Rewrite TODO.md sentence by sentence (closes #135)

TODO.md is the project's own task list, judged by the same rules as
README.md: short sentences, lists as bullets, nothing a newcomer reads
twice. Every completed step is kept with its date and its issue or
branch, and every fact the old entries recorded is kept too, in short
sentences. The 2026-07-22 policy-compliance checklist is folded into
the step that did the work, and the accepted divergence from the
layout policy gets a section of its own. Workflow, Status and Next
Step keep their rules unchanged.

Model: fable-5-1

README.md

@@ -461,17 +461,26 @@ exclude, is not on a persistent filesystem (see "Rules for the walk"), or, with
 `-x`, is on a different filesystem than that operand, because that operand's
 walk does not enter such a directory and so does not reach it.
 
-An operand that is a symlink (never followed, not even as an operand), socket,
-FIFO, or device node, or a directory named `.zfs`, is not scanned. `scan` prints
-a one-line warning naming the path and what it is, counts it as skipped, and
-drops it from the scanned operands before reading the database. Another operand
-beneath it is still scanned. The records stored beneath it are not deleted: they
-are treated like any other record outside the scanned operands. If it lies under
-another operand, they are under that operand instead, and are treated like any
-other record there. This is not an error: a scan whose every operand is dropped
-walks nothing and exits 0. An operand that is not on a persistent filesystem
-(see "Rules for the walk") is dropped the same way. The line `scan` prints for
-it is not a warning, though, and it is not counted as skipped.
+An operand is not scanned when it is:
+
+- a symlink, which `scan` never follows, not even as an operand;
+- a socket, FIFO or device node;
+- at or inside a directory named `.zfs`.
+
+An operand reached through a symlink into a `.zfs` directory is not scanned
+either.
+
+This holds even when the operand lies under another operand. `scan` prints a
+one-line warning naming the path and what it is, counts it as skipped, and drops
+it from the scanned operands before reading the database. An operand beneath a
+symlink operand is still scanned. The records stored beneath the dropped operand
+are not deleted: they are treated like any other record outside the scanned
+operands. If it lies under another operand, they are under that operand instead,
+and are treated like any other record there. This is not an error: a scan whose
+every operand is dropped walks nothing and exits 0. An operand that is not on a
+persistent filesystem (see "Rules for the walk") is dropped the same way. The
+line `scan` prints for it is not a warning, though, and it is not counted as
+skipped.
 
 `scan` synchronizes the database with the filesystem state under the scanned
 operands:

TODO.md

@@ -38,8 +38,14 @@ are known.
   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
-  `main_test.go` cite "Settings", where their rules now live (2026-10-26,
-  https://git.eeqj.de/sneak/sfdupes/issues/135)
+  `main_test.go` cite "Settings", where their rules now live. One comment each
+  in `scan_test.go`, `trees_test.go` and `exclude_test.go` cites what the README
+  now says (2026-10-26, https://git.eeqj.de/sneak/sfdupes/issues/135)
+
+- an operand at or inside a directory named `.zfs` is never scanned, whether
+  given alone or under another operand. `scan` warns about it, counts it as
+  skipped and does not walk it (2026-10-26,
+  https://git.eeqj.de/sneak/sfdupes/issues/142)
 
 - A file or directory removed while the scan runs is not an error, in the walk
   or in the hash phase. The scan prints no line for it and does not count it as
@@ -73,8 +79,8 @@ are known.
     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` copied again
-  from `sneak/prompts` `next` at `0653579`. Two steps now come before
+- `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`;
@@ -213,11 +219,16 @@ are known.
   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, such as records or groups. stdout and the summary line are
-  unchanged. When stdout and stderr are the same file, as one terminal is, no
-  line of stdout shares a line with the display. When they are not, the display
-  keeps being drawn while stdout waits on a slow reader (2026-10-16,
-  https://git.eeqj.de/sneak/sfdupes/issues/113)
+  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 the phase starts and shows:
@@ -245,8 +256,8 @@ are known.
   "Database" says when `scan` writes each file (2026-10-16,
   https://git.eeqj.de/sneak/sfdupes/issues/111)
 
-- The canonical files and model scripts copied again from `sneak/prompts` `next`
-  at `e3f79c4`:
+- 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
@@ -271,11 +282,10 @@ are known.
     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 the
-  outer operand's walk cannot reach it. That is the case when a directory
-  between the two operands, 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 directories checked start at its directory. The
+- 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 directories checked start at its directory. The
   records of files gone from below it are deleted (2026-10-14,
   https://git.eeqj.de/sneak/sfdupes/issues/106)
 
@@ -338,7 +348,7 @@ are known.
 
