Merge pull request #342 from shern-point/fix/tool-string-schema-protection

Fix/tool string schema protection
2026-05-04 00:15:28 +08:00 · 2026-04-28 16:37:44 +08:00
parent 63271aea8c fa3e6d040d
commit 40ebc8e942
23 changed files with 672 additions and 80 deletions
--- a/docs/prompt-compatibility.md
+++ b/docs/prompt-compatibility.md
@@ -153,6 +153,7 @@ OpenAI Chat / Responses 在标准化后、current input file 之前，会默认
 工具调用正例现在优先示范官方 DSML 风格：`<|DSML|tool_calls>` → `<|DSML|invoke name="...">` → `<|DSML|parameter name="...">`。
 兼容层仍接受旧式纯 `<tool_calls>` wrapper，但提示词会优先要求模型输出官方 DSML 标签，并强调不能只输出 closing wrapper 而漏掉 opening tag。需要注意：这是“兼容 DSML 外壳，内部仍以 XML 解析语义为准”，不是原生 DSML 全链路实现；DSML 标签会在解析入口归一化回现有 XML 标签后继续走同一套 parser。
 数组参数使用 `<item>...</item>` 子节点表示；当某个参数体只包含 item 子节点时，Go / Node 解析器会把它还原成数组，避免 `questions` / `options` 这类 schema 中要求 array 的参数被误解析成 `{ "item": ... }` 对象。若模型把完整结构化 XML fragment 误包进 CDATA，兼容层会在保护 `content` / `command` 等原文字段的前提下，尝试把非原文字段中的 CDATA XML fragment 还原成 object / array。不过，如果 CDATA 只是单个平面的 XML/HTML 标签，例如 `<b>urgent</b>` 这种行内标记，兼容层会保留原始字符串，不会强行升成 object / array；只有明显表示结构的 CDATA 片段，例如多兄弟节点、嵌套子节点或 `item` 列表，才会触发结构化恢复。
+在 assistant 最终回包阶段，如果某个 tool 参数在声明 schema 中明确是 `string`，兼容层会在把解析后的 `tool_calls` / `function_call` 重新序列化成 OpenAI / Responses / Claude 可见参数前，递归把该路径上的 number / bool / object / array 统一转成字符串；其中 object / array 会压成紧凑 JSON 字符串。这个保护只对 schema 明确声明为 string 的路径生效，不会改写本来就是 `number` / `boolean` / `object` / `array` 的参数。这样可以兼容 DeepSeek 输出了结构化片段、但上游客户端工具 schema 又严格要求字符串参数的场景（例如 `content`、`prompt`、`path`、`taskId` 等）。
 正例中的工具名只会来自当前请求实际声明的工具；如果当前请求没有足够的已知工具形态，就省略对应的单工具、多工具或嵌套示例，避免把不可用工具名写进 prompt。
 对执行类工具，脚本内容必须进入执行参数本身：`Bash` / `execute_command` 使用 `command`，`exec_command` 使用 `cmd`；不要把脚本示范成 `path` / `content` 文件写入参数。

--- a/internal/format/openai/render_chat.go
+++ b/internal/format/openai/render_chat.go
@@ -6,12 +6,12 @@ import (
 	"time"
 )

-func BuildChatCompletion(completionID, model, finalPrompt, finalThinking, finalText string, toolNames []string) map[string]any {
+func BuildChatCompletion(completionID, model, finalPrompt, finalThinking, finalText string, toolNames []string, toolsRaw any) map[string]any {
 	detected := toolcall.ParseAssistantToolCallsDetailed(finalText, finalThinking, toolNames)
-	return BuildChatCompletionWithToolCalls(completionID, model, finalPrompt, finalThinking, finalText, detected.Calls)
+	return BuildChatCompletionWithToolCalls(completionID, model, finalPrompt, finalThinking, finalText, detected.Calls, toolsRaw)
 }

-func BuildChatCompletionWithToolCalls(completionID, model, finalPrompt, finalThinking, finalText string, detected []toolcall.ParsedToolCall) map[string]any {
+func BuildChatCompletionWithToolCalls(completionID, model, finalPrompt, finalThinking, finalText string, detected []toolcall.ParsedToolCall, toolsRaw any) map[string]any {
 	finishReason := "stop"
 	messageObj := map[string]any{"role": "assistant", "content": finalText}
 	if strings.TrimSpace(finalThinking) != "" {
@@ -19,7 +19,7 @@ func BuildChatCompletionWithToolCalls(completionID, model, finalPrompt, finalThi
 	}
 	if len(detected) > 0 {
 		finishReason = "tool_calls"
-		messageObj["tool_calls"] = toolcall.FormatOpenAIToolCalls(detected)
+		messageObj["tool_calls"] = toolcall.FormatOpenAIToolCalls(detected, toolsRaw)
 		messageObj["content"] = nil
 	}

--- a/internal/format/openai/render_responses.go
+++ b/internal/format/openai/render_responses.go
@@ -9,19 +9,19 @@ import (
 	"github.com/google/uuid"
 )

-func BuildResponseObject(responseID, model, finalPrompt, finalThinking, finalText string, toolNames []string) map[string]any {
+func BuildResponseObject(responseID, model, finalPrompt, finalThinking, finalText string, toolNames []string, toolsRaw any) map[string]any {
 	// Strict mode: only standalone, structured tool-call payloads are treated
 	// as executable tool calls.
 	detected := toolcall.ParseAssistantToolCallsDetailed(finalText, finalThinking, toolNames)
-	return BuildResponseObjectWithToolCalls(responseID, model, finalPrompt, finalThinking, finalText, detected.Calls)
+	return BuildResponseObjectWithToolCalls(responseID, model, finalPrompt, finalThinking, finalText, detected.Calls, toolsRaw)
 }

-func BuildResponseObjectWithToolCalls(responseID, model, finalPrompt, finalThinking, finalText string, detected []toolcall.ParsedToolCall) map[string]any {
+func BuildResponseObjectWithToolCalls(responseID, model, finalPrompt, finalThinking, finalText string, detected []toolcall.ParsedToolCall, toolsRaw any) map[string]any {
 	exposedOutputText := finalText
 	output := make([]any, 0, 2)
 	if len(detected) > 0 {
 		exposedOutputText = ""
-		output = append(output, toResponsesFunctionCallItems(detected)...)
+		output = append(output, toResponsesFunctionCallItems(detected, toolsRaw)...)
 	} else {
 		content := make([]any, 0, 2)
 		if finalThinking != "" {
@@ -74,12 +74,13 @@ func BuildResponseObjectFromItems(responseID, model, finalPrompt, finalThinking,
 	}
 }

-func toResponsesFunctionCallItems(toolCalls []toolcall.ParsedToolCall) []any {
+func toResponsesFunctionCallItems(toolCalls []toolcall.ParsedToolCall, toolsRaw any) []any {
 	if len(toolCalls) == 0 {
 		return nil
 	}
+	normalizedCalls := toolcall.NormalizeParsedToolCallsForSchemas(toolCalls, toolsRaw)
 	out := make([]any, 0, len(toolCalls))
-	for _, tc := range toolCalls {
+	for _, tc := range normalizedCalls {
 		if strings.TrimSpace(tc.Name) == "" {
 			continue
 		}
--- a/internal/format/openai/render_test.go
+++ b/internal/format/openai/render_test.go
@@ -1,8 +1,11 @@
 package openai

 import (
+	"encoding/json"
 	"strings"
 	"testing"
+
+	"ds2api/internal/toolcall"
 )

 func TestBuildResponseObjectKeepsFencedToolPayloadAsText(t *testing.T) {
@@ -13,6 +16,7 @@ func TestBuildResponseObjectKeepsFencedToolPayloadAsText(t *testing.T) {
 		"",
 		"```json\n{\"tool_calls\":[{\"name\":\"search\",\"input\":{\"q\":\"golang\"}}]}\n```",
 		[]string{"search"},
+		nil,
 	)

 	outputText, _ := obj["output_text"].(string)
@@ -42,6 +46,7 @@ func TestBuildResponseObjectReasoningOnlyFallsBackToOutputText(t *testing.T) {
 		"internal thinking content",
 		"",
 		nil,
+		nil,
 	)

 	outputText, _ := obj["output_text"].(string)
@@ -75,6 +80,7 @@ func TestBuildResponseObjectPromotesToolCallFromThinkingWhenTextEmpty(t *testing
 		`<tool_calls><invoke name="search"><parameter name="q">from-thinking</parameter></invoke></tool_calls>`,
 		"",
 		[]string{"search"},
+		nil,
 	)

