diff --git a/bin/gstack-config b/bin/gstack-config
index e99a940b..1147addd 100755
--- a/bin/gstack-config
+++ b/bin/gstack-config
@@ -23,7 +23,9 @@ case "${1:-}" in
     VALUE="${3:?Usage: gstack-config set <key> <value>}"
     mkdir -p "$STATE_DIR"
     if grep -qE "^${KEY}:" "$CONFIG_FILE" 2>/dev/null; then
-      sed -i '' "s/^${KEY}:.*/${KEY}: ${VALUE}/" "$CONFIG_FILE"
+      # Portable in-place edit (BSD sed uses -i '', GNU sed uses -i without arg)
+      _tmpfile="$(mktemp "${CONFIG_FILE}.XXXXXX")"
+      sed "s/^${KEY}:.*/${KEY}: ${VALUE}/" "$CONFIG_FILE" > "$_tmpfile" && mv "$_tmpfile" "$CONFIG_FILE"
     else
       echo "${KEY}: ${VALUE}" >> "$CONFIG_FILE"
     fi
diff --git a/scripts/resolvers/preamble.ts b/scripts/resolvers/preamble.ts
index fe0ba77e..4e5092f8 100644
--- a/scripts/resolvers/preamble.ts
+++ b/scripts/resolvers/preamble.ts
@@ -24,8 +24,10 @@ _PROACTIVE=$(${ctx.paths.binDir}/gstack-config get proactive 2>/dev/null || echo
 _PROACTIVE_PROMPTED=$([ -f ~/.gstack/.proactive-prompted ] && echo "yes" || echo "no")
 _BRANCH=$(git branch --show-current 2>/dev/null || echo "unknown")
 echo "BRANCH: $_BRANCH"
+_SKILL_PREFIX=$(${ctx.paths.binDir}/gstack-config get skill_prefix 2>/dev/null || echo "false")
 echo "PROACTIVE: $_PROACTIVE"
 echo "PROACTIVE_PROMPTED: $_PROACTIVE_PROMPTED"
+echo "SKILL_PREFIX: $_SKILL_PREFIX"
 source <(${ctx.paths.binDir}/gstack-repo-mode 2>/dev/null) || true
 REPO_MODE=\${REPO_MODE:-unknown}
 echo "REPO_MODE: $REPO_MODE"
@@ -51,6 +53,11 @@ types (e.g., /qa, /ship). If you would have auto-invoked a skill, instead briefl
 "I think /skillname might help here — want me to run it?" and wait for confirmation.
 The user opted out of proactive behavior.
 
+If \`SKILL_PREFIX\` is \`"true"\`, the user has namespaced skill names. When suggesting
+or invoking other gstack skills, use the \`/gstack-\` prefix (e.g., \`/gstack-qa\` instead
+of \`/qa\`, \`/gstack-ship\` instead of \`/ship\`). Disk paths are unaffected — always use
+\`${ctx.paths.skillRoot}/[skill-name]/SKILL.md\` for reading skill files.
+
 If output shows \`UPGRADE_AVAILABLE <old> <new>\`: read \`${ctx.paths.skillRoot}/gstack-upgrade/SKILL.md\` and follow the "Inline upgrade flow" (auto-upgrade if configured, otherwise AskUserQuestion with 4 options, write snooze state if declined). If \`JUST_UPGRADED <from> <to>\`: tell user "Running gstack v{to} (just updated!)" and continue.`;
 }
 
diff --git a/setup b/setup
index 71306839..995833ae 100755
--- a/setup
+++ b/setup
@@ -24,12 +24,14 @@ esac
 HOST="claude"
 LOCAL_INSTALL=0
 SKILL_PREFIX=1
+SKILL_PREFIX_FLAG=0
 while [ $# -gt 0 ]; do
   case "$1" in
     --host) [ -z "$2" ] && echo "Missing value for --host (expected claude, codex, kiro, or auto)" >&2 && exit 1; HOST="$2"; shift 2 ;;
     --host=*) HOST="${1#--host=}"; shift ;;
     --local) LOCAL_INSTALL=1; shift ;;
-    --no-prefix) SKILL_PREFIX=0; shift ;;
+    --prefix)    SKILL_PREFIX=1; SKILL_PREFIX_FLAG=1; shift ;;
+    --no-prefix) SKILL_PREFIX=0; SKILL_PREFIX_FLAG=1; shift ;;
     *) shift ;;
   esac
 done
@@ -39,6 +41,44 @@ case "$HOST" in
   *) echo "Unknown --host value: $HOST (expected claude, codex, kiro, or auto)" >&2; exit 1 ;;
 esac
 
