fix: only allow going up in history when not already in history if input is empty (#654)

\+ cleanup below input help to be "ctrl+c to exit | "/" to see commands
| enter to send" now that we have command autocompletion
\+ minor other drive-by code cleanups

---------

Signed-off-by: Thibault Sottiaux <tibo@openai.com>

codex-cli/tests/terminal-chat-input-multiline.test.tsx

@@ -24,35 +24,6 @@ vi.mock("../src/utils/input-utils.js", () => ({
 }));
 
 describe("TerminalChatInput multiline functionality", () => {
-  it("renders the multiline editor component", async () => {
-    const props: ComponentProps<typeof TerminalChatInput> = {
-      isNew: false,
-      loading: false,
-      submitInput: () => {},
-      confirmationPrompt: null,
-      explanation: undefined,
-      submitConfirmation: () => {},
-      setLastResponseId: () => {},
-      setItems: () => {},
-      contextLeftPercent: 50,
-      openOverlay: () => {},
-      openDiffOverlay: () => {},
-      openModelOverlay: () => {},
-      openApprovalOverlay: () => {},
-      openHelpOverlay: () => {},
-      onCompact: () => {},
-      interruptAgent: () => {},
-      active: true,
-      thinkingSeconds: 0,
-    };
-
-    const { lastFrameStripped } = renderTui(<TerminalChatInput {...props} />);
-    const frame = lastFrameStripped();
-
-    // Check that the help text mentions shift+enter for new line
-    expect(frame).toContain("shift+enter for new line");
-  });
-
   it("allows multiline input with shift+enter", async () => {
     const submitInput = vi.fn();