fix(scripts): refuse to start dev-headless on a port somebody else holds

dev-headless.sh checked the PID in *this* worktree's .dev/app.pid and
nothing else, so an app orphaned by a deleted worktree went on listening
with nothing left to stop it — `make dev-stop` only kills the pid it
wrote. The new app then started, failed to bind, exited, and every
subsequent curl and playwright-cli call went to the other process: the
harness reported facts about an app nobody asked for.

That fails a long way from its cause. It presented as "no such table:
libraries" against a *freshly created* YJ_HOME, which reads exactly like
applySchema or staleshape.go having gone wrong, with a zero-byte app.log
beside it saying nothing.

The startup wait cannot catch this, because its health check is satisfied
by any app on the port — which is precisely the failure — so the check is
before the launch and refuses rather than warns. It names the holder's
pid, cmdline and /proc/<pid>/cwd, which is what identifies the checkout
and says "(deleted)" for the case this exists for. It does not suggest
`make dev-stop`: the PID-file check has already passed, so by
construction dev-stop does not know about this process and would report
success while changing nothing. --port already covers the legitimate
second-app case.

The second, cheaper guard the report asks for goes in after the wait:
"the port answered" is not "the app we started answered", so a dead
APP_PID at that point is now an error with the log tail rather than a
success message about somebody else's process.

Closes #119

scripts/dev-headless.sh

@@ -97,6 +97,55 @@ if [ -f "$PID_FILE" ] && kill -0 "$(cat "$PID_FILE")" 2>/dev/null; then
 fi
 rm -f "$PID_FILE"
 
+# ── Refuse to inherit somebody else's port ───────────────────────────
+# The PID check above only knows about *this* worktree: `make dev-stop`
+# kills the pid in this .dev/app.pid and nothing else.  Several worktrees
+# of this repo share the default port, so an app orphaned by a deleted
+# worktree goes on listening with nothing left to stop it.
+#
+# Without this check the new app starts, fails to bind, exits — and every
+# curl and playwright-cli call afterwards goes to the *other* process, so
+# the harness reports facts about an app nobody asked for.  That is not a
+# quiet wrongness either: it presented as
+# "no such table: libraries" against a freshly created YJ_HOME, which
+# reads exactly like applySchema or staleshape.go having gone wrong and
+# is a frightening place to start looking.
+#
+# The startup wait below cannot catch it, because the health check is
+# satisfied by *any* app on the port — which is precisely the failure.
+# So it is refused here, before anything is launched, rather than warned
+# about.  --port already exists for the legitimate second-app case.
+port_holder() {
+	command -v ss >/dev/null || return 0
+	ss -lptn "sport = :$PORT" 2>/dev/null | grep -oP 'pid=\K[0-9]+' | head -n 1
+}
+
+if curl -sf -o /dev/null --max-time 2 "http://localhost:$PORT/" ||
+	[ -n "$(port_holder)" ]; then
+	holder="$(port_holder)"
+	echo "dev-headless: :$PORT is already in use; refusing to start" >&2
+	if [ -n "$holder" ]; then
+		# /proc/<pid>/cwd names the checkout it belongs to, and says
+		# "(deleted)" for the orphaned-worktree case that is the whole
+		# reason this is worth a check.
+		cwd="$(readlink "/proc/$holder/cwd" 2>/dev/null || echo unknown)"
+		cmd="$(tr '\0' ' ' <"/proc/$holder/cmdline" 2>/dev/null || echo unknown)"
+		echo "  pid  $holder  ($cmd)" >&2
+		echo "  cwd  $cwd" >&2
+		# The PID-file check above has already passed, so whatever this
+		# is, `make dev-stop` does not know about it — saying otherwise
+		# sends you to a command that will report success and change
+		# nothing.  Never `pkill -f` here either: the pattern would
+		# match this script's own command line.
+		echo "  'make dev-stop' will not touch it (it is not in" >&2
+		echo "  ${PID_FILE#"$REPO_ROOT"/}): kill $holder, or pass --port." >&2
+	else
+		echo "  The holder could not be identified (no ss, or it belongs" >&2
+		echo "  to another user). Try: ss -lptn 'sport = :$PORT'" >&2
+	fi
+	exit 1
+fi
+
 # ── Choose the YJ_HOME ───────────────────────────────────────────────
 # A seed is a YJ_HOME that a previous run of the app produced, tarred
 # up (see scripts/seed-sandbox.sh).  Restoring it means starting *in*
@@ -200,6 +249,20 @@ until curl -sf -o /dev/null "http://localhost:$PORT/"; do
 	sleep 0.25
 done
 
+# The loop above exits on the first answer from the port, and "something
+# answered" is not "the app we started answered".  The pre-launch guard
+# makes that unlikely rather than impossible — a race, or a listener
+# started in between — and the check is one signal, so it is worth making
+# here too.  An empty log beside a dead pid is the "it exited immediately
+# and nothing said so" case that the original report spent its time on.
+if ! kill -0 "$APP_PID" 2>/dev/null; then
+	echo "dev-headless: :$PORT answered, but the app we started (pid" >&2
+	echo "  $APP_PID) is gone — something else holds the port." >&2
+	tail -n 30 "$LOG_FILE" >&2
+	rm -f "$PID_FILE"
+	exit 1
+fi
+
 cat <<EOF
 dev-headless: up
   url      http://localhost:$PORT

scripts/issue.sh

@@ -38,10 +38,8 @@
 # Where a body is taken and no --body-file is given, it is read from stdin.
 #
 # Environment:
-#   GITEA_TOKEN   a PAT with write:issue.  `claim` and `mine` additionally
-#                 need to know your username: set GITEA_USER, or give the
-#                 token read:user and it is looked up.
-#   GITEA_USER    your Gitea login.  Optional; see above.
+#   GITEA_TOKEN   a PAT with write:issue (plus write:repository and read:user,
+#                 which the rest of this repo's tooling reaches for)
 #   GITEA_URL     defaults to https://git.ljones.me
 #   GITEA_REPO    defaults to yonlu/yellowjacket
 set -euo pipefail
@@ -83,29 +81,7 @@ read_body() {
 	if [ "$file" = "-" ]; then cat; else cat "$file"; fi
 }
 
-# The one lookup in this script that needs a scope beyond write:issue.
-# `GET /user` requires read:user, and it is reached for exactly two reasons:
-# to name the assignee in `claim`, and to filter in `mine`.  A token scoped to
-# the work this script does — write:issue — therefore failed at `claim`, which
-# is the one step the workflow requires before the first edit, so the whole
-# documented process was blocked by its own tooling.
-#
-# GITEA_USER short-circuits it, which is what lets a least-privilege token do
-# the job.  The lookup stays as the fallback because it is right when the
-# scope is there and needs no setup at all.
-me() {
-	if [ -n "${GITEA_USER:-}" ]; then
-		printf '%s' "$GITEA_USER"
-		return
-	fi
-	curl -sS -H "Authorization: token $GITEA_TOKEN" "$server/api/v1/user" |
-		python3 "$py" login ||
-		{
-			echo "issue.sh: could not resolve your username. Set GITEA_USER, or" >&2
-			echo "issue.sh: re-issue GITEA_TOKEN with read:user." >&2
-			exit 1
-		}
-}
+me() { curl -sS -H "Authorization: token $GITEA_TOKEN" "$server/api/v1/user" | python3 "$py" login; }
 
 label_id() { call GET "/labels?limit=100" | python3 "$py" label-id "$1"; }