diff --git a/apps/hub/src/sidecar/data-root.ts b/apps/hub/src/sidecar/data-root.ts
index 953d14da..f692cc2a 100644
--- a/apps/hub/src/sidecar/data-root.ts
+++ b/apps/hub/src/sidecar/data-root.ts
@@ -1,4 +1,12 @@
-/** Local sidecar state root. Never a launch-specific coding directory. */
+import { resolve } from "node:path";
+
+/**
+ * Local sidecar state root. Never a launch-specific coding directory.
+ *
+ * Absolute because sidecars run with `vendor/interchange` as their working
+ * directory; a relative root would put their state there instead of beside the
+ * hub's.
+ */
 export function localSidecarDataRoot(hubDataDir: string): string {
-  return `${hubDataDir}/local-sidecars`;
+  return resolve(hubDataDir, "local-sidecars");
 }
diff --git a/apps/hub/src/sidecar/local-provisioner.ts b/apps/hub/src/sidecar/local-provisioner.ts
index 981cd82f..9f14ca64 100644
--- a/apps/hub/src/sidecar/local-provisioner.ts
+++ b/apps/hub/src/sidecar/local-provisioner.ts
@@ -503,10 +503,15 @@ export function createLocalProcessSidecarProvisioner({
       });
       return;
     }
-    manifest = stored;
+    // The data dir follows the hub's data root, not the manifest: a manifest written when the root was relative
+    // points the sidecar, which runs from vendor/interchange, at a directory under it.
+    const restored =
+      stored.dataDir === dataDir ? stored : { ...stored, dataDir };
+    if (restored !== stored) await manifests.write(restored);
+    manifest = restored;
     for (const hold of live) holds.set(hold.allocationId, hold);
     await manifests.writeHolds(live);
-    const child = await start(stored);
+    const child = await start(restored);
     log({
       level: "info",
       msg: "local_sidecar_respawned",