feat(plugin): auto-inject retrieves on the conversation, not the typed words alone (#4364)

The prompt hook sent only the operator's message, so a mid-session
follow-up ("yes do that") named nothing a note, lesson or rule could
match. The hook now reads the tail of the last assistant reply from the
transcript and sends it as `ctx`; the notes and rule arms append it to a
short prompt (<= 280 chars), prompt first, capped at 600 chars. No model
tokens: it is embedding input, and the injected menu's budget is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugin/hooks/scribe_autoinject.sh

@@ -49,6 +49,7 @@ event_flat=$(printf '%s' "$event" | scribe_json_flat)
 prompt=$(scribe_json_pick "$event_flat" '.prompt')
 session_id=$(scribe_json_pick "$event_flat" '.session_id')
 event_cwd=$(scribe_json_pick "$event_flat" '.cwd')
+transcript=$(scribe_json_pick "$event_flat" '.transcript_path')
 
 # Nothing to retrieve against.
 [ -n "$prompt" ] || exit 0
@@ -79,6 +80,16 @@ q=$(printf '%s' "$prompt" | head -c 2000)
 q_enc=$(printf '%s' "$q" | scribe_urlenc) || exit 0
 [ -n "$q_enc" ] || exit 0
 
+# What the conversation is about, for a prompt too short to say (#4364). Sent
+# beside `q`, never folded into it: the server decides whether the prompt is
+# thin enough to need it, for the notes and rule arms alike. Capped at
+# 600 chars here as well as there, so the URL stays small whatever the reply.
+ctx_q=""
+ctx=$(scribe_recent_context "$transcript")
+if [ -n "$ctx" ]; then
+  ctx_enc=$(printf '%s' "$ctx" | scribe_urlenc) && [ -n "$ctx_enc" ] && ctx_q="&ctx=${ctx_enc}"
+fi
+
 # Scope to this directory's project — a `.scribe` marker, else the git remote.
 repo_dir=${event_cwd:-${CLAUDE_PROJECT_DIR:-$PWD}}
 scope=$(scribe_scope_query "$repo_dir")
@@ -120,7 +131,7 @@ fi
 
 body=$(curl -fsS --max-time 5 \
   -H "Authorization: Bearer ${token}" \
-  "${url%/}/api/plugin/retrieve?q=${q_enc}${repo_q}${exclude_q}" 2>/dev/null) || exit 0
+  "${url%/}/api/plugin/retrieve?q=${q_enc}${ctx_q}${repo_q}${exclude_q}" 2>/dev/null) || exit 0
 [ -n "$body" ] || exit 0
 
 body_flat=$(printf '%s' "$body" | scribe_json_flat)