fix(edit-history): bounded image probe, linear path scan (review of #693)

- probeLocalPaths: every agent-printed candidate goes through
  probePathKind() first (no pastCap, bulk scan), sequentially; only a path
  that answered 'file' gets realpath + stat. A path on a mount that stopped
  answering no longer hangs the sync, a queued sync or remove().
- PATH_TOKEN_RE: branch 4 starts only at a token boundary (`:` excluded so
  URLs stay ignored), branch 1 stops at `:`. Linear in the line length
  (30,000 `#` took ~3 s before).
- Load older yields to the event loop between the files it parses.
- GET /edits answers unsupported without loading a store.
- CLAUDE.md paragraph trimmed to the rules; probe and regex rules added to
  architecture-invariants#edit-history-panel.

Tests: stall test through the real sync and probe with a stat that never
settles; time-budget tests with 30,000-character inputs and a 139-result
base64 chunk; route test asserts no store load for unsupported sessions.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -736,6 +736,8 @@ Matching semantics: a query containing `/` matches the relative path, otherwise
 
 ⚠️ **Images only through existing file surfaces.** A Bash image candidate counts only when the file's mtime lies in the call's window (start − 2 s … end + 2 s) and no entry already covers that file version; `SendUserFile` images need no window. The panel shows a thumbnail only inside the workspace, through the confined `file-raw` route. An image outside it gets no thumbnail (each would mint an attachment id per render); a click opens the shared file preview, which registers it once through `POST /api/sessions/:id/attachments` with `notify: false` (its extension allowlist and `isSensitivePath` apply). SVGs get no thumbnail. No route of this feature serves a file, least of all a transcript path.
 
+⚠️ **Transcript paths are agent-printed, so they are probed BOUNDED and scanned in linear time** (#516; #693 review). `probeLocalPaths()` sends each candidate through `probePathKind()` (no `pastCap`: a bulk scan), one at a time, and only a path that answered `'file'` gets `realpath` + `stat`; a path on a mount that stopped answering costs one stalled stat, never a sync, a queued sync or `remove()` that cannot finish (`test/edit-history-probe-stall.test.ts`). `PATH_TOKEN_RE` runs synchronously in the request, over Bash output of up to 30,000 characters: an unquoted token may start only at a token boundary (line start or a token-ending character, `:` excluded so URLs stay ignored), and the `file://` branch stops at `:`. A lookbehind that merely excludes some characters lets a match start at every character of a long token and rescan it, quadratic in the line (2.7 s for 30,000 `#`). Time-budget regression tests in `test/edit-history-parse.test.ts`. "Load older" yields to the event loop between the files it parses (up to 3 × 8 MiB).
+
 Paths, agent descriptions and diff lines render via `textContent` only (browser test with a hostile path). The header button uses the marker-class pattern (`btn-edit-history--hidden`) and stays off phones (`mobile.css`, locked in `test/mobile-header-buttons-policy.test.ts`). Remote, Docker and non-claude sessions answer `unsupported` and are never read.
 
 ### Config backups