diff --git a/packages/core/script/fsevents-diagnostic.mjs b/packages/core/script/fsevents-diagnostic.mjs
new file mode 100644
index 0000000000..00658f49d7
--- /dev/null
+++ b/packages/core/script/fsevents-diagnostic.mjs
@@ -0,0 +1,57 @@
+import watcher from "@parcel/watcher"
+import { execFileSync } from "node:child_process"
+import fs from "node:fs/promises"
+import os from "node:os"
+import path from "node:path"
+
+const rounds = Number(process.env.FSEVENTS_ROUNDS ?? 100)
+const width = Number(process.env.FSEVENTS_WIDTH ?? 25)
+const root = await fs.mkdtemp(path.join(os.tmpdir(), "opencode-fsevents-"))
+const targets = Array.from({ length: width }, (_, index) => path.join(root, `project-${index}`))
+await Promise.all(targets.map((target) => fs.mkdir(target)))
+
+function openFiles() {
+  try {
+    return Number(execFileSync("sh", ["-c", `lsof -p ${process.pid} 2>/dev/null | wc -l`], { encoding: "utf8" }).trim())
+  } catch {
+    return -1
+  }
+}
+
+function sample(round) {
+  const memory = process.memoryUsage()
+  console.log(
+    JSON.stringify({
+      round,
+      subscriptions: round * width,
+      rss: memory.rss,
+      heapUsed: memory.heapUsed,
+      external: memory.external,
+      openFiles: openFiles(),
+    }),
+  )
+}
+
+try {
+  sample(0)
+  for (let round = 1; round <= rounds; round++) {
+    const subscriptions = await Promise.all(
+      targets.map((target) => watcher.subscribe(target, () => {}, { backend: "fs-events" })),
+    )
+    await Promise.all(
+      targets.map((target, index) => fs.writeFile(path.join(target, "event.txt"), `${round}-${index}`)),
+    )
+    await new Promise((resolve) => setTimeout(resolve, 10))
+    await Promise.all(subscriptions.map((subscription) => subscription.unsubscribe()))
+
+    if (round % 10 === 0 || round === rounds) sample(round)
+  }
+
+  if (globalThis.gc) {
+    globalThis.gc()
+    await new Promise((resolve) => setTimeout(resolve, 100))
+    sample("after-gc")
+  }
+} finally {
+  await fs.rm(root, { recursive: true, force: true })
+}
diff --git a/packages/core/test/filesystem/watcher-stress.test.ts b/packages/core/test/filesystem/watcher-stress.test.ts
new file mode 100644
index 0000000000..34338d90a4
--- /dev/null
+++ b/packages/core/test/filesystem/watcher-stress.test.ts
@@ -0,0 +1,46 @@
+import watcher from "@parcel/watcher"
+import { describe, expect, test } from "bun:test"
+import fs from "node:fs/promises"
+import os from "node:os"
+import path from "node:path"
+
+const backend = process.platform === "darwin" ? "fs-events" : process.platform === "linux" ? "inotify" : undefined
+const describeNative = backend ? describe : describe.skip
+
+async function descriptors() {
+  if (process.platform === "linux") return fs.readdir("/proc/self/fd").then((entries) => entries.length)
+  return Number(Bun.spawnSync(["sh", "-c", `lsof -p ${process.pid} 2>/dev/null | wc -l`]).stdout.toString().trim())
+}
+
+describeNative("native watcher stress diagnostic", () => {
+  test(
+    "releases native descriptors after repeated subscription churn",
+    async () => {
+      const root = await fs.mkdtemp(path.join(os.tmpdir(), "opencode-watcher-stress-"))
+      const targets = Array.from({ length: 20 }, (_, index) => path.join(root, `project-${index}`))
+      await Promise.all(targets.map((target) => fs.mkdir(target)))
+      const before = await descriptors()
+
+      try {
+        for (let round = 0; round < 100; round++) {
+          const subscriptions = await Promise.all(
+            targets.map((target) => watcher.subscribe(target, () => {}, { backend })),
+          )
+          await Promise.all(
+            targets.map((target, index) => fs.writeFile(path.join(target, "event.txt"), `${round}-${index}`)),
+          )
+          await Promise.all(subscriptions.map((subscription) => subscription.unsubscribe()))
+        }
+
+        Bun.gc(true)
+        await Bun.sleep(250)
+        const after = await descriptors()
+        console.log(JSON.stringify({ subscriptions: targets.length * 100, before, after }))
+        expect(after - before).toBeLessThanOrEqual(4)
+      } finally {
+        await fs.rm(root, { recursive: true, force: true })
+      }
+    },
+    60_000,
+  )
+})