feat(tools): stream shell_run output live into the TUI

README.md

@@ -74,9 +74,10 @@ responses OpenAI Responses API /v1/responses
 ```
 
 The Responses API client converts the conversation history to Responses input
-items (`user`/`assistant`/`system` messages, `function_call`, and
+items (`user`/`assistant` messages, `function_call`, and
-`function_call_output`), streams `response.output_text.delta` events, and
+`function_call_output`), sends the system prompt as the top-level
-supports function calling through `response.output_item.added`,
+`instructions` field, streams `response.output_text.delta` events, and supports
+function calling through `response.output_item.added`,
 `response.function_call_arguments.delta`, and `response.output_item.done`.
 
 `models` is required. `/model model <name>` is restricted to that list. Each
@@ -98,10 +99,11 @@ none, middle, high, xhigh, max
 ```
 
 When configured or changed with `/model thinking ...`, the value is sent as a
-top-level request field named `thinking`. For OpenAI reasoning models on the
+top-level request field. The default field depends on `api_type`: `chat` uses
-Responses API, set `thinking_param: reasoning` so the level is sent as the
+`thinking`, while `responses` uses the official `reasoning` field, sent as
-official `reasoning: {"effort": ...}` field; agentu maps its `middle` level to
+`{"effort": ...}` with agentu's `middle` level mapped to the official `medium`
-the official `medium` value and passes `none`, `high`, `xhigh`, `max` through.
+value (`none`, `high`, `xhigh`, `max` pass through). Override with
+`thinking_param` if a provider expects a different field name.
 
 ## CLI Flags
 
@@ -165,7 +167,8 @@ Web tools are also available in read-only mode:
 
 - `file_write` for creating or replacing whole files
 - `file_edit` for surgical line-range or pattern edits to existing files
-- `shell_run` for non-interactive shell commands
+- `shell_run` for non-interactive shell commands; output streams live into the
+  TUI while the command runs instead of appearing only after completion
 
 Use `--yolo` for prompts that ask agentu to run or inspect local commands, for
 example:

internal/agent/agent.go

@@ -24,6 +24,7 @@ const (
 	toolLogArgumentLimit          = 400
 	toolLogOutputPreviewBytes     = 4096
 	toolLogOutputMarker           = "[output]"
+	toolStreamLogLimit            = tools.MaxToolOutputBytes
 
 	summarizerSystemPrompt = "You are a conversation summarizer. Summarize the following conversation history into a concise but detailed summary. Preserve:\n" +
 		"- Key facts, decisions, and conclusions\n" +
@@ -182,6 +183,7 @@ func (a *Agent) SetLastUsage(usage *llm.Usage) {
 	copy := *usage
 	a.lastUsage = &copy
 }
+
 // compactRetainedTokenBudget returns the number of estimated tokens to retain
 // based on compactRecentRetentionPercent, using integer ceiling division.
 func compactRetainedTokenBudget(totalTokens int) int {
@@ -237,7 +239,6 @@ func compactRecentStart(messages []llm.Message, prefixEnd int) int {
 	return compactTurnBoundary(messages, prefixEnd, start)
 }
 
-
 // Compact summarizes older conversation messages while preserving the system
 // prompt and recent messages intact.
 func (a *Agent) Compact(ctx context.Context) error {
@@ -495,32 +496,75 @@ func (a *Agent) toolDefinitions() []llm.Tool {
 	return a.toolRegistry.Definitions()
 }
 
-func (a *Agent) executeTool(ctx context.Context, call llm.ToolCall) string {
+func (a *Agent) executeTool(ctx context.Context, call llm.ToolCall, logs io.Writer) (string, bool) {
 	name := call.Function.Name
 
 	if a.toolRegistry == nil {
-		return tools.FormatError(fmt.Errorf("tool registry is disabled"))
+		return tools.FormatError(fmt.Errorf("tool registry is disabled")), false
 	}
 	tool, ok := a.toolRegistry.Get(name)
 	if !ok {
-		return tools.FormatError(fmt.Errorf("unknown tool: %s", name))
+		return tools.FormatError(fmt.Errorf("unknown tool: %s", name)), false
 	}
 
 	args := strings.TrimSpace(call.Function.Arguments)
 	if args == "" {
 		args = "{}"
 	}
+	raw := json.RawMessage(args)
 
