feat(fleet): brain-home split — fleet state under ~/.mosaic, templates stay config-home (#1298)

Co-authored-by: Jason Woltje <[email protected]>

packages/mosaic/src/fleet/brain-home.spec.ts

@@ -0,0 +1,114 @@
+import { mkdir, mkdtemp, rm } from 'node:fs/promises';
+import { homedir, tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import {
+  brainHomeIsActive,
+  fleetAgentEnvDir,
+  fleetProfilesDir,
+  fleetRolesLocalDir,
+  fleetStateDir,
+  resolveBrainHome,
+  type BrainHomeOptions,
+} from './brain-home.js';
+
+describe('fleet brain-home resolution', (): void => {
+  let cleanup: string | undefined;
+
+  const savedBrainEnv = process.env['MOSAIC_BRAIN_HOME'];
+
+  beforeEach((): void => {
+    delete process.env['MOSAIC_BRAIN_HOME'];
+  });
+
+  afterEach(async (): Promise<void> => {
+    if (savedBrainEnv === undefined) {
+      delete process.env['MOSAIC_BRAIN_HOME'];
+    } else {
+      process.env['MOSAIC_BRAIN_HOME'] = savedBrainEnv;
+    }
+    if (cleanup !== undefined) {
+      await rm(cleanup, { recursive: true, force: true });
+      cleanup = undefined;
+    }
+  });
+
+  async function makeTmp(): Promise<string> {
+    const root = await mkdtemp(join(tmpdir(), 'mosaic-brain-home-'));
+    cleanup = root;
+    return root;
+  }
+
+  it('MOSAIC_BRAIN_HOME env wins over every other signal', (): void => {
+    process.env['MOSAIC_BRAIN_HOME'] = '/explicit/brain';
+    expect(resolveBrainHome('/any/mosaic-home')).toBe('/explicit/brain');
+    expect(fleetAgentEnvDir('/any/mosaic-home')).toBe('/explicit/brain/fleet/agents');
+    expect(brainHomeIsActive('/any/mosaic-home')).toBe(true);
+  });
+
+  it('injected envBrainHome wins identically (test seam)', (): void => {
+    const opts: BrainHomeOptions = { envBrainHome: '/injected/brain' };
+    expect(resolveBrainHome('/any/mosaic-home', opts)).toBe('/injected/brain');
+    expect(fleetAgentEnvDir('/any/mosaic-home', opts)).toBe('/injected/brain/fleet/agents');
+  });
+
+  it('a non-default mosaicHome never adopts the canonical brain (hermetic legacy)', (): void => {
+    const mosaicHome = '/tmp/not-the-default-config-home';
+    expect(resolveBrainHome(mosaicHome)).toBe(mosaicHome);
+    expect(brainHomeIsActive(mosaicHome)).toBe(false);
+    expect(fleetAgentEnvDir(mosaicHome)).toBe(join(mosaicHome, 'fleet', 'agents'));
+  });
+
+  it('the default config home adopts the brain when it carries fleet/agents', async (): Promise<void> => {
+    const root = await makeTmp();
+    const brain = join(root, 'brain');
+    await mkdir(join(brain, 'fleet', 'agents'), { recursive: true });
+    const configHome = join(root, 'config', 'mosaic');
+    const opts: BrainHomeOptions = { homes: { brain, configDefault: configHome } };
+
+    expect(resolveBrainHome(configHome, opts)).toBe(brain);
+    expect(fleetAgentEnvDir(configHome, opts)).toBe(join(brain, 'fleet', 'agents'));
+    expect(fleetRolesLocalDir(configHome, opts)).toBe(join(brain, 'fleet', 'roles.local'));
+    expect(fleetProfilesDir(configHome, opts)).toBe(join(brain, 'fleet', 'profiles'));
+    expect(fleetStateDir(configHome, opts)).toBe(join(brain, 'fleet'));
+    expect(brainHomeIsActive(configHome, opts)).toBe(true);
+  });
+
+  it('the default config home stays legacy when no brain exists', async (): Promise<void> => {
+    const root = await makeTmp();
+    const configHome = join(root, 'config', 'mosaic');
+    const opts: BrainHomeOptions = {
+      homes: { brain: join(root, 'brain'), configDefault: configHome },
+    };
+
+    expect(resolveBrainHome(configHome, opts)).toBe(configHome);
+    expect(brainHomeIsActive(configHome, opts)).toBe(false);
+  });
+
+  it('an empty MOSAIC_BRAIN_HOME is ignored, not treated as set', (): void => {
+    process.env['MOSAIC_BRAIN_HOME'] = '   ';
+    expect(resolveBrainHome('/tmp/legacy-home')).toBe('/tmp/legacy-home');
+  });
+
+  it('adoption requires fleet/agents specifically, not any brain content', async (): Promise<void> => {
+    const root = await makeTmp();
+    const brain = join(root, 'brain');
+    await mkdir(join(brain, 'fleet'), { recursive: true }); // fleet without agents
+    const configHome = join(root, 'config', 'mosaic');
+    const opts: BrainHomeOptions = { homes: { brain, configDefault: configHome } };
+
+    expect(resolveBrainHome(configHome, opts)).toBe(configHome);
+  });
+
+  it('real-home control: a host brain is adopted only through the default home', (): void => {
+    // Control on the un-injected path: this host carries ~/.mosaic/fleet/agents,
+    // so the default config home resolves to the brain or legacy — both valid
+    // canonical endpoints — while a non-default home never adopts.
+    const defaultHome = join(homedir(), '.config', 'mosaic');
+    const resolved = resolveBrainHome(defaultHome);
+    expect([defaultHome, join(homedir(), '.mosaic')]).toContain(resolved);
+    expect(resolveBrainHome(join(homedir(), 'elsewhere', 'mosaic'))).toBe(
+      join(homedir(), 'elsewhere', 'mosaic'),
+    );
+  });
+});

packages/mosaic/src/fleet/brain-home.ts

@@ -0,0 +1,76 @@
+import { existsSync } from 'node:fs';
+import { homedir } from 'node:os';
+import { join, resolve } from 'node:path';
+
+/**
+ * Overridable resolution inputs (tests inject tmp homes; production reads
+ * the environment and the real home directory).
+ */
+export interface BrainHomeOptions {
+  /** Explicit brain home; defaults to `MOSAIC_BRAIN_HOME`. */
+  readonly envBrainHome?: string;
+  /**
+   * Canonical homes used for adoption. Defaults derive from the real
+   * `homedir()`: `{ brain: ~/.mosaic, configDefault: ~/.config/mosaic }`.
+   */
+  readonly homes?: { readonly brain: string; readonly configDefault: string };
+}
+
+/**
+ * Brain-home resolution — the three-tree fleet split (stack canon
+ * `docs/STRUCTURE-CANON.md` §2, first carried by the USC estate brain):
+ *
+ *   config home (~/.config/mosaic)  framework templates + dispatch state:
+ *                                   fleet/roles (baseline), fleet/roster.yaml,
+ *                                   fleet/run (heartbeats), fleet/services
+ *   brain home  (~/.mosaic)         user-owned fleet state, committed:
+ *                                   fleet/agents/<seat>.env.*, fleet/roles.local,
+ *                                   fleet/profiles working copies
+ *
+ * Resolution order:
+ *   1. `MOSAIC_BRAIN_HOME` env (explicit, always wins)
+ *   2. canonical `~/.mosaic` — adopted ONLY when mosaicHome is the real
+ *      default config home AND `~/.mosaic/fleet/agents` exists. Custom
+ *      `--mosaic-home` values (tests, sandboxes, canaries) never trigger
+ *      adoption, keeping them hermetic and deterministic.
+ *   3. mosaicHome itself (legacy single-tree behavior).
+ */
+export function resolveBrainHome(mosaicHome: string, options: BrainHomeOptions = {}): string {
+  const explicit = options.envBrainHome ?? process.env['MOSAIC_BRAIN_HOME'];
+  if (explicit !== undefined && explicit.trim() !== '') {
+    return explicit;
+  }
+  const homes = options.homes ?? {
+    brain: join(homedir(), '.mosaic'),
+    configDefault: join(homedir(), '.config', 'mosaic'),
+  };
+  if (resolve(mosaicHome) !== resolve(homes.configDefault)) {
+    return mosaicHome;
+  }
+  return existsSync(join(homes.brain, 'fleet', 'agents')) ? homes.brain : mosaicHome;
+}
+
+/** True when fleet state resolves somewhere other than the config home. */
+export function brainHomeIsActive(mosaicHome: string, options: BrainHomeOptions = {}): boolean {
+  return resolve(resolveBrainHome(mosaicHome, options)) !== resolve(mosaicHome);
+}
+
+/** Fleet state root (brain home when active, else the config home). */
+export function fleetStateDir(mosaicHome: string, options: BrainHomeOptions = {}): string {
+  return join(resolveBrainHome(mosaicHome, options), 'fleet');
+}
+
+/** Seat launch envs — `<brainHome>/fleet/agents` when a brain is active. */
+export function fleetAgentEnvDir(mosaicHome: string, options: BrainHomeOptions = {}): string {
+  return join(fleetStateDir(mosaicHome, options), 'agents');
+}
+
+/** PRESERVE-protected persona override layer — `<brainHome>/fleet/roles.local`. */
+export function fleetRolesLocalDir(mosaicHome: string, options: BrainHomeOptions = {}): string {
+  return join(fleetStateDir(mosaicHome, options), 'roles.local');
+}
+
+/** System-type profiles (user working copies) — `<brainHome>/fleet/profiles`. */
+export function fleetProfilesDir(mosaicHome: string, options: BrainHomeOptions = {}): string {
+  return join(fleetStateDir(mosaicHome, options), 'profiles');
+}

