feat: Add personalization settings with custom instructions (#965)

You will assume the role and speech patterns of a cowboy from the old west. I want you to really lean into this when you work on tasks for me, even if they are modern in nature such as coding or math related.

Author: charlesvien

apps/twig/src/main/services/agent/schemas.ts

@@ -45,6 +45,7 @@ export const startSessionInput = z.object({
   runMode: z.enum(["local", "cloud"]).optional(),
   adapter: z.enum(["claude", "codex"]).optional(),
   additionalDirectories: z.array(z.string()).optional(),
+  customInstructions: z.string().max(2000).optional(),
 });
 
 export type StartSessionInput = z.infer<typeof startSessionInput>;
@@ -160,6 +161,7 @@ export const reconnectSessionInput = z.object({
   /** Additional directories Claude can access beyond cwd (for worktree support) */
   additionalDirectories: z.array(z.string()).optional(),
   permissionMode: z.string().optional(),
+  customInstructions: z.string().max(2000).optional(),
 });
 
 export type ReconnectSessionInput = z.infer<typeof reconnectSessionInput>;

apps/twig/src/main/services/agent/service.ts

@@ -177,6 +177,8 @@ interface SessionConfig {
   additionalDirectories?: string[];
   /** Permission mode to use for the session */
   permissionMode?: string;
+  /** Custom instructions injected into the system prompt */
+  customInstructions?: string;
 }
 
 interface ManagedSession {
@@ -368,12 +370,19 @@ export class AgentService extends TypedEventEmitter<AgentServiceEvents> {
     return servers;
   }
 
-  private buildPostHogSystemPrompt(credentials: Credentials): {
+  private buildSystemPrompt(
+    credentials: Credentials,
+    customInstructions?: string,
+  ): {
     append: string;
   } {
-    return {
-      append: `PostHog context: use project ${credentials.projectId} on ${credentials.apiHost}. When using PostHog MCP tools, operate only on this project.`,
-    };
+    let prompt = `PostHog context: use project ${credentials.projectId} on ${credentials.apiHost}. When using PostHog MCP tools, operate only on this project.`;
+
+    if (customInstructions) {
+      prompt += `\n\nUser custom instructions:\n${customInstructions}`;
+    }
+
+    return { append: prompt };
   }
 
   private getPostHogMcpUrl(apiHost: string): string {
@@ -426,6 +435,7 @@ export class AgentService extends TypedEventEmitter<AgentServiceEvents> {
       adapter,
       additionalDirectories,
       permissionMode,
+      customInstructions,
     } = config;
 
     // Preview sessions don't need a real repo — use a temp directory
@@ -522,7 +532,10 @@ export class AgentService extends TypedEventEmitter<AgentServiceEvents> {
         if (!config.sessionId) {
           throw new Error("Cannot resume session without sessionId");
         }
-        const systemPrompt = this.buildPostHogSystemPrompt(credentials);
+        const systemPrompt = this.buildSystemPrompt(
+          credentials,
+          customInstructions,
+        );
         const resumeResponse = await connection.extMethod(
           "_posthog/session/resume",
           {
@@ -553,7 +566,10 @@ export class AgentService extends TypedEventEmitter<AgentServiceEvents> {
         configOptions = resumeMeta?.configOptions;
         agentSessionId = config.sessionId;
       } else {
-        const systemPrompt = this.buildPostHogSystemPrompt(credentials);
+        const systemPrompt = this.buildSystemPrompt(
+          credentials,
+          customInstructions,
+        );
         const newSessionResponse = await connection.newSession({
           cwd: repoPath,
           mcpServers,
@@ -1267,6 +1283,8 @@ For git operations while detached:
           : undefined,
       permissionMode:
         "permissionMode" in params ? params.permissionMode : undefined,
+      customInstructions:
+        "customInstructions" in params ? params.customInstructions : undefined,
     };
   }
 

apps/twig/src/renderer/features/sessions/service/service.ts

@@ -24,6 +24,7 @@ import {
   mergeConfigOptions,
   sessionStoreSetters,
 } from "@features/sessions/stores/sessionStore";
+import { useSettingsStore } from "@features/settings/stores/settingsStore";
 import { track } from "@renderer/lib/analytics";
 import { logger } from "@renderer/lib/logger";
 import {
@@ -324,6 +325,7 @@ export class SessionService {
         "mode",
       )?.currentValue;
 
+      const { customInstructions } = useSettingsStore.getState();
       const result = await trpcVanilla.agent.reconnect.mutate({
         taskId,
         taskRunId,
@@ -335,6 +337,7 @@ export class SessionService {
         sessionId,
         adapter: resolvedAdapter,
         permissionMode: persistedMode,
+        customInstructions: customInstructions || undefined,
       });
 
       if (result) {
@@ -496,6 +499,8 @@ export class SessionService {
       throw new Error("Failed to create task run. Please try again.");
     }
 
