scan: drop the stray [flags] from the usage line (closes #169 )

The scan Use string already names every flag, so cobra no longer appends its generic [flags]. A test checks the usage line in the help and in the usage error against the one README.md shows. Model: opus-5-5
2026-11-11 03:55:16 +00:00
16 changed files with 1018 additions and 1386 deletions
@@ -21,7 +21,7 @@ file takes too long. It has five subcommands. `scan` walks the filesystem and
 records the files it finds in an SQLite database. SQLite keeps a whole database
 in one file. The database is kept between runs. A rescan reads only new and
 changed files. That makes `scan` cheap enough to run every day from `cron`, the
-system's job scheduler. `report`, `trees` and `info` work from the database and
+system's job scheduler. `report`, `trees` and `info` read the database alone and
 can run at any time. `dwim` scans `/` and then prints the `trees` report, for a
 first look at a new machine with one command.
@@ -98,15 +98,13 @@ Each `-v` flag below makes a bind mount, which shows a host directory at a path
 inside the container. Bind-mount `/var/lib/sfdupes` to keep the database between
 runs. Mount the tree to scan at the same path inside the container as on the
 host. Read-only access is enough. The database then records the host's paths,
-and so do the reports. `report` and `trees` need that mount too. Without it,
+and so do the reports.
 every recorded path counts as gone, and each report holds only its header line.
 ```sh
 make docker
 docker run --rm -v /srv:/srv:ro -v /var/lib/sfdupes:/var/lib/sfdupes \
    sfdupes scan /srv
-docker run --rm -v /srv:/srv:ro -v /var/lib/sfdupes:/var/lib/sfdupes \
+docker run --rm -v /var/lib/sfdupes:/var/lib/sfdupes sfdupes report > dupes.tsv
    sfdupes report > dupes.tsv
 ```
 ### Daily scan from `cron`
@@ -161,10 +159,8 @@ to keep is your choice.
 A row is a candidate, not proof:
- The reports show each file as it was when a scan last recorded it. They check
+- The reports show each file as it was when a scan last recorded it. A file may
-  only that each copy still exists: the file, or the directory at the top of a
+  have changed or gone since.
  tree. A file may have changed since, and a file inside a tree may be gone. Run
  `scan` again to bring the reports up to date.
 - A file of 100 MiB or more is compared only on samples of its content (see
  "Duplicate detection").
 - Two paths that are hard links, two names for one file, are listed as
@@ -212,9 +208,8 @@ makes the comparison exact. Reading samples cuts a 150 GiB file to about 150 MiB
 of reads, at the price of a comparison that is not exact.
 The hashes live in a database that is kept between runs. A rescan reads only new
-files, and files whose size or modification time (mtime) differs from their
+files, and files whose size changed or whose modification time (mtime) is newer
-record. All analysis then works from the database. The reports only check that
+than recorded. All analysis then works from the database alone.
 each copy they name still exists.
 The goal is whole duplicated trees, not only single files. A download extracted
 twice, or a project copied once too often, is such a tree. It can be removed as
@@ -240,10 +235,9 @@ In order:
   the files of the directories it is reading.
 3. **Rescan cheaply, analyze from the database.** The scan keeps its database
   between runs, and an unchanged file is never read again. `report`, `trees`
-   and `info` work from the database and never read a scanned file. `report` and
+   and `info` work from the database alone and never touch the scanned
-   `trees` check only that each copy they name still exists, and leave out a
+   filesystem. `scan` is built to run from `cron`. The reports run at any time,
-   copy that is gone. `scan` is built to run from `cron`. The reports run at any
+   against what the database holds.
   time, against what the database holds.
 4. **Keep the streams apart.** Everything on stdout is machine-readable data.
   Everything for a human reader, such as progress and warnings, goes to stderr.
@@ -254,14 +248,15 @@ In order:
 - `report` prints the file-level duplicate report from the database.
 - `trees` prints the duplicate-tree report from the database.
 - `info` prints the database's details.
- `dwim` scans `/`, then prints the duplicate-tree report.
+- `dwim` scans `/` with the default excludes, then prints the duplicate-tree
  report.
 ```
-sfdupes scan [--workers N] [-x] [--no-default-excludes] [--exclude PATH]... PATH...
+sfdupes scan [--workers N] [-x] [--no-default-excludes] PATH...
 sfdupes report > dupes.tsv
 sfdupes trees > dupetrees.tsv
 sfdupes info
-sfdupes dwim [--workers N] [-x] [--no-default-excludes] [--exclude PATH]...
+sfdupes dwim
 sfdupes --version
 sfdupes [command] --help
 ```
@@ -291,34 +286,22 @@ The reference below is also the program's specification.
  database is `/var/lib/sfdupes/db.sqlite`. There is no command-line flag for
  it. The path names the file exactly, whatever characters it holds. A relative
  path is relative to the working directory.
- `--workers N` (`scan`, `dwim`) sets how many directories `scan` reads at once
+- `--workers N` (`scan`) sets how many directories `scan` reads at once while it
-  while it lists the trees. It also sets how many files `scan` reads at once
+  lists the trees. It also sets how many files `scan` reads at once while it
-  while it hashes them. The default is the number of CPUs. `N` must be at
+  hashes them. The default is the number of CPUs. `N` must be at least 1. A
-  least 1. A smaller value is a usage error, reported in one line on stderr with
+  smaller value is a usage error, reported in one line on stderr with exit 2
-  exit 2 before anything is scanned.
+  before anything is scanned.
- `-x`, `--one-file-system` (`scan`, `dwim`) keeps the walk of each operand out
+- `-x`, `--one-file-system` (`scan`) keeps the walk of each operand out of
-  of directories on other filesystems, as the same flag does for `du` and
+  directories on other filesystems, as the same flag does for `du` and `rsync`.
-  `rsync`. By default the walk also enters directories on other filesystems.
+  By default the walk also enters directories on other filesystems.
- `--no-default-excludes` (`scan`, `dwim`) lets the walk enter the default
+- `--no-default-excludes` (`scan`) lets the walk enter the default excludes.
-  excludes. Those are the system and temporary directories the walk otherwise
+  Those are the system and temporary directories the walk otherwise leaves out,
-  leaves out, such as `/var/tmp` on Linux (see "Rules for the walk").
+  such as `/var/tmp` on Linux (see "Rules for the walk").
 - `--exclude PATH` (`scan`, `dwim`) keeps the walk out of `PATH` and everything
  below it. `PATH` may be a directory or a file. The flag may be given more than
  once. The walk knows `PATH` by its device ID and inode number, as it knows the
  database files (see "Rules for the walk"). So the walk leaves `PATH` out
  whatever path leads to it. That includes a hard link to a file given as
  `PATH`. A symlink given as `PATH` excludes its target. An empty `PATH`, as in
  `--exclude ""`, is a usage error, reported in one line on stderr with exit 2
  before anything is scanned. A `PATH` that does not exist, or whose real path
  `scan` cannot find, is a fatal error. So is an operand at or below one (see
  "Operands").
 - `--version`, `-v` prints `sfdupes VERSION` (see "Install") to stdout and
  exits 0. It writes nothing to stderr.
 - `--help`, `-h`, alone or after a subcommand, prints the help text to stderr
-  and exits 0. It writes nothing to stdout. The help of `sfdupes` and of `scan`
+  and exits 0. It writes nothing to stdout. `sfdupes scan --help` also lists the
-  names the database. The help of `report`, `trees`, `info` and `dwim` says what
+  default excludes of the system it runs on, and the filesystem types the walk
  each prints. `sfdupes scan --help` and `sfdupes dwim --help` also list the
  default excludes of the system they run on, and the filesystem types the walk
  never records anything on.
 ### Duplicate detection
@@ -372,10 +355,6 @@ default. An operand may be a directory or a regular file.
 - An operand that does not exist is a fatal error, and so is a symlink whose
  target does not exist. `scan` then stops before it walks anything, and exits
  with code 1.
 - An operand at or below an `--exclude` path is a fatal error too. The message
  names the operand and the `--exclude` path. `scan` compares the operand and
  each directory above it with the `--exclude` paths by device ID and inode
  number, not by name.
 - Each operand is resolved to its real path before the walk, as `realpath`
  prints it. A relative operand is joined to the working directory as `pwd -P`
  prints it. Every symlink in the path is then followed. A `..` after a symlink
@@ -431,16 +410,17 @@ operands:
 - A file not yet in the database is hashed and inserted.
 - A file already in the database is not read again when its size and mtime match
-  its record. This is what makes a daily rescan cheap.
+  its record. The mtime matches when it is not newer than the recorded one. This
  is what makes a daily rescan cheap.
 - When such a file's size on disk differs from its recorded `disk_size`, `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 up to seconds after
  the write. A block is the unit in which a filesystem allocates disk space. A
  file scanned within those seconds gets its real `disk_size` at the next scan.
- `scan` hashes a file again when its size or its mtime differs from its record.
+- `scan` hashes a file again when its size differs or its mtime is newer. The
-  An older mtime counts as much as a newer one. A file put back by `cp -p`,
+  mtime is compared to the nanosecond, as finely as the filesystem records it. A
-  `rsync -a` or a restore from backup often has an older mtime. The mtime is
+  same-size rewrite counts as a change whenever the filesystem gives it a later
-  compared to the nanosecond, as finely as the filesystem records it.
+  mtime, even within the same second.
 - The scan deletes each record under a scanned operand whose file it could not
  verify. That covers deleted files, and paths the scan could not stat or read
  this run. To stat a file is to read its details, such as its size, without
@@ -451,16 +431,15 @@ operands:
  scanned on different schedules into one database.
 - The scan keeps every record at or below a path that the walk leaves out for
  one of these reasons:
    - it is an `--exclude` path;
    - it is a default exclude;
    - it is not on a persistent filesystem;
    - with `-x`, it is a directory on another filesystem than its operand.
    Such records count as outside the scanned operands. So with `-x`, a
    filesystem mounted under an operand can be scanned on its own schedule into
-    the same database. An operand may itself lie at or inside such a path, other
+    the same database. An operand may itself lie at or inside such a path, as
-    than an `--exclude` path (see "Operands"). Its walk verifies the records
+    "Operands" describes. Its walk verifies the records below it, so they are
-    below it, so they are deleted when their files are gone.
+    deleted when their files are gone.
 #### Phases
@@ -559,17 +538,6 @@ walk practical on large or busy storage pools.
    The path is not counted as skipped. The records below it are kept, as
    described under "What a scan does to the database".
 - The walk never enters or records an `--exclude` path, nor anything below it.
  For each one it reaches, `scan` prints a line on stderr naming it:
    ```
    scan: skipped /srv/cache (--exclude)
    ```
    The path is not counted as skipped. The scan keeps the records at and below
    it, as described under "What a scan does to the database".
    `--no-default-excludes` does not change this rule.
 - Below an operand, the walk does not enter a default exclude. On Linux, the
  default excludes hold temporary files and the kernel's view of the running
  system. They depend on the system, and `sfdupes scan --help` lists those of
@@ -644,8 +612,7 @@ from a thread of its own and never blocks the workers.
  it repeats another or lies under another;
 - the progress display of each phase (see "Progress"). `scan` prints each
  warning for a skipped path as it happens. It prints a line the same way for
-  each path left out as an `--exclude` path, as a default exclude or as not on a
+  each path left out as a default exclude or as not on a persistent filesystem;
  persistent filesystem;
 - the summary line;
 - a warning when a report still has the database open as the scan ends (see
  "Concurrent reads").
@@ -688,29 +655,21 @@ and `scan` leaves it ignored.
 `report` reads every record from the database. It takes no positional arguments.
 A positional argument is anything on the command line that is not a flag, such
-as the paths `scan` takes. `report` never opens a scanned file. It checks that
+as the paths `scan` takes. `report` never touches the scanned filesystem. It
-each path in a group still exists, and looks at no other path. The check is
+neither stats nor opens any path in the records. It reads the database and
-`lstat`, the system call that looks up a path without following a symlink:
+writes to stdout and stderr, and nothing else. Its output is the same whether or
-
+not the scanned filesystem is still mounted.
 - A path is gone when `lstat` finds that it, or a directory above it, does not
  exist.
 - Any other error, such as a permission error, counts as present. So a user who
  may not look inside a directory still sees its copies.
 The check does not notice a file that changed after the scan. Run `scan` again
 to bring the report up to date.
 Processing:
 - Records are grouped by signature, the four values
  `(size, head, tail, content)`.
- In a group with two or more paths, a path that is gone is left out. A group
+- Every group with two or more paths is a duplicate group.
  that still has two or more paths is a duplicate group.
 - Empty files form no group, because removing one frees nothing.
 - Within a group, paths are sorted in byte order. The first is `first`, and
  every other path is a `dupe`.
 - Groups are ordered by size, largest first, then by `first` path. The output is
-  the same for the same database contents and the same paths on disk.
+  the same for the same database contents.
 `report` has two phases, each with its own progress display on stderr (see
 "Progress"). `open` opens the database. `read` gets the number of records from
@@ -763,9 +722,8 @@ report: 14 records read, 4 duplicate groups, 7 dupe files, 10.0 KiB reclaimable
 `trees` reads the same database as `report` and takes no positional arguments.
 It reports whole duplicate directory trees. Two directories are duplicate trees
 when they hold the same relative paths, and each path holds a file with the same
-signature in both. It rebuilds the directory tree from the paths in the records,
+signature in both. Like `report`, it never touches the scanned filesystem. It
-split on `/`. Like `report`, it never opens a scanned file. It checks only that
+rebuilds the directory tree from the paths in the records, split on `/`.
 the directory at the top of each copy still exists, as `report` checks a path.
 Definitions:
@@ -792,13 +750,10 @@ Processing:
  directories that all have the same digest. The parents' group, or an
  ancestor's, already implies it. A group is always reported when it holds
  sibling directories, or when its members' parents have different digests.
 - A directory that is gone is dropped from its group. A group left with fewer
  than two directories is not reported.
 - Within a group, paths are sorted in byte order. The first is `first`, and
  every other path is a `dupe`.
 - Groups are ordered by total tree size, largest first, then by `first` path.
-  The output is the same for the same database contents and the same paths on
+  The output is the same for the same database contents.
  disk.
 Two limitations are accepted:
@@ -812,9 +767,8 @@ Two limitations are accepted:
 `trees` has four phases, each with its own progress display on stderr (see
 "Progress"). `open` opens the database. `read` gets the number of records from
 the `totals` table, then reads them in path order. It builds the directory tree
-and computes the digests as it goes. `group` groups the directories by digest,
+and computes the digests as it goes. `group` groups the directories by digest
-picks the groups to report and checks that their directories still exist.
+and picks the groups to report. `write` writes them to stdout.
 `write` writes the groups to stdout.
 #### Trees output format
@@ -857,25 +811,14 @@ trees: 14 records read, 1 duplicate tree groups, 1 dupe trees, 3.0 KiB reclaimab
 ### `dwim` mode
 `dwim`, short for "do what I mean", scans a new machine and reports its
-duplicate trees in one command. It takes no positional arguments. Like `scan`,
+duplicate trees in one command. It takes no positional arguments and no flags of
-it should run as root, so that it can read every file.
