fix(web): bind copied session selection to file identity

[ooiuuii]

Problem

Fixes #583.

Copying a Pi JSONL Session preserves its ID. The Web adapter currently treats that ID alone as ownership of the live SessionManager: reading a copy can return the original transcript, renaming the copy can write the original, and selecting the copy can skip the runtime switch. An ID-only frontend lookup can also drift to a newer copy during refresh.

Value

Keep the displayed, selected and edited Session bound to its actual file. A copied history entry must not silently alias the active original. If switching succeeds but confirming the new snapshot fails, the stale page must not send Session-bound operations until confirmation succeeds.

Approach

• Reuse the live manager only when both ID and resolved file path match; preserve the existing synthetic path for the in-memory Session.
• Apply that ownership check to reads, rename, default selection, projection retention and the HTTP selection shortcut. The runtime's file-aware switching implementation is unchanged.
• Have the store consume the existing controller: web plus path identity instead of deriving ownership from ID equality.
• Require the existing confirmed selectedPath at prompt, model/thinking and command-discovery gates and in Composer. No new state machine or API fields. A successful refresh restores normal operation.

The backend and these necessary UI consumers repair one file-identity invariant. Splitting them would leave the same copied-ID failure reachable. Stop/cancellation identity, general multi-client concurrency, archive policy and new Session schemas are outside this PR.

Validation

Baseline: f6b49ae59605b1276b8267f2886d22c03f01533c; source checkout tests, Node 22.22.3 and Bun 1.3.14 on Windows. Fixtures contain synthetic data in isolated temporary directories, not user histories or provider calls.

• Native SessionManager creates and persists a real JSONL, which is copied and independently modified. Three regressions fail before the fix: selected-file transcript, rename target, and authenticated loopback /api/sessions/select runtime switching.
• Actual store actions add two refresh/canonical-retry regressions and four failed-confirmation/Composer cases. They prove that a populated original snapshot plus a successful same-ID copy switch followed by a network error or invalid projection cannot issue prompt/model/thinking/command requests; sending resumes after a valid snapshot.
• node --experimental-strip-types --test tests/web/pi-adapter.test.ts tests/web/web-host.test.ts tests/web/artifact-host.test.ts — 62/62 pass.
• node node_modules/vitest/vitest.mjs run tests/web/web-store.spec.ts tests/web/app-render.spec.ts — 149/149 pass.
• bun run check and git diff --check — pass. Tracked web/dist/app.js regenerated by the normal build.
• Scoped structured review (autoreview --mode local --engine codex --model gpt-6-astra --thinking xhigh --no-web-search): final helper exit 0, no actionable findings. Two verified same-identity consumer gaps were fixed before this final review; no unrelated follow-ups folded in.
• Full local suite is not claimed green: separate clean-baseline host timeouts and Windows background-process cleanup hangs prevent a reliable global local result. Fresh branch CI remains the broader verification gate; no test timeouts or unrelated fixtures changed here.

Impact

• User-visible: copied sessions show their own transcript, rename their own file, and activate correctly; an unconfirmed page disables sending until refreshed successfully.
• Model-visible context/tools: no schema or tool changes; transcript comes from the selected file.
• Runtime/lifecycle: live-manager reuse and UI operation admission respect file identity; underlying Pi switching/cancellation unchanged.
• Persisted config/data: no migration, format change or ID rewriting.
• Compatibility/risk: uses existing paths/controller projection and optional Composer fallback; no path case-folding, permission changes or new configuration.