Show agent liveness, stuck/zombie detection and parse errors in admin

api/openapi.yaml

@@ -802,9 +802,19 @@ components:
 
     Status:
       type: object
-      required: [started_at, db_bytes, last_event_seq, projects, active_tasks, sse_clients, live_agents, running_turns, queued_turns, caps, rate_limits]
+      required: [started_at, db_bytes, last_event_seq, projects, active_tasks, sse_clients, live_agents, running_turns, queued_turns, caps, rate_limits, agent_processes, zombies, stuck_after_seconds, protocol_errors]
       properties:
         live_agents: { type: integer, description: Agent processes currently running. }
+        agent_processes:
+          type: array
+          description: Every agent process byre is tracking, idle sessions included.
+          items: { $ref: "#/components/schemas/AgentProcess" }
+        zombies:
+          type: array
+          description: Sessions marked running with no live process, and agent processes byre has no session for.
+          items: { $ref: "#/components/schemas/Zombie" }
+        stuck_after_seconds: { type: integer, description: How long a running turn may go without a stream event before it counts as stuck. }
+        protocol_errors: { $ref: "#/components/schemas/ProtocolErrors" }
         running_turns:
           type: array
           description: Turns running now, oldest session first.
@@ -842,3 +852,55 @@ components:
         session_id: { type: string }
         task_id: { type: string }
         vendor: { type: string }
+
+    AgentProcess:
+      type: object
+      required: [session_id, task_id, vendor, pid, state, last_event_at, health]
+      properties:
+        session_id: { type: string }
+        task_id: { type: string }
+        vendor: { type: string }
+        pid: { type: integer }
+        state: { type: string, description: The session's state, as on AgentSession. }
+        last_event_at: { type: string, format: date-time, description: When the process last wrote a line to its stream, or when it started. }
+        health:
+          type: string
+          enum: [ok, stuck, exited]
+          x-enum-varnames: [HealthOk, HealthStuck, HealthExited]
+          description: stuck means a turn is running and no stream event has arrived for stuck_after_seconds; exited means the process is gone.
+
+    Zombie:
+      type: object
+      required: [kind, detail]
+      properties:
+        kind:
+          type: string
+          enum: [running_without_process, process_without_session]
+        detail: { type: string }
+        session_id: { type: string }
+        task_id: { type: string }
+        pid: { type: integer }
+
+    ProtocolErrors:
+      type: object
+      required: [counts, recent]
+      properties:
+        counts:
+          type: object
+          description: Stream lines the adapter couldn't parse or didn't recognise since byre started, keyed by vendor.
+          additionalProperties: { type: integer }
+        recent:
+          type: array
+          description: The most recent ones, newest first.
+          items: { $ref: "#/components/schemas/ProtocolError" }
+
+    ProtocolError:
+      type: object
+      required: [vendor, session_id, at, reason, raw, size]
+      properties:
+        vendor: { type: string }
+        session_id: { type: string }
+        at: { type: string, format: date-time }
+        reason: { type: string }
+        raw: { type: string, description: The line as received, cut to its first 4 KiB. }
+        size: { type: integer, description: The line's full length in bytes. }