fix(vision): file-ref mode + media pipeline fixes for image visibility (#511)

* fix(vision): file-ref mode + media pipeline fixes for image visibility

Replace inline base64 image loading with file path references when
read_image provider is configured. LLM calls read_image(path=...)
instead of receiving 25K-250K tokens of base64 per image.

Changes:
- Agent loop: skip base64 context storage in file-ref mode, only
  load historical images for inline fallback
- New enrichImagePaths() enriches ALL user messages with file paths
  (not just current turn) so historical images are accessible
- System prompt: imperative tool summaries ("REQUIRED when you see
  <media:image> tags") + dedicated "Media Files" section
- Slack: store mediaPaths in pending history + CollectMedia on mention
- Feishu: add CollectMedia for group context history media
- RC-1 fix: save enriched content (with media IDs/paths) to DB
  instead of raw req.Message

Closes #509

* fix(vision): resolve Claude review — Feishu early media + skip loadImages in file-ref mode

- Feishu: download media BEFORE mention gate (step 4) and store file
  paths in pending history via Media field. Reuse early-resolved
  MediaInfo at step 10 to avoid double-download. CollectMedia now
  returns actual paths instead of empty.
- Agent loop: guard loadImages() behind !deferToReadImageTool so
  file-ref mode avoids unnecessary disk I/O + base64 encoding.

internal/channels/feishu/bot.go

@@ -60,14 +60,32 @@ func (c *Channel) handleMessageEvent(ctx context.Context, event *MessageEvent) {
 	// 3. Resolve sender name (cached)
 	senderName := c.resolveSenderName(ctx, mc.SenderID)
 
-	// 4. Group policy
+	// 4. Resolve media BEFORE mention gate so non-mentioned messages
+	// also have their files downloaded and stored in pending history.
+	var earlyMedia []media.MediaInfo
+	switch mc.ContentType {
+	case "image", "file", "audio", "video", "sticker":
+		earlyMedia = c.resolveMediaFromMessage(ctx, mc.MessageID, mc.ContentType, msg.Content)
+	case "post":
+		if imageKeys := extractPostImageKeys(msg.Content); len(imageKeys) > 0 {
+			earlyMedia = c.resolvePostImages(ctx, mc.MessageID, imageKeys)
+		}
+	}
+	var earlyMediaPaths []string
+	for _, m := range earlyMedia {
+		if m.FilePath != "" {
+			earlyMediaPaths = append(earlyMediaPaths, m.FilePath)
+		}
+	}
+
+	// 5. Group policy
 	if mc.ChatType == "group" {
 		if !c.checkGroupPolicy(ctx, mc.SenderID, mc.ChatID) {
 			slog.Debug("feishu group message rejected by policy", "sender_id", mc.SenderID, "chat_id", mc.ChatID)
 			return
 		}
 
-		// 5. RequireMention check — record to history if not mentioned
+		// 6. RequireMention check — record to history if not mentioned
 		requireMention := true
 		if c.cfg.RequireMention != nil {
 			requireMention = *c.cfg.RequireMention
@@ -81,6 +99,7 @@ func (c *Channel) handleMessageEvent(ctx context.Context, event *MessageEvent) {
 				Sender:    senderName,
 				SenderID:  mc.SenderID,
 				Body:      mc.Content,
+				Media:     earlyMediaPaths,
 				Timestamp: time.Now(),
 				MessageID: messageID,
 			}, c.historyLimit)
@@ -173,23 +192,26 @@ func (c *Channel) handleMessageEvent(ctx context.Context, event *MessageEvent) {
 		}
 	}
 
-	// 10. Resolve inbound media (image, file, audio, video, sticker)
+	// 10. Build media list from early-resolved media (step 4) + reply media.
+	// Media was already downloaded before the mention gate — reuse results.
 	var mediaList []media.MediaInfo
-	// Reply media first (context), current media second.
+	// Reply media first (context), current-message media second.
 	if len(replyMediaList) > 0 {
 		mediaList = append(mediaList, replyMediaList...)
 	}
-	switch mc.ContentType {
-	case "image", "file", "audio", "video", "sticker":
-		mediaList = append(mediaList, c.resolveMediaFromMessage(ctx, mc.MessageID, mc.ContentType, msg.Content)...)
-	case "post":
-		if imageKeys := extractPostImageKeys(msg.Content); len(imageKeys) > 0 {
-			mediaList = append(mediaList, c.resolvePostImages(ctx, mc.MessageID, imageKeys)...)
+	mediaList = append(mediaList, earlyMedia...)
+
+	// 10b. Collect media from pending history (files downloaded by earlier non-mentioned messages).
+	var mediaFiles []bus.MediaFile
+	if mc.ChatType == "group" && c.historyLimit > 0 {
+		if histMediaPaths := c.groupHistory.CollectMedia(chatID); len(histMediaPaths) > 0 {
+			for _, p := range histMediaPaths {
+				mediaFiles = append(mediaFiles, bus.MediaFile{Path: p}) // cannot use append(slice, other...) — different types
+			}
 		}
 	}
 
 	// 11. Process media: STT transcription, document extraction, build tags
-	var mediaFiles []bus.MediaFile
 	if len(mediaList) > 0 {
 		var extraContent string
 		for i := range mediaList {