Builds on #23502.
## Why
#23502 adds the app-server `thread/settings/update` API and matching
`thread/settings/updated` notification. The TUI already lets users
change thread-scoped settings such as model, reasoning effort, service
tier, approvals, permissions, personality, and collaboration mode, but
those updates need to flow through the app server so embedded and
connected clients observe the same thread state.
This is a rework (simplification) of PR
https://github.com/openai/codex/pull/22510. It has the same
functionality, but the underlying `thread/settings/update` api is now
simpler in that it no longer returns the effective settings as a
response. Now, clients receive the effective settings only through the
`thread/settings/updated` notification.
## What Changed
This updates the TUI to send `thread/settings/update` whenever those
thread-scoped settings change and to treat the RPC response as the
authoritative acknowledgement. It also routes `thread/settings/updated`
notifications back into cached session state and the visible chat widget
so active and inactive threads stay in sync after app-server-originated
changes.
The implementation is kept to the TUI layer: settings conversion and
merge logic live under `codex-rs/tui/src/app/thread_settings.rs`, with
dispatch/routing hooks in the existing app and chat widget paths.
## Verification
I manually tested using `codex app-server --listen unix://` and then
launching two copies of the TUI that use the same local app server. I
then resumed the same thread on both and verified that changes like plan
mode, fast mode, model, reasoning effort, etc. are reflected "live" in
the second client when modified in the first and vice versa.
## Why
After the terminal-probe work in #23175, fresh-session startup still
waits for `thread/start` before the chat input can become usable. The
chat widget already has the machinery to hold early submissions until a
session is configured, so fresh `thread/start` does not need to stay on
the input-ready hot path.
Refs #16335.
## What
This PR starts fresh app-server threads in a background task, reports
completion through a startup app event, and attaches the primary session
once `thread/start` returns. Resume and fork startup paths remain
synchronous.
## Benchmark
In the local pty startup benchmark, this PR's pre-optimization base
branch, #23175, measured about 152ms median from launch to accepted chat
input. The stacked result measured about 66ms median, for an approximate
additional savings of 85-95ms. For broader context, the original `main`
baseline before either startup optimization was about 250.5ms median. We
also measured Codex 0.117.0 on the same machine at about 64.6ms median,
so the stacked branch is back in the old-startup-time range.
## Stack
1. [#23175: [1 of 2] Optimize TUI startup terminal
probes](https://github.com/openai/codex/pull/23175) — base PR
2. [#23176: [2 of 2] Start fresh TUI thread in
background](https://github.com/openai/codex/pull/23176) — this PR
## Verification
- `cargo test -p codex-tui`
## Why
`chatwidget.rs` is still carrying too many unrelated responsibilities in
one file. #22269 started a five-phase effort to move coherent behavior
domains into focused modules while keeping `chatwidget.rs` as the
composition layer.
This PR is phase 2 of that plan. It extracts the input and submission
flow as a mechanical move before the later protocol, popup/status, and
constructor/orchestration phases.
## What Changed
- Added `codex-rs/tui/src/chatwidget/input_flow.rs` for composer input
results, queued user-message draining, pending-input previews, and
mode-specific submission entry points.
- Added `codex-rs/tui/src/chatwidget/input_submission.rs` for
user-message construction/submission, shell prompt submission,
structured mention resolution, and blocked image draft restoration.
- Added `codex-rs/tui/src/chatwidget/input_restore.rs` for
initial-message submission, pending steer restoration after interrupts,
and thread input snapshot/restore behavior.
- Registered the new modules and removed the moved `ChatWidget` impl
methods from `codex-rs/tui/src/chatwidget.rs`.
## Follow-On Refactor Phases
The five-phase plan from #22269 is:
- Phase 1: mechanical helper and state moves. Completed in #22269.
- Phase 2: extract input and submission flow, including queued user
messages, shell prompt submission, pending steer restoration, and thread
input snapshot/restore behavior. This PR.
- 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.
Eric TrautandGitHub