feat: componentize GStack 2 runtime and release integrity

bin/gstack-config

@@ -34,7 +34,9 @@ const defaults = Object.freeze({
   routing_declined: false,
   telemetry: "off",
   auto_upgrade: false,
-  update_check: true,
+  // Skill installation and update discovery belong to the Agent Skills CLI.
+  // GStack never performs a passive network update check by default.
+  update_check: false,
   skill_prefix: false,
   checkpoint_mode: "explicit",
   checkpoint_push: false,

bin/gstack-update-check

@@ -23,18 +23,18 @@ VERSION_FILE="$GSTACK_DIR/VERSION"
 REMOTE_URL="${GSTACK_REMOTE_URL:-https://raw.githubusercontent.com/garrytan/gstack/main/VERSION}"
 REMOTE_REPO="${GSTACK_REMOTE_REPO:-https://github.com/garrytan/gstack.git}"
 
-# ─── Force flag (busts cache + snooze for standalone /gstack-upgrade) ──
-if [ "${1:-}" = "--force" ]; then
-  rm -f "$CACHE_FILE"
-  rm -f "$SNOOZE_FILE"
-fi
-
-# ─── Step 0: Check if updates are disabled ────────────────────
-_UC=$("$GSTACK_DIR/bin/gstack-config" get update_check 2>/dev/null || true)
-if [ "$_UC" = "false" ]; then
+# Agent Skills owns normal update discovery and installation (`npx skills
+# update`). Skill preambles still call this compatibility
+# helper, so fail closed before any state mutation or network access unless a
+# user explicitly invoked the legacy forced check.
+if [ "${1:-}" != "--force" ]; then
   exit 0
 fi
 
+# ─── Explicit legacy check: bust cache + snooze ───────────────
+rm -f "$CACHE_FILE"
+rm -f "$SNOOZE_FILE"
+
 # ─── Migration: fix stale Codex descriptions (one-time) ───────
 # Existing installs may have .agents/skills/gstack/SKILL.md with oversized
 # descriptions (>1024 chars) that Codex rejects. We can't regenerate from