diff --git a/src/tools/delegate-task/background-task.ts b/src/tools/delegate-task/background-task.ts
index aedd0b3eb..fd273fb95 100644
--- a/src/tools/delegate-task/background-task.ts
+++ b/src/tools/delegate-task/background-task.ts
@@ -2,6 +2,7 @@ import type { DelegateTaskArgs, ToolContextWithMetadata } from "./types"
 import type { ExecutorContext, ParentContext } from "./executor-types"
 import type { FallbackEntry } from "../../shared/model-requirements"
 import { getTimingConfig } from "./timing"
+import { buildTaskPrompt } from "./prompt-builder"
 import { storeToolMetadata } from "../../features/tool-metadata-store"
 import { formatDetailedError } from "./error-formatting"
 import { getSessionTools } from "../../shared/session-tools-store"
@@ -20,9 +21,10 @@ export async function executeBackgroundTask(
   const { manager } = executorCtx
 
   try {
+    const effectivePrompt = buildTaskPrompt(args.prompt, agentToUse)
     const task = await manager.launch({
       description: args.description,
-      prompt: args.prompt,
+      prompt: effectivePrompt,
       agent: agentToUse,
       parentSessionID: parentContext.sessionID,
       parentMessageID: parentContext.messageID,
diff --git a/src/tools/delegate-task/index.ts b/src/tools/delegate-task/index.ts
index 5e8f7c817..5c50066e9 100644
--- a/src/tools/delegate-task/index.ts
+++ b/src/tools/delegate-task/index.ts
@@ -1,4 +1,4 @@
-export { createDelegateTask, resolveCategoryConfig, buildSystemContent } from "./tools"
+export { createDelegateTask, resolveCategoryConfig, buildSystemContent, buildTaskPrompt } from "./tools"
 export type { DelegateTaskToolOptions, SyncSessionCreatedEvent, BuildSystemContentInput } from "./tools"
 export type * from "./types"
 export * from "./constants"
diff --git a/src/tools/delegate-task/prompt-builder.ts b/src/tools/delegate-task/prompt-builder.ts
index 8230fed78..ddae1ce59 100644
--- a/src/tools/delegate-task/prompt-builder.ts
+++ b/src/tools/delegate-task/prompt-builder.ts
@@ -3,6 +3,14 @@ import { buildPlanAgentSystemPrepend, isPlanAgent } from "./constants"
 import { buildSystemContentWithTokenLimit } from "./token-limiter"
 
 const FREE_OR_LOCAL_PROMPT_TOKEN_LIMIT = 24000
+const PLAN_AGENT_PROMPT_APPEND = `
+
+Additional requirements for this planning request:
+- Answer in English.
+- Write the plan in English.
+- Plan well for ultrawork execution.
+- Use TDD-oriented planning.
+- Include a clear atomic commit strategy.`
 
 function usesFreeOrLocalModel(model: { providerID: string; modelID: string; variant?: string } | undefined): boolean {
   if (!model) {
@@ -52,3 +60,11 @@ export function buildSystemContent(input: BuildSystemContentInput): string | und
     effectiveMaxPromptTokens
   )
 }
+
+export function buildTaskPrompt(prompt: string, agentName: string | undefined): string {
+  if (!isPlanAgent(agentName)) {
+    return prompt
+  }
+
+  return `${prompt}${PLAN_AGENT_PROMPT_APPEND}`
+}
diff --git a/src/tools/delegate-task/sync-continuation.ts b/src/tools/delegate-task/sync-continuation.ts
index b716b3948..d24ba4574 100644
--- a/src/tools/delegate-task/sync-continuation.ts
+++ b/src/tools/delegate-task/sync-continuation.ts
@@ -11,6 +11,7 @@ import { formatDuration } from "./time-formatter"
 import { syncContinuationDeps, type SyncContinuationDeps } from "./sync-continuation-deps"
 import { setSessionTools } from "../../shared/session-tools-store"
 import { normalizeSDKResponse } from "../../shared"
+import { buildTaskPrompt } from "./prompt-builder"
 
 export async function executeSyncContinuation(
   args: DelegateTaskArgs,
@@ -82,6 +83,7 @@ export async function executeSyncContinuation(
     }
 
