docs(adr): ids sort in natural order everywhere (improvise-cq1q.1)

Defines natural order, applies it to the display suffix, and adds a
Status row for the conflict with CellKey's String::cmp order: RecordHash
values change and saved data lines reorder; the loader canonicalises.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

context/adr/007-stable-identities-amendment-1.md

@@ -18,6 +18,7 @@ true. Where the amendment replaces an ADR 007 rule or an existing behaviour:
 | 1 | `measure_item_names` merges a formula into a stored measure of the same name | a formula never merges: it gets its own id, `profit-<n>` beside a stored `profit` |
 | 2 | a display already in use in a scope is refused | equal displays in a scope are shown with a gapless ` #2`, ` #3`, … suffix in id order |
 | 2 | `CellKey` pairs are `(CategoryId, ItemId)` | `(CategoryId, ItemHandle)` |
+| 4 | ids sort by plain string order (`CellKey::new` sorts with `String::cmp`, and the writer orders data lines by their text) | ids sort in natural order. `CellKey`'s canonical coordinate order changes with it, so `RecordHash` values change (they are on the wire, not in files), and a saved file's data lines and their coordinates are written in the new order; the loader canonicalises keys, so the data read back is the same |
 | 2, 5 | a collapsed entry and a group reference name a group by name | by its id |
 | 4 | casefold; a run of U+0020 spaces becomes one `_`; strip characters outside `a`–`z`, `0`–`9`, `-`, `_`; remove a leading `_` | casefold; every character outside `a`–`z`, `0`–`9` and `-` becomes `_`; runs of `_` collapse; leading and trailing `_` and `-` are removed; `n` is prepended before a leading digit |
 | 5 | a hand-written id uses the alphabet `a`–`z`, `0`–`9`, `-`, `_` | a hand-written id obeys every syntax rule of a generated id |
@@ -104,10 +105,9 @@ cost`); a dimension target is rare, for a derived dimension.
   the same display, they are shown with a suffix: the first keeps the bare display, and
   the rest get ` #2`, ` #3`, … (a space, then `#` and the number) as a gapless
   sequence in the order their ids sort.
-  - The order is the ids' plain string order, the order `CellKey` already sorts ids
-    in, not the counter's numeric order. So
-    `profit`, `profit-1` and `profit-2` show as `Profit`, `Profit #2` and `Profit #3`,
-    and `profit-10` sorts before `profit-2`.
+  - The order is the ids' natural order (clause 4), so `profit`, `profit-1`,
+    `profit-2` and `profit-10` show as `Profit`, `Profit #2`, `Profit #3` and
+    `Profit #4`.
   - Gapless: if the thing shown as `Profit #2` is removed, `Profit #3` becomes
     `Profit #2`.
   - The suffix is computed when a display is shown, from the things that share it, and
@@ -159,6 +159,12 @@ also what the counter may make of `east`. They never collide, because every id a
 document holds is taken however it was made: a display slugging to a held `east-1`
 becomes `east-1-<n>`, and a held counter candidate is skipped.
 
+**Ids are always sorted in natural order**, wherever ids are ordered. Split each id into
+alternating runs of digits and non-digits; compare the runs pairwise, a digit run by its
+numeric value and a non-digit run by byte order; when two digit runs have equal value,
+the shorter (fewer leading zeros) sorts first; when one id runs out of runs first, it
+sorts first. So `profit`, `profit-1`, `profit-2`, `profit-10`, and `a-7` before `a-007`.
+
 **Hand-written ids obey every syntax rule of a generated id.** `east-1`, `item-4` and
 `q1_-_2024` load; `-east`, `east-`, `2024`, `a__b` and `_draft` are refused at load.