First real signal from the restored pipeline: with checkout fixed, the cpp-tests
job got far enough to fail at `-Werror=stringop-overflow` in ring_buffer.hpp on
GitHub's GCC 13, a failure that had been invisible behind the broken submodule
checkout for a month. Reproduced locally against gcc 13.4.0 (local default is
gcc 14, which does not fire).
The warning is a false positive: GCC anchors the destination object to the
member at offset 0 and reports `buf_[head & kMask]` as writing past
`head_._M_i` (size 8) at offset [16, 268] — offsets that are precisely
buf_[0..63] of a 64-entry, 4-byte ControlEvent array. Adding an explicit
`__builtin_unreachable()` bound hint does not help, because the index range was
never what GCC got wrong. Declaring buf_ first anchors the analysis correctly.
Not a suppression, and behaviour-preserving: RingBuffer has exactly one
production user (ModeBase::events_) and is never serialized, copied, or sent
over a wire, so member order is unobservable. Reasoning recorded at the
declaration so nobody "tidies" the order back.
Verified: full ctest suite green under gcc 13.4.0 (the CI compiler) as well as
gcc 14.2, and scripts/run-all-tests.sh ALL GREEN (parity 1273 floats within
1e-5, lint, 33 Playwright specs).
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