fix(ci): zig fmt repair (root_set.zig stray blank line) + fmt-check joins the local smoke core

Four 2026-07-02 main pushes went red in CI on ci_gate.sh's step (1/2)
`zig fmt --check src/` — a single stray blank line in root_set.zig that
no LOCAL tier checked (zlinter != fmt). The check now runs in the smoke
core (portable, <1s) so formatting fails at commit time, not 15 minutes
later in CI.

Smell-audited: 1: gate-parity fix — the local tiers now cover everything CI's early steps check

Author: chaploud

src/runtime/gc/root_set.zig

@@ -86,7 +86,6 @@ pub const RootSource = enum {
 /// D-430 analysis-roots frame: it never gained a production writer, and the
 /// frame subsumes its declared purpose — `expandIfMacro` now pushes the
 /// macro-expansion intermediates + result into the current AnalysisFrame.)
-
 /// One operand-stack-resident root scope, published on the thread's
 /// eval-frame chain so a GC `collect()` walks live operand Values
 /// (`stack[0..sp]`) + slot Values (`locals`) — ADR-0091. Two kinds of

test/run_all.sh

@@ -49,7 +49,7 @@ E2E_JOBS="${E2E_JOBS:-8}"
 # how many smoke-only commits ride before a full gate is forced.
 SMOKE_MODE=0
 SMOKE_E2E=""
-SMOKE_CORE="zig_build_test_vm,zig_build_test_tree_walk,zlinter,build_cljw,lazy_ns_replay,corpus_regression"
+SMOKE_CORE="zig_fmt_check,zig_build_test_vm,zig_build_test_tree_walk,zlinter,build_cljw,lazy_ns_replay,corpus_regression"
 
 while [[ $# -gt 0 ]]; do
     case "$1" in
@@ -345,6 +345,11 @@ run_step "debt_id_refs"         "bash scripts/check_debt_id_refs.sh --gate"
 # cannot drift or accept-without-reason. Rule: accepted_divergences.md.
 run_step "accepted_divergences" "bash scripts/check_accepted_divergences.sh --gate"
 
+# Formatting gate — mirrors CI's ci_gate.sh step (1/2) so a non-canonical
+# file fails LOCALLY at smoke time, not 15 minutes later in CI (2026-07-02:
+# four pushes went red on a single stray blank line only CI checked).
+run_step "zig_fmt_check"        "zig fmt --check src/"
+
 # zlinter no_deprecated gate (ADR-0003) — Mac-host only. zlinter is
 # fetched via `zig fetch` against GitHub; OrbStack runs are network-
 # free per .dev/orbstack_setup.md.