feat: Engineering Knowledge Layer V1 — entities + relationships

Layer 2 of the AtoCore architecture. Adds typed engineering entities
with relationships on top of the flat memory/state/chunk substrate.

Schema:
- entities table: id, entity_type, name, project, description,
  properties (JSON), status, confidence, source_refs, timestamps
- relationships table: source_entity_id, target_entity_id,
  relationship_type, confidence, source_refs

15 entity types: project, system, subsystem, component, interface,
requirement, constraint, decision, material, parameter,
analysis_model, result, validation_claim, vendor, process

12 relationship types: contains, part_of, interfaces_with,
satisfies, constrained_by, affected_by_decision, analyzed_by,
validated_by, depends_on, uses_material, described_by, supersedes

Service layer: full CRUD + get_entity_with_context (returns an
entity with its relationships and all related entities in one call).

API endpoints:
- POST /entities — create entity
- GET /entities — list/filter by type, project, status, name
- GET /entities/{id} — entity + relationships + related entities
- POST /relationships — create relationship

Schema auto-initialized on app startup via init_engineering_schema().

7 tests covering entity CRUD, relationships, context traversal,
filtering, name search, and validation.

Test count: 290 -> 297.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atocore/api/routes.py

@@ -30,6 +30,16 @@ from atocore.interactions.service import (
     list_interactions,
     record_interaction,
 )
+from atocore.engineering.service import (
+    ENTITY_TYPES,
+    RELATIONSHIP_TYPES,
+    create_entity,
+    create_relationship,
+    get_entities,
+    get_entity,
+    get_entity_with_context,
+    get_relationships,
+)
 from atocore.memory.extractor import (
     EXTRACTOR_VERSION,
     MemoryCandidate,
@@ -926,6 +936,144 @@ def api_dashboard() -> dict:
     }
 
 
+# --- Engineering Knowledge Layer (Layer 2) ---
+
+
+class EntityCreateRequest(BaseModel):
+    entity_type: str
+    name: str
+    project: str = ""
+    description: str = ""
+    properties: dict | None = None
+    status: str = "active"
+    confidence: float = 1.0
+    source_refs: list[str] | None = None
+
+
+class RelationshipCreateRequest(BaseModel):
+    source_entity_id: str
+    target_entity_id: str
+    relationship_type: str
+    confidence: float = 1.0
+    source_refs: list[str] | None = None
+
+
+@router.post("/entities")
+def api_create_entity(req: EntityCreateRequest) -> dict:
+    """Create a new engineering entity."""
+    try:
+        entity = create_entity(
+            entity_type=req.entity_type,
+            name=req.name,
+            project=req.project,
+            description=req.description,
+            properties=req.properties,
+            status=req.status,
+            confidence=req.confidence,
+            source_refs=req.source_refs,
+        )
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+    return {"status": "ok", "id": entity.id, "entity_type": entity.entity_type, "name": entity.name}
+
+
+@router.get("/entities")
+def api_list_entities(
+    entity_type: str | None = None,
+    project: str | None = None,
+    status: str = "active",
+    name_contains: str | None = None,
+    limit: int = 100,
+) -> dict:
+    """List engineering entities with optional filters."""
+    entities = get_entities(
+        entity_type=entity_type,
+        project=project,
+        status=status,
+        name_contains=name_contains,
+        limit=limit,
+    )
+    return {
+        "entities": [
+            {
+                "id": e.id,
+                "entity_type": e.entity_type,
+                "name": e.name,
+                "project": e.project,
+                "description": e.description,
+                "properties": e.properties,
+                "status": e.status,
+                "confidence": e.confidence,
+            }
+            for e in entities
+        ],
+        "count": len(entities),
+    }
+
+
+@router.get("/entities/{entity_id}")
+def api_get_entity(entity_id: str) -> dict:
+    """Get an entity with its relationships and related entities."""
+    result = get_entity_with_context(entity_id)
+    if result is None:
+        raise HTTPException(status_code=404, detail=f"Entity not found: {entity_id}")
+    entity = result["entity"]
+    return {
+        "entity": {
+            "id": entity.id,
+            "entity_type": entity.entity_type,
+            "name": entity.name,
+            "project": entity.project,
+            "description": entity.description,
+            "properties": entity.properties,
+            "status": entity.status,
+            "confidence": entity.confidence,
+            "source_refs": entity.source_refs,
+            "created_at": entity.created_at,
+            "updated_at": entity.updated_at,
+        },
+        "relationships": [
+            {
+                "id": r.id,
+                "source_entity_id": r.source_entity_id,
+                "target_entity_id": r.target_entity_id,
+                "relationship_type": r.relationship_type,
+                "confidence": r.confidence,
+            }
+            for r in result["relationships"]
+        ],
+        "related_entities": {
+            eid: {
+                "entity_type": e.entity_type,
+                "name": e.name,
+                "project": e.project,
+                "description": e.description[:200],
+            }
+            for eid, e in result["related_entities"].items()
+        },
+    }
+
+
+@router.post("/relationships")
+def api_create_relationship(req: RelationshipCreateRequest) -> dict:
+    """Create a relationship between two entities."""
+    try:
+        rel = create_relationship(
+            source_entity_id=req.source_entity_id,
+            target_entity_id=req.target_entity_id,
+            relationship_type=req.relationship_type,
+            confidence=req.confidence,
+            source_refs=req.source_refs,
+        )
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+    return {
+        "status": "ok",
+        "id": rel.id,
+        "relationship_type": rel.relationship_type,
+    }
+
+
 @router.get("/admin/backup/{stamp}/validate")
 def api_validate_backup(stamp: str) -> dict:
     """Validate that a previously created backup is structurally usable."""