backend, web: support for resuming streams

docs/api/rest.md

@@ -39,6 +39,22 @@ Chat upload limits:
 ```
 - OpenAI model lists are filtered to models that are expected to work with the backend's Responses API implementation.
 
+## Active Runs
+
+### `GET /v1/active-runs`
+- Response:
+```json
+{
+  "chats": ["chat-id-with-active-stream"],
+  "searches": ["search-id-with-active-stream"]
+}
+```
+
+Behavior notes:
+- Lists in-memory chat/search streams that are still running on this server process.
+- Clients should use this after app start or page refresh to restore per-row generating indicators.
+- The lists are not durable across server restarts.
+
 ## Chats
 
 ### `GET /v1/chats`
@@ -260,6 +276,32 @@ Search run notes:
 - Persists answer text/citations + ranked results.
 - If both search and answer fail, endpoint returns an error.
 
+### `POST /v1/searches/:searchId/run/stream`
+- Body: same as `POST /v1/searches/:searchId/run`
+- Response: `text/event-stream`
+
+Events:
+- `search_results`: `{ "requestId": string|null, "results": SearchResultItem[] }`
+- `search_error`: `{ "error": string }`
+- `answer`: `{ "answerText": string|null, "answerRequestId": string|null, "answerCitations": SearchDetail["answerCitations"] }`
+- `answer_error`: `{ "error": string }`
+- terminal `done`: `{ "search": SearchDetail }`
+- terminal `error`: `{ "message": string }`
+
+Behavior notes:
+- The stream is owned by the backend after it starts. If the original HTTP client disconnects, the backend keeps running and persists the final search state.
+- While a search stream is active, `GET /v1/active-runs` includes the `searchId`.
+- If a stream is already active for the same `searchId`, this endpoint attaches to the existing stream instead of starting a second run.
+
+### `POST /v1/searches/:searchId/run/stream/attach`
+- Body: none
+- Response: `text/event-stream` with the same event names as `POST /v1/searches/:searchId/run/stream`
+- Not found: `404 { "message": "active search stream not found" }`
+
+Behavior notes:
+- Replays buffered events for the active in-memory stream, then emits new events until `done` or `error`.
+- Intended for clients that discovered a pending search via `GET /v1/active-runs`, such as after browser refresh.
+
 ## Type Shapes
 
 `ChatSummary`

docs/api/streaming-chat.md

@@ -4,6 +4,7 @@ This document defines the server-sent events (SSE) contract for chat completions
 
 Endpoint:
 - `POST /v1/chat-completions/stream`
+- `POST /v1/chats/:chatId/stream/attach`
 
 Transport:
 - HTTP response uses `Content-Type: text/event-stream; charset=utf-8`
@@ -61,6 +62,23 @@ Notes:
 - For persisted streams, backend stores only new non-assistant input history rows to avoid duplicates.
 - Attachments are optional and are persisted under `message.metadata.attachments` on stored user messages when `persist` is `true`.
 
+Persisted chat streams with a `chatId` are backend-owned active runs:
+- Once started, the backend keeps the stream running even if the HTTP client disconnects or refreshes.
+- While running, `GET /v1/active-runs` includes the `chatId`.
+- Starting a second persisted stream for the same active `chatId` returns `409`.
+- Clients can reattach with `POST /v1/chats/:chatId/stream/attach`.
+
+## Attach Endpoint
+
+`POST /v1/chats/:chatId/stream/attach`
+- Body: none.
+- Response uses the same `text/event-stream` transport and event names as `POST /v1/chat-completions/stream`.
+- Replays buffered events for the active in-memory stream, then emits new events until `done` or `error`.
+- Returns `404 { "message": "active chat stream not found" }` if no stream is currently active for that chat.
+- Authentication is the same as all other API endpoints.
+
+This endpoint is intended for clients that restored an active `chatId` from `GET /v1/active-runs`, especially after browser refresh. Replayed `delta` events may include text that was originally emitted before the client attached.
