v1.46.2: re-check of v1.46.1 — HP-1461-01, -02

HP-1461-01: collection was tied to config/set, which is the right scope for
what a commit supersedes but leaves a file nobody references with no future
write to notice it — cancel a dialog after the upload finished, drop the
connection just after, or call the upload API directly. The daily sweep added
in v1.46.1 only removed streaming temporaries, so the documented 'a cancelled
attachment is collected an hour later' did not hold on an instance nobody
edits. The scheduled pass now loads the stored config under the same write_lock
a commit uses and runs collect_attachments/collect_plans with it as BOTH sides:
nothing counts as superseded, referenced files are preserved, aged unreferenced
ones go. Doing it under the lock keeps it from deciding on a snapshot a commit
is about to replace.

HP-1461-02: _reloadLayoutOnly captured the dirty set AFTER flushing the pending
write, and the flush empties it first — so during a real drag (where a write is
already scheduled) the snapshot was empty and the server's older position was
merged over the user's move. The snapshot is taken before the flush, by value,
and a _sentPos map now holds positions that are sent but unacknowledged, which
closes the same window for a write that was already in flight.

Tests: the upload test now cancels the request task for real (the previous one
claimed to and only walked error paths); smoke_layout_sync schedules a genuine
debounced write and delays it — verified failing on a v1.46.1 build with
exactly the reported symptom; a new backend test reloads the entry and asserts
the scheduled sweep takes an aged cancelled attachment and an orphan plan while
keeping everything the config still references.
Docs: CHANGELOG.md + CHANGELOG.ru.md + ARCHITECTURE.md + TESTING.md + STATUS.md.

docs/ARCHITECTURE.md

@@ -198,8 +198,13 @@ uploads agree on one name and quietly overwrite each other. It also budgets the
 length so the result survives the sanitiser the content view applies to the
 request, since a name the view rewrites is a file written and never served.
 Streaming temporaries live in the files root under `.upload-`, are removed on
-every exit path of the request, and are swept at startup and daily for the
-cases a process death leaves behind. A new icon has no id yet, so its
+every exit path of the request (including cancellation, which is a
+BaseException and slips past `except Exception`), and are swept at startup and
+daily. That scheduled pass also runs the two collectors with the stored
+configuration as *both* sides — nothing superseded, so every referenced file is
+kept and only aged unreferenced ones go. Without it, collection would only ever
+happen when somebody saves, and a file uploaded into a dialog that was then
+cancelled would wait for a write that may never come. A new icon has no id yet, so its
 files go to a per-dialog staging folder and move to the real id once the config
 write is accepted — the same copy → save → cleanup order as a rebind.
 `config/set` collects what its commit superseded, and anything unreferenced and