check-prompt-snapshots costs 200-310s per PR regenerating real prompt
stacks, but snapshots only change when the generator's import graph or
its fixtures do. The manifest now computes that reach (same pattern as
QA smoke gating: always-run surface regex incl. the codex extension
whose test API loads via a dynamic module id, plus import-graph walk
from the snapshot helper; deletions and null diffs fail safe to
running). Unaffected PR diffs skip the lane with an explicit log line;
pushes and dispatches always run.
* perf(ci): diff-gate QA smoke by CLI import graph and isolate prompt snapshots lane
* fix(ci): run prompt snapshot lane unconditionally
* fix(ci): treat QA lane orchestration files as QA-impacting
