diff --git a/.github/workflows/preview-sweep.yml b/.github/workflows/preview-sweep.yml
new file mode 100644
index 000000000..b498c2864
--- /dev/null
+++ b/.github/workflows/preview-sweep.yml
@@ -0,0 +1,43 @@
+name: Preview sweep
+
+# Safety net for the per-PR previews (.github/workflows/preview.yml): force
+# pushes, cancelled runs, or teardown failures can orphan a preview stack.
+# Nightly, list every deployed preview and destroy any whose PR is no longer
+# open.
+
+on:
+  schedule:
+    - cron: "23 5 * * *"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pull-requests: read
+
+jobs:
+  sweep:
+    name: Destroy previews for closed PRs
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: 1.3.11
+
+      - name: Sweep
+        env:
+          CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_PREVIEW_API_TOKEN }}
+          CLOUDFLARE_ACCOUNT_ID: ${{ vars.CLOUDFLARE_PREVIEW_ACCOUNT_ID }}
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          set -euo pipefail
+          for pr in $(bun apps/host-cloudflare/scripts/preview.ts list | jq -r '.[].pr'); do
+            state="$(gh pr view "$pr" --repo "$GITHUB_REPOSITORY" --json state -q .state 2>/dev/null || echo UNKNOWN)"
+            if [ "$state" != "OPEN" ]; then
+              echo "PR #$pr is $state — destroying its preview"
+              bun apps/host-cloudflare/scripts/preview.ts destroy --pr "$pr"
+            else
+              echo "PR #$pr is open — keeping its preview"
+            fi
+          done
diff --git a/.github/workflows/preview.yml b/.github/workflows/preview.yml
new file mode 100644
index 000000000..3d3bef13f
--- /dev/null
+++ b/.github/workflows/preview.yml
@@ -0,0 +1,117 @@
+name: Preview
+
+# Per-PR preview deploys of the Cloudflare host to a dedicated preview account.
+# Every same-repo PR gets its own isolated stack (Worker + D1 + Access app)
+# behind Cloudflare Access; it is torn down when the PR closes. Fork PRs are
+# skipped — they must not run with the deploy token.
+#
+# Required repo configuration:
+#   secret CLOUDFLARE_PREVIEW_API_TOKEN  — scoped token (Workers/D1/R2/Access edit)
+#   var    CLOUDFLARE_PREVIEW_ACCOUNT_ID — the preview Cloudflare account
+#   var    PREVIEW_ACCESS_TEAM_DOMAIN    — Zero Trust team domain
+#   var    PREVIEW_ACCESS_EMAILS         — comma-separated emails allowed through Access
+
+on:
+  pull_request:
+    types: [opened, reopened, synchronize, closed]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+concurrency:
+  group: preview-${{ github.event.pull_request.number }}
+  cancel-in-progress: ${{ github.event.action != 'closed' }}
+
+jobs:
+  deploy:
+    name: Deploy preview
+    if: github.event.action != 'closed' && github.event.pull_request.head.repo.full_name == github.repository
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: 1.3.11
+
+      - run: bun install --frozen-lockfile
+
+      - name: Deploy
+        id: deploy
+        working-directory: apps/host-cloudflare
+        env:
+          CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_PREVIEW_API_TOKEN }}
+          CLOUDFLARE_ACCOUNT_ID: ${{ vars.CLOUDFLARE_PREVIEW_ACCOUNT_ID }}
+          PREVIEW_ACCESS_TEAM_DOMAIN: ${{ vars.PREVIEW_ACCESS_TEAM_DOMAIN }}
+          PREVIEW_ACCESS_EMAILS: ${{ vars.PREVIEW_ACCESS_EMAILS }}
+        run: bun scripts/preview.ts deploy --pr ${{ github.event.pull_request.number }}
+
+      - name: Comment preview URL
+        uses: actions/github-script@v7
+        env:
+          PREVIEW_URL: ${{ steps.deploy.outputs.url }}
+        with:
+          script: |
+            const marker = "<!-- executor-preview -->";
+            const body = [
+              marker,
+              "### Cloudflare preview",
+              "",
+              `| | |`,
+              `|---|---|`,
+              `| Console | ${process.env.PREVIEW_URL} |`,
+              `| MCP | \`${process.env.PREVIEW_URL}/mcp\` |`,
+              `| Deployed commit | ${context.payload.pull_request.head.sha} |`,
+              "",
+              "Sign-in is Cloudflare Access (one-time PIN to an allowed email). " +
+                "The preview has its own database and encryption key; it is destroyed when this PR closes.",
+            ].join("\n");
+            const { data: comments } = await github.rest.issues.listComments({
+              ...context.repo,
+              issue_number: context.issue.number,
+              per_page: 100,
+            });
+            const existing = comments.find((c) => c.body && c.body.startsWith(marker));
+            if (existing) {
+              await github.rest.issues.updateComment({ ...context.repo, comment_id: existing.id, body });
+            } else {
+              await github.rest.issues.createComment({ ...context.repo, issue_number: context.issue.number, body });
+            }
+
+  teardown:
+    name: Tear down preview
+    if: github.event.action == 'closed' && github.event.pull_request.head.repo.full_name == github.repository
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: 1.3.11
+
+      # destroy talks straight to the Cloudflare API — no install needed.
