trigger aborts, and assert that
-  the scan fails instead of hanging and that the goroutine count returns to its
-  pre-scan baseline. Other tests cancel a scan part-way through the walk and
-  assert that it stops at the guard with every record intact. Direct tests of
-  `sendEvent`, the walk workers, `dispatchDirs`, `feedHashJobs`, `hashWorker`
-  and `hashPhase` cover the remaining cancellation branches of both pools
-  (2026-08-09, branch `hash-pool-cleanup`,
-  https://git.eeqj.de/sneak/sfdupes/issues/6)
-
-- The database is closed on every fatal exit path. `fatalf` and its `os.Exit(1)`
-  are gone, so the deferred `db.Close()`, and with it the SQLite WAL checkpoint,
-  runs when a subcommand fails. `runScan`, `runReport`, `runTrees`,
-  `loadRecords` and `resolveRoots` return errors instead. The single exit point
-  is `run` in `main.go`. It maps a `fatalError` to exit 1 and cobra's own
-  argument and flag errors to exit 2, so a runtime failure is never reported as
-  a usage error or printed with the usage text. `main_test.go` drives the CLI
-  in-process and asserts the exit codes from README "Error handling" and the
-  stdout/stderr split. That includes a fatal error after the database is open
-  leaving no `-wal` or `-shm` file behind, for `scan`, `report` or `trees`
-  (2026-08-09, branch `db-close-on-fatal`,
-  https://git.eeqj.de/sneak/sfdupes/issues/4)
-
-- `golangci-lint` updated to v2.12.2 with the canonical config, merged as
-  `38a01bd`. The pinned linter in the `Dockerfile` lint stage and
-  `script/bootstrap` went from v2.12.1 to v2.12.2, and `.golangci.yml` was
-  replaced with the canonical file. The linter settings (`lll`, `funlen`,
-  `cyclop`, `dupl` thresholds) now live under `linters.settings`, per the v2
-  schema, so they are applied. No new lint findings surfaced (2026-08-09, branch
-  `golangci-v2.12.2`, https://git.eeqj.de/sneak/sfdupes/issues/3)
-
-- Makefile targets converted to scripts-to-rule-them-all `script/` entrypoints,
-  like the other managed repos. All 12 entrypoints exist:
-    - `bootstrap`, `setup` and `projectname`;
-    - `test`, `lint`, `fmt`, `fmt-check` and `check`;
-    - `docker`, `cibuild`, `precommit` and `install-precommit`.
-
-    Every Makefile target is a thin shim over them (2026-07-26, commit
-    `3abeacf`, https://git.eeqj.de/sneak/sfdupes/issues/1)
-
-- The binary is the default Make target: plain `make` builds `sfdupes`, where it
-  used to run `check` plus `build`. `make build` remains as an alias
-  (2026-07-24, branch `make-default-target`)
-
-- Scan-wide phases, concurrent operands and batched updates. All operands seed
-  the shared walk pool, and every pass runs once over the whole scan, so totals
-  and ETAs are scan-global. The per-operand walk, hash and update cycles and
-  their stderr announcements are gone. The update pass commits in batched
-  transactions. The filesystem is authoritative and the database an
-  eventually-consistent reflection of it, so scan-level atomicity is not
-  required (2026-07-24, branch `scan-wide-phases`)
-
-- The stat pass split back out of the walk. Phases are strictly sequential
-  again, per operand, with parallelism only inside each phase:
-    - walk;
-    - stat;
-    - hash;
-    - update.
-
-    The walk enumerates paths with per-directory workers, and the stat pass
-    lstats them with per-file workers, restoring the exact total and ETA of the
-    stat bar (2026-07-24, branch `parallel-phases`)
-
-- Each operand is announced on stderr before its passes. With per-operand walk,
-  hash and update cycles, a multi-operand run such as `scan /srv/*` showed pass
-  totals that looked like the whole run's (2026-07-24, branch
-  `scan-operand-progress`)
-
-- Parallel walk. The walk pass was a single goroutine and took hours at about 20
-  million files on a busy pool: 22 million files in 4 hours on a ZFS server. It
-  is now a per-directory worker-pool traversal that records size and mtime
-  during the walk, folding away the separate stat pass and halving metadata I/O.
-  Each `PATH` operand commits in its own transaction, so an interrupted scan
-  keeps completed operands (2026-07-24, branch `parallel-walk`)
-
-- Persistent scan database. `scan` maintains a SQLite database
-  (`modernc.org/sqlite`, pure Go, cgo stays disabled), keyed by absolute path,
-  that survives between runs. A rescan hashes only new or changed files, by
-  mtime and size. It deletes the records of files vanished from under the
-  scanned operands and leaves records outside them untouched, so `scan` can be
-  cronned daily. `report` and `trees` read the database, with no positional
-  arguments, instead of a scan stream. The database is at
-  `/var/lib/sfdupes/db.sqlite`, overridable via `SFDUPES_DATABASE`. WAL
+- persistent scan database (2026-07-24, branch `persistent-database`): `scan`
+  now maintains a SQLite database (`modernc.org/sqlite`, pure Go, cgo stays
+  disabled) keyed by absolute path that survives between runs — a rescan hashes
+  only new or changed files (by mtime/size), deletes records for files vanished
+  from under the scanned operands, and leaves records outside them untouched, so
+  `scan` can be cronned daily; `report` and `trees` read the database (no
+  positional arguments) instead of a scan stream. Database at
+  `/var/lib/sfdupes/db.sqlite`, overridable via `SFDUPES_DATABASE`; WAL
   journaling plus a single-transaction update keep a report run during a scan
-  safe (2026-07-24, branch `persistent-database`)
-
-- The `origin` remote (`git@git.eeqj.de:sneak/sfdupes.git`) added, `v0.0.1`
-  tagged, and `main` plus tags pushed (2026-07-23)
-
-- `scan` CLI rework. Required `PATH...` operands via cobra replace the `/srv`
-  `-root` default. The new `-x`/`--one-file-system` flag (GNU convention) stops
-  at filesystem boundaries, which are crossed by default (2026-07-23, branch
-  `scan-required-paths`)
-
-- The repo was brought into compliance with `REPO_POLICIES.md` (the version of
-  2026-07-06), the existing repo checklist and the Go styleguide. The audit of
-  2026-07-22 found these gaps, and the branch closed them:
-    - `.gitignore`, with OS, editor, Go and secrets patterns; the compiled
-      `sfdupes` binary and `files.dat` had been sitting untracked in the tree;
-    - `.editorconfig`;
-    - `LICENSE` and the README License section. MIT was assumed from house
-      convention, for the owner to confirm;
-    - `REPO_POLICIES.md` in the repo root;
-    - the canonical `.golangci.yml`, with the 150 findings it raised fixed;
-    - the `Makefile` targets `test`, `lint`, `fmt`, `fmt-check`, `docker` and
-      `hooks`, and a `check` target that no longer depends on `build`;
-    - a test suite, which the policy required with a 30-second timeout and the
-      conditional `-v` rerun. It covers parsing, grouping, digests, suppression,
-      hashing and the scan pipeline, at 64% coverage;
-    - a multistage `Dockerfile` with hash-pinned images, a fail-fast lint stage
-      and a build stage running `make check`, plus `.dockerignore`;
-    - `.gitea/workflows/check.yml`, running `docker build .` on push with the
-      checkout action pinned by commit SHA;
-    - the README sections the policy requires: a Description first line with the
-      name, purpose, category, license and author, then Getting Started,
-      Rationale, TODO, License and Author;
-    - the stale README non-goal "no git repository setup and no CI" removed;
-    - the pre-commit hook installed.
-
-    The code was already `gofmt`-clean, so no standalone formatting commit was
-    needed (2026-07-23, branch `repo-policy-compliance`)
-
-- `git init` with a README-only first commit; the code baseline committed on
-  `main` (2026-07-22)
-
-- `scan`, `report` and `trees` subcommands implemented (pre-git history)
+  safe
+- add the `origin` remote (`git@git.eeqj.de:sneak/sfdupes.git`), tag `v0.0.1`,
+  and push `main` plus tags (2026-07-23)
+- `scan` CLI rework (2026-07-23, branch `scan-required-paths`): required
+  `PATH...` operands via cobra flags replacing the `/srv` `-root` default; new
+  `-x`/`--one-file-system` flag (GNU convention) to stop at filesystem
+  boundaries, which are crossed by default
+- bring the repo into full policy compliance (2026-07-23, branch
+  `repo-policy-compliance`; checklist below)
+- `git init` with README-only first commit; code baseline committed on `main`
+  (2026-07-22)
+- implement `scan`, `report`, and `trees` subcommands (pre-git history)
 
 # Future Steps
 
-- Possible later features, out of scope per README: full-content verification of
-  candidates, and helper scripts for removal.
+- possible later features (explicitly out of scope per README): full-content
+  verification of candidates, removal-script helpers
 
