chore(format): prettier docs/fleet/PRD-fleet-suite.md (pre-existing main violation)

Pre-existing repo-wide format:check failure on origin/main (markdown table
alignment only — no content change). Picked up to unblock the pre-push gate;
flagged to the Lead. Not part of the P5 composer change.

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

docs/TASKS.md

@@ -45,3 +45,9 @@ Active workstream is **W1 — Federation v1**. Workers should:
 - Status: PR open, awaiting maintainer merge ratification (fleet-governing change).
 - Cut always-injected contract AGENTS+TOOLS+RUNTIME 8,827→4,122 tok (−53%); all 12 hard gates intact.
 - Validation: deterministic gate-checklist PASS; headless A/B thin 7/9 vs monolith 5/9. Detail: scratchpads/contract-thin-core.md.
+
+## P5 — Overlay composer + cross-harness (#604) — feat/p5-overlay-composer
+
+- Status: in progress. R7 (compose-contract) + R8 (cross-harness) + R9 (composer test).
+- `composeContract({harness, mosaicHome})` pure fn + `.local` overlay deltas-by-value; `mosaic compose-contract <harness>` command; AGENTS bare-launch nudge; composer spec (per-tier anchor + Tier-3 byte-equality). Detail: scratchpads/p5-overlay-composer.md.
+- Defer to P6: CONTRIBUTING.md + compliance matrix; line-count CI ceiling; aiguide; alpha tag.

docs/fleet/PRD-fleet-suite.md

@@ -20,8 +20,9 @@ functional, we use the fleet itself to continue the work.
 ## Requirements
 
 ### A. Configure-without-AI CLI
+
 | ID  | Requirement                                                                                                   |
-|---|---|
+| --- | ------------------------------------------------------------------------------------------------------------- |
 | R1  | `mosaic fleet` command set is functional end-to-end (init/install/start/stop/status/ps/verify + agent verbs). |
 | R2  | `mosaic fleet init` is an interactive, **AI-free** CLI wizard.                                                |
 | R3  | Init asks the **configuration type**: `general`, `coding`, `research`, `hybrid`, … (extensible).              |
@@ -32,24 +33,27 @@ functional, we use the fleet itself to continue the work.
 | R17 | Fleet controls are **simple and intuitive**.                                                                  |
 
 ### B. Comms & orchestrator chat-ops
+
 | ID  | Requirement                                                                                                                       |
-|---|---|
+| --- | --------------------------------------------------------------------------------------------------------------------------------- |
 | R6  | Init can wire the orchestrator to a chat connector — **Telegram / Discord / Matrix / Slack** — for command + comms.               |
 | R7  | Designed with the end-goal of **Matrix comms on a locally-controlled server**.                                                    |
 | R16 | Fleet supports **tmux AND Matrix** comms, **user-configurable** at init or any time. Not all users want Matrix.                   |
 | R19 | **"Mos" orchestrator on Discord** (`chan 1517622518662434996` / `srv 1112631390438166618`) on `w-jarvis` — the first live target. |
 
 ### C. Runtime, health, lifecycle
+
 | ID  | Requirement                                                                        |
-|---|---|
+| --- | ---------------------------------------------------------------------------------- |
 | R9  | Fleet is **mutable by the orchestrator agent** — add/remove agents per need.       |
 | R13 | Fleet **gracefully handles Pi + Claude harness updates** — keep harnesses current. |
 | R14 | The **Pi harness is customized** for proper tool usage, etc.                       |
 | R15 | **Agent heartbeat** properly configured for **Claude AND GPT/Pi** agents.          |
 
 ### D. Surfaces, testing, docs
+
 | ID  | Requirement                                                                         |
-|---|---|
+| --- | ----------------------------------------------------------------------------------- |
 | R18 | Fleet built so the **webUI can view / monitor / terminate / butt-in** on a session. |
 | R11 | Installed and **tested on both `w-jarvis` and `dragon-lin`**.                       |
 | R12 | **Documentation**: how to install, configure, and use the fleet.                    |
@@ -66,7 +70,7 @@ functional, we use the fleet itself to continue the work.
 ## Phases (incremental, each shippable)
 
 | Phase                             | Deliverable                                                                                                                         | Notes                                 |
-|---|---|---|
+| --------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------- |
 | **F1 Presets + init wizard**      | preset rosters (general/coding/research/hybrid) + always-orchestrator + AI-free `fleet init` selecting a preset; re-init idempotent | R1–R5, R8, R10, R17                   |
 | **F2 Connector + Mos-on-Discord** | orchestrator chat-connector config (Discord first) + **Mos live on Discord `1517…`/`1112…`** on w-jarvis                            | R6, R19, partial R16                  |
 | **F3 Heartbeat + harness**        | HB confirmed for claude + pi/gpt; **custom Pi harness** (tool usage, native HB, model self-report); graceful harness updates        | R13, R14, R15                         |