+its own. Like `scan`, it should run as root, so that it can read every file.
-`dwim` takes these flags of `scan`, with the same meaning (see "Settings"):
+`dwim` runs what `sfdupes scan /` runs with no flags. The walk skips the default
-
+excludes and crosses into other filesystems. `--workers` keeps its default. The
 - `--workers N`;
 - `-x`, `--one-file-system`;
 - `--no-default-excludes`;
 - `--exclude PATH`, which may be given more than once.
 `dwim` runs what `sfdupes scan /` runs with the same flags. With no flags, the
 walk skips the default excludes and crosses into other filesystems. The
 database, its creation and the scan lock are those of `scan`. Then `dwim` runs
 what `sfdupes trees` runs. The largest trees come first.
 ```
 sfdupes dwim -x --exclude /srv/cache
 ```
 The report goes to stdout, exactly as `trees` prints it. On stderr comes what
 `scan` prints, then what `trees` prints, then one last line:
@@ -883,8 +826,8 @@ The report goes to stdout, exactly as `trees` prints it. On stderr comes what
 dwim: run "sfdupes trees" to print this report again
 ```
-The database keeps the scan, so `sfdupes trees` prints the report again later,
+The database keeps the scan, so `sfdupes trees` prints the same report later,
-even after the terminal is gone. It then leaves out a copy deleted in between.
+even after the terminal is gone.
 `SIGINT` or `SIGTERM` stops the scan as it stops `scan` (see "Stopping a scan").
 `dwim` then prints no report and exits 1. A fatal scan error also ends it before
@@ -1176,10 +1119,9 @@ in, and a phase that may wait in two places names both, as `disk/db`:
 - `hash` says `disk/db`, because it reads files and writes their records to the
  database between them.
 - `load`, `update` and the `read` phase of `trees` say `db`.
- The `read` phase of `report` says `db/disk/out`. It checks that the paths of
+- The `read` phase of `report` says `db/out`, because it writes the report to
-  each group still exist, and writes the report to stdout, while it reads.
+  stdout while it reads.
- `group` of `trees` says `cpu/disk`, for work in memory and the check that each
+- `group` of `trees` says `cpu`, for work in memory, and its `write` says `out`.
  copy still exists. Its `write` says `out`.
 - A phase still waiting for its total says what it waits for, and nothing more.
 On a terminal:
@@ -1237,9 +1179,6 @@ showing the count it stopped at.
 - `1`: a fatal error, a `scan` stopped by `SIGINT` or `SIGTERM`, or a `dwim`
  stopped by either during its scan. A fatal error is one of these:
    - an operand that does not exist, or whose real path `scan` cannot find;
    - an `--exclude` path that does not exist, or whose real path `scan` cannot
      find;
    - an operand at or below an `--exclude` path;
    - a list of mounted filesystems that `scan` cannot read;
    - another `scan` holding the lock (see "The scan lock");
    - a database, its directory or its lock file that cannot be created or
@@ -1259,7 +1198,6 @@ showing the count it stopped at.
      `--workers abc`;
    - `scan` with no operand;
    - `--workers` below 1;
    - an empty `--exclude` value, as in `--exclude ""`;
    - `report`, `trees`, `info` or `dwim` with a positional argument.
 A fatal error is reported on stderr, starting with `sfdupes:`. A failed write to
@@ -1423,8 +1361,8 @@ commands of their own:
  not a goal. `modernc.org/sqlite` is pure Go too, so the binary builds without
  cgo. The `Makefile` exports `CGO_ENABLED=0`. The test build is the one
  exception, because the race detector needs cgo (see `script/test`).
- `report` and `trees` give the same output for the same database contents and
+- `report` and `trees` give the same output for the same database contents,
-  the same paths on disk, whatever order the records were inserted in.
+  whatever order the records were inserted in.
 ### Definition of done
@@ -1489,7 +1427,7 @@ All of the following, run in this directory, must pass:
    The test suite automates this scenario (see
    `internal/sfdupes/scan_test.go`). It also checks that `report` and `trees`
-    leave out a copy removed after the scan.
+    never touch the scanned filesystem.
 ## TODO
@@ -4,7 +4,7 @@
  the tracker yet is filed as an issue first.
 - Branch from `next`.
 - Do the work, with tests, in small focused commits.
- Delete Next Step from `TODO.md`, in the same commit as the work.
+- 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
@@ -15,7 +15,8 @@
 - 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.
+  the `1.0.0` milestone are what remains before the tag. This file records
  history and process, not the queue.
 # Next Step
@@ -23,6 +24,752 @@
  https://git.eeqj.de/sneak/sfdupes/milestone/17. The issues are not restated
  here, because a copy drifts as soon as the tracker moves.
 # Completed Steps
 Newest first. An entry ends with its date and its issue or branch, where those
 are known.
 - The usage line of `scan` no longer ends in `[flags]`. It is the line
  `README.md` shows under "Subcommands" (2026-11-11,
  https://git.eeqj.de/sneak/sfdupes/issues/169)
 - `report` and `trees` leave out empty files. `report` writes no group of size
  0, and `trees` writes no group whose trees hold 0 bytes. An empty file still
  counts toward a tree's digest (2026-11-11,
  https://git.eeqj.de/sneak/sfdupes/issues/178)
 - The Go code moved out of the repository root. `cmd/sfdupes/main.go` is the
  command, and it calls `Main` in the package `internal/sfdupes`. `main.go`
  became `internal/sfdupes/cli.go`. Every other file kept its name. The install
  path is now `sneak.berlin/go/sfdupes/cmd/sfdupes` (2026-11-10,
  https://git.eeqj.de/sneak/sfdupes/issues/157)
 - New subcommand `dwim`. It runs what `sfdupes scan /` runs with no flags, then
  what `sfdupes trees` runs. Its last line on stderr says that `sfdupes trees`
  prints the report again (2026-11-06,
  https://git.eeqj.de/sneak/sfdupes/issues/154)
 - `scan` resolves each operand to its real path, symlinks followed, before the
  walk. A symlink operand is scanned at its target instead of skipped. With
  `/srv/link` a symlink to a directory outside `/srv`, `scan /srv /srv/link/sub`
  walks `sub` on its own instead of dropping it and deleting its records
  (2026-11-06, https://git.eeqj.de/sneak/sfdupes/issues/144)
 - `README.md` and a comment in `internal/sfdupes/scan.go` no longer say ZFS
  counts a new file's blocks only seconds after the write. The count can land in
  under a second. Both now say up to seconds after the write, as the comment on
  `diskSizeOf` in `internal/sfdupes/scan_test.go` does (2026-11-03,
  https://git.eeqj.de/sneak/sfdupes/issues/152)
 - The three disk size tests in `internal/sfdupes/scan_test.go` no longer fail at
  random on ZFS. `unix.Sync` can return before ZFS has counted a file's blocks,
  and one ZFS commit can take a file through several sizes. The test that needs
  the size to change waits for it, for at most 30 seconds. Each test reads the
  size before and after its scan. The rewrite test rescans until the two reads
  match, then compares exactly. The other two fail only on a `disk_size` outside
  the two reads (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/150)
 - `TODO.md` rewritten from scratch by the same rules as `README.md`, sentence by
  sentence. 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
  (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/135)
 - `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 every setting and every subcommand. Development and testing come last.
  Every statement was checked against the code on `next`. Five comments in
  `internal/sfdupes/cli_test.go` cite "Settings", where their rules now live.
  One comment each in these files cites what the README now says:
    - `internal/sfdupes/scan_test.go`;
    - `internal/sfdupes/trees_test.go`;
    - `internal/sfdupes/exclude_test.go`.
    (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/135)
 - Each record holds `disk_size`, the bytes the file takes on disk. That is its
  allocated blocks, `st_blocks` × 512, from the `lstat` call the walk already
  makes. `trees` prints a `disk_size` column after `size`. It is the sum over
  the `dupe` copy's files. On a compressed or sparse file `disk_size` 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)
 - The database keeps the number of records and the sum of their sizes in the one
  row of a `totals` table. Three triggers on `files` keep that row current.
  `info` reads that row. 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. That wins back part of that time (2026-10-27,
  https://git.eeqj.de/sneak/sfdupes/issues/146)
 - 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
  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
  with the spinner, the hash phase's included. A phase with an exact total ends
  its line with its percent and a 10-column bar at the terminal's right edge.
  The bar no longer moves as the line's length changes. A line too wide for the
  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
  bytes of a SHA-256. That is 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)
 - The hash phase gives three hashes to every file that the walk records. `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, which counted the sizes of every walked file and of every
      record outside the operands. A file was hashed only when the census showed
      another file of its size;
    - the records without hashes;
    - the content phase.
    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` were copied
  again 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`;
    - the package install in `builder`.
    Docker keeps them until one of these changes:
    - the base image;
    - the install line;
    - `go.mod` or `go.sum`.
    Every step that checks or compiles the code still comes after
    `ARG CACHEBUST`. `golangci-lint run` also keeps the linter's own cache.
    README says the same (2026-10-18,
    https://git.eeqj.de/sneak/sfdupes/issues/109)
 - The release rule was set. Until 1.0, each tip of `main` that passes the build
  gets the next `v0.0.N` tag.
  `go install sneak.berlin/go/sfdupes/cmd/sfdupes@latest` then 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. That is 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;
    - how to check an installed binary.
    (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, so a `..` in it
  stays. 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,
  https://git.eeqj.de/sneak/sfdupes/issues/119)
 - `scan` never records its own database. Once the database and its `.lock` file
  are open, it notes the device and inode of each of these:
    - the database file;
    - its `-wal` and `-shm` files;
    - the `.lock` file.
    The walk passes over any file with the device and inode of one of them,
    however it reaches the file. It prints no line for such a file and counts
    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,
  such as `tmpfs` or `proc`. Such a filesystem is one the kernel makes up or
  keeps in memory. `scan` matches them by device ID, however the walk or the
  content phase reaches a path. 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, /var/tmp
    ```
    On macOS they are:
    ```
    /dev, /private/tmp, /private/var/tmp, /private/var/vm
    /System/Volumes/VM, /System/Volumes/Data
    ```
    A Windows list exists in the code but is not used. 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. 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)
 - A progress display's rate covers the items completed over the last 5 seconds.
  When stderr is not a terminal, it covers the items since the line before. It
  falls to 0 while nothing completes. 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 line shows
  `stalled` and where the phase waits in place of the rate, as
  `stalled disk/db`. The places are:
    - `disk`;
    - `db`;
    - `out`, for stdout;
    - `cpu`.
    A phase that may wait in two places names both. Each phase's word is set in
    the code that defines the phase. A line too wide for the terminal loses its
    bar first, then its rate or those words. Four parts stay whole:
    - the phase;
    - the progress;
    - the elapsed time;
    - the ETA, the time remaining.
    The content phase had one display for its checks and one for its reads. Both
    lost those words on an 80-column terminal, at counts like those of README's
    example. That happened for most elapsed times and ETAs in minutes. Every
    other phase kept them whenever the elapsed time and the ETA were both in
    minutes. The content phase writes its last partial batch, the records not
    yet 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 records have `head` and `tail` hashes;
    - how many records 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, a read of the database at one moment. The counts
    come 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 and holds
  only those of the size it is reading. It 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, from `[1/4] open` to
  `[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;
    - 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)
 - Each `scan` phase's progress display names the phase and its place among the
  five, as `[2/5] walk`. It runs from the moment that the phase starts. It
  shows:
    - the progress;
    - the elapsed time;
    - the ETA, the time remaining.
    `load` counts the records first. The walk's total is estimated from the
    records under the operands. The content phase takes its total from SQLite's
    grouping alone. Until the first record is returned, it says it is searching
    the database. On a terminal a phase with an exact total draws its line
    followed by the bar of the progress-bar library. 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 the
    terminal is, even after it is made narrower during a phase. A line too wide
    leaves out its rate, then its bar. The rest stays whole. The line is cut
    short only when the rest alone does not fit, as below about 70 columns late
    in a large scan. When stderr is not a terminal, 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. The line says whether that path is the default
  or comes 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 were copied again 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. Gone are
      `Dockerfile.lint`, `script/verify-lint-image-pin` and `make test-race`;
    - every `docker build` in `script/` passes a new `CACHEBUST` value. Every
      stage of the `Dockerfile` declares it 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. 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;
    - a coding agent's settings file is deleted.
    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;
    - the install of `git` and `make` in the build stage.
    Docker keeps them between builds. Every step that checks or compiles the
    code 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 a
  directory between the two, the inner one included, is on a different
  filesystem than the outer one. The inner operand is then walked on its own.
  For a regular-file operand the check starts at its directory. 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
  under its operand, instead of deleting them. It counts their sizes in the size
  census (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 that is now a FIFO or device node 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)
 - 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,
  https://git.eeqj.de/sneak/sfdupes/issues/12)
 - The narration was cut 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)
 - `make test-race` ran the test suite under the race detector in a cgo-enabled
  container, outside `make check`. 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.
  `make test-race` is gone (2026-10-04,
  https://git.eeqj.de/sneak/sfdupes/issues/18)
 - A bare `docker build .` failed, naming `script/cibuild` and `script/docker`,
  rather than serve the gates, the lint and test steps, from cache. 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)
 - `make fmt` and `make fmt-check` run `prettier` over all Markdown, and the
  Gitea workflow checks it. All Markdown was 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;
    - the `report` and `trees` summary lines;
    - every subcommand going through `runE`.
    (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/16)
 - `.golangci.yml` was replaced with the current canonical copy, which uses
  `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
  `internal/sfdupes/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
  (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 `internal/sfdupes/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)
 - Four inaccurate comments in `internal/sfdupes/cancel_test.go` were corrected,
  and `walkCancelInFlightDirs` was renamed 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,
  https://git.eeqj.de/sneak/sfdupes/issues/17)
 - `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
  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)
 - `--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,
  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,
  https://git.eeqj.de/sneak/sfdupes/issues/14)
 - Progress prints at once on a non-terminal and uses a real terminal test.
  Warnings print through a spinner instead of racing its redraw (2026-10-03,
  https://git.eeqj.de/sneak/sfdupes/issues/13)
 - These operands are warned about and skipped, and the records beneath them are
  kept:
    - symlinks;
    - sockets;
    - FIFOs;
    - device nodes;
    - `.zfs` directories.
    (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`
  (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,
  https://git.eeqj.de/sneak/sfdupes/issues/8)
 - Four characters are escaped in `report`, `trees` and warning paths:
    - tab;
    - newline;
    - carriage return;
    - backslash.
