events: LiveEvent::Note becomes struct variant so serde can actually serialize it

hive-ag3nt/src/events.rs

@@ -105,7 +105,16 @@ pub enum LiveEvent {
     /// Free-form note from the harness (e.g. "claude exited 0",
     /// "stream-json parse error: ..."). Useful when stream-json itself
     /// fails so the UI doesn't just go silent.
-    Note(String),
+    ///
+    /// Must be a struct variant (not `Note(String)`): internally-tagged
+    /// enums can't flatten a tag onto a primitive newtype, and serde
+    /// fails serialization at runtime — silently, because the SSE
+    /// handler's `filter_map(... .ok()? ...)` swallows the error. From
+    /// 2025-08 through 2026-05 every `Note` emission was a no-op + the
+    /// sqlite history persisted them as the literal string `"null"`.
+    /// The web UI's `note` renderer already reads `ev.text`, so the
+    /// wire shape matches without a JS change.
+    Note { text: String },
     /// Turn finished. `ok=false` means claude exited non-zero or the
     /// harness hit a transport error.
     TurnEnd { ok: bool, note: Option<String> },
@@ -138,7 +147,7 @@ impl EventStore {
         let kind = match event {
             LiveEvent::TurnStart { .. } => "turn_start",
             LiveEvent::Stream(_) => "stream",
-            LiveEvent::Note(_) => "note",
+            LiveEvent::Note { .. } => "note",
             LiveEvent::TurnEnd { .. } => "turn_end",
         };
         let payload = serde_json::to_string(event).unwrap_or_else(|_| "null".into());