     const allowTask = isPlanFamily(resumeAgent)
+    const effectivePrompt = buildTaskPrompt(args.prompt, resumeAgent)
     const tools = {
       ...(resumeAgent ? getAgentToolRestrictions(resumeAgent) : {}),
       task: allowTask,
@@ -97,7 +99,7 @@ export async function executeSyncContinuation(
         ...(resumeModel !== undefined ? { model: resumeModel } : {}),
         ...(resumeVariant !== undefined ? { variant: resumeVariant } : {}),
         tools,
-        parts: [{ type: "text", text: args.prompt }],
+        parts: [{ type: "text", text: effectivePrompt }],
       },
     })
    } catch (promptError) {
diff --git a/src/tools/delegate-task/sync-prompt-sender.ts b/src/tools/delegate-task/sync-prompt-sender.ts
index 49ee2e2e7..fe4f8a693 100644
--- a/src/tools/delegate-task/sync-prompt-sender.ts
+++ b/src/tools/delegate-task/sync-prompt-sender.ts
@@ -1,5 +1,6 @@
 import type { DelegateTaskArgs, OpencodeClient } from "./types"
 import { isPlanFamily } from "./constants"
+import { buildTaskPrompt } from "./prompt-builder"
 import {
   promptSyncWithModelSuggestionRetry,
   promptWithModelSuggestionRetry,
@@ -43,6 +44,7 @@ export async function sendSyncPrompt(
   deps: SendSyncPromptDeps = sendSyncPromptDeps
 ): Promise<string | null> {
   const allowTask = isPlanFamily(input.agentToUse)
+  const effectivePrompt = buildTaskPrompt(input.args.prompt, input.agentToUse)
   const tools = {
     task: allowTask,
     call_omo_agent: true,
@@ -57,7 +59,7 @@ export async function sendSyncPrompt(
       agent: input.agentToUse,
       system: input.systemContent,
       tools,
-      parts: [createInternalAgentTextPart(input.args.prompt)],
+      parts: [createInternalAgentTextPart(effectivePrompt)],
       ...(input.categoryModel
         ? { model: { providerID: input.categoryModel.providerID, modelID: input.categoryModel.modelID } }
         : {}),
diff --git a/src/tools/delegate-task/tools.test.ts b/src/tools/delegate-task/tools.test.ts
index bb0b5ec29..8f7ebb79f 100644
--- a/src/tools/delegate-task/tools.test.ts
+++ b/src/tools/delegate-task/tools.test.ts
@@ -2896,6 +2896,37 @@ describe("sisyphus-task", () => {
     })
   })
 
+  describe("buildTaskPrompt", () => {
+    test("appends English ULW TDD and commit guidance for plan agent", () => {
+      // given
+      const { buildTaskPrompt } = require("./tools")
+      const prompt = "Create a work plan for this feature"
+
+      // when
+      const result = buildTaskPrompt(prompt, "plan")
+
+      // then
+      expect(result).toContain(prompt)
+      expect(result).toContain("Answer in English.")
+      expect(result).toContain("Write the plan in English.")
+      expect(result).toContain("Plan well for ultrawork execution.")
+      expect(result).toContain("Use TDD-oriented planning.")
+      expect(result).toContain("Include a clear atomic commit strategy.")
+    })
+
+    test("does not append plan guidance for non-plan agents", () => {
+      // given
+      const { buildTaskPrompt } = require("./tools")
+      const prompt = "Investigate this module"
+
+      // when
+      const result = buildTaskPrompt(prompt, "explore")
+
+      // then
+      expect(result).toBe(prompt)
+    })
+  })
+
   describe("modelInfo detection via resolveCategoryConfig", () => {
     test("catalog model is used for category with catalog entry", () => {
       // given - ultrabrain has catalog entry
diff --git a/src/tools/delegate-task/tools.ts b/src/tools/delegate-task/tools.ts
index fcd691f1f..68c7dc4af 100644
--- a/src/tools/delegate-task/tools.ts
+++ b/src/tools/delegate-task/tools.ts
@@ -23,7 +23,7 @@ import {
 
 export { resolveCategoryConfig } from "./categories"
 export type { SyncSessionCreatedEvent, DelegateTaskToolOptions, BuildSystemContentInput } from "./types"
-export { buildSystemContent } from "./prompt-builder"
+export { buildSystemContent, buildTaskPrompt } from "./prompt-builder"
 
 export function createDelegateTask(options: DelegateTaskToolOptions): ToolDefinition {
   const { userCategories } = options
diff --git a/src/tools/delegate-task/unstable-agent-task.ts b/src/tools/delegate-task/unstable-agent-task.ts
index 9a0b16c69..c455d7311 100644
--- a/src/tools/delegate-task/unstable-agent-task.ts
+++ b/src/tools/delegate-task/unstable-agent-task.ts
@@ -1,6 +1,7 @@
 import type { DelegateTaskArgs, ToolContextWithMetadata } from "./types"
 import type { ExecutorContext, ParentContext, SessionMessage } from "./executor-types"
 import { DEFAULT_SYNC_POLL_TIMEOUT_MS, getTimingConfig } from "./timing"
+import { buildTaskPrompt } from "./prompt-builder"
 import { storeToolMetadata } from "../../features/tool-metadata-store"
 import { formatDuration } from "./time-formatter"
 import { formatDetailedError } from "./error-formatting"
@@ -20,9 +21,10 @@ export async function executeUnstableAgentTask(
   const { manager, client, syncPollTimeoutMs } = executorCtx
 
   try {
+    const effectivePrompt = buildTaskPrompt(args.prompt, agentToUse)
     const task = await manager.launch({
       description: args.description,
-      prompt: args.prompt,
+      prompt: effectivePrompt,
       agent: agentToUse,
       parentSessionID: parentContext.sessionID,
       parentMessageID: parentContext.messageID,