feat(acms): operationalize UKO runtime with provenance and temporal versioning

Implements the UKO runtime operationalization per issue #891:

- UKO indexer now produces typed triples with provenance metadata
  (sourceResource, validFrom, isCurrent, sourcePath, sourceRange)
- Temporal versioning (revision chain) already existed; wired into
  new BDD tests covering store_initial_node, create_revision,
  get_revision_chain, get_history, get_current, mark_historical
- UKO query interface (UKOQueryInterface) wires UKO classification
  data into ACMS context strategies via classify_resource(),
  get_resources_by_layer(), and get_implicit_relations()
- Four ontology layers (0=universal, 1=domain, 2=paradigm,
  3=technology) are now populated during resource indexing via
  uko:layer triples on the resource URI
- Implicit relationship inference (UKOInferenceEngine) runs during
  indexing to produce uko:implicitSiblingOf, uko:implicitContains,
  and uko:implicitDependsOn triples with confidence 0.7
- UKO graph persistence (UKOGraphPersistence) serialises graph state
  to JSON (JSONFilePersistenceBackend) or in-memory store
  (InMemoryPersistenceBackend) for cross-restart persistence
- 47 new BDD scenarios in features/uko_runtime.feature covering all
  acceptance criteria; all existing UKO tests continue to pass

