fix(ui): show federated prompt arguments in Admin UI instead of empty list

[shoummu1]

📌 Summary

Prompts registered via federated MCP servers always showed an empty argument list in the Admin UI. The arguments panel displayed {} instead of the actual argument names, descriptions, and required flags defined in the upstream MCP server.

🔗 Related Issue

Closes: #3447

🔁 Reproduction Steps

See #3447. Briefly:

1. Register an MCP server that exposes a prompt with arguments (e.g. greet_user(name, style)).
2. Open the Admin UI → Prompts → click the registered prompt.
3. The Arguments panel shows {} and the Test Prompt form shows no input fields.

🐞 Root Cause

In gateway_service.py, every code path that creates or updates a federated DbPrompt hardcoded argument_schema={}, discarding the argument metadata returned by the upstream server in the prompts/list MCP response.

As a result, convert_prompt_to_read() in prompt_service.py (which reconstructs the arguments list by iterating over argument_schema["properties"]) always returned an empty list, so the UI had nothing to render.

Additionally, in admin.js the fallback for missing arguments used || {} (an object) instead of || [] (an array), and there was no human-readable "No arguments" message for prompts that genuinely have none.

💡 Fix Description

Backend (gateway_service.py):

• Added static helper _build_prompt_argument_schema(prompt) that converts the MCP arguments list (items with name, description, required) into the internal {"type": "object", "properties": {...}, "required": [...]} JSON schema — consistent with what prompt_service.py already does for user-created prompts.
• Applied this helper in all 4 locations where argument_schema={} was hardcoded: federation create, federation orphan-reassign, _update_or_create_prompts create branch, and _update_or_create_prompts update branch.
• Added argument_schema to the change-detection condition so that an upstream argument change triggers a DB update.

Frontend (admin.js):

• Fixed || {} → || [] fallback in the edit modal (correct type for validateJson).
• Replaced the raw JSON.stringify(prompt.arguments || {}) in the view details panel with a conditional that renders "No arguments" when the list is empty and a formatted JSON array otherwise.

🧪 Verification

Check	Command	Status
Lint suite	make lint	Passed
Unit tests	make test	Passed
Coverage ≥ 90 %	make coverage	Passed
Manual regression no longer fails	Register MCP server with prompt arguments → Admin UI now shows argument list and test form fields	Passed

📐 MCP Compliance (if relevant)

• Matches current MCP spec (prompts/list argument metadata: name, description, required)
• No breaking change to MCP clients

✅ Checklist

• Code formatted (make black isort pre-commit)
• No secrets/credentials committed

[marekdano]

@shoummu1 - can you please resolve conflicts?

[shoummu1]

@marekdano Thanks! I've rebased and resolved the conflicts in this PR.

[marekdano]

Summary
This PR addresses prompt argument display issues in the Admin UI and reverts a previous database schema change for A2A agents.

✅ Positive Changes

1. Prompt Argument Schema Population (gateway_service.py)
   - Added _build_prompt_argument_schema() static method to properly convert MCP prompt arguments into JSON schema format
   - Method correctly handles: empty arguments, missing attributes, descriptions, and required fields
   - Integrated into both _sync_gateway_metadata() and _update_or_create_prompts()
   - Excellent test coverage with 3 comprehensive unit tests

2. UI Fix (admin.js)
   - Fixed empty arguments display to show "No arguments" instead of empty JSON object
   - Improved user experience when viewing prompts without arguments

3. Test Quality
   - Well-structured tests for _build_prompt_argument_schema()
   - Tests cover edge cases (empty, missing attributes, None descriptions)
   - Updated existing tests to expect proper schema structure

Code Quality:
- ✅ Follows coding standards (type hints, docstrings)
- ✅ Good test coverage for new functionality
- ✅ Proper error handling in _build_prompt_argument_schema()

It was also manually tested, and I can confirm that arguments in prompts display as expected.

LGTM

[crivetimihai]

Rebased onto main (clean, no conflicts) and added 4 tests for full differential coverage of the new code paths.

Backend review — All 4 locations where argument_schema={} was hardcoded are now correctly using _build_prompt_argument_schema(). The helper is consistent with the existing inline pattern in prompt_service.py, with the intentional difference that required is derived from MCP metadata rather than template placeholders — correct for federated prompts. Change detection at line 4322 properly handles None from old DB rows via or {}.

Frontend review — The || {} → || [] fix is correct (prompt.arguments is an array). The "No arguments" fallback is a good UX improvement. Compatible with buildPromptTestForm() which already expects array items with name/description/required.

Security — No new endpoints, no auth changes, no unsanitized user input. No issues.

Tests added (commit 729d68c):

• test_build_prompt_argument_schema_arguments_none — handles arguments=None
• test_update_or_create_prompts_new_prompt_with_arguments — real arguments flow through to argument_schema
• test_update_or_create_prompts_argument_schema_change_triggers_update — schema-only change triggers update
• test_update_or_create_prompts_no_update_when_schema_unchanged — no spurious update when schema is identical

All 49 tests pass.