test(conformance): drive 0014 state-migration fixtures 039-046

New tests/conformance/test_state_migration.py drives all 8 spec
state-migration fixtures end-to-end against the real engine
(SQLite JSON-mode backend, real graph compile, real resume path).

Harness pieces:

- Migration mock library: add_new_field_default, add_v2_field,
  add_v3_field, identity_passthrough, raises_keyerror,
  should_not_run, irrelevant. Each fixture's migrate: <name>
  resolves through the library.
- _MigrationTrace wraps each mock to capture invocation order
  for the migrations_run / migration_count /
  single_migration_invocation / migration_order_matches_chain
  assertions. Consecutive duplicates collapse (fixture 043 runs
  each step once for outer + once for each parent under the
  lockstep ordering; the assertion is per-step, not per-entity).
- _seed_record persists a checkpoint matching the fixture's
  seeded_record: block before invoke(resume_invocation=...) so
  the resume path has data to load.

Harness/model adjustments:

- StateSchema in tests/conformance/harness/directives.py gains
  optional schema_version (default '') and the required field
  knob (no-default Pydantic field, used by fixture 044's
  required_v2_field deserialization-failure case).
- _DEFERRED_FIXTURES in test_fixture_parsing.py loses the
  039-046 rows; the CasesFixture model parses them via permissive
  extras on CaseSpec.
- Initial-state construction in the resume path uses
  state_cls.model_construct() so fixtures with required fields
  (044) can pass a placeholder past Pydantic's validator before
  the resume even starts; the engine loads state from the
  checkpoint, not from the placeholder.

Protocol-attribute shape:

- Checkpointer.supports_state_migration declared as
  bool = False (not ClassVar) so SQLiteCheckpointer can set
  the value per-instance in __init__ based on serialization mode.
  Backends with a static answer (InMemoryCheckpointer) override
  at the class level with bool = False — Pyright accepts
  either shape because Protocol attribute conformance ignores
  the ClassVar marker on subclasses.

Author: chris-colinsky

src/openarmature/checkpoint/backends/memory.py

@@ -12,7 +12,6 @@
 
 import asyncio
 from collections.abc import Iterable
-from typing import ClassVar
 
 from ..protocol import CheckpointFilter, CheckpointRecord, CheckpointSummary
 
@@ -41,8 +40,12 @@ class InMemoryCheckpointer:
 
     # Per spec §10.12.1: in-memory storage holds live typed-state
     # references, so there's no class-independent intermediate form
-    # the migration registry could consume.
-    supports_state_migration: ClassVar[bool] = False
+    # the migration registry could consume. Declared at the class
+    # level (not as a per-instance attribute) since the answer is
+    # constructor-independent; the Protocol declaration in
+    # ``protocol.py`` types this as ``bool`` (not ``ClassVar[bool]``)
+    # so Pyright accepts a class-attribute override here.
+    supports_state_migration: bool = False
 
     def __init__(self) -> None:
         self._records: dict[str, CheckpointRecord] = {}

src/openarmature/checkpoint/protocol.py

@@ -34,7 +34,7 @@
 
 from collections.abc import Iterable
 from dataclasses import dataclass, field
-from typing import Any, ClassVar, Protocol
+from typing import Any, Protocol
 
 
 # Spec: realizes pipeline-utilities §10.2 NodePosition. Field semantics
@@ -162,7 +162,16 @@ class Checkpointer(Protocol):
     migrations are registered — the registry has no chance to bridge.
     """
 
-    supports_state_migration: ClassVar[bool] = False
+    # Declared as an instance attribute (not ``ClassVar``) so backends
+    # can compute it at construction time when the answer depends on
+    # constructor args. SQLiteCheckpointer is the concrete case:
+    # JSON-mode supports migration, pickle-mode doesn't, and the mode
+    # is a per-instance constructor arg. Backends with a static answer
+    # (InMemoryCheckpointer is always False) override at the class
+    # level with ``ClassVar[bool] = False``; pyright is happy with
+    # either shape because Protocol attribute conformance ignores the
+    # ClassVar marker on subclasses.
+    supports_state_migration: bool = False
 
     async def save(self, invocation_id: str, record: CheckpointRecord) -> None:
         """Persist ``record`` for ``invocation_id``. After return the

tests/conformance/harness/directives.py

@@ -56,16 +56,27 @@ class StateFieldSpec(_ForbidExtras):
     The ``alt_reducer`` knob exists only for ``graph-engine/007-compile-errors``'s
     ``conflicting_reducers`` case — fixtures intentionally declare two reducers
     on one field to verify the engine fails compile with the right category.
+
+    The ``required`` knob (used by the state-migration deserialization-
+    failure fixture 044) marks a field as having no default — Pydantic's
+    natural "required" shape. The default-when-omitted falls through
+    via the ``default`` field above.
     """
 
     type: str
     default: Any = None
     reducer: str | None = None
     alt_reducer: str | None = None
+    required: bool = False
 
 
 class StateSchema(_ForbidExtras):
     fields: dict[str, StateFieldSpec]
+    # User-facing state-schema version per pipeline-utilities §10.2
+    # (proposal 0014). The state-migration fixtures (039-046) declare
+    # this on each case's ``state`` block; non-migration fixtures
+    # omit it (defaults to empty-string sentinel).
+    schema_version: str = ""
 
 
 # ---------------------------------------------------------------------------

tests/conformance/test_fixture_parsing.py

@@ -40,17 +40,10 @@ def _id(case: tuple[str, Path]) -> str:
     "pipeline-utilities/036-parallel-branches-with-branch-middleware-retry": "0011 parallel branches (PR-5)",
     "pipeline-utilities/037-parallel-branches-determinism": "0011 parallel branches (PR-5)",
     "pipeline-utilities/038-parallel-branches-compose-with-fan-out": "0011 parallel branches (PR-5)",
-    # proposal 0014 — state migration (PR-4)
-    "pipeline-utilities/039-state-migration-additive-field": "0014 state migration (PR-4)",
-    "pipeline-utilities/040-state-migration-chain": "0014 state migration (PR-4)",
-    "pipeline-utilities/041-state-migration-missing": "0014 state migration (PR-4)",
-    "pipeline-utilities/042-state-migration-versions-match-no-op": "0014 state migration (PR-4)",
-    "pipeline-utilities/043-state-migration-parent-states-migrated": "0014 state migration (PR-4)",
-    "pipeline-utilities/044-state-migration-post-migration-deserialization-fails": (
-        "0014 state migration (PR-4)"
-    ),
-    "pipeline-utilities/045-state-migration-no-path-in-registry": "0014 state migration (PR-4)",
-    "pipeline-utilities/046-state-migration-function-raises": "0014 state migration (PR-4)",
+    # proposal 0014's state-migration fixtures (039-046) were removed
+    # from this list as part of PR-4; the CasesFixture model already
+    # parses the seeded_record / migrations shape via its permissive
+    # extras (CaseSpec uses ``model_config = ConfigDict(extra="allow")``).
     # proposal 0015's llm-provider fixtures (009-020) were removed
     # from this list as part of PR-2; the typed harness parses the
     # content-block message shape via LlmCallSpec's permissive