+
 ## Event Stream Contract
 
 Event order:

server/src/active-streams.ts

@@ -0,0 +1,59 @@
+export type SseStreamEvent = {
+  event: string;
+  data: unknown;
+};
+
+type SseStreamListener = (event: SseStreamEvent) => void;
+
+export class ActiveSseStream {
+  private readonly events: SseStreamEvent[] = [];
+  private readonly listeners = new Set<SseStreamListener>();
+  private completed = false;
+  private resolveDone!: () => void;
+
+  readonly done: Promise<void>;
+
+  constructor() {
+    this.done = new Promise((resolve) => {
+      this.resolveDone = resolve;
+    });
+  }
+
+  get isCompleted() {
+    return this.completed;
+  }
+
+  emit(event: string, data: unknown) {
+    if (this.completed) return;
+    const entry = { event, data };
+    this.events.push(entry);
+    for (const listener of this.listeners) {
+      listener(entry);
+    }
+  }
+
+  complete(finalEvent?: SseStreamEvent) {
+    if (this.completed) return;
+    if (finalEvent) {
+      this.emit(finalEvent.event, finalEvent.data);
+    }
+    this.completed = true;
+    this.listeners.clear();
+    this.resolveDone();
+  }
+
+  subscribe(listener: SseStreamListener) {
+    for (const event of this.events) {
+      listener(event);
+    }
+
+    if (this.completed) {
+      return () => {};
+    }
+
+    this.listeners.add(listener);
+    return () => {
+      this.listeners.delete(listener);
+    };
+  }
+}

server/src/routes.ts

@@ -1,12 +1,13 @@
 import { performance } from "node:perf_hooks";
 import { z } from "zod";
-import type { FastifyInstance } from "fastify";
+import type { FastifyInstance, FastifyReply, FastifyRequest } from "fastify";
+import { ActiveSseStream, type SseStreamEvent } from "./active-streams.js";
 import { prisma } from "./db.js";
 import { requireAdmin } from "./auth.js";
 import { env } from "./env.js";
 import { buildComparableAttachments } from "./llm/message-content.js";
 import { runMultiplex } from "./llm/multiplexer.js";
-import { runMultiplexStream } from "./llm/streaming.js";
+import { runMultiplexStream, type StreamEvent } from "./llm/streaming.js";
 import { getModelCatalogSnapshot } from "./llm/model-catalog.js";
 import { openaiClient } from "./llm/providers.js";
 import { exaClient } from "./search/exa.js";
@@ -120,6 +121,26 @@ const CompletionMessageSchema = z
     }
   });
 
+const CompletionStreamBody = z
+  .object({
+    chatId: z.string().optional(),
+    persist: z.boolean().optional(),
+    provider: z.enum(["openai", "anthropic", "xai"]),
+    model: z.string().min(1),
+    messages: z.array(CompletionMessageSchema),
+    temperature: z.number().min(0).max(2).optional(),
+    maxTokens: z.number().int().positive().optional(),
+  })
+  .superRefine((value, ctx) => {
+    if (value.persist === false && value.chatId) {
+      ctx.addIssue({
+        code: z.ZodIssueCode.custom,
+        message: "chatId must be omitted when persist is false",
+        path: ["chatId"],
+      });
+    }
+  });
+
 function mergeAttachmentsIntoMetadata(metadata: unknown, attachments?: ChatAttachment[]) {
   if (!attachments?.length) return metadata as any;
   if (!metadata || typeof metadata !== "object" || Array.isArray(metadata)) {
@@ -293,6 +314,246 @@ function buildSseHeaders(originHeader: string | undefined) {
   return headers;
 }
 
+type SearchRunRequest = z.infer<typeof SearchRunBody>;
+
+const activeChatStreams = new Map<string, ActiveSseStream>();
+const activeSearchStreams = new Map<string, ActiveSseStream>();
+
+function getErrorMessage(err: unknown) {
+  return err instanceof Error ? err.message : String(err);
+}
+
+function writeSseEvent(reply: FastifyReply, event: SseStreamEvent) {
+  if (reply.raw.destroyed || reply.raw.writableEnded) return;
+  reply.raw.write(`event: ${event.event}\n`);
+  reply.raw.write(`data: ${JSON.stringify(event.data)}\n\n`);
+}
+
+async function streamActiveRun(req: FastifyRequest, reply: FastifyReply, stream: ActiveSseStream) {
+  reply.raw.writeHead(200, buildSseHeaders(typeof req.headers.origin === "string" ? req.headers.origin : undefined));
+  reply.raw.flushHeaders?.();
