fix: raise specific error for interrupt responses without active interrupt state

[giulio-leone]

Summary

Fixes #1644

When interrupt responses (list[InterruptResponseContent]) are passed to an agent that is not in interrupt state (e.g. fresh instance, serverless handler without session management), _convert_prompt_to_messages now raises a clear ValueError instead of the generic:

ValueError: Input prompt must be of type: `str | list[Contentblock] | Messages | None`.

Root Cause

_convert_prompt_to_messages validates the input prompt but did not recognize interrupt response payloads ([{"interruptResponse": {...}}]) as a valid input type. These dicts don't match Message (no role/content keys) or ContentBlock (no text/image/etc. keys), so the method fell through to messages is None and raised a generic ValueError.

When the interrupt state IS activated, this code path is never reached because line 926-927 returns [] early. The bug only surfaces when the agent is not in interrupt state — typically in stateless/serverless setups where the agent is reconstructed per request.

Fix

Added a detection branch in _convert_prompt_to_messages that recognizes interruptResponse payloads and raises a specific, actionable error message guiding users to preserve the agent instance or use session management.

Test

Added test_agent__call__resume_interrupt_not_activated — verifies that passing interrupt responses to a non-interrupt agent raises the new specific ValueError instead of the generic one.

All 114 agent tests + 16 interrupt tests pass.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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[giulio-leone]

Friendly ping — raises a specific error when an interrupt response is received but no active interrupt state exists, replacing a confusing generic error.