feat(fleet): enhancer role + two-agent floor (orchestrator + enhancer) (#614)

From Jason's north-star (docs/fleet/north-star.md, #613): every fleet has a
two-agent floor — orchestrator + enhancer minimum. Builds on #612's init-R5.

- Presets (general/coding/research/hybrid): add enhancer (claude, class:
  enhancer, persistent_persona) as a core always-on agent. minimal/local-canary
  unchanged.
- fleet.ts: countEnhancers helper; init guarantee extended — non-minimal
  profiles must yield exactly 1 orchestrator AND >=1 enhancer (hard-fail);
  removeAgentFromRoster refuses to drop the sole enhancer (symmetric with the
  sole-orchestrator guard) so the floor holds at runtime, not just init.
- framework/fleet/roles/enhancer.md: the enhancer mandate (monitor -> analyze ->
  plan -> upgrade tools/skills/harness WITH orchestrator -> file Mosaic Stack
  bug reports) + boundaries (does NOT code or review).

Verified: 155 fleet tests green (countEnhancers; sole-enhancer remove guard;
remove-allows-when-another; init two-agent-floor; every-non-minimal-preset-has-
enhancer; updated preset rosters). tsc/eslint/prettier/sanitize clean. TDD on
the init guarantee + remove protection.

Stacked on #612 (feat/fleet-polish-bundle); rebases clean onto main after #612.

Refs #614, #613

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

docs/TASKS.md

@@ -62,3 +62,7 @@ Active workstream is **W1 — Federation v1**. Workers should:
 ## Fleet-polish bundle — boot-survival symmetry (#611) — feat/fleet-polish-bundle
 
 - Status: implemented + tested. disable-on-remove (boot-resurrection bug, TDD) + add-enable + init-R5 hard guarantee. 4 new + 147 existing fleet tests green. Detail: scratchpads/fleet-polish-bundle.md.
+
+## Fleet enhancer role + two-agent floor (#614) — feat/fleet-enhancer-floor (stacked on #612)
+
+- Status: implemented + tested. enhancer added to 4 presets; init guarantees 1 orchestrator + >=1 enhancer; remove protects the sole enhancer; enhancer role doc. 155 fleet tests green. Detail: scratchpads/fleet-enhancer-floor.md.

docs/scratchpads/fleet-enhancer-floor.md

@@ -0,0 +1,26 @@
+# Fleet enhancer role + two-agent floor (#614)
+
+- **Issue:** #614 · **Branch:** `feat/fleet-enhancer-floor` (stacked on #612 `feat/fleet-polish-bundle`)
+- **Doctrine:** `docs/fleet/north-star.md` (PR #613) — every fleet = orchestrator + enhancer minimum.
+
+## Changes
+
+- **Presets** (general, coding, research, hybrid): add `enhancer` (claude, `class: enhancer`,
+  `persistent_persona: true`) as a core always-on agent alongside the orchestrator. minimal/local-canary
+  unchanged.
+- **fleet.ts**: `countEnhancers` helper; init guarantee extended — non-minimal profiles must yield
+  exactly 1 orchestrator AND >=1 enhancer (hard-fail otherwise); `removeAgentFromRoster` refuses to drop
+  the sole enhancer (symmetric with the sole-orchestrator guard) so the floor holds at runtime, not just init.
+- **Role doc**: `framework/fleet/roles/enhancer.md` — the enhancer mandate (monitor → analyze → plan →
+  upgrade tools/skills/harness WITH orchestrator → file Mosaic Stack bug reports) + boundaries (does NOT
+  code or review).
+
+## Verification
+
+- 155 fleet tests green (new: countEnhancers; remove-sole-enhancer guard; remove-allows-when-another;
+  init two-agent-floor; every-non-minimal-preset-has-enhancer; updated preset rosters). tsc/eslint/
+  prettier/sanitize clean. TDD on the init guarantee + remove protection.
+
+## Stacking
+
+Built on #612's init-R5 code. PR shows #612 + enhancer until #612 merges; then rebase onto main → clean.

