diff --git a/internal/adapter/openai/prompt_build_test.go b/internal/adapter/openai/prompt_build_test.go
index bc89bd6..0d7e1c5 100644
--- a/internal/adapter/openai/prompt_build_test.go
+++ b/internal/adapter/openai/prompt_build_test.go
@@ -87,3 +87,17 @@ func TestBuildOpenAIFinalPrompt_VercelPreparePathKeepsFinalAnswerInstruction(t *
 		t.Fatalf("vercel prepare finalPrompt should not require fenced tool calls: %q", finalPrompt)
 	}
 }
+
+func TestBuildOpenAIFinalPromptWithThinkingAddsContinuationContract(t *testing.T) {
+	messages := []any{
+		map[string]any{"role": "user", "content": "继续回答上一个问题"},
+	}
+
+	finalPrompt, _ := buildOpenAIFinalPrompt(messages, nil, "", true)
+	if !strings.Contains(finalPrompt, "Continue the conversation from the full prior context") {
+		t.Fatalf("expected continuation contract in thinking prompt, got=%q", finalPrompt)
+	}
+	if !strings.Contains(finalPrompt, "final user-facing answer only in reasoning") {
+		t.Fatalf("expected visible-answer contract in thinking prompt, got=%q", finalPrompt)
+	}
+}
diff --git a/internal/prompt/messages.go b/internal/prompt/messages.go
index d882f34..993eeef 100644
--- a/internal/prompt/messages.go
+++ b/internal/prompt/messages.go
@@ -30,6 +30,11 @@ func MessagesPrepareWithThinking(messages []map[string]any, thinkingEnabled bool
 		Text string
 	}
 	processed := make([]block, 0, len(messages))
+	if thinkingEnabled {
+		if instruction := buildConversationContinuityInstructions(thinkingEnabled); strings.TrimSpace(instruction) != "" {
+			processed = append(processed, block{Role: "system", Text: instruction})
+		}
+	}
 	for _, m := range messages {
 		role, _ := m["role"].(string)
 		text := NormalizeContent(m["content"])
@@ -88,6 +93,17 @@ func formatRoleBlock(marker, text, endMarker string) string {
 	return out
 }
 
+func buildConversationContinuityInstructions(thinkingEnabled bool) string {
+	lines := []string{
+		"Continue the conversation from the full prior context and the latest tool results.",
+		"Treat earlier messages as binding context; answer the user's current request as a continuation, not a restart.",
+	}
+	if thinkingEnabled {
+		lines = append(lines, "Keep reasoning internal. Do not leave the final user-facing answer only in reasoning; always provide the answer in visible assistant content.")
+	}
+	return strings.Join(lines, "\n")
+}
+
 func NormalizeContent(v any) string {
 	if v == nil {
 		return ""
diff --git a/internal/prompt/messages_test.go b/internal/prompt/messages_test.go
index 6d9a034..8be34b2 100644
--- a/internal/prompt/messages_test.go
+++ b/internal/prompt/messages_test.go
@@ -58,17 +58,23 @@ func TestNormalizeContentArrayFallsBackToContentWhenTextEmpty(t *testing.T) {
 	}
 }
 
-func TestMessagesPrepareWithThinkingIgnoresThinkingFlag(t *testing.T) {
+func TestMessagesPrepareWithThinkingAddsContinuityContract(t *testing.T) {
 	messages := []map[string]any{{"role": "user", "content": "Question"}}
 	gotThinking := MessagesPrepareWithThinking(messages, true)
 	gotPlain := MessagesPrepareWithThinking(messages, false)
-	if gotThinking != gotPlain {
-		t.Fatalf("expected thinking flag to be ignored, got %q vs %q", gotThinking, gotPlain)
+	if gotThinking == gotPlain {
+		t.Fatalf("expected thinking-enabled prompt to include extra continuity instructions")
 	}
 	if !strings.HasSuffix(gotThinking, "<｜Assistant｜>") {
-		t.Fatalf("expected assistant suffix without think tags, got %q", gotThinking)
+		t.Fatalf("expected assistant suffix, got %q", gotThinking)
 	}
-	if strings.Contains(gotThinking, "<think>") || strings.Contains(gotThinking, "</think>") {
-		t.Fatalf("did not expect think tags in prompt, got %q", gotThinking)
+	if !strings.Contains(gotThinking, "Continue the conversation from the full prior context") {
+		t.Fatalf("expected continuity instruction in thinking prompt, got %q", gotThinking)
+	}
+	if !strings.Contains(gotThinking, "final user-facing answer only in reasoning") {
+		t.Fatalf("expected visible-answer instruction in thinking prompt, got %q", gotThinking)
+	}
+	if strings.Contains(gotPlain, "Continue the conversation from the full prior context") {
+		t.Fatalf("did not expect thinking-only instruction in plain prompt, got %q", gotPlain)
 	}
 }