-# Accepted Divergences
+# Repo Policy Compliance
 
-- Flat single-package layout, with the `.go` files in the repo root. That is
-  fine for a small single-binary tool per the Go styleguide, and the tracker
-  audit agrees.
+Audited 2026-07-22 against `REPO_POLICIES.md` (2026-07-06), the existing repo
+checklist, and the Go styleguide. Code is already gofmt-clean, so no standalone
+formatting commit is needed.
+
+- [x] `.gitignore` missing — the compiled `sfdupes` binary and `files.dat` sit
+      untracked in the tree; needs OS/editor/Go artifacts plus secrets patterns
+- [x] `.editorconfig` missing
+- [x] `LICENSE` missing and README has no License section (MIT assumed from
+      house convention — user to confirm)
+- [x] `REPO_POLICIES.md` missing from repo root
+- [x] `.golangci.yml` missing (install canonical copy); code must then pass
+      `make lint` (150 findings fixed; `make lint` is clean)
+- [x] `Makefile` lacks required targets `test`, `lint`, `fmt`, `fmt-check`,
+      `docker`, `hooks`; `check` currently depends on `build`, which writes the
+      binary (`make check` must not modify files)
+- [x] no tests — `go test ./...` has nothing to run; policy requires real tests
+      with a 30-second timeout and the conditional `-v` rerun pattern (suite
+      covers parsing, grouping, digests, suppression, hashing, and the scan
+      pipeline; 64% coverage)
+- [x] `Dockerfile` missing — Go multistage with hash-pinned images: fail-fast
+      lint stage, build stage running `make check`
+- [x] `.dockerignore` missing
+- [x] `.gitea/workflows/check.yml` missing (`docker build .` on push, checkout
+      action pinned by commit SHA)
+- [x] README lacks required sections: Description first line
+      (name/purpose/category/license/author), Getting Started, Rationale, TODO,
+      License, Author
+- [x] README non-goal "no git repository setup and no CI" is stale now that the
+      repo is under git with CI
+- [x] pre-commit hook not installed (`make hooks` once the target exists)
+
+Accepted divergences (no action):
+
+- flat single-package layout with `.go` files in the repo root — fine for a
+  small single-binary tool per the Go styleguide; the tracker audit agrees

db.go

@@ -47,14 +47,15 @@ const dbFilePerm = 0o644
 const lockFilePerm = 0o600
 
 // createTableSQL is the schema applied to a fresh database. Paths are
-// BLOBs because Unix paths are raw bytes, not guaranteed UTF-8. mtime
-// holds whole Unix seconds and mtime_nsec the nanoseconds within that
-// second. head, tail and content each hold the raw 32 bytes of a
-// SHA-256.
+// BLOBs because Unix paths are raw bytes, not guaranteed UTF-8.
+// disk_size holds the bytes the file takes on disk. mtime holds whole
+// Unix seconds and mtime_nsec the nanoseconds within that second. head,
+// tail and content each hold the raw 32 bytes of a SHA-256.
 const createTableSQL = `
 CREATE TABLE files (
     path       BLOB PRIMARY KEY,
     size       INTEGER NOT NULL,
+    disk_size  INTEGER NOT NULL,
     mtime      INTEGER NOT NULL,
     mtime_nsec INTEGER NOT NULL,
     head       BLOB NOT NULL,
@@ -69,14 +70,59 @@ const createIndexSQL = `
 CREATE INDEX files_signature ON files (size, head, tail, content)
 `
 
+// createTotalsSQL creates the totals table, which holds one row: the
+// number of records and the sizes of all records added up. Counting
+// them over files would read every record. The three triggers below
+// keep the row current, in the transaction of each change to files.
+const createTotalsSQL = `
+CREATE TABLE totals (
+    records INTEGER NOT NULL,
+    size    INTEGER NOT NULL
+)
+`
+
+// insertTotalsSQL adds the one row of totals, for an empty files table.
+const insertTotalsSQL = `
+INSERT INTO totals (records, size) VALUES (0, 0)
+`
+
+// totalsAfterInsertSQL counts each inserted record into totals.
+const totalsAfterInsertSQL = `
+CREATE TRIGGER totals_after_insert AFTER INSERT ON files BEGIN
+    UPDATE totals SET records = records + 1, size = size + NEW.size;
+END
+`
+
+// totalsAfterDeleteSQL takes each deleted record out of totals.
+const totalsAfterDeleteSQL = `
+CREATE TRIGGER totals_after_delete AFTER DELETE ON files BEGIN
+    UPDATE totals SET records = records - 1, size = size - OLD.size;
+END
+`
+
+// totalsAfterUpdateSQL replaces a record's old size in totals with its
+// new one. scan's upsert of an existing record is such an update.
+const totalsAfterUpdateSQL = `
+CREATE TRIGGER totals_after_update AFTER UPDATE OF size ON files BEGIN
+    UPDATE totals SET size = size + NEW.size - OLD.size;
+END
+`
+
+// recordCountSQL reads the number of records from totals.
+const recordCountSQL = `
+SELECT records FROM totals
+`
+
 // upsertSQL inserts one file record, replacing any existing record for
 // the same path.
 const upsertSQL = `
-INSERT INTO files (path, size, mtime, mtime_nsec, head, tail, content)
-VALUES (?, ?, ?, ?, ?, ?, ?)
+INSERT INTO files (
+    path, size, disk_size, mtime, mtime_nsec, head, tail, content
+)
+VALUES (?, ?, ?, ?, ?, ?, ?, ?)
 ON CONFLICT (path) DO UPDATE SET
-    size = excluded.size, mtime = excluded.mtime,
-    mtime_nsec = excluded.mtime_nsec,
+    size = excluded.size, disk_size = excluded.disk_size,
+    mtime = excluded.mtime, mtime_nsec = excluded.mtime_nsec,
     head = excluded.head, tail = excluded.tail,
     content = excluded.content
 `
@@ -150,9 +196,14 @@ func createDatabaseDirectory(path string) error {
 // scanParams are the connection parameters for scan: read-write, with
 // WAL journaling and a busy timeout, so a report can run while a cron
 // scan is in progress. closeScanDatabase leaves WAL mode again.
+//
+// Each write to files fires a trigger, so SQLite keeps a statement
+// journal for it. temp_store(MEMORY) keeps that journal in memory,
+// which costs far less than a temporary file.
 const scanParams = "_pragma=busy_timeout(10000)" +
 	"&_pragma=journal_mode(WAL)" +
-	"&_pragma=synchronous(NORMAL)"
+	"&_pragma=synchronous(NORMAL)" +
+	"&_pragma=temp_store(MEMORY)"
 
 // reportParams are the connection parameters for report, trees and
 // info: read-only, with the same busy timeout. They set no journal
@@ -426,14 +477,14 @@ func createSchema(ctx context.Context, db *sql.DB) error {
 
 	defer func() { _ = tx.Rollback() }()
 
-	_, err = tx.ExecContext(ctx, createTableSQL)
-	if err != nil {
-		return fmt.Errorf("create schema: %w", err)
-	}
-
-	_, err = tx.ExecContext(ctx, createIndexSQL)
-	if err != nil {
-		return fmt.Errorf("create schema: %w", err)
+	for _, stmt := range []string{
+		createTableSQL, createIndexSQL, createTotalsSQL, insertTotalsSQL,
+		totalsAfterInsertSQL, totalsAfterDeleteSQL, totalsAfterUpdateSQL,
+	} {
+		_, err = tx.ExecContext(ctx, stmt)
+		if err != nil {
+			return fmt.Errorf("create schema: %w", err)
+		}
 	}
 
 	_, err = tx.ExecContext(ctx,
@@ -480,7 +531,7 @@ func loadFileRows(ctx context.Context, db *sql.DB, total func(n int64),
 
 	var n int64
 
-	err = tx.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
+	err = tx.QueryRowContext(ctx, recordCountSQL).Scan(&n)
 	if err != nil {
 		return fmt.Errorf("count records: %w", err)
 	}
@@ -488,8 +539,8 @@ func loadFileRows(ctx context.Context, db *sql.DB, total func(n int64),
 	total(n)
 
 	rows, err := tx.QueryContext(ctx,
-		"SELECT path, size, mtime, mtime_nsec, head, tail, content "+
-			"FROM files ORDER BY path")
+		"SELECT path, size, disk_size, mtime, mtime_nsec, head, tail, "+
+			"content FROM files ORDER BY path")
 	if err != nil {
 		return fmt.Errorf("read records: %w", err)
 	}
@@ -503,7 +554,8 @@ func loadFileRows(ctx context.Context, db *sql.DB, total func(n int64),
 			r                         scanRec
 		)
 
