fix(agent): stream replay hardening

alembic/versions/243a597b6a3a_add_curr_run_id_to_agent_session_history.py

@@ -0,0 +1,40 @@
+"""add curr_run_id to agent_session_history
+
+Revision ID: 243a597b6a3a
+Revises: e1a2b3c4d5f6
+Create Date: 2026-05-27 10:43:33.204849
+
+"""
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "243a597b6a3a"
+down_revision: str | None = "e1a2b3c4d5f6"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "agent_session_history",
+        sa.Column("curr_run_id", sa.UUID(), nullable=True),
+    )
+    op.create_index(
+        op.f("ix_agent_session_history_curr_run_id"),
+        "agent_session_history",
+        ["curr_run_id"],
+        unique=False,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index(
+        op.f("ix_agent_session_history_curr_run_id"),
+        table_name="agent_session_history",
+    )
+    op.drop_column("agent_session_history", "curr_run_id")

frontend/src/client/schemas.gen.ts

@@ -4037,6 +4037,46 @@ export const $AgentSessionStatus = {
   description: "Lifecycle state for an agent session turn.",
 } as const
 
+export const $AgentSessionStatusRead = {
+  properties: {
+    turn_status: {
+      $ref: "#/components/schemas/AgentSessionStatus",
+      default: "idle",
+    },
+    curr_run_id: {
+      anyOf: [
+        {
+          type: "string",
+          format: "uuid",
+        },
+        {
+          type: "null",
+        },
+      ],
+      title: "Curr Run Id",
+    },
+    prompt: {
+      anyOf: [
+        {
+          type: "string",
+        },
+        {
+          type: "null",
+        },
+      ],
+      title: "Prompt",
+      description:
+        "Human prompt that started the active run, for observer clients to render (user messages cannot stream over the Vercel protocol).",
+    },
+  },
+  type: "object",
+  title: "AgentSessionStatusRead",
+  description: `Lightweight session lifecycle status for cheap polling.
+
+Clients poll this (instead of the full message history) to learn when a turn
+starts elsewhere and attach to the live stream.`,
+} as const
+
 export const $AgentSessionUpdate = {
   properties: {
     title: {

frontend/src/client/services.gen.ts

@@ -171,6 +171,8 @@ import type {
   AgentSessionsForkSessionResponse,
   AgentSessionsGetSessionData,
   AgentSessionsGetSessionResponse,
+  AgentSessionsGetSessionStatusData,
+  AgentSessionsGetSessionStatusResponse,
   AgentSessionsGetSessionVercelData,
   AgentSessionsGetSessionVercelResponse,
   AgentSessionsListSessionsData,
@@ -6613,6 +6615,31 @@ export const agentSessionsGetSessionVercel = (
   })
 }
 
+/**
+ * Get Session Status
+ * Lifecycle status for polling without loading message history.
+ * @param data The data for the request.
+ * @param data.sessionId
+ * @param data.workspaceId
+ * @returns AgentSessionStatusRead Successful Response
+ * @throws ApiError
+ */
+export const agentSessionsGetSessionStatus = (
+  data: AgentSessionsGetSessionStatusData
+): CancelablePromise<AgentSessionsGetSessionStatusResponse> => {
+  return __request(OpenAPI, {
+    method: "GET",
+    url: "/workspaces/{workspace_id}/agent/sessions/{session_id}/status",
+    path: {
+      session_id: data.sessionId,
+      workspace_id: data.workspaceId,
+    },
+    errors: {
+      422: "Validation Error",
+    },
+  })
+}
+
 /**
  * Cancel Session
  * Request graceful cancellation for the active agent session turn.

frontend/src/client/types.gen.ts

@@ -954,6 +954,21 @@ export type AgentSessionStatus =
   | "stopped"
   | "failed"
 
+/**
+ * Lightweight session lifecycle status for cheap polling.
+ *
+ * Clients poll this (instead of the full message history) to learn when a turn
+ * starts elsewhere and attach to the live stream.
+ */
+export type AgentSessionStatusRead = {
+  turn_status?: AgentSessionStatus
+  curr_run_id?: string | null
+  /**
+   * Human prompt that started the active run, for observer clients to render (user messages cannot stream over the Vercel protocol).
+   */
+  prompt?: string | null
+}
+
 /**
  * Request schema for updating an agent session.
  */
@@ -10781,6 +10796,13 @@ export type AgentSessionsGetSessionVercelResponse =
   | AgentSessionReadVercel
   | ChatReadVercel
 
+export type AgentSessionsGetSessionStatusData = {
+  sessionId: string
+  workspaceId: string
+}
+
+export type AgentSessionsGetSessionStatusResponse = AgentSessionStatusRead
+
 export type AgentSessionsCancelSessionData = {
   requestBody?: AgentSessionCancelRequest | null
   sessionId: string
@@ -15780,6 +15802,21 @@ export type $OpenApiTs = {
       }
     }
   }
+  "/workspaces/{workspace_id}/agent/sessions/{session_id}/status": {
+    get: {
+      req: AgentSessionsGetSessionStatusData
+      res: {
+        /**
+         * Successful Response
+         */
+        200: AgentSessionStatusRead
+        /**
+         * Validation Error
+         */
+        422: HTTPValidationError
+      }
+    }
+  }
   "/workspaces/{workspace_id}/agent/sessions/{session_id}/cancel": {
     post: {
       req: AgentSessionsCancelSessionData

frontend/src/components/chat/chat-session-pane.tsx

@@ -102,6 +102,7 @@ import {
   makeContinueMessage,
   parseChatError,
   useCancelChatTurn,
+  useSessionStatus,
   useUpdateChat,
   useVercelChat,
 } from "@/hooks/use-chat"
@@ -279,12 +280,26 @@ export function ChatSessionPane({
     () => (chat?.messages || []).map(toUIMessage),
     [chat?.messages]
   )
+  // Cheap status poll drives attaching to a live turn (started by another tab).
+  // `prompt` carries the active turn's user message so observer tabs can show
+  // it (the Vercel stream protocol only streams assistant messages).
+  const {
+    turnStatus,
+    currRunId,
+    prompt: activePrompt,
+  } = useSessionStatus({
+    chatId: isReadonly ? undefined : chat?.id,
+    workspaceId,
+  })
   const { sendMessage, messages, status, regenerate, lastError, clearError } =
     useVercelChat({
       chatId: chat?.id,
       workspaceId,
       messages: uiMessages,
       modelInfo,
+      turnStatus,
+      currRunId,
+      activePrompt,
     })
 
   // Track pending message sends to avoid duplicate sends