Add the entries that landed on next to TODO.md

Catches `TODO.md` up with `next`. The `README.md` entry takes the text
that landed, word for word. The entry of this rewrite takes the date
2026-11-02. The entries of #146
and #147 are added in their
place, newest first, in short sentences, with every fact, date and link
kept. Nothing else changes.

Model: fable-5-1

TODO.md

@@ -32,7 +32,7 @@ are known.
 - `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
-  (2026-10-26, https://git.eeqj.de/sneak/sfdupes/issues/135)
+  (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
@@ -40,7 +40,23 @@ are known.
   Every statement was checked against the code on `next`. Five comments in
   `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)
+  now says (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