diff --git a/src/lib/execution/adapters.mjs b/src/lib/execution/adapters.mjs
new file mode 100644
index 00000000..ae4365f8
--- /dev/null
+++ b/src/lib/execution/adapters.mjs
@@ -0,0 +1,7 @@
+// Built-in execution adapters. Importing this registry has no side effects:
+// processes are only created when the runner selects an adapter for a worker.
+import { OPENCODE_EXECUTION_ADAPTER } from './opencode.mjs';
+
+export const EXECUTION_ADAPTERS = Object.freeze(new Map([
+  ['opencode', OPENCODE_EXECUTION_ADAPTER],
+]));
diff --git a/src/lib/execution/runner.mjs b/src/lib/execution/runner.mjs
new file mode 100644
index 00000000..17841d03
--- /dev/null
+++ b/src/lib/execution/runner.mjs
@@ -0,0 +1,129 @@
+// Host-neutral execution coordinator. It owns scheduling, deadlines, and
+// lifecycle cleanup; adapters own each host's transport and protocol details.
+import { validateExecutionAdapter, validateWorkerResult } from './schema.mjs';
+import { EXECUTION_ADAPTERS } from './adapters.mjs';
+
+const nowIso = () => new Date().toISOString();
+
+function workerFailure(worker, /** @type {{status?:string, exitCategory?:string, failure?:any, startedAt?:string, clock?:()=>string}} */
+  { status = 'failed', exitCategory = 'worker_error', failure = null, startedAt, clock = nowIso } = {}) {
+  const endedAt = clock();
+  return validateWorkerResult({
+    workerId: worker.id, activity: worker.activity, role: worker.role, host: worker.host,
+    status, exitCategory, startedAt: startedAt ?? endedAt, endedAt,
+    durationMs: Math.max(0, Date.parse(endedAt) - Date.parse(startedAt ?? endedAt)),
+    provider: null, providerProvenance: 'unknown', configuredModel: worker.configuredModel ?? null,
+    observedModel: null, sessionId: null, transcriptRefs: [], failure, usage: null,
+  });
+}
+
+function boundedFailure(error) {
+  return { reason: String(error?.message ?? error ?? 'execution failed').slice(0, 240) };
+}
+
+async function observeBeforeDeadline(adapter, state, timeoutMs) {
+  if (!Number.isFinite(timeoutMs) || timeoutMs <= 0) return { timedOut: false, observation: await adapter.observe(state) };
+  let timer;
+  try {
+    return await Promise.race([
+      adapter.observe(state).then((observation) => ({ timedOut: false, observation })),
+      new Promise((resolve) => { timer = setTimeout(() => resolve({ timedOut: true }), timeoutMs); }),
+    ]);
+  } finally { clearTimeout(timer); }
+}
+
+/** Execute one worker and guarantee cleanup after every prepared state. */
+export async function executeWorker(worker, adapter, {
+  cwd = process.cwd(), timeoutMs = 120_000, clock = nowIso,
+} = /** @type {{cwd?:string, timeoutMs?:number, clock?:()=>string}} */ ({})) {
+  const startedAt = clock();
+  let state = null;
+  try {
+    const ready = await adapter.readiness({ worker, cwd });
+    if (!ready?.ready) return workerFailure(worker, {
+      exitCategory: ready?.exitCategory ?? 'cli_unavailable', failure: { reason: 'host is not ready' }, startedAt, clock,
+    });
+    state = await adapter.prepare({ worker, cwd });
+    state = await adapter.launch(state);
+    const watched = await observeBeforeDeadline(adapter, state, timeoutMs);
+    if (watched.timedOut) {
+      await adapter.cancel(state);
+      return adapter.interpret(state, { type: 'timeout' });
+    }
+    return validateWorkerResult(adapter.interpret(state, watched.observation));
+  } catch (error) {
+    return workerFailure(worker, { exitCategory: 'protocol_error', failure: boundedFailure(error), startedAt, clock });
+  } finally {
+    if (state) {
+      try { await adapter.cleanup(state); } catch { /* terminal result is already authoritative */ }
+    }
+  }
+}
+
+function validatePlan(plan) {
+  if (!plan || !Array.isArray(plan.workers)) throw new TypeError('execution plan requires workers');
+  const ids = new Set();
+  for (const worker of plan.workers) {
+    if (!worker || typeof worker !== 'object' || typeof worker.id !== 'string' || !worker.id
+      || typeof worker.activity !== 'string' || typeof worker.role !== 'string' || typeof worker.host !== 'string') {
+      throw new TypeError('execution worker requires id, activity, role, and host');
+    }
+    if (ids.has(worker.id)) throw new Error(`execution plan has duplicate worker id "${worker.id}"`);
+    ids.add(worker.id);
+  }
+  for (const worker of plan.workers) {
+    for (const dependency of worker.dependsOn ?? []) {
+      if (!ids.has(dependency)) throw new Error(`worker "${worker.id}" depends on unknown worker "${dependency}"`);
+      if (dependency === worker.id) throw new Error(`worker "${worker.id}" cannot depend on itself`);
+    }
+  }
+}
+
+function adapterFor(adapters, host) {
+  const adapter = adapters instanceof Map ? adapters.get(host) : adapters?.[host];
+  return adapter ? validateExecutionAdapter(adapter) : null;
+}
+
+/** Run a materialized routing plan as a bounded-concurrency dependency DAG.
