fix(storage): harden source train continuity refresh

polylogue/storage/sqlite/durable_change_train.py

@@ -1126,6 +1126,10 @@ def _refresh_released_source_train_continuity_locked(
 
     _require_nonempty(operation_id, label="source mutation operation id")
     _require_nonempty(evidence_ref, label="source continuity evidence ref")
+    if pre_mutation_evidence.tier is not ArchiveTier.SOURCE:
+        raise DurableSourceContinuitySemanticError(
+            "source continuity refresh requires source-tier pre-mutation evidence"
+        )
     if not mutation_receipt.is_file() or mutation_receipt.is_symlink():
         raise DurableChangeTrainError("source mutation receipt is not a real file")
     if not backup_manifest.is_file() or backup_manifest.is_symlink():

tests/unit/storage/test_blob_ref_liveness.py

@@ -24,6 +24,7 @@
     stage_blob_ref_liveness,
 )
 from polylogue.storage.blob_store import BlobStore
+from polylogue.storage.sqlite.archive_tiers import ARCHIVE_VERSION_BY_TIER
 from polylogue.storage.sqlite.archive_tiers.bootstrap import initialize_active_archive_root
 from polylogue.storage.sqlite.archive_tiers.source_write import deterministic_blob_hash, deterministic_raw_session_id
 from polylogue.storage.sqlite.archive_tiers.types import ArchiveTier
@@ -290,10 +291,11 @@ def test_apply_refuses_a_fresh_mutation_while_continuity_recovery_is_pending(tmp
 def test_apply_refuses_an_unreleased_source_train_before_writing_a_receipt(tmp_path: Path) -> None:
     archive_root = _source_archive(tmp_path)
     manifest_root = archive_root / ".maintenance-state" / "durable-change-trains"
-    manifest_root.mkdir(parents=True)
-    manifest_root.joinpath("source-029.json").write_text(
+    manifest_root.mkdir(parents=True, exist_ok=True)
+    source_version = ARCHIVE_VERSION_BY_TIER[ArchiveTier.SOURCE]
+    manifest_root.joinpath(f"source-{source_version:03}.json").write_text(
         resources.files("polylogue.storage.sqlite.migrations.source")
-        .joinpath("029.train.json")
+        .joinpath(f"{source_version:03}.train.json")
         .read_text(encoding="utf-8"),
         encoding="utf-8",
     )

tests/unit/storage/test_durable_change_train.py

@@ -507,6 +507,15 @@ def record_refresh_fsync(path: Path) -> None:
             operation_id=_EMPTY_LIVENESS_DIGEST,
             evidence_ref="proof:mutation-1",
         )
+    with pytest.raises(DurableSourceContinuitySemanticError, match="source-tier pre-mutation evidence"):
+        refresh_released_source_train_continuity(
+            tmp_path,
+            mutation_receipt=mutation_receipt,
+            backup_manifest=backup_manifest,
+            pre_mutation_evidence=replace(before, tier=ArchiveTier.USER),
+            operation_id=_EMPTY_LIVENESS_DIGEST,
+            evidence_ref="proof:mutation-wrong-tier",
+        )
     operator_cwd = tmp_path / "operator-cwd"
     operator_cwd.mkdir()
     monkeypatch.chdir(tmp_path)