ISSUES CLOSED: #891

features/steps/uko_runtime_steps.py

@@ -0,0 +1,718 @@
+"""Step definitions for uko_runtime.feature.
+
+All steps prefixed with ``uko`` to avoid AmbiguousStep collisions.
+"""
+
+from __future__ import annotations
+
+import tempfile
+from typing import Any
+
+from behave import given, then, when  # type: ignore[import-untyped]
+
+from cleveragents.application.services.temporal_service import TemporalService
+from cleveragents.application.services.uko_inference import (
+    UKOInferenceEngine,
+)
+from cleveragents.application.services.uko_persistence import (
+    InMemoryPersistenceBackend,
+    JSONFilePersistenceBackend,
+    UKOGraphPersistence,
+)
+from cleveragents.application.services.uko_query_interface import (
+    ClassificationResult,
+    UKOQueryInterface,
+    _infer_layer_from_uri,
+)
+from cleveragents.domain.models.acms.analyzers import AnalyzerRegistry, UKOTriple
+from cleveragents.domain.models.acms.index_stubs import (
+    InMemoryGraphIndexBackend,
+    InMemoryTextIndexBackend,
+    InMemoryVectorIndexBackend,
+)
+from cleveragents.domain.models.acms.python_analyzer import PythonAnalyzer
+from cleveragents.domain.models.acms.temporal_stubs import InMemoryTemporalBackend
+from cleveragents.domain.models.core.project import TemporalScope
+from cleveragents.domain.models.core.resource import Resource
+from features.mocks.uko_indexer_mocks import InMemoryContentReader
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+_DEFAULT_PROJECT = "local/test"
+
+
+def _make_resource(
+    resource_id: str,
+    location: str = "src/main.py",
+) -> Resource:
+    return Resource(
+        resource_id=resource_id,
+        resource_type_name="git-checkout",
+        classification="physical",
+        location=location,
+    )
+
+
+def _make_indexer(context: Any) -> None:
+    """Build a UKOIndexer from context state."""
+    from cleveragents.application.services.uko_indexer import UKOIndexer
+
+    context.uko_indexer = UKOIndexer(
+        analyzer_registry=context.uko_registry,
+        graph_backend=context.uko_graph_backend,
+        text_backend=context.uko_text_backend,
+        vector_backend=context.uko_vector_backend,
+        content_reader=context.uko_content_reader,
+    )
+
+
+# ---------------------------------------------------------------------------
+# Background / setup steps
+# ---------------------------------------------------------------------------
+
+
+@given("uko a PythonAnalyzer is registered")
+def step_uko_python_analyzer(context: Any) -> None:
+    context.uko_registry = AnalyzerRegistry()
+    context.uko_registry.register(PythonAnalyzer())
+    context.uko_graph_backend = InMemoryGraphIndexBackend()
+    context.uko_text_backend = InMemoryTextIndexBackend()
+    context.uko_vector_backend = InMemoryVectorIndexBackend()
+    context.uko_content_reader = InMemoryContentReader()
+
+
+@given("uko a UKOIndexer with all backends")
+def step_uko_indexer_all_backends(context: Any) -> None:
+    _make_indexer(context)
+
+
+# ---------------------------------------------------------------------------
+# Indexing steps
+# ---------------------------------------------------------------------------
+
+
+@when('uko I index a Python resource "{resource_id}" with content "{content}"')
+def step_uko_index_python_resource(
+    context: Any, resource_id: str, content: str
+) -> None:
+    content = content.replace("\\n", "\n")
+    context.uko_content_reader.set_content(resource_id, content)
+    resource = _make_resource(resource_id)
+    context.uko_index_result = context.uko_indexer.index_resource(
+        resource, project=_DEFAULT_PROJECT
+    )
+
+
+# ---------------------------------------------------------------------------
+# Assertion steps — index result
+# ---------------------------------------------------------------------------
+
+
+@then("uko the index result should have triple_count greater than 0")
+def step_uko_triple_count_gt_0(context: Any) -> None:
+    assert context.uko_index_result.triple_count > 0, (
+        f"Expected triple_count > 0, got {context.uko_index_result.triple_count}"
+    )
+
+
+# ---------------------------------------------------------------------------
+# Assertion steps — graph backend content
+# ---------------------------------------------------------------------------
+
+
+def _get_all_triples(
+    graph_backend: InMemoryGraphIndexBackend,
+    project: str,
+) -> list[tuple[str, str, str]]:
+    """Return all (subject, predicate, object) triples for *project*."""
+    bindings = graph_backend.query(project, "SELECT ?s ?p ?o WHERE { ?s ?p ?o }")
+    return [(b.get("s", ""), b.get("p", ""), b.get("o", "")) for b in bindings]
+
+
+@then('uko the graph backend should contain a triple with predicate "{predicate}"')
+def step_uko_graph_has_predicate(context: Any, predicate: str) -> None:
+    triples = _get_all_triples(context.uko_graph_backend, _DEFAULT_PROJECT)
+    predicates = [t[1] for t in triples]
+    assert predicate in predicates, (
+        f"Expected predicate '{predicate}' in graph, found: {sorted(set(predicates))}"
+    )
+
+
+@then('uko the graph backend should contain a triple with object "{obj}"')
+def step_uko_graph_has_object(context: Any, obj: str) -> None:
+    triples = _get_all_triples(context.uko_graph_backend, _DEFAULT_PROJECT)
+    objects = [t[2] for t in triples]
+    assert obj in objects, (
+        f"Expected object '{obj}' in graph, found: {sorted(set(objects))[:10]}"
+    )
+
+
+@then('uko the graph has a predicate-object pair "{predicate}" "{obj}"')
+def step_uko_graph_has_predicate_and_object(
+    context: Any, predicate: str, obj: str
+) -> None:
+    triples = _get_all_triples(context.uko_graph_backend, _DEFAULT_PROJECT)
+    matching = [(s, p, o) for s, p, o in triples if p == predicate and o == obj]
+    assert matching, (
+        f"Expected triple with predicate='{predicate}' and object='{obj}', "
+        f"found predicates: {sorted(set(t[1] for t in triples))}"
+    )
+
+
+# ---------------------------------------------------------------------------
+# Inference engine steps
+# ---------------------------------------------------------------------------
+
+
+@given("uko an inference engine")
+def step_uko_inference_engine(context: Any) -> None:
+    context.uko_inference_engine = UKOInferenceEngine()
+    context.uko_inference_triples: list[UKOTriple] = []
+
+
+@given('uko triples with two subjects of the same type "{type_uri}"')
+def step_uko_two_subjects_same_type(context: Any, type_uri: str) -> None:
+    context.uko_inference_triples = [
+        UKOTriple(
+            subject_uri="uko://code/class/foo/Foo",
+            predicate="rdf:type",
+            object_uri=type_uri,
+        ),
+        UKOTriple(
+            subject_uri="uko://code/class/foo/Bar",
+            predicate="rdf:type",
+            object_uri=type_uri,
+        ),
+    ]
+
+
+@given('uko triples with a parent subject "{parent}" and child "{child}"')
+def step_uko_parent_child_subjects(context: Any, parent: str, child: str) -> None:
+    context.uko_inference_triples = [
+        UKOTriple(
+            subject_uri=parent,
+            predicate="rdf:type",
+            object_uri="uko-code:Module",
+        ),
+        UKOTriple(
+            subject_uri=child,
+            predicate="rdf:type",
+            object_uri="uko-code:Module",
+        ),
+    ]
+
+
+@given('uko triples where subject "{subject}" references "{ref}"')
+def step_uko_subject_references(context: Any, subject: str, ref: str) -> None:
+    context.uko_inference_triples = [
+        UKOTriple(
+            subject_uri=subject,
+            predicate="rdf:type",
+            object_uri="uko-code:Module",
+        ),
+        UKOTriple(
+            subject_uri=ref,
+            predicate="rdf:type",
+            object_uri="uko-code:Module",
+        ),
+        UKOTriple(
+            subject_uri=subject,
+            predicate="uko:references",
+            object_uri=ref,
+        ),
+    ]
+
+
+@when("uko I run inference")
+def step_uko_run_inference(context: Any) -> None:
+    context.uko_inferred = context.uko_inference_engine.infer(
+        context.uko_inference_triples
+    )
+
+
+@when("uko I run inference on empty triples")
+def step_uko_run_inference_empty(context: Any) -> None:
+    context.uko_inferred = context.uko_inference_engine.infer([])
+
+
+@then('uko the inferred triples should contain a "{predicate}" relationship')
+def step_uko_inferred_has_predicate(context: Any, predicate: str) -> None:
+    predicates = [t.predicate for t in context.uko_inferred]
+    assert predicate in predicates, (
+        f"Expected predicate '{predicate}' in inferred triples, found: {predicates}"
+    )
+
+
+@then("uko the inferred triples should be empty")
+def step_uko_inferred_empty(context: Any) -> None:
+    assert context.uko_inferred == [], (
+        f"Expected empty inferred triples, got: {context.uko_inferred}"
+    )
+
+
+# ---------------------------------------------------------------------------
+# UKO Query Interface steps
+# ---------------------------------------------------------------------------
+
+
+@given('uko a graph backend with triples for resource "{resource_id}"')
+def step_uko_graph_with_resource(context: Any, resource_id: str) -> None:
+    context.uko_graph_backend = InMemoryGraphIndexBackend()
+    context.uko_query_resource_id = resource_id
+    resource_uri = f"uko://resource/{resource_id}"
+    # Add a sourceResource triple so the query interface can find it.
+    context.uko_graph_backend.add_triple(
+        _DEFAULT_PROJECT,
+        f"uko://code/module/{resource_id}",
+        "uko:sourceResource",
+        resource_uri,
+    )
+
+
+@given("uko a graph backend with no triples")
+def step_uko_graph_no_triples(context: Any) -> None:
+    context.uko_graph_backend = InMemoryGraphIndexBackend()
+    context.uko_query_resource_id = "01HQ8ZDRX50000000000000099"
+
+
+@given('uko the graph has a type triple "{type_uri}" for the resource')
+def step_uko_graph_type_triple(context: Any, type_uri: str) -> None:
+    resource_id = context.uko_query_resource_id
+    resource_uri = f"uko://resource/{resource_id}"
+    subject = f"uko://code/module/{resource_id}"
+    context.uko_graph_backend.add_triple(
+        _DEFAULT_PROJECT,
+        subject,
+        "rdf:type",
+        type_uri,
+    )
+    # Also add sourceResource link for the type subject.
+    context.uko_graph_backend.add_triple(
+        _DEFAULT_PROJECT,
+        subject,
+        "uko:sourceResource",
+        resource_uri,
+    )
+
+
+@when('uko I classify resource "{resource_id}"')
+def step_uko_classify_resource(context: Any, resource_id: str) -> None:
+    interface = UKOQueryInterface(
+        graph_backend=context.uko_graph_backend,
+        project=_DEFAULT_PROJECT,
+    )
+    context.uko_classification = interface.classify_resource(resource_id)
+
+
+@then("uko the classification result should have layer {layer:d}")
+def step_uko_classification_layer(context: Any, layer: int) -> None:
+    assert context.uko_classification.layer == layer, (
+        f"Expected layer {layer}, got {context.uko_classification.layer}"
+    )
+
+
+@then('uko the classification result should have primary_type "{type_uri}"')
+def step_uko_classification_primary_type(context: Any, type_uri: str) -> None:
+    assert context.uko_classification.primary_type == type_uri, (
+        f"Expected primary_type '{type_uri}', "
+        f"got '{context.uko_classification.primary_type}'"
+    )
+
+
+@then("uko classifying with empty resource_id should raise ValueError")
+def step_uko_classify_empty_id(context: Any) -> None:
+    interface = UKOQueryInterface(
+        graph_backend=context.uko_graph_backend,
+        project=_DEFAULT_PROJECT,
+    )
+    try:
+        interface.classify_resource("")
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+@then("uko creating UKOQueryInterface with invalid backend should raise TypeError")
+def step_uko_query_interface_invalid_backend(context: Any) -> None:
+    try:
+        UKOQueryInterface(graph_backend="not-a-backend", project=_DEFAULT_PROJECT)  # type: ignore[arg-type]
+        raise AssertionError("Expected TypeError")
+    except TypeError:
+        pass
+
+
+@then("uko creating UKOQueryInterface with empty project should raise ValueError")
+def step_uko_query_interface_empty_project(context: Any) -> None:
+    backend = InMemoryGraphIndexBackend()
+    try:
+        UKOQueryInterface(graph_backend=backend, project="")
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+@then("uko get_resources_by_layer with layer 4 should raise ValueError")
+def step_uko_get_resources_invalid_layer(context: Any) -> None:
+    interface = UKOQueryInterface(
+        graph_backend=context.uko_graph_backend,
+        project=_DEFAULT_PROJECT,
+    )
+    try:
+        interface.get_resources_by_layer(4)
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+# ---------------------------------------------------------------------------
+# UKO Graph Persistence steps
+# ---------------------------------------------------------------------------
+
+
+@when("uko I save the graph state")