-		err = rows.Scan(&path, &r.size, &sec, &nsec, &head, &tail, &content)
+		err = rows.Scan(&path, &r.size, &r.diskSize, &sec, &nsec,
+			&head, &tail, &content)
 		if err != nil {
 			return fmt.Errorf("read record: %w", err)
 		}
@@ -538,10 +590,11 @@ ORDER BY size DESC, head DESC, tail DESC, content DESC
 `
 
 // loadSignatureRows gives total the number of records, then streams
-// every record's signature and path to fn, without its mtime, in the
-// order of signatureRowsSQL. The count and the records are read in one
-// transaction, so they agree while a scan is committing. An error from
-// fn stops the reading and is returned as it is.
+// every record's signature and path to fn, without its mtime or its
+// disk_size, in the order of signatureRowsSQL. The count and the
+// records are read in one transaction, so they agree while a scan is
+// committing. An error from fn stops the reading and is returned as it
+// is.
 func loadSignatureRows(ctx context.Context, db *sql.DB,
 	total func(n int64), fn func(r scanRec) error,
 ) error {
@@ -556,7 +609,7 @@ func loadSignatureRows(ctx context.Context, db *sql.DB,
 
 	var n int64
 
-	err = tx.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
+	err = tx.QueryRowContext(ctx, recordCountSQL).Scan(&n)
 	if err != nil {
 		return fmt.Errorf("count records: %w", err)
 	}
@@ -622,7 +675,7 @@ func (r *scanRec) setHashes(head, tail, content []byte) error {
 func countRecords(ctx context.Context, db *sql.DB) (int64, error) {
 	var n int64
 
-	err := db.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
+	err := db.QueryRowContext(ctx, recordCountSQL).Scan(&n)
 	if err != nil {
 		return 0, fmt.Errorf("count records: %w", err)
 	}
@@ -630,12 +683,10 @@ func countRecords(ctx context.Context, db *sql.DB) (int64, error) {
 	return n, nil
 }
 
-// databaseCountsSQL counts the records and adds up their sizes, in one
-// pass over the table. A SUM over no rows is NULL, so on an empty table
-// the SUM falls back to 0.
+// databaseCountsSQL reads the number of records and the sizes of all
+// records added up from totals.
 const databaseCountsSQL = `
-SELECT COUNT(*), COALESCE(SUM(size), 0)
-FROM files
+SELECT records, size FROM totals
 `
 
 // databaseCounts is what info reads from the database: its schema
@@ -678,15 +729,15 @@ func readDatabaseCounts(ctx context.Context,
 	return c, nil
 }
 
-// loadFileMeta streams every record's path, size and mtime to fn. Scan
-// change detection needs no hash values, and skipping the hash columns
-// keeps the scan's in-memory index small on multi-million-file
-// databases.
+// loadFileMeta streams every record's path, size, disk_size and mtime
+// to fn. Scan change detection needs no hash values, and skipping the
+// hash columns keeps the scan's in-memory index small on
+// multi-million-file databases.
 func loadFileMeta(ctx context.Context, db *sql.DB,
-	fn func(path string, size int64, mtime time.Time),
+	fn func(path string, m fileMeta),
 ) error {
 	rows, err := db.QueryContext(ctx,
-		"SELECT path, size, mtime, mtime_nsec FROM files")
+		"SELECT path, size, disk_size, mtime, mtime_nsec FROM files")
 	if err != nil {
 		return fmt.Errorf("read records: %w", err)
 	}
@@ -695,16 +746,19 @@ func loadFileMeta(ctx context.Context, db *sql.DB,
 
 	for rows.Next() {
 		var (
-			path            []byte
-			size, sec, nsec int64
+			path      []byte
+			m         fileMeta
+			sec, nsec int64
 		)
 
-		err = rows.Scan(&path, &size, &sec, &nsec)
+		err = rows.Scan(&path, &m.size, &m.diskSize, &sec, &nsec)
 		if err != nil {
 			return fmt.Errorf("read record: %w", err)
 		}
 
-		fn(string(path), size, time.Unix(sec, nsec))
+		m.mtime = time.Unix(sec, nsec)
+
+		fn(string(path), m)
 	}
 
 	err = rows.Err()
@@ -722,21 +776,21 @@ func loadFileMeta(ctx context.Context, db *sql.DB,
 // WAL small and let concurrent reports observe progress.
 const updateBatchSize = 10000
 
-// applyChanges writes one scan's database changes — upserts for new and
-// changed files, deletes for vanished ones — in batched transactions.
-// Progress is rendered on prog (one increment per change).
+// applyChanges writes upserts for new and changed files and deletes for
+// vanished ones, in batched transactions. Progress is rendered on prog
+// (one increment per change).
 func applyChanges(ctx context.Context, db *sql.DB, upserts []scanRec,
 	deletes []string, prog *progress,
 ) error {
 	for batch := range slices.Chunk(upserts, updateBatchSize) {
-		err := applyBatch(ctx, db, batch, nil, prog)
+		err := applyBatch(ctx, db, batch, nil, nil, prog)
 		if err != nil {
 			return err
 		}
 	}
 
 	for batch := range slices.Chunk(deletes, updateBatchSize) {
-		err := applyBatch(ctx, db, nil, batch, prog)
+		err := applyBatch(ctx, db, nil, nil, batch, prog)
 		if err != nil {
 			return err
 		}
@@ -745,10 +799,26 @@ func applyChanges(ctx context.Context, db *sql.DB, upserts []scanRec,
 	return nil
 }
 
-// applyBatch commits one batch of upserts and deletes in a single
-// transaction.
+// applyDiskSizes writes the disk_size of each of recs into its record,
+// in batched transactions, and leaves the rest of the record alone.
+// Progress is rendered on prog (one increment per record).
+func applyDiskSizes(ctx context.Context, db *sql.DB, recs []fileRec,
+	prog *progress,
+) error {
+	for batch := range slices.Chunk(recs, updateBatchSize) {
+		err := applyBatch(ctx, db, nil, batch, nil, prog)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// applyBatch commits one batch of upserts, disk_size updates and
+// deletes in a single transaction.
 func applyBatch(ctx context.Context, db *sql.DB, upserts []scanRec,
-	deletes []string, prog *progress,
+	diskSizes []fileRec, deletes []string, prog *progress,
 ) error {
 	tx, err := db.BeginTx(ctx, nil)
 	if err != nil {
@@ -762,6 +832,11 @@ func applyBatch(ctx context.Context, db *sql.DB, upserts []scanRec,
 		return err
 	}
 
+	err = execDiskSizes(ctx, tx, diskSizes, prog)
+	if err != nil {
+		return err
+	}
+
 	err = execDeletes(ctx, tx, deletes, prog)
 	if err != nil {
 		return err
@@ -787,7 +862,7 @@ func execUpserts(ctx context.Context, tx *sql.Tx, upserts []scanRec,
 	defer func() { _ = st.Close() }()
 
 	for _, r := range upserts {
-		_, err = st.ExecContext(ctx, []byte(r.path), r.size,
+		_, err = st.ExecContext(ctx, []byte(r.path), r.size, r.diskSize,
 			r.mtime.Unix(), r.mtime.Nanosecond(),
 			r.head[:], r.tail[:], r.content[:])
 		if err != nil {
@@ -800,6 +875,31 @@ func execUpserts(ctx context.Context, tx *sql.Tx, upserts []scanRec,
 	return nil
 }
 
+// execDiskSizes sets the disk_size of the record of each of recs. It
+// does not touch size, so the totals triggers do not fire.
+func execDiskSizes(ctx context.Context, tx *sql.Tx, recs []fileRec,
+	prog *progress,
+) error {
+	st, err := tx.PrepareContext(ctx,
+		"UPDATE files SET disk_size = ? WHERE path = ?")
+	if err != nil {
+		return fmt.Errorf("prepare disk_size update: %w", err)
+	}
+
+	defer func() { _ = st.Close() }()
+
+	for _, r := range recs {
+		_, err = st.ExecContext(ctx, r.diskSize, []byte(r.path))
+		if err != nil {
+			return fmt.Errorf("update disk_size of %s: %w", r.path, err)
+		}
+
+		prog.increment()
+	}
+
+	return nil
+}
+
 // execDeletes removes the records for paths no longer present.
 func execDeletes(ctx context.Context, tx *sql.Tx, deletes []string,
 	prog *progress,

db_test.go

@@ -535,17 +535,12 @@ func TestLoadRowsRefuseWrongSizeHash(t *testing.T) {
 	}
 }
 
-// TestSignatureRowsNeedNoSort checks that SQLite reads signatureRowsSQL
-// from the files_signature index alone, with nothing to sort: the
-// first record comes at once, so report's read phase counts each
-// record as it comes rather than waiting on SQLite for all of them.
-func TestSignatureRowsNeedNoSort(t *testing.T) {
-	t.Parallel()
+// queryPlan returns the detail of each line of SQLite's EXPLAIN QUERY
+// PLAN for query.
+func queryPlan(t *testing.T, db *sql.DB, query string) []string {
+	t.Helper()
 