    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`. The Gitea workflow 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)
 - 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 ran after the update phase. It read a file 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. It never read a file gone or
  changed since its record was written. `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)
 - The dead `files.dat` references were removed from `Makefile`, `.gitignore` and
  `.dockerignore` (2026-09-21, branch `next`,
  https://git.eeqj.de/sneak/sfdupes/issues/22)
 - The lint-image pin comments and `FROM` form in `Dockerfile` and
  `Dockerfile.lint` were fixed. 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` is gone,
  and so is `script/verify-lint-image-pin`, which compared the two pins
  (2026-08-10, branch `next`, https://git.eeqj.de/sneak/sfdupes/issues/25)
 - All linting ran in Docker, via `Dockerfile.lint` and `script/lint`. 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. `script/lint` builds that phase alone, and the
  build stage depends on it 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)
 - 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 that `script/bootstrap` pinned. Builds then took up
  to 5m14s from an empty cache, 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 defeated for the gate steps, so `script/cibuild` and
  `script/docker` cannot report a pass they did not earn. The `Dockerfile`
  copies the tree before its gates. On an unchanged tree Docker served them from
  cache, and the build exited 0 without running them. 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. Every stage of the `Dockerfile`
  declares it before every step that checks or compiles the code. 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)
 - `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 reference derived from it. Any installed version that was
  not the pin was reinstalled, whether:
    - older;
    - newer;
    - absent;
    - 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. The version check
    was verified by bootstrapping this host from v2.10.1 to v2.12.2, and again
    to a no-op. Stub runs of the script under `dash` covered:
    - a thirteen-input version-parse matrix;
    - a shadowed install, which must exit non-zero;
    - an install destination not on `PATH`;
    - `GOBIN` set;
    - a wedged binary, which must hit the timeout.
    `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, since 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 passed from `cmd.Context()` as the first parameter, through:
    - `runScan`;
    - `syncScan`;
    - both worker pools;
    - the whole database layer.
    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 that it
    never reached looks vanished to the update phase. That phase's own `BeginTx`
    also fails on the cancelled context before deleting anything. The guard is
    still the barrier once an interrupted scan may commit what it has. Tests
    drive `run(scan)` against a database whose insert trigger aborts. They
    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, deterministically, by counting the scan's own checks of
    `ctx.Done()`. They assert that it stops at the guard with every record
    intact. It then holds a partial size census and a still-populated record
    index. Direct tests cover the remaining cancellation branches of both pools.
    They test:
    - `sendEvent`;
    - the walk workers;
    - `dispatchDirs`;
    - `feedHashJobs`;
    - `hashWorker`;
    - `hashPhase`.
    (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()` runs when a subcommand fails, and with
  it the SQLite WAL checkpoint. These return errors instead:
    - `runScan`;
    - `runReport`;
    - `runTrees`;
    - `loadRecords`;
    - `resolveRoots`.
    The single exit point is `run` in `internal/sfdupes/cli.go`. It maps a
    `fatalError`, anything a subcommand returned, 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, nor printed with the usage text.
    `internal/sfdupes/cli_test.go` drives the CLI in-process and asserts the
    exit codes from README "Error handling" and the stdout/stderr split. It also
    checks that a fatal error after the database is open leaves 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` was 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. Four thresholds now live under
  `linters.settings`, as the v2 schema requires, so they are applied:
    - `lll`;
    - `funlen`;
    - `cyclop`;
    - `dupl`.
    No new lint findings surfaced (2026-08-09, branch `golangci-v2.12.2`,
    https://git.eeqj.de/sneak/sfdupes/issues/3)
 - `Makefile` targets were 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 does nothing but call its script (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`)
 - The phases became scan-wide, with concurrent operands and batched updates. All
  operands seed the shared walk pool, and every pass runs once over the whole
  scan. So the totals and ETAs cover the whole scan. The per-operand walk, hash
  and update cycles and their stderr announcements are gone. The update pass
  writes in batches, each in its own transaction. The filesystem is
  authoritative and the database follows it, so one scan's changes need not land
  all at once (2026-07-24, branch `scan-wide-phases`)
 - The stat pass was 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. That restores 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`)
 - The walk became parallel. The walk pass was a single goroutine and took hours
  at about 20 million files on a busy pool. One ZFS server took 4 hours for 22
  million files. It is now a walk by a pool of per-directory workers that
  records size and mtime as it goes. That folds away the separate stat pass and
  halves the metadata reads. Each `PATH` operand commits in its own transaction,
  so an interrupted scan keeps completed operands (2026-07-24, branch
  `parallel-walk`)
 - `scan` gained a persistent database. It maintains an SQLite database that
  survives between runs, with the absolute path as each record's key. The driver
  is `modernc.org/sqlite`, pure Go, so cgo stays disabled. 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 run daily from `cron`. `report` and `trees` read the
  database, with no positional arguments, instead of a scan stream. The database
  is at `/var/lib/sfdupes/db.sqlite`, and `SFDUPES_DATABASE` overrides that. 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`, was added. `v0.0.1`
  was tagged, and `main` and the tags were pushed (2026-07-23)
 - The `scan` command line was reworked. Required `PATH...` operands, parsed by
  cobra, replace the `/srv` `-root` default. The new `-x`, `--one-file-system`
  flag follows the GNU convention and stops at filesystem boundaries, which the
  walk crosses 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 the standard patterns for secrets and for OS, editor
      and Go files. 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 its 150 findings fixed, so that
      `make lint` is clean;
    - the `Makefile` targets the policy requires:
        - `test` and `lint`;
        - `fmt` and `fmt-check`;
        - `docker` and `hooks`.
        `check` depended on `build`, which wrote the binary. `make check` must
        not modify files, so `check` no longer depends on `build`;
    - a test suite, which the policy required with a 30-second timeout and the
      conditional `-v` rerun. At 64% coverage, it covers:
        - parsing and grouping;
        - digests and suppression;
        - hashing and the scan pipeline;
    - a multistage `Dockerfile` and `.dockerignore`. The `Dockerfile` had:
        - hash-pinned images;
        - a lint stage that failed fast;
        - a build stage that ran `make check`;
    - `.gitea/workflows/check.yml`, running `docker build .` on push with the
      checkout action pinned by commit SHA;
    - the README sections the policy requires. The first is a Description whose
      first line names the project, its purpose and category, its license and
      its author. Then come Getting Started and Rationale, and at the end TODO,
      License and Author;
    - the stale README non-goal "no git repository setup and no CI" removed;
    - the pre-commit hook, installed with `make hooks` once that target existed.
    The code was already `gofmt`-clean, so no standalone formatting commit was
    needed (2026-07-23, branch `repo-policy-compliance`)
 - `git init` was run, with a README-only first commit. The code baseline was
  committed on `main` (2026-07-22)
 - The `scan`, `report` and `trees` subcommands were implemented (pre-git
  history)
 # Future Steps
 - Possible later features, out of scope per README, are a byte-for-byte check of
@@ -358,9 +358,8 @@ func TestRunScanInterrupted(t *testing.T) {
 	stderr := captureStderr(t)
 	dir := buildSmokeTree(t)
-	opts := scanOptions{workers: walkCancelWorkers}
+	err := runScan(t.Context(), []string{dir}, walkCancelWorkers, false,
-
+		false)
 	err := runScan(t.Context(), []string{dir}, opts)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -383,7 +382,8 @@ func TestRunScanInterrupted(t *testing.T) {
 	go func() {
 		defer close(done)
-		err = runScan(cancelledContext(t), []string{dir}, opts)
+		err = runScan(cancelledContext(t), []string{dir}, walkCancelWorkers,
 			false, false)
 	}()
 	awaitReturn(t, done, "runScan")
@@ -410,7 +410,8 @@ func TestRunScanInterrupted(t *testing.T) {
 			got, before)
 	}
-	err = runScan(t.Context(), []string{dir}, opts)
+	err = runScan(t.Context(), []string{dir}, walkCancelWorkers, false,
 		false)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -436,7 +437,7 @@ func TestRunScanInterruptedMidHash(t *testing.T) {
 	dir := buildWalkCancelTree(t)
 	err := runScan(newWalkClock(hashCancelAtDone), []string{dir},
-		scanOptions{workers: walkCancelWorkers})
+		walkCancelWorkers, false, false)
 	if !errors.Is(err, errInterrupted) {
 		t.Fatalf("runScan interrupted mid-hash = %v, want %v",
 			err, errInterrupted)
@@ -10,7 +10,6 @@ import (
 	"os"
 	"runtime"
 	"runtime/debug"
 	"slices"
 	"github.com/spf13/cobra"
 )
@@ -32,82 +31,15 @@ const (
 	cmdDwim   = "dwim"
 )
 // databaseHelp is the paragraph of the root and scan help that names
 // the database (README "Location").
 const databaseHelp = "scan and dwim store what they find in a database " +
 	"file. report, trees\nand info read it. The file is $" + databaseEnv +
 	" when that is set and\nnot empty, and otherwise " +
 	defaultDatabasePath + ", where creating it\nneeds root.\n"
 // escapesHelp is the paragraph of the report and trees help on how
 // paths are escaped (README "Report output format").
 const escapesHelp = `Four characters in a path are escaped, so each row stays one line:
  \\  a backslash
  \t  a tab
  \n  a newline
  \r  a carriage return
 `
 // reportHelp, treesHelp, infoHelp and dwimHelp follow the one-line
 // summary in the help of their subcommands.
 const (
 	reportHelp = `The report is tab-separated text on stdout: a header line, then one
 row per duplicate file. The columns are:
  first   the path that sorts first, byte by byte, in its group of copies
  dupe    another copy of that file
  size    the file's size in bytes
 Rows are ordered by size, largest first, then by path.
 ` + escapesHelp
 	treesHelp = `The report is tab-separated text on stdout: a header line, then one
 row per duplicate directory tree. The columns are:
  first      the path that sorts first, byte by byte, in its group of copies
  dupe       another copy of that tree
  files      the number of regular files in one copy
  size       their total size in bytes
  disk_size  the bytes the dupe copy takes on disk
 Rows are ordered by size, largest first, then by path.
 ` + escapesHelp
 	infoHelp = `The details go to stdout, one per line. Each line holds a name and its
 value, separated by a tab:
  database                the path, and where it came from
  database file size      in bytes, then rounded, as 2147483648 (2.0 GiB)
  -wal file size          in bytes, then rounded; only if a -wal file exists
  modified                when the database file last changed, in UTC
  schema version          the version of the database's layout
  records                 the number of records
  size of recorded files  their total size, in bytes, then rounded
 `
 	dwimHelp = `dwim runs what "sfdupes scan /" runs with the same flags, then what
 "sfdupes trees" runs. Run it as root, so that the scan can read every
 file. The scan is stored in the database, as scan stores it, so
 "sfdupes trees" prints the report again later.
 `
 )
 // errNoSubcommand is returned by the root command when it is invoked
 // without a subcommand. That is a usage error, and the usage text
 // cobra prints for it is the whole message.
 var errNoSubcommand = errors.New("no subcommand")
-// errWorkersBelowOne is the usage error for a --workers value below 1.
+// errWorkersBelowOne is the usage error for a scan --workers value
 // below 1.
 var errWorkersBelowOne = errors.New("--workers must be at least 1")
 // errEmptyExcludeValue is the usage error for an empty --exclude value,
 // as from --exclude "$DIR" with DIR unset. Taken as a path, it
 // would name the working directory.
 var errEmptyExcludeValue = errors.New("--exclude must not be empty")
 // Version is the build version, injected at link time via -ldflags
 // (see the Makefile); empty when the linker set none, as for a binary
 // built by go install. buildVersion turns it into what --version prints.
@@ -255,116 +187,65 @@ func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 		}),
 	}
-	root.Long = root.Short + ".\n\n" + databaseHelp
+	dwimCmd := &cobra.Command{
-	reportCmd.Long = reportCmd.Short + ".\n\n" + reportHelp
+		Use:   cmdDwim,
-	treesCmd.Long = treesCmd.Short + ".\n\n" + treesHelp
+		Short: "Scan / with the default excludes, then print the duplicate-tree report",
-	infoCmd.Long = infoCmd.Short + ".\n\n" + infoHelp
+		Args:  cobra.NoArgs,
 		RunE: runE(func(ctx context.Context, _ []string) error {
 			return runDwim(ctx, "/", stdout)
 		}),
 	}
-	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd,
+	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd, dwimCmd)
 		newDwimCommand(stdout))
 	return root
 }
-// scanOptions holds the values of the flags that scan and dwim share:
+// newScanCommand builds the scan subcommand, with its --workers, -x and
-// --workers, -x, --no-default-excludes and --exclude.
+// --no-default-excludes flags. Its help lists the default excludes of
-type scanOptions struct {
+// the system it runs on, and the filesystem types it never records
-	workers           int
+// anything on.
 	oneFS             bool
 	noDefaultExcludes bool
 	excludePaths      []string
 }
 // scanFlagsUsage names the flags that scan and dwim share, for their
 // usage lines.
 const scanFlagsUsage = "[--workers N] [-x] [--no-default-excludes] " +
 	"[--exclude PATH]..."
 // addScanFlags adds the flags that scan and dwim share to cmd, which
 // stores their values in opts.
 func addScanFlags(cmd *cobra.Command, opts *scanOptions) {
 	cmd.Flags().IntVar(&opts.workers, "workers", runtime.NumCPU(),
 		"concurrent workers for the walk and hash phases")
 	cmd.Flags().BoolVarP(&opts.oneFS, "one-file-system", "x", false,
 		"do not cross filesystem boundaries")
 	cmd.Flags().BoolVar(&opts.noDefaultExcludes, "no-default-excludes",
 		false, "enter the default excludes, the paths listed above")
 	// A string array, not a slice, so a comma in a path is not a
 	// separator.
 	cmd.Flags().StringArrayVar(&opts.excludePaths, "exclude", nil,
 		"never enter or record `PATH` or anything below it; repeatable")
 }
 // check rejects the flag values that are usage errors, before the
 // command runs. It is the PreRunE of scan and dwim.
 func (o *scanOptions) check(cmd *cobra.Command, _ []string) error {
 	err := checkScanWorkers(cmd, o.workers)
 	if err != nil {
 		return err
 	}
 	return rejectEmptyExcludeValue(cmd, o.excludePaths)
 }
 // newScanCommand builds the scan subcommand. Its help names the
 // database, and lists the default excludes of the system it runs on and
 // the filesystem types it never records anything on.
 func newScanCommand() *cobra.Command {
-	var opts scanOptions
+	var (
 		scanWorkers           int
 		scanOneFS             bool
 		scanNoDefaultExcludes bool
 	)
 	short := "Walk trees and synchronize the scan database"
 	scanCmd := &cobra.Command{
-		Use: cmdScan + " " + scanFlagsUsage + " PATH...",
+		Use: cmdScan + " [--workers N] [-x] [--no-default-excludes] PATH...",
 		// The Use line already names every flag, so cobra must not
 		// append its generic "[flags]" to it.
