!explain via ❓ reaction: thread-reply with a 3-bullet TL;DR

When a user reacts ❓ on one of Pete's posts, fetch the article body,
ask Ollama for a 3-bullet summary, and post it as a threaded reply
rooted at the original story event. Per-process cooldown of 5min per
story keeps repeated reactions from re-summarizing.

- ingestion.FetchArticleBody: visible <p> text capped at 8000 chars
- classifier.OllamaClient.GenerateText: non-JSON variant
- storage.GetStoryByGUID: full row lookup
- matrix.PostThreadedReply: m.thread + m.in_reply_to fallback
- poster.SetReactionCallback: optional hook fired after recording
- New package: internal/explainer

internal/poster/tracker.go

@@ -2,6 +2,7 @@ package poster
 
 import (
 	"log/slog"
+	"sync"
 	"time"
 
 	"pete/internal/storage"
@@ -9,6 +10,24 @@ import (
 	"maunium.net/go/mautrix/id"
 )
 
+// ReactionCallback is an optional hook fired after a reaction is recorded.
+// Used to wire reaction-driven features (e.g. ❓ → summary) without coupling
+// poster to those packages.
+type ReactionCallback func(roomID id.RoomID, targetEventID id.EventID, guid, channel, emoji string)
+
+var (
+	reactionCallbackMu sync.RWMutex
+	reactionCallback   ReactionCallback
+)
+
+// SetReactionCallback installs a hook called after every recorded reaction.
+// Pass nil to clear. Safe to call before or after the matrix client starts.
+func SetReactionCallback(fn ReactionCallback) {
+	reactionCallbackMu.Lock()
+	reactionCallback = fn
+	reactionCallbackMu.Unlock()
+}
+
 // HandleReaction processes a reaction event by mapping it back to the story GUID.
 func HandleReaction(roomID id.RoomID, eventID id.EventID, targetEventID id.EventID, emoji string, userID id.UserID) {
 	guid, channel, found := storage.LookupPostGUID(string(targetEventID))
@@ -24,4 +43,11 @@ func HandleReaction(roomID id.RoomID, eventID id.EventID, targetEventID id.Event
 		"emoji", emoji,
 		"user", userID,
 	)
+
+	reactionCallbackMu.RLock()
+	cb := reactionCallback
+	reactionCallbackMu.RUnlock()
+	if cb != nil {
+		go cb(roomID, targetEventID, guid, channel, emoji)
+	}
 }