server: fix event file fallthrough when fid lookup fails

If fidOK was false for the event file, we fell through to the
default stream handling path which doesn't work for events.
Now we return 'bad fid' error instead of falling through.

cmd/olliesrv/server.go

@@ -606,46 +606,47 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 			// lives until the client disconnects or clunks the fid
 			clientConnCtx := cs.ctx
 			cs.mu.RUnlock()
-			if fidOK {
+			if !fidOK {
+				return errFcall(fc, "bad fid")
+			}
+			f.mu.Lock()
+			filter := f.eventFilter
+			eventCh := f.eventCh
+			f.mu.Unlock()
+
+			// Create subscription on first read (filter defaults to "*" for all events)
+			if eventCh == nil {
+				if filter == "" {
+					filter = "*"
+				}
+				subCtx, cancel := context.WithCancel(clientConnCtx)
+				ch := session.SubscribeEventsFiltered(subCtx, filter)
 				f.mu.Lock()
-				filter := f.eventFilter
-				eventCh := f.eventCh
+				f.eventFilter = filter
+				f.eventCh = ch
+				f.eventCancel = cancel
 				f.mu.Unlock()
+				eventCh = ch
+			}
 
-				// Create subscription on first read (filter defaults to "*" for all events)
-				if eventCh == nil {
-					if filter == "" {
-						filter = "*"
-					}
-					subCtx, cancel := context.WithCancel(clientConnCtx)
-					ch := session.SubscribeEventsFiltered(subCtx, filter)
-					f.mu.Lock()
-					f.eventFilter = filter
-					f.eventCh = ch
-					f.eventCancel = cancel
-					f.mu.Unlock()
-					eventCh = ch
+			// Read from subscription — blocks until event arrives
+			select {
+			case ev, ok := <-eventCh:
+				if !ok {
+					return &plan9.Fcall{Type: plan9.Rread, Tag: fc.Tag, Count: 0}
 				}
-
-				// Read from subscription — blocks until event arrives
-				select {
-				case ev, ok := <-eventCh:
-					if !ok {
-						return &plan9.Fcall{Type: plan9.Rread, Tag: fc.Tag, Count: 0}
-					}
-					line := ev.Topic
-					if ev.Payload != "" {
-						line += " " + ev.Payload
-					}
-					content := []byte(line + "\n")
-					count := int(fc.Count)
-					if count > len(content) {
-						count = len(content)
-					}
-					return &plan9.Fcall{Type: plan9.Rread, Tag: fc.Tag, Count: uint32(count), Data: content[:count]}
-				case <-ctx.Done():
-					return errFcall(fc, "interrupted")
+				line := ev.Topic
+				if ev.Payload != "" {
+					line += " " + ev.Payload
 				}
+				content := []byte(line + "\n")
+				count := int(fc.Count)
+				if count > len(content) {
+					count = len(content)
+				}
+				return &plan9.Fcall{Type: plan9.Rread, Tag: fc.Tag, Count: uint32(count), Data: content[:count]}
+			case <-ctx.Done():
+				return errFcall(fc, "interrupted")
 			}
 		}