diff --git a/docs/changelog.d/708-release-evidence-git-metadata-timeout.md b/docs/changelog.d/708-release-evidence-git-metadata-timeout.md
new file mode 100644
index 000000000..de75454cf
--- /dev/null
+++ b/docs/changelog.d/708-release-evidence-git-metadata-timeout.md
@@ -0,0 +1,5 @@
+# Release evidence Git metadata timeout
+
+## Fixed
+
+- Bound `git rev-parse` in the release evidence index builder with a fail-closed timeout.
diff --git a/scripts/build_release_evidence_index.py b/scripts/build_release_evidence_index.py
index 6547a2c4e..e4aef6804 100644
--- a/scripts/build_release_evidence_index.py
+++ b/scripts/build_release_evidence_index.py
@@ -18,6 +18,9 @@
     from _bounded_json import read_json_object
 
 
+GIT_METADATA_TIMEOUT_SECONDS = 5
+
+
 REQUIRED_COVERAGE = {
     "acceptance_summary",
     "sales_readiness_manifest",
@@ -45,6 +48,7 @@ def _sha256(path: Path) -> str:
 
 
 def _source_commit(repo_root: Path) -> str:
+    """Return HEAD SHA, failing closed when Git metadata lookup times out."""
     try:
         completed = subprocess.run(
             ["git", "rev-parse", "HEAD"],
@@ -52,7 +56,10 @@ def _source_commit(repo_root: Path) -> str:
             capture_output=True,
             text=True,
             check=True,
+            timeout=GIT_METADATA_TIMEOUT_SECONDS,
         )
+    except subprocess.TimeoutExpired as exc:
+        raise RuntimeError("source commit lookup timed out") from exc
     except Exception:
         return "unknown"
     return completed.stdout.strip() or "unknown"
diff --git a/tests/test_release_evidence_git_metadata_timeout.py b/tests/test_release_evidence_git_metadata_timeout.py
new file mode 100644
index 000000000..639d8754f
--- /dev/null
+++ b/tests/test_release_evidence_git_metadata_timeout.py
@@ -0,0 +1,40 @@
+"""Fail-first reliability contracts for release evidence Git metadata reads."""
+
+from __future__ import annotations
+
+import importlib.util
+import subprocess
+from pathlib import Path
+
+import pytest
+
+
+def _load_release_index():
+    """Load the release evidence index builder for boundary tests."""
+    script = Path(__file__).resolve().parents[1] / "scripts" / "build_release_evidence_index.py"
+    spec = importlib.util.spec_from_file_location("build_release_evidence_index", script)
+    assert spec is not None
+    module = importlib.util.module_from_spec(spec)
+    assert spec.loader is not None
+    spec.loader.exec_module(module)
+    return module
+
+
+def test_source_commit_bounds_git_metadata_lookup(monkeypatch, tmp_path: Path) -> None:
+    """A hung ``git rev-parse`` must fail closed under a package-owned deadline."""
+    module = _load_release_index()
+    observed_timeouts: list[object] = []
+
+    def timeout_run(*args, **kwargs):
+        observed_timeouts.append(kwargs.get("timeout"))
+        raise subprocess.TimeoutExpired(
+            cmd=args[0] if args else kwargs.get("args", ["git", "rev-parse", "HEAD"]),
+            timeout=kwargs.get("timeout"),
+        )
+
+    monkeypatch.setattr(module.subprocess, "run", timeout_run)
+
+    with pytest.raises(RuntimeError, match="source commit lookup timed out"):
+        module._source_commit(tmp_path)
+
+    assert observed_timeouts == [module.GIT_METADATA_TIMEOUT_SECONDS]