From a3dda8af420ce76ea46ecaa61a3f2bb547005e36 Mon Sep 17 00:00:00 2001
From: OrcaWin <alpha-eng@stably.ai>
Date: Thu, 15 Oct 2026 20:52:31 -0700
Subject: [PATCH] perf(typecheck): check shared tests only in the Node project
 (#29381)

Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>
---
 .github/CONTRIBUTING.md                       |  6 +++
 .../typecheck-project-coverage.test.mjs       | 54 +++++++++++++++++++
 config/tsconfig.tc.cli.json                   |  7 +++
 config/tsconfig.tc.web.json                   |  7 +++
 4 files changed, 74 insertions(+)
 create mode 100644 config/scripts/typecheck-project-coverage.test.mjs

diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
index cf1493d14f7..4050eadb0a3 100644
--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -60,6 +60,12 @@ pnpm test
 pnpm build
 ```
 
+For repeated local typechecks, use `pnpm tc` (or `pnpm tc:node`, `pnpm tc:web`,
+and `pnpm tc:cli`). These keep TypeScript's incremental cache. CI uses
+`pnpm typecheck:ci` with Bun for full checks. Shared tests are checked by the
+Node project; shared production code is checked in all three environments.
+Run `pnpm tc:node` after editing shared tests, or `pnpm tc` to check everything.
+
 Add high-quality tests for behavior changes and bug fixes. Prefer tests that would actually catch a regression, not shallow coverage that only exercises the happy path.
 
 If your change affects UI or interaction behavior, verify it on the platforms it could impact.
diff --git a/config/scripts/typecheck-project-coverage.test.mjs b/config/scripts/typecheck-project-coverage.test.mjs
new file mode 100644
index 00000000000..1d4b7f93c97
--- /dev/null
+++ b/config/scripts/typecheck-project-coverage.test.mjs
@@ -0,0 +1,54 @@
+import { globSync } from 'node:fs'
+import { resolve } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import ts from 'typescript-api'
+import { describe, expect, it } from 'vitest'
+import { TYPECHECK_PROJECTS } from './run-typecheck-projects-in-parallel.mjs'
+
+const root = fileURLToPath(new URL('../..', import.meta.url))
+const isTest = (file) => /\.(?:test|spec)\.(?:[cm]?ts|tsx)$/.test(file)
+const projects = TYPECHECK_PROJECTS.filter((project) => project.config.startsWith('config/')).map(
+  ({ config }) => {
+    const parsed = ts.getParsedCommandLineOfConfigFile(resolve(root, config), undefined, {
+      ...ts.sys,
+      onUnRecoverableConfigFileDiagnostic(diagnostic) {
+        throw new Error(ts.flattenDiagnosticMessageText(diagnostic.messageText, '\n'))
+      }
+    })
+    if (!parsed || parsed.errors.length) {
+      throw new Error(`Cannot parse ${config}`)
+    }
+    return { config, files: new Set(parsed.fileNames.map((file) => resolve(file))) }
+  }
+)
+
+function typedFiles(directory) {
+  return globSync(`${directory}/**/*`, { cwd: root }).filter((file) =>
+    /\.(?:[cm]?ts|tsx)$/.test(file)
+  )
+}
+
+describe('typecheck project coverage', () => {
+  it('checks every shared test exactly once, in the scheduled Node project', () => {
+    const tests = typedFiles('src/shared').filter(isTest)
+    expect(tests.length).toBeGreaterThan(0)
+    const violations = tests.flatMap((file) => {
+      const owners = projects.filter((project) => project.files.has(resolve(root, file)))
+      return owners.length === 1 && owners[0].config === 'config/tsconfig.node.json'
+        ? []
+        : [{ file, owners: owners.map((owner) => owner.config) }]
+    })
+    expect(violations).toEqual([])
+  })
+
+  it('keeps all shared production files in every root typecheck project', () => {
+    const files = typedFiles('src/shared').filter((file) => !isTest(file))
+    expect(files.length).toBeGreaterThan(0)
+    const missing = projects.flatMap((project) =>
+      files
+        .filter((file) => !project.files.has(resolve(root, file)))
+        .map((file) => ({ config: project.config, file }))
+    )
+    expect(missing).toEqual([])
+  })
+})
diff --git a/config/tsconfig.tc.cli.json b/config/tsconfig.tc.cli.json
index c613dd688d9..b587fa5f3e9 100644
--- a/config/tsconfig.tc.cli.json
+++ b/config/tsconfig.tc.cli.json
@@ -1,5 +1,12 @@
 {
   "extends": "./tsconfig.cli.json",
+  // Shared tests are checked by tsconfig.node.json; shared production code stays in every project.
+  "exclude": [
+    "../src/shared/**/*.test.ts",
+    "../src/shared/**/*.test.tsx",
+    "../src/shared/**/*.spec.ts",
+    "../src/shared/**/*.spec.tsx"
+  ],
   "compilerOptions": {
     "module": "Node20",
     "moduleResolution": "node16"
diff --git a/config/tsconfig.tc.web.json b/config/tsconfig.tc.web.json
index a79e96077b6..7bd6a6a5009 100644
--- a/config/tsconfig.tc.web.json
+++ b/config/tsconfig.tc.web.json
@@ -1,5 +1,12 @@
 {
   "extends": "./tsconfig.web.json",
+  // Shared tests are checked by tsconfig.node.json; shared production code stays in every project.
+  "exclude": [
+    "../src/shared/**/*.test.ts",
+    "../src/shared/**/*.test.tsx",
+    "../src/shared/**/*.spec.ts",
+    "../src/shared/**/*.spec.tsx"
+  ],
   "include": [
     "../src/renderer/src/env.d.ts",
     "../src/renderer/src/**/*",