 	output, _ := obj["output"].([]any)
@@ -86,3 +92,88 @@ func TestBuildResponseObjectPromotesToolCallFromThinkingWhenTextEmpty(t *testing
 		t.Fatalf("expected function_call output, got %#v", first["type"])
 	}
 }
+
+func TestBuildChatCompletionWithToolCallsCoercesSchemaDeclaredStringArguments(t *testing.T) {
+	toolsRaw := []any{
+		map[string]any{
+			"type": "function",
+			"function": map[string]any{
+				"name": "Write",
+				"parameters": map[string]any{
+					"type": "object",
+					"properties": map[string]any{
+						"content": map[string]any{"type": "string"},
+						"taskId":  map[string]any{"type": "string"},
+					},
+				},
+			},
+		},
+	}
+	obj := BuildChatCompletionWithToolCalls(
+		"chat_test",
+		"gpt-4o",
+		"prompt",
+		"",
+		"",
+		[]toolcall.ParsedToolCall{{
+			Name: "Write",
+			Input: map[string]any{
+				"content": map[string]any{"message": "hi"},
+				"taskId":  1,
+			},
+		}},
+		toolsRaw,
+	)
+	choices, _ := obj["choices"].([]map[string]any)
+	message, _ := choices[0]["message"].(map[string]any)
+	toolCalls, _ := message["tool_calls"].([]map[string]any)
+	fn, _ := toolCalls[0]["function"].(map[string]any)
+	args := map[string]any{}
+	if err := json.Unmarshal([]byte(fn["arguments"].(string)), &args); err != nil {
+		t.Fatalf("decode arguments failed: %v", err)
+	}
+	if args["content"] != `{"message":"hi"}` {
+		t.Fatalf("expected content stringified by schema, got %#v", args["content"])
+	}
+	if args["taskId"] != "1" {
+		t.Fatalf("expected taskId stringified by schema, got %#v", args["taskId"])
+	}
+}
+
+func TestBuildResponseObjectWithToolCallsCoercesSchemaDeclaredStringArguments(t *testing.T) {
+	toolsRaw := []any{
+		map[string]any{
+			"type": "function",
+			"function": map[string]any{
+				"name": "Write",
+				"parameters": map[string]any{
+					"type": "object",
+					"properties": map[string]any{
+						"content": map[string]any{"type": "string"},
+					},
+				},
+			},
+		},
+	}
+	obj := BuildResponseObjectWithToolCalls(
+		"resp_test",
+		"gpt-4o",
+		"prompt",
+		"",
+		"",
+		[]toolcall.ParsedToolCall{{
+			Name:  "Write",
+			Input: map[string]any{"content": []any{"a", 1}},
+		}},
+		toolsRaw,
+	)
+	output, _ := obj["output"].([]any)
+	first, _ := output[0].(map[string]any)
+	args := map[string]any{}
+	if err := json.Unmarshal([]byte(first["arguments"].(string)), &args); err != nil {
+		t.Fatalf("decode response arguments failed: %v", err)
+	}
+	if args["content"] != `["a",1]` {
+		t.Fatalf("expected response content stringified by schema, got %#v", args["content"])
+	}
+}
--- a/internal/httpapi/openai/chat/chat_history_test.go
+++ b/internal/httpapi/openai/chat/chat_history_test.go
@@ -194,7 +194,7 @@ func TestHandleStreamContextCancelledMarksHistoryStopped(t *testing.T) {
 	rec := httptest.NewRecorder()
 	resp := makeOpenAISSEHTTPResponse(`data: {"p":"response/content","v":"hello"}`, `data: [DONE]`)

-	h.handleStream(rec, req, resp, "cid-stop", "deepseek-v4-flash", "prompt", false, false, nil, session)
+	h.handleStream(rec, req, resp, "cid-stop", "deepseek-v4-flash", "prompt", false, false, nil, nil, session)

 	snapshot, err := historyStore.Snapshot()
 	if err != nil {
--- a/internal/httpapi/openai/chat/chat_stream_runtime.go
+++ b/internal/httpapi/openai/chat/chat_stream_runtime.go
@@ -21,6 +21,7 @@ type chatStreamRuntime struct {
 	model        string
 	finalPrompt  string
 	toolNames    []string
+	toolsRaw     any

 	thinkingEnabled       bool
 	searchEnabled         bool
@@ -61,6 +62,7 @@ func newChatStreamRuntime(
 	searchEnabled bool,
 	stripReferenceMarkers bool,
 	toolNames []string,
+	toolsRaw any,
 	bufferToolContent bool,
 	emitEarlyToolDeltas bool,
 ) *chatStreamRuntime {
@@ -73,6 +75,7 @@ func newChatStreamRuntime(
 		model:                 model,
 		finalPrompt:           finalPrompt,
 		toolNames:             toolNames,
+		toolsRaw:              toolsRaw,
 		thinkingEnabled:       thinkingEnabled,
 		searchEnabled:         searchEnabled,
 		stripReferenceMarkers: stripReferenceMarkers,
@@ -142,7 +145,7 @@ func (s *chatStreamRuntime) finalize(finishReason string, deferEmptyOutput bool)
 	if len(detected.Calls) > 0 && !s.toolCallsDoneEmitted {
 		finishReason = "tool_calls"
 		delta := map[string]any{
-			"tool_calls": formatFinalStreamToolCallsWithStableIDs(detected.Calls, s.streamToolCallIDs),
+			"tool_calls": formatFinalStreamToolCallsWithStableIDs(detected.Calls, s.streamToolCallIDs, s.toolsRaw),
 		}
 		if !s.firstChunkSent {
 			delta["role"] = "assistant"
@@ -164,7 +167,7 @@ func (s *chatStreamRuntime) finalize(finishReason string, deferEmptyOutput bool)
 				s.toolCallsEmitted = true
 				s.toolCallsDoneEmitted = true
 				tcDelta := map[string]any{
-					"tool_calls": formatFinalStreamToolCallsWithStableIDs(evt.ToolCalls, s.streamToolCallIDs),
+					"tool_calls": formatFinalStreamToolCallsWithStableIDs(evt.ToolCalls, s.streamToolCallIDs, s.toolsRaw),
 				}
 				if !s.firstChunkSent {
 					tcDelta["role"] = "assistant"
@@ -320,7 +323,7 @@ func (s *chatStreamRuntime) onParsed(parsed sse.LineResult) streamengine.ParsedD
 						s.toolCallsEmitted = true
 						s.toolCallsDoneEmitted = true
 						tcDelta := map[string]any{
-							"tool_calls": formatFinalStreamToolCallsWithStableIDs(evt.ToolCalls, s.streamToolCallIDs),
+							"tool_calls": formatFinalStreamToolCallsWithStableIDs(evt.ToolCalls, s.streamToolCallIDs, s.toolsRaw),
 						}
 						if !s.firstChunkSent {
 							tcDelta["role"] = "assistant"
--- a/internal/httpapi/openai/chat/empty_retry_runtime.go
+++ b/internal/httpapi/openai/chat/empty_retry_runtime.go
@@ -26,14 +26,14 @@ type chatNonStreamResult struct {
 	responseMessageID     int
 }

-func (h *Handler) handleNonStreamWithRetry(w http.ResponseWriter, ctx context.Context, a *auth.RequestAuth, resp *http.Response, payload map[string]any, pow, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, historySession *chatHistorySession) {
+func (h *Handler) handleNonStreamWithRetry(w http.ResponseWriter, ctx context.Context, a *auth.RequestAuth, resp *http.Response, payload map[string]any, pow, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, historySession *chatHistorySession) {
 	attempts := 0
 	currentResp := resp
 	usagePrompt := finalPrompt
 	accumulatedThinking := ""
 	accumulatedToolDetectionThinking := ""
 	for {
-		result, ok := h.collectChatNonStreamAttempt(w, currentResp, completionID, model, usagePrompt, thinkingEnabled, searchEnabled, toolNames)
+		result, ok := h.collectChatNonStreamAttempt(w, currentResp, completionID, model, usagePrompt, thinkingEnabled, searchEnabled, toolNames, toolsRaw)
 		if !ok {
 			return
 		}
@@ -43,7 +43,7 @@ func (h *Handler) handleNonStreamWithRetry(w http.ResponseWriter, ctx context.Co
 		result.toolDetectionThinking = accumulatedToolDetectionThinking
 		detected := detectAssistantToolCalls(result.text, result.thinking, result.toolDetectionThinking, toolNames)
 		result.detectedCalls = len(detected.Calls)
-		result.body = openaifmt.BuildChatCompletionWithToolCalls(completionID, model, usagePrompt, result.thinking, result.text, detected.Calls)
+		result.body = openaifmt.BuildChatCompletionWithToolCalls(completionID, model, usagePrompt, result.thinking, result.text, detected.Calls, toolsRaw)
 		result.finishReason = chatFinishReason(result.body)
 		if !shouldRetryChatNonStream(result, attempts) {
 			h.finishChatNonStreamResult(w, result, attempts, usagePrompt, historySession)
@@ -72,7 +72,7 @@ func (h *Handler) handleNonStreamWithRetry(w http.ResponseWriter, ctx context.Co
 	}
 }

