Fix #770: Explorer backend routes return proper error status codes instead of 200 OK on failure

- routes/temporal.py: temporal_patterns raises HTTPException(500) instead of
  silently returning an empty-but-valid TemporalPatternResponse on exception
- routes/analytics.py: preserves existing partial-success body shape
  (frontend already parses this), but sets response.status_code = 207 when
  any individual metric computation fails, so callers get a real signal
  instead of an indistinguishable 200
- routes/ontology.py: POST /create now raises HTTPException(500) on
  generation failure instead of silently falling back to a partial/minimal
  ontology and returning 200 with a misleading nodes_added count

Verified via git stash comparison that pre-existing test suite failures
(58 errors, Starlette TestClient/httpx version mismatch) are unrelated to
this change - identical failure count on modified and unmodified code.

Closes #770

semantica/explorer/routes/analytics.py

@@ -1,11 +1,11 @@
-"""
+"""
 Analytics routes for graph metrics and validation.
 """
 
 import asyncio
 from typing import Optional
 
-from fastapi import APIRouter, Depends, Query
+from fastapi import APIRouter, Depends, Query, HTTPException, Response
 
 from ..dependencies import get_session
 from ..schemas import AnalyticsResponse, ValidationIssue, ValidationReportResponse
@@ -16,6 +16,7 @@ router = APIRouter(prefix="/api/analytics", tags=["Analytics"])
 
 @router.get("", response_model=AnalyticsResponse)
 async def get_analytics(
+    response: Response,
     metrics: Optional[str] = Query(
         None,
         description="Comma-separated metrics to compute: centrality,community,connectivity",
@@ -25,6 +26,7 @@ async def get_analytics(
     requested = set((metrics or "centrality,community,connectivity").split(","))
     graph_dict = await asyncio.to_thread(session.build_graph_dict)
     result: dict = {}
+    any_failed = False
 
     if "centrality" in requested and session.centrality is not None:
         try:
@@ -34,6 +36,7 @@ async def get_analytics(
             )
         except Exception as exc:
             result["centrality"] = {"error": str(exc)}
+            any_failed = True
 
     if "community" in requested and session.community is not None:
         try:
@@ -43,6 +46,7 @@ async def get_analytics(
             )
         except Exception as exc:
             result["community"] = {"error": str(exc)}
+            any_failed = True
 
     if "connectivity" in requested and session.connectivity is not None:
         try:
@@ -52,6 +56,10 @@ async def get_analytics(
             )
         except Exception as exc:
             result["connectivity"] = {"error": str(exc)}
+            any_failed = True
+
+    if any_failed:
+        response.status_code = 207
 
     return AnalyticsResponse(**result)
 

semantica/explorer/routes/ontology.py

@@ -1402,6 +1402,7 @@ async def create_ontology(
         except Exception as exc:
             logger.exception("Failed to generate ontology from sample data; falling back to minimal ontology.")
             logger.warning(f"OntologyEngine.from_data error: {exc}")
+            raise HTTPException(status_code=500, detail=str(exc))
 
     elif body.mode == "text" and body.schema_text:
         try:
@@ -1472,6 +1473,7 @@ async def create_ontology(
         except Exception as exc:
             logger.exception("Failed to generate ontology from schema text; falling back to minimal ontology.")
             logger.warning(f"OntologyEngine.from_text error: {exc}")
+            raise HTTPException(status_code=500, detail=str(exc))
 
     nodes_added = await asyncio.to_thread(session.add_nodes, nodes)
     edges_added = await asyncio.to_thread(session.add_edges, edges)

semantica/explorer/routes/temporal.py

@@ -1,4 +1,4 @@
-"""
+"""
 Temporal routes for snapshots, diffs, and pattern detection.
 """
 
@@ -8,7 +8,7 @@ import re
 from datetime import datetime, timedelta, timezone, UTC
 from typing import List, Optional
 
-from fastapi import APIRouter, Depends, Query
+from fastapi import APIRouter, Depends, Query, HTTPException
 from pydantic import BaseModel
 
 from ..dependencies import get_session
@@ -117,7 +117,7 @@ async def temporal_patterns(
         return TemporalPatternResponse(patterns=[])
     except Exception as exc:
         logger.warning("temporal_patterns failed: %s", exc, exc_info=True)
-        return TemporalPatternResponse(patterns=[])
+        raise HTTPException(status_code=500, detail=str(exc))
 
 
 @router.get("/bounds", response_model=TemporalBoundsResponse)