     (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/16)
 
-- `.golangci.yml` replaced with the current canonical copy, which uses
+- `.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)
 
@@ -357,8 +367,8 @@ are known.
 - 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 `cancel_test.go` corrected, and
-  `walkCancelInFlightDirs` renamed to `walkCancelInFlightFiles` (2026-10-04,
+- Four inaccurate comments in `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,
@@ -445,12 +455,12 @@ are known.
   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 removed from `Makefile`, `.gitignore` and
+- 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` fixed. Both pins became the policy
+  `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
@@ -575,7 +585,7 @@ are known.
     (2026-08-09, branch `db-close-on-fatal`,
     https://git.eeqj.de/sneak/sfdupes/issues/4)
 
-- `golangci-lint` updated to v2.12.2 with the canonical config, merged as
+- `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
@@ -588,7 +598,7 @@ are known.
     No new lint findings surfaced (2026-08-09, branch `golangci-v2.12.2`,
     https://git.eeqj.de/sneak/sfdupes/issues/3)
 
-- `Makefile` targets converted to scripts-to-rule-them-all `script/`
+- `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`;
@@ -601,15 +611,15 @@ are known.
   it used to run `check` plus `build`. `make build` remains as an alias
   (2026-07-24, branch `make-default-target`)
 
-- Scan-wide phases, concurrent operands and batched updates. All operands seed
-  the shared walk pool, and every pass runs once over the whole scan. So 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 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 split back out of the walk. Phases are strictly sequential
+- 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;
@@ -625,31 +635,32 @@ are known.
   totals that looked like the whole run's (2026-07-24, branch
   `scan-operand-progress`)
 
-- Parallel walk. The walk pass was a single goroutine and took hours at about 20
-  million files on a busy pool. 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`)
+- 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`)
 
-- Persistent scan database. `scan` 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
+- `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`, added. `v0.0.1`
-  tagged, and `main` and the tags pushed (2026-07-23)
+- 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)
 
-- `scan` command-line rework. 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 `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
@@ -692,10 +703,11 @@ are known.
     The code was already `gofmt`-clean, so no standalone formatting commit was
     needed (2026-07-23, branch `repo-policy-compliance`)
 
-- `git init` with a README-only first commit; the code baseline committed on
-  `main` (2026-07-22)
+- `git init` was run, with a README-only first commit. The code baseline was
+  committed on `main` (2026-07-22)
 
-- `scan`, `report` and `trees` subcommands implemented (pre-git history)
+- The `scan`, `report` and `trees` subcommands were implemented (pre-git
+  history)
 
 # Future Steps
 

main_test.go

@@ -928,24 +928,21 @@ func TestRunScanWalksOperandUnderSymlinkOperand(t *testing.T) {
 }
 
 func TestRunScanSkipsZFSOperand(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
-
 	zfs := filepath.Join(t.TempDir(), ".zfs")
-	snapshot := filepath.Join(zfs, "snapshot", "hourly")
-	f := writeFile(t, snapshot, "f", pattern(1, 10))
+	f := writeFile(t, zfs, "snapshot/hourly/f", pattern(1, 10))
 
-	// An operand beneath a .zfs directory is walked, because it is not
-	// itself named .zfs.
-	scanOK(t, snapshot)
+	// No scan records a file inside a .zfs directory, so the record
+	// beneath the operand is written straight into the database.
+	path := seedDatabase(t, []scanRec{{size: 10, path: f}})
+	t.Setenv(databaseEnv, path)
 
 	assertOperandSkipped(t, path, zfs, ".zfs directory", f)
 }
 
 // assertOperandSkipped scans operand alone and checks that it is skipped
 // as kind: a warning naming it, one skip in the summary, exit 0, and the
-// record for kept, which an earlier scan stored beneath operand, still
-// in the database at dbPath.
+// record for kept, stored beneath operand before this scan, still in the
+// database at dbPath.
 func assertOperandSkipped(t *testing.T, dbPath, operand, kind,
 	kept string,
 ) {
@@ -974,6 +971,121 @@ func assertOperandSkipped(t *testing.T, dbPath, operand, kind,
 	recordByPath(t, dbRecords(t, db), kept)
 }
 
