diff --git a/README.md b/README.md
index 8aca44c..b8a001a 100644
--- a/README.md
+++ b/README.md
@@ -56,11 +56,11 @@ Open the Worker URL, sign in with Google, claim the first owner account using `C
 
 ## Sandbox provider
 
-Codevil runs each session in either an E2B sandbox or a Cloudflare Sandbox container. The shipped `wrangler.toml` pins `SANDBOX_PROVIDER = "cloudflare"` so a deploy never switches to E2B before it is ready. To move to E2B: (1) add `E2B_API_KEY` both as a Worker secret and as a GitHub Actions secret in the `production` environment, (2) pass the manual end-to-end check, (3) set `SANDBOX_PROVIDER = "e2b"` and merge to `main`. CI then publishes the template on every deploy (see below). The Worker's code default (no var set) is `e2b`. Configure the provider with Worker vars in `packages/worker/wrangler.toml` (or an untracked `wrangler.operator.toml` overlay):
+Codevil runs each session in either an E2B sandbox or a Cloudflare Sandbox container. The shipped `wrangler.toml` sets `SANDBOX_PROVIDER = "e2b"`, which needs `E2B_API_KEY` both as a Worker secret and as a GitHub Actions secret in the `production` environment. CI publishes the template on every deploy (see below). To run sessions on Cloudflare containers instead, set `SANDBOX_PROVIDER = "cloudflare"`; existing sessions keep the provider they started on. The Worker's code default (no var set) is `e2b`. Configure the provider with Worker vars in `packages/worker/wrangler.toml` (or an untracked `wrangler.operator.toml` overlay):
 
 | Name | Kind | Default | Purpose |
 | --- | --- | --- | --- |
-| `SANDBOX_PROVIDER` | var | `e2b` in code; `cloudflare` in the shipped `wrangler.toml` | `e2b` or `cloudflare`. |
+| `SANDBOX_PROVIDER` | var | `e2b` | `e2b` or `cloudflare`. Deploys require it to be set explicitly. |
 | `E2B_API_KEY` | secret | none | Required when `SANDBOX_PROVIDER=e2b`. Upload with `pnpm exec wrangler secret put E2B_API_KEY`; never put it in `wrangler.toml`. |
 | `E2B_TEMPLATE_ID` | var | `codevil-sandbox` | E2B template the sandboxes start from, without a tag. CI deploys pin it to `<template>:<commit sha>`. |
 | `E2B_MAX_SANDBOX_SECONDS` | var | `3600` | Maximum continuous sandbox runtime; the default matches the E2B Hobby limit. |
diff --git a/packages/worker/test/deployment-config.test.mjs b/packages/worker/test/deployment-config.test.mjs
index 107cae3..a01478a 100644
--- a/packages/worker/test/deployment-config.test.mjs
+++ b/packages/worker/test/deployment-config.test.mjs
@@ -28,17 +28,18 @@ test("checked-in Worker config is portable and defaults to workers.dev", async (
   assert.match(config, /binding = "BACKUP_BUCKET"/);
 });
 
-test("checked-in Worker config keeps production on the Cloudflare sandbox until E2B is ready", async () => {
+test("checked-in Worker config runs production sessions on E2B", async () => {
   const [config, envExample] = await Promise.all([
     readFile(resolve(workerRoot, "wrangler.toml"), "utf8"),
     readFile(resolve(workerRoot, ".env.example"), "utf8"),
   ]);
-  assert.match(config, /^SANDBOX_PROVIDER = "cloudflare"$/m);
+  assert.match(config, /^SANDBOX_PROVIDER = "e2b"$/m);
   // The deploy pipeline must read the same answer, or every deploy fails.
-  assert.deepEqual(sandboxDeploymentSettings(config), { provider: "cloudflare" });
+  assert.deepEqual(sandboxDeploymentSettings(config), { provider: "e2b", templateId: "codevil-sandbox" });
+  // Rolling back is a one-line change the pipeline must also accept.
   assert.deepEqual(
-    sandboxDeploymentSettings(config.replace(/^SANDBOX_PROVIDER = "cloudflare"$/m, 'SANDBOX_PROVIDER = "e2b"')),
-    { provider: "e2b", templateId: "codevil-sandbox" },
+    sandboxDeploymentSettings(config.replace(/^SANDBOX_PROVIDER = "e2b"$/m, 'SANDBOX_PROVIDER = "cloudflare"')),
+    { provider: "cloudflare" },
   );
   assert.doesNotMatch(config, /^E2B_API_KEY\s*=/m);
   assert.match(envExample, /^E2B_API_KEY=/m);
@@ -253,7 +254,7 @@ test("sandbox-deploy-settings writes the provider outputs for the CI publish job
       encoding: "utf8",
     });
     assert.equal(result.status, 0, result.stderr);
-    assert.equal(await readFile(outputFile, "utf8"), "sandbox_provider=cloudflare\n");
+    assert.equal(await readFile(outputFile, "utf8"), "sandbox_provider=e2b\ne2b_template_id=codevil-sandbox\n");
   } finally {
     await rm(dir, { recursive: true, force: true });
   }
diff --git a/packages/worker/wrangler.toml b/packages/worker/wrangler.toml
index 2e3a35e..ae384f3 100644
--- a/packages/worker/wrangler.toml
+++ b/packages/worker/wrangler.toml
@@ -7,12 +7,13 @@ upload_source_maps = true
 
 [vars]
 EMAIL_PROVIDER = "none"
-# Production stays on Cloudflare until E2B is ready. Switch to "e2b" only after
-# setting E2B_API_KEY as a Worker secret and a GitHub Actions secret and passing
-# the manual E2B end-to-end check. With "e2b", the CI deploy publishes this
-# commit's template and pins E2B_TEMPLATE_ID to "<id>:<commit sha>".
+# New sessions run on E2B. This needs E2B_API_KEY as a Worker secret and as a
+# GitHub Actions secret in the production environment; the CI deploy publishes
+# this commit's template and pins E2B_TEMPLATE_ID to "<id>:<commit sha>".
+# Set "cloudflare" to roll back: new sessions return to Cloudflare containers,
+# and existing sessions keep the provider they started on.
 # (Code default with no var at all is "e2b"; deploys require this to be explicit.)
-SANDBOX_PROVIDER = "cloudflare"
+SANDBOX_PROVIDER = "e2b"
 E2B_TEMPLATE_ID = "codevil-sandbox"
 CODEVIL_WEB_ORIGIN = "http://localhost:5173,http://localhost:8787"
 # Leaving CODEVIL_PREVIEW_ORIGIN unset keeps preview URLs on the portable