fix(agent): tolerate unknown Claude stream message types

Newer Claude Code CLIs emit stream message types the bundled SDK
was not compiled against — `rate_limit_event` being the one that
surfaced — and serde aborted the whole chat stream on the first
one ("unknown variant rate_limit_event").

The `Message` enum gains a `#[serde(other)] Unknown` catch-all so
any unmodelled `type` deserializes cleanly instead of failing the
parse; `hooks.rs` and `chat_claude.rs` match it as a silent no-op
(an unknown event carries no hook payload and no chat turn).

crates/op-host-desktop/src/chat_claude.rs

@@ -213,9 +213,14 @@ async fn handle_message(msg: Message, tx: &mpsc::Sender<ChatDelta>) -> Option<(b
             };
             Some((true, reason))
         }
-        Message::System { .. } | Message::User { .. } | Message::StreamEvent { .. } => {
-            // Init / context / partial-stream events — the chat
-            // widget doesn't surface them today; silent.
+        Message::System { .. }
+        | Message::User { .. }
+        | Message::StreamEvent { .. }
+        | Message::Unknown => {
+            // Init / context / partial-stream events plus any
+            // message type the SDK doesn't model (e.g.
+            // `rate_limit_event`) — the chat widget doesn't surface
+            // them today; silent.
             None
         }
     }

vendor/anthropic-agent-sdk/src/hooks.rs

@@ -576,6 +576,8 @@ impl HookManager {
             }
 
             Message::StreamEvent { .. } => {}
+            // Unmodelled message types carry no hook payload.
+            Message::Unknown => {}
         }
 
         Ok(outputs)

vendor/anthropic-agent-sdk/src/types/messages.rs

@@ -220,6 +220,14 @@ pub enum Message {
         #[serde(skip_serializing_if = "Option::is_none")]
         parent_tool_use_id: Option<String>,
     },
+    /// Any message `type` this SDK build does not model. Newer
+    /// Claude Code CLIs emit events the SDK was not compiled
+    /// against — e.g. `rate_limit_event` — and serde would
+    /// otherwise abort the whole stream on the first one. Routing
+    /// unknown tags here keeps the stream alive; downstream
+    /// consumers simply ignore an `Unknown`.
+    #[serde(other)]
+    Unknown,
 }
 
 #[cfg(test)]