diff --git a/packages/console/app/src/routes/zen/util/handler.ts b/packages/console/app/src/routes/zen/util/handler.ts
index ee73b056de..2fe008c1c6 100644
--- a/packages/console/app/src/routes/zen/util/handler.ts
+++ b/packages/console/app/src/routes/zen/util/handler.ts
@@ -39,6 +39,7 @@ import { createRateLimiter } from "./rateLimiter"
 import { createDataDumper } from "./dataDumper"
 import { createTrialLimiter } from "./trialLimiter"
 import { createStickyTracker } from "./stickyProviderTracker"
+import { relay } from "./stream"
 import { LiteData } from "@opencode-ai/console-core/lite.js"
 import { Resource } from "@opencode-ai/console-resource"
 import { i18n, type Key } from "~/i18n"
@@ -254,80 +255,41 @@ export async function handler(
     const streamConverter = createStreamPartConverter(providerInfo.format, opts.format)
     const usageParser = providerInfo.createUsageParser()
     const binaryDecoder = providerInfo.createBinaryStreamDecoder()
-    const stream = new ReadableStream({
-      start(c) {
-        const reader = res.body?.getReader()
-        const decoder = new TextDecoder()
-        const encoder = new TextEncoder()
-
-        let buffer = ""
-        let responseLength = 0
-
-        function pump(): Promise<void> {
-          return (
-            reader?.read().then(async ({ done, value: rawValue }) => {
-              if (done) {
-                logger.metric({
-                  response_length: responseLength,
-                  "timestamp.last_byte": Date.now(),
-                })
-                dataDumper?.flush()
-                await rateLimiter?.track()
-                const usage = usageParser.retrieve()
-                if (usage) {
-                  const usageInfo = providerInfo.normalizeUsage(usage)
-                  const costInfo = calculateCost(modelInfo, usageInfo)
-                  await trialLimiter?.track(usageInfo)
-                  await trackUsage(sessionId, billingSource, authInfo, modelInfo, providerInfo, usageInfo, costInfo)
-                  await reload(billingSource, authInfo, costInfo)
-                  const cost = calculateOccurredCost(billingSource, costInfo)
-                  c.enqueue(encoder.encode(buildCostChunk(opts.format, cost)))
-                }
-                c.close()
-                return
-              }
-
-              if (responseLength === 0) {
-                const now = Date.now()
-                logger.metric({
-                  time_to_first_byte: now - startTimestamp,
-                  "timestamp.first_byte": now,
-                })
-              }
-
-              const value = binaryDecoder ? binaryDecoder(rawValue) : rawValue
-              if (!value) return
-
-              responseLength += value.length
-              buffer += decoder.decode(value, { stream: true })
-              dataDumper?.provideStream(buffer)
-
-              const parts = buffer.split(providerInfo.streamSeparator)
-              buffer = parts.pop() ?? ""
-
-              for (let part of parts) {
-                logger.debug("PART: " + part)
-
-                part = part.trim()
-                usageParser.parse(part)
-
-                if (providerInfo.format !== opts.format) {
-                  part = streamConverter(part)
-                  c.enqueue(encoder.encode(part + "\n\n"))
-                }
-              }
-
-              if (providerInfo.format === opts.format) {
-                c.enqueue(value)
-              }
-
-              return pump()
-            }) || Promise.resolve()
-          )
-        }
-
-        return pump()
+    const metric = (values: Record<string, unknown>) =>
+      logger.metric({
+        request: requestId,
+        session: sessionId,
+        client: ocClient,
+        provider: providerInfo.id,
+        model: modelInfo.id,
+        ...values,
