diff --git a/docs/scratchpads/1051-mosaic-brain-installer.md b/docs/scratchpads/1051-mosaic-brain-installer.md
index 91ce6e5a..d6c92df1 100644
--- a/docs/scratchpads/1051-mosaic-brain-installer.md
+++ b/docs/scratchpads/1051-mosaic-brain-installer.md
@@ -83,10 +83,10 @@ 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: 93/93 (secure config 4, store 43, runtime 18, 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: 95/95 (secure config 4, store 44, runtime 18, owner resolver 16, provision 5, 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] 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. `.gitignore` is canonical allowlisted content only: an existing noncanonical regular file fails closed and is never merged into publication. Symlinked `.gitignore`, layout directories, and nested migration destinations fail closed; a dirty checkout blocks provisioning before skeleton publication.
 - [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] Security-critical owner policy/registry reads have direct controls for principal UID ownership, file/ancestor permissions, and descriptor-safe regular-file reads.
 - [x] Automatic source deletion is parked per the shared-Git-identity governance ruling; remotely reachable snapshots still leave and report every source.
diff --git a/packages/mosaic/src/commands/brain-provision.spec.ts b/packages/mosaic/src/commands/brain-provision.spec.ts
index 93377cfb..a99dd930 100644
--- a/packages/mosaic/src/commands/brain-provision.spec.ts
+++ b/packages/mosaic/src/commands/brain-provision.spec.ts
@@ -292,6 +292,63 @@ describe('P7 brain provisioning orchestration', (): void => {
     expect(requests.some((request) => request.args.includes('grant'))).toBe(false);
   });
 
+  it('blocks before skeleton publication when the existing checkout is dirty', async (): Promise<void> => {
+    const provisioner = await loadProvisioner('MB-REQ-06 dirty checkout publication gate');
+    const root = tempRoot();
+    const input = baseInput(root);
+    mkdirSync(join(input.root, '.git'), { recursive: true });
+    const requests: CommandRequest[] = [];
+
+    const result = await provisioner.provisionBrain(input, {
+      run: (request): CommandResult => {
+        requests.push(request);
+        if (request.program === 'mosaic') {
+          return request.args[2] === 'outside-seat'
+            ? {
+                status: 10,
+                stdout: validateResult('refused', 'no-token-for-identity', 'outside-seat'),
+                stderr: 'refused reason=no-token-for-identity',
+              }
+            : { status: 0, stdout: validateResult('ok', 'validation-verified'), stderr: '' };
+        }
+        const command = request.args.join(' ');
+        if (command.includes('ls-remote')) {
+          return {
+            status: 128,
+            stdout: '',
+            stderr: 'credential helper refused reason=no-token-for-identity',
+          };
+        }
+        if (command.includes('rev-parse --is-inside-work-tree')) {
+          return { status: 0, stdout: 'true\n', stderr: '' };
+        }
+        if (command.includes('remote get-url origin')) {
+          return {
+            status: 0,
+            stdout: 'https://git.example.invalid/durable-owner/mosaic-brain.git\n',
+            stderr: '',
+          };
+        }
+        if (command.includes('branch --show-current')) {
+          return { status: 0, stdout: 'main\n', stderr: '' };
+        }
+        if (command.includes('status --porcelain')) {
+          return { status: 0, stdout: '?? .gitignore\n', stderr: '' };
+        }
+        return { status: 99, stdout: '', stderr: 'unexpected publication command' };
+      },
+      fetch: ownerFetch(),
+      absentControlName: (): string => 'generated-absent-control',
+    });
+
+    expect(result).toMatchObject({
+      status: 'blocked',
+      reasonCode: 'brain-postcondition-failed',
+    });
+    expect(requests.some((request) => request.args.includes('commit'))).toBe(false);
+    expect(requests.some((request) => request.args.includes('push'))).toBe(false);
+  });
+
   it('clones, seeds, resolves owner, migrates, pushes on each write, and archives source only after reachability', async (): Promise<void> => {
     const provisioner = await loadProvisioner('MB-REQ-07 complete migration transaction');
     const root = tempRoot();
diff --git a/packages/mosaic/src/commands/brain-provision.ts b/packages/mosaic/src/commands/brain-provision.ts
index 7fed8ff3..8889a153 100644
--- a/packages/mosaic/src/commands/brain-provision.ts
+++ b/packages/mosaic/src/commands/brain-provision.ts
@@ -175,6 +175,8 @@ export async function provisionBrain(
       finding.code === 'brain-not-git-repository' ||
       finding.code === 'brain-remote-mismatch' ||
       finding.code === 'brain-branch-mismatch' ||
+      finding.code === 'brain-uncommitted-state' ||
+      finding.code === 'brain-git-state-indeterminate' ||
       finding.code.startsWith('brain-write-access-'),
   );
   if (blockingCloneFindings.length > 0) {
diff --git a/packages/mosaic/src/commands/brain-store.spec.ts b/packages/mosaic/src/commands/brain-store.spec.ts
index 2d8a81d3..9590f403 100644
--- a/packages/mosaic/src/commands/brain-store.spec.ts
+++ b/packages/mosaic/src/commands/brain-store.spec.ts
@@ -359,6 +359,16 @@ describe('R6 — brain layout refuses secret material', (): void => {
     );
   });
 
+  it('refuses existing noncanonical gitignore content instead of publishing it', async (): Promise<void> => {
+    const sut = await loadSut('MB-REQ-06 unapproved gitignore content');
+    const root = tempRoot();
+    const ignore = join(root, '.gitignore');
+    writeFileSync(ignore, '# token=fixture-value\n*.token\n');
+
+    expect(() => sut.createBrainSkeleton(root)).toThrow(/brain-layout-ignore-content-unsafe/);
+    expect(readFileSync(ignore, 'utf8')).toBe('# token=fixture-value\n*.token\n');
+  });
+
   it('refuses a symlinked layout directory without writing a tracked placeholder outside the brain', async (): Promise<void> => {
     const sut = await loadSut('MB-REQ-06 no-follow brain layout');
     const root = tempRoot();
diff --git a/packages/mosaic/src/commands/brain-store.ts b/packages/mosaic/src/commands/brain-store.ts
index 77599016..72389625 100644
--- a/packages/mosaic/src/commands/brain-store.ts
+++ b/packages/mosaic/src/commands/brain-store.ts
@@ -10,7 +10,6 @@ import {
   openSync,
   readdirSync,
   readFileSync,
-  renameSync,
   rmSync,
   unlinkSync,
   writeFileSync,
@@ -400,21 +399,22 @@ export function createBrainSkeleton(root: string): {
       throw new Error('brain-layout-ignore-unsafe');
     }
   }
-  const existing = existsSync(ignorePath)
-    ? readFileSync(ignorePath, 'utf8')
-        .split(/\r?\n/)
-        .filter((line: string): boolean => line.length > 0)
-    : [];
-  const merged = [...existing];
-  for (const rule of GITIGNORE_RULES) {
-    if (!merged.includes(rule)) merged.push(rule);
-  }
-  const content = `${merged.join('\n')}\n`;
-  if (!existsSync(ignorePath) || readFileSync(ignorePath, 'utf8') !== content) {
+  const content = `${GITIGNORE_RULES.join('\n')}\n`;
+  if (existsSync(ignorePath)) {
+    const snapshot = stableSourceSnapshot(ignorePath);
+    if (!snapshot.content.equals(Buffer.from(content, 'utf8'))) {
+      throw new Error('brain-layout-ignore-content-unsafe');
+    }
+  } else {
     const temporary = `${ignorePath}.tmp-${process.pid}-${randomUUID()}`;
-    writeFileSync(temporary, content, { encoding: 'utf8', mode: 0o644, flag: 'wx' });
-    syncFile(temporary);
-    renameSync(temporary, ignorePath);
+    try {
+      writeFileSync(temporary, content, { encoding: 'utf8', mode: 0o644, flag: 'wx' });
+      syncFile(temporary);
+      linkSync(temporary, ignorePath);
+      syncFile(ignorePath);
+    } finally {
+      rmSync(temporary, { force: true });
+    }
     created.push(ignorePath);
     publicationEntries.push({ path: ignorePath, content: new TextEncoder().encode(content) });
   }