+
+  let unsubscribe = () => {};
+  let closed = false;
+  const closedPromise = new Promise<void>((resolve) => {
+    const onClose = () => {
+      closed = true;
+      unsubscribe();
+      reply.raw.off("close", onClose);
+      resolve();
+    };
+    reply.raw.on("close", onClose);
+    stream.done.finally(() => {
+      reply.raw.off("close", onClose);
+    });
+  });
+
+  unsubscribe = stream.subscribe((event) => writeSseEvent(reply, event));
+  await Promise.race([stream.done, closedPromise]);
+  unsubscribe();
+
+  if (!closed && !reply.raw.destroyed && !reply.raw.writableEnded) {
+    reply.raw.end();
+  }
+
+  return reply;
+}
+
+function mapChatStreamEvent(ev: StreamEvent): SseStreamEvent {
+  if (ev.type === "tool_call") return { event: "tool_call", data: ev.event };
+  return { event: ev.type, data: ev };
+}
+
+function startActiveChatStream(chatId: string, body: z.infer<typeof CompletionStreamBody>) {
+  const stream = new ActiveSseStream();
+  activeChatStreams.set(chatId, stream);
+
+  void (async () => {
+    let sawTerminalEvent = false;
+    try {
+      for await (const ev of runMultiplexStream(body)) {
+        const event = mapChatStreamEvent(ev);
+        if (ev.type === "done" || ev.type === "error") {
+          sawTerminalEvent = true;
+          stream.complete(event);
+          break;
+        }
+        stream.emit(event.event, event.data);
+      }
+
+      if (!sawTerminalEvent) {
+        stream.complete({ event: "error", data: { message: "chat stream ended unexpectedly" } });
+      }
+    } catch (err) {
+      stream.complete({ event: "error", data: { message: getErrorMessage(err) } });
+    } finally {
+      activeChatStreams.delete(chatId);
+    }
+  })();
+
+  return stream;
+}
+
+async function executeSearchRunStream(searchId: string, body: SearchRunRequest, stream: ActiveSseStream) {
+  const startedAt = performance.now();
+  const query = body.query?.trim();
+  if (!query) {
+    stream.complete({ event: "error", data: { message: "query is required" } });
+    return;
+  }
+
+  const normalizedTitle = body.title?.trim() || query.slice(0, 80);
+
+  try {
+    const exa = exaClient();
+    const searchPromise = exa.search(query, {
+      type: body.type ?? "auto",
+      numResults: body.numResults ?? 10,
+      includeDomains: body.includeDomains,
+      excludeDomains: body.excludeDomains,
+      moderation: true,
+      userLocation: "US",
+      contents: false,
+    } as any);
+    const answerPromise = exa.answer(query, {
+      text: true,
+      model: "exa",
+      userLocation: "US",
+    });
+
+    let searchResponse: any | null = null;
+    let answerResponse: any | null = null;
+    let enrichedResults: any[] | null = null;
+    let searchError: string | null = null;
+    let answerError: string | null = null;
+
+    const searchSettled = searchPromise.then(
+      async (value) => {
+        searchResponse = value;
+        const previewResults = (value?.results ?? []).map((result: any, index: number) => mapSearchResultPreview(result, index));
+        stream.emit("search_results", {
+          requestId: value?.requestId ?? null,
+          results: previewResults,
+        });
+
+        const urls = (value?.results ?? []).map((result: any) => result?.url).filter((url: string | undefined) => typeof url === "string");
+        if (!urls.length) return;
+
+        try {
+          const contentsResponse = await exa.getContents(urls, {
+            text: { maxCharacters: 1200 },
+            highlights: {
+              query,
+              maxCharacters: 320,
+              numSentences: 2,
+              highlightsPerUrl: 2,
+            },
+          } as any);
+          const byUrl = new Map<string, any>();
+          for (const contentItem of contentsResponse?.results ?? []) {
+            byUrl.set(normalizeUrlForMatch(contentItem?.url), contentItem);
+          }
+
+          enrichedResults = (value?.results ?? []).map((result: any) => {
+            const contentItem = byUrl.get(normalizeUrlForMatch(result?.url));
