fix: add resolveEmailPrompt tests and consolidate prompt builders (#474)

src/core/prompts.ts

@@ -233,14 +233,18 @@ something they need to know or act on.
 }
 
 /**
- * Email prompt (silent mode) - for Gmail polling
+ * Email prompt (silent mode) - for Gmail polling.
+ * When customPrompt is provided it replaces the default body text.
  */
 export function buildEmailPrompt(
   account: string,
   emailCount: number,
   emailData: string,
-  time: string
+  time: string,
+  customPrompt?: string,
 ): string {
+  const body = customPrompt
+    ?? 'Review and summarize important emails. Use `lettabot-message send --text "..."` to notify the user if needed.';
   return `
 ${SILENT_MODE_PREFIX}
 
@@ -257,37 +261,7 @@ To notify your human about important emails, run:
 NEW EMAILS (${emailCount}):
 ${emailData}
 
-Review and summarize important emails. Use \`lettabot-message send --text "..."\` to notify the user if needed.
-`.trim();
-}
-
-/**
- * Custom email prompt - wraps user-provided text with silent mode envelope
- */
-export function buildCustomEmailPrompt(
-  customPrompt: string,
-  account: string,
-  emailCount: number,
-  emailData: string,
-  time: string
-): string {
-  return `
-${SILENT_MODE_PREFIX}
-
-TRIGGER: Email polling
-ACCOUNT: ${account}
-TIME: ${time}
-
-━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
-
-YOUR TEXT OUTPUT IS PRIVATE - only you can see it.
-To notify your human, run:
-  lettabot-message send --text "Your message here"
-
-${customPrompt}
-
-NEW EMAILS (${emailCount}):
-${emailData}
+${body}
 `.trim();
 }
 

src/polling/service.test.ts

@@ -1,5 +1,8 @@
-import { describe, it, expect } from 'vitest';
-import { parseGmailAccounts } from './service.js';
+import { describe, it, expect, afterEach } from 'vitest';
+import { mkdtempSync, writeFileSync, rmSync } from 'node:fs';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+import { parseGmailAccounts, resolveEmailPrompt } from './service.js';
 
 describe('parseGmailAccounts', () => {
   it('returns empty array for undefined', () => {
@@ -89,3 +92,80 @@ describe('parseGmailAccounts', () => {
     ]);
   });
 });
+
+describe('resolveEmailPrompt', () => {
+  let tmpDir: string;
+
+  afterEach(() => {
+    if (tmpDir) rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it('returns undefined when no prompts configured', () => {
+    expect(resolveEmailPrompt({ account: 'a@gmail.com' })).toBeUndefined();
+  });
+
+  it('returns account-specific inline prompt', () => {
+    expect(resolveEmailPrompt(
+      { account: 'a@gmail.com', prompt: 'Check urgent' },
+      'global prompt',
+    )).toBe('Check urgent');
+  });
+
+  it('reads account-specific promptFile', () => {
+    tmpDir = mkdtempSync(join(tmpdir(), 'poll-test-'));
+    writeFileSync(join(tmpDir, 'acct.txt'), '  File prompt content  ');
+    expect(resolveEmailPrompt(
+      { account: 'a@gmail.com', promptFile: 'acct.txt' },
+      undefined, undefined, tmpDir,
+    )).toBe('File prompt content');
+  });
+
+  it('account inline prompt wins over account promptFile', () => {
+    tmpDir = mkdtempSync(join(tmpdir(), 'poll-test-'));
+    writeFileSync(join(tmpDir, 'acct.txt'), 'from file');
+    expect(resolveEmailPrompt(
+      { account: 'a@gmail.com', prompt: 'inline wins', promptFile: 'acct.txt' },
+      undefined, undefined, tmpDir,
+    )).toBe('inline wins');
+  });
+
+  it('falls back to global prompt when account has none', () => {
+    expect(resolveEmailPrompt(
+      { account: 'a@gmail.com' },
+      'global prompt',
+    )).toBe('global prompt');
+  });
+
+  it('falls back to global promptFile', () => {
+    tmpDir = mkdtempSync(join(tmpdir(), 'poll-test-'));
+    writeFileSync(join(tmpDir, 'global.txt'), 'global file content');
+    expect(resolveEmailPrompt(
+      { account: 'a@gmail.com' },
+      undefined, 'global.txt', tmpDir,
+    )).toBe('global file content');
+  });
+
+  it('global inline prompt wins over global promptFile', () => {
+    tmpDir = mkdtempSync(join(tmpdir(), 'poll-test-'));
+    writeFileSync(join(tmpDir, 'global.txt'), 'from file');
+    expect(resolveEmailPrompt(
+      { account: 'a@gmail.com' },
+      'global inline', 'global.txt', tmpDir,
+    )).toBe('global inline');
+  });
+
+  it('falls through gracefully when account promptFile is missing', () => {
+    expect(resolveEmailPrompt(
+      { account: 'a@gmail.com', promptFile: 'nonexistent.txt' },
+      'fallback global',
+      undefined, '/tmp',
+    )).toBe('fallback global');
+  });
+
+  it('falls through gracefully when global promptFile is missing', () => {
+    expect(resolveEmailPrompt(
+      { account: 'a@gmail.com' },
+      undefined, 'nonexistent.txt', '/tmp',
+    )).toBeUndefined();
+  });
+});