 	toolCtx, cancel := context.WithTimeout(ctx, a.toolTimeout)
 	defer cancel()
-	output, err := tool.Execute(toolCtx, json.RawMessage(args))
+
+	if streaming, ok := tool.(tools.StreamingTool); ok {
+		return a.executeStreamingTool(streaming, toolCtx, raw, name, args, logs)
+	}
+
+	output, err := tool.Execute(toolCtx, raw)
 	if err != nil {
 		if output != "" {
-			return output + "\n" + tools.FormatError(err)
+			return output + "\n" + tools.FormatError(err), false
 		}
-		return tools.FormatError(err)
+		return tools.FormatError(err), false
 	}
-	return output
+	return output, false
+}
+
+func (a *Agent) executeStreamingTool(streaming tools.StreamingTool, ctx context.Context, raw json.RawMessage, name, args string, logs io.Writer) (string, bool) {
+	var streamed int
+	emit := func(chunk string) error {
+		if chunk == "" || logs == nil {
+			return nil
+		}
+		if streamed >= toolStreamLogLimit {
+			return nil
+		}
+		if len(chunk) > toolStreamLogLimit-streamed {
+			chunk = chunk[:toolStreamLogLimit-streamed]
+			streamed = toolStreamLogLimit
+			_, err := fmt.Fprintf(logs, "\n[tool] %s %s\n%s\n%s\n[streaming output truncated after %d bytes]", name, compact(args, toolLogArgumentLimit), toolLogOutputMarker, chunk, toolStreamLogLimit)
+			return err
+		}
+		streamed += len(chunk)
+		_, err := fmt.Fprintf(logs, "\n[tool] %s %s\n%s\n%s", name, compact(args, toolLogArgumentLimit), toolLogOutputMarker, chunk)
+		return err
+	}
+
+	output, err := streaming.ExecuteStream(ctx, raw, emit)
+	if logs != nil {
+		if err != nil {
+			_ = emit("\n" + tools.FormatError(err))
+		} else if streamed == 0 {
+			_ = emit("(no output)")
+		}
+	}
+	if err != nil {
+		if output != "" {
+			return output + "\n" + tools.FormatError(err), true
+		}
+		return tools.FormatError(err), true
+	}
+	return output, true
 }
 
 func (a *Agent) hasMutatingCall(calls []llm.ToolCall) bool {
@@ -550,9 +594,9 @@ func (a *Agent) executeTools(ctx context.Context, calls []llm.ToolCall, logs io.
 	if a.hasMutatingCall(calls) {
 		// Sequential: avoid racing mutating tools.
 		for i, call := range calls {
-			output := a.executeTool(ctx, call)
+			output, streamed := a.executeTool(ctx, call, logs)
 			results[i] = toolExecutionResult{call: call, output: output}
-			if logs != nil {
+			if logs != nil && !streamed {
 				logToolOutput(logs, call, output)
 			}
 		}
@@ -566,9 +610,9 @@ func (a *Agent) executeTools(ctx context.Context, calls []llm.ToolCall, logs io.
 		wg.Add(1)
 		go func(idx int, c llm.ToolCall) {
 			defer wg.Done()
-			output := a.executeTool(ctx, c)
+			output, streamed := a.executeTool(ctx, c, logs)
 			results[idx] = toolExecutionResult{call: c, output: output}
-			if logs != nil {
+			if logs != nil && !streamed {
 				mu.Lock()
 				logToolOutput(logs, c, output)
 				mu.Unlock()

