fix(antigravity): Add overload recovery flow

Add a Unix activation script, Antigravity-specific installer guidance,
and cross-platform recovery documentation so users can reduce the
live skill set when truncation or context overload appears.

Regenerate the canonical bundle/catalog artifacts after merging the
stale goldrush-api removal so main stays release-ready.

Refs #381

scripts/activate-skills.sh

@@ -0,0 +1,153 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd -- "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+DEFAULT_BASE_DIR="${HOME:-$PWD}/.gemini/antigravity"
+BASE_DIR="${AG_BASE_DIR:-$DEFAULT_BASE_DIR}"
+SKILLS_DIR="${AG_SKILLS_DIR:-$BASE_DIR/skills}"
+LIBRARY_DIR="${AG_LIBRARY_DIR:-$BASE_DIR/skills_library}"
+ARCHIVE_PREFIX="${AG_ARCHIVE_PREFIX:-$BASE_DIR/skills_archive}"
+REPO_SKILLS_DIR="${AG_REPO_SKILLS_DIR:-$SCRIPT_DIR/../skills}"
+BUNDLE_HELPER="${AG_BUNDLE_HELPER:-$SCRIPT_DIR/../tools/scripts/get-bundle-skills.py}"
+PYTHON_BIN="${AG_PYTHON_BIN:-}"
+SKILLS_LIST_FILE="$(mktemp "${TMPDIR:-/tmp}/ag-skills.XXXXXX")"
+
+cleanup() {
+  rm -f "$SKILLS_LIST_FILE"
+}
+
+trap cleanup EXIT
+
+find_copy_dirs() {
+  local src_dir="$1"
+  local dest_dir="$2"
+
+  mkdir -p "$dest_dir"
+
+  while IFS= read -r -d '' item; do
+    cp -RP "$item" "$dest_dir/"
+  done < <(find "$src_dir" -mindepth 1 -maxdepth 1 \( -type d -o -type l \) -print0 2>/dev/null)
+}
+
+find_move_dirs() {
+  local src_dir="$1"
+  local dest_dir="$2"
+
+  mkdir -p "$dest_dir"
+
+  while IFS= read -r -d '' item; do
+    mv "$item" "$dest_dir/"
+  done < <(find "$src_dir" -mindepth 1 -maxdepth 1 ! -name '.' ! -name '..' -print0 2>/dev/null)
+}
+
+resolve_python() {
+  if [[ -n "$PYTHON_BIN" ]]; then
+    printf '%s\n' "$PYTHON_BIN"
+    return 0
+  fi
+
+  if command -v python3 >/dev/null 2>&1; then
+    command -v python3
+    return 0
+  fi
+
+  if command -v python >/dev/null 2>&1; then
+    command -v python
+    return 0
+  fi
+
+  return 1
+}
+
+is_safe_skill_id() {
+  [[ "$1" =~ ^[A-Za-z0-9._-]+$ ]]
+}
+
+echo "Activating Antigravity skills..."
+
+DO_CLEAR=0
+EXTRA_ARGS=()
+
+for arg in "$@"; do
+  if [[ "$arg" == "--clear" ]]; then
+    DO_CLEAR=1
+  else
+    EXTRA_ARGS+=("$arg")
+  fi
+done
+
+if [[ -d "$REPO_SKILLS_DIR" ]]; then
+  echo "Syncing library with repository source..."
+  find_copy_dirs "$REPO_SKILLS_DIR" "$LIBRARY_DIR"
+fi
+
+if [[ ! -d "$LIBRARY_DIR" ]]; then
+  echo "Initializing skills library from local state..."
+  mkdir -p "$LIBRARY_DIR"
+
+  if [[ -d "$SKILLS_DIR" ]]; then
+    echo "  + Moving current skills to library..."
+    find_move_dirs "$SKILLS_DIR" "$LIBRARY_DIR"
+  fi
+
+  while IFS= read -r archive_dir; do
+    [[ -n "$archive_dir" ]] || continue
+    echo "  + Merging skills from $(basename "$archive_dir")..."
+    find_copy_dirs "$archive_dir" "$LIBRARY_DIR"
+  done < <(find "$BASE_DIR" -mindepth 1 -maxdepth 1 -type d -name 'skills_archive*' | sort)
+fi
+
+if [[ "$DO_CLEAR" == "1" ]]; then
+  echo "[RESET] Archiving and clearing existing skills..."
+  if [[ -d "$SKILLS_DIR" ]]; then
+    archive_dir="${ARCHIVE_PREFIX}_$(date +%Y%m%d_%H%M%S)"
+    mkdir -p "$archive_dir"
+    find_move_dirs "$SKILLS_DIR" "$archive_dir"
+  fi
+else
+  echo "[APPEND] Layering new skills onto existing folder..."
+fi
+
+mkdir -p "$SKILLS_DIR"
+
+echo "Expanding bundles..."
+
+python_path=""
+if python_path="$(resolve_python 2>/dev/null)" && [[ -f "$BUNDLE_HELPER" ]]; then
+  if [[ "${#EXTRA_ARGS[@]}" -gt 0 ]]; then
+    "$python_path" "$BUNDLE_HELPER" "${EXTRA_ARGS[@]}" >"$SKILLS_LIST_FILE" 2>/dev/null || true
+  else
+    "$python_path" "$BUNDLE_HELPER" Essentials >"$SKILLS_LIST_FILE" 2>/dev/null || true
+  fi
+fi
+
+if [[ ! -s "$SKILLS_LIST_FILE" ]]; then
+  if [[ "${#EXTRA_ARGS[@]}" -eq 0 ]]; then
+    printf '%s\n' brainstorming systematic-debugging test-driven-development >"$SKILLS_LIST_FILE"
+  else
+    : >"$SKILLS_LIST_FILE"
+    for arg in "${EXTRA_ARGS[@]}"; do
+      if is_safe_skill_id "$arg"; then
+        printf '%s\n' "$arg" >>"$SKILLS_LIST_FILE"
+      fi
+    done
+  fi
+fi
+
+echo "Restoring selected skills..."
+while IFS= read -r skill_id || [[ -n "$skill_id" ]]; do
+  [[ -n "$skill_id" ]] || continue
+
+  if [[ -e "$SKILLS_DIR/$skill_id" ]]; then
+    echo "  . $skill_id (already active)"
+  elif [[ -e "$LIBRARY_DIR/$skill_id" ]]; then
+    echo "  + $skill_id"
+    cp -RP "$LIBRARY_DIR/$skill_id" "$SKILLS_DIR/"
+  else
+    echo "  - $skill_id (not found in library)"
+  fi
+done <"$SKILLS_LIST_FILE"
+
+echo
+echo "Done! Antigravity skills are now activated."