+      })
+    const stream = relay({
+      body: res.body,
+      separator: providerInfo.streamSeparator,
+      signal: input.request.signal,
+      start: startTimestamp,
+      same: providerInfo.format === opts.format,
+      binary: binaryDecoder,
+      parse: (part) => {
+        logger.debug("PART: " + part)
+        usageParser.parse(part)
       },
+      convert: streamConverter,
+      tail: async () => {
+        await rateLimiter?.track()
+        const usage = usageParser.retrieve()
+        if (!usage) return
+        const usageInfo = providerInfo.normalizeUsage(usage)
+        const costInfo = calculateCost(modelInfo, usageInfo)
+        await trialLimiter?.track(usageInfo)
+        await trackUsage(sessionId, billingSource, authInfo, modelInfo, providerInfo, usageInfo, costInfo)
+        await reload(billingSource, authInfo, costInfo)
+        const cost = calculateOccurredCost(billingSource, costInfo)
+        return buildCostChunk(opts.format, cost)
+      },
+      metric,
+      dump: dataDumper,
     })
     return new Response(stream, {
       status: resStatus,
diff --git a/packages/console/app/src/routes/zen/util/stream.ts b/packages/console/app/src/routes/zen/util/stream.ts
new file mode 100644
index 0000000000..7bfc962d71
--- /dev/null
+++ b/packages/console/app/src/routes/zen/util/stream.ts
@@ -0,0 +1,196 @@
+const done = new Set(["[DONE]", "message_stop", "response.completed"])
+
+type Dump = {
+  provideStream: (chunk: string) => void
+  flush: () => void
+}
+
+type Opts = {
+  body: ReadableStream<Uint8Array> | null | undefined
+  separator: string
+  signal: AbortSignal
+  start: number
+  same: boolean
+  binary?: (chunk: Uint8Array) => Uint8Array | undefined
+  parse: (part: string) => void
+  convert: (part: string) => string
+  tail: () => Promise<string | undefined>
+  metric: (values: Record<string, unknown>) => void
+  dump?: Dump
+}
+
+export const eventName = (part: string) => {
+  const line = part.split("\n", 1)[0]?.trim() ?? ""
+  if (line.startsWith("event:")) return line.slice(6).trim() || "message"
+  if (part.includes("[DONE]")) return "[DONE]"
+  if (line.startsWith("data:")) return "message"
+  return "unknown"
+}
+
+const errInfo = (err: unknown) => {
+  if (err instanceof Error) {
+    return {
+      "stream.error_type": err.constructor.name,
+      "stream.error_message": err.message,
+    }
+  }
+
+  return {
+    "stream.error_type": typeof err,
+    "stream.error_message": String(err),
+  }
+}
+
+const stats = (len: number, cnt: number, seen: number, buf: string, end: string | undefined, gap: number) => ({
+  "stream.response_length": len,
+  "stream.chunk_count": cnt,
+  "stream.event_count": seen,
+  "stream.pending_length": buf.length,
+  "stream.last_event": end,
+  "stream.max_gap_ms": gap || undefined,
+})
+
+export const relay = (opts: Opts) =>
+  new ReadableStream({
+    async start(c) {
+      let phase = "start"
+      let len = 0
+      let cnt = 0
+      let seen = 0
+      let end: string | undefined
+      let gap = 0
+      let prev: number | undefined
+      let completed = false
+      let aborted = false
+      let buf = ""
+
+      if (!opts.body) {
+        opts.metric({
+          "stream.event": "missing_body",
+          "stream.phase": phase,
+        })
+        opts.dump?.flush()
+        c.close()
+        return
+      }
+
+      const reader = opts.body.getReader()
+      const dec = new TextDecoder()
+      const enc = new TextEncoder()
+      const names: Record<string, number> = {}
+
+      const abort = () => {
+        aborted = true
+        reader.cancel().catch(() => undefined)
+      }
+
+      const note = (part: string) => {
+        const name = eventName(part)
+        end = name
+        seen += 1
+        names[name] = (names[name] ?? 0) + 1