+      - name: Destroy
+        env:
+          CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_PREVIEW_API_TOKEN }}
+          CLOUDFLARE_ACCOUNT_ID: ${{ vars.CLOUDFLARE_PREVIEW_ACCOUNT_ID }}
+        run: bun apps/host-cloudflare/scripts/preview.ts destroy --pr ${{ github.event.pull_request.number }}
+
+      - name: Mark comment as torn down
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const marker = "<!-- executor-preview -->";
+            const { data: comments } = await github.rest.issues.listComments({
+              ...context.repo,
+              issue_number: context.issue.number,
+              per_page: 100,
+            });
+            const existing = comments.find((c) => c.body && c.body.startsWith(marker));
+            if (existing) {
+              await github.rest.issues.updateComment({
+                ...context.repo,
+                comment_id: existing.id,
+                body: `${marker}\n### Cloudflare preview\n\nTorn down — the PR is closed.`,
+              });
+            }
diff --git a/.oxlintrc.jsonc b/.oxlintrc.jsonc
index 2cd7c056c..7200b5bf8 100644
--- a/.oxlintrc.jsonc
+++ b/.oxlintrc.jsonc
@@ -37,10 +37,19 @@
       "error",
       {
         "forbid": [
-          { "element": "button", "message": "Use <Button> from @executor/react" },
+          {
+            "element": "button",
+            "message": "Use <Button> from @executor/react",
+          },
           { "element": "input", "message": "Use <Input> from @executor/react" },
-          { "element": "textarea", "message": "Use <Textarea> from @executor/react" },
-          { "element": "select", "message": "Use <Select> or <NativeSelect> from @executor/react" },
+          {
+            "element": "textarea",
+            "message": "Use <Textarea> from @executor/react",
+          },
+          {
+            "element": "select",
+            "message": "Use <Select> or <NativeSelect> from @executor/react",
+          },
           { "element": "table", "message": "Use <Table> from @executor/react" },
           { "element": "label", "message": "Use <Label> from @executor/react" },
         ],
@@ -53,6 +62,7 @@
         "apps/cli/src/**/*.{ts,tsx}",
         "apps/desktop/src/main.ts",
         "scripts/**/*.{ts,js}",
+        "apps/*/scripts/**/*.{ts,js}",
         "packages/kernel/runtime-*/src/**/*.{ts,tsx,js,mjs}",
       ],
       "rules": {
diff --git a/apps/host-cloudflare/.gitignore b/apps/host-cloudflare/.gitignore
index 818180624..726b7f10f 100644
--- a/apps/host-cloudflare/.gitignore
+++ b/apps/host-cloudflare/.gitignore
@@ -1,3 +1,4 @@
 dist/
 .dev.vars
 .wrangler/
+wrangler.preview.jsonc
diff --git a/apps/host-cloudflare/scripts/preview.ts b/apps/host-cloudflare/scripts/preview.ts
new file mode 100644
index 000000000..5909d7e9b
--- /dev/null
+++ b/apps/host-cloudflare/scripts/preview.ts
@@ -0,0 +1,313 @@
+// Per-PR preview deploys of the Cloudflare host.
+//
+// Each pull request gets its own fully isolated stack on a dedicated
+// Cloudflare account: a Worker (`executor-preview-pr-<n>`), its own D1
+// database, a fresh EXECUTOR_SECRET_KEY, and its own Cloudflare Access
+// application (MCP-OAuth-aware, gating the workers.dev hostname at the edge)
+// so previews are never publicly open. The R2 blob bucket is shared across
+// previews (`executor-preview-blobs`) — blobs are content-addressed overflow
+// values reached only via pointers in each preview's private D1, and leaving
+// the bucket in place keeps teardown trivial.
+//
+// Teardown is stateless by naming convention: everything a preview owns is
+// derived from its PR number, so `destroy` (and the scheduled sweeper) can
+// clean up without any deploy-time state.
