fix(session): sanitize interrupted tool calls on transport error (#51117) - #52684

Issue for this PR

Closes #51117

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When a tool call is interrupted mid-stream (e.g. by a provider transport decode error), the partial tool item in history was left un-settled without a paired tool result. On subsequent turns/drains, converting session messages to LLM request format either failed schema validation or produced dangling tool calls without corresponding tool results, permanently bricking the session.

1. publish-llm-event.ts:
   • In failAssistant, immediately publish SessionEvent.Tool.Failed for any uncalled/unsettled tools so that incomplete tool calls interrupted mid-stream do not linger as pending and poison future session drains.
2. to-llm-message.ts:
   • In toolResult, ensure that any incomplete tool calls (pending/running) that never reached durable settlement synthesize a paired error result (ToolResultPart.make) so every tool call is guaranteed to have a corresponding tool result.

How did you verify your code works?

• Ran bun test on affected test suites:
  • Updated session-runner-message.test.ts and session-runner.test.ts to reflect proper partial flush and paired tool results on failure.
  • Added session-transport-poison.test.ts unit tests covering interrupted/transport-error tool sanitization across models.

Screenshots / recordings

N/A (session transport and tool call settlement bugfix)

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR