bootstrap tests don't compile on master: t27c bin test target (axum under cfg(test)) and tests/corpus_unresolved.rs (E0716) #5448

Found while measuring #5444 (fix for #5162). cargo test --release --offline -p t27c --no-fail-fast stops on two targets that fail to compile on master. A compile error halts cargo test even with --no-fail-fast, so the bootstrap-tests job can't run any tests on master.

1. t27c bin unit-test target

error[E0433]: cannot find module or crate `axum` in this scope
error[E0432]: unresolved imports `crate::AppState`, `crate::Session`
error[E0433]: cannot find module or crate `tokio` in this scope
error[E0599]: no method named `request` found for struct `hyper_util::client::legacy::Builder`

Cause: bootstrap/src/proxy.rs gates its imports with #[cfg(any(feature = "server", test))], but axum and tokio are optional dependencies enabled only by feature = "server" (bootstrap/Cargo.toml). AppState/Session in main.rs are under #[cfg(feature = "server")]. So in a plain cargo test, cfg(test) turns the code on without its dependencies.

Fix candidates (pick one):

• gate with feature = "server" only;
• make the test target require the feature (required-features);
• run tests with --features server in CI.

2. bootstrap/tests/corpus_unresolved.rs

error[E0716] (temporary value dropped while borrowed). The line wasn't captured in this run; reproduce with cargo test --release --offline -p t27c --test corpus_unresolved.

Not touched by #5444.