UN-2946 [MISC] Fix empty Default tab in Prompt Studio Combined Output (#1956)

[MISC] [FIX] Fix empty Default tab in Prompt Studio Combined Output

The DISTINCT-ON refactor in fetch_default_output_response built the
outputs_index with str(o.prompt_id), but PromptStudioOutputManager names
its FK field ``prompt_id`` (shadowing the PK column ``prompt_id_id``), so
``o.prompt_id`` returns the related ToolStudioPrompt instance, not a UUID.
``str()`` on the instance produces ``"ToolStudioPrompt object (<uuid>)"``,
which never matches the canonical-UUID lookup keys — every prompt
resolved to "" and the Default tab rendered as an empty payload.

Use ``prompt_id_id`` for the index key. Side benefit: no N+1 from lazy
loading the related instance per row, which was the perf intent of the
original commit.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: chandrasekharan-zipstack

backend/prompt_studio/prompt_studio_output_manager_v2/output_manager_helper.py

@@ -323,8 +323,10 @@ def _resolve(tool_prompt: ToolStudioPrompt) -> str | None:
                 .order_by("prompt_id", "profile_manager_id", "-modified_at")
                 .distinct("prompt_id", "profile_manager_id")
             )
+            # ``prompt_id_id`` is the raw FK column; ``prompt_id`` returns the
+            # related ToolStudioPrompt instance (FK field shadows the PK name).
             outputs_index = {
-                (str(o.prompt_id), str(o.profile_manager_id)): o for o in outputs
+                (str(o.prompt_id_id), str(o.profile_manager_id)): o for o in outputs
             }
 
         enrichment_by_key: dict[str, Any] = {}