ESP-IDF compiles with -ggdb, and for debug builds ccache folds the cwd into
every cache key by default — CCACHE_BASEDIR does not exempt it (verified with
CCACHE_DEBUG on 4.11: 'Hashing CWD /var/lib/velxio-build/esp32s3/v_<hash>/
project/build'). Each build variant lives in its own dir, so every variant had
a private key space: eight esp32 variants of the SAME board each recompiled
all ~2100 IDF objects from scratch, the cache filled with dead per-directory
entries, and a cold Cardputer/S3 build (2263 steps) overran the 600s ninja
timeout on a busy box. CCACHE_NOHASHDIR=1 makes variants of the same
board/sdkconfig share objects; a cold variant becomes mostly cache hits. Only
DW_AT_comp_dir in .debug_info of a reused object can differ, which never
reaches the flashed .bin.
The timeout paths were silent server-side; they now log the build dir and how
many ninja steps completed, and the user-facing message says the partial
build is kept and a retry resumes.
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