packages/mosaic/framework/fleet/examples/coding.yaml

@@ -15,6 +15,10 @@ agents:
     runtime: claude
     class: orchestrator
     persistent_persona: true
+  - name: enhancer
+    runtime: claude
+    class: enhancer
+    persistent_persona: true
   - name: coder0
     runtime: pi
     class: implementer

packages/mosaic/framework/fleet/examples/general.yaml

@@ -15,6 +15,10 @@ agents:
     runtime: claude
     class: orchestrator
     persistent_persona: true
+  - name: enhancer
+    runtime: claude
+    class: enhancer
+    persistent_persona: true
   - name: generalist
     runtime: pi
     class: worker

packages/mosaic/framework/fleet/examples/hybrid.yaml

@@ -15,6 +15,10 @@ agents:
     runtime: claude
     class: orchestrator
     persistent_persona: true
+  - name: enhancer
+    runtime: claude
+    class: enhancer
+    persistent_persona: true
   - name: coder0
     runtime: pi
     class: implementer

packages/mosaic/framework/fleet/examples/research.yaml

@@ -15,6 +15,10 @@ agents:
     runtime: claude
     class: orchestrator
     persistent_persona: true
+  - name: enhancer
+    runtime: claude
+    class: enhancer
+    persistent_persona: true
   - name: researcher0
     runtime: pi
     class: researcher

packages/mosaic/framework/fleet/roles/enhancer.md

@@ -0,0 +1,41 @@
+# Enhancer — fleet role definition
+
+The **enhancer** is one half of the fleet's two-agent floor: every fleet runs, at
+minimum, an **orchestrator** and an **enhancer**. The orchestrator drives delivery;
+the enhancer makes the fleet _get better at delivering_ over time.
+
+It is a **core, always-on** agent (`class: enhancer`, `persistent_persona: true`),
+not an ephemeral per-lane worker.
+
+## Mandate
+
+The enhancer runs the fleet's **continuous-improvement loop**:
+
+1. **Monitor** fleet activity — agents, heartbeats, sessions, throughput, failures.
+2. **Analyze** for enhancements and optimizations — friction, gaps, recurring defects,
+   missing or broken tools, skill/harness shortfalls.
+3. **Plan** a remediation: a concrete improvement with rationale and expected effect.
+4. **Upgrade fleet capability — with the orchestrator** — tool creation/repair, skills,
+   harness improvements. The orchestrator owns fleet composition; the enhancer advises and
+   implements improvements to the _means of production_, not the product.
+5. **File upstream bug reports** to Mosaic Stack for real defects, so they flow back to the
+   framework for proper remediation rather than being patched over locally.
+6. **Recommend which agents are needed** — advise the orchestrator on roles to add/remove as
+   the mission evolves.
+
+## Boundaries
+
+- **Does NOT write product/source code.**
+- **Does NOT review code** (that is the code-review / security-review roles).
+- **Does NOT perform delivery tasks.**
+
+Improvement and diagnosis only. When the enhancer finds work that requires coding or review,
+it files it (bug report / recommendation) and the orchestrator materializes the right worker.
+
+## Why two, not one
+
+The orchestrator alone optimizes for _this_ delivery; the enhancer optimizes for _every future_
+delivery — self-healing the fleet's tools, skills, and harnesses, and routing real defects
+upstream. Together they are the irreducible core; every other role is added on demand.
+
+> Doctrine: `docs/fleet/north-star.md` (two-agent floor + role library).

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

@@ -20,6 +20,7 @@ import {
   buildTmuxListSessionsCommand,
   classifySendResult,
   countOrchestrators,
+  countEnhancers,
   detectDrift,
   enableFleetUnits,
   FLEET_PROFILES,
@@ -1076,9 +1077,9 @@ describe('fleet-polish bundle — boot-survival symmetry', () => {
     }
   });
 
-  it('fleet init --write fails hard when a non-minimal profile lacks exactly one orchestrator', async () => {
+  it('fleet init --write enforces the two-agent floor (1 orchestrator + >=1 enhancer)', async () => {
-    // The general profile must yield exactly one orchestrator; the guarantee is
+    // The general profile must yield exactly one orchestrator AND at least one
-    // enforced (not just warned). We assert the happy path writes cleanly.
+    // enhancer; the guarantee is enforced (not just warned). Happy path writes cleanly.
     const home = await tempDir();
     const program = new Command();
     program.exitOverride();
@@ -1098,7 +1099,9 @@ describe('fleet-polish bundle — boot-survival symmetry', () => {
       ]);
       const written = await readFile(join(home, 'fleet', 'roster.yaml'), 'utf8');
       const orchestrators = (written.match(/class:\s*orchestrator/g) ?? []).length;
+      const enhancers = (written.match(/class:\s*enhancer/g) ?? []).length;
       expect(orchestrators).toBe(1);
+      expect(enhancers).toBeGreaterThanOrEqual(1);
     } finally {
       await rm(home, { recursive: true, force: true });
     }
@@ -2310,47 +2313,63 @@ describe('fleet preset rosters', () => {
     },
   );
 
