diff --git a/launchpad/AGENTS.md b/launchpad/AGENTS.md
index ea52844d271..8c757f15f00 100644
--- a/launchpad/AGENTS.md
+++ b/launchpad/AGENTS.md
@@ -226,6 +226,13 @@ gh pr create --base launchpad
   place it is stated without admin.
 - **Do not force-push during review.** Push new commits instead — force-pushing hides
   what changed from the reviewer.
+- **Run `gh repo set-default launchpad-26/buzz` once per clone, before the first
+  `gh issue create` or `gh pr create`.** Without it, `gh`'s default-repo resolution
+  targets `block/buzz` — the parent repository — for any command with no explicit
+  `--repo`. A write aimed at this fork (an issue, a PR comment) silently lands on
+  upstream's public tracker instead, and the mistake is not visible until someone
+  looks there. The setting lands in the shared `.git/config`, so it covers every
+  worktree of the clone, not just the one it was run in.
 
 Before running any git command, activate the toolchain or hooks fail on `PATH`:
 
diff --git a/launchpad/README.md b/launchpad/README.md
index 8b80be52119..da44a8e3f6a 100644
--- a/launchpad/README.md
+++ b/launchpad/README.md
@@ -115,6 +115,13 @@ or the CLI.
 Branch from `launchpad`, commit with `-s` (the DCO check is not optional), and expect to
 need one approving review — the branch is protected and you can't approve your own.
 
+**Run `gh repo set-default launchpad-26/buzz` once per clone.** This fork's default
+branch resolution otherwise targets `block/buzz` — the parent repository — for any `gh`
+command with no explicit `--repo`, including `gh issue create` and `gh pr comment`. A
+command aimed at this fork silently lands on upstream's public tracker instead. The
+setting lands in the shared `.git/config`, so one invocation covers every worktree of
+the clone too.
+
 ---
 
 ## What's in this directory
diff --git a/launchpad/scripts/test-gh-set-default-guidance.sh b/launchpad/scripts/test-gh-set-default-guidance.sh
new file mode 100755
index 00000000000..04c164ccdf0
--- /dev/null
+++ b/launchpad/scripts/test-gh-set-default-guidance.sh
@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+# Verifies #136's fix: both launchpad/README.md and launchpad/AGENTS.md tell
+# contributors to run `gh repo set-default launchpad-26/buzz` once per clone,
+# so a gh command with no explicit --repo does not silently target block/buzz.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+LAUNCHPAD_DIR="${SCRIPT_DIR}/.."
+
+PASS=0
+FAIL=0
+
+check() {
+  local label=$1 ok=$2
+  if [ "${ok}" = "0" ]; then
+    echo "PASS: ${label}"
+    PASS=$((PASS + 1))
+  else
+    echo "FAIL: ${label}"
+    FAIL=$((FAIL + 1))
+  fi
+}
+
+for f in README.md AGENTS.md; do
+  status=1
+  grep -q "gh repo set-default launchpad-26/buzz" "${LAUNCHPAD_DIR}/${f}" && status=0
+  check "${f} tells contributors to run gh repo set-default" "${status}"
+done
+
+echo ""
+echo "==================================================="
+echo "${PASS} passed, ${FAIL} failed"
+[ "${FAIL}" -eq 0 ]