-	db := openTestDB(t)
-
-	rows, err := db.QueryContext(t.Context(),
-		"EXPLAIN QUERY PLAN "+signatureRowsSQL)
+	rows, err := db.QueryContext(t.Context(), "EXPLAIN QUERY PLAN "+query)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -573,12 +568,164 @@ func TestSignatureRowsNeedNoSort(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	return plan
+}
+
+// TestSignatureRowsNeedNoSort checks that SQLite reads signatureRowsSQL
+// from the files_signature index alone, with nothing to sort: the
+// first record comes at once, so report's read phase counts each
+// record as it comes rather than waiting on SQLite for all of them.
+func TestSignatureRowsNeedNoSort(t *testing.T) {
+	t.Parallel()
+
+	db := openTestDB(t)
+
+	plan := queryPlan(t, db, signatureRowsSQL)
+
 	want := []string{"SCAN files USING COVERING INDEX files_signature"}
 	if !slices.Equal(plan, want) {
 		t.Errorf("query plan = %q, want %q", plan, want)
 	}
 }
 
+// TestCountsReadOnlyTotals checks that SQLite answers the queries for
+// the number of records and their total size from the one row of
+// totals. A plan that reads files or its index reads every record.
+func TestCountsReadOnlyTotals(t *testing.T) {
+	t.Parallel()
+
+	db := openTestDB(t)
+
+	for _, query := range []string{recordCountSQL, databaseCountsSQL} {
+		plan := queryPlan(t, db, query)
+
+		want := []string{"SCAN totals"}
+		if !slices.Equal(plan, want) {
+			t.Errorf("query plan of %q = %q, want %q", query, plan, want)
+		}
+	}
+}
+
+// TestCountsComeFromTotals sets the row of totals to numbers that files
+// does not hold, then checks that scan's load phase, the read phases of
+// trees and report, and info each report the numbers from totals.
+func TestCountsComeFromTotals(t *testing.T) {
+	t.Parallel()
+
+	// files is empty, so a count over files gives 0 records of 0 bytes.
+	const records, size = 7, 9000
+
+	db := openTestDB(t)
+
+	_, err := db.ExecContext(t.Context(),
+		"UPDATE totals SET records = ?, size = ?", records, size)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	scanTotal, err := countRecords(t.Context(), db)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var treesTotal, reportTotal int64
+
+	err = loadFileRows(t.Context(), db,
+		func(n int64) { treesTotal = n }, func(scanRec) {})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = loadSignatureRows(t.Context(), db,
+		func(n int64) { reportTotal = n },
+		func(scanRec) error { return nil })
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	info, err := readDatabaseCounts(t.Context(), db)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for name, got := range map[string]int64{
+		"scan's load":   scanTotal,
+		"trees' read":   treesTotal,
+		"report's read": reportTotal,
+		"info":          info.records,
+	} {
+		if got != records {
+			t.Errorf("%s: %d records, want %d from totals",
+				name, got, records)
+		}
+	}
+
+	if info.size != size {
+		t.Errorf("info: size %d, want %d from totals", info.size, size)
+	}
+}
+
+// assertTotalsMatchFiles fails unless the row of totals holds the
+// number of records and the sizes of all records added up, as counted
+// over files.
+func assertTotalsMatchFiles(t *testing.T, db *sql.DB) {
+	t.Helper()
+
+	got, err := readDatabaseCounts(t.Context(), db)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var records, size int64
+
+	err = db.QueryRowContext(t.Context(),
+		"SELECT COUNT(*), COALESCE(SUM(size), 0) FROM files").
+		Scan(&records, &size)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if got.records != records || got.size != size {
+		t.Errorf("totals = %d records of %d bytes, files holds %d of %d",
+			got.records, got.size, records, size)
+	}
+}
+
+// TestTotalsMatchFiles scans the smoke tree, rescans it after two files
+// change size, and rescans it after two files are removed. After each
+// scan the row of totals must agree with files.
+func TestTotalsMatchFiles(t *testing.T) {
+	t.Parallel()
+
+	dir := buildSmokeTree(t)
+	db := openTestDB(t)
+
+	syncTree(t, db, dir)
+	assertTotalsMatchFiles(t, db)
+
+	writeFile(t, dir, "a/one.bin", pattern(10, 2500))
+	writeFile(t, dir, "t1/f1", pattern(30, 1000))
+
+	if st := syncTree(t, db, dir); st.updated != 2 {
+		t.Fatalf("rescan stats = %+v, want 2 updated", st)
+	}
+
+	assertTotalsMatchFiles(t, db)
+
+	for _, name := range []string{"a/unique.bin", "t2/sub/f2"} {
+		err := os.Remove(filepath.Join(dir, name))
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	if st := syncTree(t, db, dir); st.removed != 2 {
+		t.Fatalf("rescan stats = %+v, want 2 removed", st)
+	}
+
+	assertTotalsMatchFiles(t, db)
+}
+
 func TestApplyChangesRoundTrip(t *testing.T) {
 	t.Parallel()
 

info.go

@@ -26,11 +26,11 @@ func infoPhase(name string) string {
 // it. Any database problem, including a missing database, is fatal.
 //
 // The work runs in two phases, each under a progress display of its
-// own on stderr: open (open the database) and count (count the records,
-// with one query). Each display ends before the next phase starts, and
-// before an error is returned to be printed. The details are written
-// once the last display has ended, so no display is drawn while they
-// are written.
+// own on stderr: open (open the database) and count (read the number of
+// records and their total size from the totals table). Each display
+// ends before the next phase starts, and before an error is returned
+// to be printed. The details are written once the last display has
+// ended, so no display is drawn while they are written.
 func runInfo(ctx context.Context, stdout io.Writer) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
@@ -56,7 +56,7 @@ func runInfo(ctx context.Context, stdout io.Writer) error {
 
 	defer func() { _ = db.Close() }()
 
-	// One query counts everything, so the phase never has a total.
+	// One row holds both counts, so the phase never has a total.
 	prog = newProgress(progressParams{
 		label: infoPhase("count"), total: -1,
 		waitingFor: countingRecords,

main_test.go

@@ -180,9 +180,9 @@ func capture(t *testing.T, std **os.File) func() string {
 }
 
 // brokenDatabase writes a database that opens cleanly and passes the
-// schema-version check but has no files table, so the first query
-// fails with the database already open: a fatal error on a path that
-// owns an open database. It closes the database the way scan does.
+// schema-version check but has no tables, so the first query fails
+// with the database already open: a fatal error on a path that owns an
+// open database. It closes the database the way scan does.
 func brokenDatabase(t *testing.T) string {
 	t.Helper()
 
@@ -265,8 +265,9 @@ func TestRunFatalAfterOpenClosesDatabase(t *testing.T) {
 			assertFatalOutput(t, stderr.String(), stdout())
 
 			// Proof that the failure happened after the open: only a
-			// query against the opened database can report this.
-			if !strings.Contains(stderr.String(), "no such table: files") {
+			// query against the opened database can report this. Each
+			// subcommand's first query reads totals.
+			if !strings.Contains(stderr.String(), "no such table: totals") {
 				t.Errorf("stderr = %q, want the failure to come from a "+
 					"query on the open database", stderr.String())
 			}
@@ -817,6 +818,23 @@ func scanFixture(t *testing.T) []string {
 	return dupes
 }
 
+// storedDiskSize returns the disk_size of the record for path in the
+// database at dbPath. A test of a trees run compares with this rather
+// than with a new lstat, which on ZFS can differ from the scan's (see
+// diskSizeOf).
+func storedDiskSize(t *testing.T, dbPath, path string) int64 {
+	t.Helper()
+
+	db, err := openReportDatabase(t.Context(), dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() { _ = db.Close() }()
+
+	return recordByPath(t, dbRecords(t, db), path).diskSize
+}
+
 // scanOK runs scan over operands, fails the test unless it exits 0 with
 // nothing on stdout, and returns everything it printed to stderr.
 func scanOK(t *testing.T, operands ...string) string {
@@ -928,24 +946,21 @@ func TestRunScanWalksOperandUnderSymlinkOperand(t *testing.T) {
 }
 
 func TestRunScanSkipsZFSOperand(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
-
 	zfs := filepath.Join(t.TempDir(), ".zfs")
-	snapshot := filepath.Join(zfs, "snapshot", "hourly")
-	f := writeFile(t, snapshot, "f", pattern(1, 10))
+	f := writeFile(t, zfs, "snapshot/hourly/f", pattern(1, 10))
 