+    const { customInstructions: startCustomInstructions } =
+      useSettingsStore.getState();
     const result = await trpcVanilla.agent.start.mutate({
       taskId,
       taskRunId: taskRun.id,
@@ -505,6 +510,7 @@ export class SessionService {
       projectId: auth.projectId,
       permissionMode: executionMode,
       adapter,
+      customInstructions: startCustomInstructions || undefined,
     });
 
     const session = this.createBaseSession(taskRun.id, taskId, taskTitle);
@@ -602,6 +608,8 @@ export class SessionService {
     sessionStoreSetters.setSession(session);
 
     try {
+      const { customInstructions: previewCustomInstructions } =
+        useSettingsStore.getState();
       const result = await trpcVanilla.agent.start.mutate({
         taskId: PREVIEW_TASK_ID,
         taskRunId,
@@ -610,6 +618,7 @@ export class SessionService {
         apiHost: auth.apiHost,
         projectId: auth.projectId,
         adapter: params.adapter,
+        customInstructions: previewCustomInstructions || undefined,
       });
 
       if (abort.signal.aborted) {

apps/twig/src/renderer/features/settings/components/SettingsDialog.tsx

@@ -10,6 +10,7 @@ import {
   Folder,
   GearSix,
   Keyboard,
+  Palette,
   User,
   Wrench,
 } from "@phosphor-icons/react";
@@ -20,6 +21,7 @@ import { AccountSettings } from "./sections/AccountSettings";
 import { AdvancedSettings } from "./sections/AdvancedSettings";
 import { ClaudeCodeSettings } from "./sections/ClaudeCodeSettings";
 import { GeneralSettings } from "./sections/GeneralSettings";
+import { PersonalizationSettings } from "./sections/PersonalizationSettings";
 import { ShortcutsSettings } from "./sections/ShortcutsSettings";
 import { UpdatesSettings } from "./sections/UpdatesSettings";
 import { WorkspacesSettings } from "./sections/WorkspacesSettings";
@@ -35,6 +37,11 @@ const SIDEBAR_ITEMS: SidebarItem[] = [
   { id: "general", label: "General", icon: <GearSix size={16} /> },
   { id: "account", label: "Account", icon: <User size={16} /> },
   { id: "workspaces", label: "Workspaces", icon: <Folder size={16} /> },
+  {
+    id: "personalization",
+    label: "Personalization",
+    icon: <Palette size={16} />,
+  },
   { id: "claude-code", label: "Claude Code", icon: <Code size={16} /> },
   { id: "shortcuts", label: "Shortcuts", icon: <Keyboard size={16} /> },
   { id: "updates", label: "Updates", icon: <ArrowsClockwise size={16} /> },
@@ -45,6 +52,7 @@ const CATEGORY_TITLES: Record<SettingsCategory, string> = {
   general: "General",
   account: "Account",
   workspaces: "Workspaces",
+  personalization: "Personalization",
   "claude-code": "Claude Code",
   shortcuts: "Shortcuts",
   updates: "Updates",
@@ -55,6 +63,7 @@ const CATEGORY_COMPONENTS: Record<SettingsCategory, React.ComponentType> = {
   general: GeneralSettings,
   account: AccountSettings,
   workspaces: WorkspacesSettings,
+  personalization: PersonalizationSettings,
   "claude-code": ClaudeCodeSettings,
   shortcuts: ShortcutsSettings,
   updates: UpdatesSettings,

apps/twig/src/renderer/features/settings/components/sections/PersonalizationSettings.tsx

