Fix flaky recursion in recursive forward-reference resolution#4754
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Liam-DeVoe
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Resolving recursive forward references such as A = list[Union["A", str]] recursed once per available stack frame until hitting a RecursionError, then fell back to a deferred strategy. Termination therefore depended on the ambient stack depth, which made resolution flaky (spurious RecursionError and other intermittent failures). Break the cycle eagerly by deferring when we re-enter resolution of a type whose forward reference we are already resolving, so resolution uses a small and constant amount of stack. https://claude.ai/code/session_01F7S7ua4joqKCzxbMxQWj5R
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Resolving recursive forward references such as
A = list[Union["A", str]]recursed once per available stack frame until hitting a RecursionError, then fell back to a deferred strategy. Termination therefore depended on the ambient stack depth, which made resolution flaky (spurious RecursionError and other intermittent failures). Break the cycle eagerly by deferring when we re-enter resolution of a type whose forward reference we are already resolving, so resolution uses a small and constant amount of stack.