virtfs: refactor Stream to accept (readFn, signalFn)

Same pattern as BlockOnce: framework handles the blocking loop.
readFn takes a base string, returns (data, nextBase, error).
signal fires when new data may be available.

Chat stream handlers now use Stream(a.ChatRead, a.ChatSignal).
StreamRaw retained for custom handlers.

streamChat() in support.go is now dead code (replaced by ChatRead).

cmd/olliesrv/internal/agent/agent.go

@@ -59,11 +59,13 @@ type Agent struct {
 	onStateChange   func(agentID, state string) // optional callback for state changes
 
 	// Chat log — the rendered output stream, exposed via 9P.
-	chatMu   sync.RWMutex
-	chatLog  []byte
-	chatVers uint32
-	chatCond *sync.Cond
-	plan     []byte
+	chatMu       sync.RWMutex
+	chatLog      []byte
+	chatVers     uint32
+	chatCond     *sync.Cond
+	chatSignalMu sync.Mutex
+	chatSignalCh chan struct{}
+	plan         []byte
 }
 
 // Backend returns the active backend from the runtime.
@@ -136,6 +138,10 @@ func (ag *Agent) AppendChat(data []byte) {
 	ag.chatVers++
 	ag.chatMu.Unlock()
 	ag.chatCond.Broadcast()
+	ag.chatSignalMu.Lock()
+	close(ag.chatSignalCh)
+	ag.chatSignalCh = make(chan struct{})
+	ag.chatSignalMu.Unlock()
 }
 
 // EnsureTrailingNewline appends a newline if the log doesn't end with one.
@@ -154,9 +160,41 @@ func (ag *Agent) ChatMu() *sync.RWMutex { return &ag.chatMu }
 // ChatCond returns the condvar for blocking chat readers.
 func (ag *Agent) ChatCond() *sync.Cond { return ag.chatCond }
 
+// ChatSignal returns the current chat signal channel (closed on new chat data).
+func (ag *Agent) ChatSignal() <-chan struct{} {
+	ag.chatSignalMu.Lock()
+	ch := ag.chatSignalCh
+	ag.chatSignalMu.Unlock()
+	return ch
+}
+
 // ChatLog returns the raw chat log bytes (caller must hold ChatMu.RLock).
 func (ag *Agent) ChatLog() []byte { return ag.chatLog }
 
+// ChatRead returns new chat data since the given offset (base).
+// Returns (data, nextBase, error). If no new data, returns empty data.
+func (ag *Agent) ChatRead(base string) ([]byte, string, error) {
+	var offset int
+	if base != "" {
+		fmt.Sscanf(base, "%d", &offset)
+	} else {
+		ag.chatMu.RLock()
+		offset = len(ag.chatLog)
+		ag.chatMu.RUnlock()
+	}
+	ag.chatMu.RLock()
+	log := ag.chatLog
+	if len(log) <= offset {
+		ag.chatMu.RUnlock()
+		return nil, fmt.Sprintf("%d", offset), nil
+	}
+	data := make([]byte, len(log)-offset)
+	copy(data, log[offset:])
+	newOffset := len(log)
+	ag.chatMu.RUnlock()
+	return data, fmt.Sprintf("%d", newOffset), nil
+}
+
 // Plan returns a copy of the plan.
 func (ag *Agent) Plan() []byte {
 	ag.chatMu.RLock()
@@ -834,6 +872,7 @@ func NewAgent(cfg AgentParams) *Agent {
 		state:           "idle",
 	}
 	ag.signalCh = make(chan struct{})
+	ag.chatSignalCh = make(chan struct{})
 	ag.chatCond = sync.NewCond(ag.chatMu.RLocker())
 	ag.initChatHandler()
 	ag.SetSessionEnv(cfg.SessionID)

