diff --git a/biome.jsonc b/biome.jsonc
index ef1b2bb0..d38b6d60 100644
--- a/biome.jsonc
+++ b/biome.jsonc
@@ -14,7 +14,7 @@
       "*.mjs",
       "scripts/**/*.mjs",
       "src/**/*.{css,ts,tsx}",
-      "tests/**/*.{ts,tsx}",
+      "tests/**/*.{mjs,ts,tsx}",
       "!src/generated"
     ]
   },
diff --git a/eslint.config.mjs b/eslint.config.mjs
index 2ec67e42..100a77b1 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -4,7 +4,7 @@ import tseslint from "typescript-eslint";
 import codexPanelEslintPlugin from "./scripts/lint/eslint-plugin-codex-panel.mjs";
 
 const typeScriptFiles = ["src/**/*.{ts,tsx}", "tests/**/*.{ts,tsx}"];
-const nodeJavaScriptFiles = ["*.mjs", "scripts/**/*.mjs"];
+const nodeJavaScriptFiles = ["*.mjs", "scripts/**/*.mjs", "tests/**/*.mjs"];
 const typeScriptConfigFiles = ["*.config.ts"];
 const lintedTypeScriptFiles = [...typeScriptFiles, ...typeScriptConfigFiles];
 const unsafeAnyTypeScriptRules = {
diff --git a/scripts/check-plan.mjs b/scripts/check-plan.mjs
new file mode 100644
index 00000000..3abcff00
--- /dev/null
+++ b/scripts/check-plan.mjs
@@ -0,0 +1,46 @@
+export const biomeLintCommand = "biome lint --no-errors-on-unmatched --diagnostic-level=warn --error-on-warnings";
+export const biomeCheckCommand = "biome check --no-errors-on-unmatched --diagnostic-level=warn --error-on-warnings";
+
+export function commandPlan({ ciMode, lintOnly }) {
+  if (lintOnly) {
+    return {
+      phases: [{ name: "lint", commands: lintCommands({ ciMode }) }],
+    };
+  }
+
+  return {
+    phases: [
+      { name: "check", commands: checkCommands({ ciMode }) },
+      { name: "build", commands: [{ name: "build", command: "node esbuild.config.mjs" }] },
+    ],
+  };
+}
+
+function checkCommands({ ciMode }) {
+  const suffix = ciMode ? ":ci" : "";
+
+  return [
+    { name: "typecheck", command: `npm run --silent typecheck${suffix}` },
+    { name: "test", command: `npm run --silent test${suffix}` },
+    { name: "lint:biome", command: biomeCheckCommand },
+    ...nonBiomeLintCommands({ ciMode, namePrefix: "lint:" }),
+  ];
+}
+
+function lintCommands({ ciMode, namePrefix = "" }) {
+  return [{ name: `${namePrefix}biome`, command: biomeLintCommand }, ...nonBiomeLintCommands({ ciMode, namePrefix })];
+}
+
+function nonBiomeLintCommands({ ciMode, namePrefix = "" }) {
+  const eslintCacheArgs = ciMode ? "" : " --cache --cache-strategy content --cache-location node_modules/.cache/eslint/.eslintcache";
+
+  return [
+    {
+      name: `${namePrefix}eslint`,
+      command: `eslint src tests scripts "*.config.ts" "*.config.mjs" --max-warnings=0${eslintCacheArgs}`,
+    },
+    { name: `${namePrefix}css`, command: 'stylelint "src/**/*.css" --max-warnings=0' },
+    { name: `${namePrefix}css-usage`, command: "node scripts/lint/check-css-usage.mjs" },
+    { name: `${namePrefix}unused`, command: "knip --no-progress" },
+  ];
+}
diff --git a/scripts/check.mjs b/scripts/check.mjs
index c34dbfc0..910a7d86 100644
--- a/scripts/check.mjs
+++ b/scripts/check.mjs
@@ -1,4 +1,5 @@
 import concurrently from "concurrently";
+import { commandPlan } from "./check-plan.mjs";
 
 const args = process.argv.slice(2);
 const validArgs = new Set(["--ci", "--lint"]);
@@ -16,15 +17,11 @@ const concurrentOptions = {
   padPrefix: true,
   prefix: "name",
 };
-const biomeLintCommand = "biome lint --no-errors-on-unmatched --diagnostic-level=warn --error-on-warnings";
-const biomeCheckCommand = "biome check --no-errors-on-unmatched --diagnostic-level=warn --error-on-warnings";
 