-func (h *Handler) collectChatNonStreamAttempt(w http.ResponseWriter, resp *http.Response, completionID, model, usagePrompt string, thinkingEnabled, searchEnabled bool, toolNames []string) (chatNonStreamResult, bool) {
+func (h *Handler) collectChatNonStreamAttempt(w http.ResponseWriter, resp *http.Response, completionID, model, usagePrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any) (chatNonStreamResult, bool) {
 	if resp.StatusCode != http.StatusOK {
 		defer func() { _ = resp.Body.Close() }()
 		body, _ := io.ReadAll(resp.Body)
@@ -88,7 +88,7 @@ func (h *Handler) collectChatNonStreamAttempt(w http.ResponseWriter, resp *http.
 		finalText = replaceCitationMarkersWithLinks(finalText, result.CitationLinks)
 	}
 	detected := detectAssistantToolCalls(finalText, finalThinking, finalToolDetectionThinking, toolNames)
-	respBody := openaifmt.BuildChatCompletionWithToolCalls(completionID, model, usagePrompt, finalThinking, finalText, detected.Calls)
+	respBody := openaifmt.BuildChatCompletionWithToolCalls(completionID, model, usagePrompt, finalThinking, finalText, detected.Calls, toolsRaw)
 	return chatNonStreamResult{
 		thinking:              finalThinking,
 		toolDetectionThinking: finalToolDetectionThinking,
@@ -139,8 +139,8 @@ func shouldRetryChatNonStream(result chatNonStreamResult, attempts int) bool {
 		strings.TrimSpace(result.text) == ""
 }

-func (h *Handler) handleStreamWithRetry(w http.ResponseWriter, r *http.Request, a *auth.RequestAuth, resp *http.Response, payload map[string]any, pow, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, historySession *chatHistorySession) {
-	streamRuntime, initialType, ok := h.prepareChatStreamRuntime(w, resp, completionID, model, finalPrompt, thinkingEnabled, searchEnabled, toolNames, historySession)
+func (h *Handler) handleStreamWithRetry(w http.ResponseWriter, r *http.Request, a *auth.RequestAuth, resp *http.Response, payload map[string]any, pow, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, historySession *chatHistorySession) {
+	streamRuntime, initialType, ok := h.prepareChatStreamRuntime(w, resp, completionID, model, finalPrompt, thinkingEnabled, searchEnabled, toolNames, toolsRaw, historySession)
 	if !ok {
 		return
 	}
@@ -182,7 +182,7 @@ func (h *Handler) handleStreamWithRetry(w http.ResponseWriter, r *http.Request,
 	}
 }

-func (h *Handler) prepareChatStreamRuntime(w http.ResponseWriter, resp *http.Response, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, historySession *chatHistorySession) (*chatStreamRuntime, string, bool) {
+func (h *Handler) prepareChatStreamRuntime(w http.ResponseWriter, resp *http.Response, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, historySession *chatHistorySession) (*chatStreamRuntime, string, bool) {
 	if resp.StatusCode != http.StatusOK {
 		defer func() { _ = resp.Body.Close() }()
 		body, _ := io.ReadAll(resp.Body)
@@ -207,7 +207,7 @@ func (h *Handler) prepareChatStreamRuntime(w http.ResponseWriter, resp *http.Res
 	}
 	streamRuntime := newChatStreamRuntime(
 		w, rc, canFlush, completionID, time.Now().Unix(), model, finalPrompt,
-		thinkingEnabled, searchEnabled, h.compatStripReferenceMarkers(), toolNames,
+		thinkingEnabled, searchEnabled, h.compatStripReferenceMarkers(), toolNames, toolsRaw,
 		len(toolNames) > 0, h.toolcallFeatureMatchEnabled() && h.toolcallEarlyEmitHighConfidence(),
 	)
 	return streamRuntime, initialType, true
--- a/internal/httpapi/openai/chat/handler.go
+++ b/internal/httpapi/openai/chat/handler.go
@@ -144,8 +144,8 @@ func filterIncrementalToolCallDeltasByAllowed(deltas []toolstream.ToolCallDelta,
 	return shared.FilterIncrementalToolCallDeltasByAllowed(deltas, seenNames)
 }

-func formatFinalStreamToolCallsWithStableIDs(calls []toolcall.ParsedToolCall, ids map[int]string) []map[string]any {
-	return shared.FormatFinalStreamToolCallsWithStableIDs(calls, ids)
+func formatFinalStreamToolCallsWithStableIDs(calls []toolcall.ParsedToolCall, ids map[int]string, toolsRaw any) []map[string]any {
+	return shared.FormatFinalStreamToolCallsWithStableIDs(calls, ids, toolsRaw)
 }

 func detectAssistantToolCalls(text, exposedThinking, detectionThinking string, toolNames []string) toolcall.ToolCallParseResult {
--- a/internal/httpapi/openai/chat/handler_chat.go
+++ b/internal/httpapi/openai/chat/handler_chat.go
@@ -109,10 +109,10 @@ func (h *Handler) ChatCompletions(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if stdReq.Stream {
-		h.handleStreamWithRetry(w, r, a, resp, payload, pow, sessionID, stdReq.ResponseModel, stdReq.FinalPrompt, stdReq.Thinking, stdReq.Search, stdReq.ToolNames, historySession)
+		h.handleStreamWithRetry(w, r, a, resp, payload, pow, sessionID, stdReq.ResponseModel, stdReq.FinalPrompt, stdReq.Thinking, stdReq.Search, stdReq.ToolNames, stdReq.ToolsRaw, historySession)
 		return
 	}
-	h.handleNonStreamWithRetry(w, r.Context(), a, resp, payload, pow, sessionID, stdReq.ResponseModel, stdReq.FinalPrompt, stdReq.Thinking, stdReq.Search, stdReq.ToolNames, historySession)
+	h.handleNonStreamWithRetry(w, r.Context(), a, resp, payload, pow, sessionID, stdReq.ResponseModel, stdReq.FinalPrompt, stdReq.Thinking, stdReq.Search, stdReq.ToolNames, stdReq.ToolsRaw, historySession)
 }

 func (h *Handler) autoDeleteRemoteSession(ctx context.Context, a *auth.RequestAuth, sessionID string) {
@@ -148,7 +148,7 @@ func (h *Handler) autoDeleteRemoteSession(ctx context.Context, a *auth.RequestAu
 	}
 }

-func (h *Handler) handleNonStream(w http.ResponseWriter, resp *http.Response, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, historySession *chatHistorySession) {
+func (h *Handler) handleNonStream(w http.ResponseWriter, resp *http.Response, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, historySession *chatHistorySession) {
 	if resp.StatusCode != http.StatusOK {
 		defer func() { _ = resp.Body.Close() }()
 		body, _ := io.ReadAll(resp.Body)
@@ -176,7 +176,7 @@ func (h *Handler) handleNonStream(w http.ResponseWriter, resp *http.Response, co
 		writeUpstreamEmptyOutputError(w, finalText, finalThinking, result.ContentFilter)
 		return
 	}
-	respBody := openaifmt.BuildChatCompletionWithToolCalls(completionID, model, finalPrompt, finalThinking, finalText, detected.Calls)
+	respBody := openaifmt.BuildChatCompletionWithToolCalls(completionID, model, finalPrompt, finalThinking, finalText, detected.Calls, toolsRaw)
 	finishReason := "stop"
 	if choices, ok := respBody["choices"].([]map[string]any); ok && len(choices) > 0 {
 		if fr, _ := choices[0]["finish_reason"].(string); strings.TrimSpace(fr) != "" {
@@ -189,7 +189,7 @@ func (h *Handler) handleNonStream(w http.ResponseWriter, resp *http.Response, co
 	writeJSON(w, http.StatusOK, respBody)
 }

-func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *http.Response, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, historySession *chatHistorySession) {
+func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *http.Response, completionID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, historySession *chatHistorySession) {
 	defer func() { _ = resp.Body.Close() }()
 	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(resp.Body)
@@ -230,6 +230,7 @@ func (h *Handler) handleStream(w http.ResponseWriter, r *http.Request, resp *htt
 		searchEnabled,
 		stripReferenceMarkers,
 		toolNames,
+		toolsRaw,
 		bufferToolContent,
 		emitEarlyToolDeltas,
 	)
--- a/internal/httpapi/openai/chat/handler_toolcall_test.go
+++ b/internal/httpapi/openai/chat/handler_toolcall_test.go
@@ -93,7 +93,7 @@ func TestHandleNonStreamReturns429WhenUpstreamOutputEmpty(t *testing.T) {
 	)
 	rec := httptest.NewRecorder()

-	h.handleNonStream(rec, resp, "cid-empty", "deepseek-v4-flash", "prompt", false, false, nil, nil)
+	h.handleNonStream(rec, resp, "cid-empty", "deepseek-v4-flash", "prompt", false, false, nil, nil, nil)
 	if rec.Code != http.StatusTooManyRequests {
 		t.Fatalf("expected status 429 for empty upstream output, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -112,7 +112,7 @@ func TestHandleNonStreamReturnsContentFilterErrorWhenUpstreamFilteredWithoutOutp
 	)
 	rec := httptest.NewRecorder()