docs/scratchpads/p5-overlay-composer.md

@@ -0,0 +1,43 @@
+# P5 — Overlay composer + cross-harness (compose-contract)
+
+- **Issue:** #604 · **Branch:** `feat/p5-overlay-composer` · **Lineage:** #542 → constitution alpha
+- **Requirements:** R7 (compose-contract) + R8 (cross-harness) + R9 (composer test)
+- **Design of record:** `docs/design/framework-constitution/{DESIGN.md §3.2, PRD.md §4}` (on `feat/framework-constitution-alpha`)
+
+## Locked design (sequential-thinking)
+
+Current `launch.ts` assembly (`buildComposedPrompt`) injects by value: mission + PRD + hard-gate +
+CONSTITUTION + AGENTS + USER + TOOLS + runtime. It does **not** inject SOUL or STANDARDS (those are
+read-on-demand per the gutted AGENTS dispatcher), and has no `.local` overlay support.
+
+**Decision (ASSUMPTION — recorded for the PR):** overlays are injected as **deltas by value** under
+labeled sections; base files keep their existing residency.
+
+- `USER.local.md` → appended directly under the `# User Profile` block (USER is injected).
+- `SOUL.local.md` + `STANDARDS.local.md` → a trailing `# Operator Overlays` section (their bases are
+  load-on-demand, so only the small delta is injected — not the full base prose).
+- **Why:** honors DESIGN §3.2 ("model gets one pre-merged blob, no read-merge ritual") while preserving
+  the P3 byte-budget tiering (don't re-inject large SOUL/STANDARDS prose). Precedence order kept: base
+  layers first, operator overlays at recency.
+- Base-only is automatic when a `.local` file is absent (`readOptional`).
+
+## Plan
+
+| #   | Task                                                                                                   | File                                    |
+| --- | ------------------------------------------------------------------------------------------------------ | --------------------------------------- |
+| 1   | Extract `composeContract({harness, mosaicHome})` pure fn; `buildComposedPrompt` delegates              | `src/commands/launch.ts`                |
+| 2   | Overlay logic (USER.local under profile; SOUL/STANDARDS.local in `# Operator Overlays`)                | `src/commands/launch.ts`                |
+| 3   | `mosaic compose-contract <harness>` command → prints blob to stdout                                    | `src/commands/launch.ts`                |
+| 4   | Bare-launch overlay nudge in self-load fallback                                                        | `framework/defaults/AGENTS.md`          |
+| 5   | `compose-contract.spec.ts`: per-tier anchor, Tier-3 byte-equality, overlay present/absent, per-harness | `src/commands/compose-contract.spec.ts` |
+
+## Deferred to P6
+
+CONTRIBUTING.md + harness×gate compliance matrix; resident line-count CI ceiling; `aiguide` reconcile;
+alpha tag `mosaic-vX.Y.Z-alpha`.
+
+## Status
+
+- [x] Phase scaffold (branch, issue #604, scratchpad, TASKS)
+- [ ] Implementation (tasks 1–5)
+- [ ] prettier + vitest green; PR via wrapper → Lead (rides 0.0.39; 0.0.38 mid-cut)

packages/mosaic/framework/defaults/AGENTS.md

@@ -9,7 +9,10 @@ overwritten on upgrade. (Layer model: `constitution/LAYER-MODEL.md`.)
 1. Your context already includes `CONSTITUTION.md` + `USER.md` + the TOOLS index + the runtime
    contract (injected by `mosaic` launch) — do not re-read those. **If you were launched bare**
    (a harness started without `mosaic`, so the law is NOT in your context), read
-   `~/.config/mosaic/CONSTITUTION.md` now, before your first action.
+   `~/.config/mosaic/CONSTITUTION.md` now, before your first action. A bare launch also gets
+   **base contracts only** — operator overlays (`*.local.md`) are composed by the launcher, so if
+   `SOUL.local.md`/`USER.local.md`/`STANDARDS.local.md` exist, relaunch via `mosaic <harness>` (or run
+   `mosaic doctor`) to pick them up.
 2. Read `SOUL.md` (agent persona — small, once).
 3. Read project-local `AGENTS.md` / `CLAUDE.md` if present (these may only make behavior stricter).
 4. Read guides ONLY as triggered by the table below — pull role-relevant depth on demand, not up front.

packages/mosaic/framework/runtime/pi/mosaic-extension.ts

@@ -9,8 +9,16 @@
  *   4. Memory routing — remind agent to use ~/.config/mosaic/memory/
  */
 
