diff --git a/packages/core/src/core/coreToolScheduler.test.ts b/packages/core/src/core/coreToolScheduler.test.ts
index 04dfdb378..b2bfe4335 100644
--- a/packages/core/src/core/coreToolScheduler.test.ts
+++ b/packages/core/src/core/coreToolScheduler.test.ts
@@ -4391,11 +4391,34 @@ describe('extractToolFilePaths', () => {
     expect(extractToolFilePaths('glob', { pattern: 'src/**/*.tsx' })).toEqual([
       'src/**/*.tsx',
     ]);
-    // Both `path` (search root) and `pattern` (selector) when both
-    // present.
+  });
+
+  it('joins glob.path + glob.pattern into the effective selector', () => {
+    // Regression: glob({ path: 'src', pattern: '**/*.ts' }) actually
+    // searches src/**/*.ts. Emitting them as separate candidates
+    // ('src', '**/*.ts') would NOT activate a skill keyed on
+    // `paths: ['src/**/*.ts']`, because neither component matches the
+    // skill glob in isolation. Join them with path.join so the
+    // effective-selector candidate reflects what the tool really
+    // touched. (The standalone `path` candidate is still emitted by the
+    // generic block above so a broad skill keyed on `paths: ['src/**']`
+    // still matches.)
     expect(
       extractToolFilePaths('glob', { path: 'src', pattern: '**/*.ts' }),
-    ).toEqual(['src', '**/*.ts']);
+    ).toEqual(['src', 'src/**/*.ts']);
+  });
+
+  it('joins absolute glob.path with pattern (registry guard rejects downstream)', () => {
+    // glob({ path: '/tmp/external', pattern: '**/*.ts' }) joins to an
+    // absolute path. SkillActivationRegistry's project-root guard
+    // rejects it; the test pins the joined shape so absolute roots
+    // stay distinguishable from project-relative ones.
+    expect(
+      extractToolFilePaths('glob', {
+        path: '/tmp/external',
+        pattern: '**/*.ts',
+      }),
+    ).toEqual(['/tmp/external', '/tmp/external/**/*.ts']);
   });
 
   it('does not extract pattern for non-glob tools', () => {
diff --git a/packages/core/src/core/coreToolScheduler.ts b/packages/core/src/core/coreToolScheduler.ts
index 3e00231cc..faf7a64d2 100644
--- a/packages/core/src/core/coreToolScheduler.ts
+++ b/packages/core/src/core/coreToolScheduler.ts
@@ -47,6 +47,7 @@ import type {
   Part,
   PartListUnion,
 } from '@google/genai';
+import * as path from 'node:path';
 import { ToolNames } from '../tools/tool-names.js';
 import { CONCURRENCY_SAFE_KINDS } from '../tools/tools.js';
 import { isShellCommandReadOnly } from '../utils/shellReadOnlyChecker.js';
@@ -247,10 +248,24 @@ export function extractToolFilePaths(
     for (const p of pathsField) push(p);
   }
   if (toolName === ToolNames.GLOB) {
-    // Glob-only: include `pattern` as a path-shaped selector. Don't add
-    // it for grep_search even though grep also has a `pattern` field —
-    // grep's pattern is a regex, not a path glob, and would false-match.
-    push(obj['pattern']);
+    // Glob-only: derive the effective selector from `path` + `pattern`.
+    // The previous version pushed `pattern` standalone, but the glob
+    // call actually searches `<path>/<pattern>` — so a skill keyed on
+    // `paths: ['src/**/*.ts']` would not activate from
+    // `glob({ path: 'src', pattern: '**/*.ts' })` because the candidate
+    // was just `**/*.ts`. Joining matches what the tool really touched.
+    // (Don't add `pattern` for grep_search even though it also has a
+    // `pattern` field — grep's pattern is a regex, not a path glob,
+    // and would false-match.)
+    const pathField = obj['path'];
+    const patternField = obj['pattern'];
+    if (typeof patternField === 'string' && patternField.length > 0) {
+      if (typeof pathField === 'string' && pathField.length > 0) {
+        push(path.join(pathField, patternField));
+      } else {
+        push(patternField);
+      }
+    }
   }
   return out;
 }
diff --git a/packages/core/src/skills/skill-activation.test.ts b/packages/core/src/skills/skill-activation.test.ts
index 71cd81870..899ca78cf 100644
--- a/packages/core/src/skills/skill-activation.test.ts
+++ b/packages/core/src/skills/skill-activation.test.ts
@@ -201,3 +201,50 @@ describe('resolveProjectRelativePath', () => {
     ).toBe('src/App.tsx');
   });
 });
+
+describe('extractToolFilePaths → SkillActivationRegistry integration', () => {
+  // Regression: feed the real candidate output for a `glob` call into
+  // the registry and assert end-to-end activation. The earlier per-field
+  // extraction (path + pattern as separate candidates) silently failed
+  // to activate skills keyed on the joined effective selector — there
+  // was no test exercising the path that mattered.
+  it('activates a skill keyed on src/**/*.ts from glob({ path: "src", pattern: "**/*.ts" })', async () => {
+    const { extractToolFilePaths } = await import(
+      '../core/coreToolScheduler.js'
+    );
+    const candidates = extractToolFilePaths('glob', {
+      path: 'src',
+      pattern: '**/*.ts',
+    });
+    const reg = new SkillActivationRegistry(
+      [makeSkill({ name: 'tsx-helper', paths: ['src/**/*.ts'] })],
+      '/project',
+    );
+    // Hand each candidate the registry the way coreToolScheduler does;
+    // collect the union.
+    const activated = new Set<string>();
+    for (const c of candidates) {
+      for (const n of reg.matchAndConsume(c)) activated.add(n);
+    }
+    expect(Array.from(activated)).toEqual(['tsx-helper']);
+  });
+
+  it('does NOT activate from external glob.path (project-root guard wins)', async () => {
+    const { extractToolFilePaths } = await import(
+      '../core/coreToolScheduler.js'
+    );
+    const candidates = extractToolFilePaths('glob', {
+      path: '/tmp/external',
+      pattern: '**/*.ts',
+    });
+    const reg = new SkillActivationRegistry(
+      [makeSkill({ name: 'broad', paths: ['**/*.ts'] })],
+      '/project',
+    );
+    const activated = new Set<string>();
+    for (const c of candidates) {
+      for (const n of reg.matchAndConsume(c)) activated.add(n);
+    }
+    expect(activated.size).toBe(0);
+  });
+});