diff --git a/.github/docker/Dockerfile.ci b/.github/docker/Dockerfile.ci
index 97b5b6b55..aef646180 100644
--- a/.github/docker/Dockerfile.ci
+++ b/.github/docker/Dockerfile.ci
@@ -33,9 +33,11 @@ RUN printf 'Acquire::Retries "5";\nAcquire::http::Timeout "30";\nAcquire::https:
 #   bash bins shell out to it (macOS ships python3; the base image doesn't).
 # file: skill-validation's no-compiled-binaries-in-git check runs `file --mime-type`.
 # poppler-utils: make-pdf's e2e gates hard-require pdftotext/pdffonts/pdfinfo in CI.
+# zsh: the sourced-helper guard sources every skill helper under bash and zsh
+#   (macOS's default shell) and fails under CI=true when zsh is missing.
 RUN for i in 1 2 3; do \
       apt-get update && apt-get install -y --no-install-recommends \
-        git curl unzip xz-utils ca-certificates jq bc gpg python3 python3-venv file poppler-utils gcc libc6-dev && break || \
+        git curl unzip xz-utils ca-certificates jq bc gpg python3 python3-venv file poppler-utils gcc libc6-dev zsh && break || \
       (echo "apt retry $i/3 after failure"; sleep 10); \
     done \
     && rm -rf /var/lib/apt/lists/*
diff --git a/.github/workflows/free-tests.yml b/.github/workflows/free-tests.yml
index 33e04fae5..516978e13 100644
--- a/.github/workflows/free-tests.yml
+++ b/.github/workflows/free-tests.yml
@@ -102,7 +102,8 @@ jobs:
   # $TMPDIR sits under /var/folders and /var is a symlink to /private/var, so
   # code that compares a realpath with an unresolved path passes on Linux's
   # /tmp and fails here (#2982). TMPDIR is deliberately left at the runner's
-  # default, and the job fails if that layout is not symlinked.
+  # default, and the job fails if that layout is not symlinked. It also sources
+  # the Codex probe from zsh, macOS's default shell (#3024; no paid call).
   macos-named-regressions:
     runs-on: macos-latest
     timeout-minutes: 20
@@ -124,6 +125,13 @@ jobs:
           git config --global user.email "free-tests-ci@gstack.test"
           git config --global user.name "Free Tests CI"
           git config --global init.defaultBranch main
+      - name: Codex probe selects a model when sourced from zsh (macOS default shell, no paid call)
+        working-directory: ${{ runner.temp }}
+        run: |
+          set -euo pipefail
+          out="$(zsh -c 'source "$GITHUB_WORKSPACE/bin/gstack-codex-probe" && _gstack_codex_select_model exec' 2>&1)"
+          printf '%s\n' "$out"
+          printf '%s\n' "$out" | grep -E '^CODEX_MODEL: [A-Za-z0-9._:/-]+ \(exec; source: '
       - name: Run the named macOS regressions on the default temp root
         run: |
           set -euo pipefail
@@ -131,7 +139,7 @@ jobs:
           resolved="$(realpath "$tmp")"
           echo "temp root: $tmp -> $resolved"
           test "$resolved" != "${tmp%/}"
-          files=(test/gstack-design-detect.test.ts browse/test/chromium-profile-isolation.test.ts test/cso-git-hardening.test.ts test/plan-count-file-permission.test.ts test/spec-quality-gate-secret-sink.test.ts test/gstack-memory-ingest.test.ts)
+          files=(test/gstack-design-detect.test.ts browse/test/chromium-profile-isolation.test.ts test/cso-git-hardening.test.ts test/plan-count-file-permission.test.ts test/spec-quality-gate-secret-sink.test.ts test/gstack-memory-ingest.test.ts test/regression-issue3024-zsh-sourced-helpers.test.ts)
           for file in "${files[@]}"; do test -f "$file"; done
           bun test "${files[@]}"
 
diff --git a/test/regression-issue3024-zsh-sourced-helpers.test.ts b/test/regression-issue3024-zsh-sourced-helpers.test.ts
index 9494e9b9b..f144a710c 100644
--- a/test/regression-issue3024-zsh-sourced-helpers.test.ts
+++ b/test/regression-issue3024-zsh-sourced-helpers.test.ts
@@ -285,4 +285,23 @@ describe('#3024: sourced helpers work under bash and zsh', () => {
       fs.rmSync(empty, { recursive: true, force: true });
     }
   });
+
+  test('CI keeps zsh: the free lane and the eval image install it, and the macOS lane sources the probe from zsh', () => {
+    const workflow = Bun.YAML.parse(fs.readFileSync(path.join(ROOT, '.github/workflows/free-tests.yml'), 'utf8')) as any;
+    const runs = (job: string) => (workflow.jobs[job].steps as any[]).map(step => String(step.run ?? '')).join('\n');
+    expect(runs('free-suite')).toMatch(/apt-get install[^\n]*\bzsh\b/);
+    expect(fs.readFileSync(path.join(ROOT, '.github/docker/Dockerfile.ci'), 'utf8')).toMatch(/apt-get install -y --no-install-recommends \\\n[^\n]*\bzsh\b/);
+    const mac = workflow.jobs['macos-named-regressions'];
+    expect(mac['runs-on']).toMatch(/^macos-/);
+    const step = (mac.steps as any[]).find(s => String(s.run ?? '').includes('_gstack_codex_select_model exec'));
+    expect(step?.run).toContain(`zsh -c 'source "$GITHUB_WORKSPACE/bin/gstack-codex-probe" && _gstack_codex_select_model exec'`);
+    expect(runs('macos-named-regressions')).toContain('test/regression-issue3024-zsh-sourced-helpers.test.ts');
+    if (skipShell('zsh')) return;
+    const codexHome = fs.mkdtempSync(path.join(os.tmpdir(), 'zsh-helpers-ci-step-'));
+    try {
+      const r = run('bash', step.run, { GITHUB_WORKSPACE: ROOT, CODEX_HOME: codexHome });
+      expect(r.code).toBe(0);
+      expect(r.stdout).toMatch(/CODEX_MODEL: \S+ \(exec; source: /);
+    } finally { fs.rmSync(codexHome, { recursive: true, force: true }); }
+  });
 });