diff --git a/.github/workflows/gate.yml b/.github/workflows/gate.yml
index fa7b934..0a946f9 100644
--- a/.github/workflows/gate.yml
+++ b/.github/workflows/gate.yml
@@ -17,6 +17,11 @@ on:
         type: string
         required: false
         default: "cargo xtask ci"
+      setup-command:
+        description: "Optional setup script, run from the repository root before the gate (for example, fetch SHA-verified corpora)"
+        type: string
+        required: false
+        default: ""
       windows-command:
         description: "The gate on Windows legs; empty runs `command`"
         type: string
@@ -274,6 +279,16 @@ jobs:
           save-if: ${{ github.event_name != 'pull_request' && (github.ref_name == github.event.repository.default_branch || (inputs.cache-save-on-dispatch && github.event_name == 'workflow_dispatch')) }}
           cache-on-failure: true
 
+      - name: Caller setup
+        if: inputs.setup-command != ''
+        shell: bash
+        env:
+          SETUP: ${{ inputs.setup-command }}
+        run: |
+          set -euo pipefail
+          printf '%s\n' "$SETUP" > "$RUNNER_TEMP/gate-setup.sh"
+          bash -euo pipefail "$RUNNER_TEMP/gate-setup.sh"
+
       - name: Gate
         shell: bash
         env:
diff --git a/README.md b/README.md
index bb1b00a..8dee6e3 100644
--- a/README.md
+++ b/README.md
@@ -513,6 +513,8 @@ The quality gate for an app's pull requests and pushes to main. It runs `command
 - the app and craft-fonts (at the suite's pin, with `CRAFT_FONTS_REQUIRED=1`) checked out without
   persisted credentials, and craft-i18n when the app has `craft-i18n.rev`;
 - `packages` installed through `actions/install-apt-packages` on Linux legs (none when empty);
+- an optional `setup-command` run from the repository root before the gate, for fetching pinned
+  test data such as licensed corpora; its environment changes can be written to `$GITHUB_ENV`;
 - the channel from `rust-toolchain.toml`, or `toolchain`, with clippy, rustfmt and `targets`;
 - prebuilt cargo tools from `tools` (by default `cargo-nextest@0.9.150`);
 - `CARGO_PROFILE_DEV_DEBUG=line-tables-only` (set `dev-debug: ""` to keep the repository's
@@ -541,6 +543,11 @@ check, can be a second call with its own `command`, `os`, `tools` and `targets`,
       command: packaging/web/package.sh
 ```
 
+`setup-command` is also passed through the environment, then run with Bash from the checkout root.
+Use it for caller-specific test inputs whose contents are pinned and verified by the caller's
+fetcher. For example, a corpus-enabled workspace can fetch its locked corpus before running the
+gate and export `CRAFT_PSD_CORPUS` through `$GITHUB_ENV`; a failed fetch stops the job before tests.
+
 #### Caller Example:
 ```yaml
 name: CI
diff --git a/tests/test_gate.py b/tests/test_gate.py
index 9b2d74a..7f57120 100644
--- a/tests/test_gate.py
+++ b/tests/test_gate.py
@@ -135,6 +135,33 @@ class CallerEnvironmentTests(unittest.TestCase):
                 self.assertEqual(self.run_step(ALL=f'GOOD=1\n{line}')[0], 1)
 
 
+class CallerSetupTests(unittest.TestCase):
+    STEP = step('Caller setup')
+
+    def run_step(self, setup):
+        with tempfile.TemporaryDirectory() as directory:
+            github_env = Path(directory, 'github_env')
+            github_env.touch()
+            result = subprocess.run(
+                ['bash', '--noprofile', '--norc', '-eo', 'pipefail', '-c', self.STEP['run']],
+                cwd=directory, capture_output=True, text=True,
+                env={**os.environ, 'SETUP': setup, 'RUNNER_TEMP': directory,
+                     'GITHUB_ENV': str(github_env)})
+            return result.returncode, github_env.read_text().splitlines(), Path(directory, 'setup-ran').exists()
+
+    def test_setup_input_is_passed_through_env_before_the_gate(self):
+        self.assertEqual(set(self.STEP['env']), {'SETUP'})
+        self.assertLess(STEPS.index(self.STEP), STEPS.index(step('Gate')))
+        self.assertNotIn('${{', self.STEP['run'])
+
+    def test_setup_can_provision_data_and_export_its_path(self):
+        setup = 'touch setup-ran\necho "CRAFT_PSD_CORPUS=/corpus" >> "$GITHUB_ENV"'
+        self.assertEqual(self.run_step(setup), (0, ['CRAFT_PSD_CORPUS=/corpus'], True))
+
+    def test_setup_failure_stops_the_gate_job(self):
+        self.assertEqual(self.run_step('exit 17')[0], 17)
+
+
 class ProfileCacheTests(unittest.TestCase):
     def key(self, manifest):
         with tempfile.TemporaryDirectory() as directory: