agent ui: live event panel via SSE + stream-json

hive-ag3nt/src/events.rs

@@ -0,0 +1,63 @@
+//! Live event stream for the per-agent web UI. The harness emits one
+//! `LiveEvent` per interesting thing that happens during a turn — wake-up
+//! (the popped inbox message), every line claude prints on stdout
+//! (parsed from `--output-format stream-json`), and the turn-end summary.
+//! The web UI subscribes via SSE and renders rows live.
+//!
+//! Channel type is `tokio::sync::broadcast`. New subscribers see only
+//! future events; the dashboard JS deals with the cold-start case by
+//! showing "connecting…" until the first event arrives.
+
+use std::sync::Arc;
+
+use serde::{Deserialize, Serialize};
+use tokio::sync::broadcast;
+
+const CHANNEL_CAPACITY: usize = 256;
+
+/// One row of the agent's live stream. Serialised to JSON for SSE delivery.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum LiveEvent {
+    /// Harness popped a wake-up message and is about to invoke claude.
+    TurnStart { from: String, body: String },
+    /// One line of claude's `--output-format stream-json` stdout, parsed as
+    /// a generic JSON value (so we don't have to track every claude-code
+    /// event variant). The frontend pretty-prints by `type` field.
+    Stream(serde_json::Value),
+    /// 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),
+    /// Turn finished. `ok=false` means claude exited non-zero or the
+    /// harness hit a transport error.
+    TurnEnd { ok: bool, note: Option<String> },
+}
+
+#[derive(Clone)]
+pub struct Bus {
+    tx: Arc<broadcast::Sender<LiveEvent>>,
+}
+
+impl Bus {
+    #[must_use]
+    pub fn new() -> Self {
+        let (tx, _) = broadcast::channel(CHANNEL_CAPACITY);
+        Self { tx: Arc::new(tx) }
+    }
+
+    pub fn emit(&self, event: LiveEvent) {
+        // Lagged subscribers drop events — fine; the UI is a tail, not a log.
+        let _ = self.tx.send(event);
+    }
+
+    pub fn subscribe(&self) -> broadcast::Receiver<LiveEvent> {
+        self.tx.subscribe()
+    }
+}
+
+impl Default for Bus {
+    fn default() -> Self {
+        Self::new()
+    }
+}