diff --git a/nanobot/runtime/coordinator.py b/nanobot/runtime/coordinator.py
index dd6d03e..4facd86 100644
--- a/nanobot/runtime/coordinator.py
+++ b/nanobot/runtime/coordinator.py
@@ -412,6 +412,24 @@ def _git_output(args: list[str], cwd: Path) -> str | None:
         return None
 
 
+def _observed_product_head_source_fingerprint(workspace: Path) -> dict[str, Any] | None:
+    current_state_path = workspace / "state" / "self_evolution" / "current_state.json"
+    payload = _safe_read_json(current_state_path)
+    if not isinstance(payload, dict):
+        return None
+    observed = payload.get("observed_product_head") if isinstance(payload.get("observed_product_head"), dict) else {}
+    commit = observed.get("commit") or payload.get("product_head")
+    if not commit:
+        return None
+    return {
+        "source_repo_root": observed.get("repo_root") or str(workspace),
+        "source_commit": commit,
+        "source_branch": observed.get("branch"),
+        "source_tree": observed.get("tree"),
+        "source_authority": "observed_product_head",
+    }
+
+
 def _runtime_source_fingerprint(workspace: Path) -> dict[str, Any]:
     env_commit = os.environ.get('NANOBOT_SOURCE_COMMIT') or os.environ.get('SOURCE_COMMIT')
     if env_commit:
@@ -431,12 +449,17 @@ def _runtime_source_fingerprint(workspace: Path) -> dict[str, Any]:
             commit = _git_output(['git', 'rev-parse', 'HEAD'], repo_root)
             branch = _git_output(['git', 'rev-parse', '--abbrev-ref', 'HEAD'], repo_root)
             tree = _git_output(['git', 'rev-parse', 'HEAD^{tree}'], repo_root)
-            return {
-                'source_repo_root': str(repo_root),
-                'source_commit': commit,
-                'source_branch': branch,
-                'source_tree': tree,
-            }
+            if commit:
+                return {
+                    'source_repo_root': str(repo_root),
+                    'source_commit': commit,
+                    'source_branch': branch,
+                    'source_tree': tree,
+                    'source_authority': 'git',
+                }
+    observed_fingerprint = _observed_product_head_source_fingerprint(workspace)
+    if observed_fingerprint:
+        return observed_fingerprint
     return {
         'source_repo_root': str(workspace),
         'source_commit': None,
diff --git a/tests/test_runtime_coordinator.py b/tests/test_runtime_coordinator.py
index 10ff599..b8a6b15 100644
--- a/tests/test_runtime_coordinator.py
+++ b/tests/test_runtime_coordinator.py
@@ -35,6 +35,28 @@ def test_runtime_source_fingerprint_prefers_explicit_release_env_for_archived_ru
     }
 
 
+def test_runtime_source_fingerprint_falls_back_to_observed_product_head_when_git_is_unavailable(tmp_path, monkeypatch):
+    state_dir = tmp_path / "state" / "self_evolution"
+    state_dir.mkdir(parents=True)
+    (state_dir / "current_state.json").write_text(json.dumps({
+        "observed_product_head": {
+            "commit": "observed-product-head-123",
+            "source": "git_rev_parse_head",
+            "repo_root": "/opt/eeepc-agent/runtimes/self-evolving-agent/current",
+        },
+        "product_head": "observed-product-head-123",
+    }), encoding="utf-8")
+    monkeypatch.delenv("NANOBOT_SOURCE_COMMIT", raising=False)
+    monkeypatch.delenv("SOURCE_COMMIT", raising=False)
+    monkeypatch.setattr("nanobot.runtime.coordinator._git_output", lambda args, cwd: None)
+
+    fingerprint = _runtime_source_fingerprint(tmp_path)
+
+    assert fingerprint["source_commit"] == "observed-product-head-123"
+    assert fingerprint["source_repo_root"] == "/opt/eeepc-agent/runtimes/self-evolving-agent/current"
+    assert fingerprint["source_authority"] == "observed_product_head"
+
+
 def test_cycle_writes_block_report_when_gate_missing(tmp_path):
     execute = AsyncMock(return_value="should not run")
     now = datetime(2026, 4, 15, 12, 0, tzinfo=timezone.utc)