AGENTS.md git:20260914.81e09c6A

Immutable. This exact content is served forever at /api/v1/blob/ac3284e90ebf7976.

- Build before typechecking in a fresh worktree: `npm run build`, then `npm run typecheck`.
- Run package tests with `npm test -w <package>`. Never run vitest from the repo root with `--root`.
- Do not add a test unless a human saw the behaviour flake during manual testing or a user reported the bug. Proactive tests are banned.
- Name what every test guards in a comment above it: the report or the manual observation.
- Prove a change with a manual headless walkthrough and screenshots that show the change, viewed and compared before the PR.
- Keep the test suites to the critical few. They must stay small.
- Keep `docs/agents.md` byte for byte equal to `packages/kite3d/template/AGENTS.md`.
- Do not use em dashes in any file.
- Use Conventional Commits.
- Land every branch on main as one squash commit.