fix: distinguish Python schema extensions from official contracts

CHANGELOG.md

@@ -2,6 +2,21 @@
 
 All notable changes to this reference implementation are documented here.
 
+## Unreleased
+
+### Fixed
+
+- Namespace new Python schema-change plans and SPSS output as
+  `openstatspec-python-schema-change-plan-v0.1` and
+  `openstatspec-python-schema-change-spss-v0.1`, retaining exported constant names.
+  The former `openstatspec-transformation-plan-v0.3` remains accepted as a
+  legacy Python extension with unchanged semantics, canonical JSON, and hashes;
+  stored audits are not migrated. New compilation changes schema-plan hashes.
+- Clarify that specification `v0.5.0` has no official Plan 0.3 and that its
+  syntax-only Frontend 0.3 over Plan 0.1/0.2 is not implemented here. Legacy
+  acceptance and Python extension tests do not claim official conformance.
+  See [compatibility and migration](docs/transformations.md#contract-ownership-and-legacy-compatibility).
+
 ## 0.8.1 - 2026-09-10
 
 ### Fixed

docs/transformations.md

@@ -30,6 +30,40 @@ This is a trust boundary. JSON plans must pass
 `transformation_plan_from_dict()` and live-schema validation before mutation;
 they are never treated as arbitrary SQL.
 
+## Contract ownership and legacy compatibility
+
+Published OpenStatSpec `v0.5.0` defines Transformation Plan 0.1/0.2, not
+Plan 0.3. Its optional SPSS Frontend 0.3 is a syntax-only expansion emitting
+Plan 0.1/0.2; this adapter does **not** implement that frontend yet.
+
+Explicit `create_variable` / `delete_variable` operations (including SPSS
+`STRING` / `DELETE VARIABLES`) belong to a **Python extension**, not official
+OpenStatSpec conformance. New schema-changing compilations emit:
+
+- Plan: `openstatspec-python-schema-change-plan-v0.1`
+- Frontend: `openstatspec-python-schema-change-spss-v0.1`
+
+The exported names `TRANSFORMATION_PLAN_SCHEMA_CHANGE_CONTRACT` and
+`SPSS_FRONTEND_SCHEMA_CHANGE_CONTRACT` remain unchanged; their values now use
+these Python-owned identifiers. Plans without these explicit schema operations
+retain their existing Plan 0.1/0.2 selection and frontend identifier. Official
+Plan 0.1/0.2 still reject explicit create/delete operations.
+
+The loader and executor continue to accept the old Python plan identifier
+`openstatspec-transformation-plan-v0.3` with its original operation semantics.
+This is legacy compatibility, **not** recognition of an official Plan 0.3.
+Loading, canonical serialization, hashing, and apply preserve the supplied
+identifier; existing canonical JSON, hashes, and stored audits are not rewritten.
+Historical `openstatspec-spss-syntax-frontend-v0.3` audit values described this
+Python extension and are not evidence of official Frontend 0.3 conformance.
+
+No database migration is needed. Consumers should accept the new extension IDs
+before using new compiler output. Keep stored legacy plans and audits intact;
+recompiling schema-changing syntax now produces a new plan identity/hash even
+when its operations are identical. An intentional change of a saved plan's
+contract likewise creates a new artifact with a new hash, not an audit migration.
+Older adapter versions cannot load the new IDs.
+
 ## Install the audit schema
 
 Install the compact audit relation once before the first apply:

src/openstatspec/frontends/spss/compiler.py

@@ -18,7 +18,8 @@
 
 
 SPSS_FRONTEND_CONTRACT = "openstatspec-spss-syntax-frontend-v0.2"
-SPSS_FRONTEND_SCHEMA_CHANGE_CONTRACT = "openstatspec-spss-syntax-frontend-v0.3"
+# Python-owned schema extension, not the official syntax-only Frontend 0.3.
+SPSS_FRONTEND_SCHEMA_CHANGE_CONTRACT = "openstatspec-python-schema-change-spss-v0.1"
 
 
 @dataclass(frozen=True)

src/openstatspec/transform/plan.py

@@ -16,8 +16,15 @@
 
 TRANSFORMATION_PLAN_V1_CONTRACT = "openstatspec-transformation-plan-v0.1"
 TRANSFORMATION_PLAN_CONTRACT = "openstatspec-transformation-plan-v0.2"
-TRANSFORMATION_PLAN_SCHEMA_CHANGE_CONTRACT = "openstatspec-transformation-plan-v0.3"
-_TRANSFORMATION_PLAN_CONTRACTS = {TRANSFORMATION_PLAN_V1_CONTRACT, TRANSFORMATION_PLAN_CONTRACT, TRANSFORMATION_PLAN_SCHEMA_CHANGE_CONTRACT}
+TRANSFORMATION_PLAN_SCHEMA_CHANGE_CONTRACT = "openstatspec-python-schema-change-plan-v0.1"
+# Python extension compatibility only: never normalize legacy IDs or audit hashes.
+_SCHEMA_CHANGE_CONTRACTS = {
+    TRANSFORMATION_PLAN_SCHEMA_CHANGE_CONTRACT,
+    "openstatspec-transformation-plan-v0.3",
+}
+_TRANSFORMATION_PLAN_CONTRACTS = {
+    TRANSFORMATION_PLAN_V1_CONTRACT, TRANSFORMATION_PLAN_CONTRACT,
+} | _SCHEMA_CHANGE_CONTRACTS
 _BINARY64 = re.compile(r"[0-9a-f]{16}")
 
