feat(fleet): fleet ps surfaces unmanaged socket sessions

After building roster-agent rows (unchanged), enumerate live sessions on
the mosaic-factory socket via `tmux list-sessions -F '#{session_name}'`.
Sessions not in the roster and not the holder session (_holder) are
emitted as additional UNMANAGED rows with runtime=unknown, managed=false,
source="socket". All existing roster rows gain managed=true/source="roster".
Roster rows always appear first; unmanaged rows follow.

- Adds buildTmuxListSessionsCommand + parseTmuxListSessions helpers
- driftFlag is always false for unmanaged rows (no roster runtime to compare)
- Heartbeat, pane, and systemd info populated for unmanaged rows the same
  way as roster rows; tenant_id + host always present
- Resilient: if list-sessions fails, only roster rows are shown, no crash
- UNMANAGED flag appears in table output; managed/source fields in --json
- 8 new tests cover: command construction, session parsing, unmanaged row
  inclusion, _holder exclusion, table flag, socket failure resilience

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RMoEx7hfdFGjUiCHuN1RRi

packages/mosaic/framework/tools/fleet/start-agent-session.sh

@@ -6,6 +6,8 @@ MOSAIC_TMUX_SOCKET=${MOSAIC_TMUX_SOCKET:-mosaic-factory}
 MOSAIC_AGENT_RUNTIME=${MOSAIC_AGENT_RUNTIME:-pi}
 MOSAIC_AGENT_WORKDIR=${MOSAIC_AGENT_WORKDIR:-$HOME}
 MOSAIC_AGENT_COMMAND=${MOSAIC_AGENT_COMMAND:-}
+MOSAIC_HEARTBEAT_RUN_DIR=${MOSAIC_HEARTBEAT_RUN_DIR:-$HOME/.config/mosaic/fleet/run}
+MOSAIC_HEARTBEAT_INTERVAL=${MOSAIC_HEARTBEAT_INTERVAL:-15}
 
 if [ -z "$AGENT_NAME" ]; then
   echo "ERROR: agent name argument or MOSAIC_AGENT_NAME is required" >&2
@@ -96,5 +98,55 @@ else
 fi
 
 mkdir -p "$MOSAIC_AGENT_WORKDIR"
-exec tmux -L "$MOSAIC_TMUX_SOCKET" new-session -d -s "$AGENT_NAME" -c "$MOSAIC_AGENT_WORKDIR" \
+
+# ── Launch the tmux session (no exec — we continue to wire the heartbeat) ────
+tmux -L "$MOSAIC_TMUX_SOCKET" new-session -d -s "$AGENT_NAME" -c "$MOSAIC_AGENT_WORKDIR" \
   bash -c "$PANE_SHELL_SNIPPET"
+
+# ── Resolve the pane PID (retry briefly to let the session initialise) ────────
+PANE_PID=""
+for _retry in 1 2 3 4 5; do
+  PANE_PID=$(tmux -L "$MOSAIC_TMUX_SOCKET" list-panes \
+    -t "=${AGENT_NAME}:0.0" -F '#{pane_pid}' 2>/dev/null || true)
+  [ -n "$PANE_PID" ] && break
+  sleep 0.2
+done
+
+# ── Spawn the heartbeat sidecar (detached, best-effort) ──────────────────────
+# The sidecar writes ~/.config/mosaic/fleet/run/<AGENT>.hb atomically while the
+# pane process is alive, then exits so the file goes stale (fleet ps shows stale
+# then PANE=dead).  It is runtime-agnostic: it only cares about the pane PID.
+_start_heartbeat_sidecar() {
+  local agent="$1"
+  local pane_pid="$2"
+  local run_dir="$3"
+  local interval="$4"
+  local hb_file="${run_dir}/${agent}.hb"
+
+  mkdir -p "$run_dir"
+
+  # Write the sidecar as a self-contained bash one-liner so it carries no
+  # references to any variables from this script's environment.
+  local sidecar_script
+  sidecar_script=$(printf \
+    'hb=%s; pid=%s; iv=%s; mkdir -p "$(dirname "$hb")"; while kill -0 "$pid" 2>/dev/null; do tmp="$hb.tmp.$$"; printf "ts=%%s\npid=%%s\nstatus=ok\n" "$(date +%%Y-%%m-%%dT%%H:%%M:%%S%%z)" "$pid" > "$tmp" && mv "$tmp" "$hb"; sleep "$iv"; done' \
+    "$hb_file" "$pane_pid" "$interval")
+
+  # setsid + disown ensures the sidecar survives this script exiting.
+  # stderr/stdout go to /dev/null; failures are non-fatal.
+  if command -v setsid >/dev/null 2>&1; then
+    setsid bash -c "$sidecar_script" </dev/null >/dev/null 2>&1 &
+  else
+    bash -c "$sidecar_script" </dev/null >/dev/null 2>&1 &
+  fi
+  disown $! 2>/dev/null || true
+}
+
+if [ -n "$PANE_PID" ]; then
+  # Guard: do not let sidecar startup failures abort the launcher (set -e).
+  _start_heartbeat_sidecar "$AGENT_NAME" "$PANE_PID" \
+    "$MOSAIC_HEARTBEAT_RUN_DIR" "$MOSAIC_HEARTBEAT_INTERVAL" || \
+    echo "WARNING: heartbeat sidecar could not be started for $AGENT_NAME" >&2
+else
+  echo "WARNING: could not resolve pane PID for $AGENT_NAME — heartbeat sidecar not started" >&2
+fi

