diff --git a/packages/runtime/src/__tests__/builtin-tools.test.ts b/packages/runtime/src/__tests__/builtin-tools.test.ts
index 361c070fefa..b8eb4cec5b3 100644
--- a/packages/runtime/src/__tests__/builtin-tools.test.ts
+++ b/packages/runtime/src/__tests__/builtin-tools.test.ts
@@ -2181,6 +2181,69 @@ describe('builtin read tools path containment', () => {
     );
     assert.strictEqual(JSON.stringify(absoluteGrepResult).includes('main.ts'), true);
   });
+
+  test('Glob brace expansion cannot list entries outside the session cwd', async () => {
+    const root = await mkdtemp(join(tmpdir(), 'maka-glob-brace-'));
+    const outside = await mkdtemp(join(tmpdir(), 'maka-glob-outside-'));
+    try {
+      await mkdir(join(root, 'a'), { recursive: true });
+      await mkdir(join(root, 'b'), { recursive: true });
+      await writeFile(join(root, 'a', 'inner.txt'), 'in', 'utf8');
+      await writeFile(join(root, 'b', 'other.txt'), 'other', 'utf8');
+      await writeFile(join(outside, 'secret.txt'), 'out', 'utf8');
+      const glob = tool('Glob');
+
+      // `{a,../*}` carries no literal `..` segment, so the lexical pattern guard
+      // admits it, yet the `../*` brace branch walks above the session cwd.
+      const escaped = await runTool(glob, { pattern: '{a,../*}' }, root);
+      const escapedFiles = (escaped as { files: string[] }).files;
+      assert.strictEqual(
+        escapedFiles.some((file) => file.startsWith('../')),
+        false,
+        `glob listed entries outside the session cwd: ${JSON.stringify(escapedFiles)}`,
+      );
+      // The `../*` branch also matches the session cwd itself under its own
+      // name; glob reports that one as `.`, which is inside and stays.
+      assert.deepStrictEqual(escapedFiles.sort(), ['.', 'a']);
+
+      // Brace patterns that stay inside keep their full results.
+      const contained = await runTool(glob, { pattern: '{a/*.txt,b/*.txt}' }, root);
+      assert.deepStrictEqual((contained as { files: string[] }).files.sort(), [
+        'a/inner.txt',
+        'b/other.txt',
+      ]);
+    } finally {
+      await rm(root, { recursive: true, force: true });
+      await rm(outside, { recursive: true, force: true });
+    }
+  });
+
+  test('Glob drops matches reached through a directory symlink that leaves the session cwd', async () => {
+    const root = await mkdtemp(join(tmpdir(), 'maka-glob-link-'));
+    const outside = await mkdtemp(join(tmpdir(), 'maka-glob-linkout-'));
+    try {
+      await mkdir(join(root, 'src'), { recursive: true });
+      await writeFile(join(root, 'src', 'inner.txt'), 'in', 'utf8');
+      await writeFile(join(outside, 'secret.txt'), 'out', 'utf8');
+      await symlink(outside, join(root, 'link-out'));
+      const glob = tool('Glob');
+
+      // `resolve()` normalizes the spelling but does not follow the directory
+      // symlink, so lexical containment admits `link-out/secret.txt` even
+      // though its real location is outside; containment must be decided in
+      // real-path space, matching the skills-discovery idiom.
+      const linked = await runTool(glob, { pattern: 'link-out/**/*.txt' }, root);
+      assert.deepStrictEqual((linked as { files: string[] }).files, []);
+
+      // A symlinked directory that stays inside the root keeps its matches.
+      await symlink(join(root, 'src'), join(root, 'alias'));
+      const contained = await runTool(glob, { pattern: 'alias/*.txt' }, root);
+      assert.deepStrictEqual((contained as { files: string[] }).files, ['alias/inner.txt']);
+    } finally {
+      await rm(root, { recursive: true, force: true });
+      await rm(outside, { recursive: true, force: true });
+    }
+  });
 });
 