-	h.handleNonStream(rec, resp, "cid-empty-filtered", "deepseek-v4-flash", "prompt", false, false, nil, nil)
+	h.handleNonStream(rec, resp, "cid-empty-filtered", "deepseek-v4-flash", "prompt", false, false, nil, nil, nil)
 	if rec.Code != http.StatusBadRequest {
 		t.Fatalf("expected status 400 for filtered upstream output, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -131,7 +131,7 @@ func TestHandleNonStreamReturns429WhenUpstreamHasOnlyThinking(t *testing.T) {
 	)
 	rec := httptest.NewRecorder()

-	h.handleNonStream(rec, resp, "cid-thinking-only", "deepseek-v4-pro", "prompt", true, false, nil, nil)
+	h.handleNonStream(rec, resp, "cid-thinking-only", "deepseek-v4-pro", "prompt", true, false, nil, nil, nil)
 	if rec.Code != http.StatusTooManyRequests {
 		t.Fatalf("expected status 429 for thinking-only upstream output, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -150,7 +150,7 @@ func TestHandleNonStreamPromotesThinkingToolCallsWhenTextEmpty(t *testing.T) {
 	)
 	rec := httptest.NewRecorder()

-	h.handleNonStream(rec, resp, "cid-thinking-tool", "deepseek-v4-pro", "prompt", true, false, []string{"search"}, nil)
+	h.handleNonStream(rec, resp, "cid-thinking-tool", "deepseek-v4-pro", "prompt", true, false, []string{"search"}, nil, nil)
 	if rec.Code != http.StatusOK {
 		t.Fatalf("expected 200 for thinking tool calls, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -181,7 +181,7 @@ func TestHandleNonStreamPromotesHiddenThinkingDSMLToolCallsWhenTextEmpty(t *test
 	)
 	rec := httptest.NewRecorder()

-	h.handleNonStream(rec, resp, "cid-hidden-thinking-tool", "deepseek-v4-pro", "prompt", false, false, []string{"search"}, nil)
+	h.handleNonStream(rec, resp, "cid-hidden-thinking-tool", "deepseek-v4-pro", "prompt", false, false, []string{"search"}, nil, nil)
 	if rec.Code != http.StatusOK {
 		t.Fatalf("expected 200 for hidden thinking tool calls, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -211,7 +211,7 @@ func TestHandleStreamToolsPlainTextStreamsBeforeFinish(t *testing.T) {
 	rec := httptest.NewRecorder()
 	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)

-	h.handleStream(rec, req, resp, "cid6", "deepseek-v4-flash", "prompt", false, false, []string{"search"}, nil)
+	h.handleStream(rec, req, resp, "cid6", "deepseek-v4-flash", "prompt", false, false, []string{"search"}, nil, nil)

 	frames, done := parseSSEDataFrames(t, rec.Body.String())
 	if !done {
@@ -248,7 +248,7 @@ func TestHandleStreamIncompleteCapturedToolJSONFlushesAsTextOnFinalize(t *testin
 	rec := httptest.NewRecorder()
 	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)

-	h.handleStream(rec, req, resp, "cid10", "deepseek-v4-flash", "prompt", false, false, []string{"search"}, nil)
+	h.handleStream(rec, req, resp, "cid10", "deepseek-v4-flash", "prompt", false, false, []string{"search"}, nil, nil)

 	frames, done := parseSSEDataFrames(t, rec.Body.String())
 	if !done {
@@ -282,7 +282,7 @@ func TestHandleStreamPromotesThinkingToolCallsOnFinalizeWithoutMidstreamIntercep
 	rec := httptest.NewRecorder()
 	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)

-	h.handleStream(rec, req, resp, "cid-thinking-stream", "deepseek-v4-pro", "prompt", true, false, []string{"search"}, nil)
+	h.handleStream(rec, req, resp, "cid-thinking-stream", "deepseek-v4-pro", "prompt", true, false, []string{"search"}, nil, nil)

 	frames, done := parseSSEDataFrames(t, rec.Body.String())
 	if !done {
@@ -319,7 +319,7 @@ func TestHandleStreamPromotesHiddenThinkingDSMLToolCallsOnFinalize(t *testing.T)
 	rec := httptest.NewRecorder()
 	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)

-	h.handleStream(rec, req, resp, "cid-hidden-thinking-stream", "deepseek-v4-pro", "prompt", false, false, []string{"search"}, nil)
+	h.handleStream(rec, req, resp, "cid-hidden-thinking-stream", "deepseek-v4-pro", "prompt", false, false, []string{"search"}, nil, nil)

 	frames, done := parseSSEDataFrames(t, rec.Body.String())
 	if !done {
@@ -353,7 +353,7 @@ func TestHandleStreamEmitsDistinctToolCallIDsAcrossSeparateToolBlocks(t *testing
 	rec := httptest.NewRecorder()
 	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)

-	h.handleStream(rec, req, resp, "cid-multi", "deepseek-v4-flash", "prompt", false, false, []string{"read_file", "search"}, nil)
+	h.handleStream(rec, req, resp, "cid-multi", "deepseek-v4-flash", "prompt", false, false, []string{"read_file", "search"}, nil, nil)

 	frames, done := parseSSEDataFrames(t, rec.Body.String())
 	if !done {
@@ -390,3 +390,64 @@ func TestHandleStreamEmitsDistinctToolCallIDsAcrossSeparateToolBlocks(t *testing
 		t.Fatalf("expected distinct tool call ids across blocks, got %#v body=%s", ids, rec.Body.String())
 	}
 }
+
+func TestHandleStreamCoercesSchemaDeclaredStringArgumentsOnFinalize(t *testing.T) {
+	h := &Handler{}
+	line := func(v string) string {
+		b, _ := json.Marshal(map[string]any{"p": "response/content", "v": v})
+		return "data: " + string(b)
+	}
+	resp := makeSSEHTTPResponse(
+		line(`<tool_calls><invoke name="Write">{"input":{"content":{"message":"hi"},"taskId":1}}</invoke></tool_calls>`),
+		`data: [DONE]`,
+	)
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+	toolsRaw := []any{
+		map[string]any{
+			"type": "function",
+			"function": map[string]any{
+				"name": "Write",
+				"parameters": map[string]any{
+					"type": "object",
+					"properties": map[string]any{
+						"content": map[string]any{"type": "string"},
+						"taskId":  map[string]any{"type": "string"},
+					},
+				},
+			},
+		},
+	}
+
+	h.handleStream(rec, req, resp, "cid-string-protect", "deepseek-v4-flash", "prompt", false, false, []string{"Write"}, toolsRaw, nil)
+
+	frames, done := parseSSEDataFrames(t, rec.Body.String())
+	if !done {
+		t.Fatalf("expected [DONE], body=%s", rec.Body.String())
+	}
+	for _, frame := range frames {
+		choices, _ := frame["choices"].([]any)
+		for _, item := range choices {
+			choice, _ := item.(map[string]any)
+			delta, _ := choice["delta"].(map[string]any)
+			toolCalls, _ := delta["tool_calls"].([]any)
+			if len(toolCalls) == 0 {
+				continue
+			}
+			call, _ := toolCalls[0].(map[string]any)
+			fn, _ := call["function"].(map[string]any)
+			args := map[string]any{}
+			if err := json.Unmarshal([]byte(asString(fn["arguments"])), &args); err != nil {
+				t.Fatalf("decode streamed tool arguments failed: %v", err)
+			}
+			if args["content"] != `{"message":"hi"}` {
+				t.Fatalf("expected streamed content stringified by schema, got %#v", args["content"])
+			}
+			if args["taskId"] != "1" {
+				t.Fatalf("expected streamed taskId stringified by schema, got %#v", args["taskId"])
+			}
+			return
+		}
+	}
+	t.Fatalf("expected at least one streamed tool call delta, body=%s", rec.Body.String())
+}
--- a/internal/httpapi/openai/responses/empty_retry_runtime.go
+++ b/internal/httpapi/openai/responses/empty_retry_runtime.go
@@ -27,14 +27,14 @@ type responsesNonStreamResult struct {
 	responseMessageID     int
 }

-func (h *Handler) handleResponsesNonStreamWithRetry(w http.ResponseWriter, ctx context.Context, a *auth.RequestAuth, resp *http.Response, payload map[string]any, pow, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolChoice promptcompat.ToolChoicePolicy, traceID string) {
+func (h *Handler) handleResponsesNonStreamWithRetry(w http.ResponseWriter, ctx context.Context, a *auth.RequestAuth, resp *http.Response, payload map[string]any, pow, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, toolChoice promptcompat.ToolChoicePolicy, traceID string) {
 	attempts := 0
 	currentResp := resp
 	usagePrompt := finalPrompt
 	accumulatedThinking := ""
 	accumulatedToolDetectionThinking := ""
 	for {
-		result, ok := h.collectResponsesNonStreamAttempt(w, currentResp, responseID, model, usagePrompt, thinkingEnabled, searchEnabled, toolNames)
+		result, ok := h.collectResponsesNonStreamAttempt(w, currentResp, responseID, model, usagePrompt, thinkingEnabled, searchEnabled, toolNames, toolsRaw)
 		if !ok {
 			return
 		}
@@ -43,7 +43,7 @@ func (h *Handler) handleResponsesNonStreamWithRetry(w http.ResponseWriter, ctx c
 		result.thinking = accumulatedThinking
 		result.toolDetectionThinking = accumulatedToolDetectionThinking
 		result.parsed = detectAssistantToolCalls(result.text, result.thinking, result.toolDetectionThinking, toolNames)
-		result.body = openaifmt.BuildResponseObjectWithToolCalls(responseID, model, usagePrompt, result.thinking, result.text, result.parsed.Calls)
+		result.body = openaifmt.BuildResponseObjectWithToolCalls(responseID, model, usagePrompt, result.thinking, result.text, result.parsed.Calls, toolsRaw)

 		if !shouldRetryResponsesNonStream(result, attempts) {
 			h.finishResponsesNonStreamResult(w, result, attempts, owner, responseID, toolChoice, traceID)
@@ -68,7 +68,7 @@ func (h *Handler) handleResponsesNonStreamWithRetry(w http.ResponseWriter, ctx c
 	}
 }