+            if (!contentItem) return result;
+            return {
+              ...result,
+              text: contentItem.text ?? result.text ?? null,
+              highlights: Array.isArray(contentItem.highlights) ? contentItem.highlights : result.highlights ?? null,
+              highlightScores: Array.isArray(contentItem.highlightScores) ? contentItem.highlightScores : result.highlightScores ?? null,
+            };
+          });
+
+          stream.emit("search_results", {
+            requestId: value?.requestId ?? null,
+            results: enrichedResults.map((result: any, index: number) => mapSearchResultPreview(result, index)),
+          });
+        } catch {
+          // keep preview results if content enrichment fails
+        }
+      },
+      (reason) => {
+        searchError = reason?.message ?? String(reason);
+        stream.emit("search_error", { error: searchError });
+      }
+    );
+
+    const answerSettled = answerPromise.then(
+      (value) => {
+        answerResponse = value;
+        stream.emit("answer", {
+          answerText: parseAnswerText(value),
+          answerRequestId: value?.requestId ?? null,
+          answerCitations: (value?.citations as any) ?? null,
+        });
+      },
+      (reason) => {
+        answerError = reason?.message ?? String(reason);
+        stream.emit("answer_error", { error: answerError });
+      }
+    );
+
+    await Promise.all([searchSettled, answerSettled]);
+
+    const latencyMs = Math.round(performance.now() - startedAt);
+    const persistedResults = enrichedResults ?? searchResponse?.results ?? [];
+    const rows = persistedResults.map((result: any, index: number) => mapSearchResultRow(searchId, result, index));
+    const answerText = parseAnswerText(answerResponse);
+
+    await prisma.$transaction(async (tx) => {
+      await tx.search.update({
+        where: { id: searchId },
+        data: {
+          query,
+          title: normalizedTitle,
+          requestId: searchResponse?.requestId ?? null,
+          rawResponse: searchResponse as any,
+          latencyMs,
+          error: searchError,
+          answerText,
+          answerRequestId: answerResponse?.requestId ?? null,
+          answerCitations: (answerResponse?.citations as any) ?? null,
+          answerRawResponse: answerResponse as any,
+          answerError,
+        },
+      });
+      await tx.searchResult.deleteMany({ where: { searchId } });
+      if (rows.length) {
+        await tx.searchResult.createMany({ data: rows as any });
+      }
+    });
+
+    const search = await prisma.search.findUnique({
+      where: { id: searchId },
+      include: { results: { orderBy: { rank: "asc" } } },
+    });
+    if (!search) {
+      stream.complete({ event: "error", data: { message: "search not found" } });
+    } else {
+      stream.complete({ event: "done", data: { search } });
+    }
+  } catch (err) {
+    const message = getErrorMessage(err);
+    try {
+      await prisma.search.update({
+        where: { id: searchId },
+        data: {
+          query,
+          title: normalizedTitle,
+          latencyMs: Math.round(performance.now() - startedAt),
+          error: message,
+        },
+      });
+    } catch {
+      // keep the stream terminal event even if the backing search row disappeared
+    }
+    stream.complete({ event: "error", data: { message } });
+  } finally {
+    activeSearchStreams.delete(searchId);
+  }
+}
+
 export async function registerRoutes(app: FastifyInstance) {
   app.get("/health", { logLevel: "silent" }, async () => ({ ok: true }));
 
@@ -306,6 +567,14 @@ export async function registerRoutes(app: FastifyInstance) {
     return { providers: getModelCatalogSnapshot() };
   });
 
+  app.get("/v1/active-runs", async (req) => {
+    requireAdmin(req);
+    return {
+      chats: Array.from(activeChatStreams.keys()),
+      searches: Array.from(activeSearchStreams.keys()),
+    };
+  });
+
   app.get("/v1/chats", async (req) => {
     requireAdmin(req);
     const chats = await prisma.chat.findMany({
