feat(fleet): surface self-reported model in fleet ps

parseHeartbeat now reads an optional model= line from the heartbeat
file (written by native runtime heartbeats) into HeartbeatInfo.model,
and fleet ps surfaces it as a MODEL column (table) and in --json
(via rows[].heartbeat.model). Legacy/sidecar heartbeats omit the line
and report model=null, so the column shows '-'.

Closes the model self-report gap end-to-end with the native Pi
heartbeat writer (F3-m2): the runtime self-reports its active model
and the fleet operator can see it in ps.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EsgTQzV5YUGk1JtCLP4B83

packages/mosaic/src/commands/fleet.spec.ts

@@ -833,6 +833,17 @@ describe('fleet ps — heartbeat parsing', () => {
     expect(hb.pid).toBe(12345);
     expect(hb.status).toBe('ok');
     expect(hb.ageMs).toBe(10_000);
+    // No model= line in a legacy/sidecar heartbeat → model is null.
+    expect(hb.model).toBeNull();
+  });
+
+  it('parses a self-reported model id from a native heartbeat (model= line)', () => {
+    const ts = new Date(NOW - 5_000).toISOString();
+    const content = `ts=${ts}\npid=42\nstatus=busy\nmodel=openai-codex/gpt-5.5:high\n`;
+    const hb = parseHeartbeat(content, NOW);
+    expect(hb.model).toBe('openai-codex/gpt-5.5:high');
+    expect(hb.status).toBe('busy');
+    expect(hb.health).toBe('healthy');
   });
 
   it('reports stale when heartbeat is older than 3×interval', () => {

packages/mosaic/src/commands/fleet.ts

@@ -390,6 +390,8 @@ export interface HeartbeatInfo {
   /** healthy | stale | unknown */
   health: 'healthy' | 'stale' | 'unknown';
   ageMs: number | null;
+  /** Model id the runtime self-reported in its heartbeat (native HB only), else null. */
+  model: string | null;
 }
 
 export interface AgentPsRow {
@@ -490,15 +492,17 @@ export function heartbeatPath(agentName: string, mosaicHome = defaultMosaicHome(
  *   ts=<iso8601>
  *   pid=<pid>
  *   status=<ok|busy>
+ *   model=<model-id>   (optional — native runtime heartbeats self-report it)
  */
 export function parseHeartbeat(content: string | null, nowMs = Date.now()): HeartbeatInfo {
   if (content === null) {
-    return { ts: null, pid: null, status: null, health: 'unknown', ageMs: null };
+    return { ts: null, pid: null, status: null, health: 'unknown', ageMs: null, model: null };
   }
   const lines = content.split('\n');
   let ts: Date | null = null;
   let pid: number | null = null;
   let status: 'ok' | 'busy' | null = null;
+  let model: string | null = null;
   for (const line of lines) {
     const [key, ...rest] = line.split('=');
     const val = rest.join('=').trim();
@@ -510,6 +514,8 @@ export function parseHeartbeat(content: string | null, nowMs = Date.now()): Hear
       if (Number.isFinite(n)) pid = n;
     } else if (key === 'status' && (val === 'ok' || val === 'busy')) {
       status = val;
+    } else if (key === 'model' && val) {
+      model = val;
     }
   }
   const thresholdMs = heartbeatIntervalMs() * HEARTBEAT_HEALTHY_MULTIPLIER;
@@ -519,7 +525,7 @@ export function parseHeartbeat(content: string | null, nowMs = Date.now()): Hear
     ageMs = nowMs - ts.getTime();
     health = ageMs <= thresholdMs ? 'healthy' : 'stale';
   }
-  return { ts, pid, status, health, ageMs };
+  return { ts, pid, status, health, ageMs, model };
 }
 
 /**
@@ -1123,6 +1129,7 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
         'PID'.padEnd(8),
         'IDLE'.padEnd(8),
         'HB'.padEnd(12),
+        'MODEL'.padEnd(22),
         'FLAGS',
       ].join(' ');
       console.log(header);
@@ -1137,6 +1144,7 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
           row.heartbeat.ageMs !== null
             ? `${Math.round(row.heartbeat.ageMs / 1000)}s/${row.heartbeat.health}`
             : `unknown`;
+        const model = row.heartbeat.model ?? '-';
         const flags: string[] = [];
         if (!row.managed) flags.push('UNMANAGED');
         if (row.driftFlag) flags.push('DRIFT');
@@ -1153,6 +1161,7 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
             pid.padEnd(8),
             idle.padEnd(8),
             hbAge.padEnd(12),
+            model.padEnd(22),
             flags.join(','),
           ].join(' '),
         );