diff --git a/scripts/control-ui-i18n.ts b/scripts/control-ui-i18n.ts
index 451dbc4df52..f7a23c58e64 100644
--- a/scripts/control-ui-i18n.ts
+++ b/scripts/control-ui-i18n.ts
@@ -103,6 +103,7 @@ const DEFAULT_BATCH_CHAR_BUDGET = 2_000;
 const TRANSLATE_MAX_ATTEMPTS = 2;
 const TRANSLATE_BASE_DELAY_MS = 15_000;
 const DEFAULT_PROMPT_TIMEOUT_MS = 120_000;
+const RUN_PROCESS_OUTPUT_MAX_CHARS = 1024 * 1024;
 const PROGRESS_HEARTBEAT_MS = 30_000;
 const ENV_PROVIDER = "OPENCLAW_CONTROL_UI_I18N_PROVIDER";
 const ENV_MODEL = "OPENCLAW_CONTROL_UI_I18N_MODEL";
@@ -950,10 +951,44 @@ function estimateBatchChars(items: readonly TranslationBatchItem[]): number {
 type RunProcessOptions = {
   cwd?: string;
   input?: string;
+  maxOutputChars?: number;
   rejectOnFailure?: boolean;
 };
 
-async function runProcess(
+type ProcessOutputCapture = {
+  text: string;
+  truncatedChars: number;
+};
+
+function resolveRunProcessOutputLimit(options: RunProcessOptions): number {
+  const value = options.maxOutputChars;
+  if (typeof value !== "number" || !Number.isFinite(value) || value <= 0) {
+    return RUN_PROCESS_OUTPUT_MAX_CHARS;
+  }
+  return Math.max(1, Math.floor(value));
+}
+
+export function appendBoundedProcessOutput(
+  capture: ProcessOutputCapture,
+  chunk: unknown,
+  maxChars: number,
+): ProcessOutputCapture {
+  const nextText = capture.text + String(chunk);
+  if (nextText.length <= maxChars) {
+    return { text: nextText, truncatedChars: capture.truncatedChars };
+  }
+  const truncatedChars = capture.truncatedChars + nextText.length - maxChars;
+  return { text: nextText.slice(-maxChars), truncatedChars };
+}
+
+function formatProcessOutput(capture: ProcessOutputCapture): string {
+  if (capture.truncatedChars === 0) {
+    return capture.text;
+  }
+  return `[output truncated ${capture.truncatedChars} chars; showing tail]\n${capture.text}`;
+}
+
+export async function runProcess(
   executable: string,
   args: string[],
   options: RunProcessOptions = {},
@@ -965,13 +1000,14 @@ async function runProcess(
       stdio: ["pipe", "pipe", "pipe"],
     });
 