packages/mosaic/framework/tools/fleet/test-start-agent-session.sh

@@ -50,6 +50,10 @@ grep -qF 'already running' /tmp/mosaic-start-agent-idempotent.out || fail "dupli
 #   - Intercepts 'new-session' calls and records its arguments to a file.
 #   - For 'has-session' calls, exits 1 (session does not exist) so the script
 #     proceeds to launch instead of printing "already running".
+#   - For 'list-panes' calls, returns empty so PANE_PID stays unset and the
+#     heartbeat sidecar is NOT spawned (heartbeat is not the focus of this test;
+#     test 6 and 7 cover that path).  This prevents any real-filesystem side
+#     effects or leaked background processes.
 #   - For all other subcommands, exits 0.
 #
 # Assertions:
@@ -60,7 +64,8 @@ grep -qF 'already running' /tmp/mosaic-start-agent-idempotent.out || fail "dupli
 FAKE_BIN=$(mktemp -d)
 FAKE_RUNTIME_BIN=$(mktemp -d)
 TMUX_ARGS_FILE=$(mktemp)
-CLEANUP_DIRS+=("$FAKE_BIN" "$FAKE_RUNTIME_BIN")
+HB_RUN_DIR3=$(mktemp -d)
+CLEANUP_DIRS+=("$FAKE_BIN" "$FAKE_RUNTIME_BIN" "$HB_RUN_DIR3")
 
 # Write the fake tmux shim (uses only positional args, no sourced vars).
 cat > "$FAKE_BIN/tmux" <<SHIM
@@ -74,6 +79,11 @@ if [ "\$subcmd" = "new-session" ]; then
   printf '%s\n' "\$@" > "$TMUX_ARGS_FILE"
   exit 0
 fi
+if [ "\$subcmd" = "list-panes" ]; then
+  # Return empty: no sidecar spawned (heartbeat is not the focus of this test).
+  echo ""
+  exit 0
+fi
 exit 0
 SHIM
 chmod +x "$FAKE_BIN/tmux"
@@ -89,6 +99,7 @@ MOSAIC_AGENT_WORKDIR="$WORKDIR3" \
 MOSAIC_AGENT_RUNTIME="pi" \
 MOSAIC_RUNTIME_BIN="$FAKE_RUNTIME_BIN" \
 MOSAIC_AGENT_COMMAND="mosaic yolo pi --model openai-codex/gpt-5.5:high" \
+MOSAIC_HEARTBEAT_RUN_DIR="$HB_RUN_DIR3" \
   "$START" "$AGENT3"
 
 all_args=$(cat "$TMUX_ARGS_FILE" 2>/dev/null || true)
@@ -112,7 +123,8 @@ echo "$all_args" | grep -qF "mosaic yolo pi --model openai-codex/gpt-5.5:high" |
 # ── Test 4: when no extra runtime-bin dirs exist, exec still appears ───────────
 TMUX_ARGS_FILE2=$(mktemp)
 FAKE_BIN2=$(mktemp -d)
-CLEANUP_DIRS+=("$FAKE_BIN2")
+HB_RUN_DIR4=$(mktemp -d)
+CLEANUP_DIRS+=("$FAKE_BIN2" "$HB_RUN_DIR4")
 
