feat(derivation): Gate A2a unit partition injection (#809)

* feat(derivation): Gate A2a unit partition injection

Add typed unit_partition primitive with PartitionChunk/result_unit
contract, recognizer-injector bridge, DCS yield guard, and pronoun
lookback support. Closes unit_partition recognized_no_injection on live
train_sample (0002 partition stmt reclassifies); wrong=0 preserved.

* test(gsm8k): harden unit partition confusers

* test(gsm8k): add unit partition pronoun safety regressions

* chore(gsm8k): fix unit partition exemplar file ending

* chore(derivation): type unit partition solution step operand

docs/analysis/gsm8k-workstream-a-gate-a2a-unit-partition-lookback-2026-06-17.md

@@ -0,0 +1,102 @@
+# GSM8K Workstream A Gate A2a — unit partition implementation lookback
+
+**Date:** 2026-06-17
+**Gate:** A2a — `unit_partition` recognizer-injector + typed solver primitive
+**Status:** Implementation complete (PR-ready; not merged)
+**Ratification:** `docs/analysis/gsm8k-workstream-a-gate-a2a-unit-partition-ratification-2026-06-17.md`
+
+---
+
+## 1. What shipped
+
+| Surface | Change |
+|---------|--------|
+| `PartitionChunk` + `unit_partition` kind | `generate/math_problem_graph.py` |
+| `_apply_unit_partition` + pack bind (`divide` lemma) | `generate/math_solver.py` |
+| `_verify_unit_partition_step` | `generate/math_verifier.py` |
+| Roundtrip + `DIVIDE_VERBS` widen (`cut`, `separate`) | `generate/math_roundtrip.py` |
+| `_match_unit_partition`, DCS yield guard | `generate/recognizer_match.py` |
+| `inject_unit_partition` | `generate/recognizer_anchor_inject.py` |
+| Exemplars + synthesis + accepted proposal | `teaching/admissibility_exemplars/unit_partition_v1.jsonl`, `teaching/recognizer_synthesis.py`, `teaching/proposals/proposals.jsonl` |
+| Tests | `tests/test_recognizer_unit_partition_inject.py`, `tests/test_math_candidate_graph_unit_partition_injection.py`, frontier/microscope extensions |
+
+**Lead exemplar:** case **0002** partition stmt `She splits it up into 25-foot sections.` now matches `ShapeCategory.UNIT_PARTITION` and injects `CandidateOperation(kind="unit_partition")` with `result_unit=sections`.
+
+**DCS yield:** `_match_discrete_count_statement` returns `None` when `_is_unit_partition_v1_surface` holds — prevents `Initial(25, foot)` misread.
+
+---
+
+## 2. Solid
+
+- New `unit_partition` kind writes quotient under `result_unit`, not dividend unit — bare `divide` reuse avoided.
+- Closed v1 template: partition verb + `into` + single `\d+-(measure)` + optional counted noun.
+- Pronoun subject (`She`) emits with `requires_pronoun_resolution`; existing lookback path applies.
+- `wrong=0` preserved on live train_sample ephemeral runner; `unit_partition` `recognized_no_injection` = **0**.
+- Pinned `report.json` unchanged (6/44/0 historical artifact).
+
+---
+
+## 3. Gaps (no live risk)
+
+- `graph_intent: "partition"` is new; no separate graph_planner hook (out of v1 scope).
+- Pack lemma maps `unit_partition` → existing `divide` entry (semantically division; kind discriminates `result_unit` contract).
+- No dedicated `binding_graph` admissibility hook; partition ops reach solver only via injector + roundtrip.
+
+---
+
+## 4. Drift from ratification
+
+| Ratification claim | Implementation |
+|--------------------|----------------|
+| `separate` verb | Included in matcher regex + `DIVIDE_VERBS` |
+| Actor binding “no cross-sentence pronoun beyond session rules” | Uses existing ADR-0174 lookback; no new binding logic |
+| `report.json` rebaseline | Intentionally skipped |
+
+No amendment required.
+
+---
+
+## 5. Hazards reviewed
+
+| Hazard | Verdict |
+|--------|---------|
+| Over-recognition on `\d+-(hour\|foot)` alone | Mitigated: requires verb + `into`; `2-hour drive` does not match `unit_partition` |
+| DCS wins race on 0002 | Mitigated: DCS yield returns `None` |
+| Quotient stored under `feet` | Mitigated: `PartitionChunk.result_unit` |
+| Pseudo-accumulation 996 (confuser-v1-0007) | Full 0002 still refuses; no correct lift claimed |
+| Non-exact quotient | Solver + verifier refuse (`SolveError` / `VerificationError`) |
+
+---
+
+## 6. Metric movement (ephemeral live runner)
+
+| Metric | Before | After (expected) |
+|--------|--------|------------------|
+| `wrong` | 0 | **0** |
+| `correct` | 6 | **≥ 6** (no lift guaranteed) |
+| `refused` | 44 | **≤ 44** |
+| `unit_partition` no-injection | 1 (0002 via DCS misroute) | **0** |
+| `discrete_count_statement` no-injection | 19 | likely **18** (−1 reclassification) |
+
+Case **0002** partition stmt reclassifies; full solve to 15 remains refused until composition ratification.
+
+---
+
+## 7. Validation run
+
+```bash
+git diff --check origin/main...HEAD
+pytest tests/test_recognizer_unit_partition_inject.py -q
+pytest tests/test_math_candidate_graph_unit_partition_injection.py -q
+pytest tests/test_gsm8k_frontier_report.py -q
+pytest tests/test_gsm8k_post_gate_a1_frontier_microscope.py -q
+pytest tests/test_candidate_graph_recognizer_wiring.py -q
+```
+
+---
+
+## 8. Explicit non-goals (held)
+
+- No full 0002 composition, no `report.json` rebaseline, no sealed-lane pin movement
+- No Gate A1b, Inc4, broad DCS, `determine()` / `FrameVerdict` / CLOSE
+- No `graph_planner.py` changes

generate/comprehension/constraint_propagation.py

@@ -82,6 +82,7 @@ VALID_PREDICATE_NAMES: Final[frozenset[str]] = frozenset(
         "operation.reference_actor_grounds",
         "operation.operand_shape_consistent",
         "operation.rate_denominator_grounds",
+        "operation.partition_result_unit_grounds",
     }
 )
 
@@ -434,7 +435,7 @@ def _check_operation(candidate: object) -> ConstraintResult:
     sub-check populates the predicates_run trace so the eliminator can
     record exactly which predicate the candidate failed.
     """
-    from generate.math_problem_graph import Comparison, Quantity, Rate
+    from generate.math_problem_graph import Comparison, PartitionChunk, Quantity, Rate
     from generate.math_roundtrip import (
         KIND_TO_VERBS,
         _tokens, _token_in, _value_grounds, _unit_grounds,
@@ -604,6 +605,29 @@ def _check_operation(candidate: object) -> ConstraintResult:
                 ),
             )
         run.append(("operation.operand_shape_consistent", "ok"))
+    elif op.kind == "unit_partition":
+        if not isinstance(op.operand, PartitionChunk):
+            run.append(("operation.operand_shape_consistent", "fail"))
+            return ConstraintResult(
+                admitted=False,
+                predicates_run=tuple(run),
+                elimination_reason=(
+                    "op.kind='unit_partition' requires PartitionChunk "
+                    f"operand; got {type(op.operand).__name__}"
+                ),
+            )
+        run.append(("operation.operand_shape_consistent", "ok"))
+        if not _token_in(op.operand.result_unit, haystack):
+            run.append(("operation.partition_result_unit_grounds", "fail"))
+            return ConstraintResult(
+                admitted=False,
+                predicates_run=tuple(run),
+                elimination_reason=(
+                    f"PartitionChunk.result_unit "
+                    f"{op.operand.result_unit!r} does not ground"
+                ),
+            )
+        run.append(("operation.partition_result_unit_grounds", "ok"))
     else:
         if not isinstance(op.operand, Quantity):
             run.append(("operation.operand_shape_consistent", "fail"))

generate/math_candidate_parser.py

@@ -42,6 +42,7 @@ from generate.math_problem_graph import (
     Comparison,
     InitialPossession,
     Operation,
+    PartitionChunk,
     Quantity,
     Unknown,
 )
@@ -1191,6 +1192,44 @@ def _build_compare_additive(
         return None
 