internal/agent/agent_test.go

@@ -87,6 +87,86 @@ func TestAgentRunsToolLoop(t *testing.T) {
 	}
 }
 
+type streamToolProvider struct {
+	calls int
+	t     *testing.T
+}
+
+func (p *streamToolProvider) ChatStream(ctx context.Context, req llm.ChatRequest, emit func(llm.StreamEvent) error) error {
+	p.calls++
+	switch p.calls {
+	case 1:
+		return emit(llm.StreamEvent{ToolCalls: []llm.ToolCallDelta{
+			{Index: 0, ID: "call_1", Type: "function", Name: "test_stream", Arguments: `{}`},
+		}})
+	case 2:
+		last := req.Messages[len(req.Messages)-1]
+		if last.Role != llm.RoleTool || last.Content != "full result" {
+			p.t.Fatalf("last message = %#v", last)
+		}
+		return emit(llm.StreamEvent{Content: "done"})
+	default:
+		p.t.Fatalf("unexpected call count %d", p.calls)
+		return nil
+	}
+}
+
+type streamEchoTool struct{}
+
+func (streamEchoTool) Definition() llm.Tool {
+	return llm.Tool{
+		Type: "function",
+		Function: llm.ToolFunction{
+			Name:        "test_stream",
+			Description: "streaming test",
+			Parameters:  json.RawMessage(`{"type":"object"}`),
+		},
+	}
+}
+
+func (streamEchoTool) Execute(ctx context.Context, raw json.RawMessage) (string, error) {
+	return "full result", nil
+}
+
+func (streamEchoTool) ExecuteStream(ctx context.Context, raw json.RawMessage, emit func(string) error) (string, error) {
+	if err := emit("one\n"); err != nil {
+		return "", err
+	}
+	if err := emit("two\n"); err != nil {
+		return "", err
+	}
+	return "full result", nil
+}
+
+func TestAgentStreamsToolOutputToLogs(t *testing.T) {
+	provider := &streamToolProvider{t: t}
+	a := New(Options{
+		Provider:     provider,
+		Model:        "test",
+		SystemPrompt: "system",
+		ToolRegistry: tools.NewRegistry(streamEchoTool{}),
+	})
+
+	var out strings.Builder
+	var logs strings.Builder
+	if err := a.RunTurn(context.Background(), "stream", &out, &logs); err != nil {
+		t.Fatal(err)
+	}
+	if out.String() != "done" {
+		t.Fatalf("out = %q", out.String())
+	}
+	logText := logs.String()
+	if strings.Count(logText, "[output]") != 2 {
+		t.Fatalf("logs = %q", logText)
+	}
+	if !strings.Contains(logText, "one\n") || !strings.Contains(logText, "two\n") {
+		t.Fatalf("logs missing streamed chunks: %q", logText)
+	}
+	if strings.Contains(logText, "[output]\nfull result") {
+		t.Fatalf("logs contain duplicate full output: %q", logText)
+	}
+}
+
 type contentProvider struct {
 	called bool
 	text   string

internal/session/manager.go

@@ -68,11 +68,29 @@ func (m *Manager) Resume(id string) error {
 		return err
 	}
 	m.currentSession = sess
+	m.restoreRuntime(sess)
 	m.agent.SetMessages(sess.Messages)
 	m.agent.SetLastUsage(sess.LastUsage)
 	return nil
 }
 
+// restoreRuntime switches the manager and agent back to the provider, model,
+// and thinking level recorded on a resumed session. Values that are no longer
+// valid for the current config are skipped and the defaults remain active.
+func (m *Manager) restoreRuntime(sess *Session) {
+	if sess.Provider != "" && sess.Provider != m.providerName {
+		if _, ok := m.cfg.Providers[sess.Provider]; ok {
+			_, _ = m.SetProvider(sess.Provider)
+		}
+	}
+	if sess.Model != "" && sess.Model != m.provider.Model {
+		_, _ = m.SetModel(sess.Model)
+	}
+	if sess.Thinking != "" && sess.Thinking != m.provider.Thinking {
+		_, _ = m.SetThinking(sess.Thinking)
+	}
+}
+
 // Save persists the current session to disk.
 func (m *Manager) Save() error {
 	if m.store == nil || m.currentSession == nil {
@@ -82,6 +100,8 @@ func (m *Manager) Save() error {
 	m.currentSession.LastUsage = m.agent.LastUsage()
 	m.currentSession.Provider = m.providerName
 	m.currentSession.Model = m.provider.Model
+	m.currentSession.APIType = m.provider.APIType
+	m.currentSession.Thinking = m.provider.Thinking
 	// Auto-name if empty
 	if m.currentSession.Name == "" {
 		m.currentSession.Name = DefaultName(m.currentSession.Messages)
@@ -150,6 +170,8 @@ func (m *Manager) NewSession() (string, error) {
 			m.currentSession.Messages = msgs
 			m.currentSession.Provider = m.providerName
 			m.currentSession.Model = m.provider.Model
+			m.currentSession.APIType = m.provider.APIType
+			m.currentSession.Thinking = m.provider.Thinking
 			if m.currentSession.Name == "" {
 				m.currentSession.Name = DefaultName(msgs)
 			}
@@ -257,7 +279,7 @@ func (m *Manager) SetThinking(level string) (string, error) {
 	m.provider.Thinking = level
 	m.provider.ThinkingConfigured = true
 	if m.provider.ThinkingParam == "" {
-		m.provider.ThinkingParam = "thinking"
+		m.provider.ThinkingParam = config.DefaultThinkingParam(m.provider.APIType)
 	}
 	m.cfg.Providers[m.providerName] = m.provider
 	m.syncAgent(nil)

