feat(security): receipt core shell sinks

Wire the three core bash egress sinks through gstack-egress-lib.sh:

- gstack-telemetry-sync: the batch POST now writes the payload to a
  temp file, receipts those exact bytes fail-closed, and hands curl the
  SAME file. On refusal nothing is sent and the cursor does not
  advance, so the batch stays buffered for the next run. The HTTP
  status is recorded as the receipt outcome.
- gstack-update-check: fail-open receipts (warn + proceed) on the
  Supabase ping POST, both VERSION curls (via a local
  _receipted_version_fetch helper that skips non-network schemes), and
  git ls-remote. The ping receipt is written inside the backgrounded
  subshell, so it can never block the script's exit.
- gstack-brain-sync: fail-closed git-class receipts. The push receipt
  is written BEFORE the commit consumes the queue, so a refused receipt
  leaves the queue intact and the next run retries the whole drain
  (pinned by a new queue-intact-on-refusal test, including the
  problem/cause/fix refusal message shape). The retry-path fetch and
  retry push carry their own fail-closed receipts.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit 3c60f699acceaf1c92a218874711e05fc17dca5d)

bin/gstack-telemetry-sync

@@ -13,6 +13,9 @@ set -uo pipefail
 
 GSTACK_DIR="${GSTACK_DIR:-$(cd "$(dirname "$0")/.." && pwd)}"
 STATE_DIR="${GSTACK_STATE_DIR:-$HOME/.gstack}"
+
+# Egress receipt helpers (_receipted_curl): receipt-before-send, fail-closed.
+. "$GSTACK_DIR/bin/gstack-egress-lib.sh"
 ANALYTICS_DIR="$STATE_DIR/analytics"
 JSONL_FILE="$ANALYTICS_DIR/skill-usage.jsonl"
 CURSOR_FILE="$ANALYTICS_DIR/.last-sync-line"
@@ -114,12 +117,31 @@ RESP_FILE="$(mktemp "${TMPDIR:-/tmp}/gstack-sync-XXXXXX")" || {
   exit 0
 }
 trap 'rm -f "$RESP_FILE"' EXIT
-HTTP_CODE="$(curl -s -w '%{http_code}' --max-time 10 \
+
+# Egress receipt BEFORE the send (fail-closed): the batch is written to a
+# temp file, the receipt hashes those exact bytes, and curl sends the SAME
+# file. On refusal nothing is sent and the cursor does not advance, so the
+# batch stays buffered and the next run retries. The helper consumes the
+# payload file.
+PAYLOAD_FILE="$(mktemp "${TMPDIR:-/tmp}/gstack-sync-payload-XXXXXX")" || {
+  echo "gstack-telemetry-sync: mktemp failed — skipping this run" >&2
+  exit 0
+}
+printf '%s' "$BATCH" > "$PAYLOAD_FILE"
+DEST_HOST="${SUPABASE_URL#*://}"
+DEST_HOST="${DEST_HOST%%/*}"
+HTTP_CODE="$(GSTACK_HOME="$STATE_DIR" _receipted_curl closed telemetry-sync "$DEST_HOST" telemetry-events "telemetry=$TIER" "$PAYLOAD_FILE" \
+  curl -s -w '%{http_code}' --max-time 10 \
   -X POST "${SUPABASE_URL}/functions/v1/telemetry-ingest" \
   -H "Content-Type: application/json" \
   -H "apikey: ${ANON_KEY}" \
-  -o "$RESP_FILE" \
-  -d "$BATCH" 2>/dev/null || echo "000")"
+  -o "$RESP_FILE" || echo "000")"
+
+# Best-effort response-status record for the receipt above (overrides the
+# helper's generic exit-code outcome with the HTTP status).
+if [ -n "${_GSTACK_EGRESS_LAST_RECEIPT:-}" ]; then
+  GSTACK_HOME="$STATE_DIR" "$GSTACK_DIR/bin/gstack-egress-receipt" outcome "$_GSTACK_EGRESS_LAST_RECEIPT" "$HTTP_CODE" 2>/dev/null || true
+fi
 
 # ─── Update cursor on success (2xx) ─────────────────────────
 case "$HTTP_CODE" in