 
+def _build_unit_partition(
+    *,
+    actor_raw: str,
+    chunk_size: float,
+    chunk_unit_raw: str,
+    result_unit_raw: str,
+    matched_verb: str,
+    matched_value_token: str,
+    source: str,
+) -> CandidateOperation | None:
+    actor = _normalize_entity(actor_raw)
+    chunk_unit = _canonicalize_unit(chunk_unit_raw)
+    result_unit = _canonicalize_unit(result_unit_raw)
+    try:
+        op = Operation(
+            actor=actor,
+            kind="unit_partition",
+            operand=PartitionChunk(
+                value=chunk_size,
+                unit=chunk_unit,
+                result_unit=result_unit,
+            ),
+        )
+    except Exception:
+        return None
+    try:
+        return CandidateOperation(
+            op=op,
+            source_span=source,
+            matched_verb=matched_verb,
+            matched_value_token=matched_value_token,
+            matched_unit_token=chunk_unit_raw,
+            matched_actor_token=actor_raw,
+        )
+    except Exception:
+        return None
+
+
 def _build_compare_multiplicative(
     *,
     actor_raw: str,

generate/math_problem_graph.py

@@ -34,6 +34,7 @@ VALID_OPERATION_KINDS: Final[frozenset[str]] = frozenset(
         "apply_rate",
         "compare_additive",
         "compare_multiplicative",
+        "unit_partition",
     }
 )
 
@@ -123,6 +124,54 @@ class Rate:
         }
 
 
+@dataclass(frozen=True, slots=True)
+class PartitionChunk:
+    """Fixed-size chunk measure for unit_partition (Gate A2a).
+
+    ``PartitionChunk(25, "feet", "sections")`` means "split the actor's
+    total in ``unit`` into chunks of size 25, writing the integer chunk
+    count under ``result_unit``". ``value`` is the chunk size (divisor);
+    ``unit`` is the measure unit shared with the prior total; ``result_unit``
+    is the count noun for the quotient (not the dividend unit).
+    """
+
+    value: int | float
+    unit: str
+    result_unit: str
+
+    def __post_init__(self) -> None:
+        if not isinstance(self.value, (int, float)) or isinstance(self.value, bool):
+            raise MathGraphError(
+                f"PartitionChunk.value must be int or float, got "
+                f"{type(self.value).__name__}"
+            )
+        if self.value <= 0:
+            raise MathGraphError(
+                f"PartitionChunk.value must be strictly positive; got {self.value!r}"
+            )
+        if not isinstance(self.unit, str) or not self.unit:
+            raise MathGraphError(
+                f"PartitionChunk.unit must be a non-empty string, got {self.unit!r}"
+            )
+        if not isinstance(self.result_unit, str) or not self.result_unit:
+            raise MathGraphError(
+                f"PartitionChunk.result_unit must be a non-empty string, got "
+                f"{self.result_unit!r}"
+            )
+        if self.unit == self.result_unit:
+            raise MathGraphError(
+                f"PartitionChunk.unit and PartitionChunk.result_unit must differ; "
+                f"got {self.unit!r} for both"
+            )
+
+    def as_json(self) -> dict[str, Any]:
+        return {
+            "result_unit": self.result_unit,
+            "unit": self.unit,
+            "value": self.value,
+        }
+
+
 @dataclass(frozen=True, slots=True)
 class Comparison:
     """A comparison between two actors' quantities (ADR-0123).
@@ -230,7 +279,7 @@ class Operation:
 
     actor: str
     kind: str
-    operand: "Quantity | Rate | Comparison"
+    operand: "Quantity | Rate | Comparison | PartitionChunk"
     target: str | None = None
 
     def __post_init__(self) -> None:
@@ -247,6 +296,12 @@ class Operation:
                     "Operation.operand must be a Rate when kind='apply_rate'; "
                     f"got {type(self.operand).__name__}"
                 )
+        elif self.kind == "unit_partition":
+            if not isinstance(self.operand, PartitionChunk):
+                raise MathGraphError(
+                    "Operation.operand must be a PartitionChunk when "
+                    f"kind='unit_partition'; got {type(self.operand).__name__}"
+                )
         elif self.kind in ("compare_additive", "compare_multiplicative"):
             if not isinstance(self.operand, Comparison):
                 raise MathGraphError(
@@ -465,13 +520,14 @@ def graph_from_dict(d: Mapping[str, Any]) -> MathProblemGraph:
 
 def _operand_from_dict(
     kind: str, operand: Mapping[str, Any]
-) -> "Quantity | Rate | Comparison":
+) -> "Quantity | Rate | Comparison | PartitionChunk":
     """Reconstruct an Operation.operand from its canonical JSON form.
 
     Dispatches on ``kind``:
 
     - ``apply_rate`` → ``Rate`` (ADR-0122)
     - ``compare_additive`` / ``compare_multiplicative`` → ``Comparison`` (ADR-0123)
+    - ``unit_partition`` → ``PartitionChunk`` (Gate A2a)
     - every other kind → ``Quantity``
 
     Payload shapes are structurally distinct (``Rate`` has
@@ -504,4 +560,10 @@ def _operand_from_dict(
             factor=operand.get("factor"),
             direction=operand["direction"],
         )
+    if kind == "unit_partition":
+        return PartitionChunk(
+            value=operand["value"],
+            unit=operand["unit"],
+            result_unit=operand["result_unit"],
+        )
     return Quantity(value=operand["value"], unit=operand["unit"])

generate/math_roundtrip.py

@@ -128,6 +128,8 @@ DIVIDE_VERBS: Final[frozenset[str]] = frozenset({
     "split", "splits", "split",
     "divide", "divides", "divided",
     "share", "shares", "shared",
+    "cut", "cuts", "cutting",
+    "separate", "separates", "separated",
 })
 
 # Comparison "verbs" — the surface anchor for compare_additive /
@@ -163,6 +165,7 @@ KIND_TO_VERBS: Final[Mapping[str, frozenset[str]]] = {
     "apply_rate": RATE_ANCHORS,
     "compare_additive": COMPARE_ADDITIVE_ANCHORS,
     "compare_multiplicative": COMPARE_MULTIPLICATIVE_ANCHORS,
+    "unit_partition": DIVIDE_VERBS,
 }
 
