chore: snapshot working tree - pty_exited notifications + in-flight inference WIP

feat(booterm): structured pty_exited WS notifications. Plan-validated, impl-validated, code-reviewed green (contracts build clean, contracts test 29/29, booterm + web typecheck clean).

wip: in-progress inference/provider refactor (agents.ts, provider.ts, new llama-providers.ts, removed llama-args-validator), plus arena, dispatcher, compaction, schema changes.

openspec: pty-exit-notifications complete; x-agent-flags planned (not yet implemented).

openspec/changes/pty-exit-notifications/tasks.md

@@ -0,0 +1,39 @@
+## 1. Add PtyExitedFrame to WsFrame contract
+
+- [x] 1.1 Add `PtyExitedFrame` Zod schema to `packages/contracts/src/ws-frames.ts` with fields: `type` (literal `'pty_exited'`), `session_id` (`z.string().min(1).max(64)`, NOT uuid -- booterm IDs are `[a-zA-Z0-9_-]{1,64}`), `pane_id` (`z.string().min(1).max(64)`, same), `exit_code` (int), `last_lines` (string array), `session_title` (nullable optional), `session_description` (nullable optional), `parent_agent` (nullable optional), `timed_out` (boolean)
+- [x] 1.2 Add `PtyExitedFrame` to the `WsFrameSchema` discriminated union array
+- [x] 1.3 Add `'pty_exited'` to the `KNOWN_FRAME_TYPES` const array
+- [x] 1.4 Rebuild `@boocode/contracts` (`pnpm -C packages/contracts build`)
+
+## 2. Add getLastLines helper to booterm registry
+
+- [x] 2.1 Add `getLastLines(paneId: string, n: number): string[]` function to `apps/booterm/src/pty/registry.ts` that reads the last N non-empty lines from the ring buffer
+- [x] 2.2 Add `timedOut?: boolean` field to `SessionMeta` interface in `apps/booterm/src/pty/registry.ts`
+
+## 3. Replace booterm onExit handler with structured frame
+
+- [x] 3.1 In `apps/booterm/src/ws/attach.ts`, replace the `handle.onExit` handler to: read `registry.get(pid)` and `getLastLines(pid, 5)` BEFORE any unregister, build a structured `pty_exited` frame with `timed_out: meta?.timedOut ?? false`, send it as JSON text to the socket, then close
+- [x] 3.2 Preserve backward compatibility: the frame `type` changes from `'exit'` to `'pty_exited'` -- the old bare exit frame is replaced (not additive)
+
+## 4. Wire timed_out flag in sweepExpired (pre-wiring)
+
+- [x] 4.1 In `apps/booterm/src/pty/manager.ts` `sweepExpired`, set `meta.timedOut = true` before calling `killSession`
+- [x] 4.2 Do NOT call `registry.unregister()` in `sweepExpired` -- let the socket `close` handler do cleanup to avoid the race where `onExit` fires after unregister deletes metadata. The `killSession` call triggers the tmux exit which triggers `onExit` which reads metadata then closes the socket which triggers `unregister`.
+
+## 5. Update web frontend terminal protocol
+
+- [x] 5.1 Add `pty_exited` variant to `ServerControlFrame` union in `apps/web/src/lib/terminal-protocol.ts` with fields matching the contract: `session_id`, `pane_id`, `exit_code`, `last_lines`, `session_title`, `session_description`, `parent_agent`, `timed_out`
+- [x] 5.2 Update `parseServerFrame` to recognize `type: 'pty_exited'` and return the structured frame
+
+## 6. Handle pty_exited in useTerminalSocket
+
+- [x] 6.1 In `apps/web/src/hooks/terminal/useTerminalSocket.ts`, add a handler for `frame?.type === 'pty_exited'`: write `\r\n\x1b[2m[process exited with code ${frame.exit_code}]\x1b[0m\r\n` to xterm; if `timed_out: true`, write `\r\n\x1b[2m[process timed out and was killed]\x1b[0m\r\n` instead; if `last_lines` is non-empty, write the last line to xterm as-is
+- [x] 6.2 Ensure the legacy `{type: 'exit', code: N}` handler still works (no regression)
+
+## 7. Verify
+
+- [x] 7.1 Run `pnpm -C packages/contracts build` -- no type errors
+- [x] 7.2 Run `pnpm -C apps/booterm typecheck` -- no type errors
+- [x] 7.3 Run `npx tsc -p apps/web/tsconfig.app.json --noEmit` -- no type errors
+- [x] 7.4 Grep source for `pty_exited` -- should appear in contracts, booterm, and web
+- [x] 7.5 Run contracts drift test: `pnpm -C packages/contracts test` -- `pty_exited` in KNOWN_FRAME_TYPES matches WsFrameSchema