-	// An operand beneath a .zfs directory is walked, because it is not
-	// itself named .zfs.
-	scanOK(t, snapshot)
+	// No scan records a file inside a .zfs directory, so the record
+	// beneath the operand is written straight into the database.
+	path := seedDatabase(t, []scanRec{{size: 10, path: f}})
+	t.Setenv(databaseEnv, path)
 
 	assertOperandSkipped(t, path, zfs, ".zfs directory", f)
 }
 
 // assertOperandSkipped scans operand alone and checks that it is skipped
 // as kind: a warning naming it, one skip in the summary, exit 0, and the
-// record for kept, which an earlier scan stored beneath operand, still
-// in the database at dbPath.
+// record for kept, stored beneath operand before this scan, still in the
+// database at dbPath.
 func assertOperandSkipped(t *testing.T, dbPath, operand, kind,
 	kept string,
 ) {
@@ -974,6 +989,121 @@ func assertOperandSkipped(t *testing.T, dbPath, operand, kind,
 	recordByPath(t, dbRecords(t, db), kept)
 }
 
+// TestRunScanSkipsOperandInsideZFS scans a directory inside a .zfs
+// directory, first alone and then under another operand. Each time it
+// is warned about and counted as skipped, and nothing in it is walked.
+// The other operand is scanned as usual.
+func TestRunScanSkipsOperandInsideZFS(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := t.TempDir()
+	hourly := filepath.Join(dir, ".zfs", "snapshot", "hourly")
+	writeFile(t, hourly, "f", pattern(1, 10))
+	f := writeFile(t, dir, "f", pattern(2, 10))
+
+	warning := "walk " + hourly + ": skipping operand inside a .zfs directory\n"
+
+	for _, tc := range []struct {
+		operands []string
+		summary  string
+	}{
+		{
+			[]string{hourly},
+			"scan: 0 files seen (0 added, 0 updated, 0 removed, " +
+				"0 unchanged), 1 skipped\n",
+		},
+		{
+			[]string{dir, hourly},
+			"scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+				"0 unchanged), 1 skipped\n",
+		},
+	} {
+		stderr := scanOK(t, tc.operands...)
+		if !strings.Contains(stderr, warning) ||
+			!strings.Contains(stderr, tc.summary) {
+			t.Errorf("scan %q: stderr = %q, want %q and %q", tc.operands,
+				stderr, warning, tc.summary)
+		}
+	}
+
+	db, err := openDB(path, reportParams)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	if got := recordPaths(dbRecords(t, db)); !slices.Equal(got, []string{f}) {
+		t.Errorf("records = %q, want %q", got, []string{f})
+	}
+}
+
+// TestRunScanSkipsOperandThroughSymlinkIntoZFS scans snaps/daily, where
+// snaps is a symlink to pool/.zfs/snapshot. The operand is warned about
+// by the path given, counted as skipped, and not walked.
+func TestRunScanSkipsOperandThroughSymlinkIntoZFS(t *testing.T) {
+	t.Setenv(databaseEnv, testDBPath(t))
+
+	dir := t.TempDir()
+	writeFile(t, dir, "pool/.zfs/snapshot/daily/f", pattern(1, 10))
+
+	snaps := filepath.Join(dir, "snaps")
+
+	err := os.Symlink(filepath.Join(dir, "pool", ".zfs", "snapshot"), snaps)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	daily := filepath.Join(snaps, "daily")
+	stderr := scanOK(t, daily)
+
+	warning := "walk " + daily + ": skipping operand inside a .zfs directory\n"
+	summary := "scan: 0 files seen (0 added, 0 updated, 0 removed, " +
+		"0 unchanged), 1 skipped\n"
+
+	if !strings.Contains(stderr, warning) ||
+		!strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q and %q", stderr, warning, summary)
+	}
+}
+
+// TestRunScanWalksOperandThroughSymlink scans data/daily, where data is
+// a symlink to a directory outside any .zfs directory. The operand is
+// scanned as usual, and its file is recorded by the path given.
+func TestRunScanWalksOperandThroughSymlink(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := t.TempDir()
+	writeFile(t, dir, "pool/data/daily/f", pattern(1, 10))
+
+	data := filepath.Join(dir, "data")
+
+	err := os.Symlink(filepath.Join(dir, "pool", "data"), data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	daily := filepath.Join(data, "daily")
+	stderr := scanOK(t, daily)
+
+	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+		"0 unchanged), 0 skipped\n"
+	if !strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q", stderr, summary)
+	}
+
+	db, err := openDB(path, reportParams)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	recordByPath(t, dbRecords(t, db), filepath.Join(daily, "f"))
+}
+
 func TestRunReportSucceeds(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
@@ -1028,8 +1158,9 @@ func TestRunTreesSucceeds(t *testing.T) {
 
 	// The two directories holding the duplicate pair are duplicate
 	// trees of each other.
-	want := "first\tdupe\tfiles\tsize\n" +
-		filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) + "\t1\t300\n"
+	want := "first\tdupe\tfiles\tsize\tdisk_size\n" +
+		filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) + "\t1\t300\t" +
+		strconv.FormatInt(storedDiskSize(t, path, dupes[1]), 10) + "\n"
 	if got := stdout.String(); got != want {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
@@ -1063,9 +1194,10 @@ func TestRunReportsNeedOnlyReadAccess(t *testing.T) {
 	cases := map[string]string{
 		cmdReport: "first\tdupe\tsize\n" +
 			dupes[0] + "\t" + dupes[1] + "\t300\n",
-		cmdTrees: "first\tdupe\tfiles\tsize\n" +
+		cmdTrees: "first\tdupe\tfiles\tsize\tdisk_size\n" +
 			filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) +
-			"\t1\t300\n",
+			"\t1\t300\t" +
+			strconv.FormatInt(storedDiskSize(t, path, dupes[1]), 10) + "\n",
 	}
 
 	for name, want := range cases {
@@ -1100,8 +1232,11 @@ func assertRunsUseDatabase(t *testing.T, dir, name string) {
 		t.Errorf("report stdout = %q, want %q", got, want)
 	}
 
-	want = "first\tdupe\tfiles\tsize\n" +
-		filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) + "\t1\t300\n"
+	diskSize := storedDiskSize(t, filepath.Join(dir, name), dupes[1])
+
+	want = "first\tdupe\tfiles\tsize\tdisk_size\n" +
+		filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) + "\t1\t300\t" +
+		strconv.FormatInt(diskSize, 10) + "\n"
 	if got := runStdout(t, cmdTrees); got != want {
 		t.Errorf("trees stdout = %q, want %q", got, want)
 	}

progress.go

@@ -60,7 +60,7 @@ const fallbackWidth = 80
 const spinnerMargin = 5
 
 // countingRecords is what the display of a phase that reads the records
-// says while it counts them, before it has its total.
+// says until it has the number of records, its total.
 const countingRecords = "counting the records"
 
 // openPhase is the name of the phase in which report, trees and info

report.go

@@ -21,14 +21,16 @@ const minGroupSize = 2
 
 // scanRec is one file record from the database. The signature (size,
 // head, tail, content) is the duplicate key; mtime is informational
-// only and used by scan for change detection.
+// only and used by scan for change detection. diskSize is the bytes the
+// file takes on disk, which trees adds up.
 type scanRec struct {
-	size    int64
-	mtime   time.Time
-	head    [sha256.Size]byte
-	tail    [sha256.Size]byte
-	content [sha256.Size]byte
-	path    string
+	size     int64
+	diskSize int64
+	mtime    time.Time
+	head     [sha256.Size]byte
+	tail     [sha256.Size]byte
+	content  [sha256.Size]byte
+	path     string
 }
 
 // reportPhase names one phase of report with its place among all of
@@ -45,11 +47,11 @@ func reportPhase(name string) string {
 // problem, including a missing database, is fatal.
 //
 // The work runs in two phases, each under a progress display of its
-// own on stderr: open (open the database) and read (count the records,
-// then read them in signature order, writing each size's duplicate
-// groups to stdout once that size is read; see readReport). Each
-// display ends before the next phase starts, and before an error is
-// returned to be printed.
+// own on stderr: open (open the database) and read (read the number of
+// records from the totals table, then read the records in signature
+// order, writing each size's duplicate groups to stdout once that size
+// is read; see readReport). Each display ends before the next phase
+// starts, and before an error is returned to be printed.
 func runReport(ctx context.Context, stdout io.Writer) error {
 	dbPath, source, err := databasePath()
 	if err != nil {

report_test.go

@@ -38,8 +38,8 @@ func awkwardPairRecs() []scanRec {
 	h, tl, c := testHash("h"), testHash("t"), testHash("c")
 
 	return []scanRec{
-		{size: 5, head: h, tail: tl, content: c, path: "/d/A/f"},
-		{size: 5, head: h, tail: tl, content: c, path: awkwardDir + "/f"},
+		{size: 5, diskSize: 4096, head: h, tail: tl, content: c, path: "/d/A/f"},
+		{size: 5, diskSize: 4096, head: h, tail: tl, content: c, path: awkwardDir + "/f"},
 	}
 }
 

scan.go

@@ -52,23 +52,26 @@ const workQueueDepth = 1024
 // has already printed its line, so run prints nothing more.
 var errInterrupted = errors.New("scan interrupted")
 
-// fileRec carries one statted file between the scan phases. dev and
-// ino identify the underlying inode so hard-linked paths can share
-// one read; both are zero when the platform exposes no inode.
+// fileRec carries one statted file between the scan phases. diskSize is
+// the bytes the file takes on disk. dev and ino identify the underlying
+// inode so hard-linked paths can share one read; both are zero when the
+// platform exposes no inode.
 type fileRec struct {
-	path  string
-	size  int64
-	mtime time.Time
-	dev   uint64
-	ino   uint64
+	path     string
+	size     int64
+	diskSize int64
+	mtime    time.Time
+	dev      uint64
+	ino      uint64
 }
 
 // fileMeta is the in-memory index entry for one existing database
-// record: just enough for change detection. Hashes stay on disk; at
+// record: what the walk compares the file with. Hashes stay on disk; at
 // tens of millions of records they would dominate the scan's memory.
 type fileMeta struct {
-	size  int64
-	mtime time.Time
+	size     int64
+	diskSize int64
+	mtime    time.Time
 }
 
 // scanUnit is what every scan phase counts, as its progress display
@@ -339,11 +342,12 @@ type scanStats struct {
 // whatever remains after the walk and hash phases is deleted by the
 // update phase.
 type scanState struct {
-	db       *sql.DB
-	existing map[string]fileMeta
-	toHash   []fileRec // new and changed files: must be read
-	batch    []scanRec
-	st       scanStats
+	db        *sql.DB
+	existing  map[string]fileMeta
+	toHash    []fileRec // new and changed files: must be read
+	diskSizes []fileRec // unchanged files whose disk_size changed
+	batch     []scanRec
+	st        scanStats
 }
 
 // syncScan synchronizes the database with the filesystem under roots;
@@ -383,7 +387,8 @@ func (s *scanState) runPhases(ctx context.Context, roots []string,
 ) error {
 	// Types and filesystems are checked before pruning so that an
 	// operand under a dropped one is still scanned, not dropped as lying
-	// under it.
+	// under it, and so that an operand inside a .zfs directory gets its
+	// warning even when it lies under another operand.
 	roots = pruneRoots(s.walkableRoots(roots, rules), oneFS, rules,
 		deviceOfPath)
 
@@ -411,15 +416,15 @@ func (s *scanState) runPhases(ctx context.Context, roots []string,
 }
 
 // walkableRoots returns the operands the walk can start from: regular
-// files, and directories not named .zfs. Every other operand is warned
-// about, counted as skipped, and dropped. A dropped operand is no
-// longer a root, so the records stored beneath it are treated as if it
-// had not been given: those under no other root count as outside the
-// roots and are not deleted as unverified. An operand on a filesystem
-// in rules that is not persistent is dropped the same way, with a line
-// saying so that is not a warning, and is not counted as skipped. An
-// operand that fails lstat here is kept, and the walk warns about it
-// unless it no longer exists.
+// files, and directories not named .zfs, none of them inside a
+// directory named .zfs. Every other operand is warned about, counted as
+// skipped, and dropped. A dropped operand is no longer a root, so the
+// records stored beneath it are treated as if it had not been given:
+// those under no other root count as outside the roots and are not
+// deleted as unverified. An operand on a filesystem in rules that is not
+// persistent is dropped the same way, with a line saying so that is not
+// a warning, and is not counted as skipped. An operand that fails lstat
+// here is kept, and the walk warns about it unless it no longer exists.
 func (s *scanState) walkableRoots(roots []string, rules walkRules) []string {
 	kept := make([]string, 0, len(roots))
 
@@ -454,8 +459,8 @@ func (s *scanState) walkableRoots(roots []string, rules walkRules) []string {
 // included, so its display counts against the number of records.
 func (s *scanState) loadIndex(ctx context.Context, roots []string) error {
 	// Indexing tens of millions of records takes real time; without a
-	// display the scan looks hung before the walk begins. Counting them
-	// first gives the display its total.
+	// display the scan looks hung before the walk begins. The number of
+	// records, read first, gives the display its total.
 	prog := newProgress(progressParams{
 		label: scanPhase("load"), unit: scanUnit, total: -1,
 		waitingFor: countingRecords, stalledOn: "db",
@@ -471,24 +476,24 @@ func (s *scanState) loadIndex(ctx context.Context, roots []string) error {
 
 	s.existing = make(map[string]fileMeta)
 
-	return loadFileMeta(ctx, s.db,
-		func(path string, size int64, mtime time.Time) {
-			prog.increment()
+	return loadFileMeta(ctx, s.db, func(path string, m fileMeta) {
+		prog.increment()
 
-			if underAnyRoot(path, roots) {
-				s.existing[path] = fileMeta{size: size, mtime: mtime}
-			}
-		})
+		if underAnyRoot(path, roots) {
+			s.existing[path] = m
+		}
+	})
 }
 
 // walkPhase drains the walk and queues every new or changed file for
-// the hash phase. An unchanged file needs nothing more, and its record
-// counts as verified. A record at or below a path the walk left out,
-// because -x stopped at it, it is a default exclude, or it is not on a
-// persistent filesystem, counts as outside the roots: it is not
-// deleted. That does not hold below a root at or inside that path,
-// since that root's own walk verifies the records below it; nor is a
-// line printed for such a root.
+// the hash phase. An unchanged file is not read, and its record counts
+// as verified. When its disk_size differs from the record's, it is
+// queued for the update phase, which writes the new disk_size. A record
+// at or below a path the walk left out, because -x stopped at it, it is
+// a default exclude, or it is not on a persistent filesystem, counts as
+// outside the roots: it is not deleted. That does not hold below a root
+// at or inside that path, since that root's own walk verifies the
+// records below it; nor is a line printed for such a root.
 func (s *scanState) walkPhase(events <-chan walkEvent, roots []string) {
 	// The records the last scan left under the roots estimate how many
 	// files the walk will find. A first scan has none, and no estimate.
@@ -546,6 +551,13 @@ func (s *scanState) walkPhase(events <-chan walkEvent, roots []string) {
 		delete(s.existing, ev.rec.path)
 
 		s.st.unchanged++
+
+		// The space a file takes on disk can change while its size and
+		// mtime stay the same. ZFS, for one, counts a new file's blocks
+		// only seconds after the write.
+		if old.diskSize != ev.rec.diskSize {
+			s.diskSizes = append(s.diskSizes, ev.rec)
+		}
 	}
 
 	prog.finish()
@@ -694,12 +706,13 @@ func (s *scanState) recordRun(ctx context.Context, r hashResult) error {
 		s.resolve(rec.path)
 
 		s.batch = append(s.batch, scanRec{
-			size:    rec.size,
-			mtime:   rec.mtime,
-			head:    r.head,
-			tail:    r.tail,
-			content: r.content,
-			path:    rec.path,
+			size:     rec.size,
+			diskSize: rec.diskSize,
+			mtime:    rec.mtime,
+			head:     r.head,
+			tail:     r.tail,
+			content:  r.content,
+			path:     rec.path,
 		})
 	}
 
@@ -715,7 +728,7 @@ func (s *scanState) commitFullBatch(ctx context.Context) error {
 		return nil
 	}
 
-	err := applyBatch(ctx, s.db, s.batch, nil, nil)
+	err := applyBatch(ctx, s.db, s.batch, nil, nil, nil)
 	if err != nil {
 		return err
 	}
@@ -726,9 +739,10 @@ func (s *scanState) commitFullBatch(ctx context.Context) error {
 }
 
 // updatePhase writes the scan's tail under one progress display: the
-// final partial batch of hashed records, and deletions for every record
-// the scan did not verify (vanished files, plus paths that failed to
-// stat or hash).
+// final partial batch of hashed records, the new disk_size of every
+// unchanged file whose disk_size changed, and deletions for every
+// record the scan did not verify (vanished files, plus paths that
+// failed to stat or hash).
 func (s *scanState) updatePhase(ctx context.Context) error {
 	deletes := make([]string, 0, len(s.existing))
 	for path := range s.existing {
@@ -740,7 +754,7 @@ func (s *scanState) updatePhase(ctx context.Context) error {
 
 	s.st.removed = len(deletes)
 
-	total := len(s.batch) + len(deletes)
+	total := len(s.batch) + len(s.diskSizes) + len(deletes)
 	prog := newProgress(progressParams{
 		label: scanPhase("update"), unit: scanUnit, total: int64(total),
 		stalledOn: "db",
@@ -755,6 +769,11 @@ func (s *scanState) updatePhase(ctx context.Context) error {
 
 	s.batch = nil
 
+	err = applyDiskSizes(ctx, s.db, s.diskSizes, prog)
+	if err != nil {
+		return err
+	}
+
 	return applyChanges(ctx, s.db, nil, deletes, prog)
 }
 
