Mirror amicode #929/#964: the 3-arg promptDesignPlaceholder translate callback

packages/app/src/components/prompt-input-v2.tsx

@@ -145,7 +145,16 @@ export function usePromptInputV2Controller(props: PromptInputV2ControllerProps):
       t: (key, params) => language.t(key as Parameters<typeof language.t>[0], params as never),
     }),
   )
-  const designPlaceholder = () => promptDesignPlaceholder(mode(), placeholder())
+  // The design placeholder takes the translate callback: the helper calls it
+  // in the non-shell branch, so the 2-arg form passes undefined there —
+  // minified "n is not a function" on every non-shell composer render.
+  // #929 (59b447e7) fixed this amicode-side; the fork→overlay sync ff7b69c8
+  // regressed it back to the 2-arg call. Mirrored to the sync source per
+  // harmoniqs/amicode#964 so the next sync brings the fix, not the regression.
+  const designPlaceholder = () =>
+    promptDesignPlaceholder(mode(), placeholder(), (key, params) =>
+      language.t(key as Parameters<typeof language.t>[0], params as never),
+    )
 
   const historyComments = () => {
     const byID = new Map(comments.all().map((item) => [`${item.file}\n${item.id}`, item] as const))

packages/app/src/components/prompt-input/placeholder.test.ts

@@ -1,5 +1,37 @@
 import { describe, expect, test } from "bun:test"
-import { promptPlaceholder } from "./placeholder"
+import { promptDesignPlaceholder, promptPlaceholder } from "./placeholder"
+
+// harmoniqs/amicode#964 — the design placeholder takes the translate callback
+// (the #929 contract, mirrored to the sync source). A 2-arg call passes
+// undefined as the translate callback, which the helper calls in the
+// non-shell branch: the "n is not a function" failure Aaron hit live
+// post-cutover 2026-09-10.
+describe("promptDesignPlaceholder", () => {
+  const t = (key: string, params?: Record<string, string>) => {
+    let out = key
+    for (const [k, v] of Object.entries(params ?? {})) out = out.split(`{{${k}}}`).join(v)
+    return out
+  }
+
+  test("returns the shell placeholder verbatim in shell mode", () => {
+    expect(promptDesignPlaceholder("shell", "git status", t)).toBe("git status")
+  })
+
+  test("translates through the callback in normal mode", () => {
+    expect(promptDesignPlaceholder("normal", "fallback", t)).toBe(
+      "ui.promptInput.placeholder.normal",
+    )
+  })
+
+  test("the translate callback is REQUIRED — the regressed 2-arg call throws", () => {
+    expect(() =>
+      (promptDesignPlaceholder as unknown as (mode: "normal", placeholder: string) => string)(
+        "normal",
+        "fallback",
+      ),
+    ).toThrow(/is not a function/)
+  })
+})
 
 describe("promptPlaceholder", () => {
   const t = (key: string, params?: Record<string, string>) => `${key}${params?.example ? `:${params.example}` : ""}`

packages/app/src/components/prompt-input/placeholder.ts

@@ -14,8 +14,17 @@ export function promptPlaceholder(input: PromptPlaceholderInput) {
   return input.t("prompt.placeholder.normal", { example: input.example })
 }
 
-export function promptDesignPlaceholder(mode: PromptPlaceholderInput["mode"], placeholder: string) {
+// Mirrored from amicode's overlay (upstream v1.18.29 contract): the design
+// placeholder takes the translate callback and calls it in the non-shell
+// branch — a 2-arg call passes undefined there and throws "n is not a
+// function" on every non-shell composer render. The amicode hard-coded brand
+// line ("Ask Amico anything, ...") is superseded by the translated key the
+// ui locales already carry. See harmoniqs/amicode#929/#964.
+export function promptDesignPlaceholder(
+  mode: PromptPlaceholderInput["mode"],
+  placeholder: string,
+  t: PromptPlaceholderInput["t"],
+) {
   if (mode === "shell") return placeholder
-  // amicode: brand the composer prompt
-  return "Ask Amico anything, / for commands, @ for context..."
+  return t("ui.promptInput.placeholder.normal", { slash: "/", at: "@" })
 }