fix: persist and recover the Agent's real installation_id (heartbeat activation)

POST /v1/agents/enroll now returns installation_id; new installs persist it
to agent.env immediately. Runtime recovery precedence: existing SQLite
installation_identity -> configured INSTALLATION_ID -> authenticated
GET /v1/agents/me/identity. Recovery fails closed on missing/malformed/
mismatched identity rather than inventing a UUID (which the Hub would then
reject as a conflicting Installation on an already-enrolled Agent). An
explicit AGENT_JOBS_ENABLED gate stops the service from claiming a job right
after the first heartbeat.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

central/app/agent_distribution.py

@@ -194,6 +194,7 @@ def router(session_factory):
                              target_type="agent", target_id=str(agent.id), context={"ip": ip, "installation": enr.enrollment_uuid})
                 session.commit()
                 return {"agent_id": agent.id, "agent_token": plain_token, "tenant_id": enr.tenant_id,
+                        "installation_id": enr.enrollment_uuid,
                         "hub_url": config.settings.base_url, "hostname_mismatch": mismatch}
             except enrollment.EnrollmentRejected as rejected:
                 session.rollback()

central/app/api.py

@@ -226,6 +226,26 @@ def router(session_factory, bootstrap_token):
             return {"event_id": event.id}
         finally: session.close()
 
+    @routes.get("/agents/me/identity")
+    def agent_identity(identity=Depends(principal)):
+        """Return only the authenticated Agent's existing installation identity."""
+        session, agent = identity
+        try:
+            installation = session.scalar(select(Installation).where(Installation.agent_id == agent.id))
+            last_seen = agent.last_seen_at
+            if last_seen is not None and last_seen.tzinfo is None:
+                last_seen = last_seen.replace(tzinfo=timezone.utc)
+            online = last_seen is not None and (datetime.now(timezone.utc) - last_seen).total_seconds() <= settings.agent_online_threshold_seconds
+            return {
+                "agent_id": agent.id,
+                "installation_id": installation.installation_id if installation else None,
+                "hostname": installation.hostname if installation else None,
+                "version": agent.agent_version,
+                "status": "ONLINE" if online else "OFFLINE",
+            }
+        finally:
+            session.close()
+
     @routes.get("/agents/me")
     def agent_status(identity=Depends(principal)):
         session, agent = identity