diff --git a/internal/adapter/provider/cliproxyapi_codex/adapter.go b/internal/adapter/provider/cliproxyapi_codex/adapter.go
index e05a48c3..f102053c 100644
--- a/internal/adapter/provider/cliproxyapi_codex/adapter.go
+++ b/internal/adapter/provider/cliproxyapi_codex/adapter.go
@@ -14,6 +14,7 @@ import (
 	"time"
 
 	"github.com/awsl-project/maxx/internal/adapter/provider"
+	"github.com/awsl-project/maxx/internal/codexutil"
 	"github.com/awsl-project/maxx/internal/domain"
 	"github.com/awsl-project/maxx/internal/flow"
 	"github.com/awsl-project/maxx/internal/usage"
@@ -21,8 +22,6 @@ import (
 	"github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/executor"
 	"github.com/router-for-me/CLIProxyAPI/v6/sdk/exec"
 	"github.com/router-for-me/CLIProxyAPI/v6/sdk/translator"
-	"github.com/tidwall/gjson"
-	"github.com/tidwall/sjson"
 )
 
 // TokenCache caches access tokens
@@ -254,26 +253,7 @@ func (a *CLIProxyAPICodexAdapter) Execute(c *flow.Ctx, p *domain.Provider) error
 }
 
 func sanitizeCodexPayload(body []byte) []byte {
-	if input := gjson.GetBytes(body, "input"); input.IsArray() {
-		for i, item := range input.Array() {
-			itemType := item.Get("type").String()
-			if itemType != "message" {
-				if item.Get("role").Exists() {
-					body, _ = sjson.DeleteBytes(body, fmt.Sprintf("input.%d.role", i))
-				}
-			}
-			if itemType == "function_call" {
-				if id := item.Get("id").String(); id != "" && !strings.HasPrefix(id, "fc_") {
-					body, _ = sjson.SetBytes(body, fmt.Sprintf("input.%d.id", i), "fc_"+id)
-				}
-			}
-			if itemType == "function_call_output" {
-				if !item.Get("output").Exists() {
-					body, _ = sjson.SetBytes(body, fmt.Sprintf("input.%d.output", i), "")
-				}
-			}
-		}
-	}
+	body = codexutil.NormalizeCodexInput(body)
 	return body
 }
 
diff --git a/internal/adapter/provider/codex/adapter.go b/internal/adapter/provider/codex/adapter.go
index 2295ce21..824b14b5 100644
--- a/internal/adapter/provider/codex/adapter.go
+++ b/internal/adapter/provider/codex/adapter.go
@@ -16,6 +16,7 @@ import (
 
 	"github.com/awsl-project/maxx/internal/adapter/provider"
 	cliproxyapi "github.com/awsl-project/maxx/internal/adapter/provider/cliproxyapi_codex"
+	"github.com/awsl-project/maxx/internal/codexutil"
 	"github.com/awsl-project/maxx/internal/domain"
 	"github.com/awsl-project/maxx/internal/flow"
 	"github.com/awsl-project/maxx/internal/usage"
@@ -572,26 +573,7 @@ func applyCodexRequestTuning(c *flow.Ctx, body []byte) (string, []byte) {
 	if !gjson.GetBytes(body, "instructions").Exists() {
 		body, _ = sjson.SetBytes(body, "instructions", "")
 	}
-	if input := gjson.GetBytes(body, "input"); input.IsArray() {
-		for i, item := range input.Array() {
-			itemType := item.Get("type").String()
-			if itemType != "message" {
-				if item.Get("role").Exists() {
-					body, _ = sjson.DeleteBytes(body, fmt.Sprintf("input.%d.role", i))
-				}
-			}
-			if itemType == "function_call" {
-				if id := item.Get("id").String(); id != "" && !strings.HasPrefix(id, "fc_") {
-					body, _ = sjson.SetBytes(body, fmt.Sprintf("input.%d.id", i), "fc_"+id)
-				}
-			}
-			if itemType == "function_call_output" {
-				if !item.Get("output").Exists() {
-					body, _ = sjson.SetBytes(body, fmt.Sprintf("input.%d.output", i), "")
-				}
-			}
-		}
-	}
+	body = codexutil.NormalizeCodexInput(body)
 
 	return cacheID, body
 }
diff --git a/internal/adapter/provider/codex/adapter_test.go b/internal/adapter/provider/codex/adapter_test.go
index 5a1e6da2..dfafe67b 100644
--- a/internal/adapter/provider/codex/adapter_test.go
+++ b/internal/adapter/provider/codex/adapter_test.go
@@ -2,6 +2,7 @@ package codex
 
 import (
 	"net/http"
+	"strings"
 	"testing"
 
