diff --git a/scripts/lib/mountinfo-path.mjs b/scripts/lib/mountinfo-path.mjs
new file mode 100644
index 000000000000..9908ce8410ce
--- /dev/null
+++ b/scripts/lib/mountinfo-path.mjs
@@ -0,0 +1,17 @@
+// Decodes octal-escaped path fields in Linux procfs mount tables.
+
+// The kernel escapes space, tab, newline, and backslash as \040, \011, \012, and
+// \134 in the mount-root and mount-point fields of /proc/self/mountinfo, so a
+// verbatim comparison silently fails to match any path containing one of them.
+const MOUNT_PATH_OCTAL_ESCAPE_RE = /\\([0-7]{3})/g;
+
+/**
+ * Decode a procfs mount-table path field into its real path.
+ * @param {string} value
+ * @returns {string}
+ */
+export function decodeMountInfoPath(value) {
+  return value.replace(MOUNT_PATH_OCTAL_ESCAPE_RE, (_match, octal) =>
+    String.fromCharCode(Number.parseInt(octal, 8)),
+  );
+}
diff --git a/scripts/tsdown-build.mts b/scripts/tsdown-build.mts
index e14d1055acf3..c621dae0faad 100644
--- a/scripts/tsdown-build.mts
+++ b/scripts/tsdown-build.mts
@@ -12,6 +12,7 @@ import fs from "node:fs";
 import path from "node:path";
 import { pathToFileURL } from "node:url";
 import { BUNDLED_PLUGIN_PATH_PREFIX } from "./lib/bundled-plugin-paths.mjs";
+import { decodeMountInfoPath } from "./lib/mountinfo-path.mjs";
 import { parsePositiveInt } from "./lib/numeric-options.mjs";
 import { assertRealOutputRoot } from "./lib/output-root-guard.mjs";
 import {
@@ -502,11 +503,18 @@ function resolveCgroupMountPoints(params: MemoryLimitParams = {}) {
   for (const line of rawMountinfo.split("\n")) {
     // mountinfo separates its variable optional fields from the fstype with a lone "-".
     const [fields, describe] = line.split(" - ");
-    const [, , , root, mountPoint] = (fields ?? "").split(" ");
+    // mountinfo fields 4 and 5 are the mount root and mount point.
+    const mountFields = (fields ?? "").split(" ");
+    const rawRoot = mountFields[3];
+    const rawMountPoint = mountFields[4];
     const [fsType, , superOptions] = (describe ?? "").split(" ");
-    if (!mountPoint || !root) {
+    if (!rawMountPoint || !rawRoot) {
       continue;
     }
+    // The kernel escapes space, tab, newline, and backslash in these two fields, so
+    // matching them verbatim would miss any cgroup path containing one of them.
+    const root = decodeMountInfoPath(rawRoot);
+    const mountPoint = decodeMountInfoPath(rawMountPoint);
     if (fsType === "cgroup2") {
       unified.push({ mountPoint, root });
     } else if (fsType === "cgroup" && (superOptions ?? "").split(",").includes("memory")) {
diff --git a/test/scripts/tsdown-build.test.ts b/test/scripts/tsdown-build.test.ts
index 6d99a789b349..99a6acc291e7 100644
--- a/test/scripts/tsdown-build.test.ts
+++ b/test/scripts/tsdown-build.test.ts
@@ -453,6 +453,38 @@ describe("resolveTsdownBuildInvocation", () => {
     expect(result.options.env.NODE_OPTIONS).toBe("--max-old-space-size=4352");
   });
 
+  it("caps the tsdown heap when the cgroup mount point is octal-escaped in mountinfo", () => {
+    const slicePath = "/user.slice/user-999.slice/user@999.service";
+    // The kernel escapes a space in the mount point as \040. Matching the field
+    // verbatim misses this mount, and heap sizing silently falls back to host memory.
+    const cgroupFiles = new Map([
+      ["/proc/self/cgroup", `0::${slicePath}/app.slice/openclaw-main-update.service\n`],
+      [
+        "/proc/self/mountinfo",
+        "30 25 0:26 / /sys/fs/cgroup\\040dir rw,nosuid - cgroup2 cgroup2 rw\n",
+      ],
+      [`/sys/fs/cgroup dir${slicePath}/memory.high`, `${5 * 1024 * 1024 * 1024}\n`],
+    ]);
+
+    const result = resolveTsdownBuildInvocation({
+      nodeExecPath: "/usr/bin/node",
+      npmExecPath: "/tmp/pnpm.cjs",
+      env: {},
+      fs: {
+        readFileSync(filePath: string) {
+          const contents = cgroupFiles.get(filePath);
+          if (contents === undefined) {
+            throw new Error(`ENOENT: ${filePath}`);
+          }
+          return contents;
+        },
+      },
+    });
+
+    // 5 GiB slice budget minus the 768 MiB build headroom.
+    expect(result.options.env.NODE_OPTIONS).toBe("--max-old-space-size=4352");
+  });
+
   it("caps the tsdown heap when v1 controllers are co-mounted at the cgroup root", () => {
     const slicePath = "/user.slice/user-999.slice";
     // Co-mounted v1 puts memory.limit_in_bytes under the slice directly, with no