S4.8 — Resolution exposed in the bindings

#task #oxmpl #oxmpl/epic #oxmpl/story/size-M

Intent

Only RealVector, SO2 and SO3 expose a resolution setter in either binding, so SE2/SE3/compound users cannot follow the 0.9.0 migration note ("set the fraction to 0.005"). Python exposes no interpolate or segment length at all. Expose resolution fully so users can tune spaces and so user motion validators (S4.7) can work at the space's resolution without re-implementing its maths.

Decisions (grilling Q15)

All six spaces (RealVector, SO2, SO3, SE2, SE3, Compound) in both bindings expose: the fraction setter, longest_valid_segment_length, valid_segment_count(s1, s2), interpolate(s1, s2, t).
JS setLongestValidLineSegmentFraction is renamed setLongestValidSegmentFraction (matches Rust, Python and OMPL).
Setters respect S4.5's freeze rule (raise if the space is already in use).
SE2/SE3/compound fraction semantics: setting the fraction on a composite space sets it on every component (as OMPL's CompoundStateSpace::setLongestValidSegmentFraction); confirm against the Rust API from S4.3 and add a Rust setter if missing.

Current gaps (as of c558556)

Space	Py setter	Py length	Py interpolate	JS setter	JS length	JS interpolate
RealVector	yes	no	no	yes (old name)	yes	yes
SO2	yes	no	no	yes (old name)	yes	yes
SO3	yes	no	no	yes (old name)	yes	yes
SE2	no	no	no	no	yes	yes
SE3	no	no	no	no	yes	yes
Compound	no	no	no	no	yes	yes

Acceptance criteria

Every cell in the table above is "yes" in both bindings, plus valid_segment_count / validSegmentCount everywhere
JS rename done; old name removed (breaking, documented)
Rust: fraction setters exist for SE2/SE3/compound if they don't already
Tests per space per binding (setter changes the count; interpolate endpoints equal inputs)
just test-all green

Notes

Cut candidates if the sprint runs short: interpolate and valid_segment_count (keep the setter — the migration note depends on it). Both can be added later without breaking anyone.

Source

Agreed in the senior-engineer grilling 2026-10-08 (decisions: repo docs/planning/adr/0003-motion-validation.md; glossary: CONTEXT.md). Regeneration spec: oxmpl - sprint-005. Line references are as of origin/main c558556 (2026-10-08), before E3. E3 renames things (rand Rng→RngExt, PyO3 with_gil→attach, edition 2024), so re-grep before trusting a line number.