 try {
-  if (lintOnly) {
-    await runConcurrently(lintCommands({ ciMode }));
-  } else {
-    await runConcurrently(checkCommands({ ciMode }));
-    await runConcurrently([{ name: "build", command: "node esbuild.config.mjs" }]);
+  const plan = commandPlan({ ciMode, lintOnly });
+  for (const phase of plan.phases) {
+    await runConcurrently(phase.commands);
   }
 } catch {
   process.exit(1);
@@ -33,32 +30,3 @@ try {
 async function runConcurrently(commands) {
   await concurrently(commands, concurrentOptions).result;
 }
-
-function checkCommands({ ciMode }) {
-  const suffix = ciMode ? ":ci" : "";
-
-  return [
-    { name: "typecheck", command: `npm run --silent typecheck${suffix}` },
-    { name: "test", command: `npm run --silent test${suffix}` },
-    { name: "lint:biome", command: biomeCheckCommand },
-    ...nonBiomeLintCommands({ ciMode, namePrefix: "lint:" }),
-  ];
-}
-
-function lintCommands({ ciMode, namePrefix = "" }) {
-  return [{ name: `${namePrefix}biome`, command: biomeLintCommand }, ...nonBiomeLintCommands({ ciMode, namePrefix })];
-}
-
-function nonBiomeLintCommands({ ciMode, namePrefix = "" }) {
-  const eslintCacheArgs = ciMode ? "" : " --cache --cache-strategy content --cache-location node_modules/.cache/eslint/.eslintcache";
-
-  return [
-    {
-      name: `${namePrefix}eslint`,
-      command: `eslint src tests scripts "*.config.ts" "*.config.mjs" --max-warnings=0${eslintCacheArgs}`,
-    },
-    { name: `${namePrefix}css`, command: 'stylelint "src/**/*.css" --max-warnings=0' },
-    { name: `${namePrefix}css-usage`, command: "node scripts/lint/check-css-usage.mjs" },
-    { name: `${namePrefix}unused`, command: "knip --no-progress" },
-  ];
-}
diff --git a/tests/scripts/check-plan.test.mjs b/tests/scripts/check-plan.test.mjs
new file mode 100644
index 00000000..e760fa7c
--- /dev/null
+++ b/tests/scripts/check-plan.test.mjs
@@ -0,0 +1,43 @@
+import { describe, expect, it } from "vitest";
+import { commandPlan } from "../../scripts/check-plan.mjs";
+
+describe("check command plan", () => {
+  it("runs the local preflight checks before the build", () => {
+    expect(commandPlan({ ciMode: false, lintOnly: false }).phases).toEqual([
+      {
+        name: "check",
+        commands: [
+          { name: "typecheck", command: "npm run --silent typecheck" },
+          { name: "test", command: "npm run --silent test" },
+          { name: "lint:biome", command: "biome check --no-errors-on-unmatched --diagnostic-level=warn --error-on-warnings" },
+          {
+            name: "lint:eslint",
+            command:
+              'eslint src tests scripts "*.config.ts" "*.config.mjs" --max-warnings=0 --cache --cache-strategy content --cache-location node_modules/.cache/eslint/.eslintcache',
+          },
+          { name: "lint:css", command: 'stylelint "src/**/*.css" --max-warnings=0' },
+          { name: "lint:css-usage", command: "node scripts/lint/check-css-usage.mjs" },
+          { name: "lint:unused", command: "knip --no-progress" },
+        ],
+      },
+      {
+        name: "build",
+        commands: [{ name: "build", command: "node esbuild.config.mjs" }],
+      },
+    ]);
+  });
+
+  it("keeps lint-only mode on Biome lint", () => {
+    expect(commandPlan({ ciMode: false, lintOnly: true }).phases[0]?.commands).toContainEqual({
+      name: "biome",
+      command: "biome lint --no-errors-on-unmatched --diagnostic-level=warn --error-on-warnings",
+    });
+  });
+
+  it("omits cache-only local flags in CI mode", () => {
+    expect(commandPlan({ ciMode: true, lintOnly: false }).phases[0]?.commands).toContainEqual({
+      name: "lint:eslint",
+      command: 'eslint src tests scripts "*.config.ts" "*.config.mjs" --max-warnings=0',
+    });
+  });
+});
diff --git a/tests/scripts/development-scripts.test.ts b/tests/scripts/development-scripts.test.ts
index 6153b71f..c3b86729 100644
--- a/tests/scripts/development-scripts.test.ts
+++ b/tests/scripts/development-scripts.test.ts
@@ -116,28 +116,6 @@ describe("development scripts", () => {
     expect(report.failures).toEqual([]);
   });
 
-  it("runs Biome lint with warning-level diagnostics", async () => {
-    const cwd = await tempWorkspace();
-    const binDir = path.join(cwd, "bin");
-    await mkdir(binDir, { recursive: true });
-    await mkdir(path.join(cwd, "scripts", "lint"), { recursive: true });
-    await writeFile(path.join(cwd, "scripts", "lint", "check-css-usage.mjs"), "");
-
-    await writeCaptureBin(path.join(binDir, "biome"), "biome-args.txt");
-    await writeExitZeroBin(path.join(binDir, "eslint"));
-    await writeExitZeroBin(path.join(binDir, "stylelint"));
-    await writeExitZeroBin(path.join(binDir, "knip"));
-
-    const result = runNodeScript("scripts/check.mjs", ["--lint"], cwd, {
-      PATH: `${binDir}${path.delimiter}${process.env["PATH"] ?? ""}`,
-    });
-
-    expect(result.status).toBe(0);
-    await expect(readFile(path.join(cwd, "biome-args.txt"), "utf8")).resolves.toBe(
-      "lint\n--no-errors-on-unmatched\n--diagnostic-level=warn\n--error-on-warnings\n",
-    );
-  });
-
   it("keeps CSS usage checks quiet when every class is used", async () => {
     const cwd = await cssUsageFixture({
       "src/styles/10-component.css": ".codex-panel__used { display: block; }\n",
@@ -272,20 +250,3 @@ async function writeJson(file: string, value: unknown): Promise<void> {
 async function readJson(file: string): Promise<unknown> {
   return JSON.parse(await readFile(file, "utf8"));
 }
-
-async function writeCaptureBin(file: string, outputFile: string): Promise<void> {
-  await writeFile(
-    file,
-    [
-      "#!/usr/bin/env node",
-      "const { appendFileSync } = require('node:fs');",
-      `appendFileSync(${JSON.stringify(outputFile)}, \`\${process.argv.slice(2).join("\\n")}\\n\`);`,
-    ].join("\n"),
-  );
-  await chmod(file, 0o755);
-}
-
-async function writeExitZeroBin(file: string): Promise<void> {
-  await writeFile(file, "#!/usr/bin/env node\n");
-  await chmod(file, 0o755);
-}