+//
+//   bun scripts/preview.ts deploy --pr 123 [--skip-build]
+//   bun scripts/preview.ts destroy --pr 123
+//   bun scripts/preview.ts list            # JSON [{pr, name}] of live previews
+//
+// Env: CLOUDFLARE_API_TOKEN (Workers/D1/R2/Access edit) + CLOUDFLARE_ACCOUNT_ID
+// always; deploy additionally needs PREVIEW_ACCESS_TEAM_DOMAIN (Zero Trust team)
+// and PREVIEW_ACCESS_EMAILS (comma-separated emails allowed through Access; the
+// first one is also the admin unless PREVIEW_ADMIN_EMAILS overrides it).
+
+import { spawnSync } from "node:child_process";
+import { randomBytes } from "node:crypto";
+import { appendFileSync, readFileSync, writeFileSync } from "node:fs";
+import { resolve } from "node:path";
+
+const CF_API = "https://api.cloudflare.com/client/v4";
+const APP_DIR = resolve(import.meta.dirname, "..");
+const WORKER_PREFIX = "executor-preview-pr-";
+const SHARED_BLOBS_BUCKET = "executor-preview-blobs";
+
+const TOKEN = process.env.CLOUDFLARE_API_TOKEN ?? "";
+const ACCOUNT = process.env.CLOUDFLARE_ACCOUNT_ID ?? "";
+
+const fail = (message: string): never => {
+  process.stderr.write(`${message}\n`);
+  process.exit(1);
+};
+
+interface CfFetchResult {
+  readonly ok: boolean;
+  readonly errors: string;
+  readonly result: any;
+}
+
+const cf = async (method: string, path: string, body?: unknown): Promise<CfFetchResult> => {
+  const response = await fetch(`${CF_API}${path}`, {
+    method,
+    headers: {
+      authorization: `Bearer ${TOKEN}`,
+      "content-type": "application/json",
+    },
+    body: body === undefined ? undefined : JSON.stringify(body),
+  });
+  const json: any = await response.json().catch(() => ({ success: false, errors: [] }));
+  return {
+    ok: json.success === true,
+    errors: JSON.stringify(json.errors ?? []),
+    result: json.result,
+  };
+};
+
+const cfOk = async (method: string, path: string, body?: unknown): Promise<any> => {
+  const response = await cf(method, path, body);
+  if (!response.ok) fail(`${method} ${path} failed: ${response.errors}`);
+  return response.result;
+};
+
+/** Paginated GET that concatenates every page of `result`. */
+const cfList = async (path: string): Promise<any[]> => {
+  const all: any[] = [];
+  const separator = path.includes("?") ? "&" : "?";
+  for (let page = 1; ; page++) {
+    const items = await cfOk("GET", `${path}${separator}page=${page}&per_page=100`);
+    all.push(...items);
+    if (items.length < 100) return all;
+  }
+};
+
+const run = (command: string, args: string[], options?: { input?: string; cwd?: string }): void => {
+  const result = spawnSync(command, args, {
+    cwd: options?.cwd ?? APP_DIR,
+    stdio: [options?.input === undefined ? "ignore" : "pipe", "inherit", "inherit"],
+    input: options?.input,
+    env: process.env,
+  });
+  if (result.status !== 0) fail(`${command} ${args.join(" ")} exited with ${result.status}`);
+};
+
+const prNumber = (): number => {
+  const index = process.argv.indexOf("--pr");
+  const value = index === -1 ? Number.NaN : Number(process.argv[index + 1]);
+  if (!Number.isInteger(value) || value < 0) fail("--pr <number> is required");
+  return value;
+};
+
+const workerName = (pr: number): string => `${WORKER_PREFIX}${pr}`;
+
+// --- resources ---------------------------------------------------------------
+
+const findD1 = async (name: string): Promise<string | null> => {
+  const databases = await cfList(`/accounts/${ACCOUNT}/d1/database?name=${name}`);
+  const match = databases.find((database: any) => database.name === name);
+  return match ? match.uuid : null;
+};
+
+const ensureD1 = async (name: string): Promise<string> => {
+  const existing = await findD1(name);
+  if (existing) {
+    process.stderr.write(`reusing D1 ${name} (${existing})\n`);
+    return existing;
+  }
+  const created = await cfOk("POST", `/accounts/${ACCOUNT}/d1/database`, {
+    name,
+  });
+  process.stderr.write(`created D1 ${name} (${created.uuid})\n`);
+  return created.uuid;
+};
+
+const ensureSharedBucket = async (): Promise<void> => {
+  const existing = await cf("GET", `/accounts/${ACCOUNT}/r2/buckets/${SHARED_BLOBS_BUCKET}`);
+  if (existing.ok) return;
+  const created = await cf("POST", `/accounts/${ACCOUNT}/r2/buckets`, {
+    name: SHARED_BLOBS_BUCKET,
+  });
+  if (!created.ok) fail(`creating R2 bucket ${SHARED_BLOBS_BUCKET} failed: ${created.errors}`);
+  process.stderr.write(`created shared R2 bucket ${SHARED_BLOBS_BUCKET}\n`);
+};
+
+const workersSubdomain = async (): Promise<string> => {
+  const result = await cfOk("GET", `/accounts/${ACCOUNT}/workers/subdomain`);
+  return result.subdomain;
+};
+
+const findAccessApp = async (name: string): Promise<any | null> => {
+  const apps = await cfList(`/accounts/${ACCOUNT}/access/apps`);
+  return apps.find((app: any) => app.name === name) ?? null;
+};
+
+/**
+ * One Access application per preview, gating its workers.dev hostname at the
+ * edge. `oauth_configuration` must be present AT CREATION for the app to speak
+ * MCP OAuth (401 + resource_metadata challenge with Access as the authorization
+ * server, dynamic client registration for local MCP clients) — without it,
+ * unauthenticated /mcp requests get a browser login redirect instead.
