Un-key stage-cache rows written before the current key shape

CACHE_SHAPE_SINCE marks the last change that moved every cache key. The
run service's periodic sweep clears cache_key on rows of runs created
before it, which nothing can match any more. Their outputs stay.

backend/tests/api/routes/test_runs.py

@@ -19,7 +19,7 @@ from fluksio.core.db import engine as db_engine
 from fluksio.flow.artifacts import ArtifactStore
 from fluksio.flow.controller import FlowController
 from fluksio.flow.messages import DType, MessageSpec
-from fluksio.flow.pipeline import NodeOutcome
+from fluksio.flow.pipeline import CACHE_SHAPE_SINCE, NodeOutcome
 from fluksio.flow.runs import (
     LEASE_STALE_S,
     OUTPUT_CAP,
@@ -28,6 +28,7 @@ from fluksio.flow.runs import (
     RunService,
     _cacheable,
     new_run_id,
+    prune_stale_cache,
     resolve_references,
     seed_values,
 )
@@ -106,6 +107,38 @@ def test_what_may_be_stored_as_a_cache_entry():
     assert _cacheable(ok.model_copy(update={"output_values": big})) is None
 
 
+def test_a_row_keyed_before_the_current_shape_is_unkeyed():
+    """It matches nothing any more, but it is still the run's record."""
+    outputs = json.dumps({"study.loss": 1.0})
+    with Session(db_engine) as session:
+        for run_id, made in (
+            ("shape-old", CACHE_SHAPE_SINCE - timedelta(days=1)),
+            ("shape-new", CACHE_SHAPE_SINCE + timedelta(seconds=1)),
+        ):
+            session.add(Run(id=run_id, flow="study", status="ok", created_at=made))
+            session.add(
+                RunNode(
+                    run_id=run_id,
+                    node="study.a",
+                    cache_key=run_id,
+                    outputs=outputs,
+                )
+            )
+        session.commit()
+    try:
+        assert prune_stale_cache() == 1
+        with Session(db_engine) as session:
+            old = session.get(RunNode, ("shape-old", "study.a"))
+            new = session.get(RunNode, ("shape-new", "study.a"))
+            assert old is not None and old.cache_key == "" and old.outputs == outputs
+            assert new is not None and new.cache_key == "shape-new"
+    finally:
+        with Session(db_engine) as session:
+            for run_id in ("shape-old", "shape-new"):
+                session.delete(session.get(Run, run_id))
+            session.commit()
+
+
 # -----------------------------------------------------------------------------
 # Naming an artifact from outside the process that made it
 #