-import type { ExtensionAPI } from '@mariozechner/pi-coding-agent';
-import { existsSync, readFileSync, writeFileSync, unlinkSync, mkdirSync } from 'node:fs';
+import type { ExtensionAPI, ExtensionContext } from '@earendil-works/pi-coding-agent';
+import { Type } from 'typebox';
+import {
+  existsSync,
+  readFileSync,
+  writeFileSync,
+  unlinkSync,
+  mkdirSync,
+  renameSync,
+} from 'node:fs';
 import { join, basename } from 'node:path';
 import { homedir } from 'node:os';
 import { execSync, spawnSync } from 'node:child_process';
@@ -25,6 +33,57 @@ const MOSAIC_HOME = process.env['MOSAIC_HOME'] ?? join(homedir(), '.config', 'mo
 // Helpers
 // ---------------------------------------------------------------------------
 
+// ---------------------------------------------------------------------------
+// Native heartbeat (fleet R14/R15)
+// ---------------------------------------------------------------------------
+// When this agent runs under the Mosaic fleet (MOSAIC_AGENT_NAME set), the
+// extension writes its OWN heartbeat in the same .hb contract `fleet ps` reads
+// (ts/pid/status[/model]) and touches a `.hb.native` precedence marker so the
+// shell sidecar defers. Native HB knows the real turn state (busy/ok), so it is
+// more accurate than the pane-PID-only sidecar fallback.
+const HB_AGENT_NAME = process.env['MOSAIC_AGENT_NAME'] ?? '';
+const HB_RUN_DIR = process.env['MOSAIC_HEARTBEAT_RUN_DIR'] ?? join(MOSAIC_HOME, 'fleet', 'run');
+const HB_INTERVAL_MS = (() => {
+  const s = Number.parseInt(process.env['MOSAIC_HEARTBEAT_INTERVAL'] ?? '', 10);
+  return Number.isFinite(s) && s > 0 ? s * 1000 : 15_000;
+})();
+
+function nativeHbEnabled(): boolean {
+  return HB_AGENT_NAME.length > 0;
+}
+
+function readModelId(ctx: ExtensionContext): string | null {
+  const m = ctx.model as unknown as { id?: string; name?: string } | undefined;
+  return m?.id ?? m?.name ?? null;
+}
+
+function writeNativeHeartbeat(status: 'ok' | 'busy', model: string | null): void {
+  if (!nativeHbEnabled()) return;
+  try {
+    mkdirSync(HB_RUN_DIR, { recursive: true });
+    const hb = join(HB_RUN_DIR, `${HB_AGENT_NAME}.hb`);
+    const lines = [`ts=${nowIso()}`, `pid=${process.pid}`, `status=${status}`];
+    if (model) lines.push(`model=${model}`);
+    const tmp = `${hb}.tmp.${process.pid}`;
+    writeFileSync(tmp, lines.join('\n') + '\n');
+    renameSync(tmp, hb); // atomic replace — fleet ps never reads a partial file
+    // Precedence marker: tells the shell sidecar that native HB is authoritative.
+    writeFileSync(join(HB_RUN_DIR, `${HB_AGENT_NAME}.hb.native`), nowIso() + '\n');
+  } catch {
+    // Best-effort: never let heartbeat I/O disrupt the Pi session.
+  }
+}
+
+function clearNativeMarker(): void {
+  if (!nativeHbEnabled()) return;
+  try {
+    const m = join(HB_RUN_DIR, `${HB_AGENT_NAME}.hb.native`);
+    if (existsSync(m)) unlinkSync(m); // native stopping — let the sidecar take over
+  } catch {
+    /* ignore */
+  }
+}
+
 function safeRead(filePath: string): string | null {
   try {
     return readFileSync(filePath, 'utf-8');
@@ -187,6 +246,9 @@ function buildMissionSummary(cwd: string, mission: ActiveMission): string {
 
 export default function register(pi: ExtensionAPI) {
   let sessionCwd = process.cwd();
+  let hbStatus: 'ok' | 'busy' = 'ok';
+  let hbModel: string | null = null;
+  let hbTimer: ReturnType<typeof setInterval> | null = null;
 
   // ── Session Start ─────────────────────────────────────────────────────
   pi.on('session_start', async (_event, ctx) => {
@@ -207,10 +269,39 @@ export default function register(pi: ExtensionAPI) {
     } else {
       ctx.ui.notify('Mosaic framework loaded', 'info');
     }
+
+    // Native heartbeat: write immediately, then on an interval. Idle = 'ok';
+    // turn_start/turn_end flip the status so `fleet ps` reflects real activity.
+    if (nativeHbEnabled()) {
+      hbModel = readModelId(ctx);
+      writeNativeHeartbeat('ok', hbModel);
+      hbTimer = setInterval(() => writeNativeHeartbeat(hbStatus, hbModel), HB_INTERVAL_MS);
+      if (typeof hbTimer.unref === 'function') hbTimer.unref();
+    }
   });
 
