test(ultrawork): add byte-exact characterization test

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

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

src/hooks/keyword-detector/ultrawork/ultrawork-byte-exactness.test.ts

@@ -0,0 +1,62 @@
+/// <reference types="bun-types" />
+
+import { describe, expect, test } from "bun:test"
+import { createHash } from "node:crypto"
+import { getUltraworkMessage, getUltraworkSource } from "./index"
+import type { UltraworkSource } from "./source-detector"
+
+type UltraworkPromptBaseline = {
+  readonly name: string
+  readonly agentName: string
+  readonly modelID: string
+  readonly expectedSource: UltraworkSource
+  readonly sha256: string
+}
+
+const ULTRAWORK_PROMPT_BASELINES: readonly UltraworkPromptBaseline[] = [
+  {
+    name: "default",
+    agentName: "sisyphus",
+    modelID: "claude-sonnet-4-6",
+    expectedSource: "default",
+    sha256: "78aa43e2e2b7db307827d9ddda30a4c6a24aa35a9255efe1ee39a4476d71acca",
+  },
+  {
+    name: "gpt",
+    agentName: "sisyphus",
+    modelID: "gpt-5.5",
+    expectedSource: "gpt",
+    sha256: "8f31f0053256914e94605944b28e123c584a0ad093e0d44d5ad66da009a632ae",
+  },
+  {
+    name: "gemini",
+    agentName: "sisyphus",
+    modelID: "gemini-3.1-pro",
+    expectedSource: "gemini",
+    sha256: "5c5766549e868e7a1c87252e742e491b7015138948c6e26fb704346bb55d5d7c",
+  },
+  {
+    name: "planner",
+    agentName: "prometheus",
+    modelID: "gpt-5.5",
+    expectedSource: "planner",
+    sha256: "8897b3a11b61c12a02bfba13a76c80742bc4e5356cfc30e2f0c38464aa587bf3",
+  },
+]
+
+describe("Ultrawork prompt byte exactness", () => {
+  test("#given captured ultrawork prompt baselines #then every routed source keeps the same bytes", () => {
+    for (const baseline of ULTRAWORK_PROMPT_BASELINES) {
+      const source = getUltraworkSource(baseline.agentName, baseline.modelID)
+      const prompt = getUltraworkMessage(baseline.agentName, baseline.modelID)
+
+      expect(source, baseline.name).toBe(baseline.expectedSource)
+      expect(prompt.length, baseline.name).toBeGreaterThan(0)
+      expect(hashPrompt(prompt), baseline.name).toBe(baseline.sha256)
+    }
+  })
+})
+
+function hashPrompt(prompt: string): string {
+  return createHash("sha256").update(prompt).digest("hex")
+}