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fix(prompts): await awaitable result returned by sync prompt callback (#3709) - #3734
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Summary
Closes #3709.
When a synchronous prompt function returns an awaitable (coroutine, Task, or Future),
Prompt.render()previously ran the sync callable in a worker thread viaanyio.to_thread.run_sync(), but did not await the returned awaitable. This resulted in the coroutine object being serialized as fallback JSON/string representation:PromptResultexplicitly allowsAwaitable[SyncPromptResult]. This PR awaits any awaitable returned by the prompt callable before validating and converting messages.Root Cause
Prompt.render()ranresult = await anyio.to_thread.run_sync(...)for non-async callables, but did not checkinspect.isawaitable(result).Fix
Added
if inspect.isawaitable(result): result = await resultimmediately after running the prompt callable insrc/mcp/server/mcpserver/prompts/base.py.Test Plan
test_prompt_render_awaits_awaitable_returned_by_sync_callbackintests/server/mcpserver/prompts/test_base.py.test_base.py: 22 passed.ruff check,ruff format --check, andpyright: 0 errors.