feat(h5-session): Session Broker、run SSE replay 与 Finish 竞态修复

落地 H5 Session 架构 Patch 1–5（Broker 收口、Router decision、SSE taxonomy、goosed 边界检查），
并新增可选 MEMIND_RUN_STREAM_REPLAY run 事件回放与 H5 假交付 guard；修复 Finish 先于 agent-run
gate 导致 UI 永久 loading 的竞态，接入 verify:h5-session-patches 回归脚本。

Co-authored-by: Cursor <cursoragent@cursor.com>

src/api/client.ts

@@ -2542,12 +2542,16 @@ export function subscribeAgentRunEvents(
 ): () => void {
   let closed = false;
   let activeController: AbortController | null = null;
+  let lastEventId: string | undefined;
 
   const run = async (controller: AbortController) => {
     while (!closed && !controller.signal.aborted) {
       try {
+        const headers: Record<string, string> = { Accept: 'text/event-stream' };
+        if (lastEventId) headers['Last-Event-ID'] = lastEventId;
+
         const res = await fetch(`${API}${AGENT_RUNS_PATH}/${encodeURIComponent(runId)}/events`, {
-          headers: { Accept: 'text/event-stream' },
+          headers,
           credentials: 'same-origin',
           signal: controller.signal,
         });
@@ -2567,18 +2571,21 @@ export function subscribeAgentRunEvents(
 
         while (!closed && !controller.signal.aborted) {
           const { done, value } = await reader.read();
-          if (done) return;
+          if (done) break;
           buffer += decoder.decode(value, { stream: true });
           const chunks = buffer.split('\n\n');
           buffer = chunks.pop() ?? '';
 
           for (const chunk of chunks) {
+            let eventId: string | undefined;
             let eventName = 'message';
             let data = '';
             for (const line of chunk.split('\n')) {
+              if (line.startsWith('id:')) eventId = line.slice(3).trim();
               if (line.startsWith('event:')) eventName = line.slice(6).trim();
               if (line.startsWith('data:')) data = line.slice(5).trim();
             }
+            if (eventId) lastEventId = eventId;
             if (!data) continue;
             if (eventName === 'run') {
               const payload = JSON.parse(data) as { run: AgentRun };
@@ -2594,7 +2601,7 @@ export function subscribeAgentRunEvents(
       } catch (err) {
         if (controller.signal.aborted || closed) return;
         onError(err instanceof Error ? err : new Error(String(err)));
-        return;
+        await new Promise((resolve) => setTimeout(resolve, 1500));
       }
     }
   };