test: gate V1 side files and V3 legacy receipts; early output rejection

- analyze_jet_cv_continuation: samples are analyzed only if the sibling
  re*_s*.json receipt is the same case with run_status COMPLETE and
  source_recheck UNCHANGED; receipts without run_status (pre-recheck
  runners) are refused unless --legacy-receipts, and labelled
  LEGACY_NO_FINAL_SOURCE_RECHECK. Results carry receipt_gate.
- V3: receipts are schema 2 and need source_recheck UNCHANGED; a missing
  recheck is accepted only for frozen-mode schema 1 receipts whose
  run_case.py hash is one of the pre-recheck runners (9805383, 2cf9853,
  db3d098; hashes checked against git history in a test).
- V1/V3 refuse --output inside the checkout before source checks or CUDA
  (shared source_provenance.reject_output_inside).
- A failing recheck is recorded as RECHECK_FAILED (still invalid); the
  in-run V1 receipt write is tmp+replace.
Negative host tests for each gate. No threshold, solver or evidence edits.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/test_validation_source_provenance.py

@@ -126,5 +126,14 @@ def test_final_source_check_unchanged_changed_and_failed_recheck():
         raise RuntimeError("Source hash mismatch: src/x.py")
 
     failed = final_source_check(recorded, fails)
-    assert (failed["source_recheck"], failed["source_after"]) == ("CHANGED", None)
+    assert (failed["source_recheck"], failed["source_after"]) == ("RECHECK_FAILED", None)
     assert "Source hash mismatch" in failed["source_recheck_error"]
+
+
+def test_reject_output_inside_checkout(tmp_path):
+    from source_provenance import reject_output_inside
+
+    for output in (ROOT, ROOT / "out", ROOT / "src" / "x.json"):
+        with pytest.raises(SystemExit, match="outside the source checkout"):
+            reject_output_inside(output, ROOT)
+    reject_output_inside(tmp_path / "out", ROOT)