CODAP-1526: draw residual points with the category's shape

[kswenson]

Draws residual-plot points with the category's shape instead of always a circle. Seventh in the LEADS Point Shapes stack, on top of #2698.

Fixes CODAP-1526.

Why this exists separately

The residual plot draws its own SVG rather than going through a point renderer, so it is a fourth surface that draws a point — after the canvas renderer (#2696), PIXI (#2697) and the legend key (#2698). It stayed circles whatever the plot above it was drawn with. This is the last one.

The scope was wider than the code claimed

A comment in use-residual-plot.ts said residualPlotIsApplicable excludes legends, so the per-case legend lookup was dead. That is not what it does: it turns the plot off for a categorical legend only when the line is an LSRL. With a movable line or a plotted function a categorical legend is allowed, so the legend path is live — and per-category shapes genuinely reach these points, rather than only the display's own shape. The comment is corrected.

Rendering

A point is a <path> positioned with translate(cx, cy). The radius moves to a data-r attribute, because an outline has no radius to read back the way a circle does, and the existing fade-in machinery probes it.

The grow animation regenerates the outline rather than scaling the point. A scale() transform takes the stroke with it, and the stroke is what marks a point as selected — so a selected point would have faded in with an outline that thickened as it grew. Regenerating via attrTween leaves the whole existing fade-in intact: the named "radius" transition, the active() guard, and the deliberate choice not to redirect a transition already past its starting phase.

The shape comes from the same getLegendShapeForCase lookup the main plot uses, so the two plots agree by construction.

Testing

Seven Cypress assertions counted circle elements and now count paths. The marquee is untouched — it indexes positions it computes itself rather than querying elements.

No unit tests are added. use-residual-plot.ts has none and this change does not create a testable seam: it is d3 rendering inside a hook with layout and context dependencies, and the pure functions it leans on (pointShapePathData, residualPointStyle) are already covered. Verified manually instead — including a point fading in and a selected point fading in, which is the case that distinguishes this approach from scaling.

🤖 Generated with Claude Code

[kswenson]

Reviewing this stack — seven PRs, each based on the one below it, merging bottom-up into leads-point-shapes:

PR	Story	What it is
#2691	CODAP-1506 (part 1)	Format palette restructure — structural, no shape behavior
#2692	CODAP-1505	Per-category shape storage — model only
#2693	CODAP-1506 (part 2)	The shape controls — UI
#2696	CODAP-1504	Canvas rendering and hit testing
#2697	CODAP-1509	PIXI/WebGL rendering and hit testing
#2698	CODAP-1507	Legend keys
#2699	CODAP-1526	Residual plot — this one

CODAP-1506 is split across #2691 and #2693, so approving #2691 does not complete that story — it should not leave code review until #2693 is approved too. The other five map one-to-one.

Nothing here is superseded — this is the top of the stack, and the last of the four surfaces that draw a point.

Worth your attention:

• The fade-in. A new residual point grows from nothing, and this regenerates its outline at each step rather than scaling it — because a scale would take the stroke with it, and the stroke is how a selected point is marked. That is the part most worth a skeptical look, and the one thing here with no unit coverage.
• The corrected comment. The file claimed residual plots never have a legend, which is why the per-case lookup looked dead. It is only excluded for a categorical legend with an LSRL, so a movable line or plotted function has one and per-category shapes do reach these points.
• point-shapes.ts is unchanged from CODAP-1507: draw legend keys as the category's point shape #2698. Anything about the geometry belongs there.

This completes the set: canvas (#2696), PIXI (#2697), legend keys (#2698), residual plot (#2699). Nothing else in the codebase draws a per-case mark.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.93%. Comparing base (e6ae88f) to head (c66c838).

Files with missing lines	Patch %	Lines
...ents/graph/plots/scatter-plot/use-residual-plot.ts	83.33%	3 Missing ⚠️

Additional details and impacted files

@@                       Coverage Diff                        @@
##           CODAP-1507-legend-key-shapes    #2699      +/-   ##
================================================================
- Coverage                         87.94%   87.93%   -0.02%     
================================================================
  Files                               821      821              
  Lines                             47566    47567       +1     
  Branches                          12142    12143       +1     
================================================================
- Hits                              41834    41826       -8     
- Misses                             5716     5725       +9     
  Partials                             16       16              

Flag	Coverage Δ
cypress	69.59% <81.25%> (-0.03%)	⬇️
jest	63.25% <11.11%> (+<0.01%)	⬆️

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[cypress]

codap-v3    Run #12248

Run Properties:   Passed #12248  •  c66c838539: null

Project	codap-v3
Branch Review	CODAP-1526-residual-plot-shapes
Run status	Passed #12248
Run duration	09m 04s
Commit	c66c838539: null
Committer	null
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Test results
Failures	0
Flaky	2
Pending	82
Skipped	0
Passing	384
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[Copilot]

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