fix: feat: stream action-agent Claude output to Matrix thread (#293)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/hooks/on-stop-matrix.sh

@@ -0,0 +1,45 @@
+#!/bin/bash
+# on-stop-matrix.sh — Stop hook: post Claude response to Matrix thread.
+#
+# Called by Claude Code after each assistant turn. Reads the response from
+# the hook JSON and posts it to the Matrix thread for this action session.
+#
+# Requires env vars: MATRIX_THREAD_ID, MATRIX_TOKEN, MATRIX_HOMESERVER, MATRIX_ROOM_ID
+#
+# Usage (in .claude/settings.json):
+#   {"type": "command", "command": "/path/to/on-stop-matrix.sh"}
+
+# Exit early if Matrix thread not configured
+if [ -z "${MATRIX_THREAD_ID:-}" ] || [ -z "${MATRIX_TOKEN:-}" ] \
+   || [ -z "${MATRIX_HOMESERVER:-}" ] || [ -z "${MATRIX_ROOM_ID:-}" ]; then
+  cat > /dev/null
+  exit 0
+fi
+
+input=$(cat)
+
+# Extract response text from hook JSON
+response=$(printf '%s' "$input" | jq -r '.last_assistant_message // empty' 2>/dev/null)
+[ -z "$response" ] && exit 0
+
+# Truncate long output for readability (keep to ~4000 chars)
+MAX_LEN=4000
+if [ "${#response}" -gt "$MAX_LEN" ]; then
+  response="${response:0:$MAX_LEN}
+... [truncated]"
+fi
+
+# Post to Matrix thread
+room_encoded="${MATRIX_ROOM_ID//!/%21}"
+txn="$(date +%s%N)$$"
+
+body=$(jq -nc \
+  --arg m "$response" \
+  --arg t "$MATRIX_THREAD_ID" \
+  '{msgtype:"m.text",body:$m,"m.relates_to":{rel_type:"m.thread",event_id:$t}}')
+
+curl -s -X PUT \
+  -H "Authorization: Bearer ${MATRIX_TOKEN}" \
+  -H "Content-Type: application/json" \
+  "${MATRIX_HOMESERVER}/_matrix/client/v3/rooms/${room_encoded}/send/m.room.message/${txn}" \
+  -d "$body" > /dev/null 2>&1 || true