fix(validator): tolerate null proposed_label in RawValidationDecisionSchema

Mirrors the _coerce_proposed_label validator already on
ValidationDecisionSchema. The chunked-validation path (added in #126,
merged into this PR via ca08fb2) routes LLM output through
RawValidationDecisionSchema instead of the wire-loose
ValidationDecisionSchema, so the existing coercer didn't apply on
that path.

Failure mode (gemma4-e4b on the post-merge bench): model emits
``proposed_label: null`` for ``decision: keep`` decisions; pydantic
rejects the entire chunk's records with ``string_type`` errors;
DataDesigner drops the row. On a 5-note × 2-mode bench across 5
candidate models, this caused gemma4-e4b's success rate to crater
to 1/5 redact + 2/5 rewrite even though the model otherwise
delivers best-in-class quality (util 0.96 / leak 0.03 on the rows
that survived).

Tests cover null and int-typed proposed_label drift. 501 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mvansegbroeck

src/anonymizer/engine/schemas/detection.py

@@ -60,6 +60,23 @@ class RawValidationDecisionSchema(BaseModel):
     proposed_label: str = Field(default="")
     reason: str | None = None
 
+    @field_validator("proposed_label", mode="before")
+    @classmethod
+    def _coerce_proposed_label(cls, v: object) -> object:
+        """Mirror ValidationDecisionSchema._coerce_proposed_label.
+
+        Small models (gemma4-e4b on the chunked-validation path) emit
+        ``proposed_label: null`` when the decision is "keep" — pydantic
+        otherwise rejects None for the str-typed field, dropping the
+        whole record. The validator chunk schema needs the same loose
+        coercion the wire ValidationDecisionSchema already has.
+        """
+        if v is None:
+            return ""
+        if isinstance(v, (int, float, bool)):
+            return str(v)
+        return v
+
 
 class RawValidationDecisionsSchema(BaseModel):
     decisions: list[RawValidationDecisionSchema] = Field(default_factory=list)

tests/engine/test_schemas.py

@@ -126,6 +126,37 @@ def test_raw_validation_decisions_payload_from_raw_list() -> None:
     assert payload.decisions[0].decision.value == "keep"
 
 
+def test_raw_validation_decisions_coerces_null_proposed_label() -> None:
+    """gemma4-e4b on the chunked-validation path emits ``proposed_label: null``
+    for ``decision: keep``. The schema's _coerce_proposed_label normalizes
+    None to '' so the record survives instead of dropping (which lost the
+    whole row's worth of validator work, ~13–50s wall, in the pre-fix bench).
+    """
+    payload = RawValidationDecisionsSchema.from_raw(
+        {
+            "decisions": [
+                {"id": "city_3_10", "decision": "keep", "proposed_label": None, "reason": None},
+                {"id": "name_5_10", "decision": "keep", "proposed_label": None, "reason": "kept"},
+            ]
+        }
+    )
+    assert len(payload.decisions) == 2
+    assert payload.decisions[0].proposed_label == ""
+    assert payload.decisions[1].proposed_label == ""
+
+
+def test_raw_validation_decisions_coerces_int_proposed_label() -> None:
+    """Same coercer also handles int / bool drift (matches ValidationDecisionSchema)."""
+    payload = RawValidationDecisionsSchema.from_raw(
+        {
+            "decisions": [
+                {"id": "x", "decision": "keep", "proposed_label": 42, "reason": "nope"},
+            ]
+        }
+    )
+    assert payload.decisions[0].proposed_label == "42"
+
+
 def test_raw_validation_decisions_payload_from_malformed_list_returns_empty() -> None:
     payload = RawValidationDecisionsSchema.from_raw({"decisions": ["bad-item"]})
     assert payload.decisions == []