fix(contexts): stabilize FileManifest identity and timestamps

shepherd/packages/contexts/src/shepherd_contexts/simple_workspace/manifest.py

@@ -14,7 +14,7 @@
 import hashlib
 import os
 from dataclasses import dataclass, field
-from datetime import datetime
+from datetime import UTC, datetime
 from pathlib import Path
 
 
@@ -84,7 +84,11 @@ class FileManifest:
     """
 
     entries: tuple[FileEntry, ...]
-    created_at: datetime = field(default_factory=datetime.now)
+    created_at: datetime = field(
+        default_factory=lambda: datetime.now(tz=UTC),
+        compare=False,
+        hash=False,
+    )
 
     # Lookup cache (built lazily, not part of equality)
     _path_index: dict[str, FileEntry] | None = field(default=None, compare=False, hash=False)

shepherd/packages/contexts/tests/unit/test_simple_workspace_content_hash.py

@@ -354,3 +354,19 @@ def test_effect_replay_verifies_changeset_appended(self, sample_manifest):
         # Verify changeset was appended
         assert len(ws_after.pending_changesets) == 1
         assert ws_after.pending_changesets[0] is changeset
+
+
+class TestFileManifestIdentity:
+    """Regression pins for the C2 fix (tz-aware, comparison-exempt created_at)."""
+
+    def test_file_manifest_equality_ignores_created_at(self):
+        """Two manifests of identical file state are equal despite distinct timestamps."""
+        entries = (FileEntry(path="f.txt", size_bytes=10, mtime_ns=1, content_hash="x" * 64),)
+        m1 = FileManifest(entries=entries)  # default_factory timestamps differ per-instance
+        m2 = FileManifest(entries=entries)
+        assert m1 == m2
+        assert hash(m1) == hash(m2)
+
+    def test_file_manifest_created_at_is_tz_aware(self):
+        m = FileManifest(entries=())
+        assert m.created_at.tzinfo is not None

shepherd/packages/meta/CHANGELOG.md

@@ -7,6 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- **File manifests now have stable snapshot identity and timezone-aware timestamps.**
+  `FileManifest.created_at` is recorded in UTC and no longer participates in
+  equality or hashing, so otherwise identical file snapshots do not compare
+  unequal merely because they were captured at different times.
+
 ## [0.3.0] - 2026-07-08
 
 ### Added