 		DisableFlagsInUseLine: true,
 		Short:                 short,
-		Long: short + ".\n\n" + databaseHelp + "\n" +
+		Long:                  short + ".\n\n" + defaultExcludesHelp(runtime.GOOS),
-			defaultExcludesHelp(runtime.GOOS),
+		Args:                  cobra.MinimumNArgs(1),
-		Args:    cobra.MinimumNArgs(1),
+		PreRunE: func(cmd *cobra.Command, _ []string) error {
-		PreRunE: opts.check,
+			return checkScanWorkers(cmd, scanWorkers)
 		},
 		RunE: runE(func(ctx context.Context, args []string) error {
 			ctx, stop := interruptContext(ctx)
 			defer stop()
-			return runScan(ctx, args, opts)
+			return runScan(ctx, args, scanWorkers, scanOneFS,
 				scanNoDefaultExcludes)
 		}),
 	}
-	addScanFlags(scanCmd, &opts)
+	scanCmd.Flags().IntVar(&scanWorkers, "workers", runtime.NumCPU(),
 		"concurrent workers for the walk and hash phases")
 	scanCmd.Flags().BoolVarP(&scanOneFS, "one-file-system", "x", false,
 		"do not cross filesystem boundaries")
 	scanCmd.Flags().BoolVar(&scanNoDefaultExcludes, "no-default-excludes",
 		false, "enter the default excludes, the paths listed above")
 	return scanCmd
 }
-// newDwimCommand builds the dwim subcommand, which takes the scan flags
+// checkScanWorkers rejects a scan --workers value below 1. That is a
-// with the meaning they have for scan. Its help says what dwim runs,
+// usage error reported in one line: cobra prints the returned message
-// then lists the default excludes and the filesystem types the scan
+// without the usage text, and run exits 2.
 // never records anything on.
 func newDwimCommand(stdout io.Writer) *cobra.Command {
 	var opts scanOptions
 	short := "Scan /, then print the duplicate-tree report"
 	dwimCmd := &cobra.Command{
 		Use:                   cmdDwim + " " + scanFlagsUsage,
 		DisableFlagsInUseLine: true,
 		Short:                 short,
 		Long: short + ".\n\n" + dwimHelp + "\n" +
 			defaultExcludesHelp(runtime.GOOS),
 		Args:    cobra.NoArgs,
 		PreRunE: opts.check,
 		RunE: runE(func(ctx context.Context, _ []string) error {
 			return runDwim(ctx, "/", opts, stdout)
 		}),
 	}
 	addScanFlags(dwimCmd, &opts)
 	return dwimCmd
 }
 // checkScanWorkers rejects a --workers value below 1. That is a usage
 // error reported in one line: cobra prints the returned message without
 // the usage text, and run exits 2.
 func checkScanWorkers(cmd *cobra.Command, workers int) error {
 	if workers >= 1 {
 		return nil
@@ -375,18 +256,6 @@ func checkScanWorkers(cmd *cobra.Command, workers int) error {
 	return fmt.Errorf("%w, got %d", errWorkersBelowOne, workers)
 }
 // rejectEmptyExcludeValue rejects an empty --exclude value. That
 // is a usage error reported in one line, as for --workers below 1.
 func rejectEmptyExcludeValue(cmd *cobra.Command, excludePaths []string) error {
 	if !slices.Contains(excludePaths, "") {
 		return nil
 	}
 	cmd.SilenceUsage = true
 	return errEmptyExcludeValue
 }
 // runE adapts a subcommand implementation, or the version print, to
 // cobra's RunE. Cobra prints the error and the command's usage text for
 // every error RunE returns, but a subcommand that ran and failed has no
@@ -22,12 +22,6 @@ import (
 // error prints and a runtime failure must not.
 const usageMarker = "Usage:"
 // helpFlag asks for the help text.
 const helpFlag = "--help"
 // workersFlag is the scan and dwim flag that sets the worker count.
 const workersFlag = "--workers"
 // TestMain stops the tests at once, saying why, when their temporary
 // directory is not on a persistent filesystem: scan records nothing
 // there (README "Rules for the walk"), so most scan tests would fail
@@ -576,8 +570,7 @@ func TestRunNamesDefaultDatabase(t *testing.T) {
 	}{
 		cmdScan: {
 			run: func() error {
-				return runScan(t.Context(), []string{missing},
+				return runScan(t.Context(), []string{missing}, 1, false, false)
 					scanOptions{workers: 1})
 			},
 			want: scanWant,
 		},
@@ -668,7 +661,7 @@ func TestRunScanRejectsWorkersBelowOne(t *testing.T) {
 			var stdout, stderr bytes.Buffer
-			args := []string{cmdScan, workersFlag, workers, t.TempDir()}
+			args := []string{cmdScan, "--workers", workers, t.TempDir()}
 			code := run(args, &stdout, &stderr)
 			if code != exitUsage {
@@ -699,7 +692,7 @@ func TestRunHelp(t *testing.T) {
 	// README §Settings: help goes to stderr, exits 0, and leaves stdout
 	// empty.
-	cases := [][]string{{helpFlag}, {"-h"}, {cmdScan, helpFlag}}
+	cases := [][]string{{"--help"}, {"-h"}, {cmdScan, "--help"}}
 	for _, args := range cases {
 		var stdout, stderr bytes.Buffer
@@ -719,16 +712,6 @@ func TestRunHelp(t *testing.T) {
 				args, got)
 		}
 	}
 	// The scan help lists --exclude with its argument.
 	var stdout, stderr bytes.Buffer
 	run([]string{cmdScan, "-h"}, &stdout, &stderr)
 	if !strings.Contains(stderr.String(), excludeFlag+" PATH") {
 		t.Errorf("scan -h stderr = %q, want %s PATH", stderr.String(),
 			excludeFlag)
 	}
 }
 func TestRunScanUsageLine(t *testing.T) {
@@ -736,8 +719,7 @@ func TestRunScanUsageLine(t *testing.T) {
 	// README §Subcommands shows this usage line for scan, and the help
 	// and the usage error both print it.
-	const want = "\n  sfdupes scan [--workers N] [-x] [--no-default-excludes] " +
+	const want = "\n  sfdupes scan [--workers N] [-x] [--no-default-excludes] PATH...\n"
 		"[--exclude PATH]... PATH...\n"
 	cases := map[string][]string{
 		"help":          {cmdScan, "-h"},
@@ -760,73 +742,6 @@ func TestRunScanUsageLine(t *testing.T) {
 	}
 }
 func TestRunHelpDescribesDatabaseAndOutput(t *testing.T) {
 	t.Parallel()
 	// README §Settings: the help names the database, and says what
 	// report, trees, info and dwim print.
 	database := []string{
 		"scan and dwim store", databaseEnv, defaultDatabasePath, "needs root",
 	}
 	escapes := []string{`\\`, `\t`, `\n`, `\r`}
 	// The subcommand whose help is printed; none for the root.
 	cases := []struct {
 		subcommand []string
 		want       []string
 	}{
 		{nil, database},
 		{[]string{cmdScan}, database},
 		{
 			[]string{cmdReport},
 			append([]string{
 				"tab-separated", "\n  first ", "\n  dupe ", "\n  size ",
 				"largest first",
 			}, escapes...),
 		},
 		{
 			[]string{cmdTrees},
 			append([]string{
 				"tab-separated", "\n  first ", "\n  dupe ", "\n  files ",
 				"\n  size ", "\n  disk_size ", "largest first",
 			}, escapes...),
 		},
 		{
 			[]string{cmdInfo},
 			[]string{
 				"\n  database ", "\n  database file size ",
 				"\n  -wal file size ", "\n  modified ",
 				"\n  schema version ", "\n  records ",
 				"\n  size of recorded files ",
 			},
 		},
 		{
 			[]string{cmdDwim},
 			[]string{
 				"sfdupes scan /", "as root", "sfdupes trees", "database",
 			},
 		},
 	}
 	for _, tc := range cases {
 		var stdout, stderr bytes.Buffer
 		args := slices.Concat(tc.subcommand, []string{helpFlag})
 		code := run(args, &stdout, &stderr)
 		if code != exitOK {
 			t.Fatalf("run(%v) = %d, want %d", args, code, exitOK)
 		}
 		for _, want := range tc.want {
 			if !strings.Contains(stderr.String(), want) {
 				t.Errorf("run(%v) help lacks %q:\n%s",
 					args, want, stderr.String())
 			}
 		}
 	}
 }
 func TestRunVersion(t *testing.T) {
 	t.Parallel()
@@ -5,20 +5,19 @@ import (
 	"fmt"
 	"io"
 	"os"
 	"runtime"
 )
 // runDwim implements the dwim subcommand: it runs what "sfdupes scan
-// root" runs with the scan flags in opts, then what "sfdupes trees"
+// root" runs with no flags, then what "sfdupes trees" runs, and ends
-// runs, and ends with a line on stderr saying how to print the report
+// with a line on stderr saying how to print the report again. The dwim
-// again. The dwim command passes "/" as root. It catches SIGINT and
+// command passes "/" as root. It catches SIGINT and SIGTERM as scan
-// SIGTERM as scan does, but only during the scan. An error from the
+// does, but only during the scan. An error from the scan, an interrupt
-// scan, an interrupt included, ends it before the report. During the
+// included, ends it before the report. During the report, a signal
-// report, a signal ends it at once, as it ends trees.
+// ends it at once, as it ends trees.
-func runDwim(
+func runDwim(ctx context.Context, root string, stdout io.Writer) error {
 	ctx context.Context, root string, opts scanOptions, stdout io.Writer,
 ) error {
 	scanCtx, stop := interruptContext(ctx)
-	err := runScan(scanCtx, []string{root}, opts)
+	err := runScan(scanCtx, []string{root}, runtime.NumCPU(), false, false)
 	stop()
@@ -2,10 +2,7 @@ package sfdupes //nolint:testpackage // calls the unexported runDwim
 import (
 	"bytes"
 	"errors"
 	"os"
 	"path/filepath"
 	"runtime"
 	"strings"
 	"testing"
 )
@@ -31,7 +28,7 @@ func TestRunDwimPrintsLargestTreesFirst(t *testing.T) {
 	stderr := captureStderr(t)
-	err := runDwim(t.Context(), root, scanOptions{workers: 1}, &stdout)
+	err := runDwim(t.Context(), root, &stdout)
 	if err != nil {
 		t.Fatalf("runDwim: %v; stderr: %s", err, stderr())
 	}
@@ -70,7 +67,7 @@ func TestRunDwimScanErrorPrintsNoReport(t *testing.T) {
 	stderr := captureStderr(t)
-	err := runDwim(t.Context(), missing, scanOptions{workers: 1}, &stdout)
+	err := runDwim(t.Context(), missing, &stdout)
 	if err == nil {
 		t.Fatal("runDwim on a missing root: error = nil, want it fatal")
 	}
@@ -84,127 +81,3 @@ func TestRunDwimScanErrorPrintsNoReport(t *testing.T) {
 		t.Errorf("stderr = %q, want nothing from trees or dwim", got)
 	}
 }
 func TestRunDwimExcludeLeavesTreeOut(t *testing.T) {
 	// dwim passes its --exclude paths to the scan: an excluded copy is
 	// not recorded, so its pair is not reported.
 	t.Setenv(databaseEnv, testDBPath(t))
 	root := realTempDir(t)
 	kept := []string{
 		filepath.Dir(writeFile(t, root, "a1/f.bin", pattern(1, 300))),
 		filepath.Dir(writeFile(t, root, "a2/f.bin", pattern(1, 300))),
 	}
 	writeFile(t, root, "b1/f.bin", pattern(2, 5000))
 	excluded := filepath.Dir(writeFile(t, root, "b2/f.bin", pattern(2, 5000)))
 	var stdout bytes.Buffer
 	stderr := captureStderr(t)
 	opts := scanOptions{workers: 1, excludePaths: []string{excluded}}
 	err := runDwim(t.Context(), root, opts, &stdout)
 	if err != nil {
 		t.Fatalf("runDwim: %v; stderr: %s", err, stderr())
 	}
 	lines := strings.Split(strings.TrimSuffix(stdout.String(), "\n"), "\n")
 	if len(lines) != 2 {
 		t.Fatalf("stdout = %q, want a header and one group",
 			stdout.String())
 	}
 	want := kept[0] + "\t" + kept[1] + "\t1\t300\t"
 	if !strings.HasPrefix(lines[1], want) {
 		t.Errorf("group = %q, want it to start %q", lines[1], want)
 	}
 	skipped := "scan: skipped " + excluded + " (--exclude)\n"
 	if got := stderr(); !strings.Contains(got, skipped) {
 		t.Errorf("stderr = %q, want it to contain %q", got, skipped)
 	}
 }
 func TestRunDwimTakesScanFlags(t *testing.T) {
 	// The dwim command parses and checks the scan flags as scan does.
 	// Each case stops before the walk of / begins, and before the
 	// database is created. "dwim --exclude /" excludes its own operand.
 	cases := map[string]struct {
 		args []string
 		code int
 		want string
 	}{
 		"--exclude /": {
 			[]string{cmdDwim, excludeFlag, "/"},
 			exitFatal,
 			"sfdupes: scan /: operand excluded by --exclude /\n",
 		},
 		"--exclude empty": {
 			[]string{cmdDwim, excludeFlag, ""},
 			exitUsage,
 			"Error: --exclude must not be empty\n",
 		},
 		"--workers 0": {
 			[]string{cmdDwim, workersFlag, "0", "-x", "--no-default-excludes"},
 			exitUsage,
 			"Error: --workers must be at least 1, got 0\n",
 		},
 	}
 	for name, tc := range cases {
 		t.Run(name, func(t *testing.T) {
 			path := testDBPath(t)
 			t.Setenv(databaseEnv, path)
 			stdout := captureStdout(t)
 			stderr := captureStderr(t)
 			code := run(tc.args, os.Stdout, os.Stderr)
 			if code != tc.code {
 				t.Errorf("run(%q) = %d, want %d", tc.args, code, tc.code)
 			}
 			if !strings.HasSuffix(stderr(), tc.want) || stdout() != "" {
 				t.Errorf("stdout, stderr = %q, %q, want \"\" and stderr "+
 					"ending %q", stdout(), stderr(), tc.want)
 			}
 			_, err := os.Lstat(path)
 			if !errors.Is(err, os.ErrNotExist) {
 				t.Errorf("lstat %s: %v, want no database", path, err)
 			}
 		})
 	}
 }
 func TestRunDwimHelpListsScanFlags(t *testing.T) {
 	t.Parallel()
 	// README "Subcommands" shows this usage line for dwim.
 	const want = "\n  sfdupes dwim [--workers N] [-x] [--no-default-excludes] " +
 		"[--exclude PATH]...\n"
 	var stdout, stderr bytes.Buffer
 	run([]string{cmdDwim, "-h"}, &stdout, &stderr)
 	if !strings.Contains(stderr.String(), want) {
 		t.Errorf("dwim -h stderr = %q, want the usage line %q",
 			stderr.String(), want)
 	}
 	if !strings.Contains(stderr.String(), excludeFlag+" PATH") {
 		t.Errorf("dwim -h stderr = %q, want %s PATH", stderr.String(),
 			excludeFlag)
 	}
 	// README "Settings": the help lists the default excludes and the
 	// filesystem types the walk never records anything on.
 	help := strings.TrimSpace(defaultExcludesHelp(runtime.GOOS))
 	if !strings.Contains(stderr.String(), help) {
 		t.Errorf("dwim -h stderr = %q, want it to hold %q", stderr.String(),
 			help)
 	}
 }
@@ -1,9 +1,8 @@
 package sfdupes
-// This file holds three rules for the walk (README "Rules for the
+// This file holds two rules for the walk (README "Rules for the walk"):
 // walk"): the paths given with --exclude, which the scan never enters;
 // the default excludes, the paths a scan's walk does not enter below an
-// operand unless scan is given --no-default-excludes; and the
+// operand unless scan is given --no-default-excludes, and the
 // filesystems that are not persistent, on which the scan never records
 // or reads anything.
