feat(aircoding): AirCoding V2 baseline — deterministic multi-agent architecture

Forked from OpenCode v1.17.4 with multi-agent system:
- 5 agents: aircoding, scheduler, worker, architect, reviewer
- Deterministic DAG scheduling engine (coordinator_tick)
- Tool whitelists as hard enforcement
- AirCoding validation plugin
- V1 requirements: C4 docs, ADR, AGENTS.md, debug-log.md
- Design documents in docs/

packages/core/test/fixture/tmpdir.ts

@@ -0,0 +1,25 @@
+import fs from "fs/promises"
+import { tmpdir as osTmpdir } from "os"
+import path from "path"
+
+export const tmpdir = async () => {
+  const dir = await fs.realpath(await fs.mkdtemp(path.join(osTmpdir(), "opencode-core-test-")))
+  return {
+    path: dir,
+    async [Symbol.asyncDispose]() {
+      await remove(dir)
+    },
+  }
+}
+
+async function remove(dir: string, retries = 30): Promise<void> {
+  try {
+    await fs.rm(dir, { recursive: true, force: true })
+  } catch (error) {
+    if (retries === 0 || !error || typeof error !== "object" || !("code" in error) || error.code !== "EBUSY")
+      throw error
+    Bun.gc(true)
+    await Bun.sleep(100)
+    return remove(dir, retries - 1)
+  }
+}