 	"github.com/awsl-project/maxx/internal/domain"
@@ -14,7 +15,7 @@ func TestApplyCodexRequestTuning(t *testing.T) {
 	c.Set(flow.KeyOriginalClientType, domain.ClientTypeClaude)
 	c.Set(flow.KeyOriginalRequestBody, []byte(`{"metadata":{"user_id":"user-123"}}`))
 
-	body := []byte(`{"model":"gpt-5","stream":false,"instructions":"x","previous_response_id":"r1","prompt_cache_retention":123,"safety_identifier":"s1","max_output_tokens":77,"input":[{"type":"message","role":"user","content":"hi"},{"type":"function_call","role":"assistant","name":"t","arguments":"{}"},{"role":"tool","call_id":"c1","output":"ok"}]}`)
+	body := []byte(`{"model":"gpt-5","stream":false,"instructions":"x","previous_response_id":"r1","prompt_cache_retention":123,"safety_identifier":"s1","max_output_tokens":77,"input":[{"type":"message","role":"user","content":"hi"},{"type":"function_call","role":"assistant","name":"t","arguments":"{}","id":"toolu_01"},{"type":"function_call","name":"t2","arguments":"{}"},{"type":"function_call_output","call_id":"c1"},{"role":"tool","call_id":"c1","output":"ok"}]}`)
 	cacheID, tuned := applyCodexRequestTuning(c, body)
 
 	if cacheID == "" {
@@ -44,9 +45,19 @@ func TestApplyCodexRequestTuning(t *testing.T) {
 	if gjson.GetBytes(tuned, "input.0.role").String() != "user" {
 		t.Fatalf("expected role to be preserved for message input")
 	}
-	if gjson.GetBytes(tuned, "input.1.role").Exists() || gjson.GetBytes(tuned, "input.2.role").Exists() {
+	if gjson.GetBytes(tuned, "input.1.role").Exists() || gjson.GetBytes(tuned, "input.2.role").Exists() || gjson.GetBytes(tuned, "input.3.role").Exists() || gjson.GetBytes(tuned, "input.4.role").Exists() {
 		t.Fatalf("expected role to be removed for non-message inputs")
 	}
+	if gjson.GetBytes(tuned, "input.1.id").String() != "fc_toolu_01" {
+		t.Fatalf("expected function_call id to be prefixed with fc_")
+	}
+	missingID := gjson.GetBytes(tuned, "input.2.id").String()
+	if !strings.HasPrefix(missingID, "fc_") || missingID == "fc_" {
+		t.Fatalf("expected generated function_call id to be set and prefixed with fc_")
+	}
+	if gjson.GetBytes(tuned, "input.3.output").String() != "" {
+		t.Fatalf("expected missing function_call_output output to default to empty string")
+	}
 }
 
 func TestApplyCodexHeadersFiltersSensitiveAndPreservesUA(t *testing.T) {
diff --git a/internal/codexutil/normalize.go b/internal/codexutil/normalize.go
new file mode 100644
index 00000000..8f76c012
--- /dev/null
+++ b/internal/codexutil/normalize.go
@@ -0,0 +1,43 @@
+package codexutil
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/google/uuid"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+)
+
+func NormalizeCodexInput(body []byte) []byte {
+	input := gjson.GetBytes(body, "input")
+	if !input.IsArray() {
+		return body
+	}
+
+	for i, item := range input.Array() {
+		itemType := item.Get("type").String()
+		if itemType != "message" {
+			if item.Get("role").Exists() {
+				body, _ = sjson.DeleteBytes(body, fmt.Sprintf("input.%d.role", i))
+			}
+		}
+		if itemType == "function_call" {
+			id := strings.TrimSpace(item.Get("id").String())
+			switch {
+			case strings.HasPrefix(id, "fc_"):
+			case id == "":
+				body, _ = sjson.SetBytes(body, fmt.Sprintf("input.%d.id", i), "fc_"+uuid.NewString())
+			default:
+				body, _ = sjson.SetBytes(body, fmt.Sprintf("input.%d.id", i), "fc_"+id)
+			}
+		}
+		if itemType == "function_call_output" {
+			if !item.Get("output").Exists() {
+				body, _ = sjson.SetBytes(body, fmt.Sprintf("input.%d.output", i), "")
+			}
+		}
+	}
+
+	return body
+}