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

Rewrites `TODO.md` from scratch for
#135, by the rules applied to
`README.md` in #140. It is the
project's own task list, so every completed step keeps its date, its
issue or branch and every fact that the old entry recorded, in short
sentences, with lists as bullets. An entry superseded later says so in
one sentence.

`TODO.md` records history, so its entries were not corrected against the
code. The 2026-10-17 release-rule entry is known to be stale. One product
name in the 2026-10-15 entry is replaced by a description.

This file carries the `TODO.md` entry of
#140 word for word, so the
conflict once that merges is resolved by taking this file whole.

Model: fable-5-1

TODO.md

@@ -63,10 +63,10 @@ are known.
   `trees`. Reading a record whose hash is not 32 bytes is an error (2026-10-26,
   https://git.eeqj.de/sneak/sfdupes/issues/134)
 
-- Every file the walk records gets three hashes in the hash phase. `head` and
+- The hash phase gives three hashes to every file that the walk records. `head`
-  `tail` are the SHA-256 of its first and last 64 KiB. `content` is the SHA-256
+  and `tail` are the SHA-256 of its first and last 64 KiB. `content` is the
-  of the whole file under 100 MiB, and of 1 MiB at each gigabyte from 100 MiB
+  SHA-256 of the whole file under 100 MiB, and of 1 MiB at each gigabyte from
-  up. Gone are:
+  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
@@ -156,12 +156,12 @@ are known.
     the default excludes only, and `scan --help` lists them (2026-10-17,
     https://git.eeqj.de/sneak/sfdupes/issues/124)
 
-- The rate a progress display shows covers the items completed over the last 5
+- A progress display's rate covers the items completed over the last 5 seconds.
-  seconds. When stderr is not a terminal, it covers the items since the line
+  When stderr is not a terminal, it covers the items since the line before. It
-  before. It falls to 0 while nothing completes. A burst after a wait no longer
+  falls to 0 while nothing completes. A burst after a wait no longer reads as a
-  reads as a steady rate of over 1,000 files a second. The time remaining still
+  steady rate of over 1,000 files a second. The time remaining still comes from
-  comes from the phase's average. Once no item has completed for 10 seconds, the
+  the phase's average. Once no item has completed for 10 seconds, the line shows
-  word `stalled` and where the phase waits take the rate's place, as
+  `stalled` and where the phase waits in place of the rate, as
   `stalled disk/db`. The places are:
     - `disk`;
     - `db`;
@@ -176,12 +176,12 @@ are known.
     - the elapsed time;
     - the ETA, the time remaining.
 
-    On an 80-column terminal, at counts like those of README's example, the
+    The content phase had one display for its checks and one for its reads. Both
-    content phase's displays for its checks and its reads lost those words. That
+    lost those words on an 80-column terminal, at counts like those of README's
-    happened for most elapsed times and ETAs in minutes. Every other phase kept
+    example. That happened for most elapsed times and ETAs in minutes. Every
-    them whenever the elapsed time and the ETA were both in minutes. The content
+    other phase kept them whenever the elapsed time and the ETA were both in
-    phase writes its last partial batch, the records not yet written, under a
+    minutes. The content phase writes its last partial batch, the records not
-    display of its own (2026-10-16,
+    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
@@ -231,7 +231,8 @@ are known.
     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:
+  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.
@@ -285,8 +286,8 @@ are known.
 - 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
+  For a regular-file operand the check starts at its directory. The records of
-  records of files gone from below it are deleted (2026-10-14,
+  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
@@ -294,8 +295,8 @@ are known.
   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 replaced by a FIFO or device node after it was
+  is still a regular file. A file that is now a FIFO or device node is warned
-  statted is warned about and skipped instead of hanging the scan (2026-10-14,
+  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,
@@ -449,8 +450,8 @@ are known.
   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. A file gone or changed since its
+  gigabyte-spaced 1 MiB samples at or above. It never read a file gone or
-  record was written was never read. `report` and `trees` left out any record
+  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)
@@ -483,9 +484,9 @@ are known.
 - The Docker build stage's prerequisites were installed by running
   `script/bootstrap` instead of `apk add --no-cache make` inline.
   `script/verify-linter-pin` failed the build unless the linter copied from the
-  lint stage was the version `script/bootstrap` pinned. Builds then took up to
+  lint stage was the version that `script/bootstrap` pinned. Builds then took up
-  5m14s from an empty cache, mostly in a `chown -R` of the module cache, filed
+  to 5m14s from an empty cache, mostly in a `chown -R` of the module cache,
-  as https://git.eeqj.de/sneak/sfdupes/issues/43. Since
+  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`,
@@ -545,17 +546,18 @@ are known.
     - 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 it never
+    walk. A cancelled walk yields a partial size census, and every file that it
-    reached looks vanished to the update phase. That phase's own `BeginTx` also
+    never reached looks vanished to the update phase. That phase's own `BeginTx`
-    fails on the cancelled context before deleting anything. The guard is still
+    also fails on the cancelled context before deleting anything. The guard is
-    the barrier once an interrupted scan may commit what it has. Tests drive
+    still the barrier once an interrupted scan may commit what it has. Tests
-    `run(scan)` against a database whose insert trigger aborts. They assert that
+    drive `run(scan)` against a database whose insert trigger aborts. They
-    the scan fails instead of hanging, and that the goroutine count returns to
+    assert that the scan fails instead of hanging, and that the goroutine count
-    its pre-scan baseline. Other tests cancel a scan part-way through the walk,
+    returns to its pre-scan baseline. Other tests cancel a scan part-way through
-    deterministically, by counting the scan's own checks of `ctx.Done()`. They
+    the walk, deterministically, by counting the scan's own checks of
-    assert that it stops at the guard with every record intact. It then holds a
+    `ctx.Done()`. They assert that it stops at the guard with every record
-    partial size census and a still-populated record index. Direct tests cover
+    intact. It then holds a partial size census and a still-populated record
-    the remaining cancellation branches of both pools. They test:
+    index. Direct tests cover the remaining cancellation branches of both pools.
+    They test:
     - `sendEvent`;
     - the walk workers;
     - `dispatchDirs`;
@@ -672,8 +674,8 @@ are known.
     - `LICENSE` and the README License section. MIT was assumed from house
       convention, for the owner to confirm;
     - `REPO_POLICIES.md` in the repo root;
-    - the canonical `.golangci.yml`, with the 150 findings it raised fixed, so
+    - the canonical `.golangci.yml`, with its 150 findings fixed, so that
-      that `make lint` is clean;
+      `make lint` is clean;
     - the `Makefile` targets the policy requires:
         - `test` and `lint`;
         - `fmt` and `fmt-check`;