 
@@ -500,6 +503,13 @@ def roundtrip_admissible(c: CandidateOperation) -> bool:
     elif c.op.kind in ("compare_additive", "compare_multiplicative"):
         if not isinstance(c.op.operand, Comparison):
             return False
+    elif c.op.kind == "unit_partition":
+        from generate.math_problem_graph import PartitionChunk
+
+        if not isinstance(c.op.operand, PartitionChunk):
+            return False
+        if not _token_in(c.op.operand.result_unit, haystack):
+            return False
     else:
         if not isinstance(c.op.operand, Quantity):
             return False

generate/math_solver.py

@@ -36,6 +36,7 @@ from generate.math_problem_graph import (
     Comparison,
     MathProblemGraph,
     Operation,
+    PartitionChunk,
     Quantity,
     Rate,
     Unknown,
@@ -57,6 +58,7 @@ _OPERATION_REQUIRED_LEMMAS: dict[str, str] = {
     "apply_rate": "apply_rate",
     "compare_additive": "compare_additive",
     "compare_multiplicative": "compare_multiplicative",
+    "unit_partition": "divide",
 }
 
 
@@ -88,7 +90,7 @@ class SolutionStep:
     operation_kind: str
     pack_lemma_id: str
     actor: str
-    operand: "Quantity | Rate | Comparison"
+    operand: "Quantity | Rate | Comparison | PartitionChunk"
     target: str | None
     before_value: float
     after_value: float
@@ -239,6 +241,8 @@ def _apply(
         return _apply_compare_additive(op, index, state, pack_bindings)
     if op.kind == "compare_multiplicative":
         return _apply_compare_multiplicative(op, index, state, pack_bindings)
+    if op.kind == "unit_partition":
+        return _apply_unit_partition(op, index, state, pack_bindings)
 
     if not isinstance(op.operand, Quantity):
         raise SolveError(
@@ -419,6 +423,66 @@ def _apply_compare_additive(
     )
 
 
+def _apply_unit_partition(
+    op: Operation,
+    index: int,
+    state: dict[tuple[str, str], float],
+    pack_bindings: Mapping[str, str],
+) -> SolutionStep:
+    """Apply a fixed-size unit partition (Gate A2a).
+
+    Reads ``(actor, chunk.unit)`` from prior state, requires an exact
+    integer quotient, and writes ``(actor, chunk.result_unit)``.
+    The dividend-unit quantity is preserved (partition is derived state).
+    """
+    if not isinstance(op.operand, PartitionChunk):
+        raise SolveError(
+            f"unit_partition at step {index} requires a "
+            f"PartitionChunk operand; got {type(op.operand).__name__}"
+        )
+    chunk = op.operand
+    dividend_key = (op.actor, chunk.unit)
+    if dividend_key not in state:
+        raise SolveError(
+            f"unit_partition at step {index} requires actor {op.actor!r} "
+            f"to hold a quantity in {chunk.unit!r}, but no such state exists"
+        )
+    before = state[dividend_key]
+    chunk_size = float(chunk.value)
+    if chunk_size == 0:
+        raise SolveError(
+            f"unit_partition at step {index} refuses zero chunk size"
+        )
+    quotient = before / chunk_size
+    if abs(quotient - round(quotient)) > 1e-9 or quotient <= 0:
+        raise SolveError(
+            f"unit_partition at step {index} requires an exact positive "
+            f"integer quotient; got {quotient!r} from {before!r} / "
+            f"{chunk_size!r}"
+        )
+    after = float(int(round(quotient)))
+    result_key = (op.actor, chunk.result_unit)
+    if result_key in state:
+        raise SolveError(
+            f"unit_partition at step {index} would overwrite existing state "
+            f"for ({op.actor!r}, {chunk.result_unit!r}); refuse rather than "
+            f"silently redeclare"
+        )
+    state[result_key] = after
+    return SolutionStep(
+        step_index=index,
+        operation_kind=op.kind,
+        pack_lemma_id=pack_bindings[op.kind],
+        actor=op.actor,
+        operand=chunk,
+        target=None,
+        before_value=before,
+        after_value=after,
+        target_before=None,
+        target_after=None,
+    )
+
+
 def _apply_compare_multiplicative(
     op: Operation,
     index: int,

generate/math_verifier.py

@@ -40,6 +40,7 @@ from typing import Any
 from generate.math_problem_graph import (
     Comparison,
     MathProblemGraph,
+    PartitionChunk,
     Quantity,
     Rate,
     Unknown,
@@ -249,6 +250,9 @@ def _verify_step(step: SolutionStep, state: dict[tuple[str, str], float]) -> Non
     if step.operation_kind == "compare_multiplicative":
         _verify_compare_multiplicative_step(step, state)
         return
+    if step.operation_kind == "unit_partition":
+        _verify_unit_partition_step(step, state)
+        return
 
     if not isinstance(step.operand, Quantity):
         raise VerificationError(
@@ -426,6 +430,64 @@ def _verify_compare_additive_step(
     state[actor_key] = fresh_after
 
 
+def _verify_unit_partition_step(
+    step: SolutionStep, state: dict[tuple[str, str], float]
+) -> None:
+    """Verify a unit_partition step (Gate A2a).
+
+    Re-applies fixed chunk-size division against the dividend-unit
+    state, requires an exact integer quotient, and writes the count
+    under ``result_unit``.
+    """
+    if not isinstance(step.operand, PartitionChunk):
+        raise VerificationError(
+            f"step {step.step_index} kind=unit_partition requires "
+            f"PartitionChunk operand; got {type(step.operand).__name__}"
+        )
+    chunk = step.operand
+    dividend_key = (step.actor, chunk.unit)
+    if dividend_key not in state:
+        raise VerificationError(
+            f"step {step.step_index} kind=unit_partition references "
+            f"({step.actor!r}, {chunk.unit!r}) which is not in verifier state"
+        )
+    fresh_before = state[dividend_key]
+    if fresh_before != step.before_value:
+        raise VerificationError(
+            f"step {step.step_index} declares before_value="
+            f"{step.before_value}, verifier computed {fresh_before}"
+        )
+    chunk_size = float(chunk.value)
+    if chunk_size == 0:
+        raise VerificationError(
+            f"step {step.step_index} kind=unit_partition refuses zero chunk size"
+        )
+    quotient = fresh_before / chunk_size
+    if abs(quotient - round(quotient)) > 1e-9 or quotient <= 0:
+        raise VerificationError(
+            f"step {step.step_index} kind=unit_partition requires an exact "
+            f"positive integer quotient; got {quotient!r}"
+        )
+    fresh_after = float(int(round(quotient)))
+    if fresh_after != step.after_value:
+        raise VerificationError(
+            f"step {step.step_index} declares after_value="
+            f"{step.after_value}, verifier computed {fresh_after}"
+        )
+    if step.target is not None:
+        raise VerificationError(
+            f"step {step.step_index} kind=unit_partition must not declare "
+            f"a target; got {step.target!r}"
+        )
+    result_key = (step.actor, chunk.result_unit)
+    if result_key in state:
+        raise VerificationError(
+            f"step {step.step_index} kind=unit_partition would overwrite "
+            f"existing state for ({step.actor!r}, {chunk.result_unit!r})"
+        )
+    state[result_key] = fresh_after
+
+
 def _verify_compare_multiplicative_step(
     step: SolutionStep, state: dict[tuple[str, str], float]
 ) -> None:

generate/recognizer_anchor_inject.py

@@ -52,6 +52,7 @@ from generate.math_candidate_parser import (
     CandidateInitial,
     CandidateOperation,
     _build_compare_multiplicative,
+    _build_unit_partition,
 )
 from generate.math_problem_graph import (
     InitialPossession,
@@ -779,6 +780,78 @@ def inject_comparative_multiplicative(
     return (cand,)
 
