Currently there is no bound on the length of a user message submitted in
the TUI or through the app server interface. That means users can paste
many megabytes of text, which can lead to bad performance, hangs, and
crashes. In extreme cases, it can lead to a [kernel
panic](https://github.com/openai/codex/issues/12323).
This PR limits the length of a user input to 2**20 (about 1M)
characters. This value was chosen because it fills the entire context
window on the latest models, so accepting longer inputs wouldn't make
sense anyway.
Summary
- add a shared `MAX_USER_INPUT_TEXT_CHARS` constant in codex-protocol
and surface it in TUI and app server code
- block oversized submissions in the TUI submit flow and emit error
history cells when validation fails
- reject heavy app-server requests with JSON-RPC `-32602` and structured
`input_too_large` data, plus document the behavior
Testing
- ran the IDE extension with this change and verified that when I
attempt to paste a user message that's several MB long, it correctly
reports an error instead of crashing or making my computer hot.
- [x] Support `/apps` slash command to browse the apps in tui.
- [x] Support inserting apps to prompt using `$`.
- [x] Lots of simplification/renaming from connectors to apps.
Summary
- Preserve `text_elements` through custom prompt argument parsing and
expansion (named and numeric placeholders).
- Translate text element ranges through Shlex parsing using sentinel
substitution, and rehydrate text + element ranges per arg.
- Drop image attachments when their placeholder does not survive prompt
expansion, keeping attachments consistent with rendered elements.
- Mirror changes in TUI2 and expand tests for prompt parsing/expansion
edge cases.
Tests
- placeholders with spaces as single tokens (positional + key=value,
quoted + unquoted),
- prompt expansion with image placeholders,
- large paste + image arg combinations,
- unused image arg dropped after expansion.
## Summary
- Make `TextElement` placeholders private and add a text-backed accessor
to avoid assuming `Some`.
- Since they are optional in the protocol, we want to make sure any
accessors properly handle the None case (getting the placeholder using
the byte range in the text)
- Preserve placeholders during protocol/app-server conversions using the
accessor fallback.
- Update TUI composer/remap logic and tests to use the new
constructor/accessor.
1. Skills load once in core at session start; the cached outcome is
reused across core and surfaced to TUI via SessionConfigured.
2. TUI detects explicit skill selections, and core injects the matching
SKILL.md content into the turn when a selected skill is present.
Adds a new ItemStarted event and delivers UserMessage as the first item
type (more to come).
Renames `InputItem` to `UserInput` considering we're using the `Item`
suffix for actual items.
