[fortmarek]

Summary

Windows Rust builds did far more work than the cache could save:

• Every Windows Rust compile copied each transitive rlib into a per-crate search directory. Uncached actions cleared and recreated that directory on every build. For the Once CLI graph, that is about 6,700 copies and about 11 GB of rlibs copied, hashed, and stored again on every build. The uncached actions also made every target report bypass, so no target could reuse its build receipt.
• Rlibs now resolve from their own output directories, as on other hosts. They are already declared inputs of each compile. Proc-macro DLLs keep their staging directory, because MSVC writes sibling files next to them.
• The once workflow's Windows release graph build signed in to Tuist only after resolving the bootstrap, so the bootstrap always fell back to a Cargo build. It now selects the cache first, as the release workflow does.

Measurements

release graph build (windows-latest)	Job total	Bootstrap	Once build	Once build cache state
Before, main at the same tree as the warm #426 run	19.5 min	12.0 min (Cargo)	4.7 min	bypass
After, first run (every Windows compile key changed)	29.2 min	5.7 min (built with Once)	21.5 min (cold)	miss
After, rerun with no change	8.9 min	4.7 min (built with Once)	2.8 min	hit

The bootstrap still reports bypass: the latest released Once builds it with its own embedded prelude, which still stages rlib copies. The first release that includes this change removes those copies from the bootstrap too.