diff --git a/tests/browser/lobby.test.js b/tests/browser/lobby.test.js
index b479f23..5bbde20 100644
--- a/tests/browser/lobby.test.js
+++ b/tests/browser/lobby.test.js
@@ -973,6 +973,76 @@ lobbyTest("a start ships the length that was on screen when it was pressed", asy
   );
 });
 
+lobbyTest("a start ships the grounding snippets that were checked when it was pressed", async (page) => {
+  session = { signedIn: false, loginRequired: true };
+  await lobby(page);
+  await page.click("details.interview-context summary");
+  const txt = (name, text) => ({ name, mimeType: "text/plain", buffer: Buffer.from(text) });
+
+  await page.setInputFiles("#grounding-jd", txt("first.txt", "Must know Rust"));
+  await page.locator('#grounding-choices input[data-group="requirements"]').first().check();
+  await page.check("#grounding-consent");
+
+  const finishLogin = (() => {
+    let done;
+    holdLogin = new Promise((resolve) => (done = resolve));
+    return done;
+  })();
+  await page.fill("#github-login", "candidate");
+  await page.click("#start");
+  await page.click("#grounding-clear");
+  await page.setInputFiles("#grounding-jd", txt("second.txt", "Must know SQL"));
+  await settles(page, () => document.querySelector("#grounding-choices label")?.textContent.includes("SQL"));
+  await page.locator('#grounding-choices input[data-group="requirements"]').first().check();
+  await page.check("#grounding-consent");
+  finishLogin();
+
+  await page.waitForURL(/\/interview/);
+  const stored = await page.evaluate(() => JSON.parse(sessionStorage.getItem("codetrial.interview-grounding.v1")));
+  assert.deepEqual(stored?.requirements, ["Must know Rust"]);
+});
+
+lobbyTest("consent withdrawn during the sign-in wait stores no grounding", async (page) => {
+  session = { signedIn: false, loginRequired: true };
+  await lobby(page);
+  await page.click("details.interview-context summary");
+  await page.setInputFiles("#grounding-jd", {
+    name: "jd.txt",
+    mimeType: "text/plain",
+    buffer: Buffer.from("Must know Rust"),
+  });
+  await page.locator('#grounding-choices input[data-group="requirements"]').first().check();
+  await page.check("#grounding-consent");
+
+  const finishLogin = (() => {
+    let done;
+    holdLogin = new Promise((resolve) => (done = resolve));
+    return done;
+  })();
+  await page.fill("#github-login", "candidate");
+  await page.click("#start");
+  await page.uncheck("#grounding-consent");
+  finishLogin();
+
+  await page.waitForURL(/\/interview/);
+  const stored = await page.evaluate(() => sessionStorage.getItem("codetrial.interview-grounding.v1"));
+  assert.equal(stored, null);
+});
+
+lobbyTest("a start the grounding packet refuses does not sign in first", async (page) => {
+  session = { signedIn: false, loginRequired: true };
+  await lobby(page);
+  await page.click("details.interview-context summary");
+  await page.setInputFiles("#grounding-jd", { name: "jd.txt", mimeType: "text/plain", buffer: Buffer.from("Must know Rust") });
+  await page.locator('#grounding-choices input[data-group="requirements"]').first().check();
+
+  await page.fill("#github-login", "candidate");
+  await page.click("#start");
+  await settles(page, () => document.querySelector("#grounding-error").textContent.includes("Agree"));
+  assert.equal(session.signedIn, false, "no /api/login for a start that was never going to go");
+  assert.equal(await page.isDisabled("#start"), false);
+});
+
 lobbyTest("a start already on its way out is not undone by a later choice", async (page) => {
   // The sign-in round trip is the one window where the start handler is
   // suspended with the page still live under it, and everything the candidate
diff --git a/web/app.js b/web/app.js
index 720df78..eb5e5d1 100644
--- a/web/app.js
+++ b/web/app.js
@@ -221,8 +221,13 @@ start.addEventListener("click", async () => {
   if (profile.seniority) destination.searchParams.set("seniority", profile.seniority);
   if (profile.targetCompany) destination.searchParams.set("company", profile.targetCompany);
   const focus = nodes.practiceFocusShareInput.checked ? practiceFocus(reports) : null;
-  const selected = checkedGrounding();
-  const consented = nodes.groundingConsent.checked;
+  let packet;
+  try {
+    packet = selectedGroundingPacket(grounding, checkedGrounding(), nodes.groundingConsent.checked);
+  } catch (error) {
+    nodes.groundingError.textContent = error.message;
+    return;
+  }
 
   starting = true;
   start.disabled = true;
@@ -243,8 +248,8 @@ start.addEventListener("click", async () => {
     signInFirst = false;
   }
   start.textContent = "Starting...";
+  if (!nodes.groundingConsent.checked) packet = null;
   try {
-    const packet = selectedGroundingPacket(grounding, selected, consented);
     storeGroundingPacket(sessionStorage, packet);
     storeSharedFocus(sessionStorage, focus?.weakness ?? null);
   } catch (error) {