@@ -695,162 +964,24 @@ export async function registerRoutes(app: FastifyInstance) {
     const query = body.query?.trim() || existing.query?.trim();
     if (!query) return app.httpErrors.badRequest("query is required");
 
-    const startedAt = performance.now();
-    const normalizedTitle = body.title?.trim() || query.slice(0, 80);
-
-    reply.raw.writeHead(200, buildSseHeaders(typeof req.headers.origin === "string" ? req.headers.origin : undefined));
-
-    const send = (event: string, data: any) => {
-      if (reply.raw.writableEnded) return;
-      reply.raw.write(`event: ${event}\n`);
-      reply.raw.write(`data: ${JSON.stringify(data)}\n\n`);
-    };
-
-    try {
-      const exa = exaClient();
-      const searchPromise = exa.search(query, {
-        type: body.type ?? "auto",
-        numResults: body.numResults ?? 10,
-        includeDomains: body.includeDomains,
-        excludeDomains: body.excludeDomains,
-        moderation: true,
-        userLocation: "US",
-        contents: false,
-      } as any);
-      const answerPromise = exa.answer(query, {
-        text: true,
-        model: "exa",
-        userLocation: "US",
-      });
-
-      let searchResponse: any | null = null;
-      let answerResponse: any | null = null;
-      let enrichedResults: any[] | null = null;
-      let searchError: string | null = null;
-      let answerError: string | null = null;
-
-      const searchSettled = searchPromise.then(
-        async (value) => {
-          searchResponse = value;
-          const previewResults = (value?.results ?? []).map((result: any, index: number) => mapSearchResultPreview(result, index));
-          send("search_results", {
-            requestId: value?.requestId ?? null,
-            results: previewResults,
-          });
-
-          const urls = (value?.results ?? []).map((result: any) => result?.url).filter((url: string | undefined) => typeof url === "string");
-          if (!urls.length) return;
-
-          try {
-            const contentsResponse = await exa.getContents(urls, {
-              text: { maxCharacters: 1200 },
-              highlights: {
-                query,
-                maxCharacters: 320,
-                numSentences: 2,
-                highlightsPerUrl: 2,
-              },
-            } as any);
-            const byUrl = new Map<string, any>();
-            for (const contentItem of contentsResponse?.results ?? []) {
-              byUrl.set(normalizeUrlForMatch(contentItem?.url), contentItem);
-            }
-
-            enrichedResults = (value?.results ?? []).map((result: any) => {
-              const contentItem = byUrl.get(normalizeUrlForMatch(result?.url));
-              if (!contentItem) return result;
-              return {
-                ...result,
-                text: contentItem.text ?? result.text ?? null,
-                highlights: Array.isArray(contentItem.highlights) ? contentItem.highlights : result.highlights ?? null,
-                highlightScores: Array.isArray(contentItem.highlightScores) ? contentItem.highlightScores : result.highlightScores ?? null,
-              };
-            });
-
-            send("search_results", {
-              requestId: value?.requestId ?? null,
-              results: enrichedResults.map((result: any, index: number) => mapSearchResultPreview(result, index)),
-            });
-          } catch {
-            // keep preview results if content enrichment fails
-          }
-        },
-        (reason) => {
-          searchError = reason?.message ?? String(reason);
-          send("search_error", { error: searchError });
-        }
-      );
-
-      const answerSettled = answerPromise.then(
-        (value) => {
-          answerResponse = value;
-          send("answer", {
-            answerText: parseAnswerText(value),
-            answerRequestId: value?.requestId ?? null,
-            answerCitations: (value?.citations as any) ?? null,
-          });
-        },
-        (reason) => {
-          answerError = reason?.message ?? String(reason);
-          send("answer_error", { error: answerError });
