Pencil: Live curve fitting in Pencil Tool Options

Pencil Tool Options has a Live curve fitting checkbox, on by default.
With it off, the path shown while a Pencil stroke is drawn joins the
stroke's points with straight segments, and the release fits the curve
at the Fidelity, as it does with the option on. Choosing another tool
while a stroke is drawn also keeps the stroke fitted. The option is
saved with the tool's other options.

path.freehand takes fit (true by default): with fit false, a new path,
a continued path and a redrawn section join the points with straight
segments.

docs/target-app-parity.md

@@ -674,6 +674,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
     In the Swatches panel, Alt-dragging a swatch onto another swatch of its kind (not a tint swatch) replaces that swatch's color, gradient or pattern, and the swatch keeps its name and place.
   - **Tool double-clicks:** double-clicking a tool's button opens its options: Hand fits the artboard in the window, Zoom shows 100 %, Rotate, Scale, Reflect and Shear open their Object › Transform dialogs, the Selection, Direct Selection and Group Selection tools the Move dialog (Enter opens these seven tools' dialogs too; Move opens on the offset of the last drag or Move and with the checkboxes it was last confirmed with, so Enter, Enter repeats a move or a copy at the same spacing, as [an Adobe Community thread](https://community.adobe.com/questions-652/move-tool-771221) describes), Gradient, Eyedropper, Blend and the Liquify tools their panels or options, the Pencil, Paintbrush, Smooth, Blob Brush and Eraser tools their Tool Options (Fidelity, fill, Keep selected, the tolerances, the brush size), and (#812) the Flare tool its Flare Tool Options, the Artboard tool the active artboard's Artboard Options, the graph tools Graph Type for the selected graph, the Symbolism tools the Symbolism Tools Options (Diameter, Intensity, Symbol Set Density) and the Magic Wand tool its panel.
     Double-clicking the Line Segment, Arc, Rectangular Grid or Polar Grid tool opens its Tool Options, as step 3 of the [Rectangular Grid tool](https://helpx.adobe.com/illustrator/using/tool-techniques/rectangular-grid-tool.html) and [Arc tool](https://helpx.adobe.com/illustrator/using/tool-techniques/arc-tool.html) pages and the [Tools](https://helpx.adobe.com/illustrator/using/tools.html) page describe (#2691): the dialog a click with the tool opens, without a place to draw. Line Segment Tool Options has Length, Angle and Fill Line (a new line takes the current fill, `shape.line` `fill`); Arc Segment Tool Options its lengths, Reference Point, Type, Base Along, Slope and Fill Arc; the grids' Tool Options the Reference Point, Default Size, dividers, skews and switches. OK draws nothing: the next drag draws with the options and a click's dialog opens at them, the Length, Angle and Default Size included; Cancel changes nothing. Tests: `toolbar::tests::double_clicking_the_line_arc_and_grid_tools_opens_their_tool_options`, `line_segment_options_and_fill_line`, `grid_default_size_is_an_option_the_drag_leaves_out`, `fill_line_gives_a_new_line_the_current_fill`.
+    Live curve fitting in the Pencil Tool Options is on by default; while it is off, the path shown while a stroke is drawn joins the stroke's points with straight segments, and the release fits the curve, as [Pencil Tool Options](https://web.archive.org/web/20261002104400/https://helpx.adobe.com/illustrator/desktop/draw-shapes-and-paths/draw-shapes/pencil-tool-options.html) describes (`path.freehand` `fit`).
     In the Pencil and Paintbrush Tool Options, Edit selected paths within 0 px turns editing off, so a stroke that starts exactly on an end of a selected open path draws a new path; Close paths when ends are within 0 px turns closing off, so a stroke that ends exactly where it started stays open.
     Keep selected in the Pencil and Paintbrush Tool Options is on by default; while it is off, the path a stroke draws or continues is not selected afterwards and the rest of the selection stays as it was (`path.freehand` `keepSelected`).
     Double-clicking the Shape Builder tool opens Shape Builder Tool Options ([Shape Builder tool options](https://web.archive.org/web/20260105172244/https://helpx.adobe.com/illustrator/using/building-new-shapes-using-shape.html)): with Consider Open Filled Paths as Closed off, a filled open path cuts regions as an unfilled one does; Pick Color From Color Swatches fills merged shapes with the current fill, the Left and Right arrow keys step it through the document's color swatches, and Cursor Swatch Preview shows the current fill and the swatches before and after it above the pointer; Selection Straight Line merges what the line from a drag's first point to its last crosses ([Setting Illustrator's Shape Builder Options](https://web.archive.org/web/20260615204453/https://creativepro.com/setting-illustrators-shape-builder-options/)); with Highlight Fill off, merge mode shades no regions (`shapeBuilder.merge` `openFilledAsClosed` and `pickColorFrom`).