release: T-2 pre-publish dogfood — GATE or LAB (follow-up to #5174) #5176

The R5 change (#5174) takes the pre-publish dogfood off the T-1 lane and the T-4 preflight under the standing release policy. The review found one more place the dogfood still runs on the release path that #5174 does not change: the T-2 step.

• scripts/release/t2_preflight.sh (around line 306) runs the dogfood.
• scripts/release/prepare_bump.sh (around lines 284-285) does the same.

The question for this row: is the T-2 dogfood a GATE (it can block the release) or LAB (nightly only)? If it is LAB, it comes off the T-2 path the way R5 and R8 did, with a case table and a mutant. If it is a GATE, it needs to be ruled in under the standing gate rule. It must not get a third state (report-only, advisory, continue-on-error).

Owner: the release-fixes row owner (assigned).
Linked from: the #5174 PR.