feat: add full cancellation support to recipe executor

[bkrabach]

Summary

Adds graceful cancellation support to recipe execution, enabling users to cancel long-running recipes at any nesting depth via Ctrl+C or the recipes(operation="cancel") tool call.

Changes

SessionManager (session.py)

• Added CancellationStatus enum with states: NONE, REQUESTED, IMMEDIATE, CANCELLED
• Added cancellation methods:
  • request_cancellation(session_id, project_path, immediate=False) - Request graceful or immediate cancellation
  • clear_cancellation(session_id, project_path) - Clear cancellation status for resumption
  • get_cancellation_status(session_id, project_path) - Get current status
  • is_cancellation_requested(session_id, project_path) - Check if cancellation requested
  • is_immediate_cancellation(session_id, project_path) - Check if immediate cancellation
  • mark_cancelled(session_id, project_path, cancelled_at_step) - Mark session as cancelled

RecipeExecutor (executor.py)

• Added CancellationRequestedError exception with context (session_id, is_immediate, current_step)
• Added _check_cancellation() method to check session state
• Added _check_coordinator_cancellation() to integrate with amplifier-core's CancellationToken
• Inserted cancellation checks at all loop boundaries:
  • Before each step in flat recipe execution
  • Before each step in staged recipe execution
  • Before each iteration in sequential foreach loops
  • Before each iteration in parallel foreach loops
  • After agent steps complete (graceful checkpoint)
• Added parent_session_id propagation for nested recipe cancellation

RecipesTool (__init__.py)

• Exported CancellationRequestedError and CancellationStatus
• Added cancel operation with optional immediate flag

Tests

• Added comprehensive test suite (test_cancellation.py) with 18 tests
• Updated existing test fixtures to mock new cancellation methods

Testing

All 304 tests pass (286 existing + 18 new cancellation tests).

Usage

# Graceful cancellation (complete current step, then stop)
recipes(operation="cancel", session_id="...")

# Immediate cancellation (stop ASAP)
recipes(operation="cancel", session_id="...", immediate=True)

Cancellation also integrates with CLI's Ctrl+C signal handling via the coordinator's CancellationToken.

🤖 Generated with Amplifier

Co-Authored-By: Amplifier [email protected]