fix(web): usable past-conversation list, and search that finds past sessions

Two home-screen reports from @jordan8037310, both about history that is
present but unreachable.

#260 — "Resume Conversation" rendered 4 rows, then a button that appended
every remaining row into a `max-height: 240px` box, so 35 conversations
landed in a four-row scroll well with no ordering or filtering. Rendering
now goes through `_renderHistoryList()` over a cached corpus: 10 rows to
start, Show more/Show less that grows and shrinks the box (the height cap
is class-driven, `.history-list.expanded`), plus a filter box (name,
folder, #case label, prompts), a sort control (recent / name / folder,
pinned rows still first) and a shown-of-total count. A filter implies
expansion, so every match is visible, and the whole header hides as one
unit while a federated search is active. The A-Z sort keys off the same
string the row renders, since most rows are transcript-backed and carry
no session name at all.

#261 — the search box could not match a past project by folder name:
`harvestSources()` built its session corpus from the live in-memory map,
while past sessions come from `/api/sessions/unified` (lifecycle log +
transcript scan). Folding that scan into the request path would have cost
the search its no-filesystem-reads property, so the corpus arrives via a
bounded snapshot instead: `session-history-index.ts` is published as a
side effect of `/api/sessions/unified` (the home screen fetches it on
open, which is the same screen the search box lives on) and rebuilt
fire-and-forget, single-flight and TTL-guarded when a search finds it
stale. A result for a closed session now resumes the conversation rather
than selecting a tab that no longer exists, and is badged RESUME.

The snapshot is stored unscoped with a per-row owner and re-filtered
through canAccessOwned() on read, so multi-user sees exactly what
/api/sessions/unified exposes: own sessions only, host-wide transcript
history admin-only. Live rows are harvested first and win the dedupe.

Verified end-to-end against a real instance with 60 past sessions: cold
process answers its first search without history and its second with it;
folder-name queries return resume targets; clicking one posts the right
resumeSessionId + workingDir.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -157,6 +157,8 @@ Tests: `test/git-clone.test.ts` (pure half exhaustively, plus REAL git against a
 
 **Cross-session search** (COD-113/#133): `GET /api/search?q=&types=&limit=` federates an **in-memory** search across all live sessions — session metadata (name/workingDir/id), run-summary events, and per-session attachment-history file entries (workspace-relative path only; the server-private `externalPath` is never read). Pure core `searchSources()` in `search-service.ts` (substring-matches with hard per-type caps — no regex, so no ReDoS; no filesystem reads, so no traversal); `harvestSources()` in `search-routes.ts` gathers the in-memory sources. `SearchQuerySchema` bounds `q` (1–200), allowlists `types` (`session,event,file`), clamps `limit` (1–60). Returns the `{success,data}` envelope. Frontend: history-panel search box in `terminal-ui.js`. Types: `src/types/search.ts`.
 
+**Past sessions in the corpus** (#261): the live session map alone made every CLOSED session unfindable — searching a folder name that was sitting in the home screen's Resume list below the box returned nothing. Past sessions now come from `src/web/session-history-index.ts`: a capped (`HISTORY_INDEX_MAX_ITEMS` 400) snapshot of the unified list, read synchronously by `harvestSources()`. ⚠️ It is filled OUTSIDE the request path, which is what preserves the no-fs property above: `/api/sessions/unified` publishes it as a side effect (free — it just merged that list, and the home screen fetches it whenever it opens, which is the same screen the search box lives on), and `ensureHistorySessionIndexFresh()` — **fire-and-forget, single-flight, TTL-guarded (60s)** — kicks a rebuild when a search finds it stale. A cold process therefore answers its first search without history and its second with it; never `await` the refresher from a handler. ⚠️ The snapshot is stored **UNSCOPED** with a per-row `owner` (`undefined` = host-wide transcript history), and `harvestSources()` re-applies `canAccessOwned()` per row — the same rule `/api/sessions/unified` applies when it drops history for non-admins. A scoped (non-admin) unified request therefore re-merges unscoped before publishing, rather than writing its own subset into the shared snapshot. ⚠️ Live rows are harvested FIRST and win the dedupe, so a session that is both live and in the snapshot keeps `jumpTo.kind:'session'`; history rows get `'resume-session'` (with `claudeSessionId`/`workingDir`), because selecting a tab that no longer exists is a silent no-op the user reads as a broken result. Tests: `test/session-history-index.test.ts`, `test/routes/search-routes.test.ts`.
+
 ### Away digest
 
 **Away digest** (COD-41/#136): `GET /api/away-digest?range=&since=&until=&lastViewed=` aggregates "what happened while you were away" from the lifecycle log + run-summary events + live sessions + daily token stats + recently-completed subagents into needs-attention/completed/still-running/idle/informational sections. Pure aggregator in `web/away-digest.ts` (`resolveAwayDigestRange()` validates the window — `since-last-visit`/`1h`/`today`/`24h`/`custom`, server-local TZ; `buildAwayDigest()` classifies). Header-button modal in `panels-ui.js` (button hidden on phones — regression-guarded). ⚠️ Returns `{success:true,digest}` (a legacy raw-ish shape, consistent with the other raw GET handlers in `system-routes.ts` — `{entries}`/`{config}`/`{files}`/`getSystemStats()`); frontend + tests read `.digest`. Subagent lookback is a fixed 60-min window regardless of range.