diff --git a/.changeset/proud-ants-study.md b/.changeset/proud-ants-study.md
new file mode 100644
index 000000000..2a72c6298
--- /dev/null
+++ b/.changeset/proud-ants-study.md
@@ -0,0 +1,5 @@
+---
+"@sapiom/harness": patch
+---
+
+Give the workflow registry's atomic write a per-process temp file name, so two harness instances sharing the machine-wide workflows.json cannot publish a torn file.
diff --git a/packages/harness/src/core/workflow-registry.test.ts b/packages/harness/src/core/workflow-registry.test.ts
index 3609b23af..002d11e7f 100644
--- a/packages/harness/src/core/workflow-registry.test.ts
+++ b/packages/harness/src/core/workflow-registry.test.ts
@@ -351,9 +351,39 @@ describe("WorkflowRegistry", () => {
       expect(Array.isArray(parsed)).toBe(true);
       expect(parsed).toHaveLength(1);
 
-      // The .tmp file must NOT be left behind (rename completed).
-      const tmpPath = `${registryPath}.tmp`;
-      await expect(fs.access(tmpPath)).rejects.toThrow();
+      // No temp artefact must be left behind (rename completed). The temp name
+      // carries a pid + uuid suffix, so match on the prefix rather than one
+      // fixed path — asserting a fixed name would pass even if a differently
+      // named temp file were orphaned.
+      const base = path.basename(registryPath);
+      const leftovers = (await fs.readdir(path.dirname(registryPath))).filter((name) =>
+        name.startsWith(`${base}.tmp`),
+      );
+      expect(leftovers).toEqual([]);
+    });
+
+    it("two registries sharing one path do not collide on the temp file (the path is machine-wide)", async () => {
+      // writeQueue only serializes writers inside one instance, but the default
+      // registry path is machine-wide (~/.sapiom/harness/workflows.json), so a
+      // CLI and a desktop app run two registries over the same file. With a
+      // fixed .tmp name each would write into the other's temp and rename a
+      // half-written file over the target, which load() then swallows as an
+      // empty list — silent loss of connected workflows.
+      const other = new WorkflowRegistry(registryPath);
+      await writeMarker(path.join(tmpRoot, "proj-a"), 1);
+      await writeMarker(path.join(tmpRoot, "proj-b"), 1);
+
+      await Promise.all([registry.scan(tmpRoot), other.scan(tmpRoot)]);
+
+      const parsed = JSON.parse(await fs.readFile(registryPath, "utf8")) as unknown[];
+      expect(Array.isArray(parsed)).toBe(true);
+      expect(parsed).toHaveLength(2);
+
+      const base = path.basename(registryPath);
+      const leftovers = (await fs.readdir(path.dirname(registryPath))).filter((name) =>
+        name.startsWith(`${base}.tmp`),
+      );
+      expect(leftovers).toEqual([]);
     });
 
     it("a failed persist does not poison the queue — subsequent writes succeed", async () => {
diff --git a/packages/harness/src/core/workflow-registry.ts b/packages/harness/src/core/workflow-registry.ts
index 8474bd878..6bc6892a9 100644
--- a/packages/harness/src/core/workflow-registry.ts
+++ b/packages/harness/src/core/workflow-registry.ts
@@ -9,6 +9,7 @@
  * shared app.
  */
 
+import { randomUUID } from "node:crypto";
 import * as fs from "node:fs/promises";
 import * as os from "node:os";
 import * as path from "node:path";
@@ -186,10 +187,18 @@ export class WorkflowRegistry {
     // Atomic write: write to a temp file in the same directory (so rename is
     // same-filesystem and thus atomic on POSIX), then rename over the target.
     // A crash mid-write leaves the .tmp file, not a torn workflows.json.
-    // Mirrors the pattern used by SessionManager.persist().
-    const tmpPath = `${this.registryPath}.tmp`;
-    await fs.writeFile(tmpPath, JSON.stringify(this.workflows, null, 2));
-    await fs.rename(tmpPath, this.registryPath);
+    // The temp name is per-process and unique: writeQueue only serializes
+    // writers inside one process, and this path is machine-wide, so a second
+    // harness would otherwise write into the same .tmp concurrently and the
+    // rename would publish a torn file. Mirrors SessionManager.persist().
+    const tmpPath = `${this.registryPath}.tmp-${process.pid}-${randomUUID()}`;
+    try {
+      await fs.writeFile(tmpPath, JSON.stringify(this.workflows, null, 2));
+      await fs.rename(tmpPath, this.registryPath);
+    } catch (err) {
+      await fs.rm(tmpPath, { force: true }).catch(() => {});
+      throw err;
+    }
   }
 
   /** Chains `run` onto the write queue so concurrent mutations never