Make transport commits independent of Git identity

Why: PR #567 CI runs without a global Git user identity, causing every successful agent transport commit to fail with exit 128.

Evidence: The focused no-identity regression plus AgentExecControllerTests and AgentExecHistoryTests pass (30 executions total); git diff --check passes.

Impact: Supplies a deterministic non-secret identity only to git commit-tree; routing, receipts, and transport validation are unchanged.

Refs: #567

scripts/agent_exec.py

@@ -47,6 +47,10 @@ EXIT_SCOPE_EXPANSION = 5
 EXIT_CANCELLED = 6
 EXIT_HOST_FALLBACK = 10
 
+# Transport commits must not depend on machine-global Git identity.
+TRANSPORT_AUTHOR_NAME = "agent-exec-transport"
+TRANSPORT_AUTHOR_EMAIL = "agent-exec-transport@localhost.invalid"
+
 DEFAULT_BRANCHES = frozenset({"main", "master"})
 SECRET_PATH_MARKERS = (
     ".secrets",
@@ -1627,6 +1631,10 @@ def _create_transport_commit(
     msg = f"agent-exec transport {run_id}/{attempt_id}"
     commit = _git(
         worktree,
+        "-c",
+        f"user.name={TRANSPORT_AUTHOR_NAME}",
+        "-c",
+        f"user.email={TRANSPORT_AUTHOR_EMAIL}",
         "commit-tree",
         tree,
         "-p",

tests/test_agent_exec.py

@@ -1685,6 +1685,38 @@ class AgentExecControllerTests(unittest.TestCase):
         self.assertEqual(launched.read_text(encoding="utf-8"), "")
         self._assert_canonical_untouched()
 
+    def test_transport_commit_does_not_require_configured_git_identity(self) -> None:
+        base_head = _git(self.repo, "rev-parse", "HEAD").stdout.strip()
+        _git(self.repo, "config", "--unset-all", "user.name")
+        _git(self.repo, "config", "--unset-all", "user.email")
+        worktree = self.root / "no-identity-worktree"
+        agent_exec._create_private_attempt_clone(self.repo, worktree, base_head)
+        (worktree / "src" / "marker.txt").write_text("ok\n", encoding="utf-8")
+
+        clean_git_env = {
+            "PATH": os.environ["PATH"],
+            "GIT_CONFIG_GLOBAL": "/dev/null",
+            "GIT_CONFIG_NOSYSTEM": "1",
+        }
+        with mock.patch.dict(os.environ, clean_git_env, clear=True):
+            ref = agent_exec._create_transport_commit(
+                repo=self.repo,
+                worktree=worktree,
+                base_head=base_head,
+                run_id="no-identity",
+                attempt_id="attempt-1",
+                inventory={"paths": ["src/marker.txt"]},
+            )
+
+        identity = _git(
+            self.repo, "log", "-1", "--format=%an <%ae>|%cn <%ce>", ref
+        ).stdout.strip()
+        expected = (
+            f"{agent_exec.TRANSPORT_AUTHOR_NAME} "
+            f"<{agent_exec.TRANSPORT_AUTHOR_EMAIL}>"
+        )
+        self.assertEqual(identity, f"{expected}|{expected}")
+
 
 class AgentExecHistoryTests(unittest.TestCase):
     def setUp(self) -> None: