Dimension tool: no construction guides through a first point off the anchors

With Smart Guides on, the Dimension tool's second point snapped onto the
construction guides through the first point (Smart Guides › Construction
Guides), so a click beside a segment straight below a first point that
was not on an anchor stayed on the vertical guide instead of landing on
the segment.

The second point now has no construction guides through a first point
that is not on an anchor. After a first point picked on an anchor, the
construction guides through it still apply. The second point still snaps
to anchors, centers and alignment lines, and with Snap to Perpendicular
or Snap to Tangent on it lands where the line from the first point meets
a segment square or grazes a curve.

Docs: docs/dimensions.md, docs/target-app-parity.md.

docs/dimensions.md

@@ -15,13 +15,17 @@ The **Dimension Tool** is in the Modify section of the toolbar. Its strip offers
   path's length. A press on an anchor picks it when the pointer moves less than 8 pixels
   before the release; a longer drag drags out the dimension of the segment under the pointer. A
   curved segment is measured from end to end. With Smart Guides on, both points also snap into line with other objects'
-  anchors and centres, and the second onto the construction guides through the first; the guides
+  anchors and centres. With Snap to Perpendicular or Snap to Tangent on, the second point also
+  snaps onto a segment where the line from the first meets it square or grazes a curve. When the
+  first point was picked on an anchor, the second also snaps onto the construction guides through
+  it; any other first point has no construction guides through it. The guides
   show while hovering, before each click. VectorCraft's own rules decide where a point lands: an
   anchor within 8 pixels takes it first; a point on a guide stays on the guide where the pointer
-  is, except that it moves onto a segment within the Smart Guides snapping tolerance, or onto the
-  place where a construction guide crosses another object's alignment line within twice that
-  tolerance; a point that no anchor, guide, grid or pixel snapping places lands on the closest
-  point of a segment within 8 pixels.
+  is, except that it moves onto a segment within the Smart Guides snapping tolerance, or, on a
+  construction guide or a Snap to Glyph guide that runs at an angle, onto the place where that
+  guide crosses another object's alignment line within twice that tolerance; a point that no
+  anchor, guide, grid or pixel snapping places lands on the closest point of a segment within 8
+  pixels.
   A linear dimension is aligned, horizontal or vertical, as the
   [linear dimensions help](https://helpx.adobe.com/illustrator/desktop/measure-and-align/plot-and-measure/plot-linear-dimensions-of-objects.html)
   describes: after the second click, clicking again places an aligned dimension, and moving the

