server: event file plain read now uses per-fid subscription

Plain reads (without writing a filter first) now get a per-fid
subscription with '*' filter, identical to 'echo * | rdwrs event'.

This fixes event loss — the old EventStream path overwrote events
when multiple arrived before the reader consumed them.

cmd/olliesrv/server.go

@@ -598,7 +598,7 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 	}
 
 	if entry.StreamMode() {
-		// Special handling for event file with filter
+		// Special handling for event file — always use per-fid subscription
 		if path == "event" {
 			cs.mu.RLock()
 			f, fidOK := cs.fids[fc.Fid]
@@ -609,20 +609,22 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 				eventCh := f.eventCh
 				f.mu.Unlock()
 
-				// If filter was written, use filtered subscription
-				if filter != "" && eventCh == nil {
-					// Create subscription on first read after write
+				// Create subscription on first read (filter defaults to "*" for all events)
+				if eventCh == nil {
+					if filter == "" {
+						filter = "*"
+					}
 					subCtx, cancel := context.WithCancel(ctx)
 					ch := session.SubscribeEventsFiltered(subCtx, filter)
 					f.mu.Lock()
+					f.eventFilter = filter
 					f.eventCh = ch
 					f.eventCancel = cancel
 					f.mu.Unlock()
 					eventCh = ch
 				}
 
-				if eventCh != nil {
-					// Read from filtered subscription
+				// Read from subscription — blocks until event arrives
 				select {
 				case ev, ok := <-eventCh:
 					if !ok {
@@ -643,7 +645,6 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 				}
 			}
 		}
-		}
 
 		// Default stream handling (no filter)
 		cs.mu.RLock()