## Why
`chatwidget.rs` is still carrying too many unrelated responsibilities in
one file. After #21866 consolidated some of the state it tracks, this
starts the next phase by moving coherent state/helper clusters out of
the main module without changing behavior.
This PR is intentionally mechanical: it only moves existing functions,
structs, and helpers into focused modules so the boundaries are easier
to review before the less mechanical refactors that should follow.
## What Changed
- Moved user-message, composer, queue, pending steer, and merge/remap
helpers into `codex-rs/tui/src/chatwidget/user_messages.rs`.
- Added `codex-rs/tui/src/chatwidget/exec_state.rs` for unified exec
bookkeeping helpers.
- Added `codex-rs/tui/src/chatwidget/rate_limits.rs` for rate-limit
warning, prompt, and error classification state.
- Moved plugin list fetch and install auth-flow state into
`codex-rs/tui/src/chatwidget/plugins.rs`.
- Made a couple of test-only `VecDeque` imports explicit now that those
tests no longer inherit the parent module import.
## Verification
- `cargo test -p codex-tui` was run
## Follow-On Refactor Phases
This PR is phase 1: mechanical helper and state moves. Planned follow-up
PRs:
- Phase 2: extract input and submission flow, including queued user
messages, shell prompt submission, pending steer restoration, and thread
input snapshot/restore behavior.
- Phase 3: extract protocol, replay, streaming, and tool lifecycle
handling, while preserving active-cell grouping, transcript
invalidation, interrupt deferral, and final-message separator behavior.
- Phase 4: extract settings, popups, and status surfaces, including
model/reasoning/collaboration/personality popups, permission prompts,
rate-limit UI, and connectors helpers.
- Phase 5: clean up the remaining constructor and orchestration code
once the larger behavior domains have moved out, leaving `chatwidget.rs`
as the composition layer.
92930a8d40