fix(preflight): avoid jq SIGPIPE race in verify-changelog-sync

The Block C check used `jq -r '.[0].Changelog' | grep -qE ...` to spot
the **vX.Y.Z** marker. With `set -o pipefail`, grep -q closing stdin on
the first match makes jq trip SIGPIPE on the rest of the multi-KB
Changelog string, which the script then surfaces as a false-positive
"Changelog missing **vX.Y.Z** subblock" failure. Interactive shells
sometimes raced through fast enough to hide the issue, but the pre-push
runner hit it reliably (saw it on the v1.4.10 release-cut push attempt).

Switched the pipe to a process substitution so jq writes into a FIFO
and SIGPIPE never enters the picture. Both directions of the marker
check now stay deterministic.

scripts/verify-changelog-sync.sh

@@ -19,7 +19,12 @@ TAG="v$VER"
 grep -qE "^[[:space:]]*\*\*v${VER}[^0-9]" "$YAML" \
   || fail "$YAML changelog missing **v${VER}** subblock. Fix: add the v${VER} block at the top of the changelog field."
 
-jq -r '.[0].Changelog' "$REPO_JSON" | grep -qE "^[[:space:]]*\*\*v${VER}[^0-9]" \
+# Process substitution instead of `jq | grep -q` — grep -q closes stdin on the
+# first match, jq keeps writing the multi-KB Changelog string and trips SIGPIPE,
+# which `set -o pipefail` then turns into a false-positive FAIL. Manifested as a
+# `jq: writing output failed: Broken pipe` line plus a misleading "Changelog
+# missing **vX.Y.Z** subblock" message during pre-push runs.
+grep -qE "^[[:space:]]*\*\*v${VER}[^0-9]" <(jq -r '.[0].Changelog' "$REPO_JSON") \
   || fail "$REPO_JSON Changelog missing **v${VER}** subblock. Fix: copy the yaml changelog over."
 
 FORGE_FILE="$FORGE_DIR/${TAG}.md"