fix(process): preserve terminal cell widths during normalization (#4142)

src/process/capture/TerminalRenderer.test.ts

@@ -100,6 +100,27 @@ it("trims only after normalization sees the full-width row", async () => {
   expect(frames[0]?.lines[0]).toBe("pid <pid>");
 });
 
+it.each([
+  { data: "界", cells: 2 },
+  // The pinned xterm Unicode table treats this emoji as one cell.
+  { data: "😀", cells: 1 },
+  { data: "e\u0301", cells: 1 },
+  { data: "ab", cells: 2 },
+])(
+  "normalizes the terminal cells of $data without extra padding",
+  async ({ data, cells }) => {
+    const { frames } = await renderFrames(data, (value) =>
+      value.replaceAll(" ", "_"),
+    );
+    expect(frames[0]?.lines).toEqual([
+      data + "_".repeat(20 - cells),
+      "_".repeat(20),
+      "_".repeat(20),
+      "_".repeat(20),
+    ]);
+  },
+);
+
 it("omits rendered frames with unknown expanded size and keeps later bounded states", async () => {
   const renderer = new TerminalRenderer({
     columns: 10,

src/process/capture/TerminalRenderer.ts

@@ -131,14 +131,14 @@ export class TerminalRenderer {
     let bytes = 0;
     for (let row = 0; row < this.#terminal.rows; row += 1) {
       const line = buffer.getLine(buffer.viewportY + row);
-      const paddedLine = (
-        line?.translateToString(false, 0, this.#terminal.cols) ?? ""
-      ).padEnd(this.#terminal.cols, " ");
+      const renderedLine =
+        line?.translateToString(false, 0, this.#terminal.cols) ??
+        " ".repeat(this.#terminal.cols);
       const trailingSpaceBytes = Buffer.byteLength(
-        paddedLine.match(TRAILING_SPACES)?.[0] ?? "",
+        renderedLine.match(TRAILING_SPACES)?.[0] ?? "",
       );
       const normalized = this.options.normalize(
-        paddedLine,
+        renderedLine,
         Math.min(Number.MAX_SAFE_INTEGER, remainingBytes + trailingSpaceBytes),
       );
       if (normalized.state === "over_budget") {

tests/boundary/process/processCaptureTerminal.test.ts

@@ -7,6 +7,38 @@ import { itWithCaptureCapability } from "./processCaptureCapability.js";
 import { captureProcessScenario } from "../../../src/process/capture/ProcessHarness.js";
 import { parseProcessScenario } from "../../../src/domain/process/processScenario.js";
 
+itWithCaptureCapability(
+  "normalizes wide terminal cells without inventing blank cells",
+  async () => {
+    const result = await captureProcessScenario(
+      parseProcessScenario({
+        executable: process.execPath,
+        arguments: ["-e", 'process.stdout.write("界")'],
+        terminal: { columns: 4, rows: 1, scrollback: 0 },
+        normalization: {
+          patterns: [{ pattern: " ", replacement: "_" }],
+        },
+      }),
+    );
+    if (!result.ok) throw result.error;
+    expect(
+      result.value.frames
+        .map(({ raw_data, data }) => raw_data ?? data)
+        .join(""),
+    ).toBe("界");
+    expect(result.value.rendered_frames.at(-1)).toMatchObject({
+      columns: 4,
+      cursor_x: 2,
+      lines: ["界__"],
+    });
+    expect(result.value.cleanup).toMatchObject({
+      owned_process_group: "verified",
+      temporary_root: "removed",
+    });
+  },
+  20_000,
+);
+
 itWithCaptureCapability(
   "captures one command's terminal output, selected files, and owned cleanup",
   async () => {