packages/mosaic/src/fleet/fleet-reconciler.ts

@@ -3,6 +3,7 @@ import { lstat, open, readFile, unlink, type FileHandle } from 'node:fs/promises
 import { randomUUID } from 'node:crypto';
 import { homedir } from 'node:os';
 import { join } from 'node:path';
+import { fleetAgentEnvDir } from './brain-home.js';
 import {
   applyPreparedAgentEnvironmentProjection,
   prepareAgentEnvironmentProjection,
@@ -617,7 +618,7 @@ function defaultPrepareProjections(
         (agent: FleetRosterV2Agent): Promise<PreparedAgentEnvironmentProjection> =>
           prepareAgentEnvironmentProjection({
             mosaicHome,
-            agentEnvDir: join(mosaicHome, 'fleet', 'agents'),
+            agentEnvDir: fleetAgentEnvDir(mosaicHome),
             agentName: agent.name,
             generated: projectRosterV2AgentGeneratedEnv(roster, agent),
           }),

packages/mosaic/src/fleet/generated-env-boundary.spec.ts

@@ -176,6 +176,52 @@ describe('generated fleet agent environment boundary', (): void => {
     expect((await stat(result.generatedPath)).mode & 0o777).toBe(0o600);
   });
 
+  it('brain home: accepts and writes projections under MOSAIC_BRAIN_HOME/fleet/agents', async (): Promise<void> => {
+    const savedBrainHome = process.env['MOSAIC_BRAIN_HOME'];
+    try {
+      cleanup = await mkdtemp(join(tmpdir(), 'mosaic-generated-env-'));
+      const mosaicHome = join(cleanup, 'config-home');
+      const brainHome = join(cleanup, 'brain');
+      const agentEnvDir = join(brainHome, 'fleet', 'agents');
+      process.env['MOSAIC_BRAIN_HOME'] = brainHome;
+
+      const result = await writeAgentEnvironmentProjection({
+        mosaicHome,
+        agentEnvDir,
+        agentName: 'coder0',
+        generated: generatedValues,
+      });
+
+      // Projection landed in the brain tree, not under the config home.
+      expect(result.generatedPath).toBe(join(agentEnvDir, 'coder0.env.generated'));
+      expect((await stat(join(brainHome, 'fleet'))).mode & 0o777).toBe(0o700);
+      expect((await stat(agentEnvDir)).mode & 0o777).toBe(0o700);
+      expect((await stat(result.generatedPath)).mode & 0o777).toBe(0o600);
+      await expect(stat(join(mosaicHome, 'fleet'))).rejects.toThrow();
+
+      // A config-home agentEnvDir is now REJECTED while the brain is active —
+      // the boundary must not silently split state across two trees.
+      let rejected: unknown;
+      try {
+        await writeAgentEnvironmentProjection({
+          mosaicHome,
+          agentEnvDir: join(mosaicHome, 'fleet', 'agents'),
+          agentName: 'coder1',
+          generated: { ...generatedValues, MOSAIC_AGENT_NAME: 'coder1' },
