diff --git a/server/src/__tests__/agent-instructions-service.test.ts b/server/src/__tests__/agent-instructions-service.test.ts
index 6483707b1a6..1c1811f72fb 100644
--- a/server/src/__tests__/agent-instructions-service.test.ts
+++ b/server/src/__tests__/agent-instructions-service.test.ts
@@ -620,7 +620,9 @@ describe("agent instructions service", () => {
     ]);
 
     expect(firstOutcome).toBe("waiting");
-    await fs.rm(lockPath, { recursive: true, force: true });
+    const releasedLockPath = `${lockPath}.released`;
+    await fs.rename(lockPath, releasedLockPath);
+    await fs.rm(releasedLockPath, { recursive: true, force: true });
     await expect(materialization).resolves.toMatchObject({
       materialization: { action: "added" },
     });
@@ -667,7 +669,7 @@ describe("agent instructions service", () => {
   });
 
   it.skipIf(process.platform !== "linux")(
-    "does not evict a live lock with a stale heartbeat when identity falls back to another scheme",
+    "does not evict a live lock with a stale heartbeat when its identity scheme is unavailable",
     async () => {
       const paperclipHome = await makeTempDir("paperclip-agent-instructions-marker-fallback-");
       cleanupDirs.add(paperclipHome);
@@ -693,7 +695,7 @@ describe("agent instructions service", () => {
         `${JSON.stringify({
           pid: process.pid,
           token,
-          processStartMarker: "ps:same-live-process-in-another-format",
+          processStartMarker: "unavailable:same-live-process-in-another-format",
           createdAt: new Date().toISOString(),
         })}\n`,
         "utf8",
@@ -710,13 +712,56 @@ describe("agent instructions service", () => {
       ]);
 
       expect(firstOutcome).toBe("waiting");
-      await fs.rm(lockPath, { recursive: true, force: true });
+      const releasedLockPath = `${lockPath}.released`;
+      await fs.rename(lockPath, releasedLockPath);
+      await fs.rm(releasedLockPath, { recursive: true, force: true });
       await expect(materialization).resolves.toMatchObject({
         materialization: { action: "added" },
       });
     },
   );
 
+  it.skipIf(process.platform !== "linux")(
+    "recovers a reused PID when the owner recorded the ps fallback scheme",
+    async () => {
+      const paperclipHome = await makeTempDir("paperclip-agent-instructions-ps-reused-pid-");
+      cleanupDirs.add(paperclipHome);
+      process.env.PAPERCLIP_HOME = paperclipHome;
+      process.env.PAPERCLIP_INSTANCE_ID = "test-instance";
+      const svc = agentInstructionsService();
+      const agent = makeAgent({});
+      const managedRoot = path.join(
+        paperclipHome,
+        "instances",
+        "test-instance",
+        "companies",
+        "company-1",
+        "agents",
+        "agent-1",
+        "instructions",
+      );
+      const lockPath = `${managedRoot}.paperclip-materialize.lock`;
+      const token = "00000000-0000-4000-8000-000000000000";
+      await fs.mkdir(lockPath, { recursive: true });
+      await fs.writeFile(
+        path.join(lockPath, "owner.json"),
+        `${JSON.stringify({
+          pid: process.pid,
+          token,
+          processStartMarker: "ps:not-the-current-process-start",
+          createdAt: new Date().toISOString(),
+        })}\n`,
+        "utf8",
+      );
+      await fs.writeFile(path.join(lockPath, `heartbeat-${token}`), "", "utf8");
+
+      const result = await svc.materializeManagedBundle(agent, { "AGENTS.md": "# Stock\n" });
+
+      expect(result.materialization.action).toBe("added");
+      await expect(fs.stat(lockPath)).rejects.toThrow();
+    },
+  );
+
   it("canonicalizes line endings and ignores transient files when classifying drift", async () => {
     const paperclipHome = await makeTempDir("paperclip-agent-instructions-canonical-");
     cleanupDirs.add(paperclipHome);
diff --git a/server/src/services/agent-instructions.ts b/server/src/services/agent-instructions.ts
index f7b165d806f..d7c9a8997b5 100644
--- a/server/src/services/agent-instructions.ts
+++ b/server/src/services/agent-instructions.ts
@@ -189,9 +189,20 @@ function isProcessAlive(pid: number): boolean {
   }
 }
 
-async function processStartMarker(pid: number): Promise<string | null> {
+type ProcessStartMarkerScheme = "linux" | "ps";
+
+function processStartMarkerScheme(marker: string): ProcessStartMarkerScheme | null {
+  if (marker.startsWith("linux:")) return "linux";
+  if (marker.startsWith("ps:")) return "ps";
+  return null;
+}
+
+async function processStartMarker(
+  pid: number,
+  preferredScheme?: ProcessStartMarkerScheme,
+): Promise<string | null> {
   if (!isProcessAlive(pid)) return null;
-  if (process.platform === "linux") {
+  if (process.platform === "linux" && preferredScheme !== "ps") {
     try {
       const stat = await fs.readFile(`/proc/${pid}/stat`, "utf8");
       const commandEnd = stat.lastIndexOf(")");
@@ -203,8 +214,11 @@ async function processStartMarker(pid: number): Promise<string | null> {
     } catch {
       // Fall through to ps for non-standard procfs environments.
     }
+    if (preferredScheme === "linux") return null;
   }
 
+  if (preferredScheme === "linux") return null;
+
   return new Promise((resolve) => {
     execFile(
       "ps",
@@ -287,7 +301,8 @@ async function removeStaleManagedBundleLock(lockPath: string): Promise<boolean>
       const recordedStart = typeof owner.processStartMarker === "string"
         ? owner.processStartMarker
         : null;
-      const currentStart = await processStartMarker(pid);
+      const recordedScheme = recordedStart ? processStartMarkerScheme(recordedStart) : null;
+      const currentStart = await processStartMarker(pid, recordedScheme ?? undefined);
       if (
         recordedStart
         && currentStart