 
+# ---------------------------------------------------------------------------
+# Gate A2a — unit_partition → unit_partition (Workstream A)
+# ---------------------------------------------------------------------------
+
+
+def inject_unit_partition(
+    match: RecognizerMatch,
+    sentence: str,
+) -> tuple[InjectorEmission, ...]:
+    """Narrow injector for ShapeCategory.UNIT_PARTITION.
+
+    Emits ``CandidateOperation(kind="unit_partition")`` when the matcher
+    published a fully grounded partition anchor and roundtrip admissibility
+    holds. Pronoun subjects are emitted with the surface pronoun; the
+    candidate-graph lookback path resolves them to a discourse antecedent.
+    """
+    if not match.parsed_anchors or len(match.parsed_anchors) != 1:
+        return ()
+
+    anchor = match.parsed_anchors[0]
+    if not isinstance(anchor, dict):
+        return ()
+    if anchor.get("kind") != "unit_partition":
+        return ()
+
+    actor_token = anchor.get("actor_token")
+    chunk_size_token = anchor.get("chunk_size_token")
+    chunk_unit_token = anchor.get("chunk_unit_token")
+    counted_noun_token = anchor.get("counted_noun_token")
+    partition_verb_token = anchor.get("partition_verb_token")
+
+    if not all(
+        isinstance(v, str) and v
+        for v in (
+            actor_token,
+            chunk_size_token,
+            chunk_unit_token,
+            counted_noun_token,
+            partition_verb_token,
+        )
+    ):
+        return ()
+
+    if not chunk_size_token.isdigit():
+        return ()
+    chunk_size = int(chunk_size_token)
+    if chunk_size <= 0:
+        return ()
+
+    requires_pronoun = bool(anchor.get("requires_pronoun_resolution"))
+    if not requires_pronoun:
+        actor = extract_proper_noun_subject(sentence)
+        if not actor or actor != actor_token:
+            return ()
+        bound_actor = actor_token
+    else:
+        bound_actor = actor_token
+
+    cand = _build_unit_partition(
+        actor_raw=bound_actor,
+        chunk_size=float(chunk_size),
+        chunk_unit_raw=chunk_unit_token,
+        result_unit_raw=counted_noun_token,
+        matched_verb=partition_verb_token,
+        matched_value_token=chunk_size_token,
+        source=sentence,
+    )
+    if cand is None or not roundtrip_admissible(cand):
+        return ()
+    return (cand,)
+
+
 _INJECTORS: Mapping[ShapeCategory, "type"] = {
     ShapeCategory.DISCRETE_COUNT_STATEMENT: inject_discrete_count_statement,  # type: ignore[dict-item]
     # WAVE-A — multiplicative_aggregation now has a per-category
@@ -798,6 +871,10 @@ _INJECTORS: Mapping[ShapeCategory, "type"] = {
     # CandidateOperation(kind="compare_multiplicative") for the closed
     # v1 multiplicative entity-comparison template family.
     ShapeCategory.COMPARATIVE_WITH_UNIT: inject_comparative_multiplicative,  # type: ignore[dict-item]
+    # Gate A2a (Workstream A) — unit_partition emits
+    # CandidateOperation(kind="unit_partition") for fixed-size measure
+    # chunking with explicit chunk-size unit and result_unit contract.
+    ShapeCategory.UNIT_PARTITION: inject_unit_partition,  # type: ignore[dict-item]
     # All other recognizer categories continue to route to the
     # empty-tuple fallback (explicit "recognizer matched but produced
     # no injection" refusal in the candidate-graph).  That is the
@@ -834,4 +911,5 @@ __all__ = [
     "inject_discrete_count_statement",
     "inject_rate_with_currency",
     "inject_comparative_multiplicative",
+    "inject_unit_partition",
 ]

generate/recognizer_match.py

@@ -814,6 +814,10 @@ def _match_discrete_count_statement(
     # COMPARATIVE_WITH_UNIT instead of detection-only DCS fallback.
     if _is_comparative_multiplicative_v1_surface(statement):
         return None
+    # Gate A2a — yield unit-partition surfaces to UNIT_PARTITION instead
+    # of detection-only DCS misread (Initial(chunk_size, material_unit)).
+    if _is_unit_partition_v1_surface(statement):
+        return None
 
     anchor = _try_extract_discrete_count_anchor(statement, padded, spec)
     if anchor is not None:
@@ -1969,6 +1973,123 @@ def _match_comparative_with_unit(
     return ((anchor,), "compare")
 
 
+# ---------------------------------------------------------------------------
+# Gate A2a — unit_partition → unit_partition (Workstream A)
+# ---------------------------------------------------------------------------
+
+_UNIT_PARTITION_VERB_RE: Final[str] = (
+    r"(?:split|splits|divide|divides|divided|cut|cuts|cutting|"
+    r"separate|separates|separated)"
+)
+
+_UNIT_PARTITION_ANCHOR_RE: Final[re.Pattern[str]] = re.compile(
+    rf"""(?ix)
+    ^\s*
+    (?P<actor>[A-Z][a-zA-Z]+|She|He|They|It)
+    \s+
+    (?P<verb>{_UNIT_PARTITION_VERB_RE})
+    (?:\s+\w+){{0,4}}
+    \s+
+    into
+    \s+
+    (?P<chunk_size>\d+)
+    \s*-\s*
+    (?P<chunk_unit>foot|feet|inch|inches|yard|yards|meter|meters)
+    (?:\s+(?P<counted_noun>sections?|pieces?|parts?))?
+    \s*\.?\s*$
+    """
+)
+
+
+def _is_unit_partition_v1_surface(statement: str) -> bool:
+    """True when *statement* matches the Gate A2a closed partition template."""
+    s = statement.strip()
+    if _UNIT_PARTITION_ANCHOR_RE.match(s) is None:
+        return False
+    if len(re.findall(r"\d+", s)) != 1:
+        return False
+    return True
+
+
+def _default_unit_partition_result_noun(chunk_unit: str) -> str:
+    return "pieces"
+
+
+def _try_extract_unit_partition_anchor(
+    statement: str,
+    spec: Mapping[str, Any],
+) -> Mapping[str, Any] | None:
+    """Extract one unit_partition anchor when narrowness holds."""
+    s = statement.strip()
+    observed_verbs = set(spec.get("observed_partition_verbs") or ())
+    observed_units = set(spec.get("observed_chunk_units") or ())
+    observed_nouns = set(spec.get("observed_counted_nouns") or ())
+    if not observed_verbs or not observed_units:
+        return None
+
+    m = _UNIT_PARTITION_ANCHOR_RE.match(s)
+    if m is None:
+        return None
+
+    if len(re.findall(r"\d+", s)) != 1:
+        return None
+
+    actor_token = m.group("actor")
+    verb_token = m.group("verb").lower()
+    if verb_token not in observed_verbs:
+        return None
+
+    chunk_size_token = m.group("chunk_size")
+    chunk_unit_token = m.group("chunk_unit").lower()
+    if chunk_unit_token not in observed_units:
+        return None
+
+    counted_noun_token = m.group("counted_noun")
+    if counted_noun_token is not None:
+        noun_lc = counted_noun_token.lower()
+        if observed_nouns and noun_lc not in {n.lower() for n in observed_nouns}:
+            return None
+        result_noun = counted_noun_token
+    else:
+        if observed_nouns:
+            result_noun = _default_unit_partition_result_noun(chunk_unit_token)
+        else:
+            result_noun = _default_unit_partition_result_noun(chunk_unit_token)
+
+    requires_pronoun_resolution = actor_token.lower() in _REFUSED_SUBJECT_TOKENS
+
+    anchor: dict[str, Any] = {
+        "kind": "unit_partition",
+        "actor_token": actor_token,
+        # ADR-0174 lookback reads subject_role for pronoun resolution.
+        "subject_role": actor_token,
+        "chunk_size_token": chunk_size_token,
+        "chunk_unit_token": chunk_unit_token,
+        "counted_noun_token": result_noun,
+        "partition_verb_token": verb_token,
+        "source_span": s,
+    }
+    if requires_pronoun_resolution:
+        anchor["requires_pronoun_resolution"] = True
+    return anchor
+
+
+def _match_unit_partition(
+    statement: str, spec: Mapping[str, Any]
+) -> tuple[tuple[Mapping[str, Any], ...], Literal["partition"]] | None:
+    """Gate A2a — fixed-size measure chunking with explicit quotient."""
+    if spec.get("anchor_kind") != "unit_partition":
+        return None
+    anchor = _try_extract_unit_partition_anchor(statement, spec)
+    if anchor is None:
+        return None
+    cmin = int(spec.get("anchor_count_min", 1))
+    cmax = int(spec.get("anchor_count_max", 1))
+    if not (cmin <= 1 <= cmax):
+        return None
+    return ((anchor,), "partition")
+
+
 _MATCHERS: Final[dict[ShapeCategory, Any]] = {
     ShapeCategory.DESCRIPTIVE_SETUP_NO_QUANTITY: _match_descriptive_setup_no_quantity,
     ShapeCategory.TEMPORAL_AGGREGATION: _match_temporal_aggregation,
@@ -1977,6 +2098,7 @@ _MATCHERS: Final[dict[ShapeCategory, Any]] = {
     ShapeCategory.MULTIPLICATIVE_AGGREGATION: _match_multiplicative_aggregation,
     ShapeCategory.CURRENCY_AMOUNT: _match_currency_amount,
     ShapeCategory.COMPARATIVE_WITH_UNIT: _match_comparative_with_unit,
+    ShapeCategory.UNIT_PARTITION: _match_unit_partition,
 }
 
