diff --git a/pkg/agent/context.go b/pkg/agent/context.go
index a9db5afddc..7bd55d4ab0 100644
--- a/pkg/agent/context.go
+++ b/pkg/agent/context.go
@@ -229,8 +229,19 @@ func sanitizeHistoryForProvider(history []providers.Message) []providers.Message
 				logger.DebugCF("agent", "Dropping orphaned leading tool message", map[string]any{})
 				continue
 			}
-			last := sanitized[len(sanitized)-1]
-			if last.Role != "assistant" || len(last.ToolCalls) == 0 {
+			// Walk backwards to find the nearest assistant message,
+			// skipping over any preceding tool messages (multi-tool-call case).
+			foundAssistant := false
+			for i := len(sanitized) - 1; i >= 0; i-- {
+				if sanitized[i].Role == "tool" {
+					continue
+				}
+				if sanitized[i].Role == "assistant" && len(sanitized[i].ToolCalls) > 0 {
+					foundAssistant = true
+				}
+				break
+			}
+			if !foundAssistant {
 				logger.DebugCF("agent", "Dropping orphaned tool message", map[string]any{})
 				continue
 			}
diff --git a/pkg/agent/context_test.go b/pkg/agent/context_test.go
new file mode 100644
index 0000000000..e023c9c306
--- /dev/null
+++ b/pkg/agent/context_test.go
@@ -0,0 +1,209 @@
+package agent
+
+import (
+	"testing"
+
+	"github.com/sipeed/picoclaw/pkg/providers"
+)
+
+func msg(role, content string) providers.Message {
+	return providers.Message{Role: role, Content: content}
+}
+
+func assistantWithTools(toolIDs ...string) providers.Message {
+	calls := make([]providers.ToolCall, len(toolIDs))
+	for i, id := range toolIDs {
+		calls[i] = providers.ToolCall{ID: id, Type: "function"}
+	}
+	return providers.Message{Role: "assistant", ToolCalls: calls}
+}
+
+func toolResult(id string) providers.Message {
+	return providers.Message{Role: "tool", Content: "result", ToolCallID: id}
+}
+
+func TestSanitizeHistoryForProvider_EmptyHistory(t *testing.T) {
+	result := sanitizeHistoryForProvider(nil)
+	if len(result) != 0 {
+		t.Fatalf("expected empty, got %d messages", len(result))
+	}
+
+	result = sanitizeHistoryForProvider([]providers.Message{})
+	if len(result) != 0 {
+		t.Fatalf("expected empty, got %d messages", len(result))
+	}
+}
+
+func TestSanitizeHistoryForProvider_SingleToolCall(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "hello"),
+		assistantWithTools("A"),
+		toolResult("A"),
+		msg("assistant", "done"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 4 {
+		t.Fatalf("expected 4 messages, got %d", len(result))
+	}
+	assertRoles(t, result, "user", "assistant", "tool", "assistant")
+}
+
+func TestSanitizeHistoryForProvider_MultiToolCalls(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "do two things"),
+		assistantWithTools("A", "B"),
+		toolResult("A"),
+		toolResult("B"),
+		msg("assistant", "both done"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 5 {
+		t.Fatalf("expected 5 messages, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user", "assistant", "tool", "tool", "assistant")
+}
+
+func TestSanitizeHistoryForProvider_AssistantToolCallAfterPlainAssistant(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "hi"),
+		msg("assistant", "thinking"),
+		assistantWithTools("A"),
+		toolResult("A"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 2 {
+		t.Fatalf("expected 2 messages, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user", "assistant")
+}
+
+func TestSanitizeHistoryForProvider_OrphanedLeadingTool(t *testing.T) {
+	history := []providers.Message{
+		toolResult("A"),
+		msg("user", "hello"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 1 {
+		t.Fatalf("expected 1 message, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user")
+}
+
+func TestSanitizeHistoryForProvider_ToolAfterUserDropped(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "hello"),
+		toolResult("A"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 1 {
+		t.Fatalf("expected 1 message, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user")
+}
+
+func TestSanitizeHistoryForProvider_ToolAfterAssistantNoToolCalls(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "hello"),
+		msg("assistant", "hi"),
+		toolResult("A"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 2 {
+		t.Fatalf("expected 2 messages, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user", "assistant")
+}
+
+func TestSanitizeHistoryForProvider_AssistantToolCallAtStart(t *testing.T) {
+	history := []providers.Message{
+		assistantWithTools("A"),
+		toolResult("A"),
+		msg("user", "hello"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 1 {
+		t.Fatalf("expected 1 message, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user")
+}
+
+func TestSanitizeHistoryForProvider_MultiToolCallsThenNewRound(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "do two things"),
+		assistantWithTools("A", "B"),
+		toolResult("A"),
+		toolResult("B"),
+		msg("assistant", "done"),
+		msg("user", "hi"),
+		assistantWithTools("C"),
+		toolResult("C"),
+		msg("assistant", "done again"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 9 {
+		t.Fatalf("expected 9 messages, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user", "assistant", "tool", "tool", "assistant", "user", "assistant", "tool", "assistant")
+}
+
+func TestSanitizeHistoryForProvider_ConsecutiveMultiToolRounds(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "start"),
+		assistantWithTools("A", "B"),
+		toolResult("A"),
+		toolResult("B"),
+		assistantWithTools("C", "D"),
+		toolResult("C"),
+		toolResult("D"),
+		msg("assistant", "all done"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 8 {
+		t.Fatalf("expected 8 messages, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user", "assistant", "tool", "tool", "assistant", "tool", "tool", "assistant")
+}
+
+func TestSanitizeHistoryForProvider_PlainConversation(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "hello"),
+		msg("assistant", "hi"),
+		msg("user", "how are you"),
+		msg("assistant", "fine"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 4 {
+		t.Fatalf("expected 4 messages, got %d", len(result))
+	}
+	assertRoles(t, result, "user", "assistant", "user", "assistant")
+}
+
+func roles(msgs []providers.Message) []string {
+	r := make([]string, len(msgs))
+	for i, m := range msgs {
+		r[i] = m.Role
+	}
+	return r
+}
+
+func assertRoles(t *testing.T, msgs []providers.Message, expected ...string) {
+	t.Helper()
+	if len(msgs) != len(expected) {
+		t.Fatalf("role count mismatch: got %v, want %v", roles(msgs), expected)
+	}
+	for i, exp := range expected {
+		if msgs[i].Role != exp {
+			t.Errorf("message[%d]: got role %q, want %q", i, msgs[i].Role, exp)
+		}
+	}
+}