+ * A failed dependency blocks descendants; independent branches keep running. */
+export async function executeRunPlan(plan, {
+  adapters = EXECUTION_ADAPTERS, cwd = process.cwd(), maxConcurrent = 4, timeoutMs, clock = nowIso,
+} = /** @type {{adapters?:Record<string, any>|Map<string, any>, cwd?:string, maxConcurrent?:number, timeoutMs?:number, clock?:()=>string}} */ ({})) {
+  validatePlan(plan);
+  if (!Number.isInteger(maxConcurrent) || maxConcurrent < 1) throw new TypeError('maxConcurrent must be a positive integer');
+  const pending = new Map(plan.workers.map((worker) => [worker.id, worker]));
+  const results = new Map();
+  const running = new Map();
+
+  const start = (worker) => {
+    const adapter = adapterFor(adapters, worker.host);
+    const promise = adapter
+      ? executeWorker(worker, adapter, { cwd, timeoutMs, clock })
+      : Promise.resolve(workerFailure(worker, { exitCategory: 'cli_unavailable', failure: { reason: `no execution adapter for host "${worker.host}"` }, clock }));
+    running.set(worker.id, promise.then((result) => ({ id: worker.id, result })));
+    pending.delete(worker.id);
+  };
+
+  while (pending.size || running.size) {
+    for (const worker of pending.values()) {
+      if (running.size >= maxConcurrent) break;
+      const deps = worker.dependsOn ?? [];
+      if (!deps.every((id) => results.has(id))) continue;
+      const failed = deps.filter((id) => results.get(id).status !== 'succeeded');
+      if (failed.length) {
+        results.set(worker.id, workerFailure(worker, {
+          status: 'blocked', exitCategory: 'worker_error', failure: { reason: 'dependency_failed', dependencies: failed }, clock,
+        }));
+        pending.delete(worker.id);
+      } else start(worker);
+    }
+    if (!running.size) {
+      if (pending.size) throw new Error('execution plan contains a dependency cycle');
+      break;
+    }
+    const { id, result } = await Promise.race(running.values());
+    running.delete(id);
+    results.set(id, result);
+  }
+  return plan.workers.map((worker) => results.get(worker.id));
+}
diff --git a/tests/kit/execution-runner.test.mjs b/tests/kit/execution-runner.test.mjs
new file mode 100644
index 00000000..044ec72c
--- /dev/null
+++ b/tests/kit/execution-runner.test.mjs
@@ -0,0 +1,56 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { EXECUTION_ADAPTERS } from '../../src/lib/execution/adapters.mjs';
+import { executeRunPlan } from '../../src/lib/execution/runner.mjs';
+
+const worker = (id, host = 'opencode', dependsOn) => ({ id, activity: 'implementation', role: 'coder', host, prompt: id, ...(dependsOn ? { dependsOn } : {}) });
+const clock = () => '2026-07-29T00:00:00.000Z';
+
+test('the built-in registry exposes the supervised OpenCode transport only', () => {
+  assert.equal(EXECUTION_ADAPTERS.get('opencode').id, 'opencode-server');
+  assert.equal(EXECUTION_ADAPTERS.has('claude'), false);
+  assert.equal(EXECUTION_ADAPTERS.has('codex'), false);
+});
+
+function adapter({ observation = { type: 'idle' }, events = [] } = {}) {
+  return {
+    id: 'fake',
+    async readiness() { events.push('ready'); return { ready: true }; },
+    async prepare({ worker: w }) { events.push(`prepare:${w.id}`); return { worker: w }; },
+    async launch(state) { events.push(`launch:${state.worker.id}`); return state; },
+    async observe(state) { events.push(`observe:${state.worker.id}`); return observation; },
+    interpret(state, observed) {
+      events.push(`interpret:${state.worker.id}:${observed.type}`);
+      return {
+        workerId: state.worker.id, activity: state.worker.activity, role: state.worker.role, host: state.worker.host,
+        status: observed.type === 'timeout' ? 'timed_out' : 'succeeded', exitCategory: observed.type === 'timeout' ? 'timeout' : 'success',
+        startedAt: clock(), endedAt: clock(), durationMs: 0, provider: null, providerProvenance: 'unknown',
+        configuredModel: null, observedModel: null, sessionId: null, transcriptRefs: [], failure: null, usage: null,
+      };
+    },
+    async cancel(state) { events.push(`cancel:${state.worker.id}`); },
+    async cleanup(state) { events.push(`cleanup:${state.worker.id}`); },
+  };
+}
+
+test('runner schedules a dependency DAG and blocks only descendants of a failure', async () => {
+  const events = [];
+  const ok = adapter({ events });
+  const failed = { ...adapter({ events }), interpret(state) {
+    return { workerId: state.worker.id, activity: state.worker.activity, role: state.worker.role, host: state.worker.host,
+      status: 'failed', exitCategory: 'worker_error', startedAt: clock(), endedAt: clock(), durationMs: 0,
+      provider: null, providerProvenance: 'unknown', configuredModel: null, observedModel: null, sessionId: null, transcriptRefs: [], failure: { reason: 'no' }, usage: null };
+  } };
+  const results = await executeRunPlan({ workers: [worker('a', 'opencode'), worker('b', 'bad'), worker('c', 'opencode', ['a']), worker('d', 'opencode', ['b'])] }, {
+    adapters: { opencode: ok, bad: failed }, maxConcurrent: 2, clock,
+  });
+  assert.deepEqual(results.map((result) => result.status), ['succeeded', 'failed', 'succeeded', 'blocked']);
+  assert.ok(events.includes('launch:c'));
+  assert.ok(!events.includes('launch:d'));
+});
+
+test('runner reports an unimplemented host without attempting a lifecycle', async () => {
+  const [result] = await executeRunPlan({ workers: [worker('a', 'claude')] }, { clock });
+  assert.equal(result.exitCategory, 'cli_unavailable');
+  assert.match(result.failure.reason, /no execution adapter/);
+});