 
@@ -589,7 +596,7 @@ def __post_init__(self) -> None:
         if not isinstance(self.contract, str) or self.contract not in _TRANSFORMATION_PLAN_CONTRACTS:
             _invalid("Plan contract is not a supported transformation-plan contract.")
         if (
-            self.contract != TRANSFORMATION_PLAN_SCHEMA_CHANGE_CONTRACT
+            self.contract not in _SCHEMA_CHANGE_CONTRACTS
             and any(
                 isinstance(operation, (
                     CreateVariableOperation, DeleteVariableOperation,
@@ -598,8 +605,9 @@ def __post_init__(self) -> None:
             )
         ):
             _invalid(
-                "Create/delete schema operations require "
-                "openstatspec-transformation-plan-v0.3."
+                "Create/delete schema operations require the Python extension "
+                f"{TRANSFORMATION_PLAN_SCHEMA_CHANGE_CONTRACT} "
+                "(legacy Python v0.3 plans are also accepted, not official conformance)."
             )
         if self.contract == TRANSFORMATION_PLAN_V1_CONTRACT and any(
             isinstance(operation, (
@@ -723,7 +731,7 @@ def _match(raw: Any) -> RecodeMatch:
     _invalid("Unknown recode match kind.")
 
 def transformation_plan_from_dict(raw: Mapping[str, Any]) -> TransformationPlan:
-    """Strictly validate canonical v0.1, v0.2, or schema-change v0.3 plans."""
+    """Validate Plan 0.1/0.2 or Python schema-change plans, including legacy IDs."""
     if not isinstance(raw, Mapping):
         _invalid("Transformation plan must be an object.")
     _exact(raw, {"contract", "input_alias", "operations"}, "Transformation plan")

tests/test_inplace_transform.py

@@ -904,7 +904,7 @@ def test_public_apply_supports_non_dolt_without_building_undo(catalog) -> None:
     )) == (1, 1), "public SPSS apply must encode/hash the canonical plan once"
 
 
-def test_schema_commands_record_the_v03_frontend_contract(catalog) -> None:
+def test_schema_commands_record_python_extension_frontend_contract(catalog) -> None:
     url, path, dataset_id, _table_name = catalog
 
     openstatspec.apply_spss_in_place(
@@ -919,10 +919,52 @@ def test_schema_commands_record_the_v03_frontend_contract(catalog) -> None:
     ).fetchone()
     assert audit == (
         "spss_syntax",
-        "openstatspec-spss-syntax-frontend-v0.3",
+        "openstatspec-python-schema-change-spss-v0.1",
     )
 
 
+@pytest.mark.parametrize("contract", [
+    "openstatspec-transformation-plan-v0.3",  # Legacy acceptance, not conformance.
+    "openstatspec-python-schema-change-plan-v0.1",
+])
+def test_schema_plan_apply_preserves_identity_and_audit(catalog, contract) -> None:
+    url, path, dataset_id, table_name = catalog
+    plan = openstatspec.TransformationPlan(
+        (openstatspec.CreateVariableOperation("note", "string", 4),),
+        contract=contract,
+    )
+    with sqlite3.connect(path) as connection:
+        tables = connection.execute("SELECT name FROM sqlite_master ORDER BY name").fetchall()
+        identity = connection.execute("SELECT * FROM dataset").fetchall()
+    result = openstatspec.apply_transformation_plan_in_place(
+        database_url=url, dataset_id=dataset_id, plan=plan.as_dict(), actor="test-agent",
+    )
+    assert (result["dataset_id"], result["physical_table_name"]) == (dataset_id, table_name)
+    with sqlite3.connect(path) as connection:
+        assert connection.execute(
+            f'SELECT score, note FROM "{table_name}" ORDER BY __case_ordinal'
+        ).fetchall() == [(1.0, ""), (2.0, ""), (3.0, "")]
+        audit = connection.execute("SELECT * FROM transformation_apply").fetchone()
+        assert connection.execute(
+            "SELECT canonical_plan_json, plan_hash, source_hash, frontend_contract "
+            "FROM transformation_apply"
+        ).fetchone() == (plan.canonical_json(), plan.sha256(), plan.sha256(), None)
+    # New compilation must not migrate an existing (including legacy) audit row.
+    openstatspec.apply_spss_in_place(
+        database_url=url, dataset_id=dataset_id,
+        source_text="DELETE VARIABLES note.", actor="test-agent",
+    )
+    with sqlite3.connect(path) as connection:
+        assert connection.execute("SELECT name FROM sqlite_master ORDER BY name").fetchall() == tables
+        assert connection.execute("SELECT * FROM dataset").fetchall() == identity
+        assert connection.execute(
+            "SELECT * FROM transformation_apply WHERE apply_id = ?", (result["apply_id"],),
+        ).fetchone() == audit
+        assert [row[1] for row in connection.execute(
+            f'PRAGMA table_info("{table_name}")'
+        )] == ["__case_ordinal", "score"]
+
+
 @pytest.mark.parametrize("as_mapping", [False, True])
 def test_public_generic_plan_apply_accepts_object_and_mapping(
     catalog, as_mapping,

