feat(adapter): per-agent language instruction

Add optional 'language' config field on all local adapters (Claude, Codex,
Cursor, Gemini, OpenCode, Pi). When set, a final instruction is appended
to the rendered prompt telling the agent to produce all outputs in that
language (responses, commit messages, explanations, etc.).

- New buildLanguageInstruction() helper in adapter-utils/server-utils
- Each adapter's execute.ts imports the helper and appends it to its
  joinPromptSections call
- Each adapter's ui/build-config.ts passes v.language to adapterConfig
- Add language field to CreateConfigValues (optional string) + default

Author: ramonmatias19

packages/adapter-utils/src/server-utils.ts

@@ -263,6 +263,12 @@ export function joinPromptSections(
     .join(separator);
 }
 
+export function buildLanguageInstruction(config: Record<string, unknown>): string {
+  const language = asString(config.language, "").trim();
+  if (!language) return "";
+  return `IMPORTANT: You MUST write all your responses, comments, commit messages, and any other output in ${language}. This includes explanations, summaries, and any text you produce.`;
+}
+
 type PaperclipWakeIssue = {
   id: string | null;
   identifier: string | null;

packages/adapter-utils/src/types.ts

@@ -440,6 +440,7 @@ export interface CreateConfigValues {
   worktreeParentDir?: string;
   runtimeServicesJson?: string;
   defaultEnvironmentId?: string;
+  language?: string;
   maxTurnsPerRun: number;
   heartbeatEnabled: boolean;
   intervalSec: number;

packages/adapters/claude-local/src/server/execute.ts

@@ -27,6 +27,7 @@ import {
   buildPaperclipEnv,
   readPaperclipRuntimeSkillEntries,
   joinPromptSections,
+  buildLanguageInstruction,
   buildInvocationEnvForLogs,
   ensureAbsoluteDirectory,
   ensurePathInEnv,
@@ -489,12 +490,14 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
   const renderedPrompt = shouldUseResumeDeltaPrompt ? "" : renderTemplate(promptTemplate, templateData);
   const sessionHandoffNote = asString(context.paperclipSessionHandoffMarkdown, "").trim();
   const taskContextNote = asString(context.paperclipTaskMarkdown, "").trim();
+  const languageInstruction = buildLanguageInstruction(config);
   const prompt = joinPromptSections([
     renderedBootstrapPrompt,
     wakePrompt,
     sessionHandoffNote,
     taskContextNote,
     renderedPrompt,
+    languageInstruction,
   ]);
   const promptMetrics = {
     promptChars: prompt.length,

packages/adapters/claude-local/src/ui/build-config.ts

@@ -67,6 +67,7 @@ export function buildClaudeLocalConfig(v: CreateConfigValues): Record<string, un
   if (v.cwd) ac.cwd = v.cwd;
   if (v.instructionsFilePath) ac.instructionsFilePath = v.instructionsFilePath;
   if (v.promptTemplate) ac.promptTemplate = v.promptTemplate;
+  if (v.language) ac.language = v.language;
   if (v.bootstrapPrompt) ac.bootstrapPromptTemplate = v.bootstrapPrompt;
   if (v.model) ac.model = v.model;
   if (v.thinkingEffort) ac.effort = v.thinkingEffort;

packages/adapters/codex-local/src/server/execute.ts

@@ -31,6 +31,7 @@ import {
   stringifyPaperclipWakePayload,
   DEFAULT_PAPERCLIP_AGENT_PROMPT_TEMPLATE,
   joinPromptSections,
+  buildLanguageInstruction,
 } from "@paperclipai/adapter-utils/server-utils";
 import {
   parseCodexJsonl,
@@ -243,7 +244,7 @@ export async function ensureCodexSkillsInjected(
           if (linkSkill) {
             await linkSkill(entry.source, target);
           } else {
-            await fs.symlink(entry.source, target);
+            await fs.symlink(entry.source, target, process.platform === "win32" ? "junction" : undefined);
           }
           await onLog(
             "stdout",
@@ -615,13 +616,15 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
   })();
   const renderedPrompt = shouldUseResumeDeltaPrompt ? "" : renderTemplate(promptTemplate, templateData);
   const sessionHandoffNote = asString(context.paperclipSessionHandoffMarkdown, "").trim();
+  const languageInstruction = buildLanguageInstruction(config);
   const prompt = joinPromptSections([
     promptInstructionsPrefix,
     renderedBootstrapPrompt,
     wakePrompt,
     codexFallbackHandoffNote,
     sessionHandoffNote,
     renderedPrompt,
+    languageInstruction,
   ]);
   const promptMetrics = {
     promptChars: prompt.length,