-        }
-      );
-
-      await Promise.all([searchSettled, answerSettled]);
-
-      const latencyMs = Math.round(performance.now() - startedAt);
-      const persistedResults = enrichedResults ?? searchResponse?.results ?? [];
-      const rows = persistedResults.map((result: any, index: number) => mapSearchResultRow(searchId, result, index));
-      const answerText = parseAnswerText(answerResponse);
-
-      await prisma.$transaction(async (tx) => {
-        await tx.search.update({
-          where: { id: searchId },
-          data: {
-            query,
-            title: normalizedTitle,
-            requestId: searchResponse?.requestId ?? null,
-            rawResponse: searchResponse as any,
-            latencyMs,
-            error: searchError,
-            answerText,
-            answerRequestId: answerResponse?.requestId ?? null,
-            answerCitations: (answerResponse?.citations as any) ?? null,
-            answerRawResponse: answerResponse as any,
-            answerError,
-          },
-        });
-        await tx.searchResult.deleteMany({ where: { searchId } });
-        if (rows.length) {
-          await tx.searchResult.createMany({ data: rows as any });
-        }
-      });
-
-      const search = await prisma.search.findUnique({
-        where: { id: searchId },
-        include: { results: { orderBy: { rank: "asc" } } },
-      });
-      if (!search) {
-        send("error", { message: "search not found" });
-      } else {
-        send("done", { search });
-      }
-    } catch (err: any) {
-      await prisma.search.update({
-        where: { id: searchId },
-        data: {
-          query,
-          title: normalizedTitle,
-          latencyMs: Math.round(performance.now() - startedAt),
-          error: err?.message ?? String(err),
-        },
-      });
-      send("error", { message: err?.message ?? String(err) });
-    } finally {
-      reply.raw.end();
+    const existingStream = activeSearchStreams.get(searchId);
+    if (existingStream) {
+      return streamActiveRun(req, reply, existingStream);
     }
 
-    return reply;
+    const stream = new ActiveSseStream();
+    activeSearchStreams.set(searchId, stream);
+    void executeSearchRunStream(searchId, { ...body, query }, stream);
+    return streamActiveRun(req, reply, stream);
+  });
+
+  app.post("/v1/searches/:searchId/run/stream/attach", async (req, reply) => {
+    requireAdmin(req);
+    const Params = z.object({ searchId: z.string() });
+    const { searchId } = Params.parse(req.params);
+    const stream = activeSearchStreams.get(searchId);
+    if (!stream) return app.httpErrors.notFound("active search stream not found");
+    return streamActiveRun(req, reply, stream);
   });
 
   app.get("/v1/chats/:chatId", async (req) => {
@@ -895,6 +1026,15 @@ export async function registerRoutes(app: FastifyInstance) {
     return { message: msg };
   });
 
+  app.post("/v1/chats/:chatId/stream/attach", async (req, reply) => {
+    requireAdmin(req);
+    const Params = z.object({ chatId: z.string() });
+    const { chatId } = Params.parse(req.params);
+    const stream = activeChatStreams.get(chatId);
+    if (!stream) return app.httpErrors.notFound("active chat stream not found");
+    return streamActiveRun(req, reply, stream);
+  });
+
   // Main: create a completion via provider+model and store everything.
   app.post("/v1/chat-completions", async (req) => {
     requireAdmin(req);
@@ -935,27 +1075,7 @@ export async function registerRoutes(app: FastifyInstance) {
   app.post("/v1/chat-completions/stream", async (req, reply) => {
     requireAdmin(req);
 
-    const Body = z
-      .object({
-        chatId: z.string().optional(),
-        persist: z.boolean().optional(),
-        provider: z.enum(["openai", "anthropic", "xai"]),
-        model: z.string().min(1),
-        messages: z.array(CompletionMessageSchema),
-        temperature: z.number().min(0).max(2).optional(),
-        maxTokens: z.number().int().positive().optional(),
-      })
-      .superRefine((value, ctx) => {
