fix: replace cache marker with manifest-based metadata

Signed-off-by: Andrew Paprotsky <apaprotskyi@nvidia.com>

Author: andrewpaprotsky

Cargo.lock

@@ -35,6 +35,7 @@ google-cloud-storage = { workspace = true }
 rustls = { workspace = true }
 crc32c = { workspace = true }
 futures = { workspace = true }
+fd-lock = "4.0.4"
 
 [dev-dependencies]
 mockall = "0.13"

modelexpress_common/Cargo.toml

@@ -560,11 +560,18 @@ mod tests {
         .expect("Failed to resolve GCS path");
         fs::create_dir_all(gcs_model_dir.join("weights"))
             .expect("Failed to create GCS model directory");
-        fs::write(gcs_model_dir.join(".mx-model"), []).expect("Failed to write GCS marker");
         fs::write(gcs_model_dir.join("tokenizer.json"), b"{}")
             .expect("Failed to write GCS tokenizer");
         fs::write(gcs_model_dir.join("weights/model.bin"), b"abcd")
             .expect("Failed to write GCS weights");
+        let gcs_metadata_dir = gcs_model_dir.join(".mx");
+        fs::create_dir_all(&gcs_metadata_dir).expect("Failed to create GCS metadata directory");
+        fs::write(
+            gcs_metadata_dir.join("manifest.json"),
+            r#"{"version":1,"model":"gs://envbucket/dev/bake/qwen/rev123","files":[{"path":"tokenizer.json","size":2,"crc32c":"00000000","generation":null},{"path":"weights/model.bin","size":4,"crc32c":"00000000","generation":null}]}
+"#,
+        )
+        .expect("Failed to write GCS manifest");
 
         let ignored_dir = cache_path.join("tmp");
         fs::create_dir_all(&ignored_dir).expect("Failed to create ignored directory");