+        if (done.has(name)) completed = true
+      }
+
+      opts.signal.addEventListener("abort", abort)
+      opts.metric({
+        "stream.event": "started",
+      })
+
+      try {
+        while (true) {
+          phase = "read"
+          const raw = await reader.read()
+          if (raw.done) break
+
+          if (len === 0) {
+            const now = Date.now()
+            opts.metric({
+              time_to_first_byte: now - opts.start,
+              "timestamp.first_byte": now,
+            })
+          }
+
+          const value = opts.binary ? opts.binary(raw.value) : raw.value
+          if (!value) continue
+
+          cnt += 1
+          len += value.length
+          const now = Date.now()
+          if (prev !== undefined) gap = Math.max(gap, now - prev)
+          prev = now
+
+          const text = dec.decode(value, { stream: true })
+          buf += text
+          opts.dump?.provideStream(text)
+
+          const parts = buf.split(opts.separator)
+          buf = parts.pop() ?? ""
+
+          for (let part of parts) {
+            part = part.trim()
+            if (!part) continue
+            note(part)
+            phase = "parse"
+            opts.parse(part)
+            if (opts.same) continue
+            phase = "convert"
+            c.enqueue(enc.encode(opts.convert(part) + "\n\n"))
+          }
+
+          if (opts.same) c.enqueue(value)
+        }
+
+        const tail = dec.decode()
+        if (tail) {
+          buf += tail
+          opts.dump?.provideStream(tail)
+        }
+
+        if (buf.trim()) {
+          const part = buf.trim()
+          note(part)
+          phase = "parse"
+          opts.parse(part)
+          if (!opts.same) {
+            phase = "convert"
+            c.enqueue(enc.encode(opts.convert(part) + "\n\n"))
+          }
+          buf = ""
+        }
+
+        opts.metric({
+          response_length: len,
+          "timestamp.last_byte": Date.now(),
+        })
+        opts.dump?.flush()
+
+        phase = "tail"
+        const chunk = await opts.tail()
+        if (chunk) c.enqueue(enc.encode(chunk))
+
+        c.close()
+        opts.metric({
+          "stream.event": "finished",
+          "stream.phase": "done",
+          "stream.duration_ms": Date.now() - opts.start,
+          "stream.saw_completed": completed,
+          "stream.events": JSON.stringify(names),
+          ...stats(len, cnt, seen, buf, end, gap),
+        })
+      } catch (err) {
+        opts.metric({
+          "stream.event": aborted ? "aborted" : "error",
+          "stream.phase": phase,
+          "stream.duration_ms": Date.now() - opts.start,
+          "stream.saw_completed": completed,
+          "stream.events": JSON.stringify(names),
+          ...stats(len, cnt, seen, buf, end, gap),
+          ...errInfo(err),
+        })
+        c.error(err)
+      } finally {
+        opts.signal.removeEventListener("abort", abort)
+      }
+    },
+  })
diff --git a/packages/console/app/test/zenStream.test.ts b/packages/console/app/test/zenStream.test.ts
new file mode 100644
index 0000000000..5540429a04
--- /dev/null
+++ b/packages/console/app/test/zenStream.test.ts
@@ -0,0 +1,139 @@
+import { describe, expect, test } from "bun:test"
+import { eventName, relay } from "../src/routes/zen/util/stream"
+
+const enc = new TextEncoder()
+
+const read = (stream: ReadableStream<Uint8Array>) => new Response(stream).text()
+
+const body = (parts: string[]) =>
+  new ReadableStream<Uint8Array>({
+    async start(c) {
+      for (const part of parts) c.enqueue(enc.encode(part))
+      c.close()
+    },
+  })
+
+describe("zen stream", () => {
+  test("parses known event names", () => {
+    expect(eventName("event: response.created\ndata: {}")).toBe("response.created")
+    expect(eventName('data: {"ok":true}')).toBe("message")
