diff --git a/src/agent/interchange-loop.test.ts b/src/agent/interchange-loop.test.ts
new file mode 100644
index 000000000..dad068f69
--- /dev/null
+++ b/src/agent/interchange-loop.test.ts
@@ -0,0 +1,49 @@
+import { describe, expect, test } from "bun:test";
+import {
+  INTERCHANGE_LOOP_ENV_VAR,
+  isInterchangeLoopEnabled,
+  resolveInterchangeLoopRunner,
+} from "./interchange-loop.js";
+
+function envWith(value: string | undefined): NodeJS.ProcessEnv {
+  const env: NodeJS.ProcessEnv = {};
+  if (value !== undefined) env[INTERCHANGE_LOOP_ENV_VAR] = value;
+  return env;
+}
+
+describe("isInterchangeLoopEnabled", () => {
+  test("is disabled by default", () => {
+    expect(isInterchangeLoopEnabled(envWith(undefined))).toBe(false);
+  });
+
+  test.each(["1", "true", "TRUE", " True "])("is enabled for %j", (value) => {
+    expect(isInterchangeLoopEnabled(envWith(value))).toBe(true);
+  });
+
+  test.each(["0", "false", "yes", ""])("stays disabled for %j", (value) => {
+    expect(isInterchangeLoopEnabled(envWith(value))).toBe(false);
+  });
+
+  test("never reads process.env when an env is passed", () => {
+    const prior = process.env.CORBITS_INTERCHANGE_LOOP;
+    process.env.CORBITS_INTERCHANGE_LOOP = "1";
+    try {
+      expect(isInterchangeLoopEnabled(envWith(undefined))).toBe(false);
+    } finally {
+      if (prior === undefined) delete process.env.CORBITS_INTERCHANGE_LOOP;
+      else process.env.CORBITS_INTERCHANGE_LOOP = prior;
+    }
+  });
+});
+
+describe("resolveInterchangeLoopRunner", () => {
+  test("never throws and reports unavailable without the workflow package", async () => {
+    // `@intx/workflow` is not installed in this tree (it arrives with the
+    // 0.4.0 hub), so the seam must fall back instead of rejecting.
+    const status = await resolveInterchangeLoopRunner();
+    expect(status.status).toBe("unavailable");
+    if (status.status === "unavailable") {
+      expect(status.reason).toContain("@intx/workflow");
+    }
+  });
+});
diff --git a/src/agent/interchange-loop.ts b/src/agent/interchange-loop.ts
new file mode 100644
index 000000000..407c2357c
--- /dev/null
+++ b/src/agent/interchange-loop.ts
@@ -0,0 +1,69 @@
+/**
+ * Optional Interchange-driven core loop (CL-8267).
+ *
+ * The reactor (`@intx/agent` + `ChatDirector`) remains the only loop driver.
+ * This module is the opt-in seam for driving it through Interchange's
+ * `runWorkflow`/`runLocal` instead, without waiting on the full 0.4.0 hub.
+ *
+ * Gating: enabled only when `CORBITS_INTERCHANGE_LOOP` is `1` or `true`.
+ * Resolution is lazy and total — `@intx/workflow` is not a dependency of this
+ * package yet, so when it cannot be loaded the caller keeps the reactor path.
+ * Nothing here changes behavior unless the flag is set.
+ */
+
+export const INTERCHANGE_LOOP_ENV_VAR = "CORBITS_INTERCHANGE_LOOP";
+
+const INTERCHANGE_WORKFLOW_SPECIFIER = "@intx/workflow";
+
+export type InterchangeLoopStatus =
+  | { status: "driven"; via: "runWorkflow" | "runLocal" }
+  | { status: "unavailable"; reason: string };
+
+/** True only when the operator explicitly opts into the Interchange loop. */
+export function isInterchangeLoopEnabled(
+  env: NodeJS.ProcessEnv = process.env,
+): boolean {
+  const raw = env[INTERCHANGE_LOOP_ENV_VAR]?.trim().toLowerCase();
+  return raw === "1" || raw === "true";
+}
+
+type WorkflowModule = Record<string, unknown>;
+
+function pickDriver(loaded: WorkflowModule): InterchangeLoopStatus {
+  // Prefer the hub-backed entry point; the in-memory runner is the local
+  // fallback. Both names come from upstream `@intx/workflow`.
+  if (typeof loaded["runWorkflow"] === "function")
+    return { status: "driven", via: "runWorkflow" };
+  if (typeof loaded["runLocal"] === "function")
+    return { status: "driven", via: "runLocal" };
+  return {
+    status: "unavailable",
+    reason: `${INTERCHANGE_WORKFLOW_SPECIFIER} loaded but exports neither runWorkflow nor runLocal`,
+  };
+}
+
+/**
+ * Resolve the Interchange loop driver. Never throws and never imports
+ * statically — the package is an optional peer, absent until the workflow
+ * runtime lands. Callers fall through to the reactor on `unavailable`.
+ */
+export async function resolveInterchangeLoopRunner(): Promise<InterchangeLoopStatus> {
+  let loaded: unknown;
+  try {
+    loaded = (await import(
+      INTERCHANGE_WORKFLOW_SPECIFIER
+    )) as unknown as WorkflowModule;
+  } catch (err: unknown) {
+    const detail = err instanceof Error ? err.message : String(err);
+    return {
+      status: "unavailable",
+      reason: `${INTERCHANGE_WORKFLOW_SPECIFIER} is not installed (${detail})`,
+    };
+  }
+  if (typeof loaded !== "object" || loaded === null)
+    return {
+      status: "unavailable",
+      reason: `${INTERCHANGE_WORKFLOW_SPECIFIER} did not load as a module`,
+    };
+  return pickDriver(loaded as unknown as WorkflowModule);
+}
diff --git a/src/exec/runner.ts b/src/exec/runner.ts
index 1f4263f00..3316a49a7 100644
--- a/src/exec/runner.ts
+++ b/src/exec/runner.ts
@@ -20,6 +20,10 @@ import { formatMcpTrustQuestion } from "../trust/project-trust.js";
 import { DIRECTOR_REGISTRY } from "../agent/directors/registry.js";
 import type { DirectorId, DirectorPackage } from "../agent/directors/types.js";
 import { submitOutputDefinition } from "../agent/director.js";
+import {
+  isInterchangeLoopEnabled,
+  resolveInterchangeLoopRunner,
+} from "../agent/interchange-loop.js";
 import { handleChatDirectorEvent } from "../agent/chat-event-subscribers.js";
 import {
   CodexRefreshLockError,
@@ -469,6 +473,18 @@ export async function runExec(config: Config): Promise<ExecResult> {
   const sessionId =
     config.sessionId.length > 0 ? config.sessionId : generateSessionId();
   const startedAt = Date.now();
+  // CL-8267: optional Interchange loop seam. Off by default; when the
+  // operator opts in but the workflow runtime is absent, stay on the
+  // reactor path with a warning instead of failing the run.
+  if (isInterchangeLoopEnabled()) {
+    const loop = await resolveInterchangeLoopRunner();
+    if (loop.status === "unavailable") {
+      logger.warn(
+        "Interchange loop requested but {reason}; continuing on reactor path",
+        { reason: loop.reason },
+      );
+    }
+  }
   const workdir = sessionContextDir(config.cwd, sessionId);
   // Setup runs before the main try below: initSessionDir/loadState hit disk
   // before any session_end coverage exists, so an EACCES/EROFS here would