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nothing counts as superseded, referenced files are preserved, aged unreferenced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/TESTING.md

@@ -239,6 +239,15 @@ Run the *core flows* (marked ★ below) in each environment at least once per mi
       on the plan after a reload. Same for each tap action and each fill mode
       [auto: backend test_every_display_mode_the_editor_offers_is_accepted and
       neighbours, test_a_marker_showing_its_value_can_be_saved]
+- [ ] Nothing accumulates on an idle instance (v1.46.2, HP-1461-01): attach a
+      file, cancel the dialog, and do not save anything else — an hour later (or
+      after a restart) the file is gone, while every file the configuration
+      still references is untouched
+      [auto: backend test_scheduled_sweep_collects_what_no_commit_will]
+- [ ] A drag wins over a concurrent remote move (v1.46.2, HP-1461-02): drag an
+      icon and, while the save is still in flight, have another window move a
+      different icon — your icon stays where you put it and the other one
+      updates [auto: smoke_layout_sync]
 - [ ] Concurrent uploads of one name (v1.46.1, HP-1460-01): attach the same
       file from two browser tabs at once — two attachments, two sets of bytes,
       neither lost. A file whose name is at the length limit still downloads