tests/test_transform_frontend.py

@@ -375,14 +375,16 @@ def test_source_normalization_hash_and_positions_are_stable() -> None:
     assert compilation.frontend_contract == "openstatspec-spss-syntax-frontend-v0.2"
 
 
-def test_schema_commands_use_the_v03_frontend_contract() -> None:
+def test_schema_commands_use_python_extension_contracts() -> None:
     compilation = compile_spss_syntax(
         "STRING note (A4).",
         _schema(VariableDefinition("q1", "numeric")),
     )
 
-    assert compilation.plan.contract == "openstatspec-transformation-plan-v0.3"
-    assert compilation.frontend_contract == "openstatspec-spss-syntax-frontend-v0.3"
+    assert compilation.plan.contract == "openstatspec-python-schema-change-plan-v0.1"
+    assert compilation.frontend_contract == "openstatspec-python-schema-change-spss-v0.1"
+    assert transform_module.TRANSFORMATION_PLAN_SCHEMA_CHANGE_CONTRACT == compilation.plan.contract
+    assert transform_module.SPSS_FRONTEND_SCHEMA_CHANGE_CONTRACT == compilation.frontend_contract
 
 def test_string_comparison_fails_closed_until_exact_collation_is_supported() -> None:
     error = _error(
@@ -584,26 +586,49 @@ def test_v02_plan_and_schema_reject_decimal_format_that_cannot_fit() -> None:
         )
 
 
-def test_schema_operations_require_v03_contract() -> None:
-    operation = CreateVariableOperation("note", "string", 8)
+@pytest.mark.parametrize("contract", [
+    "openstatspec-transformation-plan-v0.1",
+    "openstatspec-transformation-plan-v0.2",
+])
+@pytest.mark.parametrize("operation", [
+    CreateVariableOperation("note", "string", 8), DeleteVariableOperation("note"),
+])
+def test_official_plan_contracts_reject_schema_operations(contract, operation) -> None:
     with pytest.raises(TransformationFrontendError) as caught:
-        TransformationPlan((operation,))
+        transformation_plan_from_dict({
+            "contract": contract, "input_alias": "parent",
+            "operations": [operation.as_dict()],
+        })
     assert caught.value.code == "invalid_transformation_plan"
 
-    plan = TransformationPlan(
-        (operation,), contract="openstatspec-transformation-plan-v0.3",
+
+def test_legacy_schema_plan_roundtrip_preserves_exact_hash() -> None:
+    serialized = (
+        '{"contract":"openstatspec-transformation-plan-v0.3","input_alias":"parent",'
+        '"operations":[{"declared_string_width":4,"op":"create_variable",'
+        '"storage_kind":"string","variable":"note"}]}'
     )
-    assert plan.contract == "openstatspec-transformation-plan-v0.3"
+    raw = json.loads(serialized)
+    legacy = transformation_plan_from_dict(raw)
+    assert canonical_plan_json(raw) == legacy.canonical_json() == serialized
+    assert canonical_plan_hash(raw) == legacy.sha256() == (
+        "3c1933c6df1ea664d506d3b7879af5141f912181884129d2861bf19e44f4e131"
+    )
+    new = transformation_plan_from_dict({
+        **raw, "contract": "openstatspec-python-schema-change-plan-v0.1",
+    })
+    assert new.operations == legacy.operations
+    assert new.sha256() != legacy.sha256()
 
 
-def test_spss_schema_commands_emit_v03_contract() -> None:
+def test_spss_schema_commands_emit_python_extension_contract() -> None:
     schema = _schema(VariableDefinition("q1", "numeric"))
     assert bind_spss_syntax(
         parse_spss_syntax("STRING note (A8)."), schema,
-    ).plan.contract == "openstatspec-transformation-plan-v0.3"
+    ).plan.contract == "openstatspec-python-schema-change-plan-v0.1"
     assert bind_spss_syntax(
         parse_spss_syntax("COMPUTE other = q1. DELETE VARIABLES q1."), schema,
-    ).plan.contract == "openstatspec-transformation-plan-v0.3"
+    ).plan.contract == "openstatspec-python-schema-change-plan-v0.1"
 
 
 def test_custom_nonempty_input_alias_is_canonical() -> None: