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

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).