Preserve the owned Pi runner across controller-only E2E restart

Separate durable runner preservation from final process retirement. Bind
restart preservation to the public run identity and observed ancestry, and
drain every retained owner after the replacement controller shuts down.

Co-authored-by: Paperclip <noreply@paperclip.ing>

tests/runner-e2e/server.ts

@@ -1,3 +1,4 @@
+import { parseRestartRunnerIdentity, type RestartRunnerIdentity } from "./process-tree-owner.js";
 import { usesInstalledCli, verifyInstalledCli } from "./installed-cli.js";
 import { runnerMatrix } from "./catalog.js";
 import { createRunnerE2EServerStopper, runnerE2EServerDetached } from "./server-stop.js";
@@ -229,6 +230,7 @@ async function waitForHealthToStop() {
 
 interface RestartRequest {
   requestId: string;
+  preserveRunner?: RestartRunnerIdentity;
 }
 
 async function readRestartRequest(): Promise<RestartRequest | null> {
@@ -254,7 +256,8 @@ async function readRestartRequest(): Promise<RestartRequest | null> {
   ) {
     return null;
   }
-  return { requestId };
+  const preserveRunner = (value as { preserveRunner?: unknown }).preserveRunner;
+  return { requestId, ...(preserveRunner === undefined ? {} : { preserveRunner: parseRestartRunnerIdentity(preserveRunner) }) };
 }
 
 async function writeRestartAck(
@@ -276,12 +279,13 @@ async function writeRestartAck(
   await rename(temporaryAckPath, restartAckPath);
 }
 
-async function restartServer(requestId: string) {
+async function restartServer({ requestId, preserveRunner }: RestartRequest) {
   activeRestartRequestId = requestId;
   appendLog(`\nRestart request ${requestId}: stopping Paperclip\n`);
   const previous = child;
   if (!previous) throw new Error("No Paperclip server is available to restart");
-  await stopServer(previous);
+  if (preserveRunner) await stopServer.forRestart(previous, preserveRunner);
+  else await stopServer(previous);
   if (child === previous) child = null;
   // Do not mistake an orphaned old server for a healthy replacement. The port
   // must stop answering before the next launcher is allowed to start.
@@ -331,13 +335,12 @@ async function supervise() {
     const request = await readRestartRequest();
     if (request && request.requestId !== lastRestartRequestId) {
       lastRestartRequestId = request.requestId;
-      await restartServer(request.requestId);
+      await restartServer(request);
     }
     await delay(200);
   }
 
-  const running = child;
-  if (running) await stopServer(running, shutdownSignal ?? "SIGTERM");
+  await stopServer.stopAll(shutdownSignal ?? "SIGTERM");
 }
 
 let exitCode = 0;
@@ -356,15 +359,10 @@ try {
       );
     }
   }
-  const running = child;
-  if (running) {
-    try {
-      await stopServer(running);
-    } catch (stopError) {
-      appendLog(
-        `Failed to stop Paperclip after supervisor failure: ${stopError instanceof Error ? stopError.message : String(stopError)}\n`,
-      );
-    }
+  try {
+    await stopServer.stopAll();
+  } catch (stopError) {
+    appendLog(`Failed to stop Paperclip after supervisor failure: ${stopError instanceof Error ? stopError.message : String(stopError)}\n`);
   }
 }