Porting wander() from Python to TypeScript

The agents drifting behind the home panel run the wander behaviour from my COS30002 coursework (Task 11): each tick, jitter a target point on a circle projected ahead of the agent, steer toward it, clamp the speed. The Python original leaned on the framework for vectors and randomness. The port keeps only the maths.

Two decisions made it testable. First, the behaviour functions are pure — plain agent data in, a force vector out, no canvas, no clock, no globals. Second, the randomness is injected: the engine passes a mulberry32 generator, so the same seed reproduces the same trajectory bit-for-bit. The unit tests pin four properties with SEED=42: the per-tick wander-angle jitter stays within ±jitter, the steering force never exceeds its clamp, speed never exceeds its clamp, and the agent never escapes the toroidal wrap margin.

The embarrassing lesson came from a review pass with mutation testing: the first version of the clamp tests could not fail. From the cruise-speed starting state, the wander target is always close to the heading, so the unclamped force never came near the limit — deleting the clamp entirely left the suite green. The fix was to start an agent well above maxSpeed and assert the clamps bind exactly: the first integration step must land on the speed limit, and the steering force must sit exactly on the force circle. Deleting either clamp now fails the suite.

A property test that cannot fail is worse than no test — it documents a guarantee nobody is checking. Seeded determinism made the difference: the same trajectory every run means a regression is a diff, not a flake.