feat(corpus-seeded-mechanisms): the mechanisms lever admits or retracts exporter records

Task 4.1 (Req 5.1, 5.2, 5.5).

- validator: MechanismEdit (admit | retract by record id) under the
  `mechanisms` lever; validate_mechanism accepts only records from the
  exporter candidate set with origin corpus, a closed guard and source
  kinds, and identifier-only shape text; free-form shapes are rejected.
- apply_mechanism_edits appends the record (admit) or a retracted
  tombstone (retract) so the log stays append-only; StoreSnapshot.restore
  reverts byte for byte. MechanismStore.load folds tombstones away.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG

src/openultrasast/improve/validator.py

@@ -8,15 +8,20 @@ impossible; the validator additionally enforces status/bounds/staging/resolution
 
 from __future__ import annotations
 
-from collections.abc import Mapping
-from dataclasses import dataclass
+import json
+import re
+from collections.abc import Mapping, Sequence
+from dataclasses import asdict, dataclass
+from pathlib import Path
 
 from ..policy import CwePolicy
 from ..ruleset import PatternRule
 from ..ruleset.store import VALID_STATUS
 
 # The only levers the loop may pull (mirrors the design's journal._VALID_LEVERS).
-VALID_LEVERS = frozenset({"rule", "policy"})
+VALID_LEVERS = frozenset({"rule", "policy", "mechanisms"})
+_IDENTIFIER = re.compile(r"^[A-Za-z_$][\w$]*$")
+MECHANISM_ACTIONS = frozenset({"admit", "retract"})
 # Policy constants the loop may tune; the 0-5 severity is intentionally absent.
 TUNABLE_POLICY_CONSTANTS = frozenset({"K", "MIN_SCORE"})
 
@@ -57,6 +62,40 @@ class PolicyConstantEdit:
         return f"policy:{self.name}:{self.from_value}->{self.to_value}"
 
 
+@dataclass(frozen=True)
+class MechanismEdit:
+    """A `mechanisms`-lever edit (corpus-seeded-mechanisms Req 5): admit or retract one exporter record by id.
+
+    The loop never writes a shape; it may only move a record the exporter derived from a trusted pair into or out of
+    the scan-time store. Free text is confined to ``rationale``.
+    """
+
+    action: str  # admit | retract
+    mechanism_id: str
+    source: str = "loo"  # loo | export
+    rationale: str = ""
+    lever: str = "mechanisms"
+
+    def key(self) -> str:
+        return f"mechanisms:{self.action}:{self.mechanism_id}"
+
+
+@dataclass(frozen=True)
+class StoreSnapshot:
+    """Bytes of the scan-time mechanism store before a round; ``restore`` is the byte-for-byte revert."""
+
+    path: Path
+    content: bytes | None  # None when the file did not exist
+
+    def restore(self) -> None:
+        if self.content is None:
+            if self.path.exists():
+                self.path.unlink()
+            return
+        self.path.parent.mkdir(parents=True, exist_ok=True)
+        self.path.write_bytes(self.content)
+
+
 @dataclass(frozen=True)
 class EvolveBounds:
     k_range: tuple[float, float] = (20.0, 200.0)
@@ -74,9 +113,42 @@ class EvolveValidator:
             self._validate_rule(edit, ruleset_by_id, policy)
         elif isinstance(edit, PolicyConstantEdit):
             self._validate_policy(edit)
+        elif isinstance(edit, MechanismEdit):
+            raise StrictValidationError("mechanism edits need the exporter candidate set: use validate_mechanism", kind="mechanism_change")
         else:
             raise StrictValidationError(f"unknown edit type {type(edit).__name__}", kind="rule_change")
 
