fix(mosaic): isolate brain publication index

docs/scratchpads/1051-mosaic-brain-installer.md

@@ -83,13 +83,13 @@ No explicit token ceiling was supplied. Working cap: 55K tokens for implementati
 - [x] C1 P5→P7 seam receipt read; no brain implementation is in C1.
 - [x] RED acceptance set committed at `cf11c6c86abae073d8b02b4014cd5447ba67f12a`; author and committer read back as `be-coder-07` and branch reachability was independently verified by `tl-mosaic`.
 - [x] Moving-contract REDs observed independently for v1.4 mismatch, R8 prerequisite ordering, owner resolver seam/allowlist, tracked skeleton/no-follow behavior, runtime observation/publication, and provider owner resolution.
-- [x] Focused implementation includes secure migration, v1.5 write-differential/subject binding, production Git+API refusal parity, provider-backed durable owner resolution that ignores non-admin `active`, required GLPI standing-process policy, P7 provision orchestration, an internal installer command, and installed `mosaic doctor` wiring. Latest focused result: 86/86 (secure config 3, store 43, runtime 12, owner resolver 16, provision 4, provision command 3, installed doctor 5).
+- [x] Focused implementation includes secure migration, v1.5 write-differential/subject binding, production Git+API refusal parity, provider-backed durable owner resolution that ignores non-admin `active`, required GLPI standing-process policy, P7 provision orchestration, an internal installer command, and installed `mosaic doctor` wiring. Latest focused result: 87/87 (secure config 3, store 43, runtime 13, owner resolver 16, provision 4, provision command 3, installed doctor 5).
 - [x] MC-CRED added the required canonical reverse registry seam `ParsedCredentialEstateRegistry.resolveByHost()` at dependency head `6ca8758f`; current local copies are temporary until dependency integration and the 32-line permissive shim has been removed.
 - [x] Identity gotcha measured: inline `MOSAIC_GIT_IDENTITY=be-coder-07` controls credential resolution but does not override `user.name`/`user.email` inherited from the linked worktree common-dir config (`coder-mos1`). The first local P7 RED commit was immediately amended before push with command-scoped `GIT_AUTHOR_*` + `GIT_COMMITTER_*`; resulting author and committer both read back as `be-coder-07`. Every subsequent authoring command must carry both identity sets and be verified.
 - [x] R6 migration reports filename- or content-secret-shaped files without copying them; arbitrary legacy content requires an approved scanner bound to the exact source snapshot, and production currently retains/reports when no approved scanner is configured. Symlinked `.gitignore`, layout directories, and nested migration destinations fail closed.
 - [x] Provider owner lookup uses manual redirect handling, a five-second abort signal, strict JSON content type/shape, and an incrementally enforced 256 KiB response ceiling.
 - [x] Automatic source deletion is parked per the shared-Git-identity governance ruling; remotely reachable snapshots still leave and report every source.
-- [x] Multi-host push-on-write retries non-fast-forward races via fetch/rebase rather than LWW, and unknown publication reachability retains both sources and local copies.
+- [x] Multi-host push-on-write uses an isolated temporary Git index, verifies the exact changed-path allowlist plus both author/committer trailers before push, retries non-fast-forward races via identity-scoped fetch/rebase rather than LWW, and retains both sources and local copies when publication reachability is unknown. A real-repository abuse test proves unrelated pre-staged secret-shaped content remains staged but never enters the published commit.
 - [ ] Installer shell P7 invocation after C1 + MC-CRED integration; production command is registered but the C1 shell has not yet called it.
 - [ ] Implementation green on merged dependency base.
 - [ ] Independent code review.

packages/mosaic/src/commands/brain-provision.spec.ts

@@ -301,6 +301,7 @@ describe('P7 brain provisioning orchestration', (): void => {
     writeFileSync(source, 'durable finding\n');
     const requests: CommandRequest[] = [];
     let commitOrdinal = 0;
+    let approvedPaths: string[] = [];
     const runner: CommandRunner = (request): CommandResult => {
       requests.push(request);
       if (request.program === 'mosaic') {
@@ -325,6 +326,24 @@ describe('P7 brain provisioning orchestration', (): void => {
         mkdirSync(join(input.root, '.git'), { recursive: true });
         return { status: 0, stdout: '', stderr: '' };
       }
+      if (command.includes(' add -- ')) {
+        const separator = request.args.indexOf('--');
+        approvedPaths = separator === -1 ? [] : [...request.args.slice(separator + 1)];
+        return { status: 0, stdout: '', stderr: '' };
+      }
+      if (command.includes('diff --cached --quiet')) {
+        return { status: 1, stdout: '', stderr: '' };
+      }
+      if (command.includes('diff-tree')) {
+        return { status: 0, stdout: `${approvedPaths.join('\0')}\0`, stderr: '' };
+      }
+      if (command.includes('show -s')) {
+        return {
+          status: 0,
+          stdout: 'seat-a\[email protected]\0seat-a\[email protected]\n',
+          stderr: '',
+        };
+      }
       if (command.includes('rev-parse --is-inside-work-tree')) {
         return { status: 0, stdout: 'true\n', stderr: '' };
       }