cmd/olliesrv/internal/fs/spec.go

@@ -418,21 +418,17 @@ func buildAgentChildren(a *agent.Agent, s *session.Session) []virtfs.FsNodeDecl
 				defer a.ChatMu().RUnlock()
 				return stripMarkers(a.ChatLog()), nil
 			}),
-			virtfs.Stream(func(cctx context.Context, base string) ([]byte, string, error) {
-				merged, cancel := mergeCtx(s.Ctx, cctx)
-				defer cancel()
-				for {
-					data, nextBase, err := streamChat(a, merged, base)
-					if err != nil || len(data) == 0 {
-						return data, nextBase, err
-					}
-					stripped := stripMarkers(data)
-					if len(stripped) > 0 {
-						return stripped, nextBase, nil
-					}
-					base = nextBase
+			virtfs.Stream(func(base string) ([]byte, string, error) {
+				data, nextBase, err := a.ChatRead(base)
+				if err != nil || len(data) == 0 {
+					return data, nextBase, err
 				}
-			}),
+				stripped := stripMarkers(data)
+				if len(stripped) > 0 {
+					return stripped, nextBase, nil
+				}
+				return nil, nextBase, nil
+			}, a.ChatSignal),
 		),
 		virtfs.FileNode("chat.raw", 0444,
 			virtfs.StatOverride(chatStat),
@@ -444,11 +440,7 @@ func buildAgentChildren(a *agent.Agent, s *session.Session) []virtfs.FsNodeDecl
 				copy(data, log)
 				return data, nil
 			}),
-			virtfs.Stream(func(cctx context.Context, base string) ([]byte, string, error) {
-				merged, cancel := mergeCtx(s.Ctx, cctx)
-				defer cancel()
-				return streamChat(a, merged, base)
-			}),
+			virtfs.Stream(a.ChatRead, a.ChatSignal),
 		),
 		virtfs.FileNode("statewait", 0444,
 			virtfs.Read(func() ([]byte, error) {

virtfs/decl.go

@@ -123,7 +123,33 @@ func Write(fn func([]byte) error) NodeOption {
 }
 
 // Stream sets a streaming read handler that blocks indefinitely.
-func Stream(fn func(context.Context, string) ([]byte, string, error)) NodeOption {
+// readFn returns (data, nextBase, error) given the current base.
+// signal returns a channel that is closed when new data may be available.
+// The framework blocks on signal until readFn returns non-empty data.
+func Stream(readFn func(base string) ([]byte, string, error), signal func() <-chan struct{}) NodeOption {
+	return func(d *FsNodeDecl) {
+		d.Stream = func(ctx context.Context, base string) ([]byte, string, error) {
+			for {
+				data, nextBase, err := readFn(base)
+				if err != nil {
+					return nil, base, err
+				}
+				if len(data) > 0 {
+					return data, nextBase, nil
+				}
+				base = nextBase
+				select {
+				case <-signal():
+				case <-ctx.Done():
+					return nil, base, nil
+				}
+			}
+		}
+	}
+}
+
+// StreamRaw sets a raw streaming read handler with custom blocking logic.
+func StreamRaw(fn func(context.Context, string) ([]byte, string, error)) NodeOption {
 	return func(d *FsNodeDecl) { d.Stream = fn }
 }
 

virtfs/decl_test.go

@@ -14,7 +14,7 @@ import (
 
 func TestNodeOptions(t *testing.T) {
 	t.Run("Stream", func(t *testing.T) {
-		spec := FileNode("test", 0444, Stream(func(ctx context.Context, base string) ([]byte, string, error) {
+		spec := FileNode("test", 0444, StreamRaw(func(ctx context.Context, base string) ([]byte, string, error) {
 			return nil, "", nil
 		}))
 		if spec.Stream == nil {
@@ -265,7 +265,7 @@ func TestOpenLeafBlockOnce(t *testing.T) {
 
 func TestOpenLeafStream(t *testing.T) {
 	spec := DirNode("/",
-		FileNode("streaming", 0444, Stream(func(ctx context.Context, base string) ([]byte, string, error) {
+		FileNode("streaming", 0444, StreamRaw(func(ctx context.Context, base string) ([]byte, string, error) {
 			return []byte("stream"), "cursor", nil
 		})),
 	)
@@ -484,7 +484,7 @@ func TestValidateMultipleBlockingModes(t *testing.T) {
 	spec := DirNode("/",
 		FileNode("bad", 0444,
 			BlockOnceRaw(func(context.Context, string) ([]byte, string, error) { return nil, "", nil }),
-			Stream(func(context.Context, string) ([]byte, string, error) { return nil, "", nil }),
+			StreamRaw(func(context.Context, string) ([]byte, string, error) { return nil, "", nil }),
 		),
 	)
 	BuildTree(spec)