[omdxp]

Summary

• memcheck: small allocations (<=4096 bytes, in 64/256/1024/4096 classes) now share guarded slab arenas instead of paying dedicated guard pages each, fixing real OOM on compile-heavy test files under -memcheck in CI
• memcheck: an unconditional exit-time sweep catches a slab overflow that's never freed before the process exits
• fls: fixed an 8-site leak of read_to_string's result in symbols.fn/completion.fn/navigation.fn
• codegen: format()'s vargs unpacking now always frees a string slot instead of assuming it's borrowed
• ci: upload coverage to Codecov; docs/tooling.md's example bumped to codecov-action v5

Test plan

• Full local suite (fun test .), 56/56
• 3-stage bootstrap to a fixed point (stage2 == stage3 binary)
• fun -fmt-check-all clean
• scripts/run_examples.sh, 0 unexpected failures
• fun test . -memcheck run in a Docker container matching CI's spec (ubuntu 24.04 arm64, 16GB RAM/16GB swap cap, 4 CPU), 53/56 - remaining 3 are this stripped container missing git/openssl-dev, confirmed unrelated to memcheck

[codecov-commenter]

Welcome to Codecov 🎉

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