feat: annotated config file + routing injection tests

gstack-config now writes a documented header on first config creation
with every supported key explained (proactive, telemetry, auto_upgrade,
skill_prefix, routing_declined, codex_reviews, skip_eng_review, etc.).
Users can edit ~/.gstack/config.yaml directly, anytime.

Also fixes grep to use ^KEY: anchoring so commented header lines don't
shadow real config values.

Tests added:
- 7 new gstack-config tests (annotated header, no duplication, comment
  safety, routing_declined get/set/reset)
- 6 new gen-skill-docs tests (preamble routing injection: bash checks,
  config reads, AskUserQuestion, decline persistence, routing rules)

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

bin/gstack-config

@@ -13,6 +13,38 @@ set -euo pipefail
 STATE_DIR="${GSTACK_STATE_DIR:-$HOME/.gstack}"
 CONFIG_FILE="$STATE_DIR/config.yaml"
 
+# Annotated header for new config files. Written once on first `set`.
+CONFIG_HEADER='# gstack configuration — edit freely, changes take effect on next skill run.
+# Docs: https://github.com/garrytan/gstack
+#
+# ─── Behavior ────────────────────────────────────────────────────────
+# proactive: true           # Auto-invoke skills when your request matches one.
+#                           # Set to false to only run skills you type explicitly.
+#
+# routing_declined: false   # Set to true to skip the CLAUDE.md routing injection
+#                           # prompt. Set back to false to be asked again.
+#
+# ─── Telemetry ───────────────────────────────────────────────────────
+# telemetry: anonymous      # off | anonymous | community
+#                           #   off       — no data sent, no local analytics
+#                           #   anonymous — counter only, no device ID
+#                           #   community — usage data + stable device ID
+#
+# ─── Updates ─────────────────────────────────────────────────────────
+# auto_upgrade: false       # true = silently upgrade on session start
+# update_check: true        # false = suppress version check notifications
+#
+# ─── Skill naming ────────────────────────────────────────────────────
+# skill_prefix: false       # true = namespace skills as /gstack-qa, /gstack-ship
+#                           # false = short names /qa, /ship
+#
+# ─── Advanced ────────────────────────────────────────────────────────
+# codex_reviews: enabled    # disabled = skip Codex adversarial reviews in /ship
+# gstack_contributor: false # true = file field reports when gstack misbehaves
+# skip_eng_review: false    # true = skip eng review gate in /ship (not recommended)
+#
+'
+
 case "${1:-}" in
   get)
     KEY="${2:?Usage: gstack-config get <key>}"
@@ -21,7 +53,7 @@ case "${1:-}" in
       echo "Error: key must contain only alphanumeric characters and underscores" >&2
       exit 1
     fi
-    grep -F "${KEY}:" "$CONFIG_FILE" 2>/dev/null | tail -1 | awk '{print $2}' | tr -d '[:space:]' || true
+    grep -E "^${KEY}:" "$CONFIG_FILE" 2>/dev/null | tail -1 | awk '{print $2}' | tr -d '[:space:]' || true
     ;;
   set)
     KEY="${2:?Usage: gstack-config set <key> <value>}"
@@ -32,12 +64,16 @@ case "${1:-}" in
       exit 1
     fi
     mkdir -p "$STATE_DIR"
+    # Write annotated header on first creation
+    if [ ! -f "$CONFIG_FILE" ]; then
+      printf '%s' "$CONFIG_HEADER" > "$CONFIG_FILE"
+    fi
     # Escape sed special chars in value and drop embedded newlines
     ESC_VALUE="$(printf '%s' "$VALUE" | head -1 | sed 's/[&/\]/\\&/g')"
-    if grep -qF "${KEY}:" "$CONFIG_FILE" 2>/dev/null; then
+    if grep -qE "^${KEY}:" "$CONFIG_FILE" 2>/dev/null; then
       # Portable in-place edit (BSD sed uses -i '', GNU sed uses -i without arg)
       _tmpfile="$(mktemp "${CONFIG_FILE}.XXXXXX")"
-      sed "s/^${KEY}:.*/${KEY}: ${ESC_VALUE}/" "$CONFIG_FILE" > "$_tmpfile" && mv "$_tmpfile" "$CONFIG_FILE"
+      sed "/^${KEY}:/s/.*/${KEY}: ${ESC_VALUE}/" "$CONFIG_FILE" > "$_tmpfile" && mv "$_tmpfile" "$CONFIG_FILE"
     else
       echo "${KEY}: ${VALUE}" >> "$CONFIG_FILE"
     fi