@@ -874,9 +893,24 @@ func sendEvent(ctx context.Context, events chan<- walkEvent,
 
 // operandWarning returns the one-line warning for an operand the walk
 // does not start from, naming the path and what it is, or "" for one it
-// does: a regular file, or a directory not named .zfs. Symlinks are
-// never followed, including as operands.
+// does: a regular file, or a directory not named .zfs, that is not
+// inside a directory named .zfs, neither as given nor with its symlinks
+// resolved. Symlinks are never followed, including as operands.
 func operandWarning(root string, fi fs.FileInfo) string {
+	// The walk never enters a .zfs directory, so it starts from nothing
+	// inside one either, not even through a symlink. An operand whose
+	// symlinks cannot be resolved is checked as given.
+	resolved, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		resolved = root
+	}
+
+	if slices.Contains(strings.Split(filepath.Dir(root), "/"), ".zfs") ||
+		slices.Contains(strings.Split(filepath.Dir(resolved), "/"), ".zfs") {
+		return fmt.Sprintf("walk %s: skipping operand inside a .zfs directory",
+			root)
+	}
+
 	var kind string
 
 	switch mode := fi.Mode(); {
@@ -945,11 +979,12 @@ func seedRoot(ctx context.Context, root string, rules walkRules,
 
 	dev, ino := inodeOfInfo(fi)
 	rec := fileRec{
-		path:  root,
-		size:  fi.Size(),
-		mtime: fi.ModTime(),
-		dev:   dev,
-		ino:   ino,
+		path:     root,
+		size:     fi.Size(),
+		diskSize: diskSizeOfInfo(fi),
+		mtime:    fi.ModTime(),
+		dev:      dev,
+		ino:      ino,
 	}
 
 	if !isDatabaseFile(rec, rules) {
@@ -1129,11 +1164,12 @@ func emitFile(ctx context.Context, p string, e fs.DirEntry,
 
 	dev, ino := inodeOfInfo(info)
 	rec := fileRec{
-		path:  p,
-		size:  info.Size(),
-		mtime: info.ModTime(),
-		dev:   dev,
-		ino:   ino,
+		path:     p,
+		size:     info.Size(),
+		diskSize: diskSizeOfInfo(info),
+		mtime:    info.ModTime(),
+		dev:      dev,
+		ino:      ino,
 	}
 
 	if !isDatabaseFile(rec, rules) {
@@ -1225,6 +1261,23 @@ func inodeOfInfo(fi fs.FileInfo) (uint64, uint64) {
 	return statDev(st), st.Ino
 }
 
+// statBlockSize is the unit of st_blocks in an lstat result on Linux and
+// macOS, whatever the filesystem's own block size.
+const statBlockSize = 512
+
+// diskSizeOfInfo returns the bytes a file takes on disk: its allocated
+// blocks, st_blocks × 512. On a compressed or sparse file it is less
+// than the file's size. It is 0 when the platform exposes no block
+// count.
+func diskSizeOfInfo(fi fs.FileInfo) int64 {
+	st, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return 0
+	}
+
+	return st.Blocks * statBlockSize
+}
+
 // hashResult carries the hashes computed for one inode run (or the
 // error that prevented computing them) from the pool's workers to the
 // hash phase. Its run leaves out the paths found removed.

scan_test.go

@@ -42,6 +42,24 @@ func writeFile(t *testing.T, dir, name string, data []byte) string {
 	return p
 }
 
+// diskSizeOf returns the bytes the file at path takes on disk, from its
+// own lstat: st_blocks counts 512-byte units. ZFS counts a new file's
+// blocks only seconds after the write, and fsync does not hasten that.
+// A test therefore calls unix.Sync, which waits for it, before the scan
+// whose disk_size it compares with this.
+func diskSizeOf(t *testing.T, path string) int64 {
+	t.Helper()
+
+	var st syscall.Stat_t
+
+	err := syscall.Lstat(path, &st)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return st.Blocks * 512
+}
+
 // pattern returns n bytes of deterministic content seeded by tag.
 func pattern(tag byte, n int) []byte {
 	data := make([]byte, n)
@@ -1228,9 +1246,9 @@ func TestScanPipeline(t *testing.T) {
 // TestScanProgressNamesEachPhase checks the plain progress lines of a
 // first scan, and of a rescan of one operand holding two of the
 // database's records. Each phase's first line names it with its place
-// among the four: load counts the records before reading them, and the
-// walk estimates its total from the records under its operand, or says
-// its time remaining is unknown when there are none.
+// among the four: load gets the number of records before reading them,
+// and the walk estimates its total from the records under its operand,
+// or says its time remaining is unknown when there are none.
 //
 //nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
 func TestScanProgressNamesEachPhase(t *testing.T) {
@@ -1416,6 +1434,116 @@ func TestScanStoresRawHashes(t *testing.T) {
 	}
 }
 
+// TestScanStoresDiskSize scans a sparse file, which takes less space on
+// disk than its length, once through its directory and once as the
+// operand itself. Each scan stores the disk_size of the file's lstat.
+func TestScanStoresDiskSize(t *testing.T) {
+	t.Parallel()
+
+	const length = 1024 * 1024
+
+	p := sparseFile(t, t.TempDir(), "sparse", length)
+	pokeAt(t, p, 0, []byte("x"))
+
+	unix.Sync() // see diskSizeOf
+
+	want := diskSizeOf(t, p)
+	if want == 0 || want >= length {
+		t.Fatalf("the file takes %d bytes on disk, want more than none "+
+			"and fewer than its length %d", want, length)
+	}
+
+	for _, operand := range []string{filepath.Dir(p), p} {
+		db := openTestDB(t)
+		syncTree(t, db, operand)
+
+		got := recordByPath(t, dbRecords(t, db), p).diskSize
+		if got != want {
+			t.Errorf("scan of %s: disk_size = %d, want %d",
+				operand, got, want)
+		}
+	}
+}
+
+// TestSyncScanRewriteUpdatesDiskSize writes into the hole of a scanned
+// sparse file and moves its mtime on. The rescan hashes the file again
+// and rewrites its record with the new disk_size.
+func TestSyncScanRewriteUpdatesDiskSize(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	db := openTestDB(t)
+	p := sparseFile(t, dir, "sparse", 1024*1024)
+	pokeAt(t, p, 0, []byte("x"))
+
+	syncTree(t, db, dir)
+
+	before := recordByPath(t, dbRecords(t, db), p).diskSize
+
+	pokeAt(t, p, 512*1024, pattern(7, 64*1024))
+
+	// The write may leave the mtime the scan recorded; a later one makes
+	// the rescan read the file again.
+	later := time.Now().Add(time.Hour)
+
+	err := os.Chtimes(p, later, later)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	unix.Sync() // see diskSizeOf
+
+	want := diskSizeOf(t, p)
+	if want == before {
+		t.Fatalf("the file still takes %d bytes on disk after the write "+
+			"into its hole", want)
+	}
+
+	st := syncTree(t, db, dir)
+	if st != (scanStats{walked: 1, updated: 1}) {
+		t.Fatalf("rescan stats = %+v, want 1 updated", st)
+	}
+
+	got := recordByPath(t, dbRecords(t, db), p).diskSize
+	if got != want {
+		t.Errorf("disk_size = %d, want %d", got, want)
+	}
+}
+
+// TestSyncScanUnchangedUpdatesDiskSize gives a file's record a
+// disk_size the file does not have, as when ZFS had not yet counted the
+// file's blocks at the last scan. The rescan writes the file's own
+// disk_size into the record without reading the file again.
+func TestSyncScanUnchangedUpdatesDiskSize(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	db := openTestDB(t)
+	p := writeFile(t, dir, "a.bin", pattern(1, 500))
+
+	syncTree(t, db, dir)
+
+	// lstat counts 512-byte units, so no file takes 1 byte on disk.
+	_, err := db.ExecContext(t.Context(),
+		"UPDATE files SET disk_size = 1 WHERE path = ?", []byte(p))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	unix.Sync() // see diskSizeOf
+
+	// A file read again would count as updated.
+	st := syncTree(t, db, dir)
+	if st != (scanStats{walked: 1, unchanged: 1}) {
+		t.Fatalf("rescan stats = %+v, want 1 unchanged", st)
+	}
+
+	got := recordByPath(t, dbRecords(t, db), p).diskSize
+	if want := diskSizeOf(t, p); got != want {
+		t.Errorf("disk_size = %d, want %d", got, want)
+	}
+}
+
 // TestSyncScanSameSecondRewrite rewrites a file in place at the same
 // size with an mtime later in the same second as the recorded one: the
 // next scan must notice the change and re-hash the file. The operand is

trees.go

@@ -22,6 +22,10 @@ type treeNode struct {
 	digest    [sha256.Size]byte
 	fileCount int64
 	totalSize int64
+	// diskSize is the bytes the directory's files take on disk. Two
+	// copies of one tree have the same totalSize, but their diskSize
+	// can differ.
+	diskSize int64
 }
 
