Replaces the wipe-on-change approach (which left ESP-IDF's nested bootloader /
managed-components build in a broken state under rapid reconfigure -
intermittent 'managed_components_list.temp.cmake: No such file'). Each distinct
configuration (board options x resolved library set, via the variant key the
caller already computes) now gets its OWN persistent project dir with its OWN
build/, never wiped or reconfigured for a different config:
- same config -> same dir -> warm ninja incremental + ccache (fast iterate);
- different config -> different dir -> isolated, consistent, no staleness,
no nested-build breakage;
- the scoped vs scan-all fallback attempts land in different dirs, so the
double-compile no longer corrupts a shared build/.
Variant dirs are LRU-bounded (_MAX_BUILD_VARIANTS per target); the global ccache
warms a fresh/evicted variant in seconds. Cleans up the old single-project
layout on first run. Fixes the cross-compile staleness for legacy AND manifest
compiles, and the fallback regression.
c996ca3717