-  it('general preset: orchestrator + one generalist worker', async () => {
+  it('general preset: orchestrator + enhancer + one generalist worker', async () => {
     const roster = await loadFleetRoster(join(examplesDir, 'general.yaml'));
-    expect(roster.agents.map((a) => a.name)).toEqual(['orchestrator', 'generalist']);
+    expect(roster.agents.map((a) => a.name)).toEqual(['orchestrator', 'enhancer', 'generalist']);
     expect(roster.agents.find((a) => a.name === 'orchestrator')?.runtime).toBe('claude');
+    expect(roster.agents.find((a) => a.name === 'enhancer')?.className).toBe('enhancer');
     expect(roster.agents.find((a) => a.name === 'generalist')?.runtime).toBe('pi');
   });
 
-  it('coding preset: orchestrator + coder0 + coder1 + reviewer', async () => {
+  it('coding preset: orchestrator + enhancer + coder0 + coder1 + reviewer', async () => {
     const roster = await loadFleetRoster(join(examplesDir, 'coding.yaml'));
     expect(roster.agents.map((a) => a.name)).toEqual([
       'orchestrator',
+      'enhancer',
       'coder0',
       'coder1',
       'reviewer',
     ]);
   });
 
-  it('research preset: orchestrator + researcher0 + researcher1 + analyst', async () => {
+  it('research preset: orchestrator + enhancer + researcher0 + researcher1 + analyst', async () => {
     const roster = await loadFleetRoster(join(examplesDir, 'research.yaml'));
     expect(roster.agents.map((a) => a.name)).toEqual([
       'orchestrator',
+      'enhancer',
       'researcher0',
       'researcher1',
       'analyst',
     ]);
   });
 
-  it('hybrid preset: orchestrator + coder0 + researcher0 + reviewer', async () => {
+  it('hybrid preset: orchestrator + enhancer + coder0 + researcher0 + reviewer', async () => {
     const roster = await loadFleetRoster(join(examplesDir, 'hybrid.yaml'));
     expect(roster.agents.map((a) => a.name)).toEqual([
       'orchestrator',
+      'enhancer',
       'coder0',
       'researcher0',
       'reviewer',
     ]);
   });
 
+  it('every non-minimal preset carries an enhancer (two-agent floor)', async () => {
+    for (const preset of ['general', 'coding', 'research', 'hybrid'] as FleetProfile[]) {
+      const roster = await loadFleetRoster(join(examplesDir, `${preset}.yaml`));
+      expect(countOrchestrators(roster)).toBe(1);
+      expect(countEnhancers(roster)).toBeGreaterThanOrEqual(1);
+      expect(roster.agents.find((a) => a.className === 'enhancer')?.runtime).toBe('claude');
+    }
+  });
+
   it('worker agents in new presets use pi runtime with model_hint openai-codex/gpt-5.5:high', async () => {
     for (const preset of ['general', 'coding', 'research', 'hybrid'] as FleetProfile[]) {
       const roster = await loadFleetRoster(join(examplesDir, `${preset}.yaml`));
-      const workers = roster.agents.filter((a) => a.name !== 'orchestrator');
+      // Core agents (orchestrator + enhancer) run claude; only ephemeral workers are pi.
+      const workers = roster.agents.filter(
+        (a) => a.className !== 'orchestrator' && a.className !== 'enhancer',
+      );
       for (const worker of workers) {
         expect(worker.runtime).toBe('pi');
         expect(worker.modelHint).toBe('openai-codex/gpt-5.5:high');
@@ -2492,6 +2511,43 @@ describe('fleet add/remove — pure helpers', () => {
     expect(updated.agents.map((a) => a.name)).toEqual(['orchestrator2', 'coder0']);
   });
 