@@ -0,0 +1,95 @@
+import { useSettingsStore } from "@features/settings/stores/settingsStore";
+import { Flex, Text, TextArea } from "@radix-ui/themes";
+import { track } from "@renderer/lib/analytics";
+import { ANALYTICS_EVENTS } from "@shared/types/analytics";
+import { useCallback, useEffect, useRef, useState } from "react";
+
+const MAX_INSTRUCTIONS_LENGTH = 2000;
+const DEBOUNCE_MS = 500;
+
+export function PersonalizationSettings() {
+  const customInstructions = useSettingsStore((s) => s.customInstructions);
+  const setCustomInstructions = useSettingsStore(
+    (s) => s.setCustomInstructions,
+  );
+
+  const [localInstructions, setLocalInstructions] =
+    useState(customInstructions);
+  const debounceRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+
+  // Sync local state when store changes externally
+  useEffect(() => {
+    setLocalInstructions(customInstructions);
+  }, [customInstructions]);
+
+  const saveInstructions = useCallback(
+    (value: string) => {
+      const current = useSettingsStore.getState().customInstructions;
+      if (value === current) return;
+      setCustomInstructions(value);
+      track(ANALYTICS_EVENTS.SETTING_CHANGED, {
+        setting_name: "custom_instructions",
+        new_value: value.length > 0,
+      });
+    },
+    [setCustomInstructions],
+  );
+
+  const handleInstructionsChange = useCallback(
+    (e: React.ChangeEvent<HTMLTextAreaElement>) => {
+      const value = e.target.value;
+      setLocalInstructions(value);
+
+      if (debounceRef.current) {
+        clearTimeout(debounceRef.current);
+      }
+      debounceRef.current = setTimeout(() => {
+        saveInstructions(value);
+      }, DEBOUNCE_MS);
+    },
+    [saveInstructions],
+  );
+
+  const handleInstructionsBlur = useCallback(() => {
+    if (debounceRef.current) {
+      clearTimeout(debounceRef.current);
+      debounceRef.current = null;
+    }
+    saveInstructions(localInstructions);
+  }, [localInstructions, saveInstructions]);
+
+  // Cleanup debounce on unmount
+  useEffect(() => {
+    return () => {
+      if (debounceRef.current) {
+        clearTimeout(debounceRef.current);
+      }
+    };
+  }, []);
+
+  return (
+    <Flex direction="column" gap="1" py="4">
+      <Flex direction="column" gap="1" className="mb-2">
+        <Text size="2" weight="medium">
+          Custom instructions
+        </Text>
+        <Text size="1" color="gray">
+          Instructions included in every agent session
+        </Text>
+      </Flex>
+      <TextArea
+        value={localInstructions}
+        onChange={handleInstructionsChange}
+        onBlur={handleInstructionsBlur}
+        maxLength={MAX_INSTRUCTIONS_LENGTH}
+        placeholder="e.g. Always write tests for new code. Prefer functional patterns."
+        rows={6}
+        size="1"
+        style={{ width: "100%", fontFamily: "var(--font-mono)" }}
+      />
+      <Text size="1" color="gray" align="right">
+        {localInstructions.length}/{MAX_INSTRUCTIONS_LENGTH}
+      </Text>
+    </Flex>
+  );
+}

apps/twig/src/renderer/features/settings/stores/settingsDialogStore.ts

@@ -4,6 +4,7 @@ export type SettingsCategory =
   | "general"
   | "account"
   | "workspaces"
+  | "personalization"
   | "claude-code"
   | "shortcuts"
   | "updates"

apps/twig/src/renderer/features/settings/stores/settingsStore.ts

@@ -26,6 +26,7 @@ interface SettingsStore {
   sendMessagesWith: SendMessagesWith;
   allowBypassPermissions: boolean;
   preventSleepWhileRunning: boolean;
+  customInstructions: string;
 
   setCompletionSound: (sound: CompletionSound) => void;
   setCompletionVolume: (volume: number) => void;
@@ -43,6 +44,7 @@ interface SettingsStore {
   setSendMessagesWith: (mode: SendMessagesWith) => void;
   setAllowBypassPermissions: (enabled: boolean) => void;
   setPreventSleepWhileRunning: (enabled: boolean) => void;
+  setCustomInstructions: (instructions: string) => void;
 }
 
 export const useSettingsStore = create<SettingsStore>()(
@@ -64,6 +66,7 @@ export const useSettingsStore = create<SettingsStore>()(
       sendMessagesWith: "enter",
       allowBypassPermissions: false,
       preventSleepWhileRunning: false,
+      customInstructions: "",
 
       setCompletionSound: (sound) => set({ completionSound: sound }),
       setCompletionVolume: (volume) => set({ completionVolume: volume }),
@@ -88,6 +91,8 @@ export const useSettingsStore = create<SettingsStore>()(
         set({ allowBypassPermissions: enabled }),
       setPreventSleepWhileRunning: (enabled) =>
         set({ preventSleepWhileRunning: enabled }),
+      setCustomInstructions: (instructions) =>
+        set({ customInstructions: instructions }),
     }),
     {
       name: "settings-storage",
@@ -109,6 +114,7 @@ export const useSettingsStore = create<SettingsStore>()(
         sendMessagesWith: state.sendMessagesWith,
         allowBypassPermissions: state.allowBypassPermissions,
         preventSleepWhileRunning: state.preventSleepWhileRunning,
+        customInstructions: state.customInstructions,
       }),
       merge: (persisted, current) => ({
         ...current,