Add typed serial settings operations

Route bounded admin mutations through the existing administration
dispatcher,
covering apply, lifecycle, persistence, authorization, and result
tracking.
Add the browser controls, automatic result refresh, regression coverage,
and
phase documentation.

docs/agent/design-decisions.md

@@ -102,6 +102,10 @@ Phase 8D.4 routes drain/lifecycle operations through a firmware-lifetime immutab
 
 **Relevant files:** `src/user_database.{h,c}`, `src/user_console.c`, `src/web_server.c`, `src/web_serial_transport.c`, `src/ssh_transport.c`
 
+## Typed serial mutations share the administration dispatcher
+
+**8D.9:** HTTPD performs bounded typed admission/result reads only; serial reconfiguration and NVS execute on the existing dispatcher so CLI commands cannot interleave. One global pending slot rejects concurrent work; copied session/principal plus non-reused ID fence stale queued work. A 30-second deadline is checked on dequeue, not a cancellation timer or execution limit. Admitted mutations may finish after revocation; completed results can be replaced. Keep explicit uncertain-outcome recovery and never automatically retry mutations. Apply/Defaults are RAM-only, Save persists working device state rather than browser drafts, and Reset follows canonical apply/persist/best-effort-rollback ordering. Navigation preserves broker clients/writer lease, while explicit serial reconfiguration can discard serial-service pending data. No generic command runner/job history is exposed. See `src/web_serial_settings.{c,h}` and `docs/phase8d9_implementation.md`.
+
 ## Browser authentication has a narrow version-pinned HTTPD boundary
 
 **8D.8 read-only settings:** Reuse bodyless GET cookie/current-admin policy and the existing bounded browser API/errors; no CSRF mutation semantics on a read. Obtain working serial config/running atomically with a zero-wait existing serial mutex, never block HTTPD on stop/reconfiguration or inspect NVS. Navigation changes view/input only, preserving both terminal sockets/lease/output; Settings session validation must not supersede serial-admission checks. One optional exact-GET URI raises only handler capacity to 17. The private adapter stages both descriptor/name allocations before publishing, avoiding the installed 5.5.0 public registration's freed table pointer on strdup failure. Serialized startup/exact matcher only, normal HTTPD allocation/free ownership; re-audit this boundary on SDK changes. Existing public registration callers are not refactored by this phase.