Found 2026-08-25 while scoping gallo-romeins-museum into bxl1-test-2 (hydraheadquest #544): the Perforce archive zip for build 2 carries a top-level Builds\ folder, so the library exe_path (rooted at C:\experiences<name>...) pointed at a missing exe after hydrabody extraction. Fixed by hand on chunky (moved Builds* up one level). Production museum body still runs build 1 with root layout and is protected only by the exe-already-present skip.
Fix properly: strip the Builds/ prefix (or normalize to the exe_path root) in the hydraperforce archive step, or add per-district exe_path support in the experience library. Re-archive gallo build 2 accordingly.