feat(launch): force-load fleet-critical Pi skills + reconcile skill docs

Pi workers launched via `mosaic [yolo] pi` never loaded any skill because
buildPiSkillArgs emitted `--no-skills` whenever MOSAIC_PI_SKILL_MODE was
unset (the default everywhere), so maintained `~/.config/mosaic/tools/`
wrappers stayed invisible and workers improvised raw `tmux send-keys` /
`tea` / `gh`. An explicit `--skill` overrides `--no-skills` for that path,
so we now force-load a small fleet-critical set (default: `mosaic-tools`)
on every Pi launch regardless of mode — no full-catalog context bloat.

- launch.ts: add DEFAULT_PI_FORCE_SKILLS + forcedPiSkillArgs(); merge into
  every buildPiSkillArgs() return path (existsSync-guarded → no-op until the
  skill is synced). Override via MOSAIC_PI_FORCE_SKILLS (colon-separated;
  empty string disables).
- launch.spec.ts: deterministic 4th-param injection + force-load coverage.
- runtime/pi/RUNTIME.md: reconcile the "skills load natively" drift with the
  real default-off + force-load + MOSAIC_PI_SKILL_MODE behavior.
- templates/agent/**: fix stale `~/.config/mosaic/rails/` → `tools/` (60
  occurrences across 12 scaffold templates; `rails/` no longer exists).

Companion skill `mosaic-tools` ships in mosaic/agent-skills.
Follow-up (NOT auto-applied): live fleet needs `mosaic-sync-skills` +
launcher upgrade to pick up the new skill on running sessions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QoYiBeKNh3BiYtAJS5Z587

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

@@ -1,6 +1,11 @@
 import { describe, it, expect, vi, beforeEach, afterEach, type MockInstance } from 'vitest';
 import { Command } from 'commander';
-import { buildPiSkillArgs, registerRuntimeLaunchers, type RuntimeLaunchHandler } from './launch.js';
+import {
+  buildPiSkillArgs,
+  piForceSkillNames,
+  registerRuntimeLaunchers,
+  type RuntimeLaunchHandler,
+} from './launch.js';
 
 /**
  * Tests for the commander wiring between `mosaic <runtime>` / `mosaic yolo <runtime>`
@@ -23,6 +28,7 @@ function buildProgram(handler: RuntimeLaunchHandler): Command {
 }
 
 const fakeSkills = ['--skill', '/skills/test-driven-development', '--skill', '/skills/pdf'];
+const fakeForced = ['--skill', '/skills/mosaic-tools'];
 
 // `process.exit` returns `never`, so vi.spyOn demands a replacement with the
 // same signature. We throw from the mock to short-circuit into test-land.
@@ -66,16 +72,42 @@ describe('registerRuntimeLaunchers — non-yolo subcommands', () => {
 });
 
 describe('buildPiSkillArgs', () => {
-  it('defaults to disabling Pi skill discovery to keep startup context small', () => {
-    expect(buildPiSkillArgs([], {}, fakeSkills)).toEqual(['--no-skills']);
+  it('disables auto-discovery but force-loads fleet-critical skills by default', () => {
+    expect(buildPiSkillArgs([], {}, fakeSkills, fakeForced)).toEqual([
+      '--no-skills',
+      '--skill',
+      '/skills/mosaic-tools',
+    ]);
   });
 
-  it('keeps explicit user skills while disabling automatic discovery', () => {
-    expect(buildPiSkillArgs(['--skill', '/tmp/custom'], {}, fakeSkills)).toEqual(['--no-skills']);
+  it('ignores _runtimeArgs (user --skill flags reach Pi via the launch handler, not here)', () => {
+    expect(buildPiSkillArgs(['--skill', '/tmp/custom'], {}, fakeSkills, fakeForced)).toEqual([
+      '--no-skills',
+      '--skill',
+      '/skills/mosaic-tools',
+    ]);
   });
 
-  it('supports legacy all-skills mode without double-loading settings skills', () => {
-    expect(buildPiSkillArgs([], { MOSAIC_PI_SKILL_MODE: 'all' }, fakeSkills)).toEqual([
+  it('emits only --no-skills when no forced skills are present on disk', () => {
+    expect(buildPiSkillArgs([], {}, fakeSkills, [])).toEqual(['--no-skills']);
+  });
+
+  it('all-skills mode merges the forced set in without duplicating discovered skills', () => {
+    expect(buildPiSkillArgs([], { MOSAIC_PI_SKILL_MODE: 'all' }, fakeSkills, fakeForced)).toEqual([
+      '--no-skills',
+      '--skill',
+      '/skills/test-driven-development',
+      '--skill',
+      '/skills/pdf',
+      '--skill',
+      '/skills/mosaic-tools',
+    ]);
+  });
+
+  it('all-skills mode does not double-load a forced skill already discovered', () => {
+    expect(
+      buildPiSkillArgs([], { MOSAIC_PI_SKILL_MODE: 'all' }, fakeSkills, ['--skill', '/skills/pdf']),
+    ).toEqual([
       '--no-skills',
       '--skill',
       '/skills/test-driven-development',
@@ -84,8 +116,27 @@ describe('buildPiSkillArgs', () => {
     ]);
   });
 
-  it('supports native Pi discovery when explicitly requested', () => {
-    expect(buildPiSkillArgs([], { MOSAIC_PI_SKILL_MODE: 'discover' }, fakeSkills)).toEqual([]);
+  it('force-loads fleet skills even under native Pi discovery', () => {
+    expect(
+      buildPiSkillArgs([], { MOSAIC_PI_SKILL_MODE: 'discover' }, fakeSkills, fakeForced),
+    ).toEqual(['--skill', '/skills/mosaic-tools']);
+  });
+});
+
+describe('piForceSkillNames', () => {
+  it('defaults to mosaic-tools when MOSAIC_PI_FORCE_SKILLS is unset', () => {
+    expect(piForceSkillNames({})).toEqual(['mosaic-tools']);
+  });
+
+  it('treats an empty string as "disable force-loading" (distinct from unset)', () => {
+    expect(piForceSkillNames({ MOSAIC_PI_FORCE_SKILLS: '' })).toEqual([]);
+  });
+
+  it('parses a colon list, trimming blanks and whitespace', () => {
+    expect(piForceSkillNames({ MOSAIC_PI_FORCE_SKILLS: 'mosaic-tools: mosaic-gitea ::' })).toEqual([
+      'mosaic-tools',
+      'mosaic-gitea',
+    ]);
   });
 });