 // treesPhase names one phase of trees with its place among all of them,
@@ -40,11 +44,11 @@ func treesPhase(name string) string {
 // database problem, including a missing database, is fatal.
 //
 // The work runs in four phases, each under a progress display of its
-// own on stderr: open (open the database), read (count the records,
-// then read them into the hierarchy), group (group the directories by
-// digest) and write (write the groups to stdout). Each display ends
-// before the next phase starts, and before an error is returned to be
-// printed.
+// own on stderr: open (open the database), read (read the number of
+// records from the totals table, then read the records into the
+// hierarchy), group (group the directories by digest) and write (write
+// the groups to stdout). Each display ends before the next phase
+// starts, and before an error is returned to be printed.
 func runTrees(ctx context.Context, stdout io.Writer) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
@@ -139,15 +143,16 @@ func readTree(ctx context.Context, db *sql.DB,
 
 // writeTreeGroups writes dupes to stdout as TSV, a header line and then
 // a row for every member of each group but its first, counting each
-// group on prog once its rows are written. stdout may be the terminal
-// prog is drawn on, so the lines go through prog's writer. It returns
-// the number of rows (dupe trees) and the bytes they could reclaim.
+// group on prog once its rows are written. The disk_size column is the
+// dupe's own. stdout may be the terminal prog is drawn on, so the lines
+// go through prog's writer. It returns the number of rows (dupe trees)
+// and the bytes they could reclaim.
 func writeTreeGroups(stdout io.Writer, dupes [][]*treeNode,
 	prog *progress,
 ) (int, int64, error) {
 	out := prog.writer(stdout)
 
-	_, err := fmt.Fprintln(out, "first\tdupe\tfiles\tsize")
+	_, err := fmt.Fprintln(out, "first\tdupe\tfiles\tsize\tdisk_size")
 	if err != nil {
 		return 0, 0, fmt.Errorf("write stdout: %w", err)
 	}
@@ -159,9 +164,9 @@ func writeTreeGroups(stdout io.Writer, dupes [][]*treeNode,
 	for _, g := range dupes {
 		first := g[0]
 		for _, n := range g[1:] {
-			_, err = fmt.Fprintf(out, "%s\t%s\t%d\t%d\n",
+			_, err = fmt.Fprintf(out, "%s\t%s\t%d\t%d\t%d\n",
 				escapePath(first.path), escapePath(n.path),
-				first.fileCount, first.totalSize)
+				first.fileCount, first.totalSize, n.diskSize)
 			if err != nil {
 				return 0, 0, fmt.Errorf("write stdout: %w", err)
 			}
@@ -232,6 +237,7 @@ func (b *treeBuilder) add(r scanRec) {
 	dir.entries = append(dir.entries, fileEntry(name, r))
 	dir.fileCount++
 	dir.totalSize += r.size
+	dir.diskSize += r.diskSize
 }
 
 // openDir starts the directory called name inside the innermost open
@@ -270,6 +276,7 @@ func (b *treeBuilder) closeTo(n int) {
 			"d\x00"+name+"\x00"+string(dir.digest[:]))
 		dir.parent.fileCount += dir.fileCount
 		dir.parent.totalSize += dir.totalSize
+		dir.parent.diskSize += dir.diskSize
 		b.dirs = append(b.dirs, dir)
 	}
 }

trees_test.go

@@ -17,18 +17,24 @@ const treesOpenLine = "[1/4] open: opening the database, elapsed 0s, " +
 
 // smokeTreeRecs mirrors the README smoke-test tree layout: /d/t1 and
 // /d/t2 are identical, /d/t3 differs from them only by one filename.
+// Each file takes one 4 KiB block on disk.
 func smokeTreeRecs() []scanRec {
 	f1Head, f1Tail, f1Content := testHash("f1h"), testHash("f1t"), testHash("f1c")
 	f2Head, f2Tail, f2Content := testHash("f2h"), testHash("f2t"), testHash("f2c")
 
 	return []scanRec{
-		{size: 3000, head: f1Head, tail: f1Tail, content: f1Content, path: "/d/t1/f1"},
-		{size: 100, head: f2Head, tail: f2Tail, content: f2Content, path: "/d/t1/sub/f2"},
-		{size: 3000, head: f1Head, tail: f1Tail, content: f1Content, path: "/d/t2/f1"},
-		{size: 100, head: f2Head, tail: f2Tail, content: f2Content, path: "/d/t2/sub/f2"},
-		{size: 3000, head: f1Head, tail: f1Tail, content: f1Content, path: "/d/t3/f1"},
-		{size: 100, head: f2Head, tail: f2Tail, content: f2Content,
-			path: "/d/t3/sub/f2renamed"},
+		{size: 3000, diskSize: 4096, head: f1Head, tail: f1Tail,
+			content: f1Content, path: "/d/t1/f1"},
+		{size: 100, diskSize: 4096, head: f2Head, tail: f2Tail,
+			content: f2Content, path: "/d/t1/sub/f2"},
+		{size: 3000, diskSize: 4096, head: f1Head, tail: f1Tail,
+			content: f1Content, path: "/d/t2/f1"},
+		{size: 100, diskSize: 4096, head: f2Head, tail: f2Tail,
+			content: f2Content, path: "/d/t2/sub/f2"},
+		{size: 3000, diskSize: 4096, head: f1Head, tail: f1Tail,
+			content: f1Content, path: "/d/t3/f1"},
+		{size: 100, diskSize: 4096, head: f2Head, tail: f2Tail,
+			content: f2Content, path: "/d/t3/sub/f2renamed"},
 	}
 }
 
@@ -198,13 +204,33 @@ func TestRunTreesEscapesPaths(t *testing.T) {
 			code, exitOK, stderr.String())
 	}
 
-	want := "first\tdupe\tfiles\tsize\n" +
-		`/d/\tone\ntwo\rthree\\four` + "\t/d/A\t1\t5\n"
+	want := "first\tdupe\tfiles\tsize\tdisk_size\n" +
+		`/d/\tone\ntwo\rthree\\four` + "\t/d/A\t1\t5\t4096\n"
 	if got := stdout.String(); got != want {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
 }
 
+// TestRunTreesDiskSize runs trees on two copies of a tree whose files
+// take different space on disk. The row's disk_size is the sum over the
+// dupe copy's files, those in its subdirectory included.
+func TestRunTreesDiskSize(t *testing.T) {
+	f, g := testHash("f"), testHash("g")
+	recs := []scanRec{
+		{size: 10, diskSize: 4096, head: f, tail: f, content: f, path: "/a/f"},
+		{size: 20, diskSize: 4096, head: g, tail: g, content: g, path: "/a/sub/g"},
+		{size: 10, diskSize: 512, head: f, tail: f, content: f, path: "/b/f"},
+		{size: 20, diskSize: 1024, head: g, tail: g, content: g, path: "/b/sub/g"},
+	}
+
+	t.Setenv(databaseEnv, seedDatabase(t, recs))
+
+	want := "first\tdupe\tfiles\tsize\tdisk_size\n/a\t/b\t2\t30\t1536\n"
+	if got := runStdout(t, cmdTrees); got != want {
+		t.Errorf("stdout = %q, want %q", got, want)
+	}
+}
+
 // TestRunTreesProgressNamesEachPhase runs trees on the smoke-test
 // records with stderr not a terminal, and checks every line it prints
 // there. After the line naming the database, each phase prints a line
@@ -226,7 +252,8 @@ func TestRunTreesProgressNamesEachPhase(t *testing.T) {
 			code, exitOK, stderr())
 	}
 
-	report := "first\tdupe\tfiles\tsize\n/d/t1\t/d/t2\t2\t3100\n"
+	report := "first\tdupe\tfiles\tsize\tdisk_size\n" +
+		"/d/t1\t/d/t2\t2\t3100\t8192\n"
 	if got := stdout.String(); got != report {
 		t.Errorf("stdout = %q, want %q", got, report)
 	}
@@ -291,7 +318,9 @@ func TestWriteTreeGroupsOnTerminal(t *testing.T) {
 		shown = append(shown, line[strings.LastIndex(line, "\r")+1:])
 	}
 
-	want := []string{"first\tdupe\tfiles\tsize", "/d/t1\t/d/t2\t2\t3100"}
+	want := []string{
+		"first\tdupe\tfiles\tsize\tdisk_size", "/d/t1\t/d/t2\t2\t3100\t8192",
+	}
 	if len(shown) < len(want) || !slices.Equal(shown[:len(want)], want) {
 		t.Errorf("terminal shows lines %q, want %q first", shown, want)
 	}