-        if (value.persist === false && value.chatId) {
-          ctx.addIssue({
-            code: z.ZodIssueCode.custom,
-            message: "chatId must be omitted when persist is false",
-            path: ["chatId"],
-          });
-        }
-      });
-
-    const parsed = Body.safeParse(req.body);
+    const parsed = CompletionStreamBody.safeParse(req.body);
     if (!parsed.success) return app.httpErrors.badRequest(parsed.error.message);
     const body = parsed.data;
 
@@ -970,23 +1090,24 @@ export async function registerRoutes(app: FastifyInstance) {
       await storeNonAssistantMessages(body.chatId, body.messages);
     }
 
+    if (body.persist !== false && body.chatId) {
+      if (activeChatStreams.has(body.chatId)) {
+        return app.httpErrors.conflict("chat completion already running");
+      }
+      const stream = startActiveChatStream(body.chatId, body);
+      return streamActiveRun(req, reply, stream);
+    }
+
     reply.raw.writeHead(200, buildSseHeaders(typeof req.headers.origin === "string" ? req.headers.origin : undefined));
     reply.raw.flushHeaders();
 
-    const send = (event: string, data: any) => {
-      reply.raw.write(`event: ${event}\n`);
-      reply.raw.write(`data: ${JSON.stringify(data)}\n\n`);
-    };
-
     for await (const ev of runMultiplexStream(body)) {
-      if (ev.type === "meta") send("meta", ev);
-      else if (ev.type === "tool_call") send("tool_call", ev.event);
-      else if (ev.type === "delta") send("delta", ev);
-      else if (ev.type === "done") send("done", ev);
-      else if (ev.type === "error") send("error", ev);
+      writeSseEvent(reply, mapChatStreamEvent(ev));
     }
 
-    reply.raw.end();
+    if (!reply.raw.destroyed && !reply.raw.writableEnded) {
+      reply.raw.end();
+    }
     return reply;
   });
 }

server/tests/active-streams.test.ts

@@ -0,0 +1,34 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { ActiveSseStream, type SseStreamEvent } from "../src/active-streams.js";
+
+test("ActiveSseStream replays buffered events to late subscribers", () => {
+  const stream = new ActiveSseStream();
+  stream.emit("delta", { text: "hel" });
+  stream.emit("delta", { text: "lo" });
+
+  const events: SseStreamEvent[] = [];
+  const unsubscribe = stream.subscribe((event) => events.push(event));
+  unsubscribe();
+
+  assert.deepEqual(events, [
+    { event: "delta", data: { text: "hel" } },
+    { event: "delta", data: { text: "lo" } },
+  ]);
+});
+
+test("ActiveSseStream replays terminal events after completion", async () => {
+  const stream = new ActiveSseStream();
+  stream.emit("delta", { text: "done" });
+  stream.complete({ event: "done", data: { text: "done" } });
+  await stream.done;
+
+  const events: SseStreamEvent[] = [];
+  stream.subscribe((event) => events.push(event));
+
+  assert.equal(stream.isCompleted, true);
+  assert.deepEqual(events, [
+    { event: "delta", data: { text: "done" } },
+    { event: "done", data: { text: "done" } },
+  ]);
+});

web/src/lib/api.ts

@@ -139,6 +139,11 @@ export type ModelCatalogResponse = {
   providers: Record<Provider, ProviderModelInfo>;
 };
 
+export type ActiveRunsResponse = {
+  chats: string[];
+  searches: string[];
+};
+
 type CompletionResponse = {
   chatId: string | null;
   message: {
@@ -217,6 +222,10 @@ export async function listModels() {
   return api<ModelCatalogResponse>("/v1/models");
 }
 
+export async function getActiveRuns() {
+  return api<ActiveRunsResponse>("/v1/active-runs");
+}
+
 export async function createChat(input?: string | CreateChatRequest) {
   const body = typeof input === "string" ? { title: input } : input ?? {};
   const data = await api<{ chat: ChatSummary }>("/v1/chats", {
@@ -333,6 +342,85 @@ type RunSearchStreamHandlers = {
   onError?: (payload: { message: string }) => void;
 };
 
+async function readSseStream(response: Response, dispatch: (eventName: string, payload: any) => void) {
+  if (!response.ok) {
+    const fallback = `${response.status} ${response.statusText}`;
+    let message = fallback;
+    try {
