Implement continuation support for Claude CLI commands

- Refactor BuildCommand to support session continuation using --continue flag.
- Introduce BuildCommandWithContinuation to handle both initial and continuation requests.
- Add BuildLastUserMessageJSONL for generating JSONL from the last user message in continuation scenarios.
- Enhance Executor to check for existing sessions and adjust command building accordingly.
- Update environment setup to ensure session data is stored correctly for persistence.

Co-authored-by: Cursor <cursoragent@cursor.com>

agent/sandbox/claude/command.go

@@ -44,19 +44,35 @@ When working with GitHub and a token is provided:
 
 // BuildCommand builds the Claude CLI command and environment variables
 // Uses stdin with --input-format stream-json for unlimited prompt length
+// isContinuation: if true, uses --continue to resume previous session (only sends last user message)
 func BuildCommand(messages []agentContext.Message, opts *Options) ([]string, map[string]string, error) {
-	// Build system prompt from conversation history
-	systemPrompt, _ := buildPrompts(messages)
+	return BuildCommandWithContinuation(messages, opts, false)
+}
 
-	// Inject sandbox environment prompt
-	if systemPrompt != "" {
-		systemPrompt = systemPrompt + "\n\n" + sandboxEnvPrompt
-	} else {
-		systemPrompt = sandboxEnvPrompt
+// BuildCommandWithContinuation builds the Claude CLI command with continuation support
+// isContinuation: if true, uses --continue to resume previous session
+func BuildCommandWithContinuation(messages []agentContext.Message, opts *Options, isContinuation bool) ([]string, map[string]string, error) {
+	// Build system prompt from conversation history (only for first request)
+	var systemPrompt string
+	if !isContinuation {
+		systemPrompt, _ = buildPrompts(messages)
+		// Inject sandbox environment prompt
+		if systemPrompt != "" {
+			systemPrompt = systemPrompt + "\n\n" + sandboxEnvPrompt
+		} else {
+			systemPrompt = sandboxEnvPrompt
+		}
 	}
 
 	// Build input JSONL for Claude CLI (stream-json format)
-	inputJSONL, err := BuildInputJSONL(messages)
+	// For continuation, only send the last user message
+	var inputJSONL []byte
+	var err error
+	if isContinuation {
+		inputJSONL, err = BuildLastUserMessageJSONL(messages)
+	} else {
+		inputJSONL, err = BuildFirstRequestJSONL(messages)
+	}
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to build input JSONL: %w", err)
 	}
@@ -80,6 +96,12 @@ func BuildCommand(messages []agentContext.Message, opts *Options) ([]string, map
 	claudeArgs = append(claudeArgs, "--include-partial-messages") // Enable realtime streaming
 	claudeArgs = append(claudeArgs, "--verbose")
 
+	// For continuation, use --continue to resume the previous session
+	// Claude CLI will read session data from $HOME/.claude/ (which is /workspace/.claude/)
+	if isContinuation {
+		claudeArgs = append(claudeArgs, "--continue")
+	}
+
 	// Add max_turns if specified
 	if opts != nil && opts.Arguments != nil {
 		if maxTurns, ok := opts.Arguments["max_turns"]; ok {
@@ -99,7 +121,7 @@ func BuildCommand(messages []agentContext.Message, opts *Options) ([]string, map
 	// System prompt may contain quotes, newlines, special characters that break shell quoting
 	var bashCmd strings.Builder
 
-	// If we have a system prompt, write it to a temp file via heredoc first
+	// If we have a system prompt (first request only), write it to a temp file via heredoc first
 	// then use --append-system-prompt-file
 	if systemPrompt != "" {
 		bashCmd.WriteString("cat << 'PROMPTEOF' > /tmp/.system-prompt.txt\n")
@@ -127,12 +149,18 @@ func BuildCommand(messages []agentContext.Message, opts *Options) ([]string, map
 }
 
 // BuildInputJSONL converts messages to Claude CLI stream-json input format
-// Each message becomes a line in JSONL format
+// Deprecated: Use BuildFirstRequestJSONL or BuildLastUserMessageJSONL instead
 func BuildInputJSONL(messages []agentContext.Message) ([]byte, error) {
+	return BuildFirstRequestJSONL(messages)
+}
+
+// BuildFirstRequestJSONL builds JSONL for the first request (all messages)
+// Sends all user and assistant messages to establish context
+func BuildFirstRequestJSONL(messages []agentContext.Message) ([]byte, error) {
 	var lines []string
 
 	for _, msg := range messages {
-		// Skip system messages (handled via --system-prompt or env var)
+		// Skip system messages (handled via --system-prompt)
 		if msg.Role == "system" {
 			continue
 		}
@@ -147,9 +175,9 @@ func BuildInputJSONL(messages []agentContext.Message) ([]byte, error) {
 
 		// Create stream-json message
 		streamMsg := map[string]interface{}{
-			"type": msg.Role, // "user" or "assistant"
+			"type": string(msg.Role), // "user" or "assistant"
 			"message": map[string]interface{}{
-				"role":    msg.Role,
+				"role":    string(msg.Role),
 				"content": content,
 			},
 		}
@@ -164,6 +192,45 @@ func BuildInputJSONL(messages []agentContext.Message) ([]byte, error) {
 	return []byte(strings.Join(lines, "\n")), nil
 }
 
