Fix centering of graphics with zero-width or zero-height bounds

[gaboolthewild]

Single points and axis-aligned lines are shifted away from the output center in SVG, canvas, and PNG rendering. The transforms replace a zero-sized span with 1 to avoid division by zero, then incorrectly use that fallback span when computing the center.

This change computes the center from the actual bounds while preserving the existing scale fallback. It fixes both the SVG transform and the shared canvas/PNG transform.

Validation:

• Added 18 regression tests covering single points, horizontal and vertical lines, both coordinate systems, both viewbox formats, SVG output, and decoded PNG pixels.
• Confirmed all 18 regressions fail against the original source and pass with the fix.
• Full test suite: 87 passed, 0 failed.
• Type check, package build, and changed-file formatting pass.

AI assistance: implemented and tested with OpenAI Codex.

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Project	Deployment	Actions	Updated
graphics-debug	Ready	Preview	Sep 21, 2026 5:14pm UTC

[gaboolthewild]

Could you confirm whether this fix, if merged, will be picked up by the contribution tracker, and whether any contributor onboarding is needed beyond GitHub Sponsors enrollment? I understand this PR has no fixed bounty and sponsorship depends on the assessed contribution score.