v2.0.5: FAST_MODEL routing + tool-use summaries + Qwen dispatch + Arena

Source-level recon of QwenLM/qwen-code (Apache-2.0) informed 4 lifts:

1. FAST_MODEL config: optional env var routes cheap LLM calls (titles,
   summaries, labeling) to a smaller model on llama-swap. auto_name.ts
   uses ctx.config.FAST_MODEL ?? session.model. Set FAST_MODEL=nemotron-
   nano-4b to avoid loading the 35B model for 20-token title generation.

2. Tool-use summaries (services/inference/tool-summaries.ts): utility
   that generates "git-commit-subject-style" labels for tool batches via
   a fast-model LLM call. System prompt + truncation logic ported from
   Qwen Code's toolUseSummary.ts. Exported via @boocode/server/inference
   for BooCoder's dispatcher to call after task completion.

3. Qwen as dispatchable agent: added to agent-probe.ts KNOWN_AGENTS.
   PTY dispatch builds: qwen -p "<task>" --output-format stream-json
   (NDJSON structured events over stdout). Env: OPENAI_BASE_URL +
   OPENAI_API_KEY points Qwen Code at llama-swap. execution_path CHECK
   constraint extended with 'qwen'.

4. Arena routes (routes/arena.ts): POST /api/arena dispatches the same
   task to N contestants (2-5, each with different agent/model), each
   getting its own task row linked by arena_id UUID. GET /api/arena/:id
   shows all contestants. POST /api/arena/:id/select/:task_id marks
   winner. Schema: arena_id column added to tasks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/coder/src/routes/arena.ts

@@ -0,0 +1,122 @@
+/**
+ * v2.0.5: Arena routes — competitive dispatch of the same task to multiple agents.
+ *
+ * POST /api/arena        — create an arena with 2-5 contestants
+ * GET  /api/arena/:id    — get all tasks in an arena
+ * POST /api/arena/:id/select/:task_id — mark a task as the arena winner
+ */
+import type { FastifyInstance } from 'fastify';
+import { z } from 'zod';
+import type { Sql } from '../db.js';
+
+const ContestantSchema = z.object({
+  agent: z.string().max(100).optional(),
+  model: z.string().max(200).optional(),
+});
+
+const CreateArenaBody = z.object({
+  project_id: z.string().uuid(),
+  input: z.string().min(1).max(64_000),
+  contestants: z.array(ContestantSchema).min(2).max(5),
+});
+
+interface TaskRow {
+  id: string;
+  agent: string | null;
+  model: string | null;
+  state: string;
+}
+
+export function registerArenaRoutes(app: FastifyInstance, sql: Sql): void {
+  // POST /api/arena — create a new arena
+  app.post('/api/arena', async (req, reply) => {
+    const parsed = CreateArenaBody.safeParse(req.body);
+    if (!parsed.success) {
+      reply.code(400);
+      return { error: 'invalid body', details: parsed.error.flatten() };
+    }
+
+    const { project_id, input, contestants } = parsed.data;
+    const arenaId = crypto.randomUUID();
+
+    const tasks: TaskRow[] = [];
+    for (const contestant of contestants) {
+      const [task] = await sql<TaskRow[]>`
+        INSERT INTO tasks (project_id, input, agent, model, arena_id)
+        VALUES (${project_id}, ${input}, ${contestant.agent ?? null}, ${contestant.model ?? null}, ${arenaId})
+        RETURNING id, agent, model, state
+      `;
+      tasks.push(task!);
+    }
+
+    reply.code(201);
+    return {
+      arena_id: arenaId,
+      tasks: tasks.map(t => ({
+        id: t.id,
+        agent: t.agent,
+        model: t.model,
+        state: t.state,
+      })),
+    };
+  });
+
+  // GET /api/arena/:arena_id — list all tasks in an arena
+  app.get<{ Params: { arena_id: string } }>('/api/arena/:arena_id', async (req, reply) => {
+    const { arena_id } = req.params;
+
+    // Validate UUID format
+    const uuidRegex = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
+    if (!uuidRegex.test(arena_id)) {
+      reply.code(400);
+      return { error: 'invalid arena_id format' };
+    }
+
+    const tasks = await sql`
+      SELECT id, project_id, state, input, output_summary, agent, model, execution_path, session_id, started_at, ended_at, created_at, arena_id
+      FROM tasks
+      WHERE arena_id = ${arena_id}
+      ORDER BY created_at
+    `;
+
+    if (tasks.length === 0) {
+      reply.code(404);
+      return { error: 'arena not found' };
+    }
+
+    return { arena_id, tasks };
+  });
+
+  // POST /api/arena/:arena_id/select/:task_id — mark the winner
+  app.post<{ Params: { arena_id: string; task_id: string } }>(
+    '/api/arena/:arena_id/select/:task_id',
+    async (req, reply) => {
+      const { arena_id, task_id } = req.params;
+
+      // Verify the task belongs to this arena
+      const rows = await sql<{ id: string; state: string; arena_id: string | null }[]>`
+        SELECT id, state, arena_id FROM tasks WHERE id = ${task_id}
+      `;
+
+      if (rows.length === 0) {
+        reply.code(404);
+        return { error: 'task not found' };
+      }
+
+      const task = rows[0]!;
+      if (task.arena_id !== arena_id) {
+        reply.code(409);
+        return { error: 'task does not belong to this arena' };
+      }
+
+      // Mark as selected via output_summary prefix (lightweight — no schema change)
+      await sql`
+        UPDATE tasks
+        SET output_summary = COALESCE('[SELECTED] ' || output_summary, '[SELECTED]')
+        WHERE id = ${task_id}
+      `;
+
+      return { selected: true, task_id, arena_id };
+    }
+  );
+}