test(perf): add plugin init regression budget

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/__tests__/perf/plugin-init.test.ts

@@ -0,0 +1,121 @@
+import { cpSync, mkdirSync, mkdtempSync, rmSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { join } from "node:path"
+
+import type { PluginInput } from "@opencode-ai/plugin"
+import { createOpencodeClient } from "@opencode-ai/sdk"
+import { describe, expect, it } from "bun:test"
+
+type InitMetrics = {
+  coldMs: number
+  warmMs: [number, number]
+  medianMs: number
+}
+
+function getMedian(values: number[]): number {
+  const sorted = [...values].sort((left, right) => left - right)
+  return sorted[Math.floor(sorted.length / 2)] ?? 0
+}
+
+function createPluginInput(directory: string): PluginInput {
+  const client = createOpencodeClient({ directory })
+
+  return {
+    client,
+    project: {
+      id: `perf-${Date.now()}`,
+      worktree: directory,
+      time: { created: Date.now() },
+    },
+    directory,
+    worktree: directory,
+    serverUrl: new URL("http://localhost"),
+    $: Bun.$,
+  }
+}
+
+async function importFreshPluginModule(): Promise<(typeof import("../../index"))["default"]> {
+  const token = `${Date.now()}-${Math.random()}`
+  return (await import(`../../index?perf=${token}`)).default
+}
+
+async function measureInitMetrics(directory: string): Promise<InitMetrics> {
+  const pluginModule = await importFreshPluginModule()
+  const measurements: number[] = []
+
+  for (let index = 0; index < 3; index += 1) {
+    const input = createPluginInput(directory)
+    const start = performance.now()
+    await pluginModule.server(input, {})
+    measurements.push(performance.now() - start)
+  }
+
+  return {
+    coldMs: measurements[0] ?? 0,
+    warmMs: [measurements[1] ?? 0, measurements[2] ?? 0],
+    medianMs: getMedian(measurements),
+  }
+}
+
+async function measureScenario(
+  label: string,
+  populateDirectory: (directory: string) => void,
+): Promise<InitMetrics> {
+  const rootDirectory = mkdtempSync(join(tmpdir(), "perf-d09-"))
+  const projectDirectory = join(rootDirectory, label)
+  const configDirectory = join(rootDirectory, "opencode-config")
+  const previousConfigDirectory = process.env.OPENCODE_CONFIG_DIR
+
+  mkdirSync(configDirectory, { recursive: true })
+  process.env.OPENCODE_CONFIG_DIR = configDirectory
+
+  try {
+    populateDirectory(projectDirectory)
+    return await measureInitMetrics(projectDirectory)
+  } finally {
+    if (previousConfigDirectory === undefined) {
+      delete process.env.OPENCODE_CONFIG_DIR
+    } else {
+      process.env.OPENCODE_CONFIG_DIR = previousConfigDirectory
+    }
+
+    rmSync(rootDirectory, { recursive: true, force: true })
+  }
+}
+
+function logMetrics(label: string, metrics: InitMetrics): void {
+  console.info(
+    `${label}: cold=${metrics.coldMs.toFixed(1)}ms warm=[${metrics.warmMs.map((value) => value.toFixed(1)).join(", ")}] median=${metrics.medianMs.toFixed(1)}ms`,
+  )
+}
+
+describe("plugin init performance", () => {
+  it("stays within the empty project init budget", async () => {
+    // given
+    const metrics = await measureScenario("empty-project", (directory) => {
+      mkdirSync(directory, { recursive: true })
+    })
+
+    // when
+    logMetrics("empty-project", metrics)
+
+    // then
+    // regression budget
+    expect(metrics.medianMs).toBeLessThan(500)
+  })
+
+  it("stays within the in-tree fixture init budget", async () => {
+    // given
+    const fixtureDirectory = new URL("./fixtures/in-tree/", import.meta.url)
+    const metrics = await measureScenario("in-tree-fixture", (directory) => {
+      cpSync(fixtureDirectory, directory, { recursive: true })
+    })
+
+    // when
+    logMetrics("in-tree-fixture", metrics)
+
+    // then
+    // regression budget
+    expect(metrics.medianMs).toBeLessThan(700)
+  })
+})