Fix zero-length stroke and dash handling

Preserve intentional zero-length geometry through `dash()` so `stroke()`
can apply its cap style instead of dropping it as a degenerate segment.

Emit cap-only geometry for open and closed zero-length subpaths,
including degenerate line, quadratic, and cubic commands. `Butt` caps
remain empty, while `Round`, `Square`, and mixed caps produce the
corresponding full or half shape.

Keep dash starts in the half-open range `[0, path_length)`, avoiding
spurious output at exact segment and open-path boundaries. Preserve
explicit zero-length dashes as `MoveTo(p)`/`LineTo(p)` pairs, and treat
zero-sum or non-finite dash inputs as undashed without relying on `NaN`
normalization.

Author: waywardmonkeys

CHANGELOG.md

@@ -18,6 +18,11 @@ This release has an [MSRV][] of 1.85.
 ## Added
 - `serde` and `schemars` support for `Axis`. ([#591][] by [@waywardmonkeys][])
 
+## Fixed
+
+- `stroke` now emits cap geometry for zero-length subpaths when round or square caps are selected. ([#597][] by [@waywardmonkeys][])
+- `dash` no longer emits spurious zero-length segments at exact dash boundaries and preserves intentional zero-length dashes. ([#597][] by [@waywardmonkeys][])
+
 ## [0.13.1][] (2026-05-13)
 
 This release has an [MSRV][] of 1.85.
@@ -317,6 +322,7 @@ Note: A changelog was not kept for or before this release
 [#580]: https://github.com/linebender/kurbo/pull/580
 [#585]: https://github.com/linebender/kurbo/pull/585
 [#591]: https://github.com/linebender/kurbo/pull/591
+[#597]: https://github.com/linebender/kurbo/pull/597
 
 [Unreleased]: https://github.com/linebender/kurbo/compare/v0.13.1...HEAD
 [0.13.1]: https://github.com/linebender/kurbo/releases/tag/v0.13.1