v2.0.0-final: dispatcher + task queue + agent probing

Phase 4 of v2.0. BooCoder can now queue tasks and dispatch them
through the inference loop autonomously.

Dispatcher (services/dispatcher.ts): in-process setInterval(5s) polls
tasks WHERE state='pending', picks one at a time, creates an isolated
session+chat, enqueues inference with the task's input as the user
message, polls for completion, marks state completed/failed with
output_summary. Single-task-at-a-time for v2.0.0; parallel dispatch
is a Phase 5+ concern. Respects onClose hook for graceful shutdown.

Task routes (routes/tasks.ts): POST /api/tasks (create), GET /api/tasks
(list with state/project filters), GET /api/tasks/:id (detail),
POST /api/tasks/:id/cancel (marks cancelled, aborts if running).

Agent probe (services/agent-probe.ts): on startup, probes PATH for
opencode/goose/claude/pi via which + --version. UPSERTs into
available_agents table. Finds nothing inside the container (expected —
Phase 5 addresses host-agent access via ACP/PTY).

Schema: ALTER TABLE tasks ADD COLUMN IF NOT EXISTS session_id (links
task to its auto-created inference session for isolation).

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

apps/coder/src/services/agent-probe.ts

@@ -0,0 +1,51 @@
+import { execFile } from 'node:child_process';
+import { promisify } from 'node:util';
+import type { Sql } from '../db.js';
+import type { FastifyBaseLogger } from 'fastify';
+
+const execFileAsync = promisify(execFile);
+
+const KNOWN_AGENTS: Array<{ name: string; supportsAcp: boolean }> = [
+  { name: 'opencode', supportsAcp: true },
+  { name: 'goose', supportsAcp: true },
+  { name: 'claude', supportsAcp: false },
+  { name: 'pi', supportsAcp: false },
+];
+
+export async function probeAgents(sql: Sql, log: FastifyBaseLogger): Promise<void> {
+  log.info('agent-probe: scanning PATH for known agents');
+
+  for (const agent of KNOWN_AGENTS) {
+    try {
+      // Check if the agent binary is on PATH
+      const { stdout: whichOut } = await execFileAsync('which', [agent.name], { timeout: 5_000 });
+      const installPath = whichOut.trim();
+      if (!installPath) continue;
+
+      // Get version
+      let version: string | null = null;
+      try {
+        const { stdout: verOut } = await execFileAsync(agent.name, ['--version'], { timeout: 10_000 });
+        version = verOut.trim().slice(0, 100);
+      } catch {
+        // Some agents may not support --version — that's fine
+      }
+
+      // UPSERT into available_agents
+      await sql`
+        INSERT INTO available_agents (name, install_path, version, supports_acp, last_probed_at)
+        VALUES (${agent.name}, ${installPath}, ${version}, ${agent.supportsAcp}, clock_timestamp())
+        ON CONFLICT (name) DO UPDATE SET
+          install_path = EXCLUDED.install_path,
+          version = EXCLUDED.version,
+          supports_acp = EXCLUDED.supports_acp,
+          last_probed_at = EXCLUDED.last_probed_at
+      `;
+      log.info({ agent: agent.name, version, installPath }, 'agent-probe: found');
+    } catch {
+      // Agent not found on PATH — skip silently
+    }
+  }
+
+  log.info('agent-probe: scan complete');
+}