diff --git a/packages/opencode/src/util/log.ts b/packages/opencode/src/util/log.ts
index 6941310bbbd..d552634dffd 100644
--- a/packages/opencode/src/util/log.ts
+++ b/packages/opencode/src/util/log.ts
@@ -57,7 +57,7 @@ export namespace Log {
 
   export async function init(options: Options) {
     if (options.level) level = options.level
-    cleanup(Global.Path.log)
+    await cleanup(Global.Path.log)
     if (options.print) return
     logpath = path.join(
       Global.Path.log,
@@ -83,7 +83,7 @@ export namespace Log {
     )
     if (files.length <= 5) return
 
-    const filesToDelete = files.slice(0, -10)
+    const filesToDelete = files.sort().slice(0, -10)
     await Promise.all(filesToDelete.map((file) => fs.unlink(file).catch(() => {})))
   }
 
diff --git a/packages/opencode/test/util/log.test.ts b/packages/opencode/test/util/log.test.ts
new file mode 100644
index 00000000000..ca3f71f6b95
--- /dev/null
+++ b/packages/opencode/test/util/log.test.ts
@@ -0,0 +1,140 @@
+import { describe, test, expect, beforeEach, afterEach, setSystemTime } from "bun:test"
+import { Log } from "../../src/util/log"
+import { Global } from "../../src/global"
+import fs from "fs/promises"
+import path from "path"
+
+describe("Log.init", () => {
+  const CLEANUP_THRESHOLD = 5
+
+  beforeEach(clearLogDir)
+  afterEach(clearLogDir)
+
+  test("creates a new log file with timestamp name", async () => {
+    setSystemTime(new Date("2026-01-07T15:00:00.000Z"))
+
+    await Log.init({ print: false })
+
+    const logFile = Log.file()
+    expect(logFile).toBeTruthy()
+    expect(path.basename(logFile)).toBe("2026-01-07T150000.log")
+    expect(await Bun.file(logFile).exists()).toBe(true)
+
+    setSystemTime()
+  })
+
+  test("creates dev.log when dev option is true", async () => {
+    await Log.init({ print: false, dev: true })
+
+    const logFile = Log.file()
+    expect(path.basename(logFile)).toBe("dev.log")
+    expect(await Bun.file(logFile).exists()).toBe(true)
+  })
+
+  test("does not delete files when at threshold", async () => {
+    const startingAt = new Date("2020-01-01")
+    const oldFiles = createLogFiles(CLEANUP_THRESHOLD, startingAt, ONE_DAY)
+    await writeFiles(oldFiles)
+
+    await Log.init({ print: false })
+
+    for (const filename of oldFiles) {
+      const file = getLogFile(filename)
+      expect(await file.exists()).toBe(true)
+    }
+  })
+
+  test("does not delete files when threshold exceeded by 5", async () => {
+    const startingAt = new Date("2020-01-01")
+    const oldFiles = createLogFiles(CLEANUP_THRESHOLD + 5, startingAt, ONE_DAY)
+    await writeFiles(oldFiles)
+
+    await Log.init({ print: false })
+
+    for (const filename of oldFiles) {
+      const file = getLogFile(filename)
+      expect(await file.exists()).toBe(true)
+    }
+  })
+
+  test("deletes the oldest file when threshold exceeded by 6", async () => {
+    const startingAt = new Date("2020-01-01")
+    const oldFiles = createLogFiles(CLEANUP_THRESHOLD + 6, startingAt, ONE_DAY)
+    await writeFiles(oldFiles)
+
+    await Log.init({ print: false })
+
+    const file = getLogFile("2020-01-01T000000.log")
+    expect(await file.exists()).toBe(false)
+  })
+
+  test("preserves the newest 10 files when threshold exceeded by 6", async () => {
+    const startingAt = new Date("2020-01-01")
+    const oldFiles = createLogFiles(CLEANUP_THRESHOLD + 6, startingAt, ONE_DAY)
+    const newestFiles = oldFiles.slice(-10)
+    await writeFiles(oldFiles)
+
+    await Log.init({ print: false })
+
+    for (const filename of newestFiles) {
+      const file = getLogFile(filename)
+      expect(await file.exists()).toBe(true)
+    }
+  })
+
+  test("does not delete dev.log during cleanup", async () => {
+    const startingAt = new Date("2020-01-01")
+    const oldFiles = createLogFiles(CLEANUP_THRESHOLD + 6, startingAt, ONE_DAY)
+    await writeFiles([...oldFiles, "dev.log"])
+
+    await Log.init({ print: false })
+
+    const file = getLogFile("dev.log")
+    expect(await file.exists()).toBe(true)
+  })
+
+  test("creates new log file after cleanup runs", async () => {
+    setSystemTime(new Date("2025-11-02T00:00:00.000Z"))
+    const startingAt = new Date("2020-01-01")
+    const oldFiles = createLogFiles(CLEANUP_THRESHOLD + 6, startingAt, ONE_DAY)
+    await writeFiles(oldFiles)
+
+    await Log.init({ print: false })
+
+    const oldestFile = getLogFile("2020-01-01T000000.log")
+    const newFile = getLogFile("2025-11-02T000000.log")
+    expect(await oldestFile.exists()).toBe(false)
+    expect(await newFile.exists()).toBe(true)
+
+    setSystemTime()
+  })
+})
+
+async function clearLogDir() {
+  const existingLogFiles = await fs.readdir(Global.Path.log).catch(() => [])
+
+  await Promise.all(
+    existingLogFiles.map((existingLogFile) => {
+      const filepath = path.join(Global.Path.log, existingLogFile)
+      return fs.unlink(filepath).catch(() => {})
+    }),
+  )
+}
+
+function writeFiles(filenames: string[]) {
+  return Promise.all(filenames.map((f) => Bun.write(path.join(Global.Path.log, f), "test")))
+}
+
+function getLogFile(filename: string) {
+  return Bun.file(path.join(Global.Path.log, filename))
+}
+
+const ONE_DAY = 1000 * 60 * 60 * 24
+
+function createLogFiles(count: number, startDate: Date, increment = ONE_DAY): string[] {
+  return Array.from({ length: count }, (_, index) => {
+    const creationOffset = index * increment
+    const fileCreatedAt = new Date(startDate.getTime() + creationOffset)
+    return fileCreatedAt.toISOString().split(".")[0].replace(/:/g, "") + ".log"
+  })
+}