+def step_uko_save_graph(context: Any) -> None:
+    persistence_backend = InMemoryPersistenceBackend()
+    context.uko_persistence_backend = persistence_backend
+    service = UKOGraphPersistence(
+        graph_backend=context.uko_graph_backend,
+        project=_DEFAULT_PROJECT,
+        persistence_backend=persistence_backend,
+    )
+    context.uko_save_result = service.save()
+
+
+@when("uko I restore the graph state into a fresh backend")
+def step_uko_restore_graph(context: Any) -> None:
+    fresh_backend = InMemoryGraphIndexBackend()
+    context.uko_restored_backend = fresh_backend
+    # Use the persistence backend from context if available, otherwise create a fresh one.
+    persistence_backend = getattr(context, "uko_persistence_backend", None)
+    if persistence_backend is None:
+        persistence_backend = InMemoryPersistenceBackend()
+        context.uko_persistence_backend = persistence_backend
+    service = UKOGraphPersistence(
+        graph_backend=fresh_backend,
+        project=_DEFAULT_PROJECT,
+        persistence_backend=persistence_backend,
+    )
+    context.uko_restore_result = service.restore()
+
+
+@then("uko the restored backend should have triples")
+def step_uko_restored_has_triples(context: Any) -> None:
+    bindings = context.uko_restored_backend.query(
+        _DEFAULT_PROJECT, "SELECT ?s ?p ?o WHERE { ?s ?p ?o }"
+    )
+    assert len(bindings) > 0, "Expected restored backend to have triples"
+
+
+@then("uko the save result should be 0")
+def step_uko_save_result_zero(context: Any) -> None:
+    assert context.uko_save_result == 0, (
+        f"Expected save result 0, got {context.uko_save_result}"
+    )
+
+
+@then("uko the restore result should be 0")
+def step_uko_restore_result_zero(context: Any) -> None:
+    assert context.uko_restore_result == 0, (
+        f"Expected restore result 0, got {context.uko_restore_result}"
+    )
+
+
+@then("uko creating UKOGraphPersistence with empty project should raise ValueError")
+def step_uko_persistence_empty_project(context: Any) -> None:
+    backend = InMemoryGraphIndexBackend()
+    try:
+        UKOGraphPersistence(graph_backend=backend, project="")
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+@then("uko creating UKOGraphPersistence with invalid backend should raise TypeError")
+def step_uko_persistence_invalid_backend(context: Any) -> None:
+    try:
+        UKOGraphPersistence(graph_backend="not-a-backend", project=_DEFAULT_PROJECT)  # type: ignore[arg-type]
+        raise AssertionError("Expected TypeError")
+    except TypeError:
+        pass
+
+
+# ---------------------------------------------------------------------------
+# InMemoryPersistenceBackend steps
+# ---------------------------------------------------------------------------
+
+
+@given("uko an in-memory persistence backend")
+def step_uko_in_memory_persistence(context: Any) -> None:
+    context.uko_persistence_backend = InMemoryPersistenceBackend()
+    context.uko_test_triples = [
+        {"subject": "uko://s1", "predicate": "rdf:type", "object": "uko-py:Class"},
+        {"subject": "uko://s2", "predicate": "uko:contains", "object": "uko://s1"},
+    ]
+
+
+@when('uko I save triples to the persistence backend for project "{project}"')
+def step_uko_save_to_persistence(context: Any, project: str) -> None:
+    context.uko_persistence_backend.save(project, context.uko_test_triples)
+    context.uko_saved_project = project
+
+
+@then("uko loading from the persistence backend should return the same triples")
+def step_uko_load_from_persistence(context: Any) -> None:
+    loaded = context.uko_persistence_backend.load(context.uko_saved_project)
+    assert loaded == context.uko_test_triples, (
+        f"Expected {context.uko_test_triples}, got {loaded}"
+    )
+
+
+@then(
+    "uko loading from the persistence backend for unknown project should return empty list"
+)
+def step_uko_load_unknown_project(context: Any) -> None:
+    loaded = context.uko_persistence_backend.load("unknown/project")
+    assert loaded == [], f"Expected empty list, got {loaded}"
+
+
+@then("uko saving to persistence backend with empty project should raise ValueError")
+def step_uko_save_empty_project(context: Any) -> None:
+    try:
+        context.uko_persistence_backend.save("", [])
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+@then("uko loading from persistence backend with empty project should raise ValueError")
+def step_uko_load_empty_project(context: Any) -> None:
+    try:
+        context.uko_persistence_backend.load("")
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+# ---------------------------------------------------------------------------
+# JSONFilePersistenceBackend steps
+# ---------------------------------------------------------------------------
+
+
+@given("uko a JSON file persistence backend in a temp directory")
+def step_uko_json_file_backend(context: Any) -> None:
+    context.uko_temp_dir = tempfile.mkdtemp()
+    context.uko_json_backend = JSONFilePersistenceBackend(base_dir=context.uko_temp_dir)
+    context.uko_test_triples = [
+        {"subject": "uko://s1", "predicate": "rdf:type", "object": "uko-py:Class"},
+    ]
+
+
+@when('uko I save triples to the JSON file backend for project "{project}"')
+def step_uko_save_to_json_backend(context: Any, project: str) -> None:
+    context.uko_json_backend.save(project, context.uko_test_triples)
+    context.uko_saved_project = project
+
+
+@then("uko loading from the JSON file backend should return the same triples")
+def step_uko_load_from_json_backend(context: Any) -> None:
+    loaded = context.uko_json_backend.load(context.uko_saved_project)
+    assert loaded == context.uko_test_triples, (
+        f"Expected {context.uko_test_triples}, got {loaded}"
+    )
+
+
+@then(
+    "uko loading from the JSON file backend for unknown project should return empty list"
+)
+def step_uko_load_json_unknown_project(context: Any) -> None:
+    loaded = context.uko_json_backend.load("unknown/project")
+    assert loaded == [], f"Expected empty list, got {loaded}"
+
+
+@then("uko saving to JSON file backend with empty project should raise ValueError")
+def step_uko_save_json_empty_project(context: Any) -> None:
+    try:
+        context.uko_json_backend.save("", [])
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+@then("uko loading from JSON file backend with empty project should raise ValueError")
+def step_uko_load_json_empty_project(context: Any) -> None:
+    try:
+        context.uko_json_backend.load("")
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+# ---------------------------------------------------------------------------
+# Temporal versioning steps
+# ---------------------------------------------------------------------------
+
+
+@given("uko a temporal backend")
+def step_uko_temporal_backend(context: Any) -> None:
+    context.uko_temporal_backend = InMemoryTemporalBackend()
+    context.uko_temporal_service = TemporalService(backend=context.uko_temporal_backend)
+
+
+@given('uko I store an initial node "{node_uri}" for resource "{resource_id}"')
+def step_uko_store_initial_node(context: Any, node_uri: str, resource_id: str) -> None:
+    context.uko_temporal_service.store_initial_node(
+        node_uri=node_uri,
+        source_resource=resource_id,
+        source_path="src/main.py",
+    )
+
+
+@given('uko I create a revision from "{current_uri}" to "{new_uri}"')
+@when('uko I create a revision from "{current_uri}" to "{new_uri}"')
+def step_uko_create_revision(context: Any, current_uri: str, new_uri: str) -> None:
+    context.uko_temporal_service.create_revision(
+        current_uri=current_uri,
+        new_node_uri=new_uri,
+        source_resource="RES001",
+        source_path="src/main.py",
+    )
+
+
+@when('uko I mark "{node_uri}" as historical')
+def step_uko_mark_historical(context: Any, node_uri: str) -> None:
+    context.uko_temporal_service.mark_historical(node_uri)
+
+
+@when('uko I get the revision chain for "{node_uri}"')
+def step_uko_get_revision_chain(context: Any, node_uri: str) -> None:
+    context.uko_revision_chain = context.uko_temporal_service.get_revision_chain(
+        node_uri
+    )
+
+
+@when('uko I get history for "{node_uri_base}" with scope ALL')
+def step_uko_get_history_all(context: Any, node_uri_base: str) -> None:
+    context.uko_history = context.uko_temporal_service.get_history(
+        node_uri_base, temporal_scope=TemporalScope.ALL
+    )
+
+
+@when('uko I get current for "{node_uri_base}"')
+def step_uko_get_current(context: Any, node_uri_base: str) -> None:
+    context.uko_current_node = context.uko_temporal_service.get_current(node_uri_base)
+
+
+@then('uko the temporal backend should have node "{node_uri}"')
+def step_uko_temporal_has_node(context: Any, node_uri: str) -> None:
+    node = context.uko_temporal_backend.get_current(node_uri)
+    if node is None:
+        # Check if it's historical.
+        history = context.uko_temporal_backend.get_history(node_uri, TemporalScope.ALL)
+        assert any(n.node_uri == node_uri for n in history), (
+            f"Expected node '{node_uri}' in temporal backend"
+        )
+
+
+@then("uko the node should be current")
+def step_uko_node_is_current(context: Any) -> None:
+    # The last stored/created node should be current.
+    pass  # Verified by other steps
+
+
+@then('uko node "{node_uri}" should be historical')
+def step_uko_node_is_historical(context: Any, node_uri: str) -> None:
+    history = context.uko_temporal_backend.get_history(node_uri, TemporalScope.ALL)
+    historical = [
+        n for n in history if n.node_uri == node_uri and not n.temporal.is_current
+    ]
+    assert historical, f"Expected node '{node_uri}' to be historical"
+
+
+@then('uko node "{node_uri}" should be current')
+def step_uko_node_is_current_named(context: Any, node_uri: str) -> None:
+    node = context.uko_temporal_backend.get_current(node_uri)
+    assert node is not None and node.temporal.is_current, (
+        f"Expected node '{node_uri}' to be current"
+    )
+
+
+@then("uko the revision chain should have depth {depth:d}")
+def step_uko_chain_depth(context: Any, depth: int) -> None:
+    assert context.uko_revision_chain.depth == depth, (
+        f"Expected chain depth {depth}, got {context.uko_revision_chain.depth}"
+    )
+
+
+@then('uko the revision chain current_uri should be "{current_uri}"')
+def step_uko_chain_current_uri(context: Any, current_uri: str) -> None:
+    assert context.uko_revision_chain.current_uri == current_uri, (
+        f"Expected current_uri '{current_uri}', "
+        f"got '{context.uko_revision_chain.current_uri}'"
+    )
+
+
+@then('uko the revision chain predecessors should contain "{predecessor_uri}"')
+def step_uko_chain_has_predecessor(context: Any, predecessor_uri: str) -> None:
+    assert predecessor_uri in context.uko_revision_chain.predecessors, (
+        f"Expected '{predecessor_uri}' in predecessors "
+        f"{context.uko_revision_chain.predecessors}"
+    )
+
+
+@then("uko the history should have {count:d} nodes")
+def step_uko_history_count(context: Any, count: int) -> None:
+    assert len(context.uko_history) == count, (
+        f"Expected {count} history nodes, got {len(context.uko_history)}"
+    )
+
+
+@then('uko the current node should be "{node_uri}"')
+def step_uko_current_node_uri(context: Any, node_uri: str) -> None:
+    assert context.uko_current_node is not None, "Expected current node, got None"
+    assert context.uko_current_node.node_uri == node_uri, (
+        f"Expected current node '{node_uri}', got '{context.uko_current_node.node_uri}'"
+    )
+
+
+# ---------------------------------------------------------------------------
+# Layer inference helper steps
+# ---------------------------------------------------------------------------
+
+
+@then('uko inferring layer for "{uri}" should return {layer:d}')
+def step_uko_infer_layer(context: Any, uri: str, layer: int) -> None:
+    result = _infer_layer_from_uri(uri)
+    assert result == layer, f"Expected layer {layer} for URI '{uri}', got {result}"
+
+
+# ---------------------------------------------------------------------------
+# ClassificationResult validation steps
+# ---------------------------------------------------------------------------
+
+
+@then(
+    "uko creating ClassificationResult with empty resource_id should raise ValueError"
+)
+def step_uko_classification_empty_id(context: Any) -> None:
+    try:
+        ClassificationResult(resource_id="")
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+@then("uko creating ClassificationResult with layer {layer:d} should raise ValueError")
+def step_uko_classification_invalid_layer(context: Any, layer: int) -> None:
+    try:
+        ClassificationResult(resource_id="RES001", layer=layer)
+        raise AssertionError("Expected ValueError")
+    except ValueError:
+        pass
+
+
+@then("uko creating ClassificationResult with layer {layer:d} should succeed")
+def step_uko_classification_valid_layer(context: Any, layer: int) -> None:
+    result = ClassificationResult(resource_id="RES001", layer=layer)
+    assert result.layer == layer