+      const body = (await response.json()) as { message?: string };
+      if (body.message) message = body.message;
+    } catch {
+      // keep fallback message
+    }
+    throw new Error(message);
+  }
+
+  if (!response.body) {
+    throw new Error("No response stream");
+  }
+
+  const reader = response.body.getReader();
+  const decoder = new TextDecoder();
+  let buffer = "";
+  let eventName = "message";
+  let dataLines: string[] = [];
+
+  const flushEvent = () => {
+    if (!dataLines.length) {
+      eventName = "message";
+      return;
+    }
+
+    const dataText = dataLines.join("\n");
+    let payload: any = null;
+    try {
+      payload = JSON.parse(dataText);
+    } catch {
+      payload = { message: dataText };
+    }
+
+    dispatch(eventName, payload);
+
+    dataLines = [];
+    eventName = "message";
+  };
+
+  while (true) {
+    const { value, done } = await reader.read();
+    if (done) break;
+
+    buffer += decoder.decode(value, { stream: true });
+    let newlineIndex = buffer.indexOf("\n");
+
+    while (newlineIndex >= 0) {
+      const rawLine = buffer.slice(0, newlineIndex);
+      buffer = buffer.slice(newlineIndex + 1);
+      const line = rawLine.endsWith("\r") ? rawLine.slice(0, -1) : rawLine;
+
+      if (!line) {
+        flushEvent();
+      } else if (line.startsWith("event:")) {
+        eventName = line.slice("event:".length).trim();
+      } else if (line.startsWith("data:")) {
+        dataLines.push(line.slice("data:".length).trimStart());
+      }
+
+      newlineIndex = buffer.indexOf("\n");
+    }
+  }
+
+  buffer += decoder.decode();
+  if (buffer.length) {
+    const line = buffer.endsWith("\r") ? buffer.slice(0, -1) : buffer;
+    if (line.startsWith("event:")) {
+      eventName = line.slice("event:".length).trim();
+    } else if (line.startsWith("data:")) {
+      dataLines.push(line.slice("data:".length).trimStart());
+    }
+  }
+  flushEvent();
+}
+
 export async function runSearchStream(
   searchId: string,
   body: SearchRunRequest,
@@ -437,6 +525,30 @@ export async function runSearchStream(
   flushEvent();
 }
 
+export async function attachSearchStream(searchId: string, handlers: RunSearchStreamHandlers, options?: { signal?: AbortSignal }) {
+  const headers = new Headers({
+    Accept: "text/event-stream",
+  });
+  if (authToken) {
+    headers.set("Authorization", `Bearer ${authToken}`);
+  }
+
+  const response = await fetch(`${API_BASE_URL}/v1/searches/${searchId}/run/stream/attach`, {
+    method: "POST",
+    headers,
+    signal: options?.signal,
+  });
+
+  await readSseStream(response, (eventName, payload) => {
+    if (eventName === "search_results") handlers.onSearchResults?.(payload);
+    else if (eventName === "search_error") handlers.onSearchError?.(payload);
+    else if (eventName === "answer") handlers.onAnswer?.(payload);
+    else if (eventName === "answer_error") handlers.onAnswerError?.(payload);
+    else if (eventName === "done") handlers.onDone?.(payload);
+    else if (eventName === "error") handlers.onError?.(payload);
+  });
+}
+
 export async function runCompletion(body: {
   chatId: string;
   provider: Provider;
@@ -556,3 +668,26 @@ export async function runCompletionStream(
   }
   flushEvent();
 }
+
+export async function attachCompletionStream(chatId: string, handlers: CompletionStreamHandlers, options?: { signal?: AbortSignal }) {
+  const headers = new Headers({
+    Accept: "text/event-stream",
+  });
+  if (authToken) {
+    headers.set("Authorization", `Bearer ${authToken}`);
+  }
+
+  const response = await fetch(`${API_BASE_URL}/v1/chats/${chatId}/stream/attach`, {
+    method: "POST",
+    headers,
+    signal: options?.signal,
+  });
+
+  await readSseStream(response, (eventName, payload) => {
+    if (eventName === "meta") handlers.onMeta?.(payload);
+    else if (eventName === "tool_call") handlers.onToolCall?.(payload);
+    else if (eventName === "delta") handlers.onDelta?.(payload);
+    else if (eventName === "done") handlers.onDone?.(payload);
+    else if (eventName === "error") handlers.onError?.(payload);
+  });
+}