diff --git a/packages/opencode/src/util/effect-log.ts b/packages/opencode/src/util/effect-log.ts
new file mode 100644
index 00000000000..59d42e7ed65
--- /dev/null
+++ b/packages/opencode/src/util/effect-log.ts
@@ -0,0 +1,56 @@
+import { Cause, Logger } from "effect"
+import { CurrentLogAnnotations, CurrentLogSpans } from "effect/References"
+
+import { Log } from "./log"
+
+function text(input: unknown): string {
+  if (Array.isArray(input)) return input.map(text).join(" ")
+  if (input instanceof Error) return input.message
+  if (typeof input === "string") return input
+  if (typeof input === "object" && input !== null) {
+    try {
+      return JSON.stringify(input)
+    } catch {
+      return String(input)
+    }
+  }
+  return String(input)
+}
+
+export function make(tags?: Record<string, unknown>) {
+  const log = Log.create(tags)
+
+  return Logger.make<unknown, void>((options) => {
+    const annotations = options.fiber.getRef(CurrentLogAnnotations as never) as Readonly<Record<string, unknown>>
+    const spans = options.fiber.getRef(CurrentLogSpans as never) as ReadonlyArray<readonly [string, number]>
+    const extra = {
+      ...annotations,
+      fiber: options.fiber.id,
+      spans: spans.length
+        ? spans.map(([label, start]) => ({
+            label,
+            duration: options.date.getTime() - start,
+          }))
+        : undefined,
+      cause: options.cause.reasons.length ? Cause.pretty(options.cause) : undefined,
+    }
+
+    if (options.logLevel === "Debug" || options.logLevel === "Trace") {
+      return log.debug(text(options.message), extra)
+    }
+
+    if (options.logLevel === "Info") {
+      return log.info(text(options.message), extra)
+    }
+
+    if (options.logLevel === "Warn") {
+      return log.warn(text(options.message), extra)
+    }
+
+    return log.error(text(options.message), extra)
+  })
+}
+
+export function layer(tags?: Record<string, unknown>, options?: { mergeWithExisting?: boolean }) {
+  return Logger.layer([make(tags)], options)
+}
diff --git a/packages/opencode/test/util/effect-log.test.ts b/packages/opencode/test/util/effect-log.test.ts
new file mode 100644
index 00000000000..e70d79b1628
--- /dev/null
+++ b/packages/opencode/test/util/effect-log.test.ts
@@ -0,0 +1,99 @@
+import { afterEach, expect, mock, spyOn, test } from "bun:test"
+import { Cause, Effect } from "effect"
+import { CurrentLogAnnotations, CurrentLogSpans } from "effect/References"
+
+import * as EffectLog from "../../src/util/effect-log"
+import { Log } from "../../src/util/log"
+
+const debug = mock(() => {})
+const info = mock(() => {})
+const warn = mock(() => {})
+const error = mock(() => {})
+
+const logger = {
+  debug,
+  info,
+  warn,
+  error,
+  tag() {
+    return logger
+  },
+  clone() {
+    return logger
+  },
+  time() {
+    return {
+      stop() {},
+      [Symbol.dispose]() {},
+    }
+  },
+}
+
+afterEach(() => {
+  debug.mockClear()
+  info.mockClear()
+  warn.mockClear()
+  error.mockClear()
+})
+
+test("EffectLog.layer routes info logs through util/log", async () => {
+  using create = spyOn(Log, "create").mockReturnValue(logger)
+
+  await Effect.runPromise(Effect.logInfo("hello").pipe(Effect.provide(EffectLog.layer({ service: "effect-test" }))))
+
+  expect(create).toHaveBeenCalledWith({ service: "effect-test" })
+  expect(info).toHaveBeenCalledWith("hello", expect.any(Object))
+})
+
+test("EffectLog.layer forwards annotations and spans to util/log", async () => {
+  using create = spyOn(Log, "create").mockReturnValue(logger)
+
+  await Effect.runPromise(
+    Effect.logInfo("hello").pipe(
+      Effect.annotateLogs({ requestId: "req-123" }),
+      Effect.withLogSpan("provider-auth"),
+      Effect.provide(EffectLog.layer({ service: "effect-test-meta" })),
+    ),
+  )
+
+  expect(create).toHaveBeenCalledWith({ service: "effect-test-meta" })
+  expect(info).toHaveBeenCalledWith(
+    "hello",
+    expect.objectContaining({
+      requestId: "req-123",
+      spans: expect.arrayContaining([
+        expect.objectContaining({
+          label: "provider-auth",
+        }),
+      ]),
+    }),
+  )
+})
+
+test("EffectLog.make formats structured messages and causes for legacy logger", () => {
+  using create = spyOn(Log, "create").mockReturnValue(logger)
+  const effect = EffectLog.make({ service: "effect-test-struct" })
+
+  effect.log({
+    message: { hello: "world" },
+    logLevel: "Warn",
+    cause: Cause.fail(new Error("boom")),
+    fiber: {
+      id: 123n,
+      getRef(ref: unknown) {
+        if (ref === CurrentLogAnnotations) return {}
+        if (ref === CurrentLogSpans) return []
+        return undefined
+      },
+    },
+    date: new Date(),
+  } as never)
+
+  expect(create).toHaveBeenCalledWith({ service: "effect-test-struct" })
+  expect(warn).toHaveBeenCalledWith(
+    '{"hello":"world"}',
+    expect.objectContaining({
+      fiber: 123n,
+    }),
+  )
+})