No Full Performance profile walked the backdrop (imagePlan) path: every
large-house fixture has plan_url null. So the #739 K1 double render -- a
warm 2.5D floor switch with a backdrop cleared the ready paper, inserted
the veil, probed the card background and rendered a second time -- was
invisible to CI by time and structurally; a temporary probe found it.
large-house-isometric-backdrop-v1 is the twin of large-house-isometric-v1
with the shipped f1.svg under a URL of its own on every floor
(plan_aspect 1, room geometry unchanged). The variant is derived in the
runner as plan-snap's is, so demo/fixtures and the bundle fingerprint do
not change. A first stable frame without the backdrop image fails the
sample. After the switchCycle window and its #735 guard, before forced
GC and outside every timed window, a probe makes six warm switches and
counts performUpdate passes until updateComplete resolves true: the K1
second pass starts after the first updateComplete resolves, so a count
taken right after the first await reads one on both sides.
evaluate.mjs rejects a candidate of this profile unless every switch took
one pass, or when the probe is missing; the base is reported, not judged
(v1.78.0 and dev before #739 take two). The budget is a copy of the
historical isometric budget under the new profile id. performance.yml
gains the isometric-backdrop matrix entry with exact-SHA comparison.
Witness: a tree with #739 reverted reads perSwitch 2 in every sample and
benchmark:compare against the branch report throws on the pass count;
v1.78.0 reads 2, the branch reads 1.
Issue: #743
User-Visible: no
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018qZfe7YS4rqEMKoVeS3GKd
