[v1rtl]

Cargo.toml had no [profile.release], so release builds used the defaults: 16 codegen units and no cross-crate LTO. The comment in release.yml saying LTO was on by default was wrong.

rustc gives each codegen unit its own copy of every closure and async body that unit uses. That left about a fifth of .text as duplicates:

• the async body of main (about 138 KB) appeared three times;
• bridge::run_leg, client::push_chunks_with_pool_inner and resolve_feed_root appeared 3–4 times each.

Fat LTO with a single codegen unit merges these copies.

Results

Measured on macOS arm64 with stripped binaries, the same form the release tarballs ship.

	before	after	change
binary	13458360	9181064	-32%
.text	9353156	6844104	-27%
gzip -9	5913667	4413281	-25%
threaded wasm (before wasm-bindgen)	4911967	4153657	-15%

All figures are bytes.

• The wasm build gets the single codegen unit but not LTO: cargo skips LTO when a lib target is both cdylib and rlib.
• hoverfly bmt on a random 50 MB file gives the same roots with both binaries and takes the same time (about 0.27 s).
• The release build and the threaded wasm release build both succeed with the new profile.

Why panics stay unwind

panic = "abort" would save another 2083856 bytes (7097208 total). But each peer session runs its libp2p swarm in its own tokio task (spawn_session_driver). With unwind, a panic in that task, for example a dependency choking on a peer's bytes, drops only that session. With abort it would end the whole upload, daemon or relay. AGENTS.md now records this so nobody switches it later.

Errors (Results, such as libp2p dial failures or resets) aren't affected either way. The setting only changes what happens on a panic.

Other changes

• release.yml now builds only --bin hoverfly. sigcheck isn't shipped, so this avoids paying for a second fat-LTO link.

Notes

• Release builds are slower. The single-threaded fat-LTO link affects release.yml, the bench workflows, CircleCI and the Dockerfile. Debug builds (cargo build) are unchanged.
• The README's "7MB gzipped, 17MB unpacked x86 Linux binary" figures should be refreshed from the next release's real artifact. I measured on arm64 macOS only.