 cat > "$FAKE_BIN2/tmux" <<SHIM2
 #!/usr/bin/env bash
@@ -122,6 +134,11 @@ if [ "\$subcmd" = "new-session" ]; then
   printf '%s\n' "\$@" > "$TMUX_ARGS_FILE2"
   exit 0
 fi
+if [ "\$subcmd" = "list-panes" ]; then
+  # Return empty: no sidecar spawned (heartbeat is not the focus of this test).
+  echo ""
+  exit 0
+fi
 exit 0
 SHIM2
 chmod +x "$FAKE_BIN2/tmux"
@@ -139,6 +156,7 @@ MOSAIC_AGENT_WORKDIR="$WORKDIR4" \
 MOSAIC_AGENT_RUNTIME="pi" \
 MOSAIC_RUNTIME_BIN="/nonexistent-dir-$$" \
 MOSAIC_AGENT_COMMAND="mosaic yolo pi" \
+MOSAIC_HEARTBEAT_RUN_DIR="$HB_RUN_DIR4" \
   "$START" "$AGENT4"
 
 all_args4=$(cat "$TMUX_ARGS_FILE2" 2>/dev/null || true)
@@ -161,7 +179,8 @@ echo "$all_args4" | grep -qF "mosaic yolo pi" || fail "pane command does not inc
 TMUX_ARGS_FILE5=$(mktemp)
 FAKE_BIN5=$(mktemp -d)
 FAKE_RUNTIME_BIN5=$(mktemp -d)  # this dir IS on the launcher's PATH below
-CLEANUP_DIRS+=("$FAKE_BIN5" "$FAKE_RUNTIME_BIN5")
+HB_RUN_DIR5=$(mktemp -d)
+CLEANUP_DIRS+=("$FAKE_BIN5" "$FAKE_RUNTIME_BIN5" "$HB_RUN_DIR5")
 
 cat > "$FAKE_BIN5/tmux" <<SHIM5
 #!/usr/bin/env bash
@@ -171,6 +190,11 @@ if [ "\$subcmd" = "new-session" ]; then
   printf '%s\n' "\$@" > "$TMUX_ARGS_FILE5"
   exit 0
 fi
+if [ "\$subcmd" = "list-panes" ]; then
+  # Return empty: no sidecar spawned (heartbeat is not the focus of this test).
+  echo ""
+  exit 0
+fi
 exit 0
 SHIM5
 chmod +x "$FAKE_BIN5/tmux"
@@ -190,6 +214,7 @@ MOSAIC_AGENT_WORKDIR="$WORKDIR5" \
 MOSAIC_AGENT_RUNTIME="pi" \
 MOSAIC_RUNTIME_BIN="$FAKE_RUNTIME_BIN5" \
 MOSAIC_AGENT_COMMAND="mosaic yolo pi" \
+MOSAIC_HEARTBEAT_RUN_DIR="$HB_RUN_DIR5" \
   "$START" "$AGENT5"
 
 all_args5=$(cat "$TMUX_ARGS_FILE5" 2>/dev/null || true)
@@ -205,4 +230,123 @@ echo "$all_args5" | grep -qF "export PATH=" || \
 echo "$all_args5" | grep -qF "$FAKE_RUNTIME_BIN5" || \
   fail "test5: candidate dir (already on launcher PATH) was NOT baked into pane PATH — regression"
 
