fix(cache): drop wall-clock timestamp from program.yaml metadata

src/registry/models.py

@@ -82,6 +82,12 @@ def mutate(
         Returns:
             A new ProgramConfig with this program as parent
         """
+        # NOTE: do NOT call .with_timestamp() here. A wall-clock timestamp
+        # on every child program would byte-change program.yaml on each
+        # iteration and bust the run-cache (which keys on the workspace's
+        # git tree SHA). Git's commit timestamp already records iteration
+        # ordering. See src/cache/run_cache.py:_get_tree_hash and the
+        # parallel comment in src/registry/sdk_utils.py.
         return ProgramConfig(
             name=name,
             parent=f"program/{self.name}",
@@ -90,4 +96,4 @@ def mutate(
             allowed_tools=allowed_tools or self.allowed_tools,
             output_format=output_format if output_format is not None else self.output_format,
             metadata=metadata or {},
-        ).with_timestamp()
+        )

src/registry/sdk_utils.py

@@ -117,7 +117,14 @@ def options_to_config(
     Returns:
         ProgramConfig ready for git storage
     """
-    base_metadata = {"created_at": datetime.now().isoformat()}
+    # NOTE: deliberately do NOT include `created_at` here. The timestamp
+    # would byte-change program.yaml on every --fresh launch, which in turn
+    # changes the workspace's git tree SHA and busts the run-cache key (see
+    # src/cache/run_cache.py:_get_tree_hash). Git's commit timestamp already
+    # records when the program was created, so the metadata field is
+    # redundant and only serves to defeat caching across re-runs of the
+    # same content.
+    base_metadata: dict[str, Any] = {}
     if metadata:
         base_metadata.update(metadata)