feat(web): expose read-only terminal session history - #397

Source-read follow-up (2026-09-09). This PR is still the leftover file-history slice, not live attach.

Status. OPEN, CHANGES_REQUESTED, mergeStateStatus: BEHIND. Head edeb7b3081ca79c0e384aef38a11d8f2d4c8a887. The 2026-09-07 review stands: SessionManager.listAll() with no directory walks every default Pi workspace and buildSessionInfo retains allMessagesText before the cwd filter and page slice; getReadOnlyTerminalSession repeats that scan. Reproduced on real default Session files. origin/main 0d17f4577fe31315fe6c95370d251bdb4e2413cf still has no pi-default / /api/terminal-sessions string. Checkout a9b40f0044ee59c360a6077c1c0bdbdbd30da10b has no Web.

What this PR actually does. GET /api/terminal-sessions lists Pi’s default store (~/.pi/agent/sessions), filters by the current Web workspace cwd, and inspects a path with loadSessionPreviewData (the origin /sessions preview loader: compaction-aware model window, ≤80 messages / 1 MiB). Every row is source: "pi-default", origin: "terminal", readOnly: true. Tests assert listAll(web-sessions) stays empty — no copy, no switchSession, no write, no UI. Protocol WebSessionSummary.source on origin is still the "web-session" literal; this PR does not widen that union.

What it is not. Opening that JSONL later is history. It does not attach the Web Host to the TUI process that still has the file open. Background Terminal / Subagent / Workflow managers are process-local objects keyed by the live SessionManager; a later file open or this preview cannot reconstruct /ps. That attach remains #76 observer/controller and is out of scope here.

Relation to /sessions. TUI /sessions is the same catalog seam plus Enter → ctx.switchSession (this process adopts the file: shutdown old runtime, session_start on the target). This PR is the preview half only. It is not compaction (same-file window) and not #154 rewind (same-file leaf move).

Please keep the P2 source-read fix on this PR (discover the selected workspace first; bound and cancel transcript work; prove unrelated workspace files are not parsed). Rebase onto current main after that. Do not expand the PR into live attach, and do not treat a future merge as “Web can see my running TUI /ps.”

Replacement-test follow-up (2026-09-09). Head still edeb7b3081ca79c0e384aef38a11d8f2d4c8a887. The 2026-09-07 P2 and the earlier file-history comment stand; this list is the fail-closed matrix that comment did not enumerate. Do not merge edeb7b3 until these lock. list(cwd) alone is not a complete replacement (buildSessionInfo still retains allMessagesText; getDefaultSessionDir mkdir is a write).

Must hold

• List candidates are only {sessions}/--<encode(workspace)>--/*.jsonl before any transcript body is opened. Zero-arg SessionManager.listAll() (and listAll(getSessionsDir())) is forbidden on this route.
• Discovery must not materialize allMessagesText before the cwd/query/page filters. Query stays name / cwd / firstMessage. HTTP JSON must not contain allMessagesText.
• Preview is loadSessionPreviewData(path, { signal }) after a path+cwd membership check — not a second full-tree listAll(). Preview ≠ Web archived-sessions.json / /resume corpus ≠ live /ps pids.
• Every row source: "pi-default", origin: "terminal", readOnly: true. No copy, switchSession, or write. After list+preview, listAll(web-sessions) still does not contain that path; GET /api/sessions still has no pi-default row.

Missing vs current 42/42 (single-fixture) tests — fail closed

1. Spy: this route never calls zero-arg listAll() (progress-only overload counts as zero-arg).
2. Two default-store workspaces under one PI_CODING_AGENT_DIR: limit=1 total === 1 and only the current cwd path is returned. Today’s total === 1 is vacuously green.
3. Unrelated workspace file is not body-opened (createReadStream / open / readFile spy) during list and during in-workspace preview. Absence of its token in the JSON is not enough.
4. "allMessagesText" absent from adapter objects and Host raw JSON.
5. Query equal to a token that exists only in another workspace’s later messages → total === 0 and that file still not opened. Do not add an allMessagesText search.
6. Preview of the other workspace path → 404 SESSION_NOT_FOUND and loader never opens it.
7. Compacted fixture: messages follow the firstKeptEntryId window (≤80 / 1 MiB); Web archive sidecar is unchanged and does not mark the TUI path.
8. After list+preview, GET /api/capabilities sessionId is still the in-memory Web id; no bt- / capability ids on the terminal-history payload; GET /api/sessions has no that path.
9. POST/PATCH/DELETE /api/terminal-sessions → 405; TUI file size/mtime/hash unchanged; Web runtime id unchanged.
10. Hidden / unbound workspace: no default-store walk.
11. AbortSignal cancelled before/during preview is not a 200.

Keep existing label / empty-web-sessions / 400 / 404 assertions. Rebase onto current main after the source-read fix. Do not expand into live attach. Do not treat a future merge as “Web can see running TUI /ps.”

Fixed and pushed as a8669c0 (merged latest main).

• Terminal Session discovery and detail now use Pi's workspace-scoped SessionManager.list(workspace) instead of global listAll().
• Workspace admission for this read-only route no longer triggers a full Web Session scan, so unrelated default workspaces are not parsed as part of the request.
• Added a regression that fails if global discovery is used while listing or previewing terminal Sessions.
• Validation: Node 24 Web adapter tests and bun run check passed.