@@ -13,7 +12,6 @@ import (
 	"fmt"
 	"io"
 	"io/fs"
 	"os"
 	"path/filepath"
 	"slices"
 	"strings"
@@ -45,25 +43,17 @@ const typesPerHelpLine = 6
 // readMountInfo reads.
 var errMountInfoLine = errors.New("unexpected line")
 // errExcludedOperand reports an operand at or below a path given with
 // --exclude.
 var errExcludedOperand = errors.New("operand excluded by --exclude")
 // walkRules holds the rules for the walk that a scan sets up as it
-// starts. excludePaths are the paths given with --exclude, each with
+// starts. excludes are the default excludes, or none with
-// the device ID and inode number of the file it names (see
+// --no-default-excludes. nonPersistent maps the device ID of every
-// excludePathInodes), which the walk neither enters nor records,
+// mounted filesystem that is not persistent to its type; the scan
-// whatever path leads to them. defaultExcludes are the default
+// records and reads nothing on one of those, whatever the flags.
-// excludes, or none with --no-default-excludes. nonPersistent maps the
+// databaseFiles are the scan's own database files, which the walk
-// device ID of every mounted filesystem that is not persistent to its
+// passes over (see databaseFiles in db.go).
 // type; the scan records and reads nothing on one of those, whatever
 // the flags. databaseFiles are the scan's own database files, which the
 // walk passes over (see databaseFiles in db.go).
 type walkRules struct {
-	excludePaths    []fileRec
+	excludes      []string
-	defaultExcludes []string
+	nonPersistent map[uint64]string
-	nonPersistent   map[uint64]string
+	databaseFiles []fileRec
 	databaseFiles   []fileRec
 }
 // defaultExcludes returns the default excludes of the system goos
@@ -107,88 +97,6 @@ func isDefaultExclude(path string, excludes []string) bool {
 	return false
 }
 // excludePathInodes returns each of paths, the --exclude values, as its
 // real path (see realPaths) with the device ID and inode number of the
 // file there. The walk compares what it reaches with those, as it does
 // with the database files, so it also leaves out an --exclude path
 // spelled another way, such as in another letter case on macOS.
 func excludePathInodes(paths []string) ([]fileRec, error) {
 	resolved, err := realPaths(paths)
 	if err != nil {
 		return nil, err
 	}
 	files := make([]fileRec, 0, len(resolved))
 	for _, path := range resolved {
 		fi, err := os.Lstat(path)
 		if err != nil {
 			return nil, err
 		}
 		dev, ino := inodeOfInfo(fi)
 		files = append(files, fileRec{path: path, dev: dev, ino: ino})
 	}
 	return files, nil
 }
 // matchingExcludePath returns the path of the one of excludePaths with
 // the device ID and inode number of fi, an lstat result, or "" when
 // there is none.
 func matchingExcludePath(fi fs.FileInfo, excludePaths []fileRec) string {
 	dev, ino := inodeOfInfo(fi)
 	f := fileRec{dev: dev, ino: ino}
 	for _, exclude := range excludePaths {
 		if sameInode(exclude, f) {
 			return exclude.path
 		}
 	}
 	return ""
 }
 // checkOperandsNotExcluded returns an error when one of roots, the
 // operands, or a directory above it is one of excludePaths, the
 // --exclude paths, by device ID and inode number. The error names the
 // operand and the --exclude path. The roots are absolute, so the
 // directories above each one end at /. A path here that lstat cannot
 // read is an error too.
 func checkOperandsNotExcluded(roots []string, excludePaths []fileRec) error {
 	for _, root := range roots {
 		for path := root; ; path = filepath.Dir(path) {
 			fi, err := os.Lstat(path)
 			if err != nil {
 				return fmt.Errorf("scan %s: %w", root, err)
 			}
 			exclude := matchingExcludePath(fi, excludePaths)
 			if exclude != "" {
 				return fmt.Errorf("scan %s: %w %s", root, errExcludedOperand,
 					exclude)
 			}
 			if path == "/" {
 				break
 			}
 		}
 	}
 	return nil
 }
 // excludePathLine returns the line the scan prints for path when fi,
 // its lstat, makes it one of rules.excludePaths, and "" when it does
 // not.
 func (rules walkRules) excludePathLine(path string, fi fs.FileInfo) string {
 	if matchingExcludePath(fi, rules.excludePaths) == "" {
 		return ""
 	}
 	return fmt.Sprintf("scan: skipped %s (--exclude)", path)
 }
 // nonPersistentFilesystemTypes returns the filesystem types that are
 // not persistent: filesystems that the kernel makes up or that are kept
 // in memory. devfs is the macOS filesystem of /dev; the others are
@@ -254,7 +162,7 @@ func readMountInfo(mountinfo io.Reader) (map[uint64]string, error) {
 	return devices, lines.Err()
 }
-// defaultExcludesHelp describes, for the scan and dwim help, the
+// defaultExcludesHelp describes, for the scan command's help, the
 // default excludes of the system goos names and, where the scan lists
 // the mounted filesystems, the types it never records anything on.
 func defaultExcludesHelp(goos string) string {
@@ -14,9 +14,6 @@ import (
 	"golang.org/x/sys/unix"
 )
 // excludeFlag is the scan flag that names a path the walk never enters.
 const excludeFlag = "--exclude"
 func TestDefaultExcludes(t *testing.T) {
 	t.Parallel()
@@ -191,7 +188,7 @@ func TestScanDoesNotEnterDefaultExclude(t *testing.T) {
 	unseen := writeFile(t, excluded, "new", pattern(2, 10))
 	st, err := syncScan(t.Context(), db, []string{dir}, 1, false,
-		walkRules{defaultExcludes: []string{excluded}})
+		walkRules{excludes: []string{excluded}})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -237,7 +234,7 @@ func TestScanWalksOperandInDefaultExclude(t *testing.T) {
 			db := openTestDB(t)
 			st, err := syncScan(t.Context(), db, roots, 1, false,
-				walkRules{defaultExcludes: []string{excluded}})
+				walkRules{excludes: []string{excluded}})
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -265,7 +262,7 @@ func TestScanNamesNoDefaultExcludeThatIsAnOperand(t *testing.T) {
 	f := writeFile(t, excluded, "f", pattern(1, 10))
 	st, err := syncScan(t.Context(), db, []string{dir, excluded}, 1, false,
-		walkRules{defaultExcludes: []string{excluded}})
+		walkRules{excludes: []string{excluded}})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -359,217 +356,6 @@ func TestRunScanNoDefaultExcludes(t *testing.T) {
 	assertRecorded(t, path, f, true)
 }
 // TestRunScanExcludeNested scans a tree through the command with an
 // --exclude path two levels below the operand. The walk records nothing
 // at or below it and says so. The record an earlier scan left there is
 // kept although its file is gone.
 func TestRunScanExcludeNested(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 	dir := realTempDir(t)
 	excluded := filepath.Join(dir, "a", "b")
 	kept := writeFile(t, dir, "a/f", pattern(1, 10))
 	gone := writeFile(t, excluded, "gone", pattern(2, 10))
 	scanOK(t, dir)
 	err := os.Remove(gone)
 	if err != nil {
 		t.Fatal(err)
 	}
 	unseen := writeFile(t, excluded, "c/new", pattern(3, 10))
 	stderr := scanOK(t, excludeFlag, excluded, dir)
 	line := "scan: skipped " + excluded + " (--exclude)\n"
 	if !strings.Contains(stderr, line) {
 		t.Errorf("stderr = %q, want %q", stderr, line)
 	}
 	assertRecorded(t, path, kept, true)
 	assertRecorded(t, path, gone, true)
 	assertRecorded(t, path, unseen, false)
 }
 // TestRunScanExcludeRepeated gives --exclude twice, once for a
 // directory and once for a file, the file through a symlink to it. The
 // walk records neither, and records the file beside them.
 func TestRunScanExcludeRepeated(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 	dir := realTempDir(t)
 	inDir := writeFile(t, dir, "skip/f", pattern(1, 10))
 	file := writeFile(t, dir, "skip-file", pattern(2, 10))
 	kept := writeFile(t, dir, "keep", pattern(3, 10))
 	link := filepath.Join(t.TempDir(), "link")
 	symlink(t, file, link)
 	scanOK(t, excludeFlag, filepath.Dir(inDir), excludeFlag, link, dir)
 	assertRecorded(t, path, inDir, false)
 	assertRecorded(t, path, file, false)
 	assertRecorded(t, path, kept, true)
 }
 // TestRunScanExcludeReachedByAnotherPath gives --exclude a directory
 // through a symlink and a file through "..", so the walk reaches
 // neither by the path given. The walk also reaches the file through a
 // hard link. It records none of these, prints a line naming each, and
 // records the file beside them.
 func TestRunScanExcludeReachedByAnotherPath(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 	dir := realTempDir(t)
 	inDir := writeFile(t, dir, "a/cache/f", pattern(1, 10))
 	file := writeFile(t, dir, "a/big", pattern(2, 10))
 	kept := writeFile(t, dir, "keep", pattern(3, 10))
 	hardLink := filepath.Join(dir, "big-link")
 	err := os.Link(file, hardLink)
 	if err != nil {
 		t.Fatal(err)
 	}
 	link := filepath.Join(t.TempDir(), "link")
 	symlink(t, filepath.Join(dir, "a"), link)
 	// Joined as text, since filepath.Join would drop the "..".
 	dotDot := dir + "/a/cache/../big"
 	stderr := scanOK(t, excludeFlag, filepath.Join(link, "cache"),
 		excludeFlag, dotDot, dir)
 	for _, skipped := range []string{filepath.Dir(inDir), file, hardLink} {
 		line := "scan: skipped " + skipped + " (--exclude)\n"
 		if !strings.Contains(stderr, line) {
 			t.Errorf("stderr = %q, want %q", stderr, line)
 		}
 	}
 	assertRecorded(t, path, inDir, false)
 	assertRecorded(t, path, file, false)
 	assertRecorded(t, path, hardLink, false)
 	assertRecorded(t, path, kept, true)
 }
 // TestRunScanExcludedOperand checks that an operand at or below an
 // --exclude path is a fatal error that names both, and so is an
 // --exclude path that does not exist. An operand that is a hard link to
 // an --exclude file is at it. Neither scan writes a database.
 func TestRunScanExcludedOperand(t *testing.T) {
 	dir := realTempDir(t)
 	sub := filepath.Join(dir, "sub")
 	f := writeFile(t, sub, "f", pattern(1, 10))
 	hardLink := filepath.Join(dir, "f-link")
 	err := os.Link(f, hardLink)
 	if err != nil {
 		t.Fatal(err)
 	}
 	cases := map[string]struct {
 		args []string
 		want string
 	}{
 		"at it": {
 			[]string{excludeFlag, sub, sub},
 			"scan " + sub + ": operand excluded by --exclude " + sub + "\n",
 		},
 		"below it": {
 			[]string{excludeFlag, dir, sub},
 			"scan " + sub + ": operand excluded by --exclude " + dir + "\n",
 		},
 		"after an operand it does not exclude": {
 			[]string{dir, excludeFlag, sub, sub},
 			"scan " + sub + ": operand excluded by --exclude " + sub + "\n",
 		},
 		"a hard link to it": {
 			[]string{excludeFlag, f, hardLink},
 			"scan " + hardLink + ": operand excluded by --exclude " + f + "\n",
 		},
 		"exclude missing": {
 			[]string{excludeFlag, filepath.Join(dir, "nope"), dir},
 			"--exclude: resolve " + filepath.Join(dir, "nope") + ": ",
 		},
 	}
 	for name, tc := range cases {
 		t.Run(name, func(t *testing.T) {
 			path := testDBPath(t)
 			t.Setenv(databaseEnv, path)
 			stdout := captureStdout(t)
 			stderr := captureStderr(t)
 			code := run(append([]string{cmdScan}, tc.args...), os.Stdout,
 				os.Stderr)
 			if code != exitFatal {
 				t.Errorf("run(scan %q) = %d, want %d", tc.args, code,
 					exitFatal)
 			}
 			assertFatalOutput(t, stderr(), stdout())
 			if !strings.Contains(stderr(), "sfdupes: "+tc.want) {
 				t.Errorf("stderr = %q, want %q", stderr(), tc.want)
 			}
 			_, err := os.Lstat(path)
 			if !errors.Is(err, os.ErrNotExist) {
 				t.Errorf("lstat %s: %v, want no database", path, err)
 			}
 		})
 	}
 }
 // TestRunScanRejectsEmptyExclude checks that an empty --exclude value,
 // given as its own argument, after "=" or after another --exclude, is
 // a usage error reported in one line before anything is scanned
 // (README "Settings").
 func TestRunScanRejectsEmptyExclude(t *testing.T) {
 	dir := t.TempDir()
 	cases := map[string][]string{
 		"separate":     {excludeFlag, "", dir},
 		"joined by =":  {excludeFlag + "=", dir},
 		"after a path": {excludeFlag, t.TempDir(), excludeFlag, "", dir},
 	}
 	for name, args := range cases {
 		t.Run(name, func(t *testing.T) {
 			path := testDBPath(t)
 			t.Setenv(databaseEnv, path)
 			var stdout, stderr bytes.Buffer
 			code := run(append([]string{cmdScan}, args...), &stdout,
 				&stderr)
 			if code != exitUsage {
 				t.Errorf("run(scan %q) = %d, want %d", args, code,
 					exitUsage)
 			}
 			want := "Error: --exclude must not be empty\n"
 			if stdout.String() != "" || stderr.String() != want {
 				t.Errorf("stdout, stderr = %q, %q, want \"\", %q",
 					stdout.String(), stderr.String(), want)
 			}
 			_, err := os.Lstat(path)
 			if !errors.Is(err, os.ErrNotExist) {
 				t.Errorf("lstat %s: %v, want no database", path, err)
 			}
 		})
 	}
 }
 // TestRunScanSkipsNonPersistentOperand scans, through the command, a
 // directory on a filesystem that is not persistent, with and without
 // --no-default-excludes: either way it is skipped, with a line saying
@@ -642,9 +642,9 @@ func TestTerminalStalledLines(t *testing.T) {
 		{label: scanPhase("hash"), stalledOn: hashStalledOn},
 		{label: scanPhase("update"), stalledOn: "db"},
 		{label: treesPhase("read"), stalledOn: "db"},
-		{label: treesPhase("group"), stalledOn: "cpu/disk"},
+		{label: treesPhase("group"), stalledOn: "cpu"},
 		{label: treesPhase("write"), stalledOn: "out"},
-		{label: reportPhase("read"), stalledOn: "db/disk/out"},
+		{label: reportPhase("read"), stalledOn: "db/out"},
 	}
 	for _, params := range phases {
@@ -4,14 +4,11 @@ import (
 	"context"
 	"crypto/sha256"
 	"database/sql"
 	"errors"
 	"fmt"
 	"io"
 	"io/fs"
 	"os"
 	"slices"
 	"strings"
 	"syscall"
 	"time"
 )
@@ -44,10 +41,10 @@ func reportPhase(name string) string {
 }
 // runReport implements the report subcommand: it prints the file-level
-// duplicates report as TSV on stdout. Of the scanned filesystem it
+// duplicates report as TSV on stdout. It never touches the scanned
-// only checks, with pathExists, that each path in a duplicate group is
+// filesystem; its only I/O is the database, stdout, and stderr. It
-// still there. It names the database on stderr before it opens it. Any
+// names the database on stderr before it opens it. Any database
-// database problem, including a missing database, is fatal.