-func (h *Handler) collectResponsesNonStreamAttempt(w http.ResponseWriter, resp *http.Response, responseID, model, usagePrompt string, thinkingEnabled, searchEnabled bool, toolNames []string) (responsesNonStreamResult, bool) {
+func (h *Handler) collectResponsesNonStreamAttempt(w http.ResponseWriter, resp *http.Response, responseID, model, usagePrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any) (responsesNonStreamResult, bool) {
 	defer func() { _ = resp.Body.Close() }()
 	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(resp.Body)
@@ -84,7 +84,7 @@ func (h *Handler) collectResponsesNonStreamAttempt(w http.ResponseWriter, resp *
 		sanitizedText = replaceCitationMarkersWithLinks(sanitizedText, result.CitationLinks)
 	}
 	textParsed := detectAssistantToolCalls(sanitizedText, sanitizedThinking, toolDetectionThinking, toolNames)
-	responseObj := openaifmt.BuildResponseObjectWithToolCalls(responseID, model, usagePrompt, sanitizedThinking, sanitizedText, textParsed.Calls)
+	responseObj := openaifmt.BuildResponseObjectWithToolCalls(responseID, model, usagePrompt, sanitizedThinking, sanitizedText, textParsed.Calls, toolsRaw)
 	return responsesNonStreamResult{
 		thinking:              sanitizedThinking,
 		toolDetectionThinking: toolDetectionThinking,
@@ -123,8 +123,8 @@ func shouldRetryResponsesNonStream(result responsesNonStreamResult, attempts int
 		strings.TrimSpace(result.text) == ""
 }

-func (h *Handler) handleResponsesStreamWithRetry(w http.ResponseWriter, r *http.Request, a *auth.RequestAuth, resp *http.Response, payload map[string]any, pow, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolChoice promptcompat.ToolChoicePolicy, traceID string) {
-	streamRuntime, initialType, ok := h.prepareResponsesStreamRuntime(w, resp, owner, responseID, model, finalPrompt, thinkingEnabled, searchEnabled, toolNames, toolChoice, traceID)
+func (h *Handler) handleResponsesStreamWithRetry(w http.ResponseWriter, r *http.Request, a *auth.RequestAuth, resp *http.Response, payload map[string]any, pow, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, toolChoice promptcompat.ToolChoicePolicy, traceID string) {
+	streamRuntime, initialType, ok := h.prepareResponsesStreamRuntime(w, resp, owner, responseID, model, finalPrompt, thinkingEnabled, searchEnabled, toolNames, toolsRaw, toolChoice, traceID)
 	if !ok {
 		return
 	}
@@ -165,7 +165,7 @@ func (h *Handler) handleResponsesStreamWithRetry(w http.ResponseWriter, r *http.
 	}
 }

-func (h *Handler) prepareResponsesStreamRuntime(w http.ResponseWriter, resp *http.Response, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolChoice promptcompat.ToolChoicePolicy, traceID string) (*responsesStreamRuntime, string, bool) {
+func (h *Handler) prepareResponsesStreamRuntime(w http.ResponseWriter, resp *http.Response, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, toolChoice promptcompat.ToolChoicePolicy, traceID string) (*responsesStreamRuntime, string, bool) {
 	if resp.StatusCode != http.StatusOK {
 		defer func() { _ = resp.Body.Close() }()
 		body, _ := io.ReadAll(resp.Body)
@@ -184,7 +184,7 @@ func (h *Handler) prepareResponsesStreamRuntime(w http.ResponseWriter, resp *htt
 	}
 	streamRuntime := newResponsesStreamRuntime(
 		w, rc, canFlush, responseID, model, finalPrompt, thinkingEnabled, searchEnabled,
-		h.compatStripReferenceMarkers(), toolNames, len(toolNames) > 0,
+		h.compatStripReferenceMarkers(), toolNames, toolsRaw, len(toolNames) > 0,
 		h.toolcallFeatureMatchEnabled() && h.toolcallEarlyEmitHighConfidence(),
 		toolChoice, traceID, func(obj map[string]any) {
 			h.getResponseStore().put(owner, responseID, obj)
--- a/internal/httpapi/openai/responses/responses_handler.go
+++ b/internal/httpapi/openai/responses/responses_handler.go
@@ -115,13 +115,13 @@ func (h *Handler) Responses(w http.ResponseWriter, r *http.Request) {

 	responseID := "resp_" + strings.ReplaceAll(uuid.NewString(), "-", "")
 	if stdReq.Stream {
-		h.handleResponsesStreamWithRetry(w, r, a, resp, payload, pow, owner, responseID, stdReq.ResponseModel, stdReq.FinalPrompt, stdReq.Thinking, stdReq.Search, stdReq.ToolNames, stdReq.ToolChoice, traceID)
+		h.handleResponsesStreamWithRetry(w, r, a, resp, payload, pow, owner, responseID, stdReq.ResponseModel, stdReq.FinalPrompt, stdReq.Thinking, stdReq.Search, stdReq.ToolNames, stdReq.ToolsRaw, stdReq.ToolChoice, traceID)
 		return
 	}
-	h.handleResponsesNonStreamWithRetry(w, r.Context(), a, resp, payload, pow, owner, responseID, stdReq.ResponseModel, stdReq.FinalPrompt, stdReq.Thinking, stdReq.Search, stdReq.ToolNames, stdReq.ToolChoice, traceID)
+	h.handleResponsesNonStreamWithRetry(w, r.Context(), a, resp, payload, pow, owner, responseID, stdReq.ResponseModel, stdReq.FinalPrompt, stdReq.Thinking, stdReq.Search, stdReq.ToolNames, stdReq.ToolsRaw, stdReq.ToolChoice, traceID)
 }

-func (h *Handler) handleResponsesNonStream(w http.ResponseWriter, resp *http.Response, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolChoice promptcompat.ToolChoicePolicy, traceID string) {
+func (h *Handler) handleResponsesNonStream(w http.ResponseWriter, resp *http.Response, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, toolChoice promptcompat.ToolChoicePolicy, traceID string) {
 	defer func() { _ = resp.Body.Close() }()
 	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(resp.Body)
@@ -148,12 +148,12 @@ func (h *Handler) handleResponsesNonStream(w http.ResponseWriter, resp *http.Res
 		return
 	}

-	responseObj := openaifmt.BuildResponseObjectWithToolCalls(responseID, model, finalPrompt, sanitizedThinking, sanitizedText, textParsed.Calls)
+	responseObj := openaifmt.BuildResponseObjectWithToolCalls(responseID, model, finalPrompt, sanitizedThinking, sanitizedText, textParsed.Calls, toolsRaw)
 	h.getResponseStore().put(owner, responseID, responseObj)
 	writeJSON(w, http.StatusOK, responseObj)
 }

-func (h *Handler) handleResponsesStream(w http.ResponseWriter, r *http.Request, resp *http.Response, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolChoice promptcompat.ToolChoicePolicy, traceID string) {
+func (h *Handler) handleResponsesStream(w http.ResponseWriter, r *http.Request, resp *http.Response, owner, responseID, model, finalPrompt string, thinkingEnabled, searchEnabled bool, toolNames []string, toolsRaw any, toolChoice promptcompat.ToolChoicePolicy, traceID string) {
 	defer func() { _ = resp.Body.Close() }()
 	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(resp.Body)
@@ -186,6 +186,7 @@ func (h *Handler) handleResponsesStream(w http.ResponseWriter, r *http.Request,
 		searchEnabled,
 		stripReferenceMarkers,
 		toolNames,
+		toolsRaw,
 		bufferToolContent,
 		emitEarlyToolDeltas,
 		toolChoice,
--- a/internal/httpapi/openai/responses/responses_stream_runtime_core.go
+++ b/internal/httpapi/openai/responses/responses_stream_runtime_core.go
@@ -22,6 +22,7 @@ type responsesStreamRuntime struct {
 	model       string
 	finalPrompt string
 	toolNames   []string
+	toolsRaw    any
 	traceID     string
 	toolChoice  promptcompat.ToolChoicePolicy

