diff --git a/ship/SKILL.md b/ship/SKILL.md
index d4d0039d8..12e4c7799 100644
--- a/ship/SKILL.md
+++ b/ship/SKILL.md
@@ -3086,6 +3086,29 @@ This step is automatic — never skip it, never ask for confirmation.
 
 ---
 
+## Step 21: Plan-tune discoverability nudge (first-successful-ship only)
+
+Plan-tune cathedral T15. After a successful ship, surface /plan-tune once
+per machine. Single line, non-blocking, marker-gated so it never re-fires.
+
+```bash
+_NUDGE_MARKER="$HOME/.gstack/.plan-tune-nudge-shown"
+_QT=$(~/.claude/skills/gstack/bin/gstack-config get question_tuning 2>/dev/null || echo "false")
+if [ ! -f "$_NUDGE_MARKER" ] && [ "$_QT" = "false" ]; then
+  echo ""
+  echo "gstack can learn from your AskUserQuestion answers. Run /plan-tune to opt in"
+  echo "— it captures which prompts you find valuable vs noisy and (with hooks installed)"
+  echo "auto-decides your never-ask preferences."
+  touch "$_NUDGE_MARKER"
+fi
+```
+
+If the marker exists, OR question_tuning is already on, the nudge is a
+no-op. The marker guarantees at-most-once per machine. To re-enable:
+`rm ~/.gstack/.plan-tune-nudge-shown` before next ship.
+
+---
+
 ## Important Rules
 
 - **Never skip tests.** If tests fail, stop.
diff --git a/ship/SKILL.md.tmpl b/ship/SKILL.md.tmpl
index 304bd6a1d..fcad36aae 100644
--- a/ship/SKILL.md.tmpl
+++ b/ship/SKILL.md.tmpl
@@ -975,6 +975,29 @@ This step is automatic — never skip it, never ask for confirmation.
 
 ---
 
+## Step 21: Plan-tune discoverability nudge (first-successful-ship only)
+
+Plan-tune cathedral T15. After a successful ship, surface /plan-tune once
+per machine. Single line, non-blocking, marker-gated so it never re-fires.
+
+```bash
+_NUDGE_MARKER="$HOME/.gstack/.plan-tune-nudge-shown"
+_QT=$(~/.claude/skills/gstack/bin/gstack-config get question_tuning 2>/dev/null || echo "false")
+if [ ! -f "$_NUDGE_MARKER" ] && [ "$_QT" = "false" ]; then
+  echo ""
+  echo "gstack can learn from your AskUserQuestion answers. Run /plan-tune to opt in"
+  echo "— it captures which prompts you find valuable vs noisy and (with hooks installed)"
+  echo "auto-decides your never-ask preferences."
+  touch "$_NUDGE_MARKER"
+fi
+```
+
+If the marker exists, OR question_tuning is already on, the nudge is a
+no-op. The marker guarantees at-most-once per machine. To re-enable:
+`rm ~/.gstack/.plan-tune-nudge-shown` before next ship.
+
+---
+
 ## Important Rules
 
 - **Never skip tests.** If tests fail, stop.