+# ── Test 6: heartbeat sidecar — pane PID resolved + .hb file written ──────────
+#
+# Uses a real tmux session (same socket as test 1 which already has $AGENT) so
+# list-panes returns a real pane PID.  We override MOSAIC_HEARTBEAT_RUN_DIR to
+# a temp dir and set a 1-second interval, then wait up to 3 s for the .hb file
+# to appear and check its content.
+
+HB_RUN_DIR=$(mktemp -d)
+CLEANUP_DIRS+=("$HB_RUN_DIR")
+
+# Re-use the session+agent created in Test 1 (still alive on $SOCKET / $AGENT).
+# We need to invoke the script for a NEW agent on the same socket to exercise
+# the heartbeat path with a real pane PID.
+AGENT6="agent6-$RANDOM"
+MOSAIC_TMUX_SOCKET="$SOCKET" \
+MOSAIC_AGENT_WORKDIR="$WORKDIR" \
+MOSAIC_AGENT_COMMAND='bash --noprofile --norc -i' \
+MOSAIC_HEARTBEAT_RUN_DIR="$HB_RUN_DIR" \
+MOSAIC_HEARTBEAT_INTERVAL="1" \
+  "$START" "$AGENT6"
+
+HB_FILE="$HB_RUN_DIR/${AGENT6}.hb"
+
+# Wait up to 5 seconds for the heartbeat file to appear.
+_waited=0
+until [ -f "$HB_FILE" ] || [ "$_waited" -ge 5 ]; do
+  sleep 0.5
+  _waited=$((_waited + 1))
+done
+
+[ -f "$HB_FILE" ] || fail "test6: heartbeat file not written at $HB_FILE within 5s"
+
+hb_content=$(cat "$HB_FILE")
+echo "--- test 6: heartbeat file content ---"
+echo "$hb_content"
+echo "--- end test 6 ---"
+
+# Verify required fields are present.
+echo "$hb_content" | grep -qE '^ts=[0-9]{4}-[0-9]{2}-[0-9]{2}T' || \
+  fail "test6: heartbeat ts field missing or malformed"
+echo "$hb_content" | grep -qE '^pid=[0-9]+' || \
+  fail "test6: heartbeat pid field missing or malformed"
+echo "$hb_content" | grep -qF 'status=ok' || \
+  fail "test6: heartbeat status=ok missing"
+
+# ── Test 7: heartbeat sidecar — targets correct .hb path per agent name ────────
+#
+# Uses the fake-tmux shim approach (like tests 3-5) to capture the sidecar
+# invocation without needing a real session.  A fake setsid shim records its
+# arguments so we can assert the sidecar script targets the expected .hb path
+# and uses the configured interval.
+
+FAKE_BIN7=$(mktemp -d)
+FAKE_RUNTIME_BIN7=$(mktemp -d)
+SETSID_ARGS_FILE=$(mktemp)
+HB_RUN_DIR7=$(mktemp -d)
+CLEANUP_DIRS+=("$FAKE_BIN7" "$FAKE_RUNTIME_BIN7" "$HB_RUN_DIR7")
+
+AGENT7="my-fleet-agent-$RANDOM"
+INTERVAL7="42"
+
+# Fake tmux: has-session → not found; new-session → ok; list-panes → known PID.
+cat > "$FAKE_BIN7/tmux" <<SHIM7
+#!/usr/bin/env bash
+subcmd="\$3"
+if [ "\$subcmd" = "has-session" ]; then exit 1; fi
+if [ "\$subcmd" = "new-session" ]; then exit 0; fi
+if [ "\$subcmd" = "list-panes" ]; then echo "88888"; exit 0; fi
+exit 0
+SHIM7
+chmod +x "$FAKE_BIN7/tmux"
+
+# Fake setsid: capture the bash -c <script> argument for inspection, then
+# background an actual bash subshell so disown succeeds in the caller.
+cat > "$FAKE_BIN7/setsid" <<'SETSID_SHIM'
+#!/usr/bin/env bash
+# argv: setsid bash -c <sidecar_script>
+# Record the full argument list to the capture file, then exit cleanly.
+printf '%s\0' "$@" > __SETSID_ARGS_FILE__
+exit 0
+SETSID_SHIM
+# Patch the placeholder with the real capture-file path (avoids heredoc expansion issues).
+sed -i "s|__SETSID_ARGS_FILE__|${SETSID_ARGS_FILE}|g" "$FAKE_BIN7/setsid"
+chmod +x "$FAKE_BIN7/setsid"
+
+SOCKET7="mosaic-agent-test7-$RANDOM-$$"
+WORKDIR7=$(mktemp -d)
+CLEANUP_DIRS+=("$WORKDIR7")
+
+PATH="$FAKE_BIN7:$PATH" \
+MOSAIC_TMUX_SOCKET="$SOCKET7" \
+MOSAIC_AGENT_WORKDIR="$WORKDIR7" \
+MOSAIC_AGENT_RUNTIME="pi" \
+MOSAIC_RUNTIME_BIN="$FAKE_RUNTIME_BIN7" \
+MOSAIC_AGENT_COMMAND="mosaic yolo pi" \
+MOSAIC_HEARTBEAT_RUN_DIR="$HB_RUN_DIR7" \
+MOSAIC_HEARTBEAT_INTERVAL="$INTERVAL7" \
+  "$START" "$AGENT7"
+
+# Give the background setsid shim a moment to finish writing the capture file.
+sleep 0.5
+
+setsid_args=$(cat "$SETSID_ARGS_FILE" 2>/dev/null | tr '\0' '\n' || true)
+rm -f "$SETSID_ARGS_FILE"
+rm -rf "$WORKDIR7"
+
+echo "--- test 7: captured setsid args ---"
+echo "$setsid_args"
+echo "--- end test 7 ---"
+
+# The sidecar script (bash -c <script>) must reference the correct .hb path.
+expected_hb="${HB_RUN_DIR7}/${AGENT7}.hb"
+echo "$setsid_args" | grep -qF "$expected_hb" || \
+  fail "test7: sidecar script does not reference correct .hb path ($expected_hb)"
+
+# The sidecar script must use the configured interval.
+echo "$setsid_args" | grep -qF "$INTERVAL7" || \
+  fail "test7: sidecar script does not reference configured interval ($INTERVAL7)"
+
 echo "ok - start-agent-session"

packages/mosaic/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@mosaicstack/mosaic",
-  "version": "0.0.35",
+  "version": "0.0.36",
   "repository": {
     "type": "git",
     "url": "https://git.mosaicstack.dev/mosaicstack/stack.git",

