Improve PR stack refreshing

[Alex Ross (alexr00)]

Fixes #9020
Fixes #9015
Fixes #9014

[Copilot]

🟡 Changes recommended

Instance-scoped notifications miss cross-folder mutations, and dissolved stacks can retain stale merge-queue state.

2 open findings

• Notify overview panels across repository instances · New
• Clear stale merge queue method after stack dissolution · New

What changed in this PR

Improves automatic stacked-PR overview refreshes after membership or PR-state changes.

Changes:

• Adds repository stack-change notifications and detailed PR change events.
• Coalesces and serializes stack refreshes, including hidden panels.
• Expands tests for refresh races, failures, and stack mutations.

File	Description
src/​github/​githubRepository.ts	Emits stack mutation events.
src/​github/​issueModel.ts	Extends change-event fields.
src/​github/​pullRequestModel.ts	Detects stack-relevant PR changes.
src/​github/​pullRequestOverview.ts	Implements event-driven stack refreshes.
src/​view/​prsTreeDataProvider.ts	Relies on repository notifications.
src/​test/​github/​createPRViewProvider.test.ts	Tests creation-time stack updates.
src/​test/​github/​pullRequestModel.test.ts	Tests events and mutation responses.
src/​test/​github/​pullRequestOverview.test.ts	Tests refresh behavior and races.
src/​test/​view/​prsTree.test.ts	Tests tree-driven stack additions.

🧠 Review effort: Balanced

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[Copilot]

🔵 Needs a closer look

Repository-instance-local notifications can leave panels stale in multi-root or worktree setups.

0 open findings

2 resolved since last review

• Clear stale merge queue method after stack dissolution
• Notify overview panels across repository instances

Previously missed (1)

In code that hasn't changed since last review

Panel misses stack updates from other workspace folders

src/​github/​pullRequestOverview.ts:350

This subscription is scoped to this panel's GitHubRepository instance. In a multi-root/worktree workspace, each FolderRepositoryManager can create a separate instance for the same owner/repository (folderRepositoryManager.ts:3059-3063), while the overview panel is shared by owner/repository/PR. A stack mutation initiated from another folder therefore fires only on that other instance and this open panel remains stale, unlike the removed panel-wide refresh. Please route stack-change notifications through a repository-manager-wide event (keyed by owner/repository) or otherwise broadcast them to matching open panels.

🧠 Review effort: Balanced