diff --git a/apis/workflows/v1/worker.proto b/apis/workflows/v1/worker.proto
index ce1c112..317659e 100644
--- a/apis/workflows/v1/worker.proto
+++ b/apis/workflows/v1/worker.proto
@@ -10,29 +10,24 @@ import "workflows/v1/core.proto";
 import "workflows/v1/task.proto";
 import "workflows/v1/workflows.proto";
 
-// HandshakeRequest is sent by the runner to a worker runtime to discover its capabilities.
-message HandshakeRequest {
-  RunnerMetadata metadata = 1;
-  // The cluster that the worker runtime is running on.
-  workflows.v1.Cluster cluster = 2;
-  // The storage locations that the worker runtime can access, for triggered automations.
-  repeated StorageLocation locations = 3;
-}
-
-// Some metadata about the runner that this worker runtime is connected to, to be able to include it in logs and traces.
-message RunnerMetadata {
+// InitializeRunnerRequest is sent by the runner to a worker runtime to discover its capabilities.
+message InitializeRunnerRequest {
   // The id of the runner that this worker runtime is connected to.
   tilebox.v1.ID runner_id = 1;
-  // The traceparent that should be used for any traces emitted by this worker runtime (outside of task execution,
-  // which has its own traceparent propagation from jobs). This allows us to correlate any logs and traces emitted
+  // The trace_parent that should be used for any traces emitted by this worker runtime (outside of task execution,
+  // which has its own trace_parent propagation from jobs). This allows us to correlate any logs and traces emitted
   // by the worker runtime with the runner that it's connected to.
-  string traceparent = 2;
+  string trace_parent = 2;
+  // The cluster that the worker runtime is running on.
+  workflows.v1.Cluster cluster = 3;
+  // The workflow (and the release) that this worker was created from.
+  workflows.v1.Workflow workflow = 4;
+  // The storage locations that the worker runtime can access, for triggered automations.
+  repeated StorageLocation locations = 5;
 }
 
 // HandshakeResponse is the response to a handshake request, containing the task identifiers that the worker can execute.
-message HandshakeResponse {
-  workflows.v1.TaskIdentifiers task_identifiers = 1;
-}
+message InitializeRunnerResponse {}
 
 // ExecuteTaskResponse is the response of a worker runtime to a request to execute a task, after the task has
 // been executed.
@@ -53,7 +48,20 @@ message ExecuteTaskResponse {
 
 // WorkerService defines the RPC interface between a runner and a a worker runtime that can execute workflow tasks.
 service WorkerService {
-  rpc Handshake(HandshakeRequest) returns (HandshakeResponse) {}
+  // ListRegisteredTasks is called by the runner to discover the task identifiers that a worker runtime can execute.
+  rpc ListRegisteredTasks(google.protobuf.Empty) returns (workflows.v1.TaskIdentifiers);
+
+  // InitializeWorker is called by the runner to initialize a worker runtime with some known metadata about the
+  // runner. This allows us to add those metadata to any logs and traces emitted by the worker.
+  rpc InitializeWorker(InitializeRunnerRequest) returns (InitializeRunnerResponse) {}
+
+  // ExecuteTask is called by the runner to execute a task on the worker runtime. The worker runtime will execute the
+  // task, and then respond with the result of the task execution, which can either be a computed task, or a failed
+  // task. If the worker runtime crashes or becomes unreachable during task execution, the runner will treat the task
+  // as failed with an unknown error.
   rpc ExecuteTask(workflows.v1.Task) returns (ExecuteTaskResponse) {}
-  rpc Shutdown(google.protobuf.Empty) returns (google.protobuf.Empty) {}
+
+  // Gracefully shuts down the worker runtime. After receiving this request, the worker runtime will
+  // cleanly shut down.
+  rpc ShutdownWorker(google.protobuf.Empty) returns (google.protobuf.Empty) {}
 }
diff --git a/apis/workflows/v1/workflows.proto b/apis/workflows/v1/workflows.proto
index 7434f47..c783969 100644
--- a/apis/workflows/v1/workflows.proto
+++ b/apis/workflows/v1/workflows.proto
@@ -114,10 +114,19 @@ message Artifact {
 // the list of task identifiers, and the command to start a worker runtime for executing the tasks in the release.
 // The fingerprint is a hash of the release content.
 message ReleaseContent {
+  // A fingerprint of the release content, which is a hash of the task identifiers, files, runner object path,
+  // and command override. Used to determine if two releases have the same content, for idempotent builds.
   string fingerprint = 1 [(buf.validate.field).string.pattern = "^[a-f0-9]{64}$"];
+  // List of task identifiers included in the release artifact.
   repeated TaskIdentifier tasks = 2 [(buf.validate.field).repeated.min_items = 1];
-  Path root = 3;
-  repeated string command = 4;
+  // List of files/directories included in the release artifact.
+  repeated Path files = 3;
+  // The python module/object path to the runner instance, e.g. "my_module.my_runner:runner".
+  string runner_object_path = 4;
+  // A custom command override for starting a worker runtime. This is optional, and if not set defaults to
+  // "uv run python -m tilebox.workflows.runner <runner_object_path>". This allows users to specify a custom command
+  // for starting the worker runtime, e.g. to set environment variables or use a different entrypoint.
+  repeated string command_override = 5;
 }
 
 // Path represents a file or directory path in the release content. If it is a directory, it can have child paths.