Add recent API request recorder with admin tab and /api/recent endpoint

Record the last 10 /v1/ API requests (including errors) in an in-memory
ring buffer. Each entry captures request headers (Authorization masked),
request body, response status, and response body — all up to 1 MB.

- recorder.go: RecentRecorder ring buffer, recordingResponseWriter,
  withRecording middleware, getRecent handler
- server.go: add recorder to Server, wrap /v1/ routes, add /api/recent
- admin.html: new 最近请求 tab with lazy-load and expandable cards
- recorder_test.go: 5 tests (ring buffer, ordering, capture, errors, API)

internal/server/recorder.go

@@ -0,0 +1,174 @@
+package server
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/http"
+	"sync"
+	"time"
+)
+
+const (
+	maxRecentEntries = 10
+	maxBodyCapture    = 1 << 20 // 1 MB per body — full request/response capture for debugging
+)
+
+// RecentEntry captures a single API request and its response for debugging.
+type RecentEntry struct {
+	Timestamp      time.Time         `json:"timestamp"`
+	Method         string            `json:"method"`
+	Path           string            `json:"path"`
+	Status         int               `json:"status"`
+	DurationMs     int64             `json:"duration_ms"`
+	RequestHeaders map[string]string `json:"request_headers"`
+	RequestBody    string            `json:"request_body"`
+	ResponseBody   string            `json:"response_body"`
+}
+
+// RecentRecorder is an in-memory ring buffer that stores the most recent API
+// requests. It is safe for concurrent use.
+type RecentRecorder struct {
+	mu      sync.Mutex
+	entries []RecentEntry
+}
+
+func NewRecentRecorder() *RecentRecorder {
+	return &RecentRecorder{}
+}
+
+// Record appends an entry, evicting the oldest when the buffer is full.
+func (r *RecentRecorder) Record(e RecentEntry) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.entries = append(r.entries, e)
+	if len(r.entries) > maxRecentEntries {
+		r.entries = r.entries[len(r.entries)-maxRecentEntries:]
+	}
+}
+
+// Entries returns a copy of the buffer in newest-first order.
+func (r *RecentRecorder) Entries() []RecentEntry {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	n := len(r.entries)
+	out := make([]RecentEntry, n)
+	for i, e := range r.entries {
+		out[n-1-i] = e // reverse: newest first
+	}
+	return out
+}
+
+// recordingResponseWriter wraps http.ResponseWriter to capture the status code
+// and a truncated copy of the response body. It implements http.Flusher so
+// streaming handlers can flush through the wrapper.
+type recordingResponseWriter struct {
+	http.ResponseWriter
+	statusCode  int
+	body        bytes.Buffer
+	totalBytes  int
+}
+
+func newRecordingResponseWriter(w http.ResponseWriter) *recordingResponseWriter {
+	return &recordingResponseWriter{ResponseWriter: w, statusCode: http.StatusOK}
+}
+
+func (w *recordingResponseWriter) WriteHeader(code int) {
+	w.statusCode = code
+	w.ResponseWriter.WriteHeader(code)
+}
+
+func (w *recordingResponseWriter) Write(b []byte) (int, error) {
+	w.totalBytes += len(b)
+	if w.body.Len() < maxBodyCapture {
+		remaining := maxBodyCapture - w.body.Len()
+		if len(b) <= remaining {
+			w.body.Write(b)
+		} else {
+			w.body.Write(b[:remaining])
+		}
+	}
+	return w.ResponseWriter.Write(b)
+}
+
+func (w *recordingResponseWriter) Flush() {
+	if f, ok := w.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	}
+}
+
+// captureRequestHeaders extracts selected request headers, masking the
+// Authorization value to avoid leaking API keys.
+func captureRequestHeaders(r *http.Request) map[string]string {
+	headers := map[string]string{}
+	for _, key := range []string{"Content-Type", "User-Agent", "Accept", "Authorization"} {
+		if v := r.Header.Get(key); v != "" {
+			if key == "Authorization" {
+				headers[key] = mask(v)
+			} else {
+				headers[key] = v
+			}
+		}
+	}
+	return headers
+}
+
+// truncateBody returns the string form of b, truncated to maxBodyCapture
+// bytes with a marker if the original was longer.
+func truncateBody(b []byte) string {
+	if len(b) > maxBodyCapture {
+		return string(b[:maxBodyCapture]) + fmt.Sprintf("\n...(truncated, total %d bytes)", len(b))
+	}
+	return string(b)
+}
+
+// formatResponseBody returns the captured response body, with a truncation
+// marker if the full response exceeded the capture limit.
+func formatResponseBody(buf *bytes.Buffer, totalBytes int) string {
+	s := buf.String()
+	if totalBytes > maxBodyCapture {
+		s += fmt.Sprintf("\n...(truncated, total %d bytes)", totalBytes)
+	}
+	return s
+}
+
+// withRecording wraps a handler so that each request's headers, body,
+// response status, and response body (truncated) are captured into the
+// server's RecentRecorder. It is applied to the /v1/ API routes so that
+// both successful and error responses are recorded.
+func (s *Server) withRecording(next http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+
+		// Read and restore the request body so the downstream handler
+		// still sees the full content.
+		var reqBody []byte
+		if r.Body != nil {
+			reqBody, _ = io.ReadAll(r.Body)
+			r.Body = io.NopCloser(bytes.NewReader(reqBody))
+		}
+
+		recW := newRecordingResponseWriter(w)
+		next(recW, r)
+
+		s.recorder.Record(RecentEntry{
+			Timestamp:      start,
+			Method:         r.Method,
+			Path:           r.URL.Path,
+			Status:         recW.statusCode,
+			DurationMs:     time.Since(start).Milliseconds(),
+			RequestHeaders: captureRequestHeaders(r),
+			RequestBody:    truncateBody(reqBody),
+			ResponseBody:   formatResponseBody(&recW.body, recW.totalBytes),
+		})
+	}
+}
+
+// getRecent handles GET /api/recent — returns the most recent API requests
+// as JSON, newest first.
+func (s *Server) getRecent(w http.ResponseWriter, r *http.Request) {
+	writeJSON(w, http.StatusOK, map[string]any{
+		"ok":       true,
+		"requests": s.recorder.Entries(),
+	})
+}