v0.18.1 file watcher retirement diagnostics update

internal/source/file/file.go

@@ -292,12 +292,21 @@ func (fs *FileSource) ensureWatcher(path string) {
 			}
 		}
 
-		fs.mu.Lock()
-		delete(fs.watchers, path)
-		fs.mu.Unlock()
+		fs.removeWatcher(path, w)
 	}()
 }
 
+// removeWatcher removes only the watcher that finished. A deleted file can be
+// recreated before its old watcher observes stop; in that case ensureWatcher
+// has already installed a replacement under the same path, which must survive.
+func (fs *FileSource) removeWatcher(path string, watcher *fileWatcher) {
+	fs.mu.Lock()
+	if fs.watchers[path] == watcher {
+		delete(fs.watchers, path)
+	}
+	fs.mu.Unlock()
+}
+
 // cleanupWatchers stops and removes watchers for files that no longer exist.
 func (fs *FileSource) cleanupWatchers() {
 	fs.mu.Lock()
@@ -369,4 +378,3 @@ func globToRegex(glob string) string {
 	regex = strings.ReplaceAll(regex, `\?`, `.`)
 	return "^" + regex + "$"
 }
-

internal/source/file/file_test.go

@@ -0,0 +1,46 @@
+package file
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"logwisp/internal/core"
+)
+
+func TestStoppedWatcherReturnsNormally(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "session.jsonl")
+	if err := os.WriteFile(path, nil, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	watcher := newFileWatcher(path, true, true, func(_ core.LogEntry) {}, nil)
+	watcher.stop()
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	if err := watcher.watch(ctx); err != nil {
+		t.Fatalf("stopped watcher returned error: %v", err)
+	}
+}
+
+func TestRemoveWatcherPreservesReplacement(t *testing.T) {
+	oldWatcher := &fileWatcher{}
+	replacement := &fileWatcher{}
+	source := &FileSource{
+		watchers: map[string]*fileWatcher{
+			"session.jsonl": replacement,
+		},
+	}
+
+	source.removeWatcher("session.jsonl", oldWatcher)
+	if got := source.watchers["session.jsonl"]; got != replacement {
+		t.Fatalf("replacement watcher = %p, want %p", got, replacement)
+	}
+
+	source.removeWatcher("session.jsonl", replacement)
+	if _, exists := source.watchers["session.jsonl"]; exists {
+		t.Fatal("finished watcher was not removed")
+	}
+}

internal/source/file/file_watcher.go

@@ -80,7 +80,7 @@ func (w *fileWatcher) watch(ctx context.Context) error {
 			return ctx.Err()
 		case <-ticker.C:
 			if w.isStopped() {
-				return fmt.Errorf("watcher stopped")
+				return nil
 			}
 			if err := w.checkFile(); err != nil {
 				// Log error but continue watching