-    let stdout = "";
-    let stderr = "";
+    const maxOutputChars = resolveRunProcessOutputLimit(options);
+    let stdout: ProcessOutputCapture = { text: "", truncatedChars: 0 };
+    let stderr: ProcessOutputCapture = { text: "", truncatedChars: 0 };
     child.stdout.on("data", (chunk) => {
-      stdout += String(chunk);
+      stdout = appendBoundedProcessOutput(stdout, chunk, maxOutputChars);
     });
     child.stderr.on("data", (chunk) => {
-      stderr += String(chunk);
+      stderr = appendBoundedProcessOutput(stderr, chunk, maxOutputChars);
     });
     child.once("error", reject);
     if (options.input !== undefined) {
@@ -980,13 +1016,25 @@ async function runProcess(
       child.stdin.end();
     }
     child.once("close", (code) => {
+      const stdoutText = formatProcessOutput(stdout);
+      const stderrText = formatProcessOutput(stderr);
       if ((code ?? 1) !== 0 && options.rejectOnFailure) {
         reject(
-          new Error(`${executable} ${args.join(" ")} failed: ${stderr.trim() || stdout.trim()}`),
+          new Error(
+            `${executable} ${args.join(" ")} failed: ${stderrText.trim() || stdoutText.trim()}`,
+          ),
         );
         return;
       }
-      resolve({ code: code ?? 1, stderr, stdout });
+      if ((code ?? 1) === 0 && stdout.truncatedChars > 0) {
+        reject(
+          new Error(
+            `${executable} ${args.join(" ")} produced more than ${maxOutputChars} stdout chars`,
+          ),
+        );
+        return;
+      }
+      resolve({ code: code ?? 1, stderr: stderrText, stdout: stdout.text });
     });
   });
 }
diff --git a/scripts/test-projects.test-support.mjs b/scripts/test-projects.test-support.mjs
index 11c17bd6a7e..513de73eb8f 100644
--- a/scripts/test-projects.test-support.mjs
+++ b/scripts/test-projects.test-support.mjs
@@ -361,6 +361,7 @@ const TOOLING_SOURCE_TEST_TARGETS = new Map([
   ["scripts/check-changed.mjs", ["test/scripts/changed-lanes.test.ts"]],
   ["scripts/check-deadcode-unused-files.mjs", ["test/scripts/check-deadcode-unused-files.test.ts"]],
   ["scripts/ci-docker-pull-retry.sh", ["test/scripts/ci-docker-pull-retry.test.ts"]],
+  ["scripts/control-ui-i18n.ts", ["test/scripts/control-ui-i18n.test.ts"]],
   [
     "scripts/deadcode-unused-files.allowlist.mjs",
     ["test/scripts/check-deadcode-unused-files.test.ts"],
@@ -432,6 +433,7 @@ const TOOLING_TEST_TARGETS = new Map([
     ["test/scripts/check-deadcode-unused-files.test.ts"],
   ],
   ["test/scripts/ci-docker-pull-retry.test.ts", ["test/scripts/ci-docker-pull-retry.test.ts"]],
+  ["test/scripts/control-ui-i18n.test.ts", ["test/scripts/control-ui-i18n.test.ts"]],
   ["test/scripts/docker-build-helper.test.ts", ["test/scripts/docker-build-helper.test.ts"]],
   ["test/scripts/docker-e2e-helper-cli.test.ts", ["test/scripts/docker-e2e-helper-cli.test.ts"]],
   ["test/scripts/kova-ci-summary.test.ts", ["test/scripts/kova-ci-summary.test.ts"]],
diff --git a/test/scripts/control-ui-i18n.test.ts b/test/scripts/control-ui-i18n.test.ts
new file mode 100644
index 00000000000..eabc672312b
--- /dev/null
+++ b/test/scripts/control-ui-i18n.test.ts
@@ -0,0 +1,40 @@
+import process from "node:process";
+import { describe, expect, it } from "vitest";
+import { appendBoundedProcessOutput, runProcess } from "../../scripts/control-ui-i18n.ts";
+
+describe("control-ui-i18n process runner", () => {
+  it("keeps a bounded process output tail", () => {
+    const first = appendBoundedProcessOutput({ text: "", truncatedChars: 0 }, "abcdef", 5);
+    const second = appendBoundedProcessOutput(first, "ghij", 5);
+
+    expect(first).toEqual({ text: "bcdef", truncatedChars: 1 });
+    expect(second).toEqual({ text: "fghij", truncatedChars: 5 });
+  });
+
+  it("bounds failure diagnostics to the newest output", async () => {
+    await expect(
+      runProcess(
+        process.execPath,
+        [
+          "-e",
+          [
+            "process.stderr.write('stderr-begin-' + 'x'.repeat(128) + '-stderr-end', () => process.exit(2));",
+          ].join(" "),
+        ],
+        { maxOutputChars: 64, rejectOnFailure: true },
+      ),
+    ).rejects.toThrow(/output truncated[\s\S]*stderr-end/u);
+  });
+
+  it("rejects successful commands before returning truncated stdout", async () => {
+    await expect(
+      runProcess(
+        process.execPath,
+        ["-e", "process.stdout.write('x'.repeat(128), () => process.exit(0));"],
+        {
+          maxOutputChars: 12,
+        },
+      ),
+    ).rejects.toThrow("produced more than 12 stdout chars");
+  });
+});
diff --git a/test/scripts/test-projects.test.ts b/test/scripts/test-projects.test.ts
index 8037219ff81..70ec10801fd 100644
--- a/test/scripts/test-projects.test.ts
+++ b/test/scripts/test-projects.test.ts
@@ -207,6 +207,13 @@ describe("scripts/test-projects changed-target routing", () => {
     });
   });
 
+  it("routes control UI i18n script changes through its regression test", () => {
+    expect(resolveChangedTestTargetPlan(["scripts/control-ui-i18n.ts"])).toEqual({
+      mode: "targets",
+      targets: ["test/scripts/control-ui-i18n.test.ts"],
+    });
+  });
+
   it("routes group visible reply config changes through channel delivery regressions", () => {
     expect(
       resolveChangedTestTargetPlan([