diff --git a/.github/utils/test_release_image_cache_sync_contract.py b/.github/utils/test_release_image_cache_sync_contract.py
new file mode 100644
index 00000000..3d363cda
--- /dev/null
+++ b/.github/utils/test_release_image_cache_sync_contract.py
@@ -0,0 +1,202 @@
+#!/usr/bin/env python3
+import os
+import subprocess
+import tempfile
+import unittest
+from pathlib import Path
+
+import yaml
+
+ROOT = Path(__file__).resolve().parents[2]
+WORKFLOW = ROOT / ".github/workflows/release-image-cache-sync.yml"
+CONTRACT_WORKFLOW = (
+    ROOT / ".github/workflows/test-release-image-cache-sync-contract.yml"
+)
+CONTRACT_PATHS = [
+    ".github/workflows/release-image-cache-sync.yml",
+    ".github/workflows/test-release-image-cache-sync-contract.yml",
+    ".github/utils/test_release_image_cache_sync_contract.py",
+]
+VALID_DIGEST_A = "sha256:" + "a" * 64
+VALID_DIGEST_B = "sha256:" + "b" * 64
+
+
+def load_workflow(path: Path) -> dict:
+    workflow = yaml.safe_load(path.read_text())
+    workflow_on = workflow.get("on", workflow.get(True))
+    if not isinstance(workflow_on, dict):
+        raise AssertionError("workflow must define an on mapping")
+    workflow["on"] = workflow_on
+    return workflow
+
+
+def step_by_id(workflow: dict, step_id: str) -> dict:
+    steps = workflow["jobs"]["release-image"]["steps"]
+    matches = [step for step in steps if step.get("id") == step_id]
+    if len(matches) != 1:
+        raise AssertionError(f"expected one step with id {step_id}, got {len(matches)}")
+    return matches[0]
+
+
+class ReleaseImageCacheSyncContractTest(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls) -> None:
+        cls.workflow = load_workflow(WORKFLOW)
+        cls.contract_workflow = load_workflow(CONTRACT_WORKFLOW)
+        cls.selector = step_by_id(cls.workflow, "select_image_index_digest")
+
+    def test_contract_workflow_trigger_matrix_is_exact(self) -> None:
+        triggers = self.contract_workflow["on"]
+        self.assertEqual(set(triggers), {"pull_request", "push"})
+        self.assertEqual(triggers["pull_request"], {"paths": CONTRACT_PATHS})
+        self.assertEqual(
+            triggers["push"],
+            {
+                "branches": ["main"],
+                "paths": CONTRACT_PATHS,
+            },
+        )
+
+        steps = self.contract_workflow["jobs"]["contract"]["steps"]
+        self.assertEqual(
+            steps[2],
+            {
+                "name": "Install contract tools",
+                "run": (
+                    "python -m pip install --disable-pip-version-check "
+                    "PyYAML==6.0.2 ruff==0.11.13"
+                ),
+            },
+        )
+        self.assertEqual(
+            steps[3],
+            {
+                "name": "Check contract lint and format",
+                "run": (
+                    "ruff check .github/utils/test_release_image_cache_sync_contract.py\n"
+                    "ruff format --check "
+                    ".github/utils/test_release_image_cache_sync_contract.py\n"
+                ),
+            },
+        )
+        self.assertEqual(
+            steps[4],
+            {
+                "name": "Run reusable workflow contract",
+                "run": "python .github/utils/test_release_image_cache_sync_contract.py",
+            },
+        )
+
+    def test_reusable_and_job_outputs_are_additive_and_exact(self) -> None:
+        workflow_outputs = self.workflow["on"]["workflow_call"]["outputs"]
+        self.assertEqual(
+            workflow_outputs["image-index-digest"]["value"],
+            "${{ jobs.release-image.outputs.image-index-digest }}",
+        )
+
+        job_outputs = self.workflow["jobs"]["release-image"]["outputs"]
+        self.assertEqual(
+            job_outputs["tag-name"], "${{ steps.get_tag_name.outputs.TAG-NAME }}"
+        )
+        self.assertEqual(
+            job_outputs["image-index-digest"],
+            "${{ steps.select_image_index_digest.outputs.image-index-digest }}",
+        )
+