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

@@ -15,6 +15,7 @@ import {
   buildSystemdEnableCommand,
   buildSystemdShowCommand,
   buildTmuxListPanesCommand,
+  buildTmuxListSessionsCommand,
   classifySendResult,
   detectDrift,
   enableFleetUnits,
@@ -29,6 +30,7 @@ import {
   parseHeartbeat,
   parseSystemdShow,
   parseTmuxListPanes,
+  parseTmuxListSessions,
   registerFleetCommand,
   resolveFleetPaths,
   RUNTIME_ACCEPTABLE_COMMANDS,
@@ -1074,6 +1076,10 @@ describe('fleet ps — JSON output shape (FR-6)', () => {
           exitCode: 0,
         };
       }
+      if (fullArgs.includes('list-sessions')) {
+        // Only the roster agent session on the socket (no unmanaged sessions)
+        return { stdout: 'canary-pi\n', stderr: '', exitCode: 0 };
+      }
       return { stdout: '', stderr: '', exitCode: 0 };
     };
 
@@ -1117,11 +1123,15 @@ describe('fleet ps — JSON output shape (FR-6)', () => {
     expect(row.runtime).toBe('pi');
     expect(row.systemdActive).toBe('active');
     expect(row.systemdEnabled).toBe('disabled');
+
+    // managed/source fields for roster agents
+    expect(row.managed).toBe(true);
+    expect(row.source).toBe('roster');
   });
 });
 
 describe('fleet ps — command sequences issued', () => {
-  it('issues systemd show + tmux list-panes per agent', async () => {
+  it('issues systemd show + tmux list-panes per agent, then list-sessions for socket discovery', async () => {
     const home = await mkdtemp(join(tmpdir(), 'mosaic-fleet-'));
     const rosterPath = join(home, 'fleet', 'roster.yaml');
     await mkdir(join(home, 'fleet'), { recursive: true });
@@ -1135,6 +1145,10 @@ describe('fleet ps — command sequences issued', () => {
     const calls: string[][] = [];
     const runner: CommandRunner = async (command, args) => {
       calls.push([command, ...args]);
+      if ([command, ...args].join(' ').includes('list-sessions')) {
+        // Only the roster agent — no unmanaged sessions
+        return { stdout: 'coder0\n', stderr: '', exitCode: 0 };
+      }
       return {
         stdout: 'ActiveState=inactive\nSubState=dead\nUnitFileState=enabled\n',
         stderr: '',
@@ -1155,6 +1169,7 @@ describe('fleet ps — command sequences issued', () => {
       expect(calls).toEqual([
         buildSystemdShowCommand('coder0'),
         buildTmuxListPanesCommand('coder0', 'mosaic-factory'),
+        buildTmuxListSessionsCommand('mosaic-factory'),
       ]);
     } finally {
       console.log = origLog;
@@ -1163,6 +1178,258 @@ describe('fleet ps — command sequences issued', () => {
   });
 });
 
+describe('buildTmuxListSessionsCommand', () => {
+  it('builds exact list-sessions command with session_name format', () => {
+    expect(buildTmuxListSessionsCommand('mosaic-factory')).toEqual([
+      'tmux',
+      '-L',
+      'mosaic-factory',
+      'list-sessions',
+      '-F',
+      '#{session_name}',
+    ]);
+  });
+
+  it('uses DEFAULT_SOCKET_NAME when socket is omitted', () => {
+    const cmd = buildTmuxListSessionsCommand();
+    expect(cmd[2]).toBe('mosaic-factory');
+  });
+});
+
+describe('parseTmuxListSessions', () => {
+  it('splits newline-delimited session names', () => {
+    expect(parseTmuxListSessions('canary-pi\n_holder\nsome-adhoc\n')).toEqual([
+      'canary-pi',
+      '_holder',
+      'some-adhoc',
+    ]);
+  });
+
+  it('returns empty array for blank output', () => {
+    expect(parseTmuxListSessions('')).toEqual([]);
+    expect(parseTmuxListSessions('  \n  \n')).toEqual([]);
+  });
+
+  it('trims whitespace from each line', () => {
+    expect(parseTmuxListSessions('  canary-pi  \n  some-adhoc  \n')).toEqual([
+      'canary-pi',
+      'some-adhoc',
+    ]);
+  });
+});
+
+describe('fleet ps — unmanaged socket sessions', () => {
+  it('includes unmanaged session row flagged UNMANAGED and excludes _holder', async () => {
+    const home = await mkdtemp(join(tmpdir(), 'mosaic-fleet-'));
+    const rosterPath = join(home, 'fleet', 'roster.yaml');
+    await mkdir(join(home, 'fleet'), { recursive: true });
+    await writeFile(
+      rosterPath,
+      [
+        'version: 1',
+        'transport: tmux',
+        'agents:',
+        '  - name: canary-pi',
+        '    runtime: pi',
+        '    class: canary',
+      ].join('\n'),
+    );
+
+    const nowMs = Date.now();
+    const activityEpoch = Math.floor((nowMs - 10_000) / 1000);
+
+    const runner: CommandRunner = async (command, args) => {
+      const full = [command, ...args].join(' ');
+      if (full.includes('list-sessions')) {
+        // Socket has: canary-pi (roster), _holder (excluded), some-adhoc (unmanaged)
+        return { stdout: 'canary-pi\n_holder\nsome-adhoc\n', stderr: '', exitCode: 0 };
+      }
+      if (full.includes('list-panes')) {
+        return { stdout: `99999 bash 0 ${activityEpoch}\n`, stderr: '', exitCode: 0 };
+      }
+      if (full.includes('systemctl') && full.includes('show')) {
+        return {
+          stdout: 'ActiveState=inactive\nSubState=dead\nUnitFileState=unknown\n',
+          stderr: '',
+          exitCode: 0,
+        };
+      }
+      return { stdout: '', stderr: '', exitCode: 0 };
+    };
+
+    const lines: string[] = [];
+    const origLog = console.log;
+    console.log = (msg: string) => {
+      lines.push(msg);
+    };
+
+    const program = new Command();
+    program.exitOverride();
+    registerFleetCommand(program, { runner, mosaicHome: home });
+
+    try {
+      await program.parseAsync(['node', 'mosaic', 'fleet', 'ps', '--json']);
+    } finally {
+      console.log = origLog;
+      await rm(home, { recursive: true, force: true });
+    }
+
+    const json = JSON.parse(lines.join('')) as AgentPsRow[];
+    expect(Array.isArray(json)).toBe(true);
+
+    // Should have 2 rows: canary-pi (roster) + some-adhoc (unmanaged); _holder excluded
+    expect(json).toHaveLength(2);
+
+    // Roster agent comes first
+    const rosterRow = json[0]!;
+    expect(rosterRow.name).toBe('canary-pi');
+    expect(rosterRow.managed).toBe(true);
+    expect(rosterRow.source).toBe('roster');
+
+    // Unmanaged session comes second
+    const unmanagedRow = json[1]!;
+    expect(unmanagedRow.name).toBe('some-adhoc');
+    expect(unmanagedRow.managed).toBe(false);
+    expect(unmanagedRow.source).toBe('socket');
+    expect(unmanagedRow.runtime).toBe('unknown');
+
+    // _holder must not appear
+    expect(json.map((r) => r.name)).not.toContain('_holder');
+
+    // tenant_id and host must be present on unmanaged rows
+    expect(typeof unmanagedRow.tenant_id).toBe('string');
+    expect(unmanagedRow.tenant_id.length).toBeGreaterThan(0);
+    expect(typeof unmanagedRow.host).toBe('string');
+    expect(unmanagedRow.host.length).toBeGreaterThan(0);
+
+    // driftFlag must be false for unmanaged (no roster runtime to compare)
