docs: emphasize build & rules-reading requirements in AGENTS.md (#2720)

AGENTS.md

@@ -4,6 +4,8 @@ Please read `CONTRIBUTING.md` which includes information for human code contribu
 
 ## Rules index
 
+> **IMPORTANT: BEFORE writing any code or making changes, you MUST read the relevant rule files from the table below.** Identify which areas your task touches and read those rule files first. Skipping this step leads to avoidable mistakes and rework.
+
 Detailed rules and learnings are in the `rules/` directory. Read the relevant file when working in that area.
 
 | File                                                                 | Read when...                                                                                     |
@@ -103,6 +105,8 @@ Use unit testing for pure business logic and util functions.
 
 ### E2E testing
 
+> **IMPORTANT: You MUST run `npm run build` before running E2E tests.** E2E tests run against the built application, not the dev server. If you have changed any application code (i.e. anything outside of test files), you MUST re-run `npm run build` before running the tests, otherwise the tests will run against stale code and results will be misleading. Only changes to test code itself (e.g. files in `e2e-tests/`) do not require a rebuild.
+
 See [rules/e2e-testing.md](rules/e2e-testing.md) for full E2E testing guidance, including Playwright tips and fixture setup.
 
 **Debugging E2E test failures with screenshots:** When an E2E test fails and you can't determine the cause from the error message alone, use the `/dyad:debug-with-playwright` skill to add screenshots at key points in the test. Playwright's built-in `screenshot: "on"` does NOT work with Electron — you must use manual `page.screenshot()` calls. The skill walks you through adding debug screenshots, running the test, viewing the captured PNGs, and cleaning up afterward.