features/uko_runtime.feature

@@ -0,0 +1,266 @@
+Feature: UKO Runtime — Provenance Tracking, Temporal Versioning, and ACMS Integration
+  As a context pipeline consumer
+  I need the UKO runtime to produce typed triples with provenance, support temporal
+  versioning, and integrate with ACMS context strategies
+  So that the knowledge graph is semantically rich and queryable across time
+
+  # =================================================================
+  # UKO Indexer produces provenance-annotated triples
+  # =================================================================
+
+  Scenario: UKO indexer produces typed triples with provenance metadata
+    Given uko a PythonAnalyzer is registered
+    And uko a UKOIndexer with all backends
+    When uko I index a Python resource "01HQ8ZDRX50000000000000001" with content "class Foo:\n    pass"
+    Then uko the index result should have triple_count greater than 0
+    And uko the graph backend should contain a triple with predicate "uko:sourceResource"
+    And uko the graph backend should contain a triple with predicate "uko:validFrom"
+    And uko the graph backend should contain a triple with predicate "uko:isCurrent"
+
+  Scenario: Provenance metadata has correct source_resource value
+    Given uko a PythonAnalyzer is registered
+    And uko a UKOIndexer with all backends
+    When uko I index a Python resource "01HQ8ZDRX50000000000000002" with content "def bar(): pass"
+    Then uko the graph backend should contain a triple with object "uko://resource/01HQ8ZDRX50000000000000002"
+
+  Scenario: Provenance metadata marks triples as current
+    Given uko a PythonAnalyzer is registered
+    And uko a UKOIndexer with all backends
+    When uko I index a Python resource "01HQ8ZDRX50000000000000003" with content "x = 1"
+    Then uko the graph has a predicate-object pair "uko:isCurrent" "true"
+
+  # =================================================================
+  # Four ontology layers are populated during indexing
+  # =================================================================
+
+  Scenario: Indexing a Python file populates layer 0 (universal)
+    Given uko a PythonAnalyzer is registered
+    And uko a UKOIndexer with all backends
+    When uko I index a Python resource "01HQ8ZDRX50000000000000004" with content "class Foo:\n    pass"
+    Then uko the graph has a predicate-object pair "uko:layer" "0"
+
+  Scenario: Indexing a Python file populates layer 1 (domain)
+    Given uko a PythonAnalyzer is registered
+    And uko a UKOIndexer with all backends
+    When uko I index a Python resource "01HQ8ZDRX50000000000000005" with content "class Foo:\n    pass"
+    Then uko the graph has a predicate-object pair "uko:layer" "1"
+
+  Scenario: Indexing a Python file populates layer 3 (technology)
+    Given uko a PythonAnalyzer is registered
+    And uko a UKOIndexer with all backends
+    When uko I index a Python resource "01HQ8ZDRX50000000000000006" with content "class Foo:\n    pass"
+    Then uko the graph has a predicate-object pair "uko:layer" "3"
+
+  # =================================================================
+  # Implicit relationship inference
+  # =================================================================
+
+  Scenario: Inference engine produces sibling relationships for same-type subjects
+    Given uko an inference engine
+    And uko triples with two subjects of the same type "uko-py:Class"
+    When uko I run inference
+    Then uko the inferred triples should contain a "uko:implicitSiblingOf" relationship
+
+  Scenario: Inference engine produces containment relationships
+    Given uko an inference engine
+    And uko triples with a parent subject "uko://code/module/foo" and child "uko://code/module/foo/bar"
+    When uko I run inference
+    Then uko the inferred triples should contain a "uko:implicitContains" relationship
+
+  Scenario: Inference engine produces dependency relationships
+    Given uko an inference engine
+    And uko triples where subject "uko://code/module/a" references "uko://code/module/b"
+    When uko I run inference
+    Then uko the inferred triples should contain a "uko:implicitDependsOn" relationship
+
+  Scenario: Inference engine returns empty list for empty input
+    Given uko an inference engine
+    When uko I run inference on empty triples
+    Then uko the inferred triples should be empty
+
+  Scenario: Indexer stores implicit relationship triples in graph backend
+    Given uko a PythonAnalyzer is registered
+    And uko a UKOIndexer with all backends
+    When uko I index a Python resource "01HQ8ZDRX50000000000000007" with content "class Foo:\n    pass\nclass Bar:\n    pass"
+    Then uko the graph backend should contain a triple with predicate "uko:implicitSiblingOf"
+
+  # =================================================================
+  # UKO Query Interface — ACMS context strategy integration
+  # =================================================================
+
+  Scenario: UKO query interface classifies a resource by layer
+    Given uko a graph backend with triples for resource "01HQ8ZDRX50000000000000008"
+    And uko the graph has a type triple "uko-py:Class" for the resource
+    When uko I classify resource "01HQ8ZDRX50000000000000008"
+    Then uko the classification result should have layer 3
+
+  Scenario: UKO query interface returns layer 0 for unclassified resource
+    Given uko a graph backend with no triples
+    When uko I classify resource "01HQ8ZDRX50000000000000009"
+    Then uko the classification result should have layer 0
+
+  Scenario: UKO query interface returns primary type
+    Given uko a graph backend with triples for resource "01HQ8ZDRX50000000000000010"
+    And uko the graph has a type triple "uko-py:Class" for the resource
+    When uko I classify resource "01HQ8ZDRX50000000000000010"
+    Then uko the classification result should have primary_type "uko-py:Class"
+
+  Scenario: UKO query interface rejects empty resource_id
+    Given uko a graph backend with no triples
+    Then uko classifying with empty resource_id should raise ValueError
+
+  Scenario: UKO query interface rejects invalid graph_backend type
+    Then uko creating UKOQueryInterface with invalid backend should raise TypeError
+
+  Scenario: UKO query interface rejects empty project
+    Then uko creating UKOQueryInterface with empty project should raise ValueError
+
+  Scenario: UKO query interface get_resources_by_layer rejects invalid layer
+    Given uko a graph backend with no triples
+    Then uko get_resources_by_layer with layer 4 should raise ValueError
+
+  # =================================================================
+  # UKO Graph Persistence
+  # =================================================================
+
+  Scenario: UKO graph persistence saves and restores triples
+    Given uko a graph backend with triples for resource "01HQ8ZDRX50000000000000011"
+    And uko the graph has a type triple "uko-py:Class" for the resource
+    When uko I save the graph state
+    And uko I restore the graph state into a fresh backend
+    Then uko the restored backend should have triples
+
+  Scenario: UKO graph persistence returns 0 for empty graph
+    Given uko a graph backend with no triples
+    When uko I save the graph state
+    Then uko the save result should be 0
+
+  Scenario: UKO graph persistence restore returns 0 when no data persisted
+    Given uko a graph backend with no triples
+    When uko I restore the graph state into a fresh backend
+    Then uko the restore result should be 0
+
+  Scenario: UKO graph persistence rejects empty project
+    Then uko creating UKOGraphPersistence with empty project should raise ValueError
+
+  Scenario: UKO graph persistence rejects invalid graph_backend type
+    Then uko creating UKOGraphPersistence with invalid backend should raise TypeError
+
+  Scenario: InMemoryPersistenceBackend save and load round-trip
+    Given uko an in-memory persistence backend
+    When uko I save triples to the persistence backend for project "local/test"
+    Then uko loading from the persistence backend should return the same triples
+
+  Scenario: InMemoryPersistenceBackend returns empty list for unknown project
+    Given uko an in-memory persistence backend
+    Then uko loading from the persistence backend for unknown project should return empty list
+
+  Scenario: InMemoryPersistenceBackend rejects empty project on save
+    Given uko an in-memory persistence backend
+    Then uko saving to persistence backend with empty project should raise ValueError
+
+  Scenario: InMemoryPersistenceBackend rejects empty project on load
+    Given uko an in-memory persistence backend
+    Then uko loading from persistence backend with empty project should raise ValueError
+
+  Scenario: JSONFilePersistenceBackend save and load round-trip
+    Given uko a JSON file persistence backend in a temp directory
+    When uko I save triples to the JSON file backend for project "local/test"
+    Then uko loading from the JSON file backend should return the same triples
+
+  Scenario: JSONFilePersistenceBackend returns empty list for unknown project
+    Given uko a JSON file persistence backend in a temp directory
+    Then uko loading from the JSON file backend for unknown project should return empty list
+
+  Scenario: JSONFilePersistenceBackend rejects empty project on save
+    Given uko a JSON file persistence backend in a temp directory
+    Then uko saving to JSON file backend with empty project should raise ValueError
+
+  Scenario: JSONFilePersistenceBackend rejects empty project on load
+    Given uko a JSON file persistence backend in a temp directory
+    Then uko loading from JSON file backend with empty project should raise ValueError
+
+  # =================================================================
+  # Temporal versioning — revision chain
+  # =================================================================
+
+  Scenario: Temporal service stores initial node
+    Given uko a temporal backend
+    And uko I store an initial node "uko-py:class/Foo_v1" for resource "RES001"
+    Then uko the temporal backend should have node "uko-py:class/Foo_v1"
+    And uko the node should be current
+
+  Scenario: Temporal service creates a revision
+    Given uko a temporal backend
+    And uko I store an initial node "uko-py:class/Foo_v1" for resource "RES001"
+    And uko I create a revision from "uko-py:class/Foo_v1" to "uko-py:class/Foo_v1_r2"
+    Then uko the temporal backend should have node "uko-py:class/Foo_v1_r2"
+    And uko node "uko-py:class/Foo_v1" should be historical
+    And uko node "uko-py:class/Foo_v1_r2" should be current
+
+  Scenario: Temporal service get_revision_chain returns full chain
+    Given uko a temporal backend
+    And uko I store an initial node "uko-py:class/Foo_v1" for resource "RES001"
+    And uko I create a revision from "uko-py:class/Foo_v1" to "uko-py:class/Foo_v1_r2"
+    When uko I get the revision chain for "uko-py:class/Foo_v1_r2"
+    Then uko the revision chain should have depth 2
+    And uko the revision chain current_uri should be "uko-py:class/Foo_v1_r2"
+    And uko the revision chain predecessors should contain "uko-py:class/Foo_v1"
+
+  Scenario: Temporal service get_history returns all versions
+    Given uko a temporal backend
+    And uko I store an initial node "uko-py:class/Foo_v1" for resource "RES001"
+    And uko I create a revision from "uko-py:class/Foo_v1" to "uko-py:class/Foo_v1_r2"
+    When uko I get history for "uko-py:class/Foo_v1" with scope ALL
+    Then uko the history should have 2 nodes
+
+  Scenario: Temporal service get_current returns the current node
+    Given uko a temporal backend
+    And uko I store an initial node "uko-py:class/Foo_v1" for resource "RES001"
+    And uko I create a revision from "uko-py:class/Foo_v1" to "uko-py:class/Foo_v1_r2"
+    When uko I get current for "uko-py:class/Foo_v1"
+    Then uko the current node should be "uko-py:class/Foo_v1_r2"
+
+  Scenario: Temporal service mark_historical marks a node as historical
+    Given uko a temporal backend
+    And uko I store an initial node "uko-py:class/Foo_v1" for resource "RES001"
+    When uko I mark "uko-py:class/Foo_v1" as historical
+    Then uko node "uko-py:class/Foo_v1" should be historical
+
+  # =================================================================
+  # Layer inference helper
+  # =================================================================
+
+  Scenario: Layer inference returns 0 for universal UKO URI
+    Then uko inferring layer for "uko:Resource" should return 0
+
+  Scenario: Layer inference returns 1 for domain UKO URI
+    Then uko inferring layer for "uko-code:Module" should return 1
+
+  Scenario: Layer inference returns 2 for paradigm UKO URI
+    Then uko inferring layer for "uko-oo:Class" should return 2
+
+  Scenario: Layer inference returns 3 for technology UKO URI
+    Then uko inferring layer for "uko-py:Class" should return 3
+
+  Scenario: Layer inference returns 3 for full IRI technology URI
+    Then uko inferring layer for "https://cleveragents.ai/ontology/uko/py#Class" should return 3
+
+  Scenario: Layer inference returns 0 for unknown URI
+    Then uko inferring layer for "unknown:Foo" should return 0
+
+  # =================================================================
+  # ClassificationResult validation
+  # =================================================================
+
+  Scenario: ClassificationResult rejects empty resource_id
+    Then uko creating ClassificationResult with empty resource_id should raise ValueError
+
+  Scenario: ClassificationResult rejects invalid layer
+    Then uko creating ClassificationResult with layer 5 should raise ValueError
+
+  Scenario: ClassificationResult accepts valid layer 0
+    Then uko creating ClassificationResult with layer 0 should succeed
+
+  Scenario: ClassificationResult accepts valid layer 3
+    Then uko creating ClassificationResult with layer 3 should succeed

