FA-4479 / Borrow checking / Member archive

Exclusive borrow excludes readers · case 04

The operation returns a result or retained state that violates this contract: A single local object grants either any number of shared borrows or one exclusive borrow. Commands are [operation,token,value]. Reads return the value or denied; writes and acquisitions return booleans. Ownership can move only with no borrows. An exclusive borrow requires a live object and no outstanding borrow of either kind.

Member previewVariant 4 · 3 implementations · 5 checks per implementation

Case scope

A controlled failure with recorded boundary checks.

Why this case matters

A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
shared readers prohibit mutation	`[true, false, true, true, false, false, false, "initial", "denied", ["initial", true, ["a", "b"], "w"]]`	`[true, false, true, false, false, false, false, "initial", "denied", ["initial", true, ["a", "b"], null]]`	Failed

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