## 27) Error response body shape is inconsistent

backend/app/routers/blocklist.py

@@ -22,7 +22,7 @@ registered *before* the ``/{id}`` routes so FastAPI resolves them correctly.
 
 from __future__ import annotations
 
-from fastapi import APIRouter, HTTPException, Query, status
+from fastapi import APIRouter, Query, status
 
 from app.dependencies import (
     AuthDep,
@@ -33,6 +33,7 @@ from app.dependencies import (
     SchedulerDep,
     SettingsDep,
 )
+from app.exceptions import BadRequestError, BlocklistSourceNotFoundError
 from app.models.blocklist import (
     BlocklistListResponse,
     BlocklistSource,
@@ -107,7 +108,7 @@ async def create_blocklist(
             blocklist_ctx.db, payload.name, str(payload.url), enabled=payload.enabled
         )
     except ValueError as exc:
-        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(exc)) from exc
+        raise BadRequestError(str(exc)) from exc
 
 
 # ---------------------------------------------------------------------------
@@ -271,7 +272,7 @@ async def get_blocklist(
     """
     source = await blocklist_service.get_source(blocklist_ctx.db, source_id)
     if source is None:
-        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Blocklist source not found.")
+        raise BlocklistSourceNotFoundError(source_id)
     return source
 
 
@@ -307,9 +308,9 @@ async def update_blocklist(
             enabled=payload.enabled,
         )
     except ValueError as exc:
-        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(exc)) from exc
+        raise BadRequestError(str(exc)) from exc
     if updated is None:
-        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Blocklist source not found.")
+        raise BlocklistSourceNotFoundError(source_id)
     return updated
 
 
@@ -335,7 +336,7 @@ async def delete_blocklist(
     """
     deleted = await blocklist_service.delete_source(blocklist_ctx.db, source_id)
     if not deleted:
-        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Blocklist source not found.")
+        raise BlocklistSourceNotFoundError(source_id)
 
 
 @router.get(
@@ -366,12 +367,9 @@ async def preview_blocklist(
     """
     source = await blocklist_service.get_source(blocklist_ctx.db, source_id)
     if source is None:
-        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Blocklist source not found.")
+        raise BlocklistSourceNotFoundError(source_id)
 
     try:
         return await blocklist_service.preview_source(source.url, http_session)
     except ValueError as exc:
-        raise HTTPException(
-            status_code=status.HTTP_502_BAD_GATEWAY,
-            detail=f"Could not fetch blocklist: {exc}",
-        ) from exc
+        raise BadRequestError(f"Could not fetch blocklist: {exc}") from exc