feat(pre-push-safety-net): scope comparison completeness and ambiguity (M1b 10.2, 10.3)

Two vetoes M1a recorded were global where the evidence is local.

Comparison required every selected base question to complete, so one unsupported
family anywhere prevented an otherwise complete target comparison. Completeness
is now demanded over the required scope: the counterpart question plus the
dependencies the change context actually recorded for it. Every other gap stays
in aggregate coverage and is still reported, never discharged. An incomplete
counterpart, an incomplete recorded dependency, an unknown-ownership boundary
and a truncated base scan all still yield unknown.

Correspondence ambiguity was recorded file-wide and inherited by every question,
so repeated unchanged lines in one file invalidated every question in the
repository and blocked the whole transaction comparison. It is now decided per
operation by the correspondence classifier: an operation needing an ambiguous
anchor stays uncomparable, while a uniquely mapped or newly introduced operation
in the same file is unaffected. The mapping is still withheld and still reported.

On the NodeGoat case the ambiguity is on the target's own file, so file-level
scoping would not have been enough; only per-operation resolution is.

1,347 tests passed, nine skipped. No capability enabled; rollout stays NO-GO.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

tests/test_model_change_context.py

@@ -169,3 +169,31 @@ def test_missing_base_without_adapter_diagnostic_stays_incomplete(tmp_path):
     )
     assert result.question_outcomes[0].status == "unresolved"
     assert "comparison_base_unavailable" in result.scope.unresolved_boundaries
+
+
+def test_correspondence_ambiguity_alone_does_not_make_every_question_incomplete(tmp_path):
+    """M1b 10.3: repeated unchanged lines in one file no longer invalidate every question."""
+    (tmp_path / "source.php").write_text("readable\n")
+    ambiguous = replace(context(), unresolved_boundaries=(b"source.php".hex() + ":ambiguous_line_correspondence",))
+    result = scan_repository(
+        tmp_path,
+        [region("source.php", "php")],
+        backend=Backend({"source.php": vector() + [row("source.php"), {"kind": "context_summary"}]}),
+        change_context=ambiguous,
+    )
+    assert result.question_outcomes[0].status == "completed"
+    # The mapping itself is still withheld and still reported in aggregate coverage.
+    assert any("ambiguous_line_correspondence" in gap for gap in result.change_context.unresolved_boundaries)
+
+
+def test_any_other_inherited_transaction_gap_still_marks_questions_incomplete(tmp_path):
+    (tmp_path / "source.php").write_text("readable\n")
+    blocked = replace(context(), unresolved_boundaries=("snapshot:lfs_blob_unavailable",))
+    result = scan_repository(
+        tmp_path,
+        [region("source.php", "php")],
+        backend=Backend({"source.php": vector() + [row("source.php"), {"kind": "context_summary"}]}),
+        change_context=blocked,
+    )
+    assert result.question_outcomes[0].status == "unresolved"
+    assert result.question_outcomes[0].reason == "change_context_incomplete"