[BUG] Desktop session PR picker shows stale merged/closed PR cards that can't be dismissed or refreshed

Preflight Checklist

• Searched existing open and closed issues — closest are #48694 and #58491 (both closed, still reproduces); this re-raises with a new data-loss finding.

What's Wrong?

The desktop app's session-attached PR picker caches the session's PRs with their state frozen at session start and never re-queries — during the session or across restarts. After PRs are merged (especially with --delete-branch), the cards persist showing stale OPEN/CI state with a yellow ⚠️ (CI can't resolve for the deleted branch). There is no way to clear them:

• No hover/X dismiss on the card
• The CI ⌄ dropdown doesn't trigger a re-fetch
• /clear doesn't remove them
• No settings.json key, env var, or slash command disables/clears the panel
• They survive a full app restart (resuming the session re-reads the cached array)

What Should Happen?

The PR picker should refresh PR state on session resume, and/or provide a supported way to dismiss/hide stale cards. Separately, the app should tolerate a malformed/edited local_*.json rather than dropping the entire session list.

Error Messages/Logs

No error surfaced to the user — only a persistent yellow ⚠️ on each stale card (CI status unresolved for a deleted branch).

Steps to Reproduce

1. In a session, create several PRs (e.g. via gh pr create).
2. Merge them with --delete-branch.
3. Observe the session PR picker cards remain, showing stale OPEN + a ⚠️, with no way to dismiss or refresh. They persist across a full app restart.

Claude Model

Not model-specific — this is a UI/state-caching bug, independent of model.

Is this a regression?

I don't know.

Claude Code Version

2.1.168 (desktop app)

Platform

Anthropic API

Operating System

macOS (Darwin 25.5.0)

Terminal/Shell

Other — Claude Code desktop app (not a terminal session)

Additional Information

Related: #48694 ("[BUG] Desktop app PR status bar shows closed/merged PRs", closed) and #58491 ("[BUG] Desktop session PR picker never refreshes after PRs merged externally — survives app restart and /clear", closed).

Important — the obvious workaround is dangerous: hand-editing the cached session file (~/Library/Application Support/Claude/claude-code-sessions/<group>/<session>/local_*.json, the prs[] array) to clear the cards can corrupt the session index and wipe the entire session list, including pinned sessions (required a restore from backup). Users should never need to touch internal state, and a single edited/malformed local file should not take down all sessions.