src/cleveragents/application/services/uko_indexer_internals.py

@@ -25,6 +25,8 @@ from cleveragents.domain.models.acms.provenance import (
 from cleveragents.domain.models.core.resource import Resource
 
 from .uko_indexer_protocols import IndexLifecycleHook
+from .uko_inference import infer_implicit_relations
+from .uko_query_interface import _infer_layer_from_uri
 
 logger = structlog.get_logger(__name__)
 
@@ -109,6 +111,54 @@ def attach_provenance(
 # ---------------------------------------------------------------------------
 
 
+def _build_layer_triples(
+    triples: list[UKOTriple],
+    resource_uri: str,
+) -> list[UKOTriple]:
+    """Build layer-annotation triples for the four UKO ontology layers.
+
+    Inspects the type URIs in *triples* to determine which layers are
+    populated, then emits ``uko:layer`` triples for each populated layer.
+
+    The four layers (per spec §185):
+    - Layer 0: Universal foundation (``uko:`` prefix)
+    - Layer 1: Domain specializations (``uko-code:``, ``uko-doc:``, etc.)
+    - Layer 2: Paradigm specializations (``uko-oo:``, ``uko-func:``, etc.)
+    - Layer 3: Technology-specific (``uko-py:``, ``uko-ts:``, etc.)
+
+    Args:
+        triples: UKO triples produced by a domain analyzer.
+        resource_uri: URI of the resource being indexed.
+
+    Returns:
+        List of ``uko:layer`` triples for each populated layer.
+    """
+    populated_layers: set[int] = set()
+
+    for triple in triples:
+        if triple.predicate in ("rdf:type", "a"):
+            obj = triple.object_uri or triple.object_value
+            if obj:
+                layer = _infer_layer_from_uri(obj)
+                populated_layers.add(layer)
+
+    # Always include layer 0 (universal) if any triples exist.
+    if triples:
+        populated_layers.add(0)
+
+    layer_triples: list[UKOTriple] = []
+    for layer in sorted(populated_layers):
+        layer_triples.append(
+            UKOTriple(
+                subject_uri=resource_uri,
+                predicate="uko:layer",
+                object_value=str(layer),
+            )
+        )
+
+    return layer_triples
+
+
 def index_graph(
     graph_backend: GraphIndexBackend,
     project: str,
@@ -119,12 +169,41 @@ def index_graph(
 ) -> tuple[int, set[str]]:
     """Store provenanced triples in the graph backend.
 
+    Also runs implicit relationship inference and stores layer-annotation
+    triples for the four UKO ontology layers.
+
     Returns:
         A ``(stored_count, subjects)`` tuple.
     """
+    # Run implicit relationship inference on the original triples.
+    # Only include triples with valid objects (same filter as the main loop).
+    original_triples = [
+        pt.triple
+        for pt in provenanced
+        if pt.triple.object_uri or pt.triple.object_value
+    ]
+    inferred = infer_implicit_relations(original_triples)
+
+    # Build layer-annotation triples (only when there are valid triples).
+    layer_triples = (
+        _build_layer_triples(original_triples, resource_uri) if original_triples else []
+    )
+
+    # Build the full list to store: original + inferred + layer triples.
+    # Do NOT mutate the input list — create a new list.
+    # Track the boundary between original and augmented triples so we
+    # can count only original triples in the returned ``stored`` count.
+    all_provenanced: list[ProvenancedTriple] = list(provenanced)
+    original_count = len(all_provenanced)
+    if provenanced and original_triples:
+        base_prov = provenanced[0].provenance
+        for t in inferred + layer_triples:
+            all_provenanced.append(ProvenancedTriple(triple=t, provenance=base_prov))
+
     subjects: set[str] = set()
     stored = 0
-    for pt in provenanced:
+    for idx_pt, pt in enumerate(all_provenanced):
+        is_original = idx_pt < original_count
         t = pt.triple
         obj = t.object_uri if t.object_uri else t.object_value
         if not obj:
@@ -146,8 +225,9 @@ def index_graph(
             )
             continue
 
-        # Data triple succeeded — count it and track subject.
-        stored += 1
+        # Data triple succeeded — count it (original triples only) and track subject.
+        if is_original:
+            stored += 1
         subjects.add(t.subject_uri)
 
         # When both object_uri and object_value are set (e.g. a
@@ -283,6 +363,7 @@ def index_vector(
 # ---------------------------------------------------------------------------
 
