fix: require idle workers for submit

crates/protocol/src/lib.rs

@@ -205,7 +205,9 @@ impl From<WorkerStatus> for WorkerStateSnapshot {
 #[cfg_attr(feature = "typescript", derive(ts_rs::TS))]
 #[serde(tag = "method", content = "params", rename_all = "snake_case")]
 pub enum Method {
-    /// Durably accept typed input for immediate activation or the session FIFO.
+    /// Durably accept typed input for immediate activation while the Worker is Idle.
+    /// Running or Paused Workers reject Submit; use Notify for advisory information
+    /// that should be incorporated into work already in progress.
     ///
     /// `submission_request_id` is generated by the authenticated caller and is
     /// used only for idempotent retry. Worker allocates the durable
@@ -724,6 +726,8 @@ pub enum ToolResultDisposition {
 #[serde(rename_all = "snake_case")]
 pub enum SubmissionDisposition {
     Started,
+    /// Compatibility value for durable receipts created before Submit became
+    /// Idle-only. New submissions are never accepted with this disposition.
     Queued,
 }
 
@@ -859,9 +863,10 @@ pub struct SessionToolAttachment {
 #[cfg_attr(feature = "typescript", derive(ts_rs::TS))]
 #[serde(tag = "event", content = "data", rename_all = "snake_case")]
 pub enum Event {
-    /// Durable Submit acceptance. A `Queued` receipt follows the durable FIFO
-    /// checkpoint. A `Started` receipt follows the pending activation checkpoint;
-    /// the corresponding [`Event::UserMessage`] marks the later history commit.
+    /// Durable Submit acceptance. New submissions are accepted only while Idle,
+    /// and a `Started` receipt follows the pending activation checkpoint; the
+    /// corresponding [`Event::UserMessage`] marks the later history commit.
+    /// `Queued` remains readable for receipts persisted by older runtimes.
     /// Repeating the same request id and exact payload returns the same receipt
     /// without appending or activating twice.
     SubmissionAccepted {