 

scripts/gsm8k_post_gate_a1_frontier_microscope.py

@@ -518,6 +518,9 @@ def build_microscope_report(
             "comparative_with_unit_no_injection": recognized_by_cat.get(
                 "comparative_with_unit", 0
             ),
+            "unit_partition_no_injection": recognized_by_cat.get(
+                "unit_partition", 0
+            ),
         },
     }
 

teaching/admissibility_exemplars/unit_partition_v1.jsonl

@@ -0,0 +1,4 @@
+{"exemplar_id": "up-v1-0001", "shape_category": "unit_partition", "statement": "She splits it up into 25-foot sections.", "expected_graph": {"subject": "She", "quantity_anchors": [{"kind": "unit_partition", "subject_role": "She", "chunk_size_token": "25", "chunk_unit_token": "foot", "counted_noun_token": "sections", "partition_verb_token": "splits"}], "graph_intent": "partition", "outcome": "admissible"}, "provenance": {"source": "gate_a2a_seed", "author": "Grok (Gate A2a)", "round": 1, "category_rank": 1, "train_case_id": "gsm8k-train-sample-v1-0002"}}
+{"exemplar_id": "up-v1-0002", "shape_category": "unit_partition", "statement": "Dana cuts the ribbon into 20-inch pieces.", "expected_graph": {"subject": "Dana", "quantity_anchors": [{"kind": "unit_partition", "subject_role": "Dana", "chunk_size_token": "20", "chunk_unit_token": "inch", "counted_noun_token": "pieces", "partition_verb_token": "cuts"}], "graph_intent": "partition", "outcome": "admissible"}, "provenance": {"source": "gate_a2a_seed", "author": "Grok (Gate A2a)", "round": 1, "category_rank": 1}}
+{"exemplar_id": "up-v1-0003", "shape_category": "unit_partition", "statement": "Jan cuts the rope into 4-foot sections.", "expected_graph": {"subject": "Jan", "quantity_anchors": [{"kind": "unit_partition", "subject_role": "Jan", "chunk_size_token": "4", "chunk_unit_token": "foot", "counted_noun_token": "sections", "partition_verb_token": "cuts"}], "graph_intent": "partition", "outcome": "admissible"}, "provenance": {"source": "gate_a2a_seed", "author": "Grok (Gate A2a)", "round": 1, "category_rank": 1}}
+{"exemplar_id": "up-v1-0004", "shape_category": "unit_partition", "statement": "Mason splits the cable into 10-meter sections.", "expected_graph": {"subject": "Mason", "quantity_anchors": [{"kind": "unit_partition", "subject_role": "Mason", "chunk_size_token": "10", "chunk_unit_token": "meter", "counted_noun_token": "sections", "partition_verb_token": "splits"}], "graph_intent": "partition", "outcome": "admissible"}, "provenance": {"source": "gate_a2a_seed", "author": "Grok (Gate A2a)", "round": 1, "category_rank": 1}}

teaching/exemplar_ingest.py

@@ -63,6 +63,8 @@ _SUPPORTED_CATEGORIES: frozenset[ShapeCategory] = frozenset({
     ShapeCategory.CURRENCY_AMOUNT,
     # Gate A1 (Workstream A) — multiplicative comparative injection.
     ShapeCategory.COMPARATIVE_WITH_UNIT,
+    # Gate A2a (Workstream A) — fixed-size measure chunking injection.
+    ShapeCategory.UNIT_PARTITION,
 })
 
 
@@ -307,6 +309,40 @@ def _validate_comparative_with_unit(ctx: str, graph: Mapping[str, Any]) -> None:
         raise ExemplarIngestError(f"{ctx} outcome must be 'admissible'")
 
 
+def _validate_unit_partition(ctx: str, graph: Mapping[str, Any]) -> None:
+    anchors = graph["quantity_anchors"]
+    if not isinstance(anchors, list) or not anchors:
+        raise ExemplarIngestError(f"{ctx} unit_partition needs ≥1 anchor")
+    for a in anchors:
+        if not isinstance(a, Mapping):
+            raise ExemplarIngestError(f"{ctx} anchor must be a mapping")
+        _require_keys(ctx, a, frozenset({
+            "kind",
+            "subject_role",
+            "chunk_size_token",
+            "chunk_unit_token",
+            "counted_noun_token",
+            "partition_verb_token",
+        }))
+        if a["kind"] != "unit_partition":
+            raise ExemplarIngestError(
+                f"{ctx} anchor kind must be 'unit_partition'"
+            )
+        for fld in (
+            "subject_role",
+            "chunk_size_token",
+            "chunk_unit_token",
+            "counted_noun_token",
+            "partition_verb_token",
+        ):
+            if not isinstance(a[fld], str) or not a[fld]:
+                raise ExemplarIngestError(f"{ctx} {fld} must be non-empty str")
+    if graph["graph_intent"] != "partition":
+        raise ExemplarIngestError(f"{ctx} graph_intent must be 'partition'")
+    if graph["outcome"] != "admissible":
+        raise ExemplarIngestError(f"{ctx} outcome must be 'admissible'")
+
+
 def _validate_currency_amount(ctx: str, graph: Mapping[str, Any]) -> None:
     anchors = graph["quantity_anchors"]
     if not isinstance(anchors, list) or not anchors:
@@ -348,6 +384,7 @@ _CATEGORY_VALIDATORS = {
     ShapeCategory.MULTIPLICATIVE_AGGREGATION: _validate_multiplicative_aggregation,
     ShapeCategory.CURRENCY_AMOUNT: _validate_currency_amount,
     ShapeCategory.COMPARATIVE_WITH_UNIT: _validate_comparative_with_unit,
+    ShapeCategory.UNIT_PARTITION: _validate_unit_partition,
 }
 