+// BuildLastUserMessageJSONL builds JSONL with only the last user message
+// Used for continuation requests where Claude CLI manages history via --continue
+func BuildLastUserMessageJSONL(messages []agentContext.Message) ([]byte, error) {
+	// Find the last user message
+	var lastUserMessage *agentContext.Message
+	for i := len(messages) - 1; i >= 0; i-- {
+		if messages[i].Role == "user" {
+			lastUserMessage = &messages[i]
+			break
+		}
+	}
+
+	if lastUserMessage == nil {
+		return nil, fmt.Errorf("no user message found")
+	}
+
+	var content interface{}
+	if lastUserMessage.Content != nil {
+		content = lastUserMessage.Content
+	} else {
+		content = ""
+	}
+
+	userMsg := map[string]interface{}{
+		"type": "user",
+		"message": map[string]interface{}{
+			"role":    "user",
+			"content": content,
+		},
+	}
+
+	jsonBytes, err := json.Marshal(userMsg)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal user message: %w", err)
+	}
+
+	return jsonBytes, nil
+}
+
 // buildPrompts extracts system prompt and user prompt from messages
 func buildPrompts(messages []agentContext.Message) (systemPrompt string, userPrompt string) {
 	var systemParts []string
@@ -234,6 +301,11 @@ func buildEnvironment(opts *Options, systemPrompt string) map[string]string {
 		return env
 	}
 
+	// Set HOME to /workspace so Claude CLI stores session data in the workspace
+	// This allows session persistence across requests for the same chat
+	// Session data is stored in $HOME/.claude/ (i.e., /workspace/.claude/)
+	env["HOME"] = "/workspace"
+
 	// claude-proxy runs on localhost:3456, Claude CLI connects to it
 	env["ANTHROPIC_BASE_URL"] = "http://127.0.0.1:3456"
 	env["ANTHROPIC_API_KEY"] = "dummy" // Proxy doesn't verify this

agent/sandbox/claude/executor.go

@@ -184,8 +184,11 @@ func (e *Executor) Stream(ctx *agentContext.Context, messages []agentContext.Mes
 		}, nil
 	}
 
+	// Check if this is a continuation (Claude CLI session exists in workspace)
+	isContinuation := e.hasExistingSession(stdCtx)
+
 	// Build Claude CLI command using stored options
-	cmd, env, err := BuildCommand(messages, e.opts)
+	cmd, env, err := BuildCommandWithContinuation(messages, e.opts, isContinuation)
 	if err != nil {
 		return nil, fmt.Errorf("failed to build command: %w", err)
 	}
@@ -262,6 +265,22 @@ func (e *Executor) shouldSkipClaudeCLI() bool {
 	return !hasPrompts && !hasSkills && !hasMCP
 }
 
+// hasExistingSession checks if Claude CLI has an existing session in the workspace
+// Claude CLI stores session data in $HOME/.claude/projects/ (which is /workspace/.claude/projects/)
+// If session data exists, we should use --continue to resume the session
+func (e *Executor) hasExistingSession(ctx context.Context) bool {
+	// Check if /workspace/.claude/projects/ directory has any content
+	// This indicates a previous session exists
+	sessionDir := e.workDir + "/.claude/projects"
+	files, err := e.manager.ListDir(ctx, e.containerName, sessionDir)
+	if err != nil {
+		// Directory doesn't exist or error reading - no existing session
+		return false
+	}
+	// If there are any files/directories in the projects folder, session exists
+	return len(files) > 0
+}
+
 // prepareEnvironment prepares the container environment before execution
 // This includes: claude-proxy config, MCP config, and Skills directory
 func (e *Executor) prepareEnvironment(ctx context.Context) error {

sandbox/manager.go

@@ -190,9 +190,24 @@ func (m *Manager) GetOrCreate(ctx context.Context, userID, chatID string) (*Cont
 	if c, ok := m.containers.Load(name); ok {
 		cont := c.(*Container)
 		cont.LastUsedAt = time.Now()
-		// Ensure IPC session exists (may have been closed)
-		m.ensureIPCSession(ctx, userID, chatID)
-		return cont, nil
+
+		// Verify container actually exists in Docker
+		// (container may have been removed externally or Docker restarted)
+		_, err := m.dockerClient.ContainerInspect(ctx, cont.ID)
+		if err != nil {
+			// Container no longer exists in Docker, remove from cache and recreate
+			m.containers.Delete(name)
+			m.mu.Lock()
+			if m.running > 0 {
+				m.running--
+			}
+			m.mu.Unlock()
+			// Fall through to create new container
+		} else {
+			// Container exists, ensure IPC session exists (may have been closed)
+			m.ensureIPCSession(ctx, userID, chatID)
+			return cont, nil
+		}
 	}
 
 	// Use mutex for creation to avoid race condition
@@ -203,9 +218,21 @@ func (m *Manager) GetOrCreate(ctx context.Context, userID, chatID string) (*Cont
 	if c, ok := m.containers.Load(name); ok {
 		cont := c.(*Container)
 		cont.LastUsedAt = time.Now()
-		// Ensure IPC session exists (may have been closed)
-		m.ensureIPCSession(ctx, userID, chatID)
-		return cont, nil
+
+		// Verify container actually exists in Docker
+		_, err := m.dockerClient.ContainerInspect(ctx, cont.ID)
+		if err != nil {
+			// Container no longer exists in Docker, remove from cache
+			m.containers.Delete(name)
+			if m.running > 0 {
+				m.running--
+			}
+			// Fall through to create new container
+		} else {
+			// Container exists, ensure IPC session exists (may have been closed)
+			m.ensureIPCSession(ctx, userID, chatID)
+			return cont, nil
+		}
 	}
 
 	// Check running container limit