 __all__: list[str] = [
+    "_build_layer_triples",
     "attach_provenance",
     "fire_on_error",
     "fire_on_indexed",

src/cleveragents/application/services/uko_inference.py

@@ -0,0 +1,174 @@
+"""UKO Implicit Relationship Inference — semantic analysis during indexing.
+
+Provides :class:`UKOInferenceEngine`, which analyses UKO triples produced
+by domain analyzers and infers additional implicit relationships based on
+semantic patterns.
+
+Implicit relationships are inferred from:
+
+1. **Co-occurrence**: Two subjects that share the same type are related
+   via ``uko:implicitSiblingOf``.
+2. **Containment**: A subject whose URI is a prefix of another subject's
+   URI is related via ``uko:implicitContains``.
+3. **Dependency**: A subject that references another subject's URI in its
+   object values is related via ``uko:implicitDependsOn``.
+
+These inferred triples are stored alongside the original triples in the
+graph backend with a confidence score below 1.0 to distinguish them from
+deterministic extractions.
+
+Based on ``docs/specification.md`` §185 — "Semantically aware — implicit
+relationships are inferred from content analysis."
+
+ISSUES CLOSED: #891
+"""
+
+from __future__ import annotations
+
+import structlog
+
+from cleveragents.domain.models.acms.analyzers import UKOTriple
+
+logger = structlog.get_logger(__name__)
+
+__all__ = [
+    "UKOInferenceEngine",
+    "infer_implicit_relations",
+]
+
+# Confidence score for inferred (implicit) relationships.
+_IMPLICIT_CONFIDENCE = 0.7
+
+# Predicates for implicit relationships.
+_PRED_SIBLING = "uko:implicitSiblingOf"
+_PRED_CONTAINS = "uko:implicitContains"
+_PRED_DEPENDS_ON = "uko:implicitDependsOn"
+
+
+class UKOInferenceEngine:
+    """Infers implicit relationships from a set of UKO triples.
+
+    Analyses the triples produced by domain analyzers and generates
+    additional triples representing inferred semantic relationships.
+    These are stored with a confidence score of 0.7 to distinguish
+    them from deterministic extractions.
+
+    Based on ``docs/specification.md`` §185 — implicit relationship
+    inference from content analysis.
+    """
+
+    def infer(
+        self,
+        triples: list[UKOTriple],
+    ) -> list[UKOTriple]:
+        """Infer implicit relationships from *triples*.
+
+        Args:
+            triples: List of UKO triples produced by a domain analyzer.
+
+        Returns:
+            List of additional inferred triples.  May be empty if no
+            implicit relationships are detected.
+        """
+        if not triples:
+            return []
+
+        inferred: list[UKOTriple] = []
+
+        # Build subject → types mapping for co-occurrence analysis.
+        subject_types: dict[str, list[str]] = {}
+        for triple in triples:
+            if triple.predicate in ("rdf:type", "a"):
+                obj = triple.object_uri or triple.object_value
+                if obj:
+                    subject_types.setdefault(triple.subject_uri, []).append(obj)
+
+        # Build subject → object_uris mapping for dependency analysis.
+        subject_refs: dict[str, set[str]] = {}
+        for triple in triples:
+            if triple.object_uri:
+                subject_refs.setdefault(triple.subject_uri, set()).add(
+                    triple.object_uri
+                )
+
+        subjects = list(subject_types.keys())
+
+        # 1. Co-occurrence: subjects sharing the same type are siblings.
+        type_to_subjects: dict[str, list[str]] = {}
+        for subj, types in subject_types.items():
+            for t in types:
+                type_to_subjects.setdefault(t, []).append(subj)
+
+        for _type_uri, type_subjects in type_to_subjects.items():
+            if len(type_subjects) < 2:
+                continue
+            # Only infer sibling relationships for the first pair to
+            # avoid O(n²) explosion on large files.
+            s1, s2 = type_subjects[0], type_subjects[1]
+            if s1 != s2:
+                inferred.append(
+                    UKOTriple(
+                        subject_uri=s1,
+                        predicate=_PRED_SIBLING,
+                        object_uri=s2,
+                        confidence=_IMPLICIT_CONFIDENCE,
+                    )
+                )
+
+        # 2. Containment: subject URI is a prefix of another subject URI.
+        for i, s1 in enumerate(subjects):
+            for s2 in subjects[i + 1 :]:
+                if s2.startswith(s1 + "/") or s2.startswith(s1 + "#"):
+                    inferred.append(
+                        UKOTriple(
+                            subject_uri=s1,
+                            predicate=_PRED_CONTAINS,
+                            object_uri=s2,
+                            confidence=_IMPLICIT_CONFIDENCE,
+                        )
+                    )
+                elif s1.startswith(s2 + "/") or s1.startswith(s2 + "#"):
+                    inferred.append(
+                        UKOTriple(
+                            subject_uri=s2,
+                            predicate=_PRED_CONTAINS,
+                            object_uri=s1,
+                            confidence=_IMPLICIT_CONFIDENCE,
+                        )
+                    )
+
+        # 3. Dependency: subject references another subject's URI.
+        subject_set = set(subjects)
+        for subj, refs in subject_refs.items():
+            for ref in refs:
+                if ref in subject_set and ref != subj:
+                    inferred.append(
+                        UKOTriple(
+                            subject_uri=subj,
+                            predicate=_PRED_DEPENDS_ON,
+                            object_uri=ref,
+                            confidence=_IMPLICIT_CONFIDENCE,
+                        )
+                    )
+
+        logger.debug(
+            "uko_inference.inferred",
+            input_count=len(triples),
+            inferred_count=len(inferred),
+        )
+        return inferred
+
+
+def infer_implicit_relations(
+    triples: list[UKOTriple],
+) -> list[UKOTriple]:
+    """Module-level convenience wrapper for :class:`UKOInferenceEngine`.
+
+    Args:
+        triples: List of UKO triples to analyse.
+
+    Returns:
+        List of inferred implicit relationship triples.
+    """
+    engine = UKOInferenceEngine()
+    return engine.infer(triples)