packages/mosaic/src/commands/brain-store-runtime.spec.ts

@@ -1,5 +1,6 @@
 import { afterEach, describe, expect, it } from 'vitest';
-import { mkdirSync, mkdtempSync, rmSync } from 'node:fs';
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { execFileSync } from 'node:child_process';
 import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 
@@ -46,6 +47,7 @@ interface PublishEvidence {
 }
 
 interface BrainRuntimeModule {
+  readonly systemCommandRunner: CommandRunner;
   collectBrainDoctorReport(
     input: {
       readonly registrySource: string;
@@ -544,6 +546,64 @@ describe('R5 production refusal control', (): void => {
 });
 
 describe('push-on-write publication', (): void => {
+  it('never commits or pushes an unrelated pre-staged secret-shaped file', async (): Promise<void> => {
+    const runtime = await loadRuntime('MB-REQ-06 isolated publication index');
+    const root = tempRoot();
+    const remote = join(root, 'remote.git');
+    const checkout = join(root, 'brain');
+    execFileSync('git', ['init', '--bare', '--initial-branch=main', remote]);
+    execFileSync('git', ['init', '--initial-branch=main', checkout]);
+    writeFileSync(join(checkout, 'README.md'), 'brain\n');
+    execFileSync('git', ['-C', checkout, 'add', 'README.md']);
+    execFileSync('git', [
+      '-C',
+      checkout,
+      '-c',
+      'user.name=fixture',
+      '-c',
+      '[email protected]',
+      'commit',
+      '-m',
+      'seed',
+    ]);
+    execFileSync('git', ['-C', checkout, 'remote', 'add', 'origin', remote]);
+    execFileSync('git', ['-C', checkout, 'push', '-u', 'origin', 'main']);
+    writeFileSync(join(checkout, '.env'), 'TEST_ONLY_SECRET=fixture-value\n');
+    execFileSync('git', ['-C', checkout, 'add', '-f', '.env']);
+    const approved = join(checkout, 'finding.md');
+    writeFileSync(approved, 'approved finding\n');
+
+    const evidence = runtime.publishBrainPaths(
+      {
+        root: checkout,
+        identity: 'seat-a',
+        paths: [approved],
+        message: 'append approved finding',
+      },
+      runtime.systemCommandRunner,
+    );
+
+    const committed = execFileSync('git', [
+      '-C',
+      checkout,
+      'diff-tree',
+      '--no-commit-id',
+      '--name-only',
+      '-r',
+      evidence.commit,
+    ]).toString();
+    const staged = execFileSync('git', [
+      '-C',
+      checkout,
+      'diff',
+      '--cached',
+      '--name-only',
+    ]).toString();
+    expect(committed.trim().split('\n')).toEqual(['finding.md']);
+    expect(staged.trim().split('\n')).toContain('.env');
+    expect(evidence.reachable).toBe(true);
+  });
+
   it('commits with command-scoped identity, pushes immediately, and proves reachability from origin/main', async (): Promise<void> => {
     const runtime = await loadRuntime('MB-REQ-07 publish-on-write reachability');
     const root = tempRoot();
@@ -558,6 +618,19 @@ describe('push-on-write publication', (): void => {
       if (command.includes('rev-parse origin/main')) {
         return { status: 0, stdout: `${remoteHead}\n`, stderr: '' };
       }
+      if (command.includes('diff --cached --quiet')) {
+        return { status: 1, stdout: '', stderr: '' };
+      }
+      if (command.includes('diff-tree')) {
+        return { status: 0, stdout: '.gitignore\0lanes/lane-a/.gitkeep\0', stderr: '' };
+      }
+      if (command.includes('show -s')) {
+        return {
+          status: 0,
+          stdout: 'seat-a\[email protected]\0seat-a\[email protected]\n',
+          stderr: '',
+        };
+      }
       return { status: 0, stdout: '', stderr: '' };
     };
 