 describe('builtin write tools path containment', () => {
diff --git a/packages/runtime/src/filesystem-executor.ts b/packages/runtime/src/filesystem-executor.ts
index 99921db8dc2..02dc70a2dd9 100644
--- a/packages/runtime/src/filesystem-executor.ts
+++ b/packages/runtime/src/filesystem-executor.ts
@@ -666,6 +666,15 @@ function createWorkspaceFilesystemExecutor(
           const { files, truncated } = await workspace.globFiles({
             cwd: base,
             pattern: operation.pattern,
+            // Brace expansion can walk above the session cwd without the
+            // pattern text ever containing a `..` segment, so the lexical
+            // guard alone cannot contain workspace globs; results are
+            // filtered against the session cwd instead. The root shares the
+            // canonical spelling of the search base (the walker's cwd), or a
+            // symlinked workspace root (/var → /private/var) would reject
+            // every legitimate entry. Host scope has no boundary to escape
+            // and keeps raw results.
+            ...(scope === 'workspace' ? { containmentRoot: await canonicalExistingPath(cwd) } : {}),
             ...(operation.limit !== undefined ? { limit: operation.limit } : {}),
             ...(abortSignal ? { abortSignal } : {}),
           });
diff --git a/packages/runtime/src/filesystem-worker/operations.ts b/packages/runtime/src/filesystem-worker/operations.ts
index 24deca9ae0c..22428f6684c 100644
--- a/packages/runtime/src/filesystem-worker/operations.ts
+++ b/packages/runtime/src/filesystem-worker/operations.ts
@@ -392,7 +392,13 @@ export async function executeFilesystemOperation(
           )),
         };
       }
-      return { kind: 'glob', ...(await globFiles({ ...operation, cwd: path })) };
+      // Brace expansion can walk above the search root without the pattern
+      // text ever containing a `..` segment, so results are filtered back to
+      // the search root the lexical guard promises.
+      return {
+        kind: 'glob',
+        ...(await globFiles({ ...operation, cwd: path, containmentRoot: path })),
+      };
     }
     case 'grep': {
       const path = await resolveExistingAllowed(
diff --git a/packages/runtime/src/glob-search.ts b/packages/runtime/src/glob-search.ts
index a514ab163fd..329efefa572 100644
--- a/packages/runtime/src/glob-search.ts
+++ b/packages/runtime/src/glob-search.ts
@@ -20,12 +20,23 @@
 import { promises as fs, readdir } from 'node:fs';
 import { resolve } from 'node:path';
 import { globIterate } from 'glob';
+import { isPathInside } from './path-containment.js';
 
 export async function globFiles(input: {
   cwd: string;
   pattern: string;
   limit?: number;
   abortSignal?: AbortSignal;
+  /**
+   * When set, matched paths that resolve outside this root are dropped. Glob
+   * expands braces before walking, so a lexically clean pattern like
+   * `{a,../*}` can still walk above its search root; the walk cannot be
+   * contained, but its results can. Matches are compared in real-path space:
+   * `resolve()` normalizes spellings but does not follow directory symlinks,
+   * so a pattern naming a `link -> ../outside` directory stays lexically
+   * inside while its real location escapes.
+   */
+  containmentRoot?: string;
 }): Promise<{ files: string[]; truncated: boolean }> {
   let failure: NodeJS.ErrnoException | undefined;
   const directories = new Set([resolve(input.cwd)]);
@@ -33,6 +44,13 @@ export async function globFiles(input: {
   const limit = input.limit ?? 200;
   let probingOverflow = false;
   let probeIncomplete = false;
+  // Containment is decided on real paths (skills-discovery idiom: realpath
+  // both sides, then the pure predicate). Cost: one realpath for the root plus
+  // at most `limit` for the kept-or-dropped matches, on an interactive tool
+  // call. A root that cannot be realpath'd is an infrastructure failure and
+  // propagates; the walk cannot claim containment it cannot place.
+  const containmentReal =
+    input.containmentRoot !== undefined ? await fs.realpath(input.containmentRoot) : undefined;
   function record(error: NodeJS.ErrnoException, path: string): void {
     // Speculative literal components may miss. A directory already admitted by
     // cwd, stat, or enumeration disappearing instead makes this walk incomplete.
@@ -71,6 +89,21 @@ export async function globFiles(input: {
       },
     },
   })) {
+    // Dropped escapes do not count toward the limit: the cap bounds returned
+    // files, not walked ones.
+    if (containmentReal !== undefined) {
+      let matchReal: string;
+      try {
+        matchReal = await fs.realpath(resolve(input.cwd, file));
+      } catch {
+        // The match cannot be placed in the root's path space. Dropping it
+        // silently would read the walk as complete, so flag incompleteness
+        // the way vanished directories already do.
+        probeIncomplete = true;
+        continue;
+      }
+      if (!isPathInside(containmentReal, matchReal)) continue;
+    }
     if (files.length >= limit) {
       // One match past the cap is the only proof the pattern had more to give.
       truncated = true;
diff --git a/packages/runtime/src/workspace-executor.ts b/packages/runtime/src/workspace-executor.ts
index fc09a8507bc..1980abe5779 100644
--- a/packages/runtime/src/workspace-executor.ts
+++ b/packages/runtime/src/workspace-executor.ts
@@ -202,6 +202,8 @@ export interface WorkspaceGlobInput {
   pattern: string;
   limit?: number;
   abortSignal?: AbortSignal;
+  /** When set, matched paths that resolve outside this root are dropped. */
+  containmentRoot?: string;
 }
 
 export interface WorkspaceGlobResult {