M5: Shift holds lines level or plumb while drawing (ortho) (#4285)

* M5: Shift holds lines level or plumb while drawing (ortho)

With Shift held, a new line or arrow runs level or plumb from where it
starts, whichever is nearer to the pointer (a CAD drawing's ortho mode),
and each new side of connected lines, a polygon or a cloud is held the
same way from the corner before, rubber band included. Dragging an end
or corner of a drawn one with Shift is held the same way; it turned to
45° steps before. The measuring tools keep their 45° steps.

measure::snap::ortho next to constrain; comment_add takes `ortho` for
line, arrow, polygon, cloud and polyline. Parity comment.draw-ortho.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Ortho: over the first corner the rubber band shows the closing side, Shift or not

From review: a click there closes the polygon or cloud to its first
corner, while the preview with Shift held showed a level or plumb side.
The click and the preview now share one rule (closes_at).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Rebase: Shift is read where main's split put the drawing input, and the ortho helpers are imported there

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Rebase: Shift holds a drawn line, not a freehand stroke (a hunk had landed in the wrong branch)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Ortho: the parity note names the closing side's exception; the test's doc comment is back above its test

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: FredApps <153173854+FredApps@users.noreply.github.com>

parity/acrobat-features.toml

@@ -4095,7 +4095,19 @@ status = "shipped"
 commands = []
 tools = ["comment_edit"]
 evidence = ["crates/annot/src/tests.rs::lines_and_polygons_are_reshaped_by_their_points", "crates/ui-egui/tests/it/comments.rs::line_ends_are_dragged_to_change_length_and_angle", "crates/automation/tests/it/automation.rs::comments_are_reshaped_through_the_tool"]
-notes = "A selected line, arrow, connected lines, polygon or cloud has a handle on each end or corner (instead of the frame); dragging one changes the length and angle (Shift holds it to 45° from the point before), with the new shape drawn while dragging, as one undo step (Edit::ReshapeAnnotation). The drawing tools keep drawing from an end (a new line starts there); the Select tool reshapes. /Rect follows the points with room for the width and arrowheads, and the appearance is drawn anew. Headless: comment_edit `points`; comment_list reports them. Measurements keep the points they measured; locked comments keep their shape. Not yet: adding or removing a corner."
+notes = "A selected line, arrow, connected lines, polygon or cloud has a handle on each end or corner (instead of the frame); dragging one changes the length and angle (Shift holds it level or plumb with the point before, comment.draw-ortho), with the new shape drawn while dragging, as one undo step (Edit::ReshapeAnnotation). The drawing tools keep drawing from an end (a new line starts there); the Select tool reshapes. /Rect follows the points with room for the width and arrowheads, and the appearance is drawn anew. Headless: comment_edit `points`; comment_list reports them. Measurements keep the points they measured; locked comments keep their shape. Not yet: adding or removing a corner."
+
+[[feature]]
+id = "comment.draw-ortho"
+title = "Shift holds lines level or plumb while drawing (ortho)"
+area = "E"
+tier = "P1"
+milestone = "M5"
+status = "shipped"
+commands = []
+tools = ["comment_add"]
+evidence = ["crates/measure/src/tests.rs::ortho_holds_a_vertex_level_or_plumb_with_the_last", "crates/ui-egui/tests/it/comments.rs::shift_holds_new_lines_and_sides_level_or_plumb", "crates/ui-egui/tests/it/comments.rs::the_rubber_band_shows_the_closing_side_with_shift_held", "crates/ui-egui/tests/it/comments.rs::line_ends_are_dragged_to_change_length_and_angle", "crates/automation/tests/it/automation.rs::lines_and_corners_are_held_level_or_plumb_through_the_tool"]
+notes = "With Shift held, a new line or arrow runs level or plumb from where it starts, whichever is nearer to the pointer (a CAD drawing's ortho mode), and each new side of connected lines, a polygon or a cloud from the corner before, the rubber band included. Over the first corner, where a click closes a polygon or cloud, the closing side runs straight to that corner, Shift or not. A dragged end or corner of a drawn one is held the same way (comment.reshape). Acrobat holds lines to 45° steps instead; on drawings and plans the level and plumb lines are the ones wanted. Headless: comment_add `ortho`. Measuring tools keep their 45° steps."
 
 [[feature]]
 id = "comment.move-preview"