`--tstack=100000000` in lakefile.toml causes `failed to create thread` in CI

[astefano]

The Loom lib in lakefile.toml passes a 100 MB per-thread stack to Lean:

moreLeanArgs = ["-Dwarn.sorry=false", "--tstack=100000000"]

When Lean builds with its default worker-thread pool, each thread requests that stack, which exceeds the limits on a GitHub Actions runner. The build dies immediately:

✖ [2/22] Building Loom.LatticeExt
failed to create thread
error: Lean exited with code 1

Building single-threaded (-j1) avoids the oversized per-thread stacks and the failure. Verified on a fork: after --tstack=100000000 → -j1, the build proceeds past LatticeExt, and with an elan-resolvable toolchain (#10) and the workflow in place (#8) it completes green (22/22 jobs).