+    expect(eventName("data: [DONE]")).toBe("[DONE]")
+  })
+
+  test("relays split OpenAI responses and logs completion", async () => {
+    const seen: string[] = []
+    const logs: Array<Record<string, unknown>> = []
+    const stream = relay({
+      body: body([
+        "event: response.created\n",
+        'data: {"type":"response.created"}\n\n',
+        "event: response.completed\n",
+        'data: {"response":{"usage":{"input_tokens":1,"output_tokens":2}}}\n\n',
+      ]),
+      separator: "\n\n",
+      signal: new AbortController().signal,
+      start: Date.now(),
+      same: true,
+      parse: (part) => {
+        seen.push(part)
+      },
+      convert: (part) => part,
+      tail: async () => undefined,
+      metric: (values) => logs.push(values),
+    })
+
+    const text = await read(stream)
+    expect(text).toContain("response.created")
+    expect(text).toContain("response.completed")
+    expect(seen).toHaveLength(2)
+    expect(logs.at(-1)?.["stream.event"]).toBe("finished")
+    expect(logs.at(-1)?.["stream.saw_completed"]).toBe(true)
+  })
+
+  test("keeps reading when binary decoder needs another chunk", async () => {
+    let calls = 0
+    const logs: Array<Record<string, unknown>> = []
+    const stream = relay({
+      body: body(["a", "b"]),
+      separator: "\n\n",
+      signal: new AbortController().signal,
+      start: Date.now(),
+      same: true,
+      binary: (chunk) => {
+        calls += 1
+        if (calls === 1) return
+        return chunk
+      },
+      parse: () => undefined,
+      convert: (part) => part,
+      tail: async () => undefined,
+      metric: (values) => logs.push(values),
+    })
+
+    const text = await read(stream)
+    expect(text).toBe("b")
+    expect(logs.at(-1)?.["stream.event"]).toBe("finished")
+  })
+
+  test("flushes a final unterminated event at EOF", async () => {
+    const seen: string[] = []
+    const logs: Array<Record<string, unknown>> = []
+    const stream = relay({
+      body: body(['event: response.completed\ndata: {"response":{"usage":{"input_tokens":1}}}']),
+      separator: "\n\n",
+      signal: new AbortController().signal,
+      start: Date.now(),
+      same: true,
+      parse: (part) => {
+        seen.push(part)
+      },
+      convert: (part) => part,
+      tail: async () => undefined,
+      metric: (values) => logs.push(values),
+    })
+
+    const text = await read(stream)
+    expect(text).toContain("response.completed")
+    expect(seen).toHaveLength(1)
+    expect(logs.at(-1)?.["stream.saw_completed"]).toBe(true)
+  })
+
+  test("closes cleanly when upstream body is missing", async () => {
+    const logs: Array<Record<string, unknown>> = []
+    const stream = relay({
+      body: null,
+      separator: "\n\n",
+      signal: new AbortController().signal,
+      start: Date.now(),
+      same: true,
+      parse: () => undefined,
+      convert: (part) => part,
+      tail: async () => undefined,
+      metric: (values) => logs.push(values),
+    })
+
+    expect(await read(stream)).toBe("")
+    expect(logs.at(-1)?.["stream.event"]).toBe("missing_body")
+  })
+
+  test("surfaces postprocess failures with stream metrics", async () => {
+    const logs: Array<Record<string, unknown>> = []
+    const stream = relay({
+      body: body(["event: response.created\ndata: {}\n\n"]),
+      separator: "\n\n",
+      signal: new AbortController().signal,
+      start: Date.now(),
+      same: true,
+      parse: () => undefined,
+      convert: (part) => part,
+      tail: async () => {
+        throw new Error("boom")
+      },
+      metric: (values) => logs.push(values),
+    })
+
+    await expect(read(stream)).rejects.toThrow("boom")
+    expect(logs.at(-1)?.["stream.event"]).toBe("error")
+    expect(logs.at(-1)?.["stream.phase"]).toBe("tail")
+  })
+})