-  // ── Session End ───────────────────────────────────────────────────────
-  pi.on('session_end', async (_event, _ctx) => {
+  // ── Turn lifecycle → accurate busy/ok heartbeat ───────────────────────
+  pi.on('turn_start', async (_event, ctx) => {
+    hbStatus = 'busy';
+    hbModel = readModelId(ctx) ?? hbModel;
+    writeNativeHeartbeat('busy', hbModel);
+  });
+  pi.on('turn_end', async (_event, ctx) => {
+    hbStatus = 'ok';
+    hbModel = readModelId(ctx) ?? hbModel;
+    writeNativeHeartbeat('ok', hbModel);
+  });
+
+  // ── Session Shutdown ──────────────────────────────────────────────────
+  // (The pi API event is 'session_shutdown'; the prior 'session_end' handler
+  // never fired — fixed here so repo hooks + lock cleanup actually run.)
+  pi.on('session_shutdown', async (_event, _ctx) => {
+    if (hbTimer) {
+      clearInterval(hbTimer);
+      hbTimer = null;
+    }
+    clearNativeMarker();
+
     // Run repo session-end hook
     runRepoHook(sessionCwd, 'session-end');
 
@@ -252,4 +343,32 @@ export default function register(pi: ExtensionAPI) {
       }
     },
   });
+
+  // ── Register mosaic_mission_status tool (model-callable) ──────────────
+  // R14 "proper tool usage": give the agent a first-class tool to load its
+  // active Mosaic mission, milestone progress, task counts, and latest
+  // scratchpad — so it self-orients on in-flight work before planning,
+  // instead of shelling out or guessing. Mirrors the /mosaic-status command
+  // but returns the summary as tool output the LLM can read.
+  pi.registerTool({
+    name: 'mosaic_mission_status',
+    label: 'Mosaic Mission Status',
+    description:
+      'Return the active Mosaic mission, milestone progress, task counts, and latest scratchpad for the current project. Returns a note when no mission is active.',
+    promptSnippet: 'Read the active Mosaic mission + task state for the current project',
+    promptGuidelines: [
+      'Use mosaic_mission_status at the start of a session or task to load the active mission, milestone progress, and open tasks before planning work.',
+    ],
+    parameters: Type.Object({}),
+    async execute(_toolCallId, _params, _signal, _onUpdate, _ctx) {
+      const mission = detectMission(sessionCwd);
+      const text = mission
+        ? buildMissionSummary(sessionCwd, mission)
+        : 'No active Mosaic mission in this project.';
+      return {
+        content: [{ type: 'text', text }],
+        details: mission ? { ...mission } : { active: false },
+      };
+    },
+  });
 }

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

@@ -90,11 +90,18 @@ MOSAIC_RUNTIME_BIN_PREFIX=$(_build_runtime_bin_prefix)
 #
 # We build the snippet as a double-quoted here-string embedded in a printf call
 # to avoid nested quoting problems.
+#
+# MOSAIC_AGENT_NAME must also be exported INTO the pane: panes inherit the tmux
+# server environment (not this script's, and not the systemd unit's), so the
+# name would otherwise be empty in-pane and the runtime's native heartbeat
+# (which gates on MOSAIC_AGENT_NAME) would never fire. %q-quote it so it is a
+# safe single bash token regardless of the name's characters.
+AGENT_NAME_Q=$(printf '%q' "$AGENT_NAME")
 
 if [ -n "$MOSAIC_RUNTIME_BIN_PREFIX" ]; then
-  PANE_SHELL_SNIPPET="export PATH=\"${MOSAIC_RUNTIME_BIN_PREFIX}:\${PATH}\"; exec ${MOSAIC_AGENT_COMMAND}"
+  PANE_SHELL_SNIPPET="export MOSAIC_AGENT_NAME=${AGENT_NAME_Q}; export PATH=\"${MOSAIC_RUNTIME_BIN_PREFIX}:\${PATH}\"; exec ${MOSAIC_AGENT_COMMAND}"
 else
-  PANE_SHELL_SNIPPET="exec ${MOSAIC_AGENT_COMMAND}"
+  PANE_SHELL_SNIPPET="export MOSAIC_AGENT_NAME=${AGENT_NAME_Q}; exec ${MOSAIC_AGENT_COMMAND}"
 fi
 
 mkdir -p "$MOSAIC_AGENT_WORKDIR"
@@ -129,7 +136,7 @@ _start_heartbeat_sidecar() {
   # references to any variables from this script's environment.
   local sidecar_script
   sidecar_script=$(printf \
-    'hb=%s; pid=%s; iv=%s; mkdir -p "$(dirname "$hb")"; while kill -0 "$pid" 2>/dev/null; do tmp="$hb.tmp.$$"; printf "ts=%%s\npid=%%s\nstatus=ok\n" "$(date +%%Y-%%m-%%dT%%H:%%M:%%S%%z)" "$pid" > "$tmp" && mv "$tmp" "$hb"; sleep "$iv"; done' \
+    'hb=%q; pid=%q; iv=%q; mkdir -p "$(dirname "$hb")"; while kill -0 "$pid" 2>/dev/null; do nat="$hb.native"; if [ -f "$nat" ] && [ "$(( $(date +%%s) - $(stat -c %%Y "$nat" 2>/dev/null || echo 0) ))" -lt "$(( iv * 2 ))" ]; then sleep "$iv"; continue; fi; tmp="$hb.tmp.$$"; 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.

