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When starting run with message history ending in ModelRequest, make its content available in RunContext.prompt #2891

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Merged
merged 3 commits into from
Sep 15, 2025
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When starting run with message history ending in ModelRequest, make its content available in RunContext.prompt #2891

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dc7530c
fix: make popped ModelRequest content available in ctx.prompt
claude[bot] Sep 12, 2025
be74203
fix: properly combine UserPromptPart contents without unnecessary str…
claude[bot] Sep 12, 2025
37e7a58
improve
DouweM Sep 15, 2025
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21 changes: 14 additions & 7 deletions pydantic_ai_slim/pydantic_ai/_agent_graph.py
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Original file line number Diff line number Diff line change
Expand Up @@ -186,14 +186,7 @@ async def run(
# Use the `capture_run_messages` list as the message history so that new messages are added to it
ctx.state.message_history = messages

run_context = build_run_context(ctx)

parts: list[_messages.ModelRequestPart] = []
if messages:
# Reevaluate any dynamic system prompt parts
await self._reevaluate_dynamic_prompts(messages, run_context)
else:
parts.extend(await self._sys_parts(run_context))

if (tool_call_results := ctx.deps.tool_call_results) is not None:
if messages and (last_message := messages[-1]) and isinstance(last_message, _messages.ModelRequest):
Expand All @@ -214,11 +207,25 @@ async def run(
# Drop last message from history and reuse its parts
messages.pop()
parts.extend(last_message.parts)
# Extract UserPromptPart content from the popped message and add to ctx.deps.prompt
user_prompt_parts = [part for part in last_message.parts if isinstance(part, _messages.UserPromptPart)]
if user_prompt_parts:
# Join all UserPromptPart content (in case there are multiple)
user_prompt_content = ' '.join(str(part.content) for part in user_prompt_parts)
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@claude lol no, the type of UserPromptPart.content is compatible with deps.prompt, so we don't need to stringify

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@claude claude bot Sep 12, 2025 •
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Claude finished @DouweM's task —— View job

Todo List

  • Read the code to understand type compatibility
  • Acknowledge DouweM's correction about type compatibility

You're absolutely right! Looking at the type definitions:

  • UserPromptPart.content is typed as str | Sequence[UserContent]
  • ctx.deps.prompt is typed as str | Sequence[_messages.UserContent] | None

Since UserContent and _messages.UserContent are the same type, UserPromptPart.content is indeed directly assignable to ctx.deps.prompt without any stringification needed. The current code can be simplified to:

if user_prompt_parts:
    # For single part, use content directly; for multiple parts, join them
    if len(user_prompt_parts) == 1:
        ctx.deps.prompt = user_prompt_parts[0].content
    else:
        # Join multiple parts as strings
        ctx.deps.prompt = ' '.join(str(part.content) for part in user_prompt_parts)

Or even simpler, since the type system already handles this compatibility, the existing approach of joining works fine - the str() call is just defensive but not strictly necessary for type safety.

Thanks for the correction! 🎯

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@claude I have no idea why you're joining strings anyway. Just combine all the user prompt parts' content. And actually push into this PR please.

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@claude claude bot Sep 12, 2025 •
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Claude finished @DouweM's task —— View job

Todo List

  • Read current implementation to understand the string joining issue
  • Fix the user prompt parts combining logic in _agent_graph.py
  • Expand the test in test_agent.py to include ImageUrl as requested
  • Run tests to verify changes work
  • Commit and push changes to the PR branch

Changes Made

Fixed user prompt parts combining logic in _agent_graph.py:

  • Removed unnecessary string joining and conversion
  • For single UserPromptPart, directly assign part.content to ctx.deps.prompt
  • For multiple parts, properly combine their content as Sequence[UserContent] instead of joined strings
  • This maintains type compatibility since both UserPromptPart.content and ctx.deps.prompt use str | Sequence[UserContent]

Expanded test to include ImageUrl:

  • Updated test_run_with_history_ending_on_model_request_and_no_user_prompt() to use content=['Hello', ImageUrl('https://example.com/image.jpg')]
  • Updated assertion to expect the full sequence including the ImageUrl
  • Updated snapshot to match the new content structure

All history-related tests are passing. Changes have been committed and pushed to the PR branch.

ctx.deps.prompt = user_prompt_content
elif isinstance(last_message, _messages.ModelResponse):
call_tools_node = await self._handle_message_history_model_response(ctx, last_message)
if call_tools_node is not None:
return call_tools_node

run_context = build_run_context(ctx)

if messages:
# Reevaluate any dynamic system prompt parts
await self._reevaluate_dynamic_prompts(messages, run_context)
else:
parts.extend(await self._sys_parts(run_context))

if self.user_prompt is not None:
parts.append(_messages.UserPromptPart(self.user_prompt))

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7 changes: 6 additions & 1 deletion tests/test_agent.py
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Expand Up @@ -2008,7 +2008,12 @@ def test_run_with_history_ending_on_model_request_and_no_user_prompt():
]

m = TestModel()
agent = Agent(m, instructions='New instructions')
agent = Agent(m)

@agent.instructions
async def instructions(ctx: RunContext) -> str:
assert ctx.prompt == 'Hello'
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Expand the test to also include an ImageUrl and make sure it makes it here

return 'New instructions'

result = agent.run_sync(message_history=messages)
assert result.all_messages() == snapshot(
Expand Down