feat(core): Add new matchers and improve negation messaging

readme.plan.md

@@ -21,17 +21,35 @@ This document captures the roadmap for evolving the `expect` / `expectAsync` API
 - [ ] Group matchers under `.string`, `.array`, `.number`, etc. for discoverability.
 
 ## Phase 6: Jest-Style Convenience
-- [ ] Add `.toMatchObject()`, `.toMatchSnapshot()`, `expect.any()`, `expect.anything()`, etc.
+- [x] Add `expect.any()` and `expect.anything()` matchers for use in `.toMatchObject()` patterns
+  (Snapshot matchers still TBD)
 
-## Phase 7: Error Messages & Diffs
-- [ ] Integrate a diffing library for clear failure output with colorized diffs.
+The next items to tackle:
 
-## Phase 8: Nested Access Chaining
-- [ ] Provide `.at(path)` or lens-based API for deep property assertions in one go.
+3. Improve negation (`.not`) messaging
+   - Today `.not` simply flips pass/fail, but the failure message isn’t very descriptive. We should capture positive/negative message templates so e.g.
+     > expect(5).not.toBeGreaterThan(3)
+     emits:
+     "Expected 5 not to be greater than 3"
 
-## Phase 9: Pluggable Reporters
-- [ ] Allow consumers to swap output format: JSON, TAP, HTML, etc.
+4. Richer error output for objects/arrays
+   - Integrate a diff library (or extend `fast-deep-equal`) to show unified diffs between expected and actual values
 
-## Phase 10: API Cleanup
-- [ ] Audit and remove legacy aliases and redundant methods.
-- [ ] Finalize deprecations and bump to a major version.
+5. More built-in matchers
+   - toBeNaN(), toBeFinite()
+   - toBeWithinRange(min, max)
+   - toHaveKeys(...), toHaveOwnKeys(...)
+   - toThrowErrorMatching(/regex/), toThrowErrorWithMessage('…')
+   - string/array: toBeEmpty() alias
+   - object: toHaveOwnProperty() shorthand
+
+6. TypeScript-friendliness
+   - Enhance `.d.ts` so editors autocomplete namespace methods (e.g. `expect(x).string.`)
+   - Statically type matcher arguments to catch wrong types at compile time
+
+7. Async assertions and timeouts improvements
+   - Support `.not.resolves`, `.rejects.toThrow()`
+   - Provide clearer timeout errors (e.g. "Expected promise to resolve within …")
+
+8. Plugin/extension API
+   - Formalize `Assertion.extend()` plugin API for shipping matcher bundles