packages/adapters/codex-local/src/ui/build-config.ts

@@ -71,6 +71,7 @@ export function buildCodexLocalConfig(v: CreateConfigValues): Record<string, unk
   if (v.cwd) ac.cwd = v.cwd;
   if (v.instructionsFilePath) ac.instructionsFilePath = v.instructionsFilePath;
   if (v.promptTemplate) ac.promptTemplate = v.promptTemplate;
+  if (v.language) ac.language = v.language;
   if (v.bootstrapPrompt) ac.bootstrapPromptTemplate = v.bootstrapPrompt;
   ac.model = v.model || DEFAULT_CODEX_LOCAL_MODEL;
   if (v.thinkingEffort) ac.modelReasoningEffort = v.thinkingEffort;

packages/adapters/cursor-local/src/server/execute.ts

@@ -37,6 +37,7 @@ import {
   stringifyPaperclipWakePayload,
   DEFAULT_PAPERCLIP_AGENT_PROMPT_TEMPLATE,
   joinPromptSections,
+  buildLanguageInstruction,
 } from "@paperclipai/adapter-utils/server-utils";
 import { DEFAULT_CURSOR_LOCAL_MODEL } from "../index.js";
 import { parseCursorJsonl, isCursorUnknownSessionError } from "./parse.js";
@@ -166,7 +167,7 @@ export async function ensureCursorSkillsInjected(
       `[paperclip] Removed maintainer-only Cursor skill "${skillName}" from ${skillsHome}\n`,
     );
   }
-  const linkSkill = options.linkSkill ?? ((source: string, target: string) => fs.symlink(source, target));
+  const linkSkill = options.linkSkill ?? ((source: string, target: string) => fs.symlink(source, target, process.platform === "win32" ? "junction" : undefined));
   for (const entry of skillsEntries) {
     const target = path.join(skillsHome, entry.runtimeName);
     try {
@@ -464,13 +465,15 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
   const renderedPrompt = shouldUseResumeDeltaPrompt ? "" : renderTemplate(promptTemplate, templateData);
   const sessionHandoffNote = asString(context.paperclipSessionHandoffMarkdown, "").trim();
   const paperclipEnvNote = renderPaperclipEnvNote(env);
+  const languageInstruction = buildLanguageInstruction(config);
   const prompt = joinPromptSections([
     instructionsPrefix,
     renderedBootstrapPrompt,
     wakePrompt,
     sessionHandoffNote,
     paperclipEnvNote,
     renderedPrompt,
+    languageInstruction,
   ]);
   const promptMetrics = {
     promptChars: prompt.length,

packages/adapters/cursor-local/src/ui/build-config.ts

@@ -62,6 +62,7 @@ export function buildCursorLocalConfig(v: CreateConfigValues): Record<string, un
   if (v.cwd) ac.cwd = v.cwd;
   if (v.instructionsFilePath) ac.instructionsFilePath = v.instructionsFilePath;
   if (v.promptTemplate) ac.promptTemplate = v.promptTemplate;
+  if (v.language) ac.language = v.language;
   if (v.bootstrapPrompt) ac.bootstrapPromptTemplate = v.bootstrapPrompt;
   ac.model = v.model || DEFAULT_CURSOR_LOCAL_MODEL;
   const mode = normalizeMode(v.thinkingEffort);

packages/adapters/gemini-local/src/server/execute.ts

@@ -30,6 +30,7 @@ import {
   ensureAbsoluteDirectory,
   ensurePaperclipSkillSymlink,
   joinPromptSections,
+  buildLanguageInstruction,
   ensurePathInEnv,
   readPaperclipRuntimeSkillEntries,
   resolvePaperclipDesiredSkillNames,
@@ -408,6 +409,7 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
   const sessionHandoffNote = asString(context.paperclipSessionHandoffMarkdown, "").trim();
   const paperclipEnvNote = renderPaperclipEnvNote(env);
   const apiAccessNote = renderApiAccessNote(env);
+  const languageInstruction = buildLanguageInstruction(config);
   const prompt = joinPromptSections([
     instructionsPrefix,
     renderedBootstrapPrompt,
@@ -416,6 +418,7 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
     paperclipEnvNote,
     apiAccessNote,
     renderedPrompt,
+    languageInstruction,
   ]);
   const promptMetrics = {
     promptChars: prompt.length,

packages/adapters/gemini-local/src/ui/build-config.ts

@@ -56,6 +56,7 @@ export function buildGeminiLocalConfig(v: CreateConfigValues): Record<string, un
   if (v.cwd) ac.cwd = v.cwd;
   if (v.instructionsFilePath) ac.instructionsFilePath = v.instructionsFilePath;
   if (v.promptTemplate) ac.promptTemplate = v.promptTemplate;
+  if (v.language) ac.language = v.language;
   if (v.bootstrapPrompt) ac.bootstrapPromptTemplate = v.bootstrapPrompt;
   ac.model = v.model || DEFAULT_GEMINI_LOCAL_MODEL;
   ac.timeoutSec = 0;