+ */
+const ensureAccessApp = async (
+  name: string,
+  hostname: string,
+  allowedEmails: readonly string[],
+): Promise<{ id: string; aud: string }> => {
+  const existing = await findAccessApp(name);
+  if (existing) {
+    process.stderr.write(`reusing Access app ${name} (aud ${existing.aud.slice(0, 8)}…)\n`);
+    return { id: existing.id, aud: existing.aud };
+  }
+  const app = await cfOk("POST", `/accounts/${ACCOUNT}/access/apps`, {
+    name,
+    type: "self_hosted",
+    domain: hostname,
+    session_duration: "24h",
+    oauth_configuration: {
+      enabled: true,
+      grant: { session_duration: "24h", access_token_lifetime: "15m" },
+      dynamic_client_registration: {
+        enabled: true,
+        allowed_uris: [],
+        allow_any_on_localhost: true,
+        allow_any_on_loopback: true,
+      },
+    },
+  });
+  await cfOk("POST", `/accounts/${ACCOUNT}/access/apps/${app.id}/policies`, {
+    name: `${name}-allowed-emails`,
+    decision: "allow",
+    include: allowedEmails.map((email) => ({ email: { email } })),
+  });
+  process.stderr.write(`created Access app ${name} for ${hostname}\n`);
+  return { id: app.id, aud: app.aud };
+};
+
+/**
+ * Derive the preview wrangler config from the committed one (same bindings,
+ * preview-specific names) so previews always deploy the real config users get.
+ * Each substitution is asserted so config drift fails loudly here instead of
+ * silently deploying previews against the wrong resources.
+ */
+const writePreviewConfig = (worker: string, databaseName: string, databaseId: string): string => {
+  const basePath = resolve(APP_DIR, "wrangler.jsonc");
+  let text = readFileSync(basePath, "utf8");
+  const substitute = (pattern: RegExp, replacement: string): void => {
+    if (!pattern.test(text))
+      fail(`wrangler.jsonc no longer matches ${pattern} — update preview.ts`);
+    text = text.replace(pattern, replacement);
+  };
+  substitute(/"name":\s*"executor-cloudflare"/, `"name": "${worker}"`);
+  substitute(/"database_name":\s*"[^"]*"/, `"database_name": "${databaseName}"`);
+  substitute(/"database_id":\s*"[^"]*"/, `"database_id": "${databaseId}"`);
+  substitute(/"bucket_name":\s*"[^"]*"/, `"bucket_name": "${SHARED_BLOBS_BUCKET}"`);
+  const outPath = resolve(APP_DIR, "wrangler.preview.jsonc");
+  writeFileSync(outPath, `// Generated by scripts/preview.ts — do not edit.\n${text}`);
+  return outPath;
+};
+
+// --- commands ----------------------------------------------------------------
+
+const deploy = async (): Promise<void> => {
+  const pr = prNumber();
+  const worker = workerName(pr);
+  const teamDomain = process.env.PREVIEW_ACCESS_TEAM_DOMAIN ?? "";
+  const allowedEmails = (process.env.PREVIEW_ACCESS_EMAILS ?? "")
+    .split(",")
+    .map((email) => email.trim())
+    .filter((email) => email.length > 0);
+  if (teamDomain.length === 0) fail("PREVIEW_ACCESS_TEAM_DOMAIN is required");
+  if (allowedEmails.length === 0) fail("PREVIEW_ACCESS_EMAILS is required");
+  const adminEmails = process.env.PREVIEW_ADMIN_EMAILS ?? allowedEmails[0]!;
+
+  const databaseId = await ensureD1(worker);
+  await ensureSharedBucket();
+  const subdomain = await workersSubdomain();
+  const hostname = `${worker}.${subdomain}.workers.dev`;
+  const app = await ensureAccessApp(worker, hostname, allowedEmails);
+  const configPath = writePreviewConfig(worker, worker, databaseId);
+
+  // turbo so workspace dependencies with build steps (@executor-js/vite-plugin)
+  // are built first — a fresh checkout has no dist/ anywhere.
+  if (!process.argv.includes("--skip-build")) {
+    run("bunx", ["turbo", "build", "--filter=@executor-js/host-cloudflare"], {
+      cwd: resolve(APP_DIR, "../.."),
+    });
+  }
+  run("bunx", [
+    "wrangler",
+    "deploy",
+    "--config",
+    configPath,
+    "--var",
+    `ACCESS_TEAM_DOMAIN:${teamDomain}`,
+    "--var",
+    `ACCESS_AUD:${app.aud}`,
+    "--var",
+    `ADMIN_EMAILS:${adminEmails}`,
+  ]);
+
+  // The at-rest encryption key: stable across redeploys of the same PR (a new
+  // key would orphan secrets already stored in the preview's D1), fresh per
+  // preview, set after deploy because the Worker must exist first.
+  const secretList = spawnSync("bunx", ["wrangler", "secret", "list", "--config", configPath], {
+    cwd: APP_DIR,
+    encoding: "utf8",
+    env: process.env,
+  });
+  if (!(secretList.stdout ?? "").includes("EXECUTOR_SECRET_KEY")) {
+    run("bunx", ["wrangler", "secret", "put", "EXECUTOR_SECRET_KEY", "--config", configPath], {
+      input: randomBytes(32).toString("hex"),
+    });
+  }
+
+  const url = `https://${hostname}`;
+  process.stderr.write(`preview live at ${url}\n`);
+  process.stdout.write(`${JSON.stringify({ pr, worker, url, mcpUrl: `${url}/mcp` })}\n`);
+  if (process.env.GITHUB_OUTPUT) {
+    appendFileSync(process.env.GITHUB_OUTPUT, `url=${url}\nworker=${worker}\n`);
+  }
+};
+
+const destroy = async (): Promise<void> => {
+  const pr = prNumber();
+  const worker = workerName(pr);
+
+  // force=true also removes the Worker's Durable Objects + their storage.
+  const script = await cf("DELETE", `/accounts/${ACCOUNT}/workers/scripts/${worker}?force=true`);
+  process.stderr.write(
+    script.ok ? `deleted worker ${worker}\n` : `worker ${worker} already gone\n`,
+  );
+
+  const databaseId = await findD1(worker);
+  if (databaseId) {
+    await cfOk("DELETE", `/accounts/${ACCOUNT}/d1/database/${databaseId}`);
+    process.stderr.write(`deleted D1 ${worker}\n`);
+  }
+
+  const app = await findAccessApp(worker);
+  if (app) {
+    await cfOk("DELETE", `/accounts/${ACCOUNT}/access/apps/${app.id}`);
+    process.stderr.write(`deleted Access app ${worker}\n`);
+  }
+};
+
+const list = async (): Promise<void> => {
+  const scripts = await cfList(`/accounts/${ACCOUNT}/workers/scripts`);
+  const previews = scripts
+    .map((script: any) => String(script.id))
+    .filter((id) => new RegExp(`^${WORKER_PREFIX}\\d+$`).test(id))
+    .map((id) => ({ pr: Number(id.slice(WORKER_PREFIX.length)), name: id }))
+    .sort((a, b) => a.pr - b.pr);
+  process.stdout.write(`${JSON.stringify(previews)}\n`);
+};
+
+// --- main --------------------------------------------------------------------
+
+if (TOKEN.length === 0) fail("CLOUDFLARE_API_TOKEN is required");
+if (ACCOUNT.length === 0) fail("CLOUDFLARE_ACCOUNT_ID is required");
+
+const command = process.argv[2];
+if (command === "deploy") await deploy();
+else if (command === "destroy") await destroy();
+else if (command === "list") await list();
+else fail("usage: preview.ts <deploy|destroy|list> [--pr <number>] [--skip-build]");