internal/session/manager_test.go

@@ -403,3 +403,132 @@ func TestManagerUsesModelContextForAgentCompaction(t *testing.T) {
 		t.Fatalf("answerCalls = %d, want 1", provider.answerCalls)
 	}
 }
+
+func TestManagerResumeRestoresRuntime(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte(`data: {"type":"response.output_text.delta","item_id":"msg_1","output_index":0,"content_index":0,"delta":"ok"}` + "\n\n"))
+		_, _ = w.Write([]byte(`data: {"type":"response.completed","response":{"id":"resp_1","status":"completed"}}` + "\n\n"))
+	}))
+	defer server.Close()
+
+	cfg := &config.Config{
+		Providers: map[string]config.ProviderConfig{
+			"chat": {
+				Name:               "chat",
+				APIType:            config.APITypeChat,
+				BaseURL:            "https://chat.example.com",
+				APIKey:             "sk-test",
+				Model:              "model-a",
+				Models:             []string{"model-a"},
+				Thinking:           "none",
+				ThinkingParam:      "thinking",
+				ThinkingConfigured: true,
+			},
+			"resp": {
+				Name:               "resp",
+				APIType:            config.APITypeResponses,
+				BaseURL:            server.URL,
+				APIKey:             "sk-test",
+				Model:              "m1",
+				Models:             []string{"m1", "m2"},
+				Thinking:           "none",
+				ThinkingParam:      "reasoning",
+				ThinkingConfigured: true,
+			},
+		},
+	}
+	assistant := agent.New(agent.Options{
+		Provider:        &recordingProvider{},
+		Model:           "model-a",
+		Thinking:        "none",
+		ThinkingParam:   "thinking",
+		ThinkingEnabled: true,
+	})
+	store, err := NewStore(filepath.Join(t.TempDir(), "sessions"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	manager, err := NewManager(cfg, assistant, server.Client(), store)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Build a session on the responses provider with a custom model and thinking.
+	manager.newSession()
+	if _, err := manager.SetProvider("resp"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := manager.SetModel("m2"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := manager.SetThinking("xhigh"); err != nil {
+		t.Fatal(err)
+	}
+	if err := manager.Save(); err != nil {
+		t.Fatal(err)
+	}
+	id := manager.CurrentSessionID()
+
+	// Drift away from the saved runtime.
+	if _, err := manager.SetProvider("chat"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := manager.SetModel("model-a"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := manager.SetThinking("none"); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := manager.Resume(id); err != nil {
+		t.Fatal(err)
+	}
+	if got := manager.CurrentProvider(); got != "resp" {
+		t.Fatalf("provider = %q, want resp", got)
+	}
+	if got := manager.CurrentModel(); got != "m2" {
+		t.Fatalf("model = %q, want m2", got)
+	}
+	if got := manager.CurrentThinking(); got != "xhigh" {
+		t.Fatalf("thinking = %q, want xhigh", got)
+	}
+	if got := manager.CurrentAPIType(); got != config.APITypeResponses {
+		t.Fatalf("api type = %q, want responses", got)
+	}
+	runtime := assistant.RuntimeInfo()
+	if runtime.ProviderName != "resp" || runtime.Model != "m2" || runtime.Thinking != "xhigh" {
+		t.Fatalf("agent runtime = %#v", runtime)
+	}
+}
+
+func TestManagerResumeFallsBackWhenRuntimeMissing(t *testing.T) {
+	manager, assistant, _ := testManager(t)
+
+	sess := &Session{
+		ID:       GenerateID(),
+		Provider: "ghost",
+		Model:    "ghost-model",
+		Thinking: "xhigh",
+		Messages: []llm.Message{{Role: llm.RoleUser, Content: "hi"}},
+	}
+	if err := manager.store.Save(sess); err != nil {
+		t.Fatal(err)
+	}
+	if err := manager.Resume(sess.ID); err != nil {
+		t.Fatal(err)
+	}
+	if got := manager.CurrentProvider(); got != "one" {
+		t.Fatalf("provider = %q, want default one", got)
+	}
+	if got := manager.CurrentModel(); got != "model-a" {
+		t.Fatalf("model = %q, want default model-a", got)
+	}
+	if got := manager.CurrentThinking(); got != "xhigh" {
+		t.Fatalf("thinking = %q, want restored xhigh", got)
+	}
+	runtime := assistant.RuntimeInfo()
+	if runtime.ProviderName != "one" || runtime.Model != "model-a" {
+		t.Fatalf("agent runtime = %#v", runtime)
+	}
+}