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

@@ -32,8 +32,15 @@ MOSAIC_AGENT_COMMAND='bash --noprofile --norc -i' \
   "$START" "$AGENT"
 
 tmux -L "$SOCKET" has-session -t "=$AGENT:0.0" || fail "agent session was not created"
+# Retry: pane_current_path briefly reflects the tmux server's cwd until the pane
+# process establishes its own cwd (the -c start dir). Poll until it settles.
+actual_dir=""
+for _ in $(seq 1 30); do
   actual_dir=$(tmux -L "$SOCKET" display-message -p -t "=$AGENT:0.0" '#{pane_current_path}')
-[ "$actual_dir" = "$WORKDIR" ] || fail "agent workdir mismatch: $actual_dir"
+  [ "$actual_dir" = "$WORKDIR" ] && break
+  sleep 0.1
+done
+[ "$actual_dir" = "$WORKDIR" ] || fail "agent workdir mismatch: $actual_dir (expected $WORKDIR)"
 
 # ── Test 2: idempotency (duplicate start prints 'already running') ─────────────
 MOSAIC_TMUX_SOCKET="$SOCKET" \

packages/mosaic/src/commands/compose-contract.spec.ts

@@ -0,0 +1,118 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { mkdtempSync, mkdirSync, writeFileSync, rmSync, readFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { composeContract } from './launch.js';
+
+/**
+ * Composer unit test (R7/R8/R9): asserts the launcher-composed runtime contract
+ *
+ *   - includes the per-tier anchors (CONSTITUTION / AGENTS / USER / runtime),
+ *   - keeps the CONSTITUTION block byte-equal to the on-disk file (Tier-3
+ *     byte-equality — the bare-launch fallback read must match what is injected),
+ *   - merges `*.local.md` operator overlays as deltas-by-value, and omits them
+ *     entirely when absent (base-only),
+ *   - selects the correct per-harness RUNTIME.md.
+ *
+ * `composeContract` takes `mosaicHome` as a param, so each test runs against an
+ * isolated fixture home. We also chdir to an empty temp cwd so the cwd-relative
+ * mission/PRD blocks contribute nothing (deterministic output).
+ */
+
+const CONSTITUTION = '# CONSTITUTION\n\nGATE-1: the non-negotiable law.\n';
+const AGENTS = '# Mosaic Agent Dispatcher\n\nLoad order + guide router.\n';
+const USER = '# operator\n\nName: Test Operator\n';
+const TOOLS = '# tools index\n';
+
+function makeHome(): { home: string; root: string } {
+  const root = mkdtempSync(join(tmpdir(), 'mosaic-compose-'));
+  const home = join(root, 'mosaic-home');
+  for (const h of ['claude', 'codex', 'opencode', 'pi']) {
+    mkdirSync(join(home, 'runtime', h), { recursive: true });
+    writeFileSync(join(home, 'runtime', h, 'RUNTIME.md'), `# ${h} runtime contract\n`);
+  }
+  writeFileSync(join(home, 'CONSTITUTION.md'), CONSTITUTION);
+  writeFileSync(join(home, 'AGENTS.md'), AGENTS);
+  writeFileSync(join(home, 'USER.md'), USER);
+  writeFileSync(join(home, 'TOOLS.md'), TOOLS);
+  return { home, root };
+}
+
+describe('composeContract — overlay composer', () => {
+  let fixture: ReturnType<typeof makeHome>;
+  let prevCwd: string;
+  let cwdDir: string;
+
+  beforeEach(() => {
+    fixture = makeHome();
+    prevCwd = process.cwd();
+    cwdDir = mkdtempSync(join(tmpdir(), 'mosaic-cwd-'));
+    process.chdir(cwdDir); // neutralize cwd-relative mission/PRD blocks
+  });
+
+  afterEach(() => {
+    process.chdir(prevCwd);
+    rmSync(fixture.root, { recursive: true, force: true });
+    rmSync(cwdDir, { recursive: true, force: true });
+  });
+
+  it('includes the per-tier anchors and the selected harness runtime', () => {
+    const out = composeContract('claude', fixture.home);
+    expect(out).toContain('GATE-1: the non-negotiable law.'); // L0
+    expect(out).toContain('Mosaic Agent Dispatcher'); // AGENTS
+    expect(out).toContain('# User Profile'); // USER header
+    expect(out).toContain('Name: Test Operator'); // USER body
+    expect(out).toContain('# Runtime-Specific Contract');
+    expect(out).toContain('# claude runtime contract');
+  });
+
+  it('keeps the CONSTITUTION block byte-equal to the on-disk file (Tier-3)', () => {
+    const out = composeContract('pi', fixture.home);
+    const onDisk = readFileSync(join(fixture.home, 'CONSTITUTION.md'), 'utf-8');
+    // The injected L0 must be a byte-equal substring of the composed blob, so a
+    // bare-launch fallback read of CONSTITUTION.md matches what was injected.
+    expect(out.includes(onDisk)).toBe(true);
+  });
+
+  it('is base-only when no *.local overlays exist', () => {
+    const out = composeContract('claude', fixture.home);
+    expect(out).not.toContain('# Operator Overlays');
+    expect(out).not.toContain('Operator Overlay (USER.local.md)');
+    expect(out).not.toContain('Persona Overlay');
+    expect(out).not.toContain('Standards Overlay');
+  });
+
+  it('merges USER.local.md directly under the operator profile', () => {
+    writeFileSync(join(fixture.home, 'USER.local.md'), 'Prefer terse status updates.\n');
+    const out = composeContract('claude', fixture.home);
+    expect(out).toContain('## Operator Overlay (USER.local.md)');
+    expect(out).toContain('Prefer terse status updates.');
+    // Overlay appears AFTER its base profile.
+    expect(out.indexOf('# User Profile')).toBeLessThan(
+      out.indexOf('## Operator Overlay (USER.local.md)'),
+    );
+  });
+
+  it('merges SOUL.local.md + STANDARDS.local.md as deltas in the Operator Overlays block', () => {
+    writeFileSync(join(fixture.home, 'SOUL.local.md'), 'Tone: dry and direct.\n');
+    writeFileSync(join(fixture.home, 'STANDARDS.local.md'), 'Require 90% coverage on auth code.\n');
+    const out = composeContract('claude', fixture.home);
+    expect(out).toContain('# Operator Overlays');
+    expect(out).toContain('## Persona Overlay (SOUL.local.md)');
+    expect(out).toContain('Tone: dry and direct.');
+    expect(out).toContain('## Standards Overlay (STANDARDS.local.md)');
+    expect(out).toContain('Require 90% coverage on auth code.');
+  });
+
+  it('ignores whitespace-only *.local overlays (no empty overlay section)', () => {
+    writeFileSync(join(fixture.home, 'SOUL.local.md'), '   \n\n');
+    const out = composeContract('claude', fixture.home);
+    expect(out).not.toContain('# Operator Overlays');
+  });
+
+  it('selects a different RUNTIME.md per harness', () => {
+    expect(composeContract('codex', fixture.home)).toContain('# codex runtime contract');
+    expect(composeContract('pi', fixture.home)).toContain('# pi runtime contract');
+    expect(composeContract('codex', fixture.home)).not.toContain('# pi runtime contract');
+  });
+});

