feat: add /command autocomplete (#317)

Add interactive slash‑command autocomplete & navigation in chat input

    Description
This PR enhances the chat input component by adding first‑class support
for slash commands (/help, /clear, /compact, etc.)
    with:

* **Live filtering:** As soon as the user types leading `/`, a list of
matching commands is shown below the prompt.
* **Arrow‑key navigation:** Up/Down arrows cycle through suggestions.
* **Enter to autocomplete:** Pressing Enter on a partial command will
fill it (without submitting) so you can add
    arguments or simply press Enter again to execute.
* **Type‑safe registry:** A new `slash‑commands.ts` file declares all
supported commands in one place, along with
    TypeScript types to prevent drift.
* **Validation:** Only registered commands will ever autocomplete or be
suggested; unknown single‑word slash inputs still
    show an “Invalid command” system message.
        * **Automated tests:**
            * Unit tests for the command registry and prefix filtering

            * Existing tests continue passing with no regressions

    Motivation
Slash commands provide a quick, discoverable way to control the agent
(clearing history, compacting context, opening overlays,
etc.). Before, users had to memorize the exact command or rely on the
generic /help list—autocomplete makes them far more
    accessible and reduces typos.

    Changes

* `src/utils/slash‑commands.ts` – defines `SlashCommand` and exports a
flat list of supported commands + descriptions
        * `terminal‑chat‑input.tsx`
            * Import and type the command registry

* Render filtered suggestions under the prompt when input starts with
`/`

* Hook into `useInput` to handle Up/Down and Enter for selection & fill

* Flag to swallow the first Enter (autocomplete) and only submit on the
next
* Updated tests in `tests/slash‑commands.test.ts` to cover registry
contents and filtering logic
        * Removed old JS version and fixed stray `@ts‑expect‑error`

    How to test locally

        1. Type `/` in the prompt—you should see matching commands.
2. Use arrows to move the highlight, press Enter to fill, then Enter
again to execute.
3. Run the full test suite (`npm test`) to verify no regressions.

    Notes

* Future work could include fuzzy matching, paging long lists, or more
visual styling.
* This change is purely additive and does not affect non‑slash inputs or
existing slash handlers.

---------

Co-authored-by: Fouad Matin <169186268+fouad-openai@users.noreply.github.com>
Co-authored-by: Thibault Sottiaux <tibo@openai.com>

codex-cli/src/utils/slash-commands.ts

@@ -0,0 +1,27 @@
+// Defines the available slash commands and their descriptions.
+// Used for autocompletion in the chat input.
+export interface SlashCommand {
+  command: string;
+  description: string;
+}
+
+export const SLASH_COMMANDS: Array<SlashCommand> = [
+  {
+    command: "/clear",
+    description: "Clear conversation history and free up context",
+  },
+  {
+    command: "/clearhistory",
+    description: "Clear command history",
+  },
+  {
+    command: "/compact",
+    description:
+      "Clear conversation history but keep a summary in context. Optional: /compact [instructions for summarization]",
+  },
+  { command: "/history", description: "Open command history" },
+  { command: "/help", description: "Show list of commands" },
+  { command: "/model", description: "Open model selection panel" },
+  { command: "/approval", description: "Open approval mode selection panel" },
+  { command: "/bug", description: "Generate a prefilled GitHub bug report" },
+];