fix: harden agent writeback safety

internal/server/server.go

@@ -3,7 +3,9 @@ package server
 import (
 	"encoding/json"
 	"errors"
+	"io"
 	"net/http"
+	"os"
 	"strings"
 
 	"codex-agent-manager/internal/agents"
@@ -14,6 +16,8 @@ import (
 	"codex-agent-manager/internal/workflow"
 )
 
+const agentDraftBodyLimit = 1 << 20
+
 func New(cfg app.Config) http.Handler {
 	mux := http.NewServeMux()
 	agentStore := agents.Store{CodexHome: cfg.CodexHome}
@@ -129,8 +133,7 @@ func parseAgentActionPath(path string) (string, string, bool) {
 
 func handleAgentValidate(w http.ResponseWriter, r *http.Request, store agents.Store, id string) {
 	var body validateRequest
-	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
-		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "请求体不是有效 JSON"})
+	if !decodeAgentJSON(w, r, &body) {
 		return
 	}
 	result, err := store.ValidateDraft(id, body.Content)
@@ -143,8 +146,7 @@ func handleAgentValidate(w http.ResponseWriter, r *http.Request, store agents.St
 
 func handleAgentWrite(w http.ResponseWriter, r *http.Request, store agents.Store, id string) {
 	var body writeRequest
-	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
-		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "请求体不是有效 JSON"})
+	if !decodeAgentJSON(w, r, &body) {
 		return
 	}
 	result, err := store.WriteDraft(id, body.Content, body.ExpectedHash)
@@ -155,14 +157,53 @@ func handleAgentWrite(w http.ResponseWriter, r *http.Request, store agents.Store
 	writeJSON(w, http.StatusOK, result)
 }
 
+func decodeAgentJSON(w http.ResponseWriter, r *http.Request, dest any) bool {
+	r.Body = http.MaxBytesReader(w, r.Body, agentDraftBodyLimit)
+	decoder := json.NewDecoder(r.Body)
+	if err := decoder.Decode(dest); err != nil {
+		writeAgentDecodeError(w, err)
+		return false
+	}
+	var extra any
+	if err := decoder.Decode(&extra); err != io.EOF {
+		if err != nil {
+			writeAgentDecodeError(w, err)
+			return false
+		}
+		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "请求体不是有效 JSON"})
+		return false
+	}
+	return true
+}
+
+func writeAgentDecodeError(w http.ResponseWriter, err error) {
+	var maxBytesErr *http.MaxBytesError
+	if errors.As(err, &maxBytesErr) {
+		writeJSON(w, http.StatusRequestEntityTooLarge, map[string]string{"error": "请求体过大"})
+		return
+	}
+	writeJSON(w, http.StatusBadRequest, map[string]string{"error": "请求体不是有效 JSON"})
+}
+
 func writeAgentError(w http.ResponseWriter, err error) {
 	status := http.StatusBadRequest
+	message := "写回失败"
 	if errors.Is(err, agents.ErrWriteConflict) {
 		status = http.StatusConflict
+		message = "内容已变化，请重新校验"
 	} else if errors.Is(err, codexhome.ErrForbiddenPath) || errors.Is(err, codexhome.ErrOutsideCodexHome) {
 		status = http.StatusForbidden
+		message = "路径不安全"
+	} else if os.IsNotExist(err) {
+		status = http.StatusNotFound
+		message = "目标智能体不存在"
+	} else if strings.Contains(err.Error(), "第 ") ||
+		strings.Contains(err.Error(), "TOML") ||
+		strings.Contains(err.Error(), "字符串字段") ||
+		strings.Contains(err.Error(), "仅支持字符串字段") {
+		message = "TOML 无效：" + err.Error()
 	}
-	writeJSON(w, status, map[string]string{"error": err.Error()})
+	writeJSON(w, status, map[string]string{"error": message})
 }
 
 func writeJSON(w http.ResponseWriter, status int, body any) {

internal/server/server_test.go

@@ -250,6 +250,69 @@ func TestAgentValidateEndpointReturnsBadRequestForInvalidBody(t *testing.T) {
 	}
 }
 
+func TestAgentValidateEndpointRejectsOversizeBody(t *testing.T) {
+	root := t.TempDir()
+	agentsDir := filepath.Join(root, "agents")
+	if err := os.MkdirAll(agentsDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(agentsDir, "backend.toml"), []byte(`name = "旧名称"`+"\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	body := `{"content":"` + strings.Repeat("a", 1024*1024+1) + `"}`
+
+	req := httptest.NewRequest(http.MethodPost, "/api/agents/backend/validate", bytes.NewBufferString(body))
+	rec := httptest.NewRecorder()
+	New(app.Config{CodexHome: root, HTTPAddr: "127.0.0.1:0"}).ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusRequestEntityTooLarge {
+		t.Fatalf("status = %d, want %d, body = %s", rec.Code, http.StatusRequestEntityTooLarge, rec.Body.String())
+	}
+	if !strings.Contains(rec.Body.String(), "请求体过大") {
+		t.Fatalf("expected Chinese oversize error, got %s", rec.Body.String())
+	}
+}
+
+func TestAgentValidateEndpointRejectsTrailingJSON(t *testing.T) {
+	root := t.TempDir()
+	agentsDir := filepath.Join(root, "agents")
+	if err := os.MkdirAll(agentsDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(agentsDir, "backend.toml"), []byte(`name = "旧名称"`+"\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	req := httptest.NewRequest(http.MethodPost, "/api/agents/backend/validate", bytes.NewBufferString(`{"content":"name = \"新名称\"\n"} {}`))
+	rec := httptest.NewRecorder()
+	New(app.Config{CodexHome: root, HTTPAddr: "127.0.0.1:0"}).ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d, body = %s", rec.Code, http.StatusBadRequest, rec.Body.String())
+	}
+	if !strings.Contains(rec.Body.String(), "请求体不是有效 JSON") {
+		t.Fatalf("expected Chinese invalid JSON error, got %s", rec.Body.String())
+	}
+}
+
+func TestAgentWritebackErrorsAreSanitized(t *testing.T) {
+	root := t.TempDir()
+	if err := os.MkdirAll(filepath.Join(root, "agents"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+
+	req := httptest.NewRequest(http.MethodPost, "/api/agents/missing/validate", bytes.NewBufferString(`{"content":"name = \"新名称\"\n"}`))
+	rec := httptest.NewRecorder()
+	New(app.Config{CodexHome: root, HTTPAddr: "127.0.0.1:0"}).ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("status = %d, want %d, body = %s", rec.Code, http.StatusNotFound, rec.Body.String())
+	}
+	if strings.Contains(rec.Body.String(), root) || strings.Contains(rec.Body.String(), "no such file") || !strings.Contains(rec.Body.String(), "目标智能体不存在") {
+		t.Fatalf("error leaked path or raw OS text: %s", rec.Body.String())
+	}
+}
+
 func TestAgentWriteEndpointCreatesBackupAndRejectsConflicts(t *testing.T) {
 	root := t.TempDir()
 	agentsDir := filepath.Join(root, "agents")