internal/session/store.go

@@ -22,6 +22,8 @@ type Session struct {
 	UpdatedAt time.Time     `json:"updated_at"`
 	Provider  string        `json:"provider"`
 	Model     string        `json:"model"`
+	APIType   string        `json:"api_type,omitempty"`
+	Thinking  string        `json:"thinking,omitempty"`
 	Messages  []llm.Message `json:"messages"`
 	LastUsage *llm.Usage    `json:"last_usage,omitempty"`
 }

internal/tools/shell.go

@@ -1,6 +1,7 @@
 package tools
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
@@ -8,6 +9,7 @@ import (
 	"os"
 	"os/exec"
 	"strings"
+	"sync"
 
 	"agentu/pkg/llm"
 )
@@ -46,6 +48,10 @@ type shellRunArgs struct {
 }
 
 func (t *ShellRunTool) Execute(ctx context.Context, raw json.RawMessage) (string, error) {
+	return t.ExecuteStream(ctx, raw, nil)
+}
+
+func (t *ShellRunTool) ExecuteStream(ctx context.Context, raw json.RawMessage, emit func(string) error) (string, error) {
 	var args shellRunArgs
 	if err := json.Unmarshal(raw, &args); err != nil {
 		return "", fmt.Errorf("parse arguments: %w", err)
@@ -66,16 +72,45 @@ func (t *ShellRunTool) Execute(ctx context.Context, raw json.RawMessage) (string
 	cmd := exec.CommandContext(ctx, shell, "-lc", args.Command)
 	cmd.Dir = workdir
 
-	output, err := cmd.CombinedOutput()
+	var mu sync.Mutex
-	text := FormatResult(string(output))
+	var combined bytes.Buffer
+	writer := &shellStreamWriter{mu: &mu, buf: &combined, emit: emit}
+	cmd.Stdout = writer
+	cmd.Stderr = writer
+
+	runErr := cmd.Run()
+	text := FormatResult(combined.String())
 	if errors.Is(ctx.Err(), context.DeadlineExceeded) {
 		return text, fmt.Errorf("command timed out: %w", ctx.Err())
 	}
-	if err != nil {
+	if runErr != nil {
 		if text != "" {
-			return text, fmt.Errorf("command failed: %w", err)
+			return text, fmt.Errorf("command failed: %w", runErr)
 		}
-		return "", fmt.Errorf("command failed: %w", err)
+		return "", fmt.Errorf("command failed: %w", runErr)
 	}
 	return text, nil
 }
+
+// shellStreamWriter captures command output for the final result while
+// forwarding every write to the streaming callback as it happens.
+type shellStreamWriter struct {
+	mu   *sync.Mutex
+	buf  *bytes.Buffer
+	emit func(string) error
+}
+
+func (w *shellStreamWriter) Write(p []byte) (int, error) {
+	w.mu.Lock()
+	n, writeErr := w.buf.Write(p)
+	w.mu.Unlock()
+	if writeErr != nil {
+		return n, writeErr
+	}
+	if w.emit != nil {
+		if err := w.emit(string(p)); err != nil {
+			return 0, err
+		}
+	}
+	return len(p), nil
+}

