#20686 acpmux: move the hub's startup into hub/startup.rs (move only; hub/mod.rs under 1000 lines)

No bead: base red, coordinator request.

cmux-tui/crates/acpmux/src/hub/mod.rs had grown to 1003 lines on feat-cmux-next, over the Rust god-file limit of 1000 and not in the baseline. Any PR that touched the file failed hosted lint (linux) on the Rust god-file check ("split it").

Move only, no logic changes. The hub's startup group moves verbatim from hub/mod.rs into an impl Hub block in the new hub/startup.rs:

• begin_startup
• finish_startup
• after_login_env
• startup_complete
• wait_startup
• verify_launchers

The only edit inside the moved code is wait_startup's visibility, pub(super) → pub(crate). In hub/mod.rs, pub(super) meant visible to the crate; from the deeper hub/startup.rs the same reach needs pub(crate). The new file adds only a module comment, four use lines and the impl Hub {} wrapper. hub/mod.rs gains mod startup;.

A line-multiset diff of the old file against the two new ones shows no other removed or added lines.

hub/mod.rs: 1003 → 888 lines.

Testing

• rustfmt --check on both files; crash ratchet OK.
• Hosted verify-cmux-tui-hosted.sh (lint, build, tests, with the login_env filter, which runs the startup tests): results below.

Changelog

none

🤖 Generated with Claude Code

---

^{Need help on this PR? Tag @codesmith-bot with what you need.}

---

Summary by cubic

Refactors the hub module by moving the startup group into a new hub/startup.rs, bringing hub/mod.rs from 1003 to 888 lines and clearing the 1000-line god-file lint check.

This is a move-only change. The startup methods (begin_startup, finish_startup, after_login_env, startup_complete, wait_startup, verify_launchers) move verbatim into an impl Hub block in the new file. The only edit is wait_startup's visibility from pub(super) to pub(crate), which preserves the same reach from the deeper module.