server: reduce statewait timeout from 5s to 500ms

When reading statewait with the same state value, the server now waits
500ms instead of 5 seconds before returning. This makes state polling
much more responsive.

cmd/olliesrv/server.go

@@ -567,7 +567,7 @@ func read(root *fs.Tree, cs *connState, fc *plan9.Fcall, ctx context.Context) *p
 			f.mu.Unlock()
 		}
 		cs.mu.RUnlock()
-		waitCtx, waitCancel := context.WithTimeout(ctx, 5*time.Second)
+		waitCtx, waitCancel := context.WithTimeout(ctx, 500*time.Millisecond)
 		defer waitCancel()
 		content, nextBase, err := entry.BlockingRead(waitCtx, base)
 		if err != nil {

virtfs/file.go

@@ -23,7 +23,7 @@ type File interface {
 	BlockingRead(ctx context.Context, base string) (content []byte, nextBase string, err error)
 
 	// Read-side contracts (mutually exclusive — at most one true):
-	//   BlockingReadMode — blocks up to 5s for next value, returns it or empty, EOF on 2nd read
+	//   BlockingReadMode — blocks up to 500ms for next value, returns it or empty, EOF on 2nd read
 	//   StreamMode       — blocks indefinitely, streams data incrementally, FD lives until EOF
 	//   RdwrMode         — write blocks until result produced, read returns result once
 	BlockingReadMode() bool
@@ -38,7 +38,7 @@ type fileConfig struct {
 	WriteFn        func([]byte) error
 	CloseFn        func() error
 	BlockingReadFn func(context.Context, string) ([]byte, string, error)
-	BlockingRead_  bool // one-shot waiter: block 5s, return once, EOF on 2nd read
+	BlockingRead_  bool // one-shot waiter: block 500ms, return once, EOF on 2nd read
 	StreamMode_    bool // indefinite stream: block forever, keep FD open
 	Rdwr_          bool // rdwr: write blocks on write, read returns result once
 }