+  it('countEnhancers counts enhancer-class agents (two-agent floor)', () => {
+    const roster: FleetRoster = {
+      ...baseRoster,
+      agents: [
+        { name: 'orchestrator', runtime: 'claude', className: 'orchestrator' },
+        { name: 'enhancer', runtime: 'claude', className: 'enhancer' },
+        { name: 'coder0', runtime: 'codex', className: 'worker' },
+      ],
+    };
+    expect(countEnhancers(roster)).toBe(1);
+    expect(countEnhancers(baseRoster)).toBe(0);
+  });
+
+  it('removeAgentFromRoster throws when removing the sole enhancer (two-agent floor)', () => {
+    const roster: FleetRoster = {
+      ...baseRoster,
+      agents: [
+        { name: 'orchestrator', runtime: 'claude', className: 'orchestrator' },
+        { name: 'enhancer', runtime: 'claude', className: 'enhancer' },
+      ],
+    };
+    expect(() => removeAgentFromRoster(roster, 'enhancer')).toThrow('sole enhancer');
+  });
+
+  it('removeAgentFromRoster allows removing an enhancer when another remains', () => {
+    const roster: FleetRoster = {
+      ...baseRoster,
+      agents: [
+        { name: 'orchestrator', runtime: 'claude', className: 'orchestrator' },
+        { name: 'enhancer', runtime: 'claude', className: 'enhancer' },
+        { name: 'enhancer2', runtime: 'claude', className: 'enhancer' },
+      ],
+    };
+    const updated = removeAgentFromRoster(roster, 'enhancer');
+    expect(updated.agents.map((a) => a.name)).toEqual(['orchestrator', 'enhancer2']);
+  });
+
   it('serializeRosterToYaml produces YAML that round-trips through loadFleetRoster', async () => {
     const yaml = serializeRosterToYaml(baseRoster);
     expect(typeof yaml).toBe('string');

packages/mosaic/src/commands/fleet.ts

@@ -881,11 +881,13 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
       await mkdir(dirname(destination), { recursive: true });
       await writeFile(destination, content);
 
-      // Guarantee R5: exactly one orchestrator for every profile except the
+      // Guarantee the two-agent floor: exactly one orchestrator AND at least
-      // sanctioned no-orchestrator `minimal` preset. A mismatch means a
+      // one enhancer for every profile except the sanctioned no-orchestrator
-      // corrupted/edited preset — fail hard rather than write a malformed fleet.
+      // `minimal` preset. A mismatch means a corrupted/edited preset — fail hard
+      // rather than write a malformed fleet.
       const written = await loadFleetRoster(destination);
       const orchCount = countOrchestrators(written);
+      const enhancerCount = countEnhancers(written);
       if (profile === 'minimal') {
         console.log(
           `Initialized ${profile} fleet: ${written.agents.length} agent(s) (no orchestrator). Next: mosaic fleet install`,
@@ -895,10 +897,17 @@ export function registerFleetCommand(program: Command, deps: FleetCommandDeps =
           `Fleet init failed: the "${profile}" roster has ${orchCount} orchestrator agent(s), ` +
             `expected exactly 1 (R5). The preset may be corrupted — re-install the framework.`,
         );
+      } else if (enhancerCount < 1) {
+        throw new Error(
+          `Fleet init failed: the "${profile}" roster has no enhancer agent. Every fleet keeps an ` +
+            `orchestrator + enhancer minimum (two-agent floor). The preset may be corrupted — ` +
+            `re-install the framework.`,
+        );
       } else {
-        const workerCount = written.agents.length - 1;
+        const workerCount = written.agents.length - 1 - enhancerCount;
         console.log(
-          `Initialized ${profile} fleet: 1 orchestrator + ${workerCount} agent(s). Next: mosaic fleet install`,
+          `Initialized ${profile} fleet: 1 orchestrator + ${enhancerCount} enhancer(s) + ` +
+            `${workerCount} worker(s). Next: mosaic fleet install`,
         );
       }
     });
@@ -1945,6 +1954,15 @@ export function countOrchestrators(roster: FleetRoster): number {
   return roster.agents.filter((a) => a.className === 'orchestrator').length;
 }
 
+/**
+ * Count enhancer agents in a parsed roster. The two-agent floor (north-star)
+ * requires every non-minimal fleet to carry at least one enhancer alongside the
+ * sole orchestrator.
+ */
+export function countEnhancers(roster: FleetRoster): number {
+  return roster.agents.filter((a) => a.className === 'enhancer').length;
+}
+
 /** Valid runtime identifiers for fleet agents. */
 export const VALID_FLEET_RUNTIMES: readonly string[] = [
   'pi',
@@ -1987,6 +2005,15 @@ export function removeAgentFromRoster(roster: FleetRoster, name: string): FleetR
       `Cannot remove agent "${name}": it is the sole orchestrator. Add another orchestrator first (R5).`,
     );
   }
+  // Two-agent floor: never drop the last enhancer (the continuous-improvement
+  // loop). Symmetric with the sole-orchestrator guard.
+  const remainingEnhancerCount = remaining.filter((a) => a.className === 'enhancer').length;
+  if (remainingEnhancerCount === 0 && agent.className === 'enhancer') {
+    throw new Error(
+      `Cannot remove agent "${name}": it is the sole enhancer. Every fleet keeps at least one ` +
+        `enhancer (two-agent floor). Add another enhancer first.`,
+    );
+  }
   return {
     ...roster,
     agents: remaining,