+// 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 (read the number of
@@ -80,14 +77,13 @@ func runReport(ctx context.Context, stdout io.Writer) error {
 	defer func() { _ = db.Close() }()
-	// The read phase checks the paths of each duplicate group on disk
+	// The read phase writes the report to stdout while it reads the
-	// and writes the report to stdout while it reads the records, so it
+	// records, so it may wait on either.
 	// may wait on any of the three.
 	prog = newProgress(progressParams{
 		label: reportPhase("read"), unit: "records", total: -1,
-		waitingFor: countingRecords, stalledOn: "db/disk/out",
+		waitingFor: countingRecords, stalledOn: "db/out",
 	})
-	report, err := readReport(ctx, db, dbPath, stdout, pathExists, prog)
+	report, err := readReport(ctx, db, dbPath, stdout, prog)
 	prog.finish()
@@ -108,15 +104,14 @@ func runReport(ctx context.Context, stdout io.Writer) error {
 // dbPath, as its total, then reads every record in signature order,
 // counting each on prog, and writes the report to stdout: the header
 // line, then the rows of each size's duplicate groups once that size is
-// read. A path for which exists returns false is left out of its group.
+// read. stdout may be the terminal prog is drawn on, so the lines go
-// stdout may be the terminal prog is drawn on, so the lines go through
+// through prog's writer. It returns what it wrote, with the totals for
-// prog's writer. It returns what it wrote, with the totals for the
+// the summary line.
 // summary line.
 func readReport(ctx context.Context, db *sql.DB, dbPath string,
-	stdout io.Writer, exists func(path string) bool, prog *progress,
+	stdout io.Writer, prog *progress,
 ) (*reportWriter, error) {
 	out := prog.writer(stdout)
-	report := &reportWriter{out: out, exists: exists}
+	report := &reportWriter{out: out}
 	_, err := fmt.Fprintln(out, "first\tdupe\tsize")
 	if err != nil {
@@ -163,10 +158,6 @@ func readReport(ctx context.Context, db *sql.DB, dbPath string,
 type reportWriter struct {
 	out io.Writer
 	// exists reports whether a path is still on disk. A path that is
 	// gone is left out of its group.
 	exists func(path string) bool
 	sig    scanRec    // the signature being read; its path is not used
 	paths  []string   // the paths read so far with sig
 	groups [][]string // the duplicate groups of sig.size, each sorted
@@ -203,18 +194,10 @@ func (w *reportWriter) add(r scanRec) error {
 	return nil
 }
-// endGroup ends the paths read with w.sig: two or more that are still
+// endGroup ends the paths read with w.sig: two or more are a duplicate
-// on disk are a duplicate group, held with its paths sorted until
+// group, held with its paths sorted until writeGroups writes it. Empty
-// writeGroups writes it. Empty files form no group, since removing one
+// files form no group, since removing one frees nothing.
 // frees nothing. Only the paths of a possible group are checked, never
 // a path with no duplicate or an empty file.
 func (w *reportWriter) endGroup() {
 	if len(w.paths) >= minGroupSize && w.sig.size > 0 {
 		w.paths = slices.DeleteFunc(w.paths, func(p string) bool {
 			return !w.exists(p)
 		})
 	}
 	if len(w.paths) < minGroupSize || w.sig.size == 0 {
 		// The paths are dropped, and their slice reused.
 		w.paths = w.paths[:0]
@@ -263,16 +246,6 @@ func (w *reportWriter) finish() error {
 	return w.writeGroups()
 }
 // pathExists reports whether path is still on disk, for report and
 // trees. It is false only when lstat finds that the path, or a
 // directory above it, is gone. Any other error counts as present, so
 // a user who may not look inside a directory still sees its copies.
 func pathExists(path string) bool {
 	_, err := os.Lstat(path)
 	return !errors.Is(err, fs.ErrNotExist) && !errors.Is(err, syscall.ENOTDIR)
 }
 // escapePath returns a path as it is written in a report column (README
 // "Report output format"): a backslash, tab, newline or carriage return
 // becomes \\, \t, \n or \r, and every other byte is kept as it is.
@@ -72,37 +72,15 @@ type dupeGroup struct {
 	paths []string
 }
 // everyPathExists stands in for pathExists where a test's records name
 // made-up paths that are not on disk.
 func everyPathExists(string) bool { return true }
 // recsOnDisk returns a new directory and recs with each path moved
 // under it, after creating an empty file at each moved path: report and
 // trees then find every path still on disk.
 func recsOnDisk(t *testing.T, recs []scanRec) (string, []scanRec) {
 	t.Helper()
 	dir := realTempDir(t)
 	moved := make([]scanRec, len(recs))
 	for i, r := range recs {
 		r.path = writeFile(t, dir, r.path, nil)
 		moved[i] = r
 	}
 	return dir, moved
 }
 // dupeGroups returns the duplicate groups report reads from db, in
 // report order, from the rows it writes: a group's rows come together,
-// each naming the group's first path. Every path counts as still on
+// each naming the group's first path.
 // disk.
 func dupeGroups(t *testing.T, db *sql.DB) []dupeGroup {
 	t.Helper()
 	var out bytes.Buffer
-	_, err := readReport(t.Context(), db, "", &out, everyPathExists, nil)
+	_, err := readReport(t.Context(), db, "", &out, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -149,8 +127,7 @@ func dupeGroupsOf(t *testing.T, recs []scanRec) []dupeGroup {
 }
 func TestRunReportEscapesPaths(t *testing.T) {
-	dir, recs := recsOnDisk(t, awkwardPairRecs())
+	t.Setenv(databaseEnv, seedDatabase(t, awkwardPairRecs()))
 	t.Setenv(databaseEnv, seedDatabase(t, recs))
 	var stdout, stderr bytes.Buffer
@@ -161,7 +138,7 @@ func TestRunReportEscapesPaths(t *testing.T) {
 	}
 	want := "first\tdupe\tsize\n" +
-		dir + `/d/\tone\ntwo\rthree\\four/f` + "\t" + dir + "/d/A/f\t5\n"
+		`/d/\tone\ntwo\rthree\\four/f` + "\t/d/A/f\t5\n"
 	if got := stdout.String(); got != want {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
@@ -195,8 +172,7 @@ func TestReportStdoutFailsWhileReading(t *testing.T) {
 	// Counts the records read, and draws nothing.
 	prog := &progress{now: time.Now}
-	_, err = readReport(t.Context(), db, "", failingWriter{},
+	_, err = readReport(t.Context(), db, "", failingWriter{}, prog)
 		everyPathExists, prog)
 	if !errors.Is(err, errWriteFailed) ||
 		!strings.HasPrefix(err.Error(), "write stdout: ") {
 		t.Errorf("error = %v, want write stdout: %v", err, errWriteFailed)
@@ -227,8 +203,7 @@ const smokeReport = "first\tdupe\tsize\n" +
 // it ends; read counts the 6 records before it reads them. The summary
 // comes last, and stdout holds the report alone.
 func TestRunReportProgressNamesEachPhase(t *testing.T) {
-	dir, recs := recsOnDisk(t, smokeTreeRecs())
+	path := seedDatabase(t, smokeTreeRecs())
 	path := seedDatabase(t, recs)
 	t.Setenv(databaseEnv, path)
 	stderr := captureStderr(t)
@@ -241,9 +216,8 @@ func TestRunReportProgressNamesEachPhase(t *testing.T) {
 			code, exitOK, stderr())
 	}
-	report := strings.ReplaceAll(smokeReport, "/d/", dir+"/d/")
+	if got := stdout.String(); got != smokeReport {
-	if got := stdout.String(); got != report {
+		t.Errorf("stdout = %q, want %q", got, smokeReport)
 		t.Errorf("stdout = %q, want %q", got, report)
 	}
 	// How each line starts; the rate at the end of a phase varies.
@@ -292,7 +266,7 @@ func TestReadReportOnTerminal(t *testing.T) {
 		waitingFor: countingRecords,
 	}, terminalWidth, time.Hour, time.Now)
-	_, err = readReport(t.Context(), db, "", os.Stderr, everyPathExists, p)
+	_, err = readReport(t.Context(), db, "", os.Stderr, p)
 	p.finish()
@@ -327,8 +301,6 @@ func TestRunReportsIgnoreInsertionOrder(t *testing.T) {
 		scanRec{size: 50, head: a, tail: a, content: a, path: "/x/1"},
 	)
 	_, recs = recsOnDisk(t, recs)
 	reversed := slices.Clone(recs)
 	slices.Reverse(reversed)
@@ -483,119 +455,6 @@ func TestDupeGroupsLeavesOutEmptyFiles(t *testing.T) {
 	}
 }
 // TestReadReportChecksOnlyPossibleDuplicates checks that report asks
 // whether a path is on disk only when its signature has two or more
 // records, and never for an empty file.
 func TestReadReportChecksOnlyPossibleDuplicates(t *testing.T) {
 	t.Parallel()
 	a, u, e := testHash("a"), testHash("u"), sha256.Sum256(nil)
 	recs := []scanRec{
 		{size: 9, head: a, tail: a, content: a, path: "/copy/1"},
 		{size: 9, head: a, tail: a, content: a, path: "/copy/2"},
 		{size: 9, head: a, tail: a, content: a, path: "/copy/3"},
 		{size: 9, head: u, tail: u, content: u, path: "/lonely"},
 		{size: 0, head: e, tail: e, content: e, path: "/empty1"},
 		{size: 0, head: e, tail: e, content: e, path: "/empty2"},
 	}
 	db := openTestDB(t)
 	err := applyChanges(t.Context(), db, recs, nil, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
 	var checked []string
 	exists := func(path string) bool {
 		checked = append(checked, path)
 		return true
 	}
 	_, err = readReport(t.Context(), db, "", io.Discard, exists, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
 	slices.Sort(checked)
 	want := []string{"/copy/1", "/copy/2", "/copy/3"}
 	if !slices.Equal(checked, want) {
 		t.Errorf("paths checked on disk = %q, want %q", checked, want)
 	}
 }
 // TestReadReportDropsGroupLeftWithOnePath checks that a group of two
 // paths, one of them gone, is no duplicate group. If kept, it would
 // write no row, but the summary line would count it.
 func TestReadReportDropsGroupLeftWithOnePath(t *testing.T) {
 	t.Parallel()
 	a := testHash("a")
 	recs := []scanRec{
 		{size: 9, head: a, tail: a, content: a, path: "/a/kept"},
 		{size: 9, head: a, tail: a, content: a, path: "/a/gone"},
 	}
 	db := openTestDB(t)
 	err := applyChanges(t.Context(), db, recs, nil, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
 	exists := func(path string) bool { return path != "/a/gone" }
 	report, err := readReport(t.Context(), db, "", io.Discard, exists, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
 	if report.dupeGroups != 0 {
 		t.Errorf("duplicate groups = %d, want 0", report.dupeGroups)
 	}
 }
 // TestReadReportKeepsGroupLeftWithTwoPaths checks that a group of three
 // paths, one of them gone, is a duplicate group of the other two.
 func TestReadReportKeepsGroupLeftWithTwoPaths(t *testing.T) {
 	t.Parallel()
 	a := testHash("a")
 	recs := []scanRec{
 		{size: 9, head: a, tail: a, content: a, path: "/b/kept1"},
 		{size: 9, head: a, tail: a, content: a, path: "/b/gone"},
 		{size: 9, head: a, tail: a, content: a, path: "/b/kept2"},
 	}
 	db := openTestDB(t)
 	err := applyChanges(t.Context(), db, recs, nil, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
 	exists := func(path string) bool { return path != "/b/gone" }
 	var out bytes.Buffer
 	report, err := readReport(t.Context(), db, "", &out, exists, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
 	if report.dupeGroups != 1 {
 		t.Errorf("duplicate groups = %d, want 1", report.dupeGroups)
 	}
 	want := "first\tdupe\tsize\n/b/kept1\t/b/kept2\t9\n"
 	if got := out.String(); got != want {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
 }
 func TestDupeGroupsContentSeparates(t *testing.T) {
 	t.Parallel()
@@ -98,47 +98,44 @@ func scanPhase(name string) string {
 // runs, and the lock is released after it. When ctx is cancelled, as by
 // the SIGINT or SIGTERM that interruptContext catches, the scan keeps
 // what it has hashed (see syncScan), prints how many files its walk
-// reached, and returns errInterrupted. opts.workers must be at least 1;
+// reached, and returns errInterrupted. workers must be at least 1; the
-// the scan and dwim commands reject anything less. Before the lock is
+// scan command rejects anything less. Before the lock is taken, the
-// taken, the scan lists the filesystems that are not persistent, on
+// scan lists the filesystems that are not persistent, on which the walk
-// which the walk records nothing; unless opts.noDefaultExcludes is set,
+// records nothing; unless noDefaultExcludes is set, the walk does not
-// the walk does not enter the default excludes either. The walk neither
+// enter the default excludes either. Once the database is open, the
-// enters nor records the paths in opts.excludePaths, the --exclude
+// scan notes its files, which the walk passes over.
-// values; an operand at or below one is a fatal error. Once the
+func runScan(ctx context.Context, roots []string, workers int,
-// database is open, the scan notes its files, which the walk passes
+	oneFS, noDefaultExcludes bool,
-// over.
