[HugoFara]

Summary

Two release blockers found while testing the 1.2.0 tree against released consumers. Neither is in 1.1.1's public behaviour; both would have shipped.

Optimizers refused linkages the numba solver cannot represent

Since 6fd257a, linkage_to_solver_data() raises NotImplementedError for a dyad it cannot type, instead of mistyping it into NaN. That is right for the solver — but Ensemble.__init__ compiled the solver template eagerly, and an Ensemble is what every optimizer returns. So on this tree:

particle_swarm_optimization(fitness, linkage_with_a_PPDyad, ...)
# NotImplementedError: The numba solver cannot represent PPDyad ...

for any linkage holding a PPDyad, a cam follower, or leggedsnake's Walker (a duck-typed container whose parts are mechanism joints). On 1.1.1 all of those optimize. Released leggedsnake 0.6.0 against this tree: 5 failures (multi_objective_optimization, chain_optimizers, NSGA walking optimization), all this.

The template is now compiled on first use — Ensemble.template, which simulate(), simulate_member() and topology_key go through. n_joints comes from the positions array; from_agents() / from_pareto_front() count the linkage's parts. An Ensemble of an unsupported linkage holds its members and scores exactly as before, and only batch simulation raises, with the same message. Slices share the compiled template.

pip install pylinkage failed on Python 3.10

mechanism.builder imports Self from typing_extensions below 3.11; the package never declared it. A bare install on 3.10 could not import pylinkage at all. Present in 1.1.1 too. Now declared with a python_version < '3.11' marker.

Verification

• pylinkage: 2554 passed under -W error::DeprecationWarning; ruff, mypy clean. Two regression tests added.
• Released leggedsnake 0.6.0 (PyPI) against the wheel from this branch: 627 passed (was 5 failed), no DeprecationWarning from pylinkage.
• leggedsnake Add a GUI #9 against this tree: 627 passed.
• Wheel installed with no extras on a fresh Python 3.10 venv: imports; no optional dependency loaded at import.