src/cleveragents/application/services/uko_persistence.py

@@ -0,0 +1,323 @@
+"""UKO Graph Persistence — persist and restore UKO graph state.
+
+Provides :class:`UKOGraphPersistence`, a service that serialises the
+in-memory UKO graph (triples stored in a :class:`GraphIndexBackend`)
+to a JSON file and restores it on application restart.
+
+This satisfies the acceptance criterion: "UKO data persists across
+application restarts."
+
+The persistence format is a JSON file containing:
+
+.. code-block:: json
+
+    {
+        "version": "1",
+        "project": "local/my-app",
+        "triples": [
+            {"subject": "...", "predicate": "...", "object": "..."}
+        ]
+    }
+
+Based on ``docs/specification.md`` §20568 — UKO classification persists
+across sessions.
+
+ISSUES CLOSED: #891
+"""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from typing import Protocol, runtime_checkable
+
+import structlog
+
+from cleveragents.domain.models.acms.index_backends import GraphIndexBackend
+
+logger = structlog.get_logger(__name__)
+
+__all__ = [
+    "UKOGraphPersistence",
+    "UKOPersistenceBackend",
+]
+
+_PERSISTENCE_VERSION = "1"
+
+
+# ---------------------------------------------------------------------------
+# Protocol for persistence backends
+# ---------------------------------------------------------------------------
+
+
+@runtime_checkable
+class UKOPersistenceBackend(Protocol):
+    """Protocol for UKO graph persistence backends.
+
+    Implementations may write to a local file, a database, or a remote
+    store.  The default implementation uses a JSON file.
+    """
+
+    def save(self, project: str, triples: list[dict[str, str]]) -> None:
+        """Persist *triples* for *project*.
+
+        Args:
+            project: Namespaced project name.
+            triples: List of ``{"subject": ..., "predicate": ...,
+                "object": ...}`` dicts.
+
+        Raises:
+            ValueError: If *project* is empty or whitespace-only.
+            OSError: If the persistence backend cannot be written.
+        """
+        ...
+
+    def load(self, project: str) -> list[dict[str, str]]:
+        """Load persisted triples for *project*.
+
+        Args:
+            project: Namespaced project name.
+
+        Returns:
+            List of ``{"subject": ..., "predicate": ..., "object": ...}``
+            dicts.  Returns an empty list if no data is persisted.
+
+        Raises:
+            ValueError: If *project* is empty or whitespace-only.
+        """
+        ...
+
+
+# ---------------------------------------------------------------------------
+# JSON file persistence backend
+# ---------------------------------------------------------------------------
+
+
+class JSONFilePersistenceBackend:
+    """Persist UKO graph triples to a JSON file.
+
+    Args:
+        base_dir: Directory where persistence files are stored.
+            Defaults to the current working directory.
+    """
+
+    def __init__(self, base_dir: str | Path = ".") -> None:
+        self._base_dir = Path(base_dir)
+
+    def _path_for(self, project: str) -> Path:
+        """Return the file path for *project*."""
+        safe_name = project.replace("/", "_").replace(":", "_")
+        return self._base_dir / f"uko_graph_{safe_name}.json"
+
+    def save(self, project: str, triples: list[dict[str, str]]) -> None:
+        """Persist *triples* to a JSON file."""
+        if not project or not project.strip():
+            raise ValueError("project must be a non-empty string")
+        self._base_dir.mkdir(parents=True, exist_ok=True)
+        path = self._path_for(project)
+        data = {
+            "version": _PERSISTENCE_VERSION,
+            "project": project,
+            "triples": triples,
+        }
+        path.write_text(json.dumps(data, indent=2), encoding="utf-8")
+        logger.debug(
+            "uko_persistence.saved",
+            project=project,
+            triple_count=len(triples),
+            path=str(path),
+        )
+
+    def load(self, project: str) -> list[dict[str, str]]:
+        """Load persisted triples from a JSON file."""
+        if not project or not project.strip():
+            raise ValueError("project must be a non-empty string")
+        path = self._path_for(project)
+        if not path.exists():
+            return []
+        try:
+            data = json.loads(path.read_text(encoding="utf-8"))
+            triples = data.get("triples", [])
+            logger.debug(
+                "uko_persistence.loaded",
+                project=project,
+                triple_count=len(triples),
+                path=str(path),
+            )
+            return triples
+        except (json.JSONDecodeError, KeyError, OSError) as exc:
+            logger.warning(
+                "uko_persistence.load_failed",
+                project=project,
+                error=str(exc),
+            )
+            return []
+
+
+# ---------------------------------------------------------------------------
+# In-memory persistence backend (for testing)
+# ---------------------------------------------------------------------------
+
+
+class InMemoryPersistenceBackend:
+    """In-memory persistence backend for testing.
+
+    Stores triples in a dict keyed by project name.  Data is lost when
+    the process exits.
+    """
+
+    def __init__(self) -> None:
+        self._store: dict[str, list[dict[str, str]]] = {}
+
+    def save(self, project: str, triples: list[dict[str, str]]) -> None:
+        """Store *triples* in memory."""
+        if not project or not project.strip():
+            raise ValueError("project must be a non-empty string")
+        self._store[project] = list(triples)
+
+    def load(self, project: str) -> list[dict[str, str]]:
+        """Load stored triples from memory."""
+        if not project or not project.strip():
+            raise ValueError("project must be a non-empty string")
+        return list(self._store.get(project, []))
+
+    def clear(self, project: str) -> None:
+        """Clear stored triples for *project*."""
+        self._store.pop(project, None)
+
+
+# ---------------------------------------------------------------------------
+# UKOGraphPersistence service
+# ---------------------------------------------------------------------------
+
+
+class UKOGraphPersistence:
+    """Service for persisting and restoring UKO graph state.
+
+    Serialises the triples stored in a :class:`GraphIndexBackend` to a
+    persistence backend (default: JSON file) and restores them on
+    application restart.
+
+    Args:
+        graph_backend: The graph index backend to persist.
+        persistence_backend: Backend for serialisation.  Defaults to
+            :class:`InMemoryPersistenceBackend` (suitable for testing).
+        project: Namespaced project name.
+    """
+
+    def __init__(
+        self,
+        graph_backend: GraphIndexBackend,
+        project: str,
+        persistence_backend: UKOPersistenceBackend | None = None,
+    ) -> None:
+        if not isinstance(graph_backend, GraphIndexBackend):
+            raise TypeError(
+                "graph_backend must satisfy GraphIndexBackend, "
+                f"got {type(graph_backend).__name__}"
+            )
+        if not project or not project.strip():
+            raise ValueError("project must be a non-empty string")
+        self._graph_backend = graph_backend
+        self._project = project
+        self._persistence_backend: UKOPersistenceBackend = (
+            persistence_backend or InMemoryPersistenceBackend()
+        )
+        logger.debug(
+            "uko_persistence.service_initialized",
+            project=project,
+        )
+
+    @property
+    def project(self) -> str:
+        """The namespaced project name."""
+        return self._project
+
+    def save(self) -> int:
+        """Persist the current graph state.
+
+        Queries all triples from the graph backend and writes them to
+        the persistence backend.
+
+        Returns:
+            Number of triples persisted.
+
+        Raises:
+            OSError: If the persistence backend cannot be written.
+        """
+        log = logger.bind(project=self._project)
+        log.info("uko_persistence.save.start")
+
+        try:
+            bindings = self._graph_backend.query(
+                self._project,
+                "SELECT ?s ?p ?o WHERE { ?s ?p ?o }",
+            )
+        except Exception as exc:
+            log.warning("uko_persistence.save.query_failed", error=str(exc))
+            return 0
+
+        triples = [
+            {
+                "subject": b.get("s", ""),
+                "predicate": b.get("p", ""),
+                "object": b.get("o", ""),
+            }
+            for b in bindings
+            if b.get("s") and b.get("p") and b.get("o")
+        ]
+
+        self._persistence_backend.save(self._project, triples)
+
+        log.info(
+            "uko_persistence.save.done",
+            triple_count=len(triples),
+        )
+        return len(triples)
+
+    def restore(self) -> int:
+        """Restore graph state from the persistence backend.
+
+        Loads persisted triples and re-inserts them into the graph
+        backend.  Skips triples that fail validation.
+
+        Returns:
+            Number of triples restored.
+        """
+        log = logger.bind(project=self._project)
+        log.info("uko_persistence.restore.start")
+
+        triples = self._persistence_backend.load(self._project)
+        if not triples:
+            log.info("uko_persistence.restore.no_data")
+            return 0
+
+        restored = 0
+        for triple in triples:
+            subject = triple.get("subject", "")
+            predicate = triple.get("predicate", "")
+            obj = triple.get("object", "")
+            if not subject or not predicate or not obj:
+                continue
+            try:
+                self._graph_backend.add_triple(
+                    self._project,
+                    subject,
+                    predicate,
+                    obj,
+                )
+                restored += 1
+            except Exception as exc:
+                log.warning(
+                    "uko_persistence.restore.triple_failed",
+                    subject=subject,
+                    predicate=predicate,
+                    error=str(exc),
+                )
+
+        log.info(
+            "uko_persistence.restore.done",
+            restored=restored,
+            total=len(triples),
+        )
+        return restored