@@ -72,6 +73,7 @@ func newResponsesStreamRuntime(
 	searchEnabled bool,
 	stripReferenceMarkers bool,
 	toolNames []string,
+	toolsRaw any,
 	bufferToolContent bool,
 	emitEarlyToolDeltas bool,
 	toolChoice promptcompat.ToolChoicePolicy,
@@ -89,6 +91,7 @@ func newResponsesStreamRuntime(
 		searchEnabled:         searchEnabled,
 		stripReferenceMarkers: stripReferenceMarkers,
 		toolNames:             toolNames,
+		toolsRaw:              toolsRaw,
 		bufferToolContent:     bufferToolContent,
 		emitEarlyToolDeltas:   emitEarlyToolDeltas,
 		streamToolCallIDs:     map[int]string{},
--- a/internal/httpapi/openai/responses/responses_stream_runtime_toolcalls.go
+++ b/internal/httpapi/openai/responses/responses_stream_runtime_toolcalls.go
@@ -220,7 +220,8 @@ func (s *responsesStreamRuntime) emitFunctionCallDeltaEvents(deltas []toolstream
 }

 func (s *responsesStreamRuntime) emitFunctionCallDoneEvents(calls []toolcall.ParsedToolCall) {
-	for idx, tc := range calls {
+	normalizedCalls := toolcall.NormalizeParsedToolCallsForSchemas(calls, s.toolsRaw)
+	for idx, tc := range normalizedCalls {
 		if strings.TrimSpace(tc.Name) == "" {
 			continue
 		}
--- a/internal/httpapi/openai/responses/responses_stream_runtime_toolcalls_finalize.go
+++ b/internal/httpapi/openai/responses/responses_stream_runtime_toolcalls_finalize.go
@@ -109,7 +109,8 @@ func (s *responsesStreamRuntime) buildCompletedResponseObject(finalThinking, fin
 		}
 	}

-	for idx, tc := range calls {
+	normalizedCalls := toolcall.NormalizeParsedToolCallsForSchemas(calls, s.toolsRaw)
+	for idx, tc := range normalizedCalls {
 		if strings.TrimSpace(tc.Name) == "" {
 			continue
 		}
--- a/internal/httpapi/openai/responses/responses_stream_test.go
+++ b/internal/httpapi/openai/responses/responses_stream_test.go
@@ -27,7 +27,7 @@ func TestHandleResponsesStreamDoesNotEmitReasoningTextCompatEvents(t *testing.T)
 		Body:       io.NopCloser(strings.NewReader(streamBody)),
 	}

-	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, nil, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, nil, nil, promptcompat.DefaultToolChoicePolicy(), "")

 	body := rec.Body.String()
 	if !strings.Contains(body, "event: response.reasoning.delta") {
@@ -57,7 +57,7 @@ func TestHandleResponsesStreamEmitsOutputTextDoneBeforeContentPartDone(t *testin
 		Body:       io.NopCloser(strings.NewReader(streamBody)),
 	}

-	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, nil, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, nil, nil, promptcompat.DefaultToolChoicePolicy(), "")
 	body := rec.Body.String()
 	if !strings.Contains(body, "event: response.output_text.done") {
 		t.Fatalf("expected response.output_text.done payload, body=%s", body)
@@ -91,7 +91,7 @@ func TestHandleResponsesStreamOutputTextDeltaCarriesItemIndexes(t *testing.T) {
 		Body:       io.NopCloser(strings.NewReader(streamBody)),
 	}

-	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, nil, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, nil, nil, promptcompat.DefaultToolChoicePolicy(), "")
 	body := rec.Body.String()

 	deltaPayload, ok := extractSSEEventPayload(body, "response.output_text.delta")
@@ -130,7 +130,7 @@ func TestHandleResponsesStreamEmitsDistinctToolCallIDsAcrossSeparateToolBlocks(t
 		Body:       io.NopCloser(strings.NewReader(streamBody)),
 	}

-	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, []string{"read_file", "search"}, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, []string{"read_file", "search"}, nil, promptcompat.DefaultToolChoicePolicy(), "")

 	body := rec.Body.String()
 	doneEvents := extractSSEEventPayloads(body, "response.function_call_arguments.done")
@@ -183,7 +183,7 @@ func TestHandleResponsesStreamRequiredToolChoiceFailure(t *testing.T) {
 		Mode:    promptcompat.ToolChoiceRequired,
 		Allowed: map[string]struct{}{"read_file": {}},
 	}
-	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, []string{"read_file"}, policy, "")
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, []string{"read_file"}, nil, policy, "")

 	body := rec.Body.String()
 	if !strings.Contains(body, "event: response.failed") {
@@ -213,7 +213,7 @@ func TestHandleResponsesStreamFailsWhenUpstreamHasOnlyThinking(t *testing.T) {
 		Body:       io.NopCloser(strings.NewReader(streamBody)),
 	}

-	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, nil, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, nil, nil, promptcompat.DefaultToolChoicePolicy(), "")

 	body := rec.Body.String()
 	if !strings.Contains(body, "event: response.failed") {
@@ -251,7 +251,7 @@ func TestHandleResponsesStreamPromotesThinkingToolCallsOnFinalizeWithoutMidstrea
 		Body:       io.NopCloser(strings.NewReader(streamBody)),
 	}

-	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, []string{"read_file"}, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, []string{"read_file"}, nil, promptcompat.DefaultToolChoicePolicy(), "")

 	body := rec.Body.String()
 	if !strings.Contains(body, "event: response.reasoning.delta") {
@@ -288,7 +288,7 @@ func TestHandleResponsesStreamPromotesHiddenThinkingDSMLToolCallsOnFinalize(t *t
 		Mode:    promptcompat.ToolChoiceRequired,
 		Allowed: map[string]struct{}{"read_file": {}},
 	}
-	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_hidden", "deepseek-v4-pro", "prompt", false, false, []string{"read_file"}, policy, "")
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_hidden", "deepseek-v4-pro", "prompt", false, false, []string{"read_file"}, nil, policy, "")

 	body := rec.Body.String()
 	if strings.Contains(body, "event: response.reasoning.delta") {
@@ -317,7 +317,7 @@ func TestHandleResponsesNonStreamRequiredToolChoiceViolation(t *testing.T) {
 		Allowed: map[string]struct{}{"read_file": {}},
 	}

-	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, []string{"read_file"}, policy, "")
+	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, []string{"read_file"}, nil, policy, "")
 	if rec.Code != http.StatusUnprocessableEntity {
 		t.Fatalf("expected 422 for required tool_choice violation, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -344,7 +344,7 @@ func TestHandleResponsesNonStreamRequiredToolChoiceIgnoresThinkingToolPayloadWhe
 		Allowed: map[string]struct{}{"read_file": {}},
 	}

-	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", true, false, []string{"read_file"}, policy, "")
+	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", true, false, []string{"read_file"}, nil, policy, "")
 	if rec.Code != http.StatusUnprocessableEntity {
 		t.Fatalf("expected 422 for required tool_choice violation, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -366,7 +366,7 @@ func TestHandleResponsesNonStreamReturns429WhenUpstreamOutputEmpty(t *testing.T)
 		)),
 	}

-	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, nil, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, nil, nil, promptcompat.DefaultToolChoicePolicy(), "")
 	if rec.Code != http.StatusTooManyRequests {
 		t.Fatalf("expected 429 for empty upstream output, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -388,7 +388,7 @@ func TestHandleResponsesNonStreamReturnsContentFilterErrorWhenUpstreamFilteredWi
 		)),
 	}

-	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, nil, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-flash", "prompt", false, false, nil, nil, promptcompat.DefaultToolChoicePolicy(), "")
 	if rec.Code != http.StatusBadRequest {
 		t.Fatalf("expected 400 for filtered empty upstream output, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -410,7 +410,7 @@ func TestHandleResponsesNonStreamReturns429WhenUpstreamHasOnlyThinking(t *testin
 		)),
 	}

-	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, nil, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, nil, nil, promptcompat.DefaultToolChoicePolicy(), "")
 	if rec.Code != http.StatusTooManyRequests {
 		t.Fatalf("expected 429 for thinking-only upstream output, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -432,7 +432,7 @@ func TestHandleResponsesNonStreamPromotesThinkingToolCallsWhenTextEmpty(t *testi
 		)),
 	}

-	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, []string{"read_file"}, promptcompat.DefaultToolChoicePolicy(), "")
+	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_test", "deepseek-v4-pro", "prompt", true, false, []string{"read_file"}, nil, promptcompat.DefaultToolChoicePolicy(), "")
 	if rec.Code != http.StatusOK {
 		t.Fatalf("expected 200 for thinking tool calls, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -462,7 +462,7 @@ func TestHandleResponsesNonStreamPromotesHiddenThinkingDSMLToolCallsWhenTextEmpt
 		Mode:    promptcompat.ToolChoiceRequired,
 		Allowed: map[string]struct{}{"read_file": {}},
 	}
-	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_hidden", "deepseek-v4-pro", "prompt", false, false, []string{"read_file"}, policy, "")
+	h.handleResponsesNonStream(rec, resp, "owner-a", "resp_hidden", "deepseek-v4-pro", "prompt", false, false, []string{"read_file"}, nil, policy, "")
 	if rec.Code != http.StatusOK {
 		t.Fatalf("expected 200 for hidden thinking tool calls, got %d body=%s", rec.Code, rec.Body.String())
 	}
@@ -480,6 +480,53 @@ func TestHandleResponsesNonStreamPromotesHiddenThinkingDSMLToolCallsWhenTextEmpt
 	}
 }

