D431 - Guest mutexes and condition variables from the C runtime allow recursion by default

Status: assumed Date: 2026-09-01

Every mutex the C++ runtime's threading layer constructs is created allowing same-thread recursive locking, and a runtime sleep request is clamped to at most one second.

Why: The runtime's own type word distinguishing a recursive mutex from a plain one is not yet measured; allowing recursion cannot itself raise a false deadlock before that measurement exists, where forbidding it could. Clamping a sleep bounds the cost of a convention mix-up between an absolute and a relative time value to a retry, not a multi-year hang.

Rejected: honouring an unmeasured recursion type bit - risks a spurious deadlock on a guess; an unclamped sleep - risks an effectively permanent hang on a time-convention mismatch.