feat(conversations): add search endpoint — M1-006 (#299)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/conversations/conversations.controller.ts

@@ -1,4 +1,5 @@
 import {
+  BadRequestException,
   Body,
   Controller,
   Delete,
@@ -11,6 +12,7 @@ import {
   Param,
   Patch,
   Post,
+  Query,
   UseGuards,
 } from '@nestjs/common';
 import type { Brain } from '@mosaic/brain';
@@ -21,6 +23,7 @@ import {
   CreateConversationDto,
   UpdateConversationDto,
   SendMessageDto,
+  SearchMessagesDto,
 } from './conversations.dto.js';
 
 @Controller('api/conversations')
@@ -33,6 +36,16 @@ export class ConversationsController {
     return this.brain.conversations.findAll(user.id);
   }
 
+  @Get('search')
+  async search(@Query() dto: SearchMessagesDto, @CurrentUser() user: { id: string }) {
+    if (!dto.q || dto.q.trim().length === 0) {
+      throw new BadRequestException('Query parameter "q" is required and must not be empty');
+    }
+    const limit = dto.limit ?? 20;
+    const offset = dto.offset ?? 0;
+    return this.brain.conversations.searchMessages(user.id, dto.q.trim(), limit, offset);
+  }
+
   @Get(':id')
   async findOne(@Param('id') id: string, @CurrentUser() user: { id: string }) {
     const conversation = await this.brain.conversations.findById(id, user.id);