src/polling/service.ts

@@ -11,12 +11,57 @@ import { resolve, join } from 'node:path';
 import type { AgentSession } from '../core/interfaces.js';
 import type { TriggerContext } from '../core/types.js';
 import type { GmailAccountConfig } from '../config/types.js';
-import { buildEmailPrompt, buildCustomEmailPrompt } from '../core/prompts.js';
+import { buildEmailPrompt } from '../core/prompts.js';
 
 import { createLogger } from '../logger.js';
 
 const log = createLogger('Polling');
 
+/**
+ * Resolve the custom prompt for a Gmail account.
+ * Pure function extracted for testability.
+ *
+ * Priority: account prompt > account promptFile > global prompt > global promptFile > undefined (built-in)
+ */
+export function resolveEmailPrompt(
+  accountConfig: GmailAccountConfig,
+  globalPrompt?: string,
+  globalPromptFile?: string,
+  workingDir?: string,
+): string | undefined {
+  // Account-specific inline prompt
+  if (accountConfig.prompt) {
+    return accountConfig.prompt;
+  }
+
+  // Account-specific promptFile
+  if (accountConfig.promptFile) {
+    try {
+      const path = workingDir ? resolve(workingDir, accountConfig.promptFile) : accountConfig.promptFile;
+      return readFileSync(path, 'utf-8').trim();
+    } catch (err) {
+      log.warn(`Failed to read promptFile for ${accountConfig.account}: ${(err as Error).message}`);
+    }
+  }
+
+  // Global inline prompt
+  if (globalPrompt) {
+    return globalPrompt;
+  }
+
+  // Global promptFile
+  if (globalPromptFile) {
+    try {
+      const path = workingDir ? resolve(workingDir, globalPromptFile) : globalPromptFile;
+      return readFileSync(path, 'utf-8').trim();
+    } catch (err) {
+      log.warn(`Failed to read global promptFile: ${(err as Error).message}`);
+    }
+  }
+
+  return undefined;
+}
+
 /**
  * Parse Gmail accounts from various formats.
  * Handles: string (comma-separated), string array, or GmailAccountConfig array.
@@ -200,41 +245,12 @@ export class PollingService {
   
   /**
    * Resolve custom prompt for an account.
-   * Priority: account-specific > global default > none (use built-in prompt)
+   * Delegates to the exported pure function.
    */
   private resolvePrompt(accountConfig: GmailAccountConfig): string | undefined {
     const gmail = this.config.gmail;
     if (!gmail) return undefined;
-    
-    // Check for account-specific prompt first
-    if (accountConfig.prompt) {
-      return accountConfig.prompt;
-    }
-    
-    // Check for account-specific promptFile
-    if (accountConfig.promptFile) {
-      try {
-        return readFileSync(resolve(this.config.workingDir, accountConfig.promptFile), 'utf-8').trim();
-      } catch (err) {
-        log.error(`Failed to read promptFile for ${accountConfig.account}:`, err);
-      }
-    }
-
-    // Fall back to global prompt
-    if (gmail.prompt) {
-      return gmail.prompt;
-    }
-
-    // Fall back to global promptFile
-    if (gmail.promptFile) {
-      try {
-        return readFileSync(resolve(this.config.workingDir, gmail.promptFile), 'utf-8').trim();
-      } catch (err) {
-        log.error(`Failed to read global promptFile:`, err);
-      }
-    }
-    
-    return undefined;
+    return resolveEmailPrompt(accountConfig, gmail.prompt, gmail.promptFile, this.config.workingDir);
   }
   
   /**
@@ -307,10 +323,8 @@ export class PollingService {
       const now = new Date();
       const time = now.toLocaleString();
       
-      // Build message using prompt builders
-      const message = customPrompt
-        ? buildCustomEmailPrompt(customPrompt, account, newEmails.length, newEmailsOutput, time)
-        : buildEmailPrompt(account, newEmails.length, newEmailsOutput, time);
+      // Build message using prompt builder
+      const message = buildEmailPrompt(account, newEmails.length, newEmailsOutput, time, customPrompt);
       
       // Build trigger context for silent mode
       const context: TriggerContext = {