+        });
+      } catch (caught: unknown) {
+        rejected = caught;
+      }
+      expect(rejected).toBeInstanceOf(AgentEnvBoundaryError);
+    } finally {
+      if (savedBrainHome === undefined) {
+        delete process.env['MOSAIC_BRAIN_HOME'];
+      } else {
+        process.env['MOSAIC_BRAIN_HOME'] = savedBrainHome;
+      }
+    }
+  });
+
   it('regenerates desired keys, relocates safe legacy local data, and quarantines forbidden legacy input', async (): Promise<void> => {
     cleanup = await mkdtemp(join(tmpdir(), 'mosaic-generated-env-'));
     const mosaicHome = join(cleanup, 'mosaic');

packages/mosaic/src/fleet/generated-env-boundary.ts

@@ -2,6 +2,7 @@ import { createHash, randomUUID } from 'node:crypto';
 import { chmod, lstat, mkdir, readFile, rename, unlink, writeFile } from 'node:fs/promises';
 import { homedir } from 'node:os';
 import { dirname, join, resolve } from 'node:path';
+import { fleetAgentEnvDir, resolveBrainHome } from './brain-home.js';
 import { compareCodePoints } from './deterministic-order.js';
 
 export type AgentEnvironmentKind = 'generated' | 'local';
@@ -528,12 +529,15 @@ async function validatePrivateProjectionDirectory(
   mosaicHome: string,
   agentEnvDir: string,
 ): Promise<void> {
-  const fleetDir = join(mosaicHome, 'fleet');
-  const expectedAgentEnvDir = join(fleetDir, 'agents');
+  // Brain-home split (canon §2): seat envs live under the brain home's
+  // fleet/agents when a brain is active; roster + templates stay config-home.
+  const expectedAgentEnvDir = fleetAgentEnvDir(mosaicHome);
   if (resolve(agentEnvDir) !== resolve(expectedAgentEnvDir)) {
     throw new AgentEnvBoundaryError('unsafe-directory', '(directory)', agentEnvDir);
   }
-  await assertManagedDirectoryIfPresent(mosaicHome, false);
+  const stateHome = resolveBrainHome(mosaicHome);
+  const fleetDir = join(stateHome, 'fleet');
+  await assertManagedDirectoryIfPresent(stateHome, false);
   await assertManagedDirectoryIfPresent(fleetDir, false);
   await assertManagedDirectoryIfPresent(agentEnvDir, true);
 }
@@ -543,8 +547,9 @@ async function ensurePrivateProjectionDirectory(
   agentEnvDir: string,
 ): Promise<void> {
   await validatePrivateProjectionDirectory(mosaicHome, agentEnvDir);
-  const fleetDir = join(mosaicHome, 'fleet');
-  await ensureManagedDirectory(mosaicHome, false);
+  const stateHome = resolveBrainHome(mosaicHome);
+  const fleetDir = join(stateHome, 'fleet');
+  await ensureManagedDirectory(stateHome, false);
   await ensureManagedDirectory(fleetDir, false);
   await ensureManagedDirectory(agentEnvDir, true);
 }