feat(hooks): add delegate-task-english-directive hook to enforce English for subagents

Appends bold uppercase English-only directive to explore, librarian,
oracle, and plan subagent prompts via tool.execute.before on the task tool.

src/config/schema/hooks.ts

@@ -51,6 +51,7 @@ export const HookNameSchema = z.enum([
   "anthropic-effort",
   "hashline-read-enhancer",
   "read-image-resizer",
+  "delegate-task-english-directive",
 ])
 
 export type HookName = z.infer<typeof HookNameSchema>

src/hooks/delegate-task-english-directive/hook.ts

@@ -0,0 +1,24 @@
+export const TARGET_SUBAGENT_TYPES = ["explore", "librarian", "oracle", "plan"] as const
+
+export const ENGLISH_DIRECTIVE =
+  "**YOU MUST ALWAYS THINK, REASON, AND RESPOND IN ENGLISH REGARDLESS OF THE USER'S QUERY LANGUAGE.**"
+
+export function createDelegateTaskEnglishDirectiveHook() {
+  return {
+    "tool.execute.before": async (
+      input: { tool: string; sessionID: string; callID: string; input: Record<string, unknown> },
+      _output: { title: string; output: string; metadata: unknown }
+    ) => {
+      if (input.tool.toLowerCase() !== "task") return
+
+      const args = input.input
+      const subagentType = args.subagent_type
+      if (typeof subagentType !== "string") return
+      if (!TARGET_SUBAGENT_TYPES.includes(subagentType as (typeof TARGET_SUBAGENT_TYPES)[number])) return
+
+      if (typeof args.prompt === "string") {
+        args.prompt = `${args.prompt}\n\n${ENGLISH_DIRECTIVE}`
+      }
+    },
+  }
+}

src/hooks/delegate-task-english-directive/index.test.ts

@@ -0,0 +1,98 @@
+import { describe, expect, it } from "bun:test"
+
+import { createDelegateTaskEnglishDirectiveHook, ENGLISH_DIRECTIVE, TARGET_SUBAGENT_TYPES } from "./index"
+
+describe("delegate-task-english-directive", () => {
+  const hook = createDelegateTaskEnglishDirectiveHook()
+  const handler = hook["tool.execute.before"]
+
+  describe("#given a task tool call with a targeted subagent_type", () => {
+    const targetTypes = ["explore", "librarian", "oracle", "plan"]
+
+    for (const subagentType of targetTypes) {
+      describe(`#when subagent_type is "${subagentType}"`, () => {
+        it(`#then should append English directive to prompt`, async () => {
+          const originalPrompt = "Find auth patterns in the codebase"
+          const input = { tool: "Task", sessionID: "ses_123", callID: "call_1", input: { subagent_type: subagentType, prompt: originalPrompt } }
+          const output = { title: "", output: "", metadata: undefined }
+
+          await handler(input, output)
+
+          expect(input.input.prompt).toBe(`${originalPrompt}\n\n${ENGLISH_DIRECTIVE}`)
+        })
+      })
+    }
+  })
+
+  describe("#given a task tool call with a non-targeted subagent_type", () => {
+    describe("#when subagent_type is 'metis'", () => {
+      it("#then should not modify the prompt", async () => {
+        const originalPrompt = "Analyze this request"
+        const input = { tool: "Task", sessionID: "ses_123", callID: "call_1", input: { subagent_type: "metis", prompt: originalPrompt } }
+        const output = { title: "", output: "", metadata: undefined }
+
+        await handler(input, output)
+
+        expect(input.input.prompt).toBe(originalPrompt)
+      })
+    })
+  })
+
+  describe("#given a task tool call using category instead of subagent_type", () => {
+    describe("#when only category is provided", () => {
+      it("#then should not modify the prompt", async () => {
+        const originalPrompt = "Fix the button styling"
+        const input = { tool: "Task", sessionID: "ses_123", callID: "call_1", input: { category: "visual-engineering", prompt: originalPrompt } }
+        const output = { title: "", output: "", metadata: undefined }
+
+        await handler(input, output)
+
+        expect(input.input.prompt).toBe(originalPrompt)
+      })
+    })
+  })
+
+  describe("#given a non-task tool call", () => {
+    describe("#when tool is 'Bash'", () => {
+      it("#then should not modify anything", async () => {
+        const input = { tool: "Bash", sessionID: "ses_123", callID: "call_1", input: { command: "ls" } }
+        const output = { title: "", output: "", metadata: undefined }
+
+        await handler(input, output)
+
+        expect(input.input).toEqual({ command: "ls" })
+      })
+    })
+  })
+
+  describe("#given a task tool call with empty prompt", () => {
+    describe("#when prompt is empty string", () => {
+      it("#then should still append directive", async () => {
+        const input = { tool: "Task", sessionID: "ses_123", callID: "call_1", input: { subagent_type: "explore", prompt: "" } }
+        const output = { title: "", output: "", metadata: undefined }
+
+        await handler(input, output)
+
+        expect(input.input.prompt).toBe(`\n\n${ENGLISH_DIRECTIVE}`)
+      })
+    })
+  })
+
+  describe("#given TARGET_SUBAGENT_TYPES constant", () => {
+    it("#then should contain exactly explore, librarian, oracle, and plan", () => {
+      expect(TARGET_SUBAGENT_TYPES).toEqual(["explore", "librarian", "oracle", "plan"])
+    })
+  })
+
+  describe("#given ENGLISH_DIRECTIVE constant", () => {
+    it("#then should be bold uppercase text", () => {
+      expect(ENGLISH_DIRECTIVE).toContain("**")
+      expect(ENGLISH_DIRECTIVE).toMatch(/[A-Z]/)
+    })
+
+    it("#then should instruct English-only thinking and responding", () => {
+      const lower = ENGLISH_DIRECTIVE.toLowerCase()
+      expect(lower).toContain("english")
+    })
+  })
+})