+// TestRunScanSkipsOperandInsideZFS scans a directory inside a .zfs
+// directory, first alone and then under another operand. Each time it
+// is warned about and counted as skipped, and nothing in it is walked.
+// The other operand is scanned as usual.
+func TestRunScanSkipsOperandInsideZFS(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := t.TempDir()
+	hourly := filepath.Join(dir, ".zfs", "snapshot", "hourly")
+	writeFile(t, hourly, "f", pattern(1, 10))
+	f := writeFile(t, dir, "f", pattern(2, 10))
+
+	warning := "walk " + hourly + ": skipping operand inside a .zfs directory\n"
+
+	for _, tc := range []struct {
+		operands []string
+		summary  string
+	}{
+		{
+			[]string{hourly},
+			"scan: 0 files seen (0 added, 0 updated, 0 removed, " +
+				"0 unchanged), 1 skipped\n",
+		},
+		{
+			[]string{dir, hourly},
+			"scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+				"0 unchanged), 1 skipped\n",
+		},
+	} {
+		stderr := scanOK(t, tc.operands...)
+		if !strings.Contains(stderr, warning) ||
+			!strings.Contains(stderr, tc.summary) {
+			t.Errorf("scan %q: stderr = %q, want %q and %q", tc.operands,
+				stderr, warning, tc.summary)
+		}
+	}
+
+	db, err := openDB(path, reportParams)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	if got := recordPaths(dbRecords(t, db)); !slices.Equal(got, []string{f}) {
+		t.Errorf("records = %q, want %q", got, []string{f})
+	}
+}
+
+// TestRunScanSkipsOperandThroughSymlinkIntoZFS scans snaps/daily, where
+// snaps is a symlink to pool/.zfs/snapshot. The operand is warned about
+// by the path given, counted as skipped, and not walked.
+func TestRunScanSkipsOperandThroughSymlinkIntoZFS(t *testing.T) {
+	t.Setenv(databaseEnv, testDBPath(t))
+
+	dir := t.TempDir()
+	writeFile(t, dir, "pool/.zfs/snapshot/daily/f", pattern(1, 10))
+
+	snaps := filepath.Join(dir, "snaps")
+
+	err := os.Symlink(filepath.Join(dir, "pool", ".zfs", "snapshot"), snaps)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	daily := filepath.Join(snaps, "daily")
+	stderr := scanOK(t, daily)
+
+	warning := "walk " + daily + ": skipping operand inside a .zfs directory\n"
+	summary := "scan: 0 files seen (0 added, 0 updated, 0 removed, " +
+		"0 unchanged), 1 skipped\n"
+
+	if !strings.Contains(stderr, warning) ||
+		!strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q and %q", stderr, warning, summary)
+	}
+}
+
+// TestRunScanWalksOperandThroughSymlink scans data/daily, where data is
+// a symlink to a directory outside any .zfs directory. The operand is
+// scanned as usual, and its file is recorded by the path given.
+func TestRunScanWalksOperandThroughSymlink(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := t.TempDir()
+	writeFile(t, dir, "pool/data/daily/f", pattern(1, 10))
+
+	data := filepath.Join(dir, "data")
+
+	err := os.Symlink(filepath.Join(dir, "pool", "data"), data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	daily := filepath.Join(data, "daily")
+	stderr := scanOK(t, daily)
+
+	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+		"0 unchanged), 0 skipped\n"
+	if !strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q", stderr, summary)
+	}
+
+	db, err := openDB(path, reportParams)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	recordByPath(t, dbRecords(t, db), filepath.Join(daily, "f"))
+}
+
 func TestRunReportSucceeds(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)

scan.go

@@ -383,7 +383,8 @@ func (s *scanState) runPhases(ctx context.Context, roots []string,
 ) error {
 	// Types and filesystems are checked before pruning so that an
 	// operand under a dropped one is still scanned, not dropped as lying
-	// under it.
+	// under it, and so that an operand inside a .zfs directory gets its
+	// warning even when it lies under another operand.
 	roots = pruneRoots(s.walkableRoots(roots, rules), oneFS, rules,
 		deviceOfPath)
 
@@ -411,15 +412,15 @@ func (s *scanState) runPhases(ctx context.Context, roots []string,
 }
 
 // walkableRoots returns the operands the walk can start from: regular
-// files, and directories not named .zfs. Every other operand is warned
-// about, counted as skipped, and dropped. A dropped operand is no
-// longer a root, so the records stored beneath it are treated as if it
-// had not been given: those under no other root count as outside the
-// roots and are not deleted as unverified. An operand on a filesystem
-// in rules that is not persistent is dropped the same way, with a line
-// saying so that is not a warning, and is not counted as skipped. An
-// operand that fails lstat here is kept, and the walk warns about it
-// unless it no longer exists.
+// files, and directories not named .zfs, none of them inside a
+// directory named .zfs. Every other operand is warned about, counted as
+// skipped, and dropped. A dropped operand is no longer a root, so the
+// records stored beneath it are treated as if it had not been given:
+// those under no other root count as outside the roots and are not
+// deleted as unverified. An operand on a filesystem in rules that is not
+// persistent is dropped the same way, with a line saying so that is not
+// a warning, and is not counted as skipped. An operand that fails lstat
+// here is kept, and the walk warns about it unless it no longer exists.
 func (s *scanState) walkableRoots(roots []string, rules walkRules) []string {
 	kept := make([]string, 0, len(roots))
 
@@ -874,9 +875,24 @@ func sendEvent(ctx context.Context, events chan<- walkEvent,
 
 // operandWarning returns the one-line warning for an operand the walk
 // does not start from, naming the path and what it is, or "" for one it
-// does: a regular file, or a directory not named .zfs. Symlinks are
-// never followed, including as operands.
+// does: a regular file, or a directory not named .zfs, that is not
+// inside a directory named .zfs, neither as given nor with its symlinks
+// resolved. Symlinks are never followed, including as operands.
 func operandWarning(root string, fi fs.FileInfo) string {
+	// The walk never enters a .zfs directory, so it starts from nothing
+	// inside one either, not even through a symlink. An operand whose
+	// symlinks cannot be resolved is checked as given.
+	resolved, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		resolved = root
+	}
+
+	if slices.Contains(strings.Split(filepath.Dir(root), "/"), ".zfs") ||
+		slices.Contains(strings.Split(filepath.Dir(resolved), "/"), ".zfs") {
+		return fmt.Sprintf("walk %s: skipping operand inside a .zfs directory",
+			root)
+	}
+
 	var kind string
 
 	switch mode := fi.Mode(); {