diff --git a/tests/restart-chaos/journey-driver.ts b/tests/restart-chaos/journey-driver.ts
index d11d111e968..3ea1a00f348 100644
--- a/tests/restart-chaos/journey-driver.ts
+++ b/tests/restart-chaos/journey-driver.ts
@@ -65,11 +65,10 @@ export function questionAnswer(interaction: Json, choice: string): { questionId:
 }
 
 /** The scripted Q3 agent: one connected-app call, then report the reviewed result. Adapted from tests/e2e/connection-reviews.spec.ts. */
-export function q3AgentScript(connectionId: string, title: string, serverBaseUrl: string): string {
-  // The wave's own loopback server. On a tailnet host, PAPERCLIP_API_URL names the machine's
-  // public URL, which reaches a different instance.
+export function q3AgentScript(connectionId: string, title: string): string {
+  // The supervisor pins PAPERCLIP_API_URL to the wave's own loopback server.
   return `
-const base = ${JSON.stringify(serverBaseUrl)} + "/api";
+const base = process.env.PAPERCLIP_API_URL.replace(/\\/+$/, "").replace(/\\/api$/, "") + "/api";
 const headers = { authorization: "Bearer " + process.env.PAPERCLIP_API_KEY, "content-type": "application/json", "x-paperclip-run-id": process.env.PAPERCLIP_RUN_ID };
 const api = async (path, method = "GET", body) => {
   const response = await fetch(base + path, { method, headers, body: body === undefined ? undefined : JSON.stringify(body) });
@@ -164,7 +163,7 @@ export class JourneyDriver {
       const agent = await api.post<Json>(`/api/companies/${lab.companyId}/agents`, {
         name: `Chaos pages agent ${plan.nonce}`, role: "engineer", title: "Connected-app journey agent",
         capabilities: "Creates one page with the chaos app after review.", adapterType: "process",
-        adapterConfig: { command: process.execPath, args: ["--input-type=module", "-e", q3AgentScript(state.connectionId, q3ToolArgument(plan.nonce), api.baseUrl)] },
+        adapterConfig: { command: process.execPath, args: ["--input-type=module", "-e", q3AgentScript(state.connectionId, q3ToolArgument(plan.nonce))] },
       });
       state.agentId = String(agent.id);
       // A scripted process run records usage with no price, which the company's default budget
diff --git a/tests/restart-chaos/journeys.test.ts b/tests/restart-chaos/journeys.test.ts
index 86ab338dcad..a025933a49e 100644
--- a/tests/restart-chaos/journeys.test.ts
+++ b/tests/restart-chaos/journeys.test.ts
@@ -1,6 +1,12 @@
 import { describe, expect, it } from "vitest";
 import { parseCommand } from "./config.js";
-import { actionRequestRows, JourneyDriver, questionAnswer, reviewClockNames, shiftReviewClockWith, type JourneyHost } from "./journey-driver.js";
+import { actionRequestRows, JourneyDriver, q3AgentScript, questionAnswer, reviewClockNames, shiftReviewClockWith, type JourneyHost } from "./journey-driver.js";
+import { waveServerUrlEnvironment } from "./supervisor.js";
+import { buildPaperclipServerEnvironment } from "../runner-e2e/harness-env.js";
+import { execFile } from "node:child_process";
+import { once } from "node:events";
+import { createServer } from "node:http";
+import type { AddressInfo } from "node:net";
 import { matrixCells, matrixMayLaunch, planMatrixWave } from "./journey-matrix.js";
 import { pkceChallenge, startOAuthApp } from "./journey-oauth-app.js";
 import {
@@ -312,3 +318,37 @@ describe("Q3 review clock", () => {
     expect(connectionUpdate.params[2]).toBeNull();
   });
 });
+
+describe("wave server URL", () => {
+  it("pins the wave's loopback origin over an ambient public API URL", () => {
+    const environment = buildPaperclipServerEnvironment(
+      { PAPERCLIP_API_URL: "https://dev-machine.example.ts.net", PATH: "/bin" },
+      { PORT: "50187", ...waveServerUrlEnvironment(50187) });
+    expect(environment.PAPERCLIP_API_URL).toBe("http://127.0.0.1:50187");
+  });
+
+  it("sends the Q3 agent's run key only to the PAPERCLIP_API_URL its server assigned", async () => {
+    const requests: Array<{ url: string; authorization: string | undefined }> = [];
+    const server = createServer((request, response) => {
+      requests.push({ url: request.url ?? "", authorization: request.headers.authorization });
+      response.setHeader("content-type", "application/json");
+      response.end(JSON.stringify(request.url?.endsWith("/interactions")
+        ? [{ status: "pending", payload: { toolAction: { tool: "create_page" } } }] : {}));
+    });
+    server.listen(0, "127.0.0.1");
+    await once(server, "listening");
+    const origin = `http://127.0.0.1:${(server.address() as AddressInfo).port}`;
+    try {
+      const output = await new Promise<string>((resolve, reject) => execFile(process.execPath,
+        ["--input-type=module", "-e", q3AgentScript("connection-1", "Chaos page")],
+        { env: { PATH: process.env.PATH, PAPERCLIP_API_URL: `${origin}/api/`, PAPERCLIP_API_KEY: "run-key",
+          PAPERCLIP_RUN_ID: "run-1", PAPERCLIP_TASK_ID: "issue-1" }, timeout: 20_000 },
+        (error, stdout, stderr) => error ? reject(new Error(`${error.message}\n${stderr}`)) : resolve(stdout)));
+      expect(output).toContain("Waiting for the saved review");
+      expect(requests.map(request => request.url)).toContain("/api/issues/issue-1/interactions");
+      expect(requests.every(request => request.url.startsWith("/api/") && request.authorization === "Bearer run-key")).toBe(true);
+    } finally {
+      server.close();
+    }
+  });
+});
diff --git a/tests/restart-chaos/supervisor.ts b/tests/restart-chaos/supervisor.ts
index 370889a48b0..e3adf831f1b 100644
--- a/tests/restart-chaos/supervisor.ts
+++ b/tests/restart-chaos/supervisor.ts
@@ -61,6 +61,16 @@ export function crashLoopShouldFire(target: (typeof CRASH_LOOP_TARGETS)[number],
   return phase === "ready";
 }
 
+/**
+ * Agents reach the server at PAPERCLIP_API_URL. An explicit value wins over the URL the server
+ * derives from its public URL (a developer's .paperclip/.env or shell can name a tailnet origin
+ * that serves a different instance). Pin this wave's own loopback origin so an agent's key for
+ * the temporary instance is only ever sent to that instance.
+ */
+export function waveServerUrlEnvironment(port: number): { PAPERCLIP_API_URL: string } {
+  return { PAPERCLIP_API_URL: `http://127.0.0.1:${port}` };
+}
+
 export interface SupervisorPaths { temporaryRoot: string; home: string; configPath: string; serverLogPath: string }
 
 /**
@@ -218,6 +228,7 @@ export class ChaosSupervisor {
       // set values. A worktree-initialized checkout's file sets
       // PAPERCLIP_IN_WORKTREE=true, which suppresses all scheduling: no run starts.
       PAPERCLIP_IN_WORKTREE: "false",
+      ...waveServerUrlEnvironment(this.port),
       ...extraEnvironment,
     };
     const environment = buildPaperclipServerEnvironment(source, overrides);