+func TestHandleResponsesStreamCoercesSchemaDeclaredStringArguments(t *testing.T) {
+	h := &Handler{}
+	req := httptest.NewRequest(http.MethodPost, "/v1/responses", nil)
+	rec := httptest.NewRecorder()
+	toolsRaw := []any{
+		map[string]any{
+			"type": "function",
+			"function": map[string]any{
+				"name": "Write",
+				"parameters": map[string]any{
+					"type": "object",
+					"properties": map[string]any{
+						"content": map[string]any{"type": "string"},
+						"taskId":  map[string]any{"type": "string"},
+					},
+				},
+			},
+		},
+	}
+	sseLine := func(v string) string {
+		b, _ := json.Marshal(map[string]any{"p": "response/content", "v": v})
+		return "data: " + string(b) + "\n"
+	}
+	streamBody := sseLine(`<tool_calls><invoke name="Write">{"input":{"content":{"message":"hi"},"taskId":1}}</invoke></tool_calls>`) + "data: [DONE]\n"
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(strings.NewReader(streamBody)),
+	}
+
+	h.handleResponsesStream(rec, req, resp, "owner-a", "resp_string_protect", "deepseek-v4-flash", "prompt", false, false, []string{"Write"}, toolsRaw, promptcompat.DefaultToolChoicePolicy(), "")
+
+	payload, ok := extractSSEEventPayload(rec.Body.String(), "response.function_call_arguments.done")
+	if !ok {
+		t.Fatalf("expected response.function_call_arguments.done payload, body=%s", rec.Body.String())
+	}
+	args := map[string]any{}
+	if err := json.Unmarshal([]byte(asString(payload["arguments"])), &args); err != nil {
+		t.Fatalf("decode streamed response arguments failed: %v", err)
+	}
+	if args["content"] != `{"message":"hi"}` {
+		t.Fatalf("expected response content stringified by schema, got %#v", args["content"])
+	}
+	if args["taskId"] != "1" {
+		t.Fatalf("expected response taskId stringified by schema, got %#v", args["taskId"])
+	}
+}
+
 func extractSSEEventPayload(body, targetEvent string) (map[string]any, bool) {
 	scanner := bufio.NewScanner(strings.NewReader(body))
 	matched := false
--- a/internal/httpapi/openai/shared/handler_toolcall_format.go
+++ b/internal/httpapi/openai/shared/handler_toolcall_format.go
@@ -70,12 +70,13 @@ func FilterIncrementalToolCallDeltasByAllowed(deltas []toolstream.ToolCallDelta,
 	return out
 }

-func FormatFinalStreamToolCallsWithStableIDs(calls []toolcall.ParsedToolCall, ids map[int]string) []map[string]any {
+func FormatFinalStreamToolCallsWithStableIDs(calls []toolcall.ParsedToolCall, ids map[int]string, toolsRaw any) []map[string]any {
 	if len(calls) == 0 {
 		return nil
 	}
+	normalizedCalls := toolcall.NormalizeParsedToolCallsForSchemas(calls, toolsRaw)
 	out := make([]map[string]any, 0, len(calls))
-	for i, c := range calls {
+	for i, c := range normalizedCalls {
 		callID := ""
 		if ids != nil {
 			callID = strings.TrimSpace(ids[i])
--- a/internal/toolcall/toolcall_edge_test.go
+++ b/internal/toolcall/toolcall_edge_test.go
@@ -9,7 +9,7 @@ import (
 func TestFormatOpenAIStreamToolCalls(t *testing.T) {
 	formatted := FormatOpenAIStreamToolCalls([]ParsedToolCall{
 		{Name: "search", Input: map[string]any{"q": "test"}},
-	})
+	}, nil)
 	if len(formatted) != 1 {
 		t.Fatalf("expected 1, got %d", len(formatted))
 	}
--- a/internal/toolcall/toolcalls_format.go
+++ b/internal/toolcall/toolcalls_format.go
@@ -7,9 +7,10 @@ import (
 	"github.com/google/uuid"
 )

-func FormatOpenAIToolCalls(calls []ParsedToolCall) []map[string]any {
+func FormatOpenAIToolCalls(calls []ParsedToolCall, toolsRaw any) []map[string]any {
+	normalized := NormalizeParsedToolCallsForSchemas(calls, toolsRaw)
 	out := make([]map[string]any, 0, len(calls))
-	for _, c := range calls {
+	for _, c := range normalized {
 		args, _ := json.Marshal(c.Input)
 		out = append(out, map[string]any{
 			"id":   "call_" + strings.ReplaceAll(uuid.NewString(), "-", ""),
@@ -23,9 +24,10 @@ func FormatOpenAIToolCalls(calls []ParsedToolCall) []map[string]any {
 	return out
 }

