## Why
The TUI currently handles keyboard shortcuts as hard-coded event matches
spread across app, composer, pager, list, approval, and navigation code.
That makes shortcuts hard to customize, makes displayed hints easy to
drift from actual behavior, and makes future keymap work riskier because
there is no central action inventory.
This PR adds the foundation for configurable, action-based keymaps
without adding the interactive remapping UI yet. Onboarding
intentionally stays on fixed startup shortcuts because users cannot
reasonably configure keymaps before completing onboarding.
This is PR1 in the keymap stack:
- PR1: #18593: configurable keymap foundation
- PR2: #18594: `/keymap` picker and guided remapping UI
- PR3: #18595: Vim composer mode and the remap option
## Design Notes
The new model resolves named actions into concrete runtime bindings once
from config, then passes those bindings to the UI surfaces that handle
input or render shortcut hints.
The main concepts are:
- **Context**: a scope where an action is active, such as `global`,
`chat`, `composer`, `editor`, `pager`, `list`, or `approval`.
- **Action**: a named operation inside a context, such as
`global.open_transcript`, `composer.submit`, or `pager.close`.
- **Binding**: one or more single-key shortcuts assigned to an action,
written as config strings such as `ctrl-t`, `alt-backspace`, or
`page-down`. Multi-step sequences such as `ctrl-x ctrl-s`, `g g`, or
leader-key flows are not part of this PR.
- **Resolution order**: context-specific config wins first, supported
global fallbacks come next, and built-in defaults fill in anything
unset.
- **Explicit unbinding**: an empty array removes an action binding in
that scope and does not fall through to a fallback binding.
- **Conflict validation**: a resolved keymap rejects duplicate active
bindings inside the same scope so one keypress cannot dispatch two
actions.
## What Changed
- Added `TuiKeymap` config support under `[tui.keymap]`, including typed
contexts/actions, key alias normalization, generated schema coverage,
and user-facing config errors.
- Added `RuntimeKeymap` resolution in `codex-rs/tui/src/keymap.rs`,
including fallback precedence, built-in defaults, explicit unbinding,
and per-context conflict validation.
- Rewired existing TUI handlers to consume resolved keymap actions
instead of directly matching hard-coded keys in each component.
- Updated key hint rendering and footer/pager/list surfaces so displayed
shortcuts follow the resolved keymap.
- Kept onboarding shortcuts fixed in
`codex-rs/tui/src/onboarding/keys.rs` instead of exposing them through
`[tui.keymap]`.
## Validation
The branch includes focused coverage for config parsing, key
normalization, runtime fallback resolution, explicit unbinding,
duplicate-key conflict validation, default keymap consistency,
onboarding startup key behavior, and UI hint snapshots affected by
resolved key bindings.
## 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