internal/tools/shell_test.go

@@ -0,0 +1,71 @@
+package tools
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"sync"
+	"testing"
+)
+
+func TestShellRunStreamsOutputWhileRunning(t *testing.T) {
+	tool := NewShellRunTool(t.TempDir())
+	var mu sync.Mutex
+	var chunks []string
+	output, err := tool.ExecuteStream(context.Background(), json.RawMessage(`{"command":"printf 'a\\n'; sleep 0.05; printf 'b\\n'"}`), func(chunk string) error {
+		mu.Lock()
+		chunks = append(chunks, chunk)
+		mu.Unlock()
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(output, "a") || !strings.Contains(output, "b") {
+		t.Fatalf("output = %q", output)
+	}
+	mu.Lock()
+	joined := strings.Join(chunks, "")
+	mu.Unlock()
+	if len(chunks) == 0 {
+		t.Fatal("expected at least one streamed chunk")
+	}
+	if !strings.Contains(joined, "a") || !strings.Contains(joined, "b") {
+		t.Fatalf("streamed chunks = %q", joined)
+	}
+}
+
+func TestShellRunExecuteCollectsFullOutput(t *testing.T) {
+	tool := NewShellRunTool(t.TempDir())
+	output, err := tool.Execute(context.Background(), json.RawMessage(`{"command":"printf 'hello world'"}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.TrimSpace(output) != "hello world" {
+		t.Fatalf("output = %q", output)
+	}
+}
+
+func TestShellRunStreamsStderrAndStdout(t *testing.T) {
+	tool := NewShellRunTool(t.TempDir())
+	var mu sync.Mutex
+	var chunks []string
+	output, err := tool.ExecuteStream(context.Background(), json.RawMessage(`{"command":"echo out; echo err >&2"}`), func(chunk string) error {
+		mu.Lock()
+		chunks = append(chunks, chunk)
+		mu.Unlock()
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(output, "out") || !strings.Contains(output, "err") {
+		t.Fatalf("output = %q", output)
+	}
+	mu.Lock()
+	joined := strings.Join(chunks, "")
+	mu.Unlock()
+	if !strings.Contains(joined, "out") || !strings.Contains(joined, "err") {
+		t.Fatalf("streamed chunks = %q", joined)
+	}
+}

internal/tools/tools.go

@@ -19,6 +19,15 @@ type Tool interface {
 	Execute(ctx context.Context, args json.RawMessage) (string, error)
 }
 
+// StreamingTool is optionally implemented by tools that can report partial
+// output while they execute. emit receives chunks of the tool's output as
+// they are produced; the returned string is still the complete result that
+// gets sent back to the model.
+type StreamingTool interface {
+	Tool
+	ExecuteStream(ctx context.Context, args json.RawMessage, emit func(string) error) (string, error)
+}
+
 // MutatingTool is optionally implemented by tools that modify external state.
 // It is used by the agent to determine whether tool calls can run in parallel.
 type MutatingTool interface {

internal/tui/app.go

@@ -683,15 +683,27 @@ func (m *model) mergeToolLog(text string) bool {
 	if incoming.output == "" {
 		return false
 	}
+	incomingHeader, _, ok := strings.Cut(text, "\n[output]\n")
+	if !ok {
+		return false
+	}
 	for i := len(m.messages) - 1; i >= 0; i-- {
 		if m.messages[i].role != roleTool {
 			continue
 		}
 		existing := parseToolLog(m.messages[i].content)
-		if existing.name == incoming.name && existing.args == incoming.args && existing.output == "" {
+		if existing.name != incoming.name || existing.args != incoming.args {
-			m.messages[i].content = text
+			continue
-			return true
 		}
+		if !strings.Contains(m.messages[i].content, "\n[output]\n") {
+			// Placeholder card from the tool-start log; first chunk fills it.
+			m.messages[i].content = text
+		} else {
+			// Streaming tools send incremental chunks; append the raw delta
+			// so line boundaries are preserved inside the same card.
+			m.messages[i].content += strings.TrimPrefix(text, incomingHeader+"\n[output]\n")
+		}
+		return true
 	}
 	return false
 }

internal/tui/app_test.go

@@ -395,6 +395,28 @@ func TestToolLogOutputUpdatesExistingToolCard(t *testing.T) {
 	}
 }
 
+func TestToolLogStreamingChunksAppendToSameCard(t *testing.T) {
+	m := newModel(context.Background(), nil, Options{ModelName: "test-model"})
+	m.messages = append(m.messages, message{role: roleTool, content: `shell_run echo hi`})
+
+	if !m.mergeToolLog("shell_run echo hi\n[output]\none\n") {
+		t.Fatal("expected first mergeToolLog to return true")
+	}
+	if !m.mergeToolLog("shell_run echo hi\n[output]\ntwo\n") {
+		t.Fatal("expected second mergeToolLog to return true")
+	}
+	if len(m.messages) != 1 {
+		t.Fatalf("messages count = %d, want 1", len(m.messages))
+	}
+	plain := stripANSI(m.renderMessages())
+	if !strings.Contains(plain, "one") || !strings.Contains(plain, "two") {
+		t.Fatalf("rendered output missing streamed lines:\n%s", plain)
+	}
+	if strings.Contains(plain, "onetwo") {
+		t.Fatalf("streamed lines were concatenated:\n%s", plain)
+	}
+}
+
 type tuiCompactProvider struct{}
 
 func (tuiCompactProvider) ChatStream(ctx context.Context, req llm.ChatRequest, emit func(llm.StreamEvent) error) error {

pkg/config/config.go

@@ -241,7 +241,7 @@ func normalizeProvider(name string, raw rawProviderConfig) ProviderConfig {
 	}
 	applyModelDefaults(&provider)
 	if provider.ThinkingConfigured && provider.ThinkingParam == "" {
-		provider.ThinkingParam = "thinking"
+		provider.ThinkingParam = DefaultThinkingParam(provider.APIType)
 	}
 	return provider
 }
@@ -268,6 +268,17 @@ func IsAPIType(value string) bool {
 	return false
 }
 
+// DefaultThinkingParam returns the default request field used for the
+// thinking level. Chat-completions providers historically use a top-level
+// "thinking" field; the OpenAI Responses API uses "reasoning" with an
+// {"effort": ...} value.
+func DefaultThinkingParam(apiType string) string {
+	if apiType == APITypeResponses {
+		return "reasoning"
+	}
+	return "thinking"
+}
+
 func normalizeModelConfigs(rawModels []rawModelConfig) ([]string, map[string]ModelConfig) {
 	models := make([]string, 0, len(rawModels))
 	configs := make(map[string]ModelConfig, len(rawModels))

pkg/config/config_test.go

@@ -441,3 +441,39 @@ providers:
 		t.Fatalf("err = %v", err)
 	}
 }
+
+func TestLoadDefaultsThinkingParamByAPIType(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("AGENTU_TEST_KEY", "sk-test")
+	path := filepath.Join(dir, "agentu.yaml")
+	if err := os.WriteFile(path, []byte(`
+providers:
+  chat:
+    api_type: chat
+    base_url: https://chat.example.com
+    api_key: ${AGENTU_TEST_KEY}
+    models:
+      - id: chat-model
+        thinking: none
+  responses:
+    api_type: responses
+    base_url: https://responses.example.com
+    api_key: ${AGENTU_TEST_KEY}
+    models:
+      - id: responses-model
+        thinking: high
+`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	cfg, err := Load(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := cfg.Providers["chat"].ThinkingParam; got != "thinking" {
+		t.Fatalf("chat thinking param = %q, want %q", got, "thinking")
+	}
+	if got := cfg.Providers["responses"].ThinkingParam; got != "reasoning" {
+		t.Fatalf("responses thinking param = %q, want %q", got, "reasoning")
+	}
+}

pkg/llm/responses.go

@@ -124,6 +124,9 @@ func buildResponsesRequest(req ChatRequest) map[string]any {
 		"input":  buildResponsesInput(req.Messages),
 		"stream": true,
 	}
+	if instructions := responsesInstructions(req.Messages); instructions != "" {
+		payload["instructions"] = instructions
+	}
 	if len(req.Tools) > 0 {
 		payload["tools"] = buildResponsesTools(req.Tools)
 	}
@@ -153,7 +156,9 @@ func buildResponsesInput(messages []Message) []any {
 	for _, msg := range messages {
 		switch msg.Role {
 		case RoleSystem:
-			items = append(items, responsesMessageInput{Role: "system", Content: msg.Content})
+			// System instructions are sent as the top-level "instructions"
+			// field and must not be duplicated inside the input array.
+			continue
 		case RoleUser:
 			items = append(items, responsesMessageInput{Role: "user", Content: msg.Content})
 		case RoleAssistant:
@@ -179,6 +184,22 @@ func buildResponsesInput(messages []Message) []any {
 	return items
 }
 