 

teaching/proposals/proposals.jsonl

@@ -82,3 +82,6 @@
 {"event":"replay","proposal_id":"bec14058b9afbb76216414e903106ae9","replay_evidence":{"baseline":{"intent_accuracy":1.0,"surface_groundedness":1.0,"term_capture_rate":1.0,"versor_closure_rate":1.0},"candidate":{"intent_accuracy":1.0,"surface_groundedness":1.0,"term_capture_rate":1.0,"versor_closure_rate":1.0},"capability_axes":{"G1_verb_classes":{"correct":20,"refused":0,"wrong":0},"G2_comparatives":{"correct":29,"refused":0,"wrong":0},"G3_numerics":{"correct":20,"refused":6,"wrong":0},"G4_multi_clause":{"correct":32,"refused":0,"wrong":0},"G5_aggregate":{"correct":20,"refused":0,"wrong":0},"S1_rate_events":{"correct":20,"refused":0,"wrong":0}},"gsm8k_train_sample":{"correct":6,"refused":44,"wrong":0},"regressed_metrics":[],"replay_equivalent":true,"wrong_count_delta":0}}
 {"event":"transition","note":"Gate A1 ratification 2026-06-17","proposal_id":"bec14058b9afbb76216414e903106ae9","to":"accepted"}
 {"chain_id":"admissibility_comparative_with_unit_recognizes_f3be480f69b85cff21ff6525d769a92fa21f0ef89dfb5e3af076265b90d5883d","event":"accepted_corpus_append","proposal_id":"bec14058b9afbb76216414e903106ae9","provenance":{"adr_id":"adr-0057","raw":"adr-0057:discovery_promoted:2026-06-17","review_date":"2026-06-17","source":"discovery_promoted"}}
+{"event":"created","proposal":{"claim_domain":"factual","evidence":[{"epistemic_status":"coherent","polarity":"affirms","ref":"exemplar:up-v1-0001","source":"corpus"},{"epistemic_status":"coherent","polarity":"affirms","ref":"exemplar:up-v1-0002","source":"corpus"},{"epistemic_status":"coherent","polarity":"affirms","ref":"exemplar:up-v1-0003","source":"corpus"},{"epistemic_status":"coherent","polarity":"affirms","ref":"exemplar:up-v1-0004","source":"corpus"},{"epistemic_status":"coherent","polarity":"affirms","ref":"exemplar:gsm8k-train-sample-v1-0002","source":"corpus"}],"operator_note":"","polarity":"affirms","proposal_id":"3ae00e14ec1688b4d1c35a393b8d7f20","proposed_chain":{"connective":"recognizes","intent":"admissibility","object":"47bc4c577fb58821ef2b4622b257e50fafe663d84e81920da894330b12beeb7e","recognizer_spec":{"canonical_pattern":{"anchor_count_max":1,"anchor_count_min":1,"anchor_kind":"unit_partition","graph_intent":"partition","observed_chunk_units":["foot","inch","meter"],"observed_counted_nouns":["pieces","sections"],"observed_partition_verbs":["cuts","splits"],"outcome":"admissible","shape_category":"unit_partition","unresolved_notes":[]},"coverage":{"anchors_unit_partition":4,"chunk_unit:foot":2,"chunk_unit:inch":1,"chunk_unit:meter":1,"counted_noun:pieces":1,"counted_noun:sections":3,"verb:cuts":2,"verb:splits":2},"exemplar_count":4,"exemplar_digest":"dc298d5c7a0781b52432c449f20094a174750027bc820aa2d5eb15c4369633b6","shape_category":"unit_partition"},"subject":"unit_partition"},"provenance":null,"replay_evidence":null,"review_state":"pending","source":{"emitted_at_revision":"gate-a2a-impl","kind":"exemplar_corpus","source_id":"dc298d5c7a0781b52432c449f20094a174750027bc820aa2d5eb15c4369633b6"},"source_candidate_id":"18eee13c7ba3a136216d83dd5f0906cda2e6024d73cc8d7eb9c53efab5b79f1c"}}
+{"event":"transition","note":"Gate A2a ratification 2026-06-17","proposal_id":"3ae00e14ec1688b4d1c35a393b8d7f20","to":"accepted"}
+{"chain_id":"admissibility_unit_partition_recognizes_47bc4c577fb58821ef2b4622b257e50fafe663d84e81920da894330b12beeb7e","event":"accepted_corpus_append","proposal_id":"3ae00e14ec1688b4d1c35a393b8d7f20","provenance":{"adr_id":"adr-0057","raw":"adr-0057:discovery_promoted:2026-06-17","review_date":"2026-06-17","source":"discovery_promoted"}}

teaching/recognizer_synthesis.py

@@ -347,6 +347,57 @@ def _synthesize_multiplicative_aggregation(
     return canonical_pattern, coverage
 
 
+def _synthesize_unit_partition(
+    corpus: ExemplarCorpus,
+) -> tuple[Mapping[str, Any], Mapping[str, int]]:
+    """Gate A2a — fixed-size measure chunking seeds."""
+    exemplars = corpus.exemplars
+    partition_verbs: list[str] = []
+    chunk_units: list[str] = []
+    counted_nouns: list[str] = []
+    anchor_counts: list[int] = []
+    coverage_verb: dict[str, int] = {}
+    coverage_unit: dict[str, int] = {}
+    coverage_noun: dict[str, int] = {}
+
+    for ex in exemplars:
+        anchors = ex.expected_graph["quantity_anchors"]
+        anchor_counts.append(len(anchors))
+        for a in anchors:
+            verb = a["partition_verb_token"]
+            unit = a["chunk_unit_token"]
+            noun = a["counted_noun_token"]
+            partition_verbs.append(verb)
+            chunk_units.append(unit)
+            counted_nouns.append(noun)
+            coverage_verb[verb] = coverage_verb.get(verb, 0) + 1
+            coverage_unit[unit] = coverage_unit.get(unit, 0) + 1
+            coverage_noun[noun] = coverage_noun.get(noun, 0) + 1
+
+    canonical_pattern: dict[str, Any] = {
+        "shape_category": ShapeCategory.UNIT_PARTITION.value,
+        "graph_intent": "partition",
+        "outcome": "admissible",
+        "anchor_kind": "unit_partition",
+        "observed_partition_verbs": _sorted_unique(partition_verbs),
+        "observed_chunk_units": _sorted_unique(chunk_units),
+        "observed_counted_nouns": _sorted_unique(counted_nouns),
+        "anchor_count_min": min(anchor_counts),
+        "anchor_count_max": max(anchor_counts),
+        "unresolved_notes": _collect_author_notes(exemplars),
+    }
+    coverage: dict[str, int] = {
+        "anchors_unit_partition": sum(anchor_counts),
+    }
+    for token, n in sorted(coverage_verb.items()):
+        coverage[f"verb:{token}"] = n
+    for token, n in sorted(coverage_unit.items()):
+        coverage[f"chunk_unit:{token}"] = n
+    for token, n in sorted(coverage_noun.items()):
+        coverage[f"counted_noun:{token}"] = n
+    return canonical_pattern, coverage
+
+
 def _synthesize_comparative_with_unit(
     corpus: ExemplarCorpus,
 ) -> tuple[Mapping[str, Any], Mapping[str, int]]:
@@ -441,6 +492,7 @@ _SYNTHESIZERS = {
     ShapeCategory.MULTIPLICATIVE_AGGREGATION: _synthesize_multiplicative_aggregation,
     ShapeCategory.CURRENCY_AMOUNT: _synthesize_currency_amount,
     ShapeCategory.COMPARATIVE_WITH_UNIT: _synthesize_comparative_with_unit,
+    ShapeCategory.UNIT_PARTITION: _synthesize_unit_partition,
 }
 