+    expect(unmanagedRow.driftFlag).toBe(false);
+  });
+
+  it('shows UNMANAGED flag in table output for unmanaged sessions', async () => {
+    const home = await mkdtemp(join(tmpdir(), 'mosaic-fleet-'));
+    const rosterPath = join(home, 'fleet', 'roster.yaml');
+    await mkdir(join(home, 'fleet'), { recursive: true });
+    await writeFile(
+      rosterPath,
+      [
+        'version: 1',
+        'transport: tmux',
+        'agents:',
+        '  - name: canary-pi',
+        '    runtime: pi',
+        '    class: canary',
+      ].join('\n'),
+    );
+
+    const runner: CommandRunner = async (command, args) => {
+      const full = [command, ...args].join(' ');
+      if (full.includes('list-sessions')) {
+        return { stdout: 'canary-pi\nsome-adhoc\n', stderr: '', exitCode: 0 };
+      }
+      if (full.includes('list-panes')) {
+        return { stdout: '0 bash 1 0\n', stderr: '', exitCode: 0 };
+      }
+      if (full.includes('systemctl') && full.includes('show')) {
+        return {
+          stdout: 'ActiveState=inactive\nSubState=dead\nUnitFileState=unknown\n',
+          stderr: '',
+          exitCode: 0,
+        };
+      }
+      return { stdout: '', stderr: '', exitCode: 0 };
+    };
+
+    const lines: string[] = [];
+    const origLog = console.log;
+    console.log = (msg: string) => {
+      lines.push(msg);
+    };
+
+    const program = new Command();
+    program.exitOverride();
+    registerFleetCommand(program, { runner, mosaicHome: home });
+
+    try {
+      await program.parseAsync(['node', 'mosaic', 'fleet', 'ps']);
+    } finally {
+      console.log = origLog;
+      await rm(home, { recursive: true, force: true });
+    }
+
+    const tableOutput = lines.join('\n');
+    // some-adhoc row must appear with UNMANAGED flag
+    expect(tableOutput).toMatch(/some-adhoc/);
+    expect(tableOutput).toMatch(/UNMANAGED/);
+    // canary-pi roster row must not have UNMANAGED
+    const rosterLine = lines.find((l) => l.includes('canary-pi'));
+    expect(rosterLine).toBeDefined();
+    expect(rosterLine).not.toMatch(/UNMANAGED/);
+  });
+
+  it('gracefully shows only roster rows when list-sessions fails (socket missing)', async () => {
+    const home = await mkdtemp(join(tmpdir(), 'mosaic-fleet-'));
+    const rosterPath = join(home, 'fleet', 'roster.yaml');
+    await mkdir(join(home, 'fleet'), { recursive: true });
+    await writeFile(
+      rosterPath,
+      [
+        'version: 1',
+        'transport: tmux',
+        'agents:',
+        '  - name: canary-pi',
+        '    runtime: pi',
+        '    class: canary',
+      ].join('\n'),
+    );
+
+    const runner: CommandRunner = async (command, args) => {
+      const full = [command, ...args].join(' ');
+      if (full.includes('list-sessions')) {
+        // Simulate socket missing
+        return { stdout: '', stderr: 'no server running on /tmp/...', exitCode: 1 };
+      }
+      if (full.includes('list-panes')) {
+        return { stdout: '12345 pi 0 0\n', stderr: '', exitCode: 0 };
+      }
+      if (full.includes('systemctl') && full.includes('show')) {
+        return {
+          stdout: 'ActiveState=inactive\nSubState=dead\nUnitFileState=enabled\n',
+          stderr: '',
+          exitCode: 0,
+        };
+      }
+      return { stdout: '', stderr: '', exitCode: 0 };
+    };
+
+    const lines: string[] = [];
+    const origLog = console.log;
+    console.log = (msg: string) => {
+      lines.push(msg);
+    };
+
+    const program = new Command();
+    program.exitOverride();
+    registerFleetCommand(program, { runner, mosaicHome: home });
+
+    try {
+      // Must not throw
+      await expect(
+        program.parseAsync(['node', 'mosaic', 'fleet', 'ps', '--json']),
+      ).resolves.toBeDefined();
+    } finally {
+      console.log = origLog;
+      await rm(home, { recursive: true, force: true });
+    }
+
+    const json = JSON.parse(lines.join('')) as AgentPsRow[];
+    // Only roster agent visible; no crash
+    expect(json).toHaveLength(1);
+    expect(json[0]!.name).toBe('canary-pi');
+    expect(json[0]!.managed).toBe(true);
+  });
+});
+
 describe('agent watch', () => {
   it('builds exact grouped-viewer creation command', () => {
     expect(