src/cleveragents/application/services/uko_query_interface.py

@@ -0,0 +1,343 @@
+"""UKO Query Interface — ACMS context strategy integration.
+
+Provides :class:`UKOQueryInterface`, a service that allows ACMS context
+strategies to query the UKO knowledge graph for resource classification
+data.  Strategies use this interface to discover which ontology layer a
+resource belongs to, what type it is, and what relationships it has.
+
+The four UKO ontology layers (per spec §185):
+
+| Layer | Name        | Description                                      |
+|-------|-------------|--------------------------------------------------|
+| 0     | Universal   | Foundation concepts (Resource, Container, etc.)  |
+| 1     | Domain      | Software, documents, data schemas, infrastructure|
+| 2     | Paradigm    | OO, functional, procedural, markdown             |
+| 3     | Technology  | Python, TypeScript, Rust, Java, PostgreSQL       |
+
+Based on ``docs/specification.md`` §185, §20568, §43924.
+
+ISSUES CLOSED: #891
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+
+import structlog
+
+from cleveragents.domain.models.acms.index_backends import GraphIndexBackend
+
+logger = structlog.get_logger(__name__)
+
+__all__ = [
+    "ClassificationResult",
+    "UKOQueryInterface",
+]
+
+# ---------------------------------------------------------------------------
+# Layer constants
+# ---------------------------------------------------------------------------
+
+#: Layer 0 — Universal foundation concepts.
+LAYER_UNIVERSAL = 0
+#: Layer 1 — Domain specializations (code, doc, data, infra).
+LAYER_DOMAIN = 1
+#: Layer 2 — Paradigm specializations (OO, functional, procedural).
+LAYER_PARADIGM = 2
+#: Layer 3 — Technology-specific (Python, TypeScript, Rust, Java).
+LAYER_TECHNOLOGY = 3
+
+# Predicate used to record the UKO layer of a resource.
+_LAYER_PREDICATE = "uko:layer"
+# Predicate used to record the primary type of a resource.
+_TYPE_PREDICATE = "rdf:type"
+# Predicate used to record the source resource ULID.
+_SOURCE_PREDICATE = "uko:sourceResource"
+
+
+# ---------------------------------------------------------------------------
+# ClassificationResult
+# ---------------------------------------------------------------------------
+
+
+@dataclass(frozen=True)
+class ClassificationResult:
+    """Classification data for a single resource from the UKO graph.
+
+    Attributes:
+        resource_id: ULID of the classified resource.
+        layer: Highest UKO layer populated for this resource (0-3).
+        primary_type: Primary UKO type URI (e.g. ``uko-py:Module``).
+        all_types: All UKO type URIs found for this resource.
+        implicit_relations: Inferred relationships (subject, predicate,
+            object) discovered during semantic analysis.
+    """
+
+    resource_id: str
+    layer: int = LAYER_UNIVERSAL
+    primary_type: str = ""
+    all_types: tuple[str, ...] = field(default_factory=tuple)
+    implicit_relations: tuple[tuple[str, str, str], ...] = field(default_factory=tuple)
+
+    def __post_init__(self) -> None:
+        if not self.resource_id or not self.resource_id.strip():
+            raise ValueError("resource_id must be a non-empty string")
+        if not (LAYER_UNIVERSAL <= self.layer <= LAYER_TECHNOLOGY):
+            raise ValueError(
+                f"layer must be between {LAYER_UNIVERSAL} and {LAYER_TECHNOLOGY}, "
+                f"got {self.layer}"
+            )
+
+
+# ---------------------------------------------------------------------------
+# UKOQueryInterface
+# ---------------------------------------------------------------------------
+
+
+class UKOQueryInterface:
+    """Service for querying UKO classification data from the graph backend.
+
+    Provides ACMS context strategies with a typed interface to the UKO
+    knowledge graph.  Strategies use this to discover resource types,
+    ontology layers, and implicit relationships without needing to
+    construct raw SPARQL queries.
+
+    Based on ``docs/specification.md`` §20568 — UKO classification
+    persists across sessions and feeds the ACMS context pipeline.
+
+    Args:
+        graph_backend: The graph index backend to query.
+        project: Namespaced project name (e.g. ``"local/my-app"``).
+    """
+
+    def __init__(
+        self,
+        graph_backend: GraphIndexBackend,
+        project: str,
+    ) -> None:
+        if not isinstance(graph_backend, GraphIndexBackend):
+            raise TypeError(
+                "graph_backend must satisfy GraphIndexBackend, "
+                f"got {type(graph_backend).__name__}"
+            )
+        if not project or not project.strip():
+            raise ValueError("project must be a non-empty string")
+        self._graph_backend = graph_backend
+        self._project = project
+        logger.debug(
+            "uko_query_interface.initialized",
+            project=project,
+        )
+
+    @property
+    def project(self) -> str:
+        """The namespaced project name."""
+        return self._project
+
+    def classify_resource(self, resource_id: str) -> ClassificationResult:
+        """Classify a resource by querying its UKO triples.
+
+        Queries the graph backend for all triples associated with the
+        given resource and extracts type, layer, and relationship data.
+
+        Args:
+            resource_id: ULID of the resource to classify.
+
+        Returns:
+            :class:`ClassificationResult` with classification data.
+            Returns a default result (layer 0, no types) if the resource
+            has not been indexed.
+
+        Raises:
+            ValueError: If *resource_id* is empty or whitespace-only.
+        """
+        if not resource_id or not resource_id.strip():
+            raise ValueError("resource_id must be a non-empty string")
+
+        log = logger.bind(resource_id=resource_id, project=self._project)
+        log.debug("uko_query_interface.classify_resource")
+
+        resource_uri = f"uko://resource/{resource_id}"
+
+        # Query all triples where this resource is the source.
+        try:
+            bindings = self._graph_backend.query(
+                self._project,
+                f"SELECT ?s ?p ?o WHERE {{ ?s uko:sourceResource <{resource_uri}> }}",
+            )
+        except Exception as exc:
+            log.warning(
+                "uko_query_interface.query_failed",
+                error=str(exc),
+            )
+            return ClassificationResult(resource_id=resource_id)
+
+        # Extract types and layer from bindings.
+        types: list[str] = []
+        max_layer = LAYER_UNIVERSAL
+        implicit_relations: list[tuple[str, str, str]] = []
+
+        for binding in bindings:
+            predicate = binding.get("p", "")
+            obj = binding.get("o", "")
+            subject = binding.get("s", "")
+
+            if predicate == _TYPE_PREDICATE and obj:
+                types.append(obj)
+                # Infer layer from type URI prefix.
+                layer = _infer_layer_from_uri(obj)
+                if layer > max_layer:
+                    max_layer = layer
+
+            elif predicate == _LAYER_PREDICATE and obj:
+                try:
+                    layer_val = int(obj)
+                    if (
+                        LAYER_UNIVERSAL <= layer_val <= LAYER_TECHNOLOGY
+                        and layer_val > max_layer
+                    ):
+                        max_layer = layer_val
+                except ValueError:
+                    pass
+
+            elif predicate.startswith("uko:implicit") and subject and obj:
+                implicit_relations.append((subject, predicate, obj))
+
+        primary_type = types[0] if types else ""
+
+        result = ClassificationResult(
+            resource_id=resource_id,
+            layer=max_layer,
+            primary_type=primary_type,
+            all_types=tuple(types),
+            implicit_relations=tuple(implicit_relations),
+        )
+
+        log.debug(
+            "uko_query_interface.classify_resource.done",
+            layer=max_layer,
+            type_count=len(types),
+        )
+        return result
+
+    def get_resources_by_layer(self, layer: int) -> list[str]:
+        """Return resource IDs classified at the given ontology layer.
+
+        Args:
+            layer: UKO layer number (0-3).
+
+        Returns:
+            List of resource ULIDs at the given layer.
+
+        Raises:
+            ValueError: If *layer* is outside 0-3.
+        """
+        if not (LAYER_UNIVERSAL <= layer <= LAYER_TECHNOLOGY):
+            raise ValueError(
+                f"layer must be between {LAYER_UNIVERSAL} and {LAYER_TECHNOLOGY}, "
+                f"got {layer}"
+            )
+
+        log = logger.bind(layer=layer, project=self._project)
+        log.debug("uko_query_interface.get_resources_by_layer")
+
+        try:
+            bindings = self._graph_backend.query(
+                self._project,
+                f'SELECT ?s ?o WHERE {{ ?s {_LAYER_PREDICATE} "{layer}" }}',
+            )
+        except Exception as exc:
+            log.warning(
+                "uko_query_interface.layer_query_failed",
+                error=str(exc),
+            )
+            return []
+
+        resource_ids: list[str] = []
+        for binding in bindings:
+            obj = binding.get("o", "")
+            # Extract resource ID from uko://resource/<id> URI.
+            if obj.startswith("uko://resource/"):
+                resource_ids.append(obj[len("uko://resource/") :])
+
+        log.debug(
+            "uko_query_interface.get_resources_by_layer.done",
+            count=len(resource_ids),
+        )
+        return resource_ids
+
+    def get_implicit_relations(
+        self,
+        resource_id: str,
+    ) -> list[tuple[str, str, str]]:
+        """Return implicit relationships inferred for a resource.
+
+        Args:
+            resource_id: ULID of the resource.
+
+        Returns:
+            List of (subject, predicate, object) tuples for implicit
+            relationships.
+
+        Raises:
+            ValueError: If *resource_id* is empty or whitespace-only.
+        """
+        if not resource_id or not resource_id.strip():
+            raise ValueError("resource_id must be a non-empty string")
+
+        result = self.classify_resource(resource_id)
+        return list(result.implicit_relations)
+
+
+# ---------------------------------------------------------------------------
+# Layer inference helpers
+# ---------------------------------------------------------------------------
+
+# URI prefix → layer mapping (mirrors UKOLoader._LAYER_IRI_PREFIXES).
+_LAYER_URI_PREFIXES: dict[str, int] = {
+    "https://cleveragents.ai/ontology/uko#": LAYER_UNIVERSAL,
+    "https://cleveragents.ai/ontology/uko/code#": LAYER_DOMAIN,
+    "https://cleveragents.ai/ontology/uko/doc#": LAYER_DOMAIN,
+    "https://cleveragents.ai/ontology/uko/data#": LAYER_DOMAIN,
+    "https://cleveragents.ai/ontology/uko/infra#": LAYER_DOMAIN,
+    "https://cleveragents.ai/ontology/uko/oo#": LAYER_PARADIGM,
+    "https://cleveragents.ai/ontology/uko/func#": LAYER_PARADIGM,
+    "https://cleveragents.ai/ontology/uko/proc#": LAYER_PARADIGM,
+    "https://cleveragents.ai/ontology/uko/py#": LAYER_TECHNOLOGY,
+    "https://cleveragents.ai/ontology/uko/ts#": LAYER_TECHNOLOGY,
+    "https://cleveragents.ai/ontology/uko/rs#": LAYER_TECHNOLOGY,
+    "https://cleveragents.ai/ontology/uko/java#": LAYER_TECHNOLOGY,
+}
+
+# Prefixed name → layer mapping.
+_LAYER_PREFIXED_PREFIXES: dict[str, int] = {
+    "uko:": LAYER_UNIVERSAL,
+    "uko-code:": LAYER_DOMAIN,
+    "uko-doc:": LAYER_DOMAIN,
+    "uko-data:": LAYER_DOMAIN,
+    "uko-infra:": LAYER_DOMAIN,
+    "uko-oo:": LAYER_PARADIGM,
+    "uko-func:": LAYER_PARADIGM,
+    "uko-proc:": LAYER_PARADIGM,
+    "uko-py:": LAYER_TECHNOLOGY,
+    "uko-ts:": LAYER_TECHNOLOGY,
+    "uko-rs:": LAYER_TECHNOLOGY,
+    "uko-java:": LAYER_TECHNOLOGY,
+}
+
+
+def _infer_layer_from_uri(uri: str) -> int:
+    """Infer the UKO layer from a type URI or prefixed name.
+
+    Returns the layer number (0-3), defaulting to 0 (universal) if
+    the URI does not match any known prefix.
+    """
+    # Check full IRIs first.
+    for prefix, layer in _LAYER_URI_PREFIXES.items():
+        if uri.startswith(prefix):
+            return layer
+    # Check prefixed names.
+    for prefix, layer in _LAYER_PREFIXED_PREFIXES.items():
+        if uri.startswith(prefix):
+            return layer
+    return LAYER_UNIVERSAL