fix(fetcher): wait for IDLE goroutines

[mvanhorn]

What?

Track every IDLE watcher goroutine on the IdleWatcher via sync.WaitGroup so StopAllAndWait catches lingering goroutines whose map entry was already replaced. Add StopAllAndWaitTimeout for shutdown paths that need a bounded wait, and switch the daemon shutdown from the fire-and-forget StopAll() to the bounded variant so one stuck IMAP connection cannot block the daemon.

Why?

Closes #731 (filed by @andrinoff). The existing pattern in fetcher/idle.go:48-60 and :72-75 does close(existing.stop); delete(w.watchers, account.ID) and leaves the goroutine to tear down in the background. If the IMAP connection is stuck (server stops responding mid-IDLE, network hangs without RST), the goroutine never exits, the map no longer holds the done channel, and StopAllAndWait() has no way to see it. The original report's suggested fix was "use WaitGroup or ensure goroutines terminate within timeout" - this PR does both.

The daemon side surfaces the problem: daemon/daemon.go:129 previously called idleWatcher.StopAll() and immediately continued to closeAllClients(). If any underlying connection hung, the lingering IDLE goroutines outlived the daemon's shutdown path with no log entry. The new bounded-wait shutdown logs idle watcher: stop timed out when goroutines don't exit within 5s, so operators see leaks instead of silently losing them.

Two new tests cover both behaviors: replaced-goroutine tracking via WaitGroup, and timeout-on-slow-exit returning ErrStopTimeout.

Testing

• go test ./fetcher/... -run TestIdleWatcher -count=1 - pass
• go test -race ./fetcher - pass (added tests plus existing tests)
• go build ./... - clean
• gofmt -l fetcher/idle.go daemon/daemon.go fetcher/idle_test.go - clean

Fixes #731

AI-assisted.

[floatpanebot]

Hi @mvanhorn! Please fix the following issues with your PR:

• Title: Is too long (65 characters). The PR title must be strictly under 40 characters.

Formatting issues have been resolved. Thank you!

[mx-gp]

I’ve reviewed the changes for potential breaking impacts. This is a solid, non-breaking fix for the goroutine leak. The addition of StopAllAndWaitTimeout and the switch to sync.WaitGroup for tracking IDLE goroutines correctly improves shutdown reliability without affecting existing public API signatures or configurations.

[andrinoff]

lgtm

[mvanhorn]

Thanks @andrinoff for merging the IdleWatcher fix that waits for the IDLE watcher goroutines.

[mvanhorn]

Really appreciate the merge @andrinoff. Tracking the IDLE watcher goroutines on a WaitGroup so StopAllAndWait catches the lingering ones is a solid fix.