 

tests/test_gsm8k_frontier_report.py

@@ -107,6 +107,36 @@ def test_post_inc3_live_runner_has_zero_rate_no_injection():
     assert cats.get("rate_with_currency", 0) == 0
 
 
+def test_post_gate_a2a_live_runner_has_zero_unit_partition_no_injection():
+    """Live train_sample: unit_partition bucket closed at injector."""
+    import re
+    from collections import Counter
+
+    from evals.gsm8k_math.train_sample.v1.runner import build_report
+    from tests.gsm8k_train_sample_baseline import assert_monotonic_serving_counts
+
+    cases_path = _REPO_ROOT / "evals/gsm8k_math/train_sample/v1/cases.jsonl"
+    cases = [
+        json.loads(line)
+        for line in cases_path.read_text(encoding="utf-8").splitlines()
+        if line.strip()
+    ]
+    report = build_report(cases)
+    assert_monotonic_serving_counts(report["counts"])
+
+    cats: Counter[str] = Counter()
+    pat = re.compile(r"category=(\w+)")
+    for row in report["per_case"]:
+        reason = row.get("reason") or ""
+        if "recognizer matched but produced no injection" not in reason:
+            continue
+        m = pat.search(reason)
+        if m:
+            cats[m.group(1)] += 1
+
+    assert cats.get("unit_partition", 0) == 0
+
+
 def test_post_gate_a1_live_runner_has_zero_comparative_no_injection():
     """Live train_sample: comparative_with_unit bucket closed at injector."""
     import re
@@ -232,6 +262,7 @@ def test_frontier_report_aligns_with_post_gate_a1_microscope_structure():
     assert sum(microscope["top_buckets"].values()) == refused
     assert microscope["closed_injector_buckets"]["rate_with_currency_no_injection"] == 0
     assert microscope["closed_injector_buckets"]["comparative_with_unit_no_injection"] == 0
+    assert microscope["closed_injector_buckets"]["unit_partition_no_injection"] == 0
 
 
 def test_inc3_connector_makes_rate_no_injection_actionable():

tests/test_gsm8k_post_gate_a1_frontier_microscope.py

@@ -54,6 +54,7 @@ def test_live_microscope_meets_monotonic_contract_and_closed_injectors():
     closed = summary["closed_injector_buckets"]
     assert closed["rate_with_currency_no_injection"] == 0
     assert closed["comparative_with_unit_no_injection"] == 0
+    assert closed["unit_partition_no_injection"] == 0
 
 
 def test_live_microscope_refusal_partition_is_complete():
@@ -107,15 +108,12 @@ def test_markdown_render_surfaces_partition_candidate():
     assert "Gate A2a unit_partition" in md
 
 
-def test_case_0002_ratification_candidate_fields():
+def test_case_0002_post_gate_a2a_reclassified_off_partition_misroute():
+    """After Gate A2a, 0002 refuses downstream (fraction give), not partition no-injection."""
     summary = build_microscope_report(_load_cases())
     row = next(
         r for r in summary["refusal_table"] if r["case_id"].endswith("0002")
     )
-    assert row["subfamily"] == "dcs_misroute_unit_partition"
+    assert "25-foot sections" not in (row.get("reason") or "")
-    assert row["candidate_next_primitive"] == "unit_partition"
+    assert summary["closed_injector_buckets"]["unit_partition_no_injection"] == 0
-    assert row["expected_movement"] == "downstream_reclassification"
+    assert row["top_refusal_bucket"] == "no_admissible_statement"
-    assert (
-        summary["recommended_next_ratification_candidate"]
-        == "Gate A2a unit_partition / chunking primitive"
-    )

tests/test_math_candidate_graph_unit_partition_injection.py

@@ -0,0 +1,108 @@
+"""Candidate-graph integration for Gate A2a unit_partition injection."""
+
+from __future__ import annotations
+
+import pytest
+
+from generate.math_candidate_graph import parse_and_solve
+from generate.math_problem_graph import Operation, PartitionChunk
+from generate.math_solver import SolveError, _apply_unit_partition
+from generate.recognizer_anchor_inject import inject_from_match
+from generate.recognizer_match import match
+from generate.recognizer_registry import load_ratified_registry
+
+
+def _run(text: str):
+    return parse_and_solve(text, sealed=False)
+
+
+def test_unit_partition_solver_lower_level_integration():
+    """Prove unit_partition apply writes chunk count under result_unit."""
+    chunk = PartitionChunk(value=25.0, unit="feet", result_unit="sections")
+    op = Operation(actor="Jan", kind="unit_partition", operand=chunk)
+    state = {("Jan", "feet"): 1000.0}
+    pack_bindings = {"unit_partition": "en_arithmetic_v1:divide"}
+
+    step = _apply_unit_partition(op, index=0, state=state, pack_bindings=pack_bindings)
+
+    assert step.operation_kind == "unit_partition"
+    assert state[("Jan", "sections")] == 40.0
+    assert state[("Jan", "feet")] == 1000.0
+
+
+def test_partition_stmt_injects_on_lead_exemplar_pair():
+    registry = load_ratified_registry()
+    stmt = "She splits it up into 25-foot sections."
+    m = match(stmt, registry)
+    assert m is not None
+    emitted = inject_from_match(m, stmt, sealed=False)
+    assert len(emitted) == 1
+    assert emitted[0].op.kind == "unit_partition"
+
+
+def test_stmt_only_partition_refuses_end_to_end():
+    res = _run("She splits it into 25-foot sections.")
+    assert res.answer is None
+    assert res.refusal_reason is not None
+
+
+def test_pronoun_partition_refuses_without_antecedent():
+    res = _run("She splits it into 25-foot sections. How many sections does she have?")
+    assert res.answer is None
+    assert res.refusal_reason is not None
+
+
+def test_pronoun_partition_refuses_multi_actor_ambiguity():
+    text = (
+        "Jan buys 1000 feet of cable. "
+        "Bob buys 200 feet of rope. "
+        "She splits it into 25-foot sections. "
+        "How many sections does Jan have?"
+    )
+    res = _run(text)
+    assert res.answer is None
+    assert res.refusal_reason is not None
+
+
+def test_non_exact_quotient_refuses_at_solver():
+    chunk = PartitionChunk(value=30.0, unit="feet", result_unit="sections")
+    op = Operation(actor="Jan", kind="unit_partition", operand=chunk)
+    state = {("Jan", "feet"): 1000.0}
+    pack_bindings = {"unit_partition": "en_arithmetic_v1:divide"}
+
+    with pytest.raises(SolveError):
+        _apply_unit_partition(op, index=0, state=state, pack_bindings=pack_bindings)
+
+
+def test_unit_mismatch_surface_does_not_solve():
+    text = "Jan buys 1000 feet of cable. Jan cuts 1000 feet into 25-inch sections."
+    res = _run(text)
+    assert res.answer is None
+
+
+def test_full_0002_still_refuses_without_composition():
+    text = (
+        "Jan buys 1000 feet of cable. "
+        "She splits it up into 25-foot sections. "
+        "She gives 1/4 of that to a friend. "
+        "She then puts half of the rest in storage. "
+        "How much does she keep on hand?"
+    )
+    res = _run(text)
+    assert res.answer is None
+    assert res.refusal_reason is not None
+
+
+def test_duration_confuser_does_not_inject_unit_partition():
+    res = _run("It is a 2-hour drive.")
+    assert res.answer is None
+
+
+def test_injected_unit_partition_does_not_create_wrong_on_isolated_rate():
+    for stmt in [
+        "Tina makes $18.00 an hour.",
+        "Alexa has a lemonade stand where she sells lemonade for $2 for one cup.",
+    ]:
+        res = parse_and_solve(stmt, sealed=False)
+        assert res.answer is None
+        assert res.refusal_reason is not None

