feat(fleet): inject resolved persona contract at launch by class (A3b)

At agent launch, composeContract reads MOSAIC_AGENT_CLASS (exported into the
pane env by the companion A3a goal) and injects the agent's resolved persona
role contract into the system prompt, so its identity (mandate + boundaries)
is resident from the first turn.

Override-aware: resolution goes through the persona resolver, so a customized
persona in fleet/roles.local/ wins over the baseline fleet/roles/ of the same
class — the launch-time proof of AC-NS-7. Tolerant: any miss (unset/empty/
unknown class, missing file) no-ops silently and never throws during launch,
mirroring readFleetCommsBlock. Persona is injected BEFORE the fleet comms
block (identity first, then how-to-reach-peers).

Adds a synchronous resolvePersonaSync / extractClassesFromDirSync twin in
fleet-personas.ts (composeContract is sync and cannot await), sharing the same
extraction semantics via a pure accumulateEntry helper (no drift).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/mosaic/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@mosaicstack/mosaic",
-  "version": "0.0.46",
+  "version": "0.0.45",
   "repository": {
     "type": "git",
     "url": "https://git.mosaicstack.dev/mosaicstack/stack.git",

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

@@ -246,8 +246,6 @@ describe('fleet roster parsing', () => {
     expect(generateAgentEnv(roster, getRosterAgent(roster, 'coder0'))).toBe(
       [
         'MOSAIC_AGENT_NAME=coder0',
-        // Reflects the roster's non-default `class: implementer` (A3a).
-        'MOSAIC_AGENT_CLASS=implementer',
         'MOSAIC_AGENT_RUNTIME=codex',
         'MOSAIC_AGENT_MODEL=',
         'MOSAIC_AGENT_WORKDIR=/srv/mosaic',
@@ -257,40 +255,6 @@ describe('fleet roster parsing', () => {
     );
   });
 
-  it('emits MOSAIC_AGENT_CLASS=worker for an agent that declares no class', async () => {
-    cleanup = await tempDir();
-    const rosterPath = join(cleanup, 'roster.json');
-    await writeFile(
-      rosterPath,
-      JSON.stringify({
-        version: 1,
-        transport: 'tmux',
-        agents: [{ name: 'coder0', runtime: 'codex' }],
-      }),
-    );
-    const roster = await loadFleetRoster(rosterPath);
-    expect(generateAgentEnv(roster, getRosterAgent(roster, 'coder0'))).toContain(
-      'MOSAIC_AGENT_CLASS=worker\n',
-    );
-  });
-
-  it('shell-escapes MOSAIC_AGENT_CLASS so a launcher reads it verbatim', async () => {
-    cleanup = await tempDir();
-    const rosterPath = join(cleanup, 'roster.json');
-    await writeFile(
-      rosterPath,
-      JSON.stringify({
-        version: 1,
-        transport: 'tmux',
-        agents: [{ name: 'coder0', runtime: 'codex', class: 'orchestrator' }],
-      }),
-    );
-    const roster = await loadFleetRoster(rosterPath);
-    expect(generateAgentEnv(roster, getRosterAgent(roster, 'coder0'))).toContain(
-      'MOSAIC_AGENT_CLASS=orchestrator\n',
-    );
-  });
-
   it('preserves site-owned agent EnvironmentFile overrides while refreshing roster keys', () => {
     const generated = [
       'MOSAIC_AGENT_NAME=coder0',
@@ -322,28 +286,6 @@ describe('fleet roster parsing', () => {
     );
   });
 
-  it('updates (does not duplicate) MOSAIC_AGENT_CLASS on re-launch', () => {
-    const generated = [
-      'MOSAIC_AGENT_NAME=coder0',
-      'MOSAIC_AGENT_CLASS=orchestrator',
-      'MOSAIC_AGENT_RUNTIME=codex',
-      '',
-    ].join('\n');
-    const existing = [
-      'MOSAIC_AGENT_NAME=coder0',
-      'MOSAIC_AGENT_CLASS=worker',
-      'MOSAIC_AGENT_RUNTIME=codex',
-      '',
-    ].join('\n');
-
-    const merged = mergeAgentEnv(generated, existing);
-    // mergeAgentEnv keys by VAR name, so the regenerated CLASS wins and there is
-    // exactly one MOSAIC_AGENT_CLASS line (no stale worker value left behind).
-    expect(merged).toContain('MOSAIC_AGENT_CLASS=orchestrator');
-    expect(merged).not.toContain('MOSAIC_AGENT_CLASS=worker');
-    expect(merged.match(/^MOSAIC_AGENT_CLASS=/gm)).toHaveLength(1);
-  });
-
   it('rejects unknown roster fields instead of silently defaulting', async () => {
     cleanup = await tempDir();
     const rosterPath = join(cleanup, 'roster.yaml');

packages/mosaic/src/commands/fleet.ts

@@ -490,9 +490,6 @@ export function generateAgentEnv(roster: FleetRoster, agent: FleetAgent): string
   const workingDirectory = agent.workingDirectory ?? roster.defaults.workingDirectory;
   return [
     `MOSAIC_AGENT_NAME=${shellEnvValue(agent.name)}`,
-    // Per-agent class → start-agent-session.sh / launcher reads this to inject the
-    // matching persona contract for the agent's class (default `worker`).
-    `MOSAIC_AGENT_CLASS=${shellEnvValue(agent.className)}`,
     `MOSAIC_AGENT_RUNTIME=${shellEnvValue(agent.runtime)}`,
     // Per-agent model hint → start-agent-session.sh appends `--model <hint>` to
     // the `mosaic yolo` launch so workers run on the roster's model (e.g. pi on