+# ─── Resolve skill prefix preference ─────────────────────────
+# Priority: CLI flag > saved config > interactive prompt (or flat default for non-TTY)
+GSTACK_CONFIG="$SOURCE_GSTACK_DIR/bin/gstack-config"
+if [ "$SKILL_PREFIX_FLAG" -eq 0 ]; then
+  _saved_prefix="$("$GSTACK_CONFIG" get skill_prefix 2>/dev/null || true)"
+  if [ "$_saved_prefix" = "true" ]; then
+    SKILL_PREFIX=1
+  elif [ "$_saved_prefix" = "false" ]; then
+    SKILL_PREFIX=0
+  else
+    # No saved preference — prompt interactively (or default flat for non-TTY)
+    if [ -t 0 ]; then
+      echo ""
+      echo "Skill naming: how should gstack skills appear?"
+      echo ""
+      echo "  1) Short names: /qa, /ship, /review"
+      echo "     Recommended. Clean and fast to type."
+      echo ""
+      echo "  2) Namespaced: /gstack-qa, /gstack-ship, /gstack-review"
+      echo "     Use this if you run other skill packs alongside gstack to avoid conflicts."
+      echo ""
+      printf "Choice [1/2] (default: 1): "
+      read -r _prefix_choice </dev/tty 2>/dev/null || _prefix_choice=""
+      case "$_prefix_choice" in
+        2) SKILL_PREFIX=1 ;;
+        *) SKILL_PREFIX=0 ;;
+      esac
+    else
+      SKILL_PREFIX=0
+    fi
+    # Save the choice for future runs
+    "$GSTACK_CONFIG" set skill_prefix "$([ "$SKILL_PREFIX" -eq 1 ] && echo true || echo false)" 2>/dev/null || true
+  fi
+else
+  # Flag was passed explicitly — persist the choice
+  "$GSTACK_CONFIG" set skill_prefix "$([ "$SKILL_PREFIX" -eq 1 ] && echo true || echo false)" 2>/dev/null || true
+fi
+
 # --local: install to .claude/skills/ in the current working directory
 if [ "$LOCAL_INSTALL" -eq 1 ]; then
   if [ "$HOST" = "codex" ]; then
@@ -266,6 +306,38 @@ cleanup_old_claude_symlinks() {
   fi
 }
 
+# ─── Helper: remove old prefixed Claude skill symlinks ────────────────────────
+# Reverse migration: when switching from gstack- prefixed names to flat names,
+# clean up stale gstack-* symlinks that point into the gstack directory.
+cleanup_prefixed_claude_symlinks() {
+  local gstack_dir="$1"
+  local skills_dir="$2"
+  local removed=()
+  for skill_dir in "$gstack_dir"/*/; do
+    if [ -f "$skill_dir/SKILL.md" ]; then
+      skill_name="$(basename "$skill_dir")"
+      [ "$skill_name" = "node_modules" ] && continue
+      # Only clean up prefixed symlinks for dirs that AREN'T already prefixed
+      # (e.g., remove gstack-qa but NOT gstack-upgrade which is the real dir name)
+      case "$skill_name" in gstack-*) continue ;; esac
+      prefixed_target="$skills_dir/gstack-$skill_name"
+      # Only remove if it's a symlink pointing into gstack/
+      if [ -L "$prefixed_target" ]; then
+        link_dest="$(readlink "$prefixed_target" 2>/dev/null || true)"
+        case "$link_dest" in
+          gstack/*|*/gstack/*)
+            rm -f "$prefixed_target"
+            removed+=("gstack-$skill_name")
+            ;;
+        esac
+      fi
+    fi
+  done
+  if [ ${#removed[@]} -gt 0 ]; then
+    echo "  cleaned up prefixed symlinks: ${removed[*]}"
+  fi
+}
+
 # ─── Helper: link generated Codex skills into a skills parent directory ──
 # Installs from .agents/skills/gstack-* (the generated Codex-format skills)
 # instead of source dirs (which have Claude paths).
@@ -393,9 +465,11 @@ fi
 
 if [ "$INSTALL_CLAUDE" -eq 1 ]; then
   if [ "$SKILLS_BASENAME" = "skills" ]; then
-    # Clean up old unprefixed symlinks from previous installs
+    # Clean up stale symlinks from the opposite prefix mode
     if [ "$SKILL_PREFIX" -eq 1 ]; then
       cleanup_old_claude_symlinks "$SOURCE_GSTACK_DIR" "$INSTALL_SKILLS_DIR"
+    else
+      cleanup_prefixed_claude_symlinks "$SOURCE_GSTACK_DIR" "$INSTALL_SKILLS_DIR"
     fi
     link_claude_skill_dirs "$SOURCE_GSTACK_DIR" "$INSTALL_SKILLS_DIR"
     if [ "$LOCAL_INSTALL" -eq 1 ]; then
@@ -497,8 +571,8 @@ if [ "$INSTALL_CODEX" -eq 1 ]; then
 fi
 
 # 8. First-time welcome + legacy cleanup
-if [ ! -d "$HOME/.gstack" ]; then
-  mkdir -p "$HOME/.gstack"
+if [ ! -f "$HOME/.gstack/.welcome-seen" ]; then
   echo "  Welcome! Run /gstack-upgrade anytime to stay current."
+  touch "$HOME/.gstack/.welcome-seen"
 fi
 rm -f /tmp/gstack-latest-version