Fixes multiple scrollback and terminal resize issues: #5538, #5576,
#8352, #12223, #16165, and #15380.
## Why
Codex writes finalized transcript output into terminal scrollback after
wrapping it for the current viewport width. A later terminal resize
could leave that scrollback shaped for the old width, so wider windows
kept narrow output and narrower windows could show stale wrapping
artifacts until enough new output replaced the visible area.
This is also the foundation PR for responsive markdown tables. Table
rendering needs finalized transcript content to be width-sensitive after
insertion, not only while content is first streaming. Markdown table
rendering itself stays in #18576.
## Stack
- PR1: resize backlog reflow and interrupt cleanup
- #18576: markdown table support
## What Changed
- Rebuild source-backed transcript history when the terminal width
changes. `terminal_resize_reflow` is introduced through the experimental
feature system, but is enabled by default for this rollout so we can
validate behavior across real terminals.
- Preserve assistant and plan stream source so finalized streaming
output can participate in resize reflow after consolidation.
- Debounce resize work, but force a final source-backed reflow when a
resize happened during active or unconsolidated streaming output.
- Clear stale pending history lines on resize so old-width wrapped
output is not emitted just before rebuilt scrollback.
- Bound replay work with `[tui.terminal_resize_reflow].max_rows`:
omitted uses terminal-specific defaults, `0` keeps all rendered rows,
and a positive value sets an explicit cap. The cap applies both while
initially replaying a resumed transcript into scrollback and when
rebuilding scrollback after terminal resize.
- Consolidate interrupted assistant streams before cleanup, then clear
pending stream output and active-tail state consistently.
- Move resize reflow and thread event buffering helpers out of `app.rs`
into dedicated TUI modules.
- Add focused coverage for resize reflow, feature-gated behavior,
streaming source preservation, interrupted output cleanup,
unicode-neutral text, terminal-specific row caps, and composer/layout
stability.
## Runtime Bounds
Resize reflow keeps only the most recent rendered rows when a row cap is
active. The default is `auto`, which maps to the detected terminal's
default scrollback size where Codex can identify it: VS Code `1000`,
Windows Terminal `9001`, WezTerm `3500`, and Alacritty `10000`.
Terminals without a dedicated mapping use the conservative fallback of
`1000` rows. Users can override this with `[tui.terminal_resize_reflow]
max_rows = N`, or set `max_rows = 0` to disable row limiting.
## Validation
- `just fmt`
- `git diff --check`
- `cargo test --manifest-path codex-rs/Cargo.toml -p codex-tui reflow`
- `cargo test --manifest-path codex-rs/Cargo.toml -p codex-tui
transcript_reflow`
- `just fix -p codex-tui`
- PR CI in progress on the squashed branch
## Why
Enterprise and business-like ChatGPT plans should get Codex's Fast
service tier by default when the user or caller has not made an explicit
service-tier choice. At the same time, callers need a durable way to
choose standard routing without adding a new persisted `standard`
service tier value. This keeps existing config compatibility while
letting core own the managed default policy.
## What changed
- Resolve the effective service tier in core at session creation:
explicit `fast` or `flex` wins, explicit null/clear or
`[notice].fast_default_opt_out = true` resolves to standard routing, and
otherwise eligible ChatGPT plans resolve to Fast when FastMode is
enabled.
- Add `[notice].fast_default_opt_out` as the persisted opt-out marker
for managed Fast defaults.
- Treat app-server/TUI `service_tier: null` as an explicit
standard/clear choice by preserving that intent through config loading.
- Update TUI rendering to use core's effective service tier for startup
and status surfaces while still keeping `config.service_tier` as the
explicit configured choice.
- Update `/fast off` to clear `service_tier`, persist the opt-out
marker, and send explicit standard for subsequent turns.
## Verification
- Added unit coverage for config override/notice handling, service-tier
resolution, runtime null clearing, and `/fast off` turn propagation.
- `cargo build -p codex-cli`
Full test suite was not run locally per author request.
## Summary
The TUI app refactor in #18753 moved the old `app.rs` tests into a
single `app/tests.rs` file. That kept the split mechanically simple, but
it left several focused unit tests far from the modules they exercise.
This PR is a follow-up that moves tests next to the code they cover.
It also adds `tui/src/app/test_support.rs` for shared fixture
construction.
This is just a mechanical refactoring (no functional changes) and does
not affect any production code.
## Why
The TUI app module had grown past the 512K source-file cap enforced by
CI/CD. This keeps the app entry point below that limit while preserving
the existing runtime behavior and test surface.
## What changed
- Kept the top-level `App` state and run-loop wiring in
`tui/src/app.rs`.
- Split app responsibilities into focused private submodules under
`tui/src/app/`, covering event dispatch, thread routing, session
lifecycle, config persistence, background requests, startup prompts,
input, history UI, platform actions, and thread event buffering.
- Moved the existing app-level tests into `tui/src/app/tests.rs` and
reused the existing snapshot location rather than adding new tests or
snapshots.
- Added module header comments for `app.rs` and the new submodules.
## Follow-up
A future cleanup can move narrow unit tests from `tui/src/app/tests.rs`
into the specific app submodules they exercise. This PR keeps the
existing app-level tests together so the refactor stays focused on the
source-file split.
## Verification
- `cargo test -p codex-tui --lib
app::tests::agent_picker_item_name_snapshot`
- `cargo test -p codex-tui --lib app::tests::clear_ui`
- `cargo test -p codex-tui --lib
app::tests::ctrl_l_clear_ui_after_long_transcript_reuses_clear_header_snapshot`
- `just fix -p codex-tui`
Full `cargo test -p codex-tui` still fails on model-catalog drift
unrelated to this refactor, including stale
`gpt-5.3-codex`/`gpt-5.1-codex` snapshot and migration expectations now
resolving to `gpt-5.4`.
Felipe Coury