Activity cancellation via queue-flag mechanism is complete

[Copilot]

Summary

All components for activity cancellation (proposals/activity-cancellation.md) are implemented and tested. This verification confirms that activities can be cooperatively cancelled when their parent orchestration reaches a terminal state, with worker capacity freed after a grace period.

Implementation already includes:

Provider contract changes:

• ExecutionState enum (Running/Terminal/Missing) returned from fetch_work_item() and renew_work_item_lock()
• ack_work_item() accepts Option<WorkItem> to drop messages without enqueueing completions
• SQLite provider implements state checks via check_execution_state() helpers

ActivityContext API:

// Activities poll for cancellation in loops
if ctx.is_cancelled() { return Err("Cancelled".into()); }

// Or use with tokio::select! for interruptible waits
tokio::select! {
    result = long_operation() => result,
    _ = ctx.cancelled() => Err("Cancelled".into()),
}

// Propagate token to spawned tasks
let token = ctx.cancellation_token();
tokio::spawn(async move { /* check token.is_cancelled() */ });

Worker dispatcher behavior:

• Renamed lock renewal task → activity manager
• Monitors execution state during renewals, triggers cancellation on Terminal/Missing
• Skips activities at fetch time if orchestration already terminal
• Grace period (default 10s) before aborting unresponsive activities
• Worker messages always dropped (ack with None) for terminal orchestrations

Checklist

• Tests added/updated
• cargo test passes locally
• Docs updated
  • Existing docs updated where behavior changed
  • New doc added under docs/ if introducing a new area
  • Linked from docs/README.md

Links / Design notes

Test coverage:

• 14 integration tests in tests/cancellation_tests.rs covering orchestration/activity cancellation scenarios
• 9 provider validation tests in src/provider_validation/cancellation.rs verifying ExecutionState semantics

Execution state check is eventually consistent:

• Race window: orchestration may terminate after renewal check but before next cycle (~25s with defaults)
• Acceptable tradeoff: avoids lock contention, false positives impossible (Terminal never transitions to Running)

Grace period semantics:

• Activity task aborted after grace period to free worker capacity
• User-spawned work that ignores cancellation token may outlive abort (documented as user responsibility)

Original prompt

Need to implement #file:activity-cancellation-queue-flag.md , branch activity-cancellation2 is already created for this.

The user has attached the following file paths as relevant context:

• proposals/activity-cancellation-queue-flag.md
• .github/copilot-instructions.md

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