Add stale approval reminder notifications

[m-nash]

Summary

• detect stale approvals after fully passing CI
• prompt before sending provider-neutral approval reminders
• suppress duplicate reminders per reviewer and commit

Testing

• dotnet test PrCopilot/PrCopilot.slnx

[Copilot]

Pull request overview

This PR adds a new “stale approval reminder” terminal flow to the PR monitor state machine: when CI is green after new commits invalidate prior approvals, the user is prompted and can optionally trigger a provider-neutral reminder message, while suppressing duplicates per reviewer + commit.

Changes:

• Introduce a new terminal state StaleApprovalCiGreen and corresponding state-machine actions/choices to send or skip reminders.
• Track reminder suppression and in-flight reminder recipients in MonitorState.
• Add unit tests and update skill/docs to describe handling of the new send_message task.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
README.md	Documents the new stale approval reminder capability.
PrCopilot/tests/PrCopilot.Tests/StateMachineTests.cs	Adds tests for stale-approval detection, prompting, and duplicate suppression.
PrCopilot/src/PrCopilot/StateMachine/TerminalStateType.cs	Adds StaleApprovalCiGreen terminal state enum value.
PrCopilot/src/PrCopilot/StateMachine/MonitorTransitions.cs	Implements detection, prompting, and reminder-execution action for stale approvals.
PrCopilot/src/PrCopilot/StateMachine/MonitorState.cs	Adds state to suppress duplicate reminders and track pending reminder recipients.
PrCopilot/skills/pr-monitor/SKILL.md	Documents how agents should handle the new send_message task provider-neutrally.

Suppressed comments (3)

PrCopilot/src/PrCopilot/StateMachine/MonitorTransitions.cs:1165

• This message says CI is “fully passing” but displays {Passed}/{Total}; Total currently includes legacy Pending statuses (and other non-passing conclusions), so the text can be misleading (e.g. 5/6 passed). Consider using an “effective” total that excludes Pending (and aligns with the terminal-state condition).

            Action = "ask_user",
            Question = $"[{timestamp}] 🔄 PR #{state.PrNumber} has fully passing CI ({state.Checks.Passed}/{state.Checks.Total} passed), but the approval from {names} is stale after new commits.",
            Choices = ["Send approval reminder", "Skip reminder", "I'll handle it myself"],
            Context = new { approvers, state.PrUrl }

PrCopilot/src/PrCopilot/StateMachine/MonitorTransitions.cs:1178

• The reminder text also claims CI is “fully passing”, but it doesn’t include the same “effective total” logic (and may not actually be fully passing depending on how Total is computed). Aligning the wording/metrics with the terminal-state condition will prevent confusing reminders.

        var message = $"CI is fully passing on PR #{state.PrNumber} ({state.PrTitle}), but your previous approval became stale after new commits. Could you take another look and re-approve? {state.PrUrl}";

PrCopilot/src/PrCopilot/StateMachine/MonitorTransitions.cs:1208

• GetUnnotifiedStaleApprovers doesn’t filter out blank/whitespace authors. FetchReviewsAsync can produce Author = "" when the API returns null/missing user logins, which would lead to empty recipients and notification keys like "{sha}:".

    private static List<string> GetUnnotifiedStaleApprovers(MonitorState state)
        => state.StaleApprovals
            .Select(a => a.Author)
            .Where(author => !state.StaleApprovalNotifications.Contains(GetStaleApprovalNotificationKey(state.HeadSha, author)))
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .ToList();

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[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

Suppressed comments (1)

PrCopilot/src/PrCopilot/StateMachine/MonitorTransitions.cs:19

• The XML doc comment for DetectTerminalState’s priority order is now incorrect: the method checks ReviewerReplied before merge conflicts (and before the other states listed). Keeping this list accurate helps future edits avoid unintentionally changing precedence.

    /// <summary>
    /// Evaluate terminal states from current PR status.
    /// Returns the highest-priority terminal state, or null if none detected.
    /// Priority order: comment → merge conflict → CI failure → CI cancelled → approved+green → stale approval+green
    /// </summary>