+    def test_both_build_branches_export_direct_digest_and_disable_attestations(
+        self,
+    ) -> None:
+        steps = self.workflow["jobs"]["release-image"]["steps"]
+        token_build = step_by_id(self.workflow, "build_with_args_token")
+        plain_build = step_by_id(self.workflow, "build_without_args_token")
+        build_steps = [
+            step for step in steps if step.get("uses") == "docker/build-push-action@v5"
+        ]
+
+        self.assertEqual(build_steps, [token_build, plain_build])
+        self.assertLess(steps.index(token_build), steps.index(self.selector))
+        self.assertLess(steps.index(plain_build), steps.index(self.selector))
+        self.assertEqual(
+            token_build["if"],
+            "${{ env.DOCKER_USER != '' && env.DOCKER_PASSWORD != '' && inputs.ARGS_TOKEN }}",
+        )
+        self.assertEqual(
+            plain_build["if"],
+            "${{ env.DOCKER_USER != '' && env.DOCKER_PASSWORD != '' && ! inputs.ARGS_TOKEN }}",
+        )
+        for build in (token_build, plain_build):
+            self.assertEqual(build["uses"], "docker/build-push-action@v5")
+            self.assertIs(build["with"]["push"], True)
+            self.assertIs(build["with"]["provenance"], False)
+            self.assertIs(build["with"]["sbom"], False)
+
+        self.assertEqual(
+            self.selector["env"],
+            {
+                "DIGEST_WITH_ARGS_TOKEN": "${{ steps.build_with_args_token.outputs.digest }}",
+                "DIGEST_WITHOUT_ARGS_TOKEN": "${{ steps.build_without_args_token.outputs.digest }}",
+            },
+        )
+
+    def run_selector(
+        self, token_digest: str = "", plain_digest: str = ""
+    ) -> subprocess.CompletedProcess:
+        with tempfile.TemporaryDirectory() as tmp:
+            output = Path(tmp) / "github-output"
+            env = os.environ.copy()
+            env.update(
+                {
+                    "DIGEST_WITH_ARGS_TOKEN": token_digest,
+                    "DIGEST_WITHOUT_ARGS_TOKEN": plain_digest,
+                    "GITHUB_OUTPUT": str(output),
+                }
+            )
+            result = subprocess.run(
+                ["bash", "-c", self.selector["run"]],
+                check=False,
+                capture_output=True,
+                text=True,
+                env=env,
+            )
+            result.github_output = output.read_text() if output.exists() else ""
+            return result
+
+    def test_token_build_digest_is_selected(self) -> None:
+        result = self.run_selector(token_digest=VALID_DIGEST_A)
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(result.github_output, f"image-index-digest={VALID_DIGEST_A}\n")
+
+    def test_plain_build_digest_is_selected(self) -> None:
+        result = self.run_selector(plain_digest=VALID_DIGEST_B)
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(result.github_output, f"image-index-digest={VALID_DIGEST_B}\n")
+
+    def test_missing_duplicate_and_malformed_digests_fail_closed(self) -> None:
+        cases = (
+            ("", ""),
+            (VALID_DIGEST_A, VALID_DIGEST_B),
+            ("sha256:" + "A" * 64, ""),
+            ("sha256:1234", ""),
+            ("not-a-digest", ""),
+        )
+        for token_digest, plain_digest in cases:
+            with self.subTest(token_digest=token_digest, plain_digest=plain_digest):
+                result = self.run_selector(token_digest, plain_digest)
+                self.assertNotEqual(result.returncode, 0)
+                self.assertEqual(result.github_output, "")
+
+    def test_selector_has_no_mutable_tag_lookup_fallback(self) -> None:
+        script = self.selector["run"]
+        forbidden = (
+            "docker manifest",
+            "imagetools",
+            "skopeo",
+            "crane",
+            "TAG-NAME",
+            "tag-name",
+        )
+        self.assertFalse([needle for needle in forbidden if needle in script])
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/.github/workflows/release-image-cache-sync.yml b/.github/workflows/release-image-cache-sync.yml