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', () => {
@@ -2892,3 +2903,33 @@ describe('fleet init wizard', () => {
     expect(content).toContain('name: coder0');
   });
 });
+
+describe('fleet ps — heartbeat path resolution', () => {
+  const savedRunDir = process.env.MOSAIC_HEARTBEAT_RUN_DIR;
+  const savedHome = process.env.MOSAIC_HOME;
+  afterEach(() => {
+    if (savedRunDir === undefined) delete process.env.MOSAIC_HEARTBEAT_RUN_DIR;
+    else process.env.MOSAIC_HEARTBEAT_RUN_DIR = savedRunDir;
+    if (savedHome === undefined) delete process.env.MOSAIC_HOME;
+    else process.env.MOSAIC_HOME = savedHome;
+  });
+
+  it('honors MOSAIC_HEARTBEAT_RUN_DIR (matches the writer sidecar override)', () => {
+    process.env.MOSAIC_HEARTBEAT_RUN_DIR = '/run/hb';
+    expect(heartbeatPath('agent-x', '/any/home')).toBe(join('/run/hb', 'agent-x.hb'));
+  });
+
+  it('honors MOSAIC_HOME when no explicit mosaicHome is given', () => {
+    delete process.env.MOSAIC_HEARTBEAT_RUN_DIR;
+    process.env.MOSAIC_HOME = '/custom/mhome';
+    expect(heartbeatPath('agent-y')).toBe(join('/custom/mhome', 'fleet', 'run', 'agent-y.hb'));
+  });
+
+  it('falls back to <mosaicHome>/fleet/run by default', () => {
+    delete process.env.MOSAIC_HEARTBEAT_RUN_DIR;
+    delete process.env.MOSAIC_HOME;
+    expect(heartbeatPath('agent-z', '/home/u/.config/mosaic')).toBe(
+      join('/home/u/.config/mosaic', 'fleet', 'run', 'agent-z.hb'),
+    );
+  });
+});

