fix(compose): stop calling a still-starting game server dead

Allocated Compose failed on a docs-only commit, so nothing functional
had changed. Its own diagnostics showed why: the game server logged a
clean `server_started` -- the exact string the readiness loop waits for
-- and the script reported "game server exited before becoming ready".

The guard asked whether the service was absent from
`compose ps --status running`, which is also true of a container that
has been created but has not started yet. On a slow runner the first
poll can land in that window, and the script concluded the server was
dead when it was still coming up. Ask whether it actually exited
instead.

Also set errtrace. This failure produced no "failed at line N" report
despite the ERR trap added in 432e5a11, because a bare `trap ... ERR`
does not fire inside functions or subshells without it -- the
instrumentation had a blind spot exactly where a readiness loop lives.

The other --status running check, after an explicit `compose stop`, is
correct and unchanged: stop is synchronous, so absence there really does
mean stopped.

Verified by two consecutive local runs.

scripts/verify_allocated_compose.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-set -euo pipefail
+set -Eeuo pipefail
 
 # Independent allocated-flow fixture for multiplayer-next.md §8.48. This
 # intentionally does not call compose.phase6-smoke.yml or reuse its ports.
@@ -88,7 +88,12 @@ for attempt in $(seq 1 180); do
   if "${compose[@]}" logs game-server 2>/dev/null | grep -q ' server_started '; then
     break
   fi
-  if ! "${compose[@]}" ps --status running --services | grep -qx game-server; then
+  # Ask whether it EXITED, not whether it is absent from the running list.
+  # Those differ: a container that has been created but has not started yet is
+  # missing from --status running too, so the previous check called a
+  # still-starting server dead on the first poll. It failed intermittently
+  # against a game server whose own logs showed a clean `server_started`.
+  if "${compose[@]}" ps -a --status exited --services 2>/dev/null | grep -qx game-server; then
     "${compose[@]}" logs game-server >&2
     echo "allocated Compose game server exited before becoming ready" >&2
     exit 1