fix(consistency): preserve immutable historical binding rows

Assistant: codex
Assistant-Model: gpt-6.1-sol
Assistant-Session: 01a1468b-63fa-7710-85dc-8f2e16b3ebfa

api/services/historical_projection.py

@@ -193,3 +193,46 @@ def bound_sources(repo_root: Path, repo_slug: str):
             raise ValueError("Historical source binding changed: " + entry["path"])
         result.append((entry, data.decode("utf-8")))
     return result
+
+
+# Only the three existing full-task Cluster bindings have immutable DB rows.
+# Other historical views retain their existing compatibility behavior.
+FROZEN_CLUSTER_BINDINGS = tuple(
+    entry for entry in BINDINGS
+    if entry["repo"] == "railiance-cluster" and "tasks" in entry
+)
+
+
+def frozen_cluster_binding(binding):
+    """Validate a claimed frozen binding; unrelated requests remain ordinary."""
+    matches = [entry for entry in FROZEN_CLUSTER_BINDINGS
+               if str(binding["workplan_id"]) == entry["uuid"]
+               or (binding["repo_slug"] == "railiance-cluster"
+                   and (binding["relative_path"] == entry["path"]
+                        or binding["filename"] == Path(entry["path"]).name))]
+    if not matches:
+        return None
+    if len(matches) != 1:
+        raise ValueError("frozen historical binding is ambiguous")
+    entry = matches[0]
+    expected = {
+        "workplan_id": entry["uuid"], "repo_slug": entry["repo"],
+        "filename": Path(entry["path"]).name, "relative_path": entry["path"],
+        "archived": True, "status": "finished",
+    }
+    if any((str(binding[key]) if key == "workplan_id" else binding[key]) != value
+           for key, value in expected.items()):
+        raise ValueError("frozen historical binding metadata changed")
+    return entry
+
+
+def validate_frozen_cluster_rows(entry, parent, tasks, repo_id):
+    """Receiving requires the exact existing terminal closure, never repair."""
+    if (parent is None or str(parent.id) != entry["uuid"]
+            or repo_id is None or parent.repo_id != repo_id
+            or parent.status not in {"done", "finished", "archived", "completed"}):
+        raise ValueError("frozen historical parent missing, foreign or nonterminal")
+    local = {str(task.id): task for task in tasks if task.workplan_id == parent.id}
+    if any(task["uuid"] not in local or local[task["uuid"]].status not in {"done", "cancel"}
+           for task in entry["tasks"]):
+        raise ValueError("frozen historical task missing, foreign or nonterminal")