Investigate concurrent named call-site cache race

[cursor]

Summary

• add bounded NDJSON diagnostics around RuntimeDispatch.NamedCallSite
• reproduce the shared-delegate concurrency failure with the supplied stress probe
• preserve instrumentation for the required confirmation run before implementing a fix

Evidence

• baseline Release probe: mismatches=1344
• instrumented Release probe: mismatches=1663
• logs confirm both refill overwrite-before-dispatch and cache validation/check-use races

No fix is included yet, per the hypothesis-driven debug workflow.

  

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Note

Medium Risk
Touches the hot path for every compiled named call site and changes cross-thread visibility of cache state; correctness is critical for multi-threaded hosts but the change is localized and covered by a concurrency regression test.

Overview
Fixes a concurrency bug in compiled named-call inline caching where separate mutable fields could be observed mid-refill, so one thread could validate against its environment and then dispatch another thread’s cached combiner.

NamedCallSite now stores a single immutable ResolvedCallSite snapshot (environment, resolution path, binding cell/version, combiner, eager shortcut) behind one cache reference, published with Volatile.Read / Volatile.Write instead of updating many fields independently.

Adds a parallel stress test that alternates two deep environment chains on one compiled (f 0) site and asserts zero result mismatches under heavy concurrent Invoke.

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