fix: stabilize agent and skill ordering in prompt descriptions (#18261)

Co-authored-by: Aiden Cline <aidenpcline@gmail.com>
Co-authored-by: Aiden Cline <63023139+rekram1-node@users.noreply.github.com>

packages/opencode/test/tool/task.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, test } from "bun:test"
+import { Agent } from "../../src/agent/agent"
+import { Instance } from "../../src/project/instance"
+import { TaskTool } from "../../src/tool/task"
+import { tmpdir } from "../fixture/fixture"
+
+describe("tool.task", () => {
+  test("description sorts subagents by name and is stable across calls", async () => {
+    await using tmp = await tmpdir({
+      config: {
+        agent: {
+          zebra: {
+            description: "Zebra agent",
+            mode: "subagent",
+          },
+          alpha: {
+            description: "Alpha agent",
+            mode: "subagent",
+          },
+        },
+      },
+    })
+
+    await Instance.provide({
+      directory: tmp.path,
+      fn: async () => {
+        const build = await Agent.get("build")
+        const first = await TaskTool.init({ agent: build })
+        const second = await TaskTool.init({ agent: build })
+
+        expect(first.description).toBe(second.description)
+
+        const alpha = first.description.indexOf("- alpha: Alpha agent")
+        const explore = first.description.indexOf("- explore:")
+        const general = first.description.indexOf("- general:")
+        const zebra = first.description.indexOf("- zebra: Zebra agent")
+
+        expect(alpha).toBeGreaterThan(-1)
+        expect(explore).toBeGreaterThan(alpha)
+        expect(general).toBeGreaterThan(explore)
+        expect(zebra).toBeGreaterThan(general)
+      },
+    })
+  })
+})