packages/mosaic/src/commands/fleet.ts

@@ -152,13 +152,16 @@ export function resolveFleetPaths(mosaicHome = defaultMosaicHome()): FleetPaths
 }
 
 function defaultMosaicHome(): string {
-  return join(homedir(), '.config', 'mosaic');
+  // Honor MOSAIC_HOME so the reader matches the writer sidecar (and the launcher),
+  // even when MOSAIC_HOME is set in the shell without an explicit --mosaic-home flag.
+  return process.env.MOSAIC_HOME ?? join(homedir(), '.config', 'mosaic');
 }
 
 function assertDefaultMosaicHomeForSystemd(mosaicHome: string): void {
-  if (resolve(mosaicHome) !== resolve(defaultMosaicHome())) {
+  const literalHome = join(homedir(), '.config', 'mosaic');
+  if (resolve(mosaicHome) !== resolve(literalHome)) {
     throw new Error(
-      `install-systemd only supports the default Mosaic home (${defaultMosaicHome()}) because the user systemd units use %h/.config/mosaic paths.`,
+      `install-systemd only supports the default Mosaic home (${literalHome}) because the user systemd units use %h/.config/mosaic paths.`,
     );
   }
 }
@@ -387,6 +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 {
@@ -475,7 +480,10 @@ export function parseTmuxListSessions(output: string): string[] {
  * Returns the heartbeat file path for an agent.
  */
 export function heartbeatPath(agentName: string, mosaicHome = defaultMosaicHome()): string {
-  return join(mosaicHome, 'fleet', 'run', `${agentName}.hb`);
+  // Honor MOSAIC_HEARTBEAT_RUN_DIR (the writer sidecar's override); otherwise the
+  // canonical <mosaicHome>/fleet/run. Keeps reader and writer on the same path.
+  const runDir = process.env.MOSAIC_HEARTBEAT_RUN_DIR ?? join(mosaicHome, 'fleet', 'run');
+  return join(runDir, `${agentName}.hb`);
 }
 
 /**
@@ -484,15 +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();
@@ -504,6 +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;
@@ -513,7 +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 };
 }
 
 /**
@@ -1117,6 +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);
@@ -1131,6 +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');
@@ -1147,6 +1161,7 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
             pid.padEnd(8),
             idle.padEnd(8),
             hbAge.padEnd(12),
+            model.padEnd(22),
             flags.join(','),
           ].join(' '),
         );
@@ -1438,15 +1453,19 @@ export function registerFleetAgentCommands(
 
       await runChecked(runner, buildAgentWatchCreateViewerCommand(agent, viewerName, socketName));
 
+      let exitCode = 0;
+      try {
         const [bin, args] = splitCommand(buildAgentWatchAttachCommand(viewerName, socketName));
-      const exitCode = await iRunner(bin, args);
-
-      // Best-effort cleanup of the viewer session regardless of how the user detached.
-      // Errors here are intentionally suppressed — the agent session is unaffected.
+        exitCode = await iRunner(bin, args);
+      } finally {
+        // ALWAYS clean up the viewer session — even if attach threw or the process was
+        // interrupted — so stale grouped *-watch-* sessions never accumulate. Errors here
+        // are intentionally suppressed; the agent session is unaffected.
         const killResult = await runner(
           ...splitCommand(buildAgentWatchKillViewerCommand(viewerName, socketName)),
         );
-      void killResult; // result is intentionally ignored
+        void killResult;
+      }
 
       if (exitCode !== 0) {
         process.exitCode = exitCode;

packages/mosaic/src/commands/launch.ts

@@ -291,12 +291,23 @@ function buildPrdBlock(): string {
 
 // ─── Runtime prompt builder ──────────────────────────────────────────────────
 
-function buildRuntimePrompt(runtime: RuntimeName): string {
+/**
+ * Compose the full runtime contract for a harness: the resident-by-value core
+ * (CONSTITUTION + AGENTS + USER + TOOLS + runtime) plus operator overlays
+ * (`*.local.md` deltas), merged in precedence order so the model gets one
+ * pre-merged blob (DESIGN §3.2 / R7). Overlays are injected as deltas by value;
+ * base files keep their existing residency (USER injected; SOUL/STANDARDS are
+ * load-on-demand, so only their small `.local` deltas are injected here).
+ *
+ * `mosaicHome` is parameterized for testability; production callers use the
+ * module-level default.
+ */
+export function composeContract(runtime: RuntimeName, mosaicHome: string = MOSAIC_HOME): string {
   const runtimeContractPaths: Record<RuntimeName, string> = {
-    claude: join(MOSAIC_HOME, 'runtime', 'claude', 'RUNTIME.md'),
-    codex: join(MOSAIC_HOME, 'runtime', 'codex', 'RUNTIME.md'),
-    opencode: join(MOSAIC_HOME, 'runtime', 'opencode', 'RUNTIME.md'),
-    pi: join(MOSAIC_HOME, 'runtime', 'pi', 'RUNTIME.md'),
+    claude: join(mosaicHome, 'runtime', 'claude', 'RUNTIME.md'),
+    codex: join(mosaicHome, 'runtime', 'codex', 'RUNTIME.md'),
+    opencode: join(mosaicHome, 'runtime', 'opencode', 'RUNTIME.md'),
+    pi: join(mosaicHome, 'runtime', 'pi', 'RUNTIME.md'),
   };
 
   const runtimeFile = runtimeContractPaths[runtime];
@@ -331,27 +342,55 @@ For required push/merge/issue-close/release actions, execute without routine con
 `);
 
   // CONSTITUTION.md (L0 — the non-negotiable law; lead with it). Tolerant of
-  // pre-constitution installs that have not been re-seeded yet.
-  const constitution = readOptional(join(MOSAIC_HOME, 'CONSTITUTION.md'));
+  // pre-constitution installs that have not been re-seeded yet. Injected by
+  // value verbatim so the bare-launch fallback read is byte-equal (R8).
+  const constitution = readOptional(join(mosaicHome, 'CONSTITUTION.md'));
   if (constitution) parts.push(constitution);
 
   // AGENTS.md
-  parts.push(readFileSync(join(MOSAIC_HOME, 'AGENTS.md'), 'utf-8'));
+  parts.push(readFileSync(join(mosaicHome, 'AGENTS.md'), 'utf-8'));
 
-  // USER.md
-  const user = readOptional(join(MOSAIC_HOME, 'USER.md'));
+  // USER.md (+ USER.local.md operator overlay, appended directly under the
+  // profile its base owns).
+  const user = readOptional(join(mosaicHome, 'USER.md'));
   if (user) parts.push('\n\n# User Profile\n\n' + user);
+  const userLocal = readOptional(join(mosaicHome, 'USER.local.md'));
+  if (userLocal.trim()) {
+    parts.push('\n\n## Operator Overlay (USER.local.md)\n\n' + userLocal);
+  }
 
   // TOOLS.md
-  const tools = readOptional(join(MOSAIC_HOME, 'TOOLS.md'));
+  const tools = readOptional(join(mosaicHome, 'TOOLS.md'));
   if (tools) parts.push('\n\n# Machine Tools\n\n' + tools);
 
+  // Operator overlays whose base layers are load-on-demand (SOUL, STANDARDS):
+  // inject only the small `.local` delta by value so the customization reaches
+  // the model without re-injecting the full base prose (preserves the byte
+  // budget). Absent `.local` files → base-only, automatically (R7 §3.2).
+  const overlayBlocks: string[] = [];
+  const soulLocal = readOptional(join(mosaicHome, 'SOUL.local.md'));
+  if (soulLocal.trim()) {
+    overlayBlocks.push('## Persona Overlay (SOUL.local.md)\n\n' + soulLocal.trim());
+  }
+  const standardsLocal = readOptional(join(mosaicHome, 'STANDARDS.local.md'));
+  if (standardsLocal.trim()) {
+    overlayBlocks.push('## Standards Overlay (STANDARDS.local.md)\n\n' + standardsLocal.trim());
+  }
+  if (overlayBlocks.length > 0) {
+    parts.push('\n\n# Operator Overlays\n\n' + overlayBlocks.join('\n\n'));
+  }
+
   // Runtime-specific contract
   parts.push('\n\n# Runtime-Specific Contract\n\n' + readFileSync(runtimeFile, 'utf-8'));
 
   return parts.join('\n');
 }
 
+/** @deprecated internal alias — use composeContract. Retained for call-site clarity. */
+function buildRuntimePrompt(runtime: RuntimeName): string {
+  return composeContract(runtime);
+}
+
 // ─── Session lock ────────────────────────────────────────────────────────────
 
 function writeSessionLock(runtime: string): void {
@@ -976,6 +1015,22 @@ export function registerLaunchCommands(program: Command): void {
     launchRuntime(runtime, extraArgs, yolo);
   });
 
+  // compose-contract — emit the composed runtime contract (base + operator
+  // overlays) for a harness to stdout, without launching. For inspection,
+  // `mosaic doctor`, diffing, and the composer test (R7).
+  program
+    .command('compose-contract <harness>')
+    .description('Print the composed runtime contract (base + *.local overlays) for a harness')
+    .action((harness: string) => {
+      const valid: RuntimeName[] = ['claude', 'codex', 'opencode', 'pi'];
+      if (!valid.includes(harness as RuntimeName)) {
+        console.error(`Unknown harness '${harness}'. Expected one of: ${valid.join(', ')}.`);
+        process.exitCode = 64;
+        return;
+      }
+      process.stdout.write(composeContract(harness as RuntimeName));
+    });
+
   // Coord (mission orchestrator)
   program
     .command('coord')