docs/target-app-parity.md

@@ -591,7 +591,8 @@ since 2026-10-01.
 **Drawing tools, Star inner radius held with Ctrl/Cmd:** While a star is dragged out, Ctrl/Cmd keeps the inner radius the star showed when the key went down, also when the key is pressed with the pointer still. `a_star_drag_holds_its_inner_radius_with_ctrl_and_straightens_with_alt` and `a_star_drag_holds_the_inner_radius_it_shows_when_ctrl_goes_down` cover it, with Alt's straight shoulders and a drag canceled with Escape.
 **Drawing tools, Dimension tool horizontal and vertical linear dimensions:** A linear dimension between two clicked points or dragged out from a segment is aligned, horizontal or vertical, chosen by where the pointer moves while it is placed, and a click again by the second point gives aligned; `dimension.create` and `dimension.update` take `orientation`, and the dimension stays linked to the anchors it measures, keeps its orientation when it or the art turns, with a line that lay outside the points kept outside them; an unlinked horizontal or vertical dimension that is reflected has its line on the reflected side. `the_pointer_chooses_aligned_horizontal_or_vertical`, `two_points_measure_horizontally_vertically_or_aligned`, `clicking_again_by_the_second_point_places_an_aligned_dimension`, `a_segment_drag_measures_horizontally_vertically_or_aligned`, `points_on_a_vertical_line_measure_aligned`, `horizontal_and_vertical_dimensions_draw_lines_along_their_axis`, `turned_horizontal_dimensions_stay_horizontal`, `a_linked_horizontal_dimension_keeps_its_gap_from_turned_art`, `a_linked_horizontal_dimension_below_or_between_its_points_follows_turned_art`, `a_reflected_horizontal_dimension_keeps_its_line_on_the_reflected_side`, `a_dimension_without_an_orientation_reads_as_aligned`, `dimension_orientation_is_checked` and `a_turned_dimension_keeps_its_line_on_its_side` cover it.
 **Drawing tools, Dimension tool points that are not anchors follow the art:** A clicked point on a segment stays at its place along the segment, also when the segment curves, and a point off the art is linked to anchors (or, when the anchors lie on one line, anchors and handles) of the path, so both ends of the dimension follow when the art is moved, scaled, turned or reflected, also when the point was placed by a Smart Guide and when the dimension is saved and opened again; a linked linear dimension of reflected art (other than art on one line) has its line on the reflected side; deleting the art, changing its anchor count or whether it is closed, turning an angle's arm into a curve, or making a measured circle or arc no longer circular leaves the dimension where it was, no longer linked, instead of removing it. `a_dimension_to_a_point_on_a_segment_follows_the_art_at_both_ends`, `a_dimension_to_a_point_off_the_art_moves_with_the_art`, `a_dimension_whose_art_changes_its_anchors_stays_where_it_was`, `a_dimension_whose_art_is_opened_stays_where_it_was`, `angle_and_arc_dimensions_whose_art_no_longer_fits_stay_where_they_were`, `a_dimension_that_cannot_be_drawn_again_keeps_its_art`, `a_linked_dimension_of_reflected_art_has_its_line_on_the_reflected_side`, `a_dimension_to_a_point_off_a_line_follows_the_line`, `a_point_off_an_arch_is_reflected_with_the_arch`, `a_point_beside_an_almost_straight_curve_follows_it`, `a_point_off_a_loop_with_its_anchors_in_one_place_follows_it`, `a_point_beside_a_reflected_line_moves_as_a_half_turn_would`, `a_point_on_a_segment_stays_on_it_when_the_segment_curves`, `a_linked_dimension_of_a_reflected_curve_has_its_line_on_the_reflected_side`, `a_dimension_of_art_reflected_across_its_points_changes_sides`, `a_dimension_between_paths_reflected_each_in_its_own_way_keeps_its_offset`, `free_points_survive_a_native_file`, `dimension_free_points_are_checked`, `points_off_anchors_are_held_against_the_path` and `a_point_smart_guides_place_is_held_against_the_path` cover it.
-**Drawing tools, Dimension tool points on a Smart Guide stay on the guide:** By VectorCraft's own rule, a clicked point that lies on a Smart Guide already, such as a point straight below the first one on the vertical construction guide through it, or one in line with an object's center, stays where the pointer is when no anchor is within 8 pixels and no segment is within the Smart Guides snapping tolerance, instead of moving onto a segment farther than that tolerance and within 8 pixels; with Snap to Grid or Snap to Pixel on, a point stays on the grid or the whole pixel those options give. `a_point_on_a_guide_stays_on_the_guide` covers it.
+**Drawing tools, Dimension tool points on a Smart Guide stay on the guide:** By VectorCraft's own rule, a clicked point that lies on a Smart Guide already, such as one in line with an object's center, stays where the pointer is when no anchor is within 8 pixels and no segment is within the Smart Guides snapping tolerance, instead of moving onto a segment farther than that tolerance and within 8 pixels; with Snap to Grid or Snap to Pixel on, a point stays on the grid or the whole pixel those options give. `a_point_on_a_guide_stays_on_the_guide` covers it.
+**Drawing tools, Dimension tool second point without construction guides through a first point off the anchors:** By VectorCraft's own rule, with Smart Guides on, the second Linear point does not snap to the construction guides through a first point that is not on an anchor, so a click beside a segment straight below such a first point lands on the segment; after a first point picked on an anchor, the construction guides through it still apply. The second point still snaps to anchors, centers and alignment lines, and with Snap to Perpendicular or Snap to Tangent on, it lands where the line from the first point meets a segment square or grazes a curve. `a_point_on_a_guide_stays_on_the_guide`, `the_second_point_after_an_anchor_lands_on_construction_guides`, `the_second_point_lands_square_to_a_segment_or_grazing_a_curve` and `linear_picks_show_and_snap_to_smart_guides` cover it.
 **Drawing tools, Dimension tool dimensions selected with their art keep their lines and label:** Object › Expand, Object › Expand Appearance and Object › Path › Outline Stroke leave a dimension selected with art it measures, directly or in selected groups without fills, strokes or effects of their own, as it is and change only the other art; when the new art no longer fits its link, the dimension stays where it was, no longer linked, and undo links it again. `expand_leaves_a_dimension_selected_with_its_art_as_it_is`, `expand_appearance_leaves_a_dimension_selected_with_its_art_as_it_is`, `outline_stroke_leaves_a_dimension_selected_with_its_art_as_it_is`, `a_dimension_selected_with_art_that_has_nothing_to_expand_changes_nothing`, `a_group_effect_expanded_reaches_the_dimension_it_holds`, `expand_keeps_a_dimension_in_its_asset_and_its_variable_binding`, `a_dimension_keeps_no_link_to_the_art_expand_replaced`, `a_dimension_outlasts_the_art_outline_stroke_or_expand_appearance_replaced`, `a_dimension_outlasts_the_stroke_expand_outlined` and `expand_appearance_in_safe_mode_leaves_a_dimension_selected_with_its_art` cover it.
 **Live trace result bounds and selection highlights exclude the retained bitmap except in source-image views:** `live_trace_result_bounds_exclude_the_retained_bitmap_at_any_angle` checks every TraceView, geometric and visual bounds and rotated result bounds. `live_trace_selection_highlight_excludes_the_retained_source_rectangle` checks result highlights and the existing ordinary-group policy. Shared editing-child traversal also preserves Shaper handling.
 **Artboard Options shares existing presets and orientation controls and can fit artwork without moving it; artwork fitting includes all drawn document art across artboards and off-board; artwork bounds are cached by active document and revision, and selection uses the shared bounds cache across artboards:** Shared existing preset definitions are reused; no external preset assets are added. Presets preserve each selected artboard's orientation, and orientation choices apply even when the active board already matches. Fit operations draft bounds until OK, affect only the active artboard and leave artwork in place. Regression coverage checks draft/Cancel, selected-set application, active-only fitting and Undo.