+) error {
 func runScan(ctx context.Context, roots []string, opts scanOptions) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
 		return err
 	}
-	printDatabasePath(dbPath, source)
+	// A database file missing now is created by lockScanDatabase below.
 	what := "database"
-	roots, err = realPaths(roots)
+	_, err = os.Stat(dbPath)
 	if errors.Is(err, fs.ErrNotExist) {
 		what = "new database"
 	}
 	fmt.Fprintf(os.Stderr, "scan: %s %s (%s)\n", what, escapePath(dbPath),
 		source)
 	roots, err = resolveRoots(roots)
 	if err != nil {
 		return err
 	}
-	var rules walkRules
+	nonPersistent, err := nonPersistentFilesystems()
 	rules.excludePaths, err = excludePathInodes(opts.excludePaths)
 	if err != nil {
 		return fmt.Errorf("--exclude: %w", err)
 	}
 	err = checkOperandsNotExcluded(roots, rules.excludePaths)
 	if err != nil {
 		return err
 	}
 	rules.nonPersistent, err = nonPersistentFilesystems()
 	if err != nil {
 		return fmt.Errorf("list the mounted filesystems: %w", err)
 	}
-	if !opts.noDefaultExcludes {
+	rules := walkRules{nonPersistent: nonPersistent}
-		rules.defaultExcludes = defaultExcludes(runtime.GOOS)
+	if !noDefaultExcludes {
 		rules.excludes = defaultExcludes(runtime.GOOS)
 	}
 	lock, err := lockScanDatabase(dbPath)
@@ -166,7 +163,7 @@ func runScan(ctx context.Context, roots []string, opts scanOptions) error {
 		return err
 	}
-	st, err := syncScan(ctx, db, roots, opts.workers, opts.oneFS, rules)
+	st, err := syncScan(ctx, db, roots, workers, oneFS, rules)
 	if errors.Is(err, context.Canceled) {
 		return interrupted(st.walked)
 	}
@@ -184,21 +181,6 @@ func runScan(ctx context.Context, roots []string, opts scanOptions) error {
 	return nil
 }
 // printDatabasePath prints on stderr the line that names the database
 // at dbPath, with source, saying whether it is new. A database file
 // missing now is new: lockScanDatabase creates it.
 func printDatabasePath(dbPath, source string) {
 	what := "database"
 	_, err := os.Stat(dbPath)
 	if errors.Is(err, fs.ErrNotExist) {
 		what = "new database"
 	}
 	fmt.Fprintf(os.Stderr, "scan: %s %s (%s)\n", what, escapePath(dbPath),
 		source)
 }
 // interruptContext returns a copy of ctx that the first SIGINT or
 // SIGTERM cancels; the scan command runs the scan under it. stop
 // releases the signals.
@@ -227,25 +209,24 @@ func interrupted(walked int) error {
 	return errInterrupted
 }
-// realPaths returns the real path of each of paths, the PATH operands
+// resolveRoots converts each PATH operand to its real path: absolute,
-// or the --exclude values: absolute, with every symlink in it followed.
+// with every symlink in it followed. Database records are keyed by
-// Database records are keyed by that path, so scan results depend
+// that path, so scan results depend neither on the working directory
-// neither on the working directory nor on the symlinks an operand was
+// nor on the symlinks an operand was given through. An operand that
-// given through. A path that cannot be resolved, because it or a
+// cannot be resolved, because it or a symlink's target does not exist
-// symlink's target does not exist or cannot be read, is a fatal error
+// or cannot be read, is a fatal error before any scanning.
-// before any scanning.
+func resolveRoots(roots []string) ([]string, error) {
-func realPaths(paths []string) ([]string, error) {
+	resolved := make([]string, 0, len(roots))
 	resolved := make([]string, 0, len(paths))
-	for _, path := range paths {
+	for _, root := range roots {
-		a, err := absolutePath(path)
+		a, err := absolutePath(root)
 		if err != nil {
-			return nil, fmt.Errorf("resolve %s: %w", path, err)
+			return nil, fmt.Errorf("resolve %s: %w", root, err)
 		}
 		r, err := filepath.EvalSymlinks(a)
 		if err != nil {
-			return nil, fmt.Errorf("resolve %s: %w", path, err)
+			return nil, fmt.Errorf("resolve %s: %w", root, err)
 		}
 		resolved = append(resolved, r)
@@ -314,7 +295,7 @@ func walkReaches(above, r string, oneFS bool, rules walkRules,
 	}
 	for ; dir != above; dir = filepath.Dir(dir) {
-		if isDefaultExclude(dir, rules.defaultExcludes) {
+		if isDefaultExclude(dir, rules.excludes) {
 			return false
 		}
@@ -437,7 +418,7 @@ 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, none of them inside a
-// directory named .zfs. The operands are real paths from realPaths,
+// directory named .zfs. The operands are real paths from resolveRoots,
 // so these checks apply to what a symlink operand points at. 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
@@ -512,11 +493,10 @@ func (s *scanState) loadIndex(ctx context.Context, roots []string) error {
 // 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
-// an --exclude path or a default exclude, or it is not on a persistent
+// a default exclude, or it is not on a persistent filesystem, counts as
-// filesystem, counts as outside the roots: it is not deleted. That does
+// outside the roots: it is not deleted. That does not hold below a root
-// not hold below a root at or inside that path, since that root's own
+// at or inside that path, since that root's own walk verifies the
-// walk verifies the records below it; nor is a line printed for such a
+// records below it; nor is a line printed for such a root.
 // 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.
@@ -565,7 +545,7 @@ func (s *scanState) walkPhase(events <-chan walkEvent, roots []string) {
 		prog.increment()
 		old, ok := s.existing[ev.rec.path]
-		if !ok || old.size != ev.rec.size || !ev.rec.mtime.Equal(old.mtime) {
+		if !ok || old.size != ev.rec.size || mtimeAfter(ev.rec.mtime, old.mtime) {
 			s.toHash = append(s.toHash, ev.rec)
 			continue
@@ -800,6 +780,16 @@ func (s *scanState) updatePhase(ctx context.Context) error {
 	return applyChanges(ctx, s.db, nil, deletes, prog)
 }
 // mtimeAfter reports whether mtime a is later than mtime b.
 // Not a.After(b): time.Time wraps an mtime past year 292 billion; Unix() undoes it.
 func mtimeAfter(a, b time.Time) bool {
 	if a.Unix() != b.Unix() {
 		return a.Unix() > b.Unix()
 	}
 	return a.Nanosecond() > b.Nanosecond()
 }
 // underAnyRoot reports whether path is any of the roots or lies under
 // one of them.
 func underAnyRoot(path string, roots []string) bool {
@@ -854,9 +844,9 @@ type dirJob struct {
 // file's statted record, a warning when fail is set, or a path the walk
 // left out: when otherFSDir is set, a directory -x did not enter
 // because it is on another filesystem than its operand, and when
-// leftOut is set, an --exclude path, a default exclude or a directory or
+// leftOut is set, a default exclude or a directory or file on a
-// file on a filesystem that is not persistent, with warn holding the
+// filesystem that is not persistent, with warn holding the line that
-// line that says so.
+// says so.
 type walkEvent struct {
 	rec        fileRec
 	warn       string
@@ -907,7 +897,7 @@ 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, that is not
-// inside a directory named .zfs. realPaths has already followed the
+// inside a directory named .zfs. resolveRoots has already followed the
 // operand's symlinks, so a symlink here is an operand replaced by one
 // after it was resolved, and is not followed.
 func operandWarning(root string, fi fs.FileInfo) string {
@@ -1138,9 +1128,8 @@ func walkOneDir(ctx context.Context, job dirJob, oneFS bool,
 // no longer exists, and one that has stopped being a regular file is
 // skipped. A file on a filesystem in rules that is not persistent, as
 // through a bind mount of one file, is not recorded: it gets an event
-// naming it instead, and so does a file given with --exclude, reached
+// naming it instead. One of the scan's own database files in rules gets
-// by any path, a hard link to it included. One of the scan's own
+// no event at all.
 // database files in rules gets no event at all.
 func emitFile(ctx context.Context, p string, e fs.DirEntry,
 	rules walkRules, events chan<- walkEvent,
 ) {
@@ -1164,10 +1153,6 @@ func emitFile(ctx context.Context, p string, e fs.DirEntry,
 	}
 	line := rules.nonPersistentLine(p, info)
 	if line == "" {
 		line = rules.excludePathLine(p, info)
 	}
 	if line != "" {
 		sendEvent(ctx, events, walkEvent{leftOut: p, warn: line})
@@ -1192,11 +1177,11 @@ func emitFile(ctx context.Context, p string, e fs.DirEntry,
 // subdirJob applies the descent rules to directory p: never enter
 // .zfs (ZFS snapshot pseudo-dirs would list every file once per
 // snapshot), never enter a directory on a filesystem in rules that is
-// not persistent, nor an --exclude path or a default exclude in rules,
+// not persistent, nor a default exclude in rules, and with -x never
-// and with -x never enter a directory on a different filesystem than
+// enter a directory on a different filesystem than its operand. For the
-// its operand. For all but .zfs it sends an event that names the
+// last three it sends an event that names the directory, so the scan
-// directory, so the scan keeps the records below it, except those below
+// keeps the records below it, except those below an operand at or
-// an operand at or inside it.
+// inside it.
 func subdirJob(ctx context.Context, p string, e fs.DirEntry,
 	parent dirJob, oneFS bool, rules walkRules,
 	events chan<- walkEvent,
@@ -1221,17 +1206,13 @@ func subdirJob(ctx context.Context, p string, e fs.DirEntry,
 	}
 	line := rules.nonPersistentLine(p, info)
 	if line == "" {
 		line = rules.excludePathLine(p, info)
 	}
 	if line != "" {
 		sendEvent(ctx, events, walkEvent{leftOut: p, warn: line})
 		return dirJob{}, false
 	}
-	if isDefaultExclude(p, rules.defaultExcludes) {
+	if isDefaultExclude(p, rules.excludes) {
 		sendEvent(ctx, events, walkEvent{
 			leftOut: p,
 			warn:    fmt.Sprintf("scan: skipped %s (default exclude)", p),
@@ -1215,7 +1215,7 @@ func assertSmokeTreeGroups(t *testing.T, dir string, db *sql.DB) {
 	super, dirs := dbTree(t, db)
-	tg := collectTreeGroups(dirs, super, everyPathExists, nil)
+	tg := collectTreeGroups(dirs, super, nil)
 	if len(tg) != 1 {
 		t.Fatalf("len(tree groups) = %d, want 1", len(tg))
 	}
@@ -1384,47 +1384,6 @@ func TestSyncScanMtimeBump(t *testing.T) {
 	}
 }
 // TestSyncScanMtimeMovedBack replaces a file with other content of the
 // same size and an older mtime, as cp -p or a restore from backup does.
 // The next scan must hash the file again.
 func TestSyncScanMtimeMovedBack(t *testing.T) {
 	t.Parallel()
 	dir := t.TempDir()
 	db := openTestDB(t)
 	a := writeFile(t, dir, "a.bin", pattern(1, 500))
 	recorded := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
 	err := os.Chtimes(a, recorded, recorded)
 	if err != nil {
 		t.Fatal(err)
 	}
 	syncTree(t, db, dir)
 	replaced := pattern(3, 500)
 	writeFile(t, dir, "a.bin", replaced)
 	older := recorded.Add(-time.Hour)
 	err = os.Chtimes(a, older, older)
 	if err != nil {
 		t.Fatal(err)
 	}
 	st := syncTree(t, db, dir)
 	if st != (scanStats{walked: 1, updated: 1}) {
 		t.Fatalf("rescan stats = %+v, want 1 updated", st)
 	}
 	assertWholeFileHashed(t, db, a, replaced)
 	if r := recordByPath(t, dbRecords(t, db), a); !r.mtime.Equal(older) {
 		t.Fatalf("mtime = %v, want %v", r.mtime, older)
 	}
 }
 // assertWholeFileHashed fails unless the record for path holds the
 // whole-file hash of data as its head, tail, and content.
 func assertWholeFileHashed(t *testing.T, db *sql.DB, path string,
@@ -2196,7 +2155,7 @@ func TestScanHashWriteFailureUnwindsPool(t *testing.T) {
 	var stderr bytes.Buffer
 	code := run([]string{
-		cmdScan, workersFlag, strconv.Itoa(hashLeakWorkers), dir,
+		cmdScan, "--workers", strconv.Itoa(hashLeakWorkers), dir,
 	}, io.Discard, &stderr)
 	if code != exitFatal {
 		t.Fatalf("run(scan) = %d, want %d; stderr: %s",
@@ -2289,7 +2248,7 @@ func TestPruneRoots(t *testing.T) {
 	// The walk of /p does not enter /p/q when it is a default exclude, so
 	// /p/q is kept, without -x too; /p/q/r lies under it and is dropped.
-	got = pruneRoots(nested, false, walkRules{defaultExcludes: []string{pqRoot}},
+	got = pruneRoots(nested, false, walkRules{excludes: []string{pqRoot}},
 		device)
 	if !slices.Equal(got, want) {
 		t.Fatalf("pruneRoots excluding %s = %q, want %q", pqRoot, got, want)
@@ -2307,86 +2266,23 @@ func TestPruneRoots(t *testing.T) {
 	}
 }
-// TestRunReportsLeaveOutRemovedCopies scans the smoke tree, then
+func TestReportsNeverTouchFilesystem(t *testing.T) {
 // removes copies the reports name. report leaves out each removed file,
 // and a group left with one path. trees checks only the root of each
 // duplicate tree: with a file under t2 removed it still names t2, and
 // with t2 removed it names nothing.
 func TestRunReportsLeaveOutRemovedCopies(t *testing.T) {
 	t.Setenv(databaseEnv, testDBPath(t))
 	dir := buildSmokeTree(t)
 	p := func(name string) string { return filepath.Join(dir, name) }
 	scanOK(t, dir)
 	for _, name := range []string{"b/copy2.bin", "tiny2", "t2/sub/f2"} {
 		err := os.Remove(p(name))
 		if err != nil {
 			t.Fatal(err)
 		}
 	}
 	want := "first\tdupe\tsize\n" +
 		p("t1/f1") + "\t" + p("t2/f1") + "\t3000\n" +
 		p("t1/f1") + "\t" + p("t3/f1") + "\t3000\n" +
 		p("a/one.bin") + "\t" + p("b/copy.bin") + "\t2000\n" +
 		p("t1/sub/f2") + "\t" + p("t3/sub/f2renamed") + "\t100\n"
 	if got := runStdout(t, cmdReport); got != want {
 		t.Errorf("report stdout = %q, want %q", got, want)
 	}
 	// disk_size, the last column, depends on the filesystem.
 	header := "first\tdupe\tfiles\tsize\tdisk_size\n"
 	want = header + p("t1") + "\t" + p("t2") + "\t2\t3100\t"
 	if got := runStdout(t, cmdTrees); !strings.HasPrefix(got, want) ||
 		strings.Count(got, "\n") != 2 {
 		t.Errorf("trees stdout = %q, want one row starting %q", got, want)
 	}
 	err := os.RemoveAll(p("t2"))
 	if err != nil {
 		t.Fatal(err)
 	}
 	if got := runStdout(t, cmdTrees); got != header {
 		t.Errorf("trees stdout after removing t2 = %q, want %q", got, header)
 	}
 }
 func TestPathExists(t *testing.T) {
 	t.Parallel()
-	dir := t.TempDir()
+	dir := buildSmokeTree(t)
-	file := writeFile(t, dir, "file", nil)
+	db := openTestDB(t)
 	locked := writeFile(t, dir, "locked/file", nil)
-	// Without search permission on its directory, a file cannot be
+	syncTree(t, db, dir)
-	// looked at by anyone but root.
+
-	err := os.Chmod(filepath.Dir(locked), 0)
+	// Remove the scanned tree entirely; the analysis must be
 	// unaffected because it reads the database alone.
 	err := os.RemoveAll(dir)
 	if err != nil {
 		t.Fatal(err)
 	}
-	// Runs before t.TempDir's own cleanup, which must delete the files.
