feat: add bounded admin WebSocket backend (Phase 8D.5)

- Require current admin cookie sessions, Origin checks and single-use
  tickets
- Reuse the shared console with session-aware authorization and slot
  allocation
- Add HTTPD-owned I/O, bounded buffering and revocation cleanup
- Prevent LRU eviction of serial clients and stale admin socket closure
- Reject unsupported web-shell mutations before side effects
- Add host regressions, a smoke client and resource accounting

Validated by user sign-off after a 15-minute full-client soak at 230400
baud, with a few broker drops under heavy output. Browser UI remains
for Phase 8D.6; numeric memory reserves remain open.

docs/agent/code-map.md

@@ -74,6 +74,13 @@ This is a semantic map, not a complete file inventory. Start here, then read the
 - 8D.3 UI: `src/web_login_ui.{c,h}` serves standalone `/login`; `web_ui.c` validates session before serial connect/restore and handles logout/401 safely. Both scripts hash-bound, auth documents/app no-store. Tests: `python3 tests/web_login_ui/run.py` and `python3 tests/web_ui_session/run.py`. Live cutover host-tested/build-verified, M1 validated by user sign-off (numeric reserves open): `docs/phase8d3_implementation.md`.
 - Asset constraint: `web_assets_data.c` is checked-in generated input to the build; do not hand-edit or regenerate casually.
 
+### Browser admin backend (8D.5)
+
+- Files: `src/web_admin_transport.{c,h}`, `src/web_admin_tickets.{c,h}`, protected registration/lifecycle in `web_server.c`, revocation through `web_serial_transport_revoke_*`, diagnostics in `web_console.c`.
+- Routes: CSRF-protected admin-only `POST /api/admin/ws-ticket`; ordinary `GET /ws/admin` with cookie/Origin/ticket/shared-console admission before explicit 101. No UI entry or broker client. One socket, two tickets, existing two shared console slots; six total HTTPD sockets, LRU disabled, 16 URI handlers.
+- Ownership: 20 ms ESP timer queues at most one HTTPD poll, no new task; HTTPD owns 1,552 B PSRAM-only payload and IO. Closure uses HTTPD-owned `shutdown`, not IDF's reusable-pointer queued close. Detach fences submitters; only successful HTTPD stop retires queued state before restart. Session/principal currentness and generation checks protect all sensitive boundaries.
+- Tests: `python3 tests/web_admin_transport/run.py --tickets`, `python3 tests/web_admin_transport/server_lifecycle.py`, `python3 tests/web_cookie_auth/run.py --admin`; manual smoke client/procedure in `tests/web_admin_transport/README.md` and `docs/phase8d5_implementation.md`. Final shutdown fix is host-tested and build-verified by the parent's sequential final `pio run`; target validation remains pending.
+
 ## SSH
 
 **Responsibility:** authenticate SSH, route users to serial and administrators to the command dispatcher, and own wolfSSH lifecycle.
@@ -110,7 +117,7 @@ This is a semantic map, not a complete file inventory. Start here, then read the
 - Ownership: dispatcher is sole `esp_console_run()` caller; the SSH owner exclusively performs post-initialization wolfSSH runtime calls.
 - Lifecycle: remote session tokens include slot generation; fixed output/history/prompt state is wiped immediately on idle close or after an executing handler returns. Admin SSH `exit` and Ctrl+D on an empty command line request bounded deferred self-disconnect after best-effort output draining.
 - Constraint: one slow command or prompt serializes all administration. Admin SSH is unavailable until command registration and UART frontend creation complete; supported deferred actions wait only for a bounded application-buffer drain heuristic.
-- 8D.4 boundary: `admin_ssh_console_open_owned()` copies transport-qualified identity and retains an immutable firmware-lifetime drain/lifecycle adapter; the existing two slots are shared. SSH compatibility admission/adapter resides in `ssh_transport.c`; no browser admin caller yet. Owners handle liveness/output; completion scratch is nonblockingly serialized. Focused host command: `python3 tests/admin_console_boundary/run.py`.
+- 8D.4/8D.5 boundary: `admin_ssh_console_open_owned()` retains explicit-index admission; runtime SSH and browser owners use `admin_ssh_console_open_available()` for the same two slots. Copied transport-qualified identity and immutable firmware-lifetime currentness/drain/lifecycle adapters; SSH publishes its allocated console index separately from its physical SSH slot. Owners handle liveness/output; dispatcher and prompt waits additionally require owner currentness (250 ms polling plus check/scheduling latency). SSH publishes locked principal copies; consumed console output is wiped. Completion scratch is nonblockingly serialized. Browser unsupported lifecycle/account mutations are rejected before execution. Focused host command: `python3 tests/admin_console_boundary/run.py`.
 
 ## Wi-Fi