+    def validate_mechanism(self, edit: MechanismEdit, candidates: Mapping[str, object]) -> None:
+        """Req 5.2: only records the exporter derived from trusted pairs, with a closed guard and identifier-only shape text."""
+        from ..semantic.variants import GUARD_KINDS, SOURCE_KINDS
+
+        if edit.action not in MECHANISM_ACTIONS:
+            raise StrictValidationError(f"mechanism edit action {edit.action!r} is not admit or retract", kind="mechanism_change")
+        record = candidates.get(edit.mechanism_id)
+        if record is None:
+            raise StrictValidationError(
+                f"unknown mechanism {edit.mechanism_id!r}: not in the exporter candidate set", kind="mechanism_change"
+            )
+        if getattr(record, "origin", "") != "corpus":
+            raise StrictValidationError(
+                f"{edit.mechanism_id}: origin {getattr(record, 'origin', '')!r} is not corpus (only exporter records)",
+                kind="mechanism_change",
+            )
+        shape = getattr(record, "shape", None)
+        if not isinstance(shape, dict):
+            raise StrictValidationError(f"{edit.mechanism_id}: record carries no shape", kind="mechanism_change")
+        if str(shape.get("guard")) not in GUARD_KINDS or str(getattr(record, "guard", "")) not in GUARD_KINDS:
+            raise StrictValidationError(
+                f"{edit.mechanism_id}: guard {shape.get('guard')!r} is not a closed guard kind", kind="mechanism_change"
+            )
+        for field_name in ("sink_name", "language", "mechanism"):
+            value = str(shape.get(field_name, ""))
+            if not _IDENTIFIER.match(value.replace("-", "_")):
+                raise StrictValidationError(f"{edit.mechanism_id}: {field_name} {value!r} is not an identifier", kind="mechanism_change")
+        kinds = shape.get("source_kinds") or []
+        if not isinstance(kinds, list) or any(str(kind) not in SOURCE_KINDS for kind in kinds):
+            raise StrictValidationError(f"{edit.mechanism_id}: source kinds {kinds!r} are not closed kinds", kind="mechanism_change")
+
     def _validate_rule(self, edit: RuleStatusEdit, ruleset_by_id: Mapping[str, PatternRule], policy: Mapping[str, CwePolicy]) -> None:
         if edit.to_status not in VALID_STATUS:
             raise StrictValidationError(f"invalid status {edit.to_status!r} for {edit.rule_id}")
@@ -99,6 +171,25 @@ class EvolveValidator:
             raise StrictValidationError(f"MIN_SCORE={edit.to_value} out of bounds {self._bounds.min_score_range}", kind="policy_change")
 
 
+def apply_mechanism_edits(edits: Sequence[MechanismEdit], candidates: object, scan_store: Path) -> StoreSnapshot:
+    """Apply admit/retract edits to the scan-time store; returns the snapshot whose ``restore`` reverts byte for byte.
+
+    Admission appends the exporter record unchanged; retraction appends a tombstone row (``retracted = true``) so the
+    log stays append-only and ``MechanismStore.load`` folds the record away.
+    """
+    snapshot = StoreSnapshot(path=scan_store, content=scan_store.read_bytes() if scan_store.exists() else None)
+    by_id = {record.id: record for record in candidates.load()}  # type: ignore[attr-defined]
+    scan_store.parent.mkdir(parents=True, exist_ok=True)
+    with scan_store.open("a") as handle:
+        for edit in edits:
+            record = by_id[edit.mechanism_id]
+            payload = asdict(record)
+            if edit.action == "retract":
+                payload["retracted"] = True
+            handle.write(json.dumps(payload, sort_keys=True) + "\n")
+    return snapshot
+
+
 def edits_to_ledger(edits: list[RuleStatusEdit], base: Mapping[str, dict[str, object]]) -> dict[str, dict[str, object]]:
     """Overlay rule-status edits onto a copy of the base ledger."""
     ledger: dict[str, dict[str, object]] = {key: dict(value) for key, value in base.items()}
@@ -112,6 +203,10 @@ def edits_to_ledger(edits: list[RuleStatusEdit], base: Mapping[str, dict[str, ob
 __all__ = [
     "EvolveBounds",
     "EvolveValidator",
+    "MECHANISM_ACTIONS",
+    "MechanismEdit",
+    "StoreSnapshot",
+    "apply_mechanism_edits",
     "PolicyConstantEdit",
     "RuleStatusEdit",
     "StrictValidationError",

src/openultrasast/semantic/mechanisms.py

@@ -37,6 +37,7 @@ class Mechanism:
     pairs: tuple[str, ...] = ()
     shape: dict[str, object] | None = None  # Shape.to_dict(); None on sandbox rows (not searchable)
     guard: str = "none"
+    retracted: bool = False  # tombstone row appended by the improve lever; load() folds the record away
 
 
 class MechanismStore:
@@ -53,7 +54,10 @@ class MechanismStore:
                 continue
             payload = json.loads(line)
             record = _mechanism_from_payload(payload)
-            by_id[record.id] = record
+            if record.retracted:
+                by_id.pop(record.id, None)
+            else:
+                by_id[record.id] = record
         return tuple(by_id.values())
 
     def append(self, mechanism: Mechanism) -> None:
@@ -340,8 +344,9 @@ def _mechanism_from_payload(payload: dict[str, object]) -> Mechanism:
         origin=str(payload.get("origin", "sandbox")),
         review_tier=str(payload.get("review_tier", "")),
         pairs=tuple(str(item) for item in pairs),
-        shape=Shape.from_dict(shape).to_dict() if isinstance(shape, dict) else None,
+        shape=dict(shape) if isinstance(shape, dict) else None,  # validated where it is used (search_tree, the lever)
         guard=str(payload.get("guard", "none")),
+        retracted=bool(payload.get("retracted", False)),
     )