src/hooks/delegate-task-english-directive/index.ts

@@ -0,0 +1 @@
+export { createDelegateTaskEnglishDirectiveHook, TARGET_SUBAGENT_TYPES, ENGLISH_DIRECTIVE } from "./hook"

src/hooks/index.ts

@@ -52,3 +52,4 @@ export { createWriteExistingFileGuardHook } from "./write-existing-file-guard";
 export { createHashlineReadEnhancerHook } from "./hashline-read-enhancer";
 export { createJsonErrorRecoveryHook, JSON_ERROR_TOOL_EXCLUDE_LIST, JSON_ERROR_PATTERNS, JSON_ERROR_REMINDER } from "./json-error-recovery";
 export { createReadImageResizerHook } from "./read-image-resizer"
+export { createDelegateTaskEnglishDirectiveHook } from "./delegate-task-english-directive"

src/plugin/hooks/create-session-hooks.ts

@@ -16,6 +16,7 @@ import {
   createRalphLoopHook,
   createEditErrorRecoveryHook,
   createDelegateTaskRetryHook,
+  createDelegateTaskEnglishDirectiveHook,
   createTaskResumeInfoHook,
   createStartWorkHook,
   createPrometheusMdOnlyHook,
@@ -60,6 +61,7 @@ export type SessionHooks = {
   taskResumeInfo: ReturnType<typeof createTaskResumeInfoHook> | null
   anthropicEffort: ReturnType<typeof createAnthropicEffortHook> | null
   runtimeFallback: ReturnType<typeof createRuntimeFallbackHook> | null
+  delegateTaskEnglishDirective: ReturnType<typeof createDelegateTaskEnglishDirectiveHook> | null
 }
 
 export function createSessionHooks(args: {
@@ -215,6 +217,10 @@ export function createSessionHooks(args: {
     ? safeHook("delegate-task-retry", () => createDelegateTaskRetryHook(ctx))
     : null
 
+  const delegateTaskEnglishDirective = isHookEnabled("delegate-task-english-directive")
+    ? safeHook("delegate-task-english-directive", () => createDelegateTaskEnglishDirectiveHook())
+    : null
+
   const startWork = isHookEnabled("start-work")
     ? safeHook("start-work", () => createStartWorkHook(ctx))
     : null
@@ -276,6 +282,7 @@ export function createSessionHooks(args: {
     ralphLoop,
     editErrorRecovery,
     delegateTaskRetry,
+    delegateTaskEnglishDirective,
     startWork,
     prometheusMdOnly,
     sisyphusJuniorNotepad,