index 6d310705..355253a0 100644
--- a/.github/workflows/release-image-cache-sync.yml
+++ b/.github/workflows/release-image-cache-sync.yml
@@ -2,6 +2,10 @@ name: Releae Image Cache And Sync To Aliyun
 
 on:
   workflow_call:
+    outputs:
+      image-index-digest:
+        description: "OCI index digest produced by the successful image build"
+        value: ${{ jobs.release-image.outputs.image-index-digest }}
     inputs:
       MAKE_OPS_PRE:
         description: "The pre ops name of makefile (e.g. generate)"
@@ -114,6 +118,7 @@ jobs:
     runs-on: ubuntu-latest
     outputs:
       tag-name: ${{ steps.get_tag_name.outputs.TAG-NAME }}
+      image-index-digest: ${{ steps.select_image_index_digest.outputs.image-index-digest }}
     steps:
       - name: Pre Check
         id: pre_check
@@ -210,6 +215,7 @@ jobs:
           password: ${{ env.DOCKER_PASSWORD }}
 
       - if: ${{ env.DOCKER_USER != '' && env.DOCKER_PASSWORD != '' && inputs.ARGS_TOKEN }}
+        id: build_with_args_token
         name: Build and Push to Docker Hub
         uses: docker/build-push-action@v5
         with:
@@ -230,6 +236,7 @@ jobs:
           sbom: false
 
       - if: ${{ env.DOCKER_USER != '' && env.DOCKER_PASSWORD != '' && ! inputs.ARGS_TOKEN }}
+        id: build_without_args_token
         name: Build and Push to Docker Hub
         uses: docker/build-push-action@v5
         with:
@@ -248,6 +255,36 @@ jobs:
           provenance: false
           sbom: false
 
+      - name: Validate and export OCI index digest
+        id: select_image_index_digest
+        shell: bash
+        env:
+          DIGEST_WITH_ARGS_TOKEN: ${{ steps.build_with_args_token.outputs.digest }}
+          DIGEST_WITHOUT_ARGS_TOKEN: ${{ steps.build_without_args_token.outputs.digest }}
+        run: |
+          set -euo pipefail
+
+          digests=()
+          if [[ -n "$DIGEST_WITH_ARGS_TOKEN" ]]; then
+            digests+=("$DIGEST_WITH_ARGS_TOKEN")
+          fi
+          if [[ -n "$DIGEST_WITHOUT_ARGS_TOKEN" ]]; then
+            digests+=("$DIGEST_WITHOUT_ARGS_TOKEN")
+          fi
+
+          if [[ ${#digests[@]} -ne 1 ]]; then
+            echo "expected exactly one successful image build digest, got ${#digests[@]}" >&2
+            exit 1
+          fi
+
+          image_index_digest="${digests[0]}"
+          if [[ ! "$image_index_digest" =~ ^sha256:[0-9a-f]{64}$ ]]; then
+            echo "image build returned an invalid OCI index digest" >&2
+            exit 1
+          fi
+
+          echo "image-index-digest=$image_index_digest" >> "$GITHUB_OUTPUT"
+
   sync-to-aliyun:
     runs-on: ubuntu-latest
     if: ${{ inputs.SYNC_ENABLE }}
diff --git a/.github/workflows/test-release-image-cache-sync-contract.yml b/.github/workflows/test-release-image-cache-sync-contract.yml
new file mode 100644
index 00000000..75a8bc72
--- /dev/null
+++ b/.github/workflows/test-release-image-cache-sync-contract.yml
@@ -0,0 +1,39 @@
+name: Test Release Image Cache Sync Contract
+
+on:
+  pull_request:
+    paths:
+      - '.github/workflows/release-image-cache-sync.yml'
+      - '.github/workflows/test-release-image-cache-sync-contract.yml'
+      - '.github/utils/test_release_image_cache_sync_contract.py'
+  push:
+    branches:
+      - main
+    paths:
+      - '.github/workflows/release-image-cache-sync.yml'
+      - '.github/workflows/test-release-image-cache-sync-contract.yml'
+      - '.github/utils/test_release_image_cache_sync_contract.py'
+
+permissions:
+  contents: read
+
+jobs:
+  contract:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Install contract tools
+        run: python -m pip install --disable-pip-version-check PyYAML==6.0.2 ruff==0.11.13
+
+      - name: Check contract lint and format
+        run: |
+          ruff check .github/utils/test_release_image_cache_sync_contract.py
+          ruff format --check .github/utils/test_release_image_cache_sync_contract.py
+
+      - name: Run reusable workflow contract
+        run: python .github/utils/test_release_image_cache_sync_contract.py