Make RefreshHelper pay attention to the error returned from OnUIThreadAndWait

Right now the function always returns nil, but this will change later in
this branch, so handle errors properly. Without that, the first capture
that assigns env.git would not run, leave env.git nil, and subsequent
code would crash.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pkg/gui/controllers/helpers/refresh_helper.go

@@ -223,10 +223,12 @@ func (self *RefreshHelper) performRefresh(options types.RefreshOptions, calledFr
 		background:        options.Background || options.DontBlockRepoSwitch,
 		backgroundRoutine: options.Background,
 	}
-	self.captureOnUIThread(calledFromWorker, env.background, func() {
+	if !self.captureOnUIThread(calledFromWorker, env.background, func() {
 		env.generation = self.c.State().GetRepoGeneration()
 		env.git = self.c.Git()
-	})
+	}) {
+		return
+	}
 	if options.BatchUIUpdates {
 		env.batch = &refreshBounceBatch{}
 	}
@@ -321,11 +323,13 @@ func (self *RefreshHelper) performRefresh(options types.RefreshOptions, calledFr
 		var capturedCommits capturedCommitState
 		var capturedReflog capturedReflogState
 		var capturedBranches capturedBranchState
-		self.captureOnUIThread(calledFromWorker, env.background, func() {
+		if !self.captureOnUIThread(calledFromWorker, env.background, func() {
 			capturedCommits = self.captureCommitsState()
 			capturedReflog = self.captureReflogState()
 			capturedBranches = self.captureBranchState()
-		})
+		}) {
+			return
+		}
 		refresh("commits and commit files", func() {
 			self.refreshCommitsAndCommitFiles(capturedCommits, options.CommitSelection, env)
 		})
@@ -355,35 +359,43 @@ func (self *RefreshHelper) performRefresh(options types.RefreshOptions, calledFr
 		// if we've asked specifically for rebase commits and not those other things
 		var rebaseHashPool *utils.StringPool
 		var rebaseCommits []*models.Commit
-		self.captureOnUIThread(calledFromWorker, env.background, func() {
+		if !self.captureOnUIThread(calledFromWorker, env.background, func() {
 			rebaseHashPool, rebaseCommits = self.captureRebaseCommitState()
-		})
+		}) {
+			return
+		}
 		refresh("rebase commits", func() { _ = self.refreshRebaseCommits(rebaseHashPool, rebaseCommits, env) })
 	}
 
 	if scopeSet.Includes(types.SUB_COMMITS) {
 		var capturedSubCommits capturedSubCommitState
-		self.captureOnUIThread(calledFromWorker, env.background, func() {
+		if !self.captureOnUIThread(calledFromWorker, env.background, func() {
 			capturedSubCommits = self.captureSubCommitState()
-		})
+		}) {
+			return
+		}
 		refresh("sub commits", func() { _ = self.refreshSubCommitsWithLimit(capturedSubCommits, env) })
 	}
 
 	// reason we're not doing this if the COMMITS type is included is that if the COMMITS type _is_ included we will refresh the commit files context anyway
 	if scopeSet.Includes(types.COMMIT_FILES) && !scopeSet.Includes(types.COMMITS) {
 		var capturedCommitFiles capturedCommitFilesState
-		self.captureOnUIThread(calledFromWorker, env.background, func() {
+		if !self.captureOnUIThread(calledFromWorker, env.background, func() {
 			capturedCommitFiles = self.captureCommitFilesState()
-		})
+		}) {
+			return
+		}
 		refresh("commit files", func() { _ = self.refreshCommitFilesContext(capturedCommitFiles, env) })
 	}
 
 	fileWg := sync.WaitGroup{}
 	if scopeSet.Includes(types.FILES) {
 		var capturedFiles capturedFilesState
-		self.captureOnUIThread(calledFromWorker, env.background, func() {
+		if !self.captureOnUIThread(calledFromWorker, env.background, func() {
 			capturedFiles = self.captureFilesState()
-		})
+		}) {
+			return
+		}
 		fileWg.Add(1)
 		refresh("files", func() {
 			_ = self.refreshFilesAndSubmodules(capturedFiles, env)
@@ -393,9 +405,11 @@ func (self *RefreshHelper) performRefresh(options types.RefreshOptions, calledFr
 
 	if scopeSet.Includes(types.STASH) {
 		var stashFilterPath string
-		self.captureOnUIThread(calledFromWorker, env.background, func() {
+		if !self.captureOnUIThread(calledFromWorker, env.background, func() {
 			stashFilterPath = self.c.Modes().Filtering.GetPath()
-		})
+		}) {
+			return
+		}
 		refresh("stash", func() { self.refreshStashEntries(stashFilterPath, env) })
 	}
 
@@ -408,9 +422,11 @@ func (self *RefreshHelper) performRefresh(options types.RefreshOptions, calledFr
 		// needs it to keep the remote-branches selection valid, and reading
 		// the Remotes context off the UI thread races its render.
 		var prevSelectedRemote *models.Remote
-		self.captureOnUIThread(calledFromWorker, env.background, func() {
+		if !self.captureOnUIThread(calledFromWorker, env.background, func() {
 			prevSelectedRemote = self.c.Contexts().Remotes.GetSelected()
-		})
+		}) {
+			return
+		}
 		branchesAndRemotesWg.Add(1)
 		refresh("remotes", func() {
 			loadedRemotes, _ = self.refreshRemotes(prevSelectedRemote, env)
@@ -1248,17 +1264,20 @@ func (self *RefreshHelper) onUIThread(background bool, f func() error) {
 // waiting for a callback that only it can run), and capturing inline also
 // guarantees the snapshot reflects the state at the moment Refresh was called,
 // before the calling handler regains control and can mutate it.
-func (self *RefreshHelper) captureOnUIThread(calledFromWorker bool, background bool, fn func()) {
+//
+// It returns false when fn didn't run because the app is shutting down, in
+// which case the caller must abandon the refresh rather than compute from a
+// snapshot that was never taken.
+func (self *RefreshHelper) captureOnUIThread(calledFromWorker bool, background bool, fn func()) bool {
 	if !calledFromWorker {
 		fn()
-		return
+		return true
 	}
 
 	if background {
-		_ = self.c.GocuiGui().OnUIThreadAndWaitBackground(fn)
-	} else {
-		_ = self.c.GocuiGui().OnUIThreadAndWait(fn)
+		return self.c.GocuiGui().OnUIThreadAndWaitBackground(fn) == nil
 	}
+	return self.c.GocuiGui().OnUIThreadAndWait(fn) == nil
 }
 
 // capturedFilesState holds the files refresh's context/model inputs, gathered