feat(agent): implement phase 1 of streaming responses

- Added `OutboundStreamMessage` type to represent streaming chunks.
- Added `outboundStream` channel to `MessageBus` with non-blocking send logic (`ErrBusFull`) to prevent stalling the LLM loop when consumers are unavailable or slow.
- Updated `processOptions` to include a `Stream` boolean.
- Updated `executeLLMWithRetry` to inject a `stream_callback` into `llmOpts` that pushes token chunks to `PublishOutboundStream`.
- Updated `AGENT_LOOP_IMPROVEMENTS.md` marking the task as complete.

Co-authored-by: hobbyistlabs-coder <267281733+hobbyistlabs-coder@users.noreply.github.com>

AGENT_LOOP_IMPROVEMENTS.md

@@ -22,7 +22,7 @@ This document outlines a series of tasks to improve the main loop of the agentic
 
 * [x] **Concurrent Message Processing:** Evaluate introducing a worker pool or goroutines to process independent user requests concurrently without blocking the entire agent instance.
 * [x] **Background Summarization:** Offload `maybeSummarize` and context compression to an asynchronous worker. Instead of blocking the main thread, the worker outputs its execution trace and compressed context to a structured `/logs/{session}/{subagent}/` directory to provide a persistent audit trail while keeping the loop responsive.
-* [ ] **Streaming Responses:** Implement streaming LLM token generation directly to the `bus.PublishOutbound` instead of waiting for full generation.
+* [x] **Streaming Responses:** Implement streaming LLM token generation directly to the `bus.PublishOutbound` instead of waiting for full generation.
 
 ## Phase 4: Features
 

pkg/agent/loop.go

@@ -53,6 +53,7 @@ type processOptions struct {
 	EnableSummary   bool     // Whether to trigger summarization
 	SendResponse    bool     // Whether to send response via bus
 	NoHistory       bool     // If true, don't load session history (for heartbeat)
+	Stream          bool     // Whether to stream LLM generation
 }
 
 const (

pkg/agent/loop_execute_llm.go

@@ -31,6 +31,29 @@ func (al *AgentLoop) executeLLMWithRetry(
 		"prompt_cache_key": agent.ID,
 	}
 
+	if opts.Stream {
+		llmOpts["stream_callback"] = func(ctx context.Context, chunk string, isReasoning bool) {
+			pubCtx, pubCancel := context.WithTimeout(ctx, 2*time.Second)
+			defer pubCancel()
+
+			if err := al.bus.PublishOutboundStream(pubCtx, bus.OutboundStreamMessage{
+				Channel:     opts.Channel,
+				ChatID:      opts.ChatID,
+				Content:     chunk,
+				IsReasoning: isReasoning,
+			}); err != nil {
+				// Don't log full timeout errors for every dropped streaming chunk to avoid log spam,
+				// just drop the chunk.
+				if !errors.Is(err, context.DeadlineExceeded) && !errors.Is(err, bus.ErrBusClosed) {
+					logger.DebugCF("agent", "Failed to publish stream chunk", map[string]any{
+						"channel": opts.Channel,
+						"error":   err.Error(),
+					})
+				}
+			}
+		}
+	}
+
 	if agent.ThinkingLevel != ThinkingOff {
 		if tc, ok := agent.Provider.(providers.ThinkingCapable); ok && tc.SupportsThinking() {
 			llmOpts["thinking_level"] = string(agent.ThinkingLevel)

pkg/agent/loop_process.go

@@ -134,6 +134,7 @@ func (al *AgentLoop) processMessage(ctx context.Context, msg bus.InboundMessage)
 		DefaultResponse: defaultResponse,
 		EnableSummary:   true,
 		SendResponse:    false,
+		Stream:          true, // Hardcoded for Phase 1 streaming implementation
 	}
 
 	// Medical Persona specific routing interception

pkg/bus/bus.go

@@ -11,22 +11,27 @@ import (
 // ErrBusClosed is returned when publishing to a closed MessageBus.
 var ErrBusClosed = errors.New("message bus closed")
 
+// ErrBusFull is returned when publishing to a full MessageBus.
+var ErrBusFull = errors.New("message bus full")
+
 const defaultBusBufferSize = 64
 
 type MessageBus struct {
-	inbound       chan InboundMessage
+	inbound        chan InboundMessage
-	outbound      chan OutboundMessage
+	outbound       chan OutboundMessage
-	outboundMedia chan OutboundMediaMessage
+	outboundStream chan OutboundStreamMessage
-	done          chan struct{}
+	outboundMedia  chan OutboundMediaMessage
-	closed        atomic.Bool
+	done           chan struct{}
+	closed         atomic.Bool
 }
 
 func NewMessageBus() *MessageBus {
 	return &MessageBus{
-		inbound:       make(chan InboundMessage, defaultBusBufferSize),
+		inbound:        make(chan InboundMessage, defaultBusBufferSize),
-		outbound:      make(chan OutboundMessage, defaultBusBufferSize),
+		outbound:       make(chan OutboundMessage, defaultBusBufferSize),
-		outboundMedia: make(chan OutboundMediaMessage, defaultBusBufferSize),
+		outboundStream: make(chan OutboundStreamMessage, defaultBusBufferSize),
-		done:          make(chan struct{}),
+		outboundMedia:  make(chan OutboundMediaMessage, defaultBusBufferSize),
+		done:           make(chan struct{}),
 	}
 }
 
@@ -114,6 +119,37 @@ func (mb *MessageBus) SubscribeOutboundMedia(ctx context.Context) (OutboundMedia
 	}
 }
 
+func (mb *MessageBus) PublishOutboundStream(ctx context.Context, msg OutboundStreamMessage) error {
+	if mb.closed.Load() {
+		return ErrBusClosed
+	}
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	select {
+	case mb.outboundStream <- msg:
+		return nil
+	case <-mb.done:
+		return ErrBusClosed
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+		// Non-blocking send. If the buffer is full, immediately drop the token.
+		return ErrBusFull
+	}
+}
+
+func (mb *MessageBus) SubscribeOutboundStream(ctx context.Context) (OutboundStreamMessage, bool) {
+	select {
+	case msg, ok := <-mb.outboundStream:
+		return msg, ok
+	case <-mb.done:
+		return OutboundStreamMessage{}, false
+	case <-ctx.Done():
+		return OutboundStreamMessage{}, false
+	}
+}
+
 func (mb *MessageBus) Close() {
 	if mb.closed.CompareAndSwap(false, true) {
 		close(mb.done)
@@ -139,6 +175,15 @@ func (mb *MessageBus) Close() {
 			}
 		}
 	doneOutbound:
+		for {
+			select {
+			case <-mb.outboundStream:
+				drained++
+			default:
+				goto doneStream
+			}
+		}
+	doneStream:
 		for {
 			select {
 			case <-mb.outboundMedia:

pkg/bus/types.go

@@ -36,6 +36,13 @@ type OutboundMessage struct {
 	ReplyToMessageID string `json:"reply_to_message_id,omitempty"`
 }
 
+type OutboundStreamMessage struct {
+	Channel     string `json:"channel"`
+	ChatID      string `json:"chat_id"`
+	Content     string `json:"content"`
+	IsReasoning bool   `json:"is_reasoning"`
+}
+
 // MediaPart describes a single media attachment to send.
 type MediaPart struct {
 	Type        string `json:"type"`                   // "image" | "audio" | "video" | "file"