+	assertSmokeDupeGroups(t, dir, db)
-	t.Cleanup(func() {
+	assertSmokeTreeGroups(t, dir, db)
 		//nolint:gosec // removing the directory needs its search bit back
 		_ = os.Chmod(filepath.Dir(locked), 0o700)
 	})
 	cases := map[string]bool{
 		dir:                                 true,
 		file:                                true,
 		locked:                              true,
 		filepath.Join(dir, "gone"):          false,
 		filepath.Join(file, "under-a-file"): false,
 	}
 	for path, want := range cases {
 		if got := pathExists(path); got != want {
 			t.Errorf("pathExists(%q) = %v, want %v", path, got, want)
 		}
 	}
 }
 func TestUnderRoot(t *testing.T) {
@@ -38,11 +38,10 @@ func treesPhase(name string) string {
 // runTrees implements the trees subcommand: it reads every record from
 // the database in path order, reconstructs the directory hierarchy from
 // the record paths, computes a Merkle-style digest per directory, and
-// prints maximal duplicate-tree groups as TSV on stdout. Of the scanned
+// prints maximal duplicate-tree groups as TSV on stdout. It never
-// filesystem it only checks, with pathExists, that the root of each
+// touches the scanned filesystem; its only I/O is the database, stdout,
-// duplicate tree is still there, never the files below it. It names the
+// and stderr. It names the database on stderr before it opens it. Any
-// database on stderr before it opens it. Any database problem,
+// database problem, including a missing database, is fatal.
 // 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 (read the number of
@@ -87,13 +86,13 @@ func runTrees(ctx context.Context, stdout io.Writer) error {
 		return fmt.Errorf("database %s: %w", dbPath, err)
 	}
-	// Grouping works in memory, then checks the root of each duplicate
+	// Grouping works in memory, so it waits on nothing but the
-	// tree on disk, so it waits on the processor or the disk.
+	// processor.
 	prog = newProgress(progressParams{
 		label: treesPhase("group"), unit: "directories",
-		total: int64(len(allDirs)), stalledOn: "cpu/disk",
+		total: int64(len(allDirs)), stalledOn: "cpu",
 	})
-	dupes := collectTreeGroups(allDirs, super, pathExists, prog)
+	dupes := collectTreeGroups(allDirs, super, prog)
 	prog.finish()
@@ -301,14 +300,12 @@ func fileEntry(name string, r scanRec) string {
 // collectTreeGroups groups directories by digest, counting each one on
 // prog as it is grouped, and returns every maximal group with two or
-// more members for which exists returns true, each group's members
+// more members, each group's members sorted by path, groups ordered by
-// sorted by path, groups ordered by tree size descending then by first
+// tree size descending then by first path ascending. A group whose
-// path ascending. A group whose trees hold 0 bytes is left out, since
+// trees hold 0 bytes is left out, since removing one frees nothing. The
-// removing one frees nothing. The groups it implies hold 0 bytes too,
+// groups it implies hold 0 bytes too, so leaving it out hides nothing.
 // so leaving it out hides nothing. exists is called only on the members
 // of maximal groups.
 func collectTreeGroups(allDirs []*treeNode, super *treeNode,
-	exists func(path string) bool, prog *progress,
+	prog *progress,
 ) [][]*treeNode {
 	groups := make(map[[sha256.Size]byte][]*treeNode)
 	for _, d := range allDirs {
@@ -326,16 +323,6 @@ func collectTreeGroups(allDirs []*treeNode, super *treeNode,
 			continue
 		}
 		// A member that is gone leaves the group. A suppressed group is
 		// still implied: its members still on disk have parents still
 		// on disk, and those parents' group is checked the same way.
 		g = slices.DeleteFunc(g, func(n *treeNode) bool {
 			return !exists(n.path)
 		})
 		if len(g) < minGroupSize {
 			continue
 		}
 		slices.SortFunc(g, func(a, b *treeNode) int {
 			return strings.Compare(a.path, b.path)
 		})
@@ -6,7 +6,6 @@ import (
 	"database/sql"
 	"os"
 	"slices"
 	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -180,7 +179,7 @@ func TestTreeNamesSortingBeforeSlash(t *testing.T) {
 		t.Fatalf("directory paths = %q, want %q", got, want)
 	}
-	groups := collectTreeGroups(dirs, super, everyPathExists, nil)
+	groups := collectTreeGroups(dirs, super, nil)
 	gotGroups := groupPaths(groups)
 	wantGroups := [][]string{{"/a", "/c"}}
@@ -196,8 +195,7 @@ func TestTreeNamesSortingBeforeSlash(t *testing.T) {
 }
 func TestRunTreesEscapesPaths(t *testing.T) {
-	dir, recs := recsOnDisk(t, awkwardPairRecs())
+	t.Setenv(databaseEnv, seedDatabase(t, awkwardPairRecs()))
 	t.Setenv(databaseEnv, seedDatabase(t, recs))
 	var stdout, stderr bytes.Buffer
@@ -208,7 +206,7 @@ func TestRunTreesEscapesPaths(t *testing.T) {
 	}
 	want := "first\tdupe\tfiles\tsize\tdisk_size\n" +
-		dir + `/d/\tone\ntwo\rthree\\four` + "\t" + dir + "/d/A\t1\t5\t4096\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)
 	}
@@ -226,11 +224,9 @@ func TestRunTreesDiskSize(t *testing.T) {
 		{size: 20, diskSize: 1024, head: g, tail: g, content: g, path: "/b/sub/g"},
 	}
 	dir, recs := recsOnDisk(t, recs)
 	t.Setenv(databaseEnv, seedDatabase(t, recs))
-	want := "first\tdupe\tfiles\tsize\tdisk_size\n" +
+	want := "first\tdupe\tfiles\tsize\tdisk_size\n/a\t/b\t2\t30\t1536\n"
 		dir + "/a\t" + dir + "/b\t2\t30\t1536\n"
 	if got := runStdout(t, cmdTrees); got != want {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
@@ -241,11 +237,10 @@ func TestRunTreesDiskSize(t *testing.T) {
 // there. After the line naming the database, each phase prints a line
 // naming it with its place among the four as it starts and another as
 // it ends. read counts the 6 records before it reads them, group counts
-// the directories, and write the 1 group. The summary comes last, and
+// the 8 directories, and write the 1 group. The summary comes last, and
 // stdout holds the report alone.
 func TestRunTreesProgressNamesEachPhase(t *testing.T) {
-	dir, recs := recsOnDisk(t, smokeTreeRecs())
+	path := seedDatabase(t, smokeTreeRecs())
 	path := seedDatabase(t, recs)
 	t.Setenv(databaseEnv, path)
 	stderr := captureStderr(t)
@@ -259,15 +254,11 @@ func TestRunTreesProgressNamesEachPhase(t *testing.T) {
 	}
 	report := "first\tdupe\tfiles\tsize\tdisk_size\n" +
-		dir + "/d/t1\t" + dir + "/d/t2\t2\t3100\t8192\n"
+		"/d/t1\t/d/t2\t2\t3100\t8192\n"
 	if got := stdout.String(); got != report {
 		t.Errorf("stdout = %q, want %q", got, report)
 	}
 	// The smoke-test records name 8 directories, / included. Moved under
 	// dir, they name one more for each slash in dir.
 	dirs := strconv.Itoa(8 + strings.Count(dir, "/"))
 	// How each line starts; the rate at the end of a phase varies.
 	want := []string{
 		"trees: database " + path + " (from " + databaseEnv + ")",
@@ -275,9 +266,8 @@ func TestRunTreesProgressNamesEachPhase(t *testing.T) {
 		treesOpenLine,
 		"[2/4] read: counting the records, elapsed 0s, remain unknown",
 		"[2/4] read: [6/6] 100%, ",
-		"[3/4] group: [0/" + dirs + "] 0%, 0 directories/s, elapsed 0s, " +
+		"[3/4] group: [0/8] 0%, 0 directories/s, elapsed 0s, remain unknown",
-			"remain unknown",
+		"[3/4] group: [8/8] 100%, ",
 		"[3/4] group: [" + dirs + "/" + dirs + "] 100%, ",
 		"[4/4] write: [0/1] 0%, 0 groups/s, elapsed 0s, remain unknown",
 		"[4/4] write: [1/1] 100%, ",
 		"trees: 6 records read, 1 duplicate tree groups, 1 dupe trees, ",
@@ -306,7 +296,7 @@ func TestRunTreesProgressNamesEachPhase(t *testing.T) {
 func TestWriteTreeGroupsOnTerminal(t *testing.T) {
 	stderr := captureStderr(t)
 	super, dirs := treeOf(t, smokeTreeRecs())
-	dupes := collectTreeGroups(dirs, super, everyPathExists, nil)
+	dupes := collectTreeGroups(dirs, super, nil)
 	// No timed draws: the display is drawn as it starts and as it ends.
 	p := startProgress(progressParams{
@@ -387,7 +377,7 @@ func TestCollectTreeGroupsMaximal(t *testing.T) {
 	super, dirs := treeOf(t, smokeTreeRecs())
-	groups := collectTreeGroups(dirs, super, everyPathExists, nil)
+	groups := collectTreeGroups(dirs, super, nil)
 	want := [][]string{{"/d/t1", "/d/t2"}}
 	if got := groupPaths(groups); !slices.EqualFunc(got, want,
@@ -411,16 +401,14 @@ func TestCollectTreeGroupsDeterministic(t *testing.T) {
 	super, dirs := treeOf(t, recs)
-	forward := groupPaths(collectTreeGroups(dirs, super, everyPathExists,
+	forward := groupPaths(collectTreeGroups(dirs, super, nil))
 		nil))
 	reversed := slices.Clone(recs)
 	slices.Reverse(reversed)
 	superR, dirsR := treeOf(t, reversed)
-	backward := groupPaths(collectTreeGroups(dirsR, superR, everyPathExists,
+	backward := groupPaths(collectTreeGroups(dirsR, superR, nil))
 		nil))
 	if !slices.EqualFunc(forward, backward, slices.Equal) {
 		t.Fatalf("output depends on record order: %v vs %v",
 			forward, backward)
@@ -440,7 +428,7 @@ func TestCollectTreeGroupsSiblings(t *testing.T) {
 	super, dirs := treeOf(t, recs)
-	got := groupPaths(collectTreeGroups(dirs, super, everyPathExists, nil))
+	got := groupPaths(collectTreeGroups(dirs, super, nil))
 	want := [][]string{{"/p/x1", "/p/x2"}}
 	if !slices.EqualFunc(got, want, slices.Equal) {
@@ -469,7 +457,7 @@ func TestCollectTreeGroupsLeavesOutEmptyTrees(t *testing.T) {
 	super, dirs := treeOf(t, recs)
-	got := groupPaths(collectTreeGroups(dirs, super, everyPathExists, nil))
+	got := groupPaths(collectTreeGroups(dirs, super, nil))
 	want := [][]string{{"/p/x1", "/p/x2"}}
 	if !slices.EqualFunc(got, want, slices.Equal) {
@@ -492,98 +480,10 @@ func TestCollectTreeGroupsDifferingParents(t *testing.T) {
 	super, dirs := treeOf(t, recs)
-	got := groupPaths(collectTreeGroups(dirs, super, everyPathExists, nil))
+	got := groupPaths(collectTreeGroups(dirs, super, nil))
 	want := [][]string{{"/p/a/x", "/q/b/x"}}
 	if !slices.EqualFunc(got, want, slices.Equal) {
 		t.Fatalf("groups = %v, want %v", got, want)
 	}
 }
 // TestCollectTreeGroupsChecksOnlyReportedCopies checks that trees asks
 // whether a directory is on disk only for the members of the groups it
 // returns. It never asks about /a/proj/sub, which lies inside a copy
 // and whose group the group of /a/proj implies.
 func TestCollectTreeGroupsChecksOnlyReportedCopies(t *testing.T) {
 	t.Parallel()
 	f, g, u := testHash("f"), testHash("g"), testHash("u")
 	recs := []scanRec{
 		{size: 10, head: f, tail: f, content: f, path: "/a/proj/f"},
 		{size: 20, head: g, tail: g, content: g, path: "/a/proj/sub/g"},
 		{size: 10, head: f, tail: f, content: f, path: "/b/proj/f"},
 		{size: 20, head: g, tail: g, content: g, path: "/b/proj/sub/g"},
 		// /a lacks this file, so /a and /b are no copies of each other.
 		{size: 30, head: u, tail: u, content: u, path: "/b/lonely"},
 	}
 	super, dirs := treeOf(t, recs)
 	var checked []string
 	exists := func(path string) bool {
 		checked = append(checked, path)
 		return true
 	}
 	got := groupPaths(collectTreeGroups(dirs, super, exists, nil))
 	want := [][]string{{"/a/proj", "/b/proj"}}
 	if !slices.EqualFunc(got, want, slices.Equal) {
 		t.Fatalf("groups = %v, want %v", got, want)
 	}
 	slices.Sort(checked)
 	if !slices.Equal(checked, want[0]) {
 		t.Errorf("directories checked on disk = %q, want %q",
 			checked, want[0])
 	}
 }
 // TestCollectTreeGroupsDropsGroupLeftWithOneCopy checks that a group of
 // two copies, one of them gone, is not returned. If kept, it would
 // write no row, but the summary line would count it.
 func TestCollectTreeGroupsDropsGroupLeftWithOneCopy(t *testing.T) {
 	t.Parallel()
 	f := testHash("f")
 	recs := []scanRec{
 		{size: 10, head: f, tail: f, content: f, path: "/c/kept/f"},
 		{size: 10, head: f, tail: f, content: f, path: "/c/gone/f"},
 	}
 	super, dirs := treeOf(t, recs)
 	exists := func(path string) bool { return path != "/c/gone" }
 	got := groupPaths(collectTreeGroups(dirs, super, exists, nil))
 	if len(got) != 0 {
 		t.Errorf("groups = %v, want none", got)
 	}
 }
 // TestCollectTreeGroupsKeepsGroupLeftWithTwoCopies checks that a group
 // of three copies, one of them gone, is returned with the other two.
 func TestCollectTreeGroupsKeepsGroupLeftWithTwoCopies(t *testing.T) {
 	t.Parallel()
 	f := testHash("f")
 	recs := []scanRec{
 		{size: 10, head: f, tail: f, content: f, path: "/d/kept1/f"},
 		{size: 10, head: f, tail: f, content: f, path: "/d/gone/f"},
 		{size: 10, head: f, tail: f, content: f, path: "/d/kept2/f"},
 	}
 	super, dirs := treeOf(t, recs)
 	exists := func(path string) bool { return path != "/d/gone" }
 	got := groupPaths(collectTreeGroups(dirs, super, exists, nil))
 	want := [][]string{{"/d/kept1", "/d/kept2"}}
 	if !slices.EqualFunc(got, want, slices.Equal) {
 		t.Errorf("groups = %v, want %v", got, want)
 	}
 }