feat(05-02): implement /open command handler

Add /open command handler that queries all project models in parallel.
Creates Discussion and Round records, persists Message for each response.
Shows typing indicator and formats output with model names.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/moai/bot/handlers/__init__.py

@@ -7,7 +7,7 @@ project management, discussion commands, and export functionality.
 from telegram.ext import Application, CommandHandler
 
 from moai.bot.handlers.commands import help_command, start_command
-from moai.bot.handlers.discussion import ask_command
+from moai.bot.handlers.discussion import ask_command, open_command
 from moai.bot.handlers.projects import project_command, projects_command
 from moai.bot.handlers.status import status_command
 
@@ -31,3 +31,4 @@ def register_handlers(app: Application) -> None:
 
     # Discussion / Q&A
     app.add_handler(CommandHandler("ask", ask_command))
+    app.add_handler(CommandHandler("open", open_command))

src/moai/bot/handlers/discussion.py

@@ -5,6 +5,9 @@ from telegram.ext import ContextTypes
 
 from moai.bot.handlers.projects import get_selected_project
 from moai.core.ai_client import MODEL_MAP, get_ai_client
+from moai.core.models import DiscussionType, RoundType
+from moai.core.orchestrator import query_models_parallel
+from moai.core.services.discussion import create_discussion, create_message, create_round
 
 
 async def ask_command(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
@@ -56,3 +59,81 @@ async def ask_command(update: Update, context: ContextTypes.DEFAULT_TYPE) -> Non
         )
     except Exception as e:
         await update.message.reply_text(f"Error: {e}")
+
+
+async def open_command(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
+    """Handle /open <question> command - ask all project models in parallel.
+
+    Requires a selected project with configured models. Creates a Discussion
+    with OPEN type and a PARALLEL round, then queries all models simultaneously.
+
+    Examples:
+        /open What is Python?
+        /open How should we approach this problem?
+    """
+    args = context.args or []
+
+    if not args:
+        await update.message.reply_text(
+            "Usage: /open <question>\n\nExample: /open What are the pros and cons of microservices?"
+        )
+        return
+
+    question = " ".join(args)
+
+    # Require a selected project
+    project = await get_selected_project(context)
+    if project is None:
+        await update.message.reply_text("No project selected. Use /project select <name> first.")
+        return
+
+    # Require configured models
+    if not project.models:
+        await update.message.reply_text(
+            "No models configured for this project.\n"
+            "Use /project models claude,gpt,gemini to set models."
+        )
+        return
+
+    # Show typing indicator while waiting for AI
+    await update.message.chat.send_action("typing")
+
+    try:
+        # Create discussion and round in database
+        discussion = await create_discussion(
+            project_id=project.id,
+            question=question,
+            discussion_type=DiscussionType.OPEN,
+        )
+        round_ = await create_round(
+            discussion_id=discussion.id,
+            round_number=1,
+            round_type=RoundType.PARALLEL,
+        )
+
+        # Query all models in parallel
+        responses = await query_models_parallel(
+            models=project.models,
+            question=question,
+            project_name=project.name,
+        )
+
+        # Persist messages and build response text
+        response_lines = [f"*Question:* {question}\n"]
+
+        for model, response in responses.items():
+            await create_message(
+                round_id=round_.id,
+                model=model,
+                content=response,
+            )
+            response_lines.append(f"*{model.title()}:*\n{response}\n")
+
+        # Send combined response
+        await update.message.reply_text(
+            "\n".join(response_lines),
+            parse_mode="Markdown",
+        )
+
+    except Exception as e:
+        await update.message.reply_text(f"Error: {e}")