The bridge's close path had no committed test. Whether a close is safe against
host threads already inside the library is the one thing about it a host cannot
establish by reading, and every check of it so far lived in a session scratchpad
and is gone.
The scenario runner under tests/ drives that path and nothing else: it parks
pollers in cultmesh_quic_next_event, closes the runtime under them, and asserts
that the close is what woke them. It consumes the bridge through the public
header, as a host does. CULTMESH_QUIC_BUILD_TESTS builds it, off by default,
because a delivery build has no business producing an executable.
CULTMESH_QUIC_DEBUG_ASSERTS, also off by default, makes the bridge state the
quiesce invariant itself rather than leaving it to whatever a sanitizer happens
to catch. Deleting the quiesce wait is otherwise falsifiable only by luck:
AddressSanitizer saw it 4 times in 48 attempts with pollers blocked mid-copy of
large frames, and never on release. With the assertion and pollers blocked it
fails on the first close.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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