@@ -632,6 +705,23 @@ describe('push-on-write publication', (): void => {
         if (command.includes('rev-parse origin/main')) {
           return { status: 0, stdout: `${remoteHead}\n`, stderr: '' };
         }
+        if (command.includes('diff --cached --quiet')) {
+          return { status: 1, stdout: '', stderr: '' };
+        }
+        if (command.includes('diff-tree')) {
+          return {
+            status: 0,
+            stdout: 'lanes/lane-a/findings/host-a.md\0',
+            stderr: '',
+          };
+        }
+        if (command.includes('show -s')) {
+          return {
+            status: 0,
+            stdout: 'seat-a\[email protected]\0seat-a\[email protected]\n',
+            stderr: '',
+          };
+        }
         return { status: 0, stdout: '', stderr: '' };
       },
     );
@@ -679,7 +769,7 @@ describe('push-on-write publication', (): void => {
     );
 
     expect(evidence).toEqual({ commit, remoteHead: commit, reachable: true });
-    expect(requests.some((request) => request.args.includes('push'))).toBe(true);
+    expect(requests.some((request) => request.args.includes('push'))).toBe(false);
   });
 
   it('does not manufacture reachability when merge-base rejects the new commit', async (): Promise<void> => {
@@ -703,6 +793,19 @@ describe('push-on-write publication', (): void => {
         if (command.includes('rev-parse origin/main')) {
           return { status: 0, stdout: `${remoteHead}\n`, stderr: '' };
         }
+        if (command.includes('diff --cached --quiet')) {
+          return { status: 1, stdout: '', stderr: '' };
+        }
+        if (command.includes('diff-tree')) {
+          return { status: 0, stdout: '.gitignore\0', stderr: '' };
+        }
+        if (command.includes('show -s')) {
+          return {
+            status: 0,
+            stdout: 'seat-a\[email protected]\0seat-a\[email protected]\n',
+            stderr: '',
+          };
+        }
         if (command.includes('merge-base --is-ancestor')) {
           return { status: 1, stdout: '', stderr: '' };
         }

packages/mosaic/src/commands/brain-store-runtime.ts

@@ -1,6 +1,7 @@
-import { existsSync } from 'node:fs';
+import { existsSync, mkdtempSync, rmSync } from 'node:fs';
 import { spawnSync } from 'node:child_process';
-import { isAbsolute, relative, resolve, sep } from 'node:path';
+import { tmpdir } from 'node:os';
+import { isAbsolute, join, relative, resolve, sep } from 'node:path';
 import {
   assessCredentialResult,
   deriveBrainTarget,
@@ -84,6 +85,15 @@ function runGit(run: CommandRunner, identity: string, args: readonly string[]):
   return run({ program: 'git', args, env: commandEnv(identity) });
 }
 
+function runGitWithEnv(
+  run: CommandRunner,
+  identity: string,
+  args: readonly string[],
+  env: Readonly<Record<string, string>>,
+): CommandResult {
+  return run({ program: 'git', args, env: { ...commandEnv(identity), ...env } });
+}
+
 export function collectBrainDoctorReport(
   input: {
     readonly registrySource: string;
@@ -316,32 +326,6 @@ export function publishBrainPaths(
   if (input.message.trim().length === 0) throw new Error('brain-publish-message-empty');
   const paths = input.paths.map((path: string): string => containedRelative(input.root, path));
 
