fix: record Linux process birth from kernel ticks

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/services/hot-restart.test.ts

@@ -89,18 +89,20 @@ describe("hot-restart path compatibility", () => {
     ).not.toBeNull();
   });
 
-  it("reads Linux process start time from proc metadata", async () => {
+  it("reads Linux process birth from kernel ticks rather than proc directory metadata", async () => {
     await expect(
       readProcessStartedAt(123, {
         platform: "linux",
-        stat: async (target) => {
-          expect(target).toBe("/proc/123");
-          return {
-            ctimeMs: Date.parse("2026-08-01T01:00:00.123Z"),
-          };
+        linuxProcessStart: {
+          clockTicksPerSecond: 100,
+          readFile: (target) => target === "/proc/stat"
+            ? `btime ${Date.parse("2026-08-01T01:00:00.000Z") / 1000}\n`
+            : target === "/proc/123/stat"
+              ? `123 (runner) S ${Array(18).fill("0").join(" ")} 123\n`
+              : (() => { throw new Error("Unexpected proc read"); })(),
         },
       }),
-    ).resolves.toBe("2026-08-01T01:00:00.123Z");
+    ).resolves.toBe("2026-08-01T01:00:01.230Z");
   });
 
   it("reads macOS process start time through ps", async () => {

server/src/services/hot-restart.ts

@@ -1,6 +1,7 @@
 import { execFile } from "node:child_process";
 import fs from "node:fs/promises";
 import path from "node:path";
+import { readLinuxProcessStartedAt, type LinuxProcessStartOptions } from "@paperclipai/paperclip-runner";
 import {
   resolvePaperclipHomeDir,
   resolvePaperclipInstanceId,
@@ -14,7 +15,6 @@ const HOT_RESTART_LOCK_STALE_MS = 30_000;
 const HOT_RESTART_LOCK_TIMEOUT_MS = 10_000;
 
 type ProcessCommandRunner = (command: string, args: string[]) => Promise<string>;
-type ProcessStatReader = (target: string) => Promise<{ ctimeMs: number }>;
 
 export type HotRestartIntentRun = {
   runId: string;
@@ -178,17 +178,15 @@ export async function readProcessStartedAt(
   pid: number,
   options: {
     platform?: NodeJS.Platform;
-    stat?: ProcessStatReader;
+    linuxProcessStart?: LinuxProcessStartOptions;
     runCommand?: ProcessCommandRunner;
   } = {},
 ) {
   const platform = options.platform ?? process.platform;
-  const stat = options.stat ?? fs.stat;
   const runCommand = options.runCommand ?? runProcessCommand;
 
   if (platform === "linux") {
-    const processStat = await stat(`/proc/${pid}`);
-    return new Date(processStat.ctimeMs).toISOString();
+    return readLinuxProcessStartedAt(pid, options.linuxProcessStart);
   }
 
   if (["darwin", "freebsd", "openbsd", "aix", "sunos"].includes(platform)) {