Import closed issues as terminal tasks (#502)

[iamnbutler]

Summary

• Fixes GitHub polling can miss issues closed before first poll #502: issue_to_task() previously skipped all non-open issues, causing issues closed before the first poll (or between poll intervals) to never be imported.
• Closed issues are now imported with a terminal state: Completed (default) or Cancelled (if closed as "not planned").
• Skip/ignore label filtering still applies to closed issues — they won't be imported if they match tasks/skip or a configured ignore label.

Test plan

• Existing scheduler tests pass (38/38)
• New test: closed_issue_imported_as_completed — verifies default closed → Completed
• New test: closed_issue_not_planned_imported_as_cancelled — verifies NotPlanned → Cancelled
• New test: closed_issue_with_skip_label_not_imported — verifies skip label still respected
• Full workspace cargo check passes

🤖 Generated with Claude Code

[github-actions]

This PR correctly solves the silent-drop problem for issues closed before or between polls. The approach — import closed issues as terminal tasks immediately — is the right design: it ensures deduplication works and avoids re-importing the same issue on future polls. Label guards (skip/ignore) run before the closed-state branch, preserving existing filter behavior. Tests cover the two main cases and the skip label invariant.

One important inconsistency to fix before shipping: issue_to_task maps Unknown closure reason to Completed (via _ fallthrough), while reconcile_task maps it to Cancelled. This means the terminal state of an issue with no state_reason differs depending on whether it was already closed at first poll time or observed transitioning during polling. See the inline comment for the fix.

Build: cargo test --workspace passes. cargo clippy --workspace -- -D warnings has one pre-existing error in crates/models/src/work_queue.rs (should_implement_trait for WorkType::from_str) — not introduced by this PR.

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References:

• §23880702709

Reviewed by PR / Review

[github-actions]

[IMPORTANT] — Correctness: Unknown closure reason is mapped inconsistently with reconcile_task.

The _ arm here catches ClosureReason::Unknown (issued closed with no state_reason) and maps it to Completed. But reconcile_task (line 297) maps Unknown → Cancelled:

// reconcile_task
ClosureReason::NotPlanned | ClosureReason::Unknown => TaskState::Cancelled,

This means the terminal state of a task depends purely on timing: the same issue closed with no state_reason becomes Completed if it was already closed at first poll, but Cancelled if it was observed transitioning during reconciliation.

To stay consistent with the reconcile path:

if is_closed {
    task.state = match issue.classify_closure() {
        Some(ClosureReason::PrMerged | ClosureReason::ManualCompletion) => TaskState::Completed,
        _ => TaskState::Cancelled, // NotPlanned, Unknown, and the unreachable None
    };
    return Some(task);
}

A test for the Unknown case (closed with no state_reason) would lock in the expected behavior.