Keep guest creation-mask state in libc behind C-linkage helpers so NID
patching preserves the shared exports. Reject a pinned descriptor whose
file identity differs from the snapshot taken before classification.
Exercise close and reuse from another thread at both acquisition windows
for writes, resize and seek, and create temporary ordinary-file fixtures
so runtime tests work without the source tree.
Constraint: NID exemptions require the literal suffix at the end of the exported symbol
Confidence: high
Scope-risk: narrow
Tested: 18 targeted Linux runtime tests with zero skips; patched_libraries for libc/libkernel/libkernel_sys; standalone ASan/UBSan with warnings as errors; source-prefix-remapped fixtures; Clang analyzer and conventions
Not-tested: Full project build and library set, Windows runtime, console hardware and titles
Directive: Device/inode validation establishes file identity, not open-file-description identity
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