-  requireSuccess(
-    runGit(run, input.identity, ['-C', input.root, 'add', '--', ...paths]),
-    'brain-git-add',
-  );
-  const commitAttempt = runGit(run, input.identity, [
-    '-C',
-    input.root,
-    '-c',
-    `user.name=${input.identity}`,
-    '-c',
-    `user.email=${input.identity}@fleet.mosaicstack.dev`,
-    'commit',
-    '-m',
-    input.message,
-  ]);
-  if (commitAttempt.status !== 0) {
-    const stagedDifference = runGit(run, input.identity, [
-      '-C',
-      input.root,
-      'diff',
-      '--cached',
-      '--quiet',
-      '--exit-code',
-    ]);
-    if (stagedDifference.status !== 0) throw new Error('brain-git-commit-failed');
-  }
   const readHead = (): string => {
     const result = runGit(run, input.identity, ['-C', input.root, 'rev-parse', 'HEAD']);
     requireSuccess(result, 'brain-git-read-commit');
@@ -349,9 +333,100 @@ export function publishBrainPaths(
     if (!COMMIT.test(value)) throw new Error('brain-git-commit-shape-invalid');
     return value;
   };
-  let commit = readHead();
-  let pushed = false;
-  for (let attempt = 0; attempt < 3; attempt += 1) {
+  const verifyCommitIdentity = (commit: string): void => {
+    const result = runGit(run, input.identity, [
+      '-C',
+      input.root,
+      'show',
+      '-s',
+      '--format=%an%x00%ae%x00%cn%x00%ce',
+      commit,
+    ]);
+    requireSuccess(result, 'brain-git-read-commit-identity');
+    const expectedEmail = `${input.identity}@fleet.mosaicstack.dev`;
+    const [author, authorEmail, committer, committerEmail] = result.stdout.trimEnd().split('\0');
+    if (
+      author !== input.identity ||
+      authorEmail !== expectedEmail ||
+      committer !== input.identity ||
+      committerEmail !== expectedEmail
+    ) {
+      throw new Error('brain-git-commit-identity-mismatch');
+    }
+  };
+  const verifyCommitPaths = (commit: string): void => {
+    const changed = runGit(run, input.identity, [
+      '-C',
+      input.root,
+      'diff-tree',
+      '--root',
+      '--no-commit-id',
+      '--name-only',
+      '-r',
+      '-z',
+      commit,
+    ]);
+    requireSuccess(changed, 'brain-git-read-commit-paths');
+    const names = changed.stdout.split('\0').filter(Boolean);
+    const approved = new Set(paths);
+    if (names.length === 0 || names.some((name: string): boolean => !approved.has(name))) {
+      throw new Error('brain-git-commit-paths-unapproved');
+    }
+  };
+
+  const base = readHead();
+  const indexRoot = mkdtempSync(join(tmpdir(), 'mosaic-brain-index-'));
+  const isolatedEnv = { GIT_INDEX_FILE: join(indexRoot, 'index') };
+  let commit = base;
+  let createdCommit = false;
+  try {
+    requireSuccess(
+      runGitWithEnv(run, input.identity, ['-C', input.root, 'read-tree', base], isolatedEnv),
+      'brain-git-isolated-index-init',
+    );
+    requireSuccess(
+      runGitWithEnv(run, input.identity, ['-C', input.root, 'add', '--', ...paths], isolatedEnv),
+      'brain-git-add',
+    );
+    const difference = runGitWithEnv(
+      run,
+      input.identity,
+      ['-C', input.root, 'diff', '--cached', '--quiet', '--exit-code', base, '--', ...paths],
+      isolatedEnv,
+    );
+    if (difference.status === 1) {
+      requireSuccess(
+        runGitWithEnv(
+          run,
+          input.identity,
+          [
+            '-C',
+            input.root,
+            '-c',
+            `user.name=${input.identity}`,
+            '-c',
+            `user.email=${input.identity}@fleet.mosaicstack.dev`,
+            'commit',
+            '-m',
+            input.message,
+          ],
+          isolatedEnv,
+        ),
+        'brain-git-commit',
+      );
+      commit = readHead();
+      verifyCommitPaths(commit);
+      verifyCommitIdentity(commit);
+      createdCommit = true;
+    } else if (difference.status !== 0) {
+      throw new Error('brain-git-isolated-diff-failed');
+    }
+  } finally {
+    rmSync(indexRoot, { recursive: true, force: true });
+  }
+
+  let pushed = !createdCommit;
+  for (let attempt = 0; createdCommit && attempt < 3; attempt += 1) {
     const push = runGit(run, input.identity, ['-C', input.root, 'push', 'origin', 'HEAD:main']);
     if (push.status === 0) {
       pushed = true;
@@ -364,10 +439,21 @@ export function publishBrainPaths(
       'brain-git-fetch-concurrent',
     );
     requireSuccess(
-      runGit(run, input.identity, ['-C', input.root, 'rebase', 'origin/main']),
+      runGit(run, input.identity, [
+        '-C',
+        input.root,
+        '-c',
+        `user.name=${input.identity}`,
+        '-c',
+        `user.email=${input.identity}@fleet.mosaicstack.dev`,
+        'rebase',
+        'origin/main',
+      ]),
       'brain-git-rebase-concurrent',
     );
     commit = readHead();
+    verifyCommitPaths(commit);
+    verifyCommitIdentity(commit);
   }
   if (!pushed) throw new Error('brain-git-push-failed');
   requireSuccess(