diff --git a/cmd/olliesrv/internal/agent/agent.go b/cmd/olliesrv/internal/agent/agent.go
index 7a97c50..d6ade3c 100644
--- a/cmd/olliesrv/internal/agent/agent.go
+++ b/cmd/olliesrv/internal/agent/agent.go
@@ -688,8 +688,8 @@ func (ag *Agent) CompactionModel() string {
 }
 
 // Queue pushes a prompt onto the agent's FIFO.
-func (ag *Agent) Queue(prompt string) {
-	ag.fifo.Push(prompt)
+func (ag *Agent) Queue(prompt string) error {
+	return ag.fifo.Push(prompt)
 }
 
 // PopQueue pops the next prompt from the FIFO.
diff --git a/cmd/olliesrv/internal/agent/fifo.go b/cmd/olliesrv/internal/agent/fifo.go
index a4f5dfb..7efe980 100644
--- a/cmd/olliesrv/internal/agent/fifo.go
+++ b/cmd/olliesrv/internal/agent/fifo.go
@@ -1,18 +1,32 @@
 package agent
 
-import "sync"
+import (
+	"fmt"
+	"sync"
+)
+
+const (
+	fifoMaxItems = 256
+	fifoMaxBytes = 4 * 1024 * 1024
+)
 
 // Fifo is a thread-safe queue for buffered prompts.
 type Fifo struct {
 	mu    sync.Mutex
 	items []string
+	bytes int
 }
 
 // Push appends a prompt to the queue.
-func (f *Fifo) Push(s string) {
+func (f *Fifo) Push(s string) error {
 	f.mu.Lock()
+	defer f.mu.Unlock()
+	if len(s) > fifoMaxBytes || len(f.items) >= fifoMaxItems || f.bytes+len(s) > fifoMaxBytes {
+		return fmt.Errorf("prompt queue limit reached")
+	}
 	f.items = append(f.items, s)
-	f.mu.Unlock()
+	f.bytes += len(s)
+	return nil
 }
 
 // Pop removes and returns the next prompt.
@@ -24,6 +38,8 @@ func (f *Fifo) Pop() (string, bool) {
 		return "", false
 	}
 	s := f.items[0]
+	f.items[0] = ""
 	f.items = f.items[1:]
+	f.bytes -= len(s)
 	return s, true
 }
diff --git a/cmd/olliesrv/internal/fs/spec.go b/cmd/olliesrv/internal/fs/spec.go
index ae22776..f9072b4 100644
--- a/cmd/olliesrv/internal/fs/spec.go
+++ b/cmd/olliesrv/internal/fs/spec.go
@@ -639,7 +639,9 @@ func buildAgentChildren(a *agent.Agent, s *session.Session) []virtfs.FsNodeDecl
 				if input == "" {
 					return nil
 				}
-				a.Queue(input)
+				if err := a.Queue(input); err != nil {
+					return err
+				}
 				// If the agent is idle, trigger processing.
 				if !a.IsRunning() {
 					if !startAsync(s.Ctx, func() {