+// responsesInstructions extracts system messages into a single instructions
+// string, which is the OpenAI Responses API way to pass developer/system
+// guidance (and the most prompt-cache friendly).
+func responsesInstructions(messages []Message) string {
+	var instructions []string
+	for _, msg := range messages {
+		if msg.Role != RoleSystem {
+			continue
+		}
+		if text := strings.TrimSpace(msg.Content); text != "" {
+			instructions = append(instructions, text)
+		}
+	}
+	return strings.Join(instructions, "\n\n")
+}
+
 func buildResponsesTools(tools []Tool) []responsesTool {
 	out := make([]responsesTool, 0, len(tools))
 	for _, tool := range tools {

pkg/llm/responses_test.go

@@ -59,12 +59,15 @@ func TestBuildResponsesRequest(t *testing.T) {
 	if raw["model"] != "gpt-test" || raw["stream"] != true {
 		t.Fatalf("model/stream = %#v / %#v", raw["model"], raw["stream"])
 	}
+	if raw["instructions"] != "be concise" {
+		t.Fatalf("instructions = %#v", raw["instructions"])
+	}
 	if raw["tool_choice"] != "auto" {
 		t.Fatalf("tool_choice = %#v", raw["tool_choice"])
 	}
 
 	input, ok := raw["input"].([]any)
-	if !ok || len(input) != 6 {
+	if !ok || len(input) != 5 {
 		t.Fatalf("input = %#v", raw["input"])
 	}
 	checkInputItem := func(index int, wantType, wantKey, wantValue string) {
@@ -80,16 +83,15 @@ func TestBuildResponsesRequest(t *testing.T) {
 			t.Fatalf("input[%d].type = %#v, want %q", index, item["type"], wantType)
 		}
 	}
-	checkInputItem(0, "", "role", "system")
+	checkInputItem(0, "", "role", "user")
-	checkInputItem(1, "", "role", "user")
+	checkInputItem(1, "", "role", "assistant")
-	checkInputItem(2, "", "role", "assistant")
+	checkInputItem(2, "function_call", "call_id", "call_1")
-	checkInputItem(3, "function_call", "call_id", "call_1")
+	checkInputItem(3, "function_call_output", "call_id", "call_1")
-	checkInputItem(4, "function_call_output", "call_id", "call_1")
+	checkInputItem(4, "", "role", "assistant")
-	checkInputItem(5, "", "role", "assistant")
+	if item := input[2].(map[string]any); item["name"] != "file_read" || item["arguments"] != `{"path":"README.md"}` {
-	if item := input[3].(map[string]any); item["name"] != "file_read" || item["arguments"] != `{"path":"README.md"}` {
 		t.Fatalf("function_call item = %#v", item)
 	}
-	if item := input[4].(map[string]any); item["output"] != "contents" {
+	if item := input[3].(map[string]any); item["output"] != "contents" {
 		t.Fatalf("function_call_output item = %#v", item)
 	}
 
@@ -117,6 +119,36 @@ func TestBuildResponsesRequest(t *testing.T) {
 	}
 }
 
+func TestResponsesInstructionsCombinesSystemMessages(t *testing.T) {
+	payload := buildResponsesRequest(ChatRequest{
+		Model: "gpt-test",
+		Messages: []Message{
+			{Role: RoleSystem, Content: "first instruction"},
+			{Role: RoleUser, Content: "hi"},
+			{Role: RoleSystem, Content: "second instruction"},
+		},
+	})
+	data, err := json.Marshal(payload)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var raw map[string]any
+	if err := json.Unmarshal(data, &raw); err != nil {
+		t.Fatal(err)
+	}
+	if raw["instructions"] != "first instruction\n\nsecond instruction" {
+		t.Fatalf("instructions = %#v", raw["instructions"])
+	}
+	input, ok := raw["input"].([]any)
+	if !ok || len(input) != 1 {
+		t.Fatalf("input = %#v", raw["input"])
+	}
+	item, ok := input[0].(map[string]any)
+	if !ok || item["role"] != "user" {
+		t.Fatalf("input[0] = %#v", input[0])
+	}
+}
+
 func TestOpenAIResponsesClientStreamsContentAndToolCalls(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path != "/v1/responses" {