packages/mosaic/src/commands/fleet.ts

@@ -389,6 +389,10 @@ export interface AgentPsRow {
   driftFlag: boolean;
   /** active but UnitFileState=disabled */
   bootEnableWarning: boolean;
+  /** true = came from roster; false = found on socket but not in roster */
+  managed: boolean;
+  /** "roster" = defined in roster.yaml; "socket" = discovered via tmux list-sessions */
+  source: 'roster' | 'socket';
 }
 
 /**
@@ -431,6 +435,26 @@ export function buildTmuxListPanesCommand(
   ];
 }
 
+/**
+ * Returns the tmux list-sessions command to enumerate all sessions on a socket.
+ * Format: `tmux -L <socket> list-sessions -F '#{session_name}'`
+ * Used to discover ad-hoc sessions that are not in the roster.
+ */
+export function buildTmuxListSessionsCommand(socketName = DEFAULT_SOCKET_NAME): string[] {
+  return ['tmux', '-L', socketName, 'list-sessions', '-F', '#{session_name}'];
+}
+
+/**
+ * Parse the output of `tmux list-sessions -F '#{session_name}'` into an array of session names.
+ * Returns an empty array on empty/blank output.
+ */
+export function parseTmuxListSessions(output: string): string[] {
+  return output
+    .split('\n')
+    .map((line) => line.trim())
+    .filter((line) => line.length > 0);
+}
+
 /**
  * Returns the heartbeat file path for an agent.
  */
@@ -897,7 +921,9 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
 
   cmd
     .command('ps')
-    .description('Show real-time status for all roster agents (systemd + tmux + heartbeat)')
+    .description(
+      'Show real-time status for all roster agents and unmanaged socket sessions (systemd + tmux + heartbeat)',
+    )
     .option('--json', 'Print JSON array')
     .action(async (opts: { json?: boolean }) => {
       const commandOpts = cmd.opts<{ mosaicHome: string; roster?: string }>();
@@ -908,6 +934,9 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
 
       const rows: AgentPsRow[] = [];
 
+      // Build the set of roster agent names for quick lookup when filtering socket sessions.
+      const rosterAgentNames = new Set(roster.agents.map((a) => a.name));
+
       for (const agent of roster.agents) {
         // systemd show
         const showResult = await runner(...splitCommand(buildSystemdShowCommand(agent.name)));
@@ -948,9 +977,75 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
           heartbeat: hb,
           driftFlag,
           bootEnableWarning,
+          managed: true,
+          source: 'roster',
         });
       }
 
+      // Enumerate all live sessions on the socket to surface unmanaged (ad-hoc) sessions.
+      // If list-sessions fails (socket not up), silently skip — show roster rows only.
+      try {
+        const listSessionsResult = await runner(
+          ...splitCommand(buildTmuxListSessionsCommand(roster.tmux.socketName)),
+        );
+        if (listSessionsResult.exitCode === 0) {
+          const socketSessions = parseTmuxListSessions(listSessionsResult.stdout);
+          const holderSession = roster.tmux.holderSession;
+
+          for (const sessionName of socketSessions) {
+            // Skip roster agents (already in rows) and the holder session (infrastructure).
+            if (rosterAgentNames.has(sessionName) || sessionName === holderSession) {
+              continue;
+            }
+
+            // tmux list-panes for pane info
+            const panesResult = await runner(
+              ...splitCommand(buildTmuxListPanesCommand(sessionName, roster.tmux.socketName)),
+            );
+            const paneInfo = parseTmuxListPanes(panesResult.stdout, nowMs);
+
+            // heartbeat — try reading the .hb file using the same path convention
+            const hbFile = heartbeatPath(sessionName, activePaths.mosaicHome);
+            let hbContent: string | null = null;
+            try {
+              hbContent = await readFile(hbFile, 'utf8');
+            } catch {
+              hbContent = null;
+            }
+            const hb = parseHeartbeat(hbContent, nowMs);
+
+            // systemd — check if mosaic-agent@<name>.service exists (usually inactive for ad-hoc)
+            const showResult = await runner(...splitCommand(buildSystemdShowCommand(sessionName)));
+            const sysInfo = parseSystemdShow(showResult.stdout);
+
+            const bootEnableWarning =
+              sysInfo.ActiveState === 'active' && sysInfo.UnitFileState === 'disabled';
+
+            rows.push({
+              name: sessionName,
+              tenant_id,
+              host,
+              // runtime unknown — not in roster
+              runtime: 'unknown',
+              systemdActive: sysInfo.ActiveState,
+              systemdEnabled: sysInfo.UnitFileState,
+              paneAlive: !paneInfo.dead,
+              panePid: paneInfo.pid,
+              paneCommand: paneInfo.command,
+              idleSeconds: paneInfo.idleSeconds,
+              heartbeat: hb,
+              // No roster runtime to compare — drift is not meaningful for unmanaged sessions
+              driftFlag: false,
+              bootEnableWarning,
+              managed: false,
+              source: 'socket',
+            });
+          }
+        }
+      } catch {
+        // list-sessions failed (socket missing or permission error) — show roster rows only
+      }
+
       if (opts.json) {
         console.log(JSON.stringify(rows, null, 2));
         return;
@@ -982,6 +1077,7 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
             ? `${Math.round(row.heartbeat.ageMs / 1000)}s/${row.heartbeat.health}`
             : `unknown`;
         const flags: string[] = [];
+        if (!row.managed) flags.push('UNMANAGED');
         if (row.driftFlag) flags.push('DRIFT');
         if (row.bootEnableWarning) flags.push('BOOT-ENABLE');