-func FormatOpenAIStreamToolCalls(calls []ParsedToolCall) []map[string]any {
+func FormatOpenAIStreamToolCalls(calls []ParsedToolCall, toolsRaw any) []map[string]any {
+	normalized := NormalizeParsedToolCallsForSchemas(calls, toolsRaw)
 	out := make([]map[string]any, 0, len(calls))
-	for i, c := range calls {
+	for i, c := range normalized {
 		args, _ := json.Marshal(c.Input)
 		out = append(out, map[string]any{
 			"index": i,
--- a/internal/toolcall/toolcalls_schema_normalize.go
+++ b/internal/toolcall/toolcalls_schema_normalize.go
@@ -0,0 +1,266 @@
+package toolcall
+
+import (
+	"encoding/json"
+	"strings"
+)
+
+func NormalizeParsedToolCallsForSchemas(calls []ParsedToolCall, toolsRaw any) []ParsedToolCall {
+	if len(calls) == 0 {
+		return calls
+	}
+	schemas := buildToolSchemaIndex(toolsRaw)
+	if len(schemas) == 0 {
+		return calls
+	}
+
+	var changedAny bool
+	out := make([]ParsedToolCall, len(calls))
+	for i, call := range calls {
+		out[i] = call
+		schema, ok := schemas[strings.ToLower(strings.TrimSpace(call.Name))]
+		if !ok || call.Input == nil {
+			continue
+		}
+		normalized, changed := normalizeToolValueWithSchema(call.Input, schema)
+		if !changed {
+			continue
+		}
+		changedAny = true
+		if input, ok := normalized.(map[string]any); ok {
+			out[i].Input = input
+		}
+	}
+	if !changedAny {
+		return calls
+	}
+	return out
+}
+
+func buildToolSchemaIndex(toolsRaw any) map[string]any {
+	tools, ok := toolsRaw.([]any)
+	if !ok || len(tools) == 0 {
+		return nil
+	}
+	out := make(map[string]any, len(tools))
+	for _, item := range tools {
+		tool, ok := item.(map[string]any)
+		if !ok {
+			continue
+		}
+		name, schema := extractToolNameAndSchema(tool)
+		if name == "" || schema == nil {
+			continue
+		}
+		out[strings.ToLower(name)] = schema
+	}
+	if len(out) == 0 {
+		return nil
+	}
+	return out
+}
+
+func extractToolNameAndSchema(tool map[string]any) (string, any) {
+	name := strings.TrimSpace(asStringValue(tool["name"]))
+	schema := tool["parameters"]
+	if schema == nil {
+		schema = tool["input_schema"]
+	}
+	if fn, ok := tool["function"].(map[string]any); ok {
+		if name == "" {
+			name = strings.TrimSpace(asStringValue(fn["name"]))
+		}
+		if schema == nil {
+			schema = fn["parameters"]
+		}
+		if schema == nil {
+			schema = fn["input_schema"]
+		}
+	}
+	return name, schema
+}
+
+func normalizeToolValueWithSchema(value any, schema any) (any, bool) {
+	if value == nil || schema == nil {
+		return value, false
+	}
+	schemaMap, ok := schema.(map[string]any)
+	if !ok || len(schemaMap) == 0 {
+		return value, false
+	}
+	if shouldCoerceSchemaToString(schemaMap) {
+		return stringifySchemaValue(value)
+	}
+	if looksLikeObjectSchema(schemaMap) {
+		obj, ok := value.(map[string]any)
+		if !ok || len(obj) == 0 {
+			return value, false
+		}
+		properties, _ := schemaMap["properties"].(map[string]any)
+		additional := schemaMap["additionalProperties"]
+		changed := false
+		out := make(map[string]any, len(obj))
+		for key, current := range obj {
+			next := current
+			var fieldChanged bool
+			if propSchema, ok := properties[key]; ok {
+				next, fieldChanged = normalizeToolValueWithSchema(current, propSchema)
+			} else if additional != nil {
+				next, fieldChanged = normalizeToolValueWithSchema(current, additional)
+			}
+			out[key] = next
+			changed = changed || fieldChanged
+		}
+		if !changed {
+			return value, false
+		}
+		return out, true
+	}
+	if looksLikeArraySchema(schemaMap) {
+		arr, ok := value.([]any)
+		if !ok || len(arr) == 0 {
+			return value, false
+		}
+		itemsSchema := schemaMap["items"]
+		if itemsSchema == nil {
+			return value, false
+		}
+		changed := false
+		out := make([]any, len(arr))
+		switch itemSchemas := itemsSchema.(type) {
+		case []any:
+			for i, item := range arr {
+				if i >= len(itemSchemas) {
+					out[i] = item
+					continue
+				}
+				next, itemChanged := normalizeToolValueWithSchema(item, itemSchemas[i])
+				out[i] = next
+				changed = changed || itemChanged
+			}
+		default:
+			for i, item := range arr {
+				next, itemChanged := normalizeToolValueWithSchema(item, itemsSchema)
+				out[i] = next
+				changed = changed || itemChanged
+			}
+		}
+		if !changed {
+			return value, false
+		}
+		return out, true
+	}
+	return value, false
+}
+
+func shouldCoerceSchemaToString(schema map[string]any) bool {
+	if schema == nil {
+		return false
+	}
+	if isStringConst(schema["const"]) {
+		return true
+	}
+	if isStringEnum(schema["enum"]) {
+		return true
+	}
+	switch v := schema["type"].(type) {
+	case string:
+		return strings.EqualFold(strings.TrimSpace(v), "string")
+	case []any:
+		return isOnlyStringLikeTypes(v)
+	case []string:
+		items := make([]any, 0, len(v))
+		for _, item := range v {
+			items = append(items, item)
+		}
+		return isOnlyStringLikeTypes(items)
+	default:
+		return false
+	}
+}
+
+func looksLikeObjectSchema(schema map[string]any) bool {
+	if schema == nil {
+		return false
+	}
+	if typ, ok := schema["type"].(string); ok && strings.EqualFold(strings.TrimSpace(typ), "object") {
+		return true
+	}
+	if _, ok := schema["properties"].(map[string]any); ok {
+		return true
+	}
+	_, hasAdditional := schema["additionalProperties"]
+	return hasAdditional
+}
+
+func looksLikeArraySchema(schema map[string]any) bool {
+	if schema == nil {
+		return false
+	}
+	if typ, ok := schema["type"].(string); ok && strings.EqualFold(strings.TrimSpace(typ), "array") {
+		return true
+	}
+	_, hasItems := schema["items"]
+	return hasItems
+}
+
+func isOnlyStringLikeTypes(values []any) bool {
+	if len(values) == 0 {
+		return false
+	}
+	hasString := false
+	for _, item := range values {
+		typ, ok := item.(string)
+		if !ok {
+			return false
+		}
+		switch strings.ToLower(strings.TrimSpace(typ)) {
+		case "string":
+			hasString = true
+		case "null":
+			continue
+		default:
+			return false
+		}
+	}
+	return hasString
+}
+
+func isStringConst(v any) bool {
+	_, ok := v.(string)
+	return ok
+}
+
+func isStringEnum(v any) bool {
+	values, ok := v.([]any)
+	if !ok || len(values) == 0 {
+		return false
+	}
+	for _, item := range values {
+		if _, ok := item.(string); !ok {
+			return false
+		}
+	}
+	return true
+}
+
+func stringifySchemaValue(value any) (any, bool) {
+	if value == nil {
+		return value, false
+	}
+	if s, ok := value.(string); ok {
+		return s, false
+	}
+	b, err := json.Marshal(value)
+	if err != nil {
+		return value, false
+	}
+	return string(b), true
+}
+
+func asStringValue(v any) string {
+	if s, ok := v.(string); ok {
+		return s
+	}
+	return ""
+}
--- a/internal/toolcall/toolcalls_schema_normalize_test.go
+++ b/internal/toolcall/toolcalls_schema_normalize_test.go
@@ -0,0 +1,112 @@
+package toolcall
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestNormalizeParsedToolCallsForSchemasCoercesDeclaredStringFieldsRecursively(t *testing.T) {
+	toolsRaw := []any{
+		map[string]any{
+			"type": "function",
+			"function": map[string]any{
+				"name": "TaskUpdate",
+				"parameters": map[string]any{
+					"type": "object",
+					"properties": map[string]any{
+						"taskId": map[string]any{"type": "string"},
+						"payload": map[string]any{
+							"type": "object",
+							"properties": map[string]any{
+								"content": map[string]any{"type": "string"},
+								"tags": map[string]any{
+									"type":  "array",
+									"items": map[string]any{"type": "string"},
+								},
+								"count": map[string]any{"type": "number"},
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	calls := []ParsedToolCall{{
+		Name: "TaskUpdate",
+		Input: map[string]any{
+			"taskId": 1,
+			"payload": map[string]any{
+				"content": map[string]any{"text": "hello"},
+				"tags":    []any{1, true, map[string]any{"k": "v"}},
+				"count":   2,
+			},
+		},
+	}}
+
+	got := NormalizeParsedToolCallsForSchemas(calls, toolsRaw)
+	if len(got) != 1 {
+		t.Fatalf("expected one normalized call, got %#v", got)
+	}
+	if got[0].Input["taskId"] != "1" {
+		t.Fatalf("expected taskId coerced to string, got %#v", got[0].Input["taskId"])
+	}
+	payload, ok := got[0].Input["payload"].(map[string]any)
+	if !ok {
+		t.Fatalf("expected payload object, got %#v", got[0].Input["payload"])
+	}
+	if payload["content"] != `{"text":"hello"}` {
+		t.Fatalf("expected nested content coerced to json string, got %#v", payload["content"])
+	}
+	if payload["count"] != 2 {
+		t.Fatalf("expected non-string count unchanged, got %#v", payload["count"])
+	}
+	tags, ok := payload["tags"].([]any)
+	if !ok {
+		t.Fatalf("expected tags slice, got %#v", payload["tags"])
+	}
+	wantTags := []any{"1", "true", `{"k":"v"}`}
+	if !reflect.DeepEqual(tags, wantTags) {
+		t.Fatalf("unexpected normalized tags: got %#v want %#v", tags, wantTags)
+	}
+}
+
+func TestNormalizeParsedToolCallsForSchemasSupportsDirectToolSchemaShape(t *testing.T) {
+	toolsRaw := []any{
+		map[string]any{
+			"name": "Write",
+			"input_schema": map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"content": map[string]any{"type": "string"},
+				},
+			},
+		},
+	}
+	calls := []ParsedToolCall{{Name: "Write", Input: map[string]any{"content": []any{"a", 1}}}}
+	got := NormalizeParsedToolCallsForSchemas(calls, toolsRaw)
+	if got[0].Input["content"] != `["a",1]` {
+		t.Fatalf("expected direct-schema content coerced to string, got %#v", got[0].Input["content"])
+	}
+}
+
+func TestNormalizeParsedToolCallsForSchemasLeavesAmbiguousUnionUnchanged(t *testing.T) {
+	toolsRaw := []any{
+		map[string]any{
+			"type": "function",
+			"function": map[string]any{
+				"name": "TaskUpdate",
+				"parameters": map[string]any{
+					"type": "object",
+					"properties": map[string]any{
+						"taskId": map[string]any{"type": []any{"string", "integer"}},
+					},
+				},
+			},
+		},
+	}
+	calls := []ParsedToolCall{{Name: "TaskUpdate", Input: map[string]any{"taskId": 1}}}
+	got := NormalizeParsedToolCallsForSchemas(calls, toolsRaw)
+	if got[0].Input["taskId"] != 1 {
+		t.Fatalf("expected ambiguous union to stay unchanged, got %#v", got[0].Input["taskId"])
+	}
+}
--- a/internal/toolcall/toolcalls_test.go
+++ b/internal/toolcall/toolcalls_test.go
@@ -6,7 +6,7 @@ import (
 )

 func TestFormatOpenAIToolCalls(t *testing.T) {
-	formatted := FormatOpenAIToolCalls([]ParsedToolCall{{Name: "search", Input: map[string]any{"q": "x"}}})
+	formatted := FormatOpenAIToolCalls([]ParsedToolCall{{Name: "search", Input: map[string]any{"q": "x"}}}, nil)
 	if len(formatted) != 1 {
 		t.Fatalf("expected 1, got %d", len(formatted))
 	}
--- a/internal/util/render.go
+++ b/internal/util/render.go
@@ -20,7 +20,7 @@ func BuildOpenAIChatCompletion(completionID, model, finalPrompt, finalThinking,
 	}
 	if len(detected) > 0 {
 		finishReason = "tool_calls"
-		messageObj["tool_calls"] = toolcall.FormatOpenAIToolCalls(detected)
+		messageObj["tool_calls"] = toolcall.FormatOpenAIToolCalls(detected, nil)
 		messageObj["content"] = nil
 	}
 	promptTokens := EstimateTokens(finalPrompt)