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/design-decisions.md

@@ -82,12 +82,14 @@ Phase 8D.2 adds a third identity: non-reused 64-bit originating web-session IDs
 
 **Consequence for future changes:** Actions that would invalidate their own SSH transport should integrate with deferred control when acknowledgement preservation matters. Prevent new input while an action is pending, keep the wait bounded, and do not describe it as guaranteed delivery.
 
-Phase 8D.4 routes drain/lifecycle operations through a firmware-lifetime immutable owner adapter on the existing control task, outside console locks. Tokens include a transport namespace; owners revalidate full identity and marshal to their transport APIs. `SELF_CLOSE` targets the invoking frontend while existing SSH action meanings remain unchanged. Unsupported actions must fail before side effects. The two console slots remain a shared bounded pool, with no hypothetical browser capacity allocated.
+Phase 8D.4 routes drain/lifecycle operations through a firmware-lifetime immutable owner adapter on the existing control task, outside console locks. Tokens include a transport namespace; owners revalidate full identity and marshal to their transport APIs. `SELF_CLOSE` targets the invoking frontend while existing SSH action meanings remain unchanged. Unsupported actions must fail before side effects. The two console slots remain a shared bounded pool, with no hypothetical browser capacity allocated. The 8D.5 prerequisite additionally requires owner currentness on the dispatcher, outside console locks, before commands and during prompts; account currentness alone cannot establish originating browser-session liveness. Recheck token identity after external validation, reject revoked submitted replies, and wipe consumed output. Polling is not a hard cancellation deadline and cannot roll back arbitrary handlers; owners retain admission/input/output/lifecycle responsibilities.
 
 **Relevant files:** `src/admin_ssh_console.c`, `src/system_console.c`, `src/ssh_console.c`, `src/ssh_transport.c`
 
 ## Authentication uses copied principals and fail-safe currentness checks
 
+**8D.5 web owner extension:** Browser and runtime SSH admission allocate from the same two console slots; a physical SSH slot is not a console index. WEB supports owner-relative self-close only and rejects unsupported network/lifecycle/account mutations at parsed command policy before execution. One web-admin socket and two tickets do not increase six-socket HTTPD capacity; disable LRU rather than evict retained serial clients. The optional owner uses one PSRAM-only payload and ESP timer scheduling, not a new task. HTTPD alone sends/shuts down its verified current fd. Do not use IDF's queued raw-`sock_db *` close from admin polling: free/reuse before that work executes could close a replacement. Detach must fence queue submissions before HTTPD stop; retire queued markers only after successful stop, retaining ownership across failures. No browser UI or generic HTTP command runner is part of this boundary.
+
 **Decision:** Network sessions retain secret-free copied principals. Account mutations invalidate generations/IDs; after commit, the command layer requests best-effort targeted transport revocation, while ongoing currentness checks are authoritative.
 
 **Rationale/evidence:** `user_database` issues principals without secrets; web/SSH check currentness during admission and active sessions. Mutating console paths call transport revocation hooks.