tests/test_recognizer_unit_partition_inject.py

@@ -0,0 +1,171 @@
+"""Gate A2a — unit_partition recognizer-anchor injection tests."""
+
+from __future__ import annotations
+
+import types
+
+import pytest
+
+from evals.refusal_taxonomy.shape_categories import ShapeCategory
+from generate.math_candidate_parser import CandidateOperation
+from generate.math_problem_graph import PartitionChunk
+from generate.math_roundtrip import roundtrip_admissible
+from generate.recognizer_anchor_inject import inject_from_match, inject_unit_partition
+from generate.recognizer_match import RecognizerMatch, match
+from generate.recognizer_registry import load_ratified_registry
+
+
+def _stub_recognizer(category: ShapeCategory) -> types.SimpleNamespace:
+    return types.SimpleNamespace(shape_category=category, canonical_pattern={})
+
+
+def _make_match(anchor: dict) -> RecognizerMatch:
+    return RecognizerMatch(
+        recognizer=_stub_recognizer(ShapeCategory.UNIT_PARTITION),
+        category=ShapeCategory.UNIT_PARTITION,
+        outcome="admissible",
+        graph_intent="partition",
+        parsed_anchors=(anchor,),
+    )
+
+
+def _anchor(
+    *,
+    actor: str = "Jan",
+    chunk_size: str = "25",
+    chunk_unit: str = "foot",
+    counted_noun: str = "sections",
+    verb: str = "splits",
+) -> dict:
+    return {
+        "kind": "unit_partition",
+        "actor_token": actor,
+        "chunk_size_token": chunk_size,
+        "chunk_unit_token": chunk_unit,
+        "counted_noun_token": counted_noun,
+        "partition_verb_token": verb,
+        "source_span": f"{actor} {verb} it into {chunk_size}-{chunk_unit} {counted_noun}.",
+    }
+
+
+@pytest.mark.parametrize(
+    "sentence,actor,chunk_size,chunk_unit,counted_noun,verb",
+    [
+        ("She splits it up into 25-foot sections.", "She", "25", "foot", "sections", "splits"),
+        ("Dana cuts the ribbon into 20-inch pieces.", "Dana", "20", "inch", "pieces", "cuts"),
+        ("Jan cuts the rope into 4-foot sections.", "Jan", "4", "foot", "sections", "cuts"),
+        ("Mason splits the cable into 10-meter sections.", "Mason", "10", "meter", "sections", "splits"),
+    ],
+)
+def test_positive_surfaces_emit_unit_partition(
+    sentence, actor, chunk_size, chunk_unit, counted_noun, verb
+):
+    registry = load_ratified_registry()
+    m = match(sentence, registry)
+    assert m is not None
+    assert m.category is ShapeCategory.UNIT_PARTITION
+    emitted = inject_from_match(m, sentence, sealed=False)
+    assert len(emitted) == 1
+    cand = emitted[0]
+    assert isinstance(cand, CandidateOperation)
+    assert cand.op.kind == "unit_partition"
+    assert isinstance(cand.op.operand, PartitionChunk)
+    assert cand.op.operand.value == float(chunk_size)
+    assert cand.matched_value_token == chunk_size
+    assert cand.matched_verb == verb
+    assert roundtrip_admissible(cand) is True
+
+
+@pytest.mark.parametrize(
+    "sentence",
+    [
+        "25-foot sections.",
+        "She splits it into 25 sections.",
+        "It is a 2-hour drive.",
+        "Jan cuts the rope into 3-foot sections and 4-foot sections.",
+        "She splits it into equal sections.",
+        "She splits it into bags.",
+        "Half of the kids go to soccer camp.",
+        "She puts 48 cookies into boxes of 6.",
+        "999 feet split into 25-foot sections.",
+    ],
+)
+def test_unit_partition_confusers_never_inject(sentence: str):
+    registry = load_ratified_registry()
+    m = match(sentence, registry)
+    if m is None:
+        return
+    assert inject_from_match(m, sentence, sealed=False) == ()
+
+
+@pytest.mark.parametrize(
+    "sentence",
+    [
+        "Jan buys 1000 feet of cable.",
+        "Tina makes $18.00 an hour.",
+        "Alice has twice as many apples as Bob.",
+        "Bob can shuck 10 oysters in 5 minutes.",
+    ],
+)
+def test_legitimate_unrelated_surfaces_do_not_emit_unit_partition(sentence: str):
+    registry = load_ratified_registry()
+    m = match(sentence, registry)
+    if m is None:
+        return
+    emitted = inject_from_match(m, sentence, sealed=False)
+    for candidate in emitted:
+        if isinstance(candidate, CandidateOperation):
+            assert candidate.op.kind != "unit_partition"
+
+
+def test_pronoun_anchor_emits_with_resolution_flag():
+    registry = load_ratified_registry()
+    stmt = "She splits it up into 25-foot sections."
+    m = match(stmt, registry)
+    assert m is not None
+    assert m.parsed_anchors[0].get("requires_pronoun_resolution") is True
+    emitted = inject_from_match(m, stmt, sealed=False)
+    assert len(emitted) == 1
+
+
+def test_dispatch_table_routes_unit_partition():
+    registry = load_ratified_registry()
+    stmt = "Jan cuts the rope into 4-foot sections."
+    m = match(stmt, registry)
+    assert m is not None
+    assert m.category is ShapeCategory.UNIT_PARTITION
+    emitted = inject_from_match(m, stmt, sealed=False)
+    assert len(emitted) == 1
+    assert emitted[0].op.operand.result_unit == "sections"
+
+
+def test_dcs_yields_unit_partition_not_initial_chunk_size():
+    registry = load_ratified_registry()
+    stmt = "She splits it up into 25-foot sections."
+    m = match(stmt, registry)
+    assert m is not None
+    assert m.category is ShapeCategory.UNIT_PARTITION
+    emitted = inject_from_match(m, stmt, sealed=False)
+    assert len(emitted) == 1
+    assert emitted[0].op.kind == "unit_partition"
+
+
+def test_direct_injector_refuses_malformed_anchor():
+    emitted = inject_unit_partition(
+        _make_match(_anchor(chunk_size="two")),
+        "Jan splits it into two-foot sections.",
+    )
+    assert emitted == ()
+
+
+def test_matched_tokens_ground_in_source_sentence():
+    sentence = "Dana cuts the ribbon into 20-inch pieces."
+    registry = load_ratified_registry()
+    m = match(sentence, registry)
+    assert m is not None
+    emitted = inject_from_match(m, sentence, sealed=False)
+    assert len(emitted) == 1
+    c = emitted[0]
+    assert c.matched_actor_token in sentence
+    assert c.matched_value_token in sentence
+    assert c.matched_unit_token in sentence