Type: threaded paths and frames aligned off the top measure the paragraphs they need

A threaded story measured each type-on-a-path frame, and each area frame
whose lines align to the center, the bottom or justify vertically, with
the whole rest of the story. A story of 1,500 one-line paragraphs through
40 such frames was laid out over about 2.1 million bytes while the frames
were measured.

- Area type without Shrink Text to Fit now takes the paragraph probe for
  every vertical alignment. A reflow pass that places less text is
  undone, so when the final layout stops before the last paragraph break
  measured, every pass placed the same lines as with the whole rest.
- Type on a path takes it when its line starts at the start bracket: no
  Dynamic Text, Optical Margin Alignment or Roman Hanging Punctuation,
  the first paragraph aligned Left, Justify Left or Auto, and vertical
  type or no right-to-left text in the rest of the story. The story is
  scanned for right-to-left text once per distribution.
- Shrink Text to Fit, the other path settings and a share that ends in
  the story's last paragraph are still measured with the whole rest.

The same 40 frames are now measured over 21,035 bytes (aligned to the
center) and 20,583 bytes (paths aligned Left). Each frame's share is
unchanged: the tests compare every slice with the whole-rest result for
both distribution entry points, across alignments, frame shapes, wraps,
path settings, right-to-left text, styles, lists and seeded stories.

docs/target-app-parity.md

@@ -1268,7 +1268,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   Exports to PDF, EPS, SVG, EMF, WMF and the raster formats warn about the area type and type on a path that they draw without the text that doesn't fit, and give their ids, as Print and Print Preview do.
   On a shaped area type frame, Inset Spacing keeps text that far from the frame's edge, holes included, measured from the edge itself rather than along the line; the archived help treats the inset as the space an area type object leaves between its text and the path that bounds it (<https://help.adobe.com/archive/en_US/illustrator/cs5/illustrator_cs5_help.pdf#page=317>, <https://web.archive.org/web/20220911143322/https://helpx.adobe.com/pdf/cs6/illustrator_reference.pdf#page=325>). A rectangular frame keeps its inset from each side as before, and a column's inner edges keep it once. Tests: `layout::region::inset_on_a_shaped_frame_is_measured_from_its_sloped_edge`, `inset_keeps_text_clear_of_a_hole_s_sloped_edges`, `inset_applies_once_at_a_column_s_edge_and_at_the_frame_s_edge`.
   An edit copies a thread's story only when it changes one of the thread's frames: with a story of 50,000 characters threaded through 8 frames with a style change at every word, moving another object took 7.8 ms and now takes 0.013 ms, and a frame of a drag took 7.2 ms and now takes 0.012 ms (release build, `threaded_story_edit_timing`).
-  When a story flows through threaded area type, each frame is measured with the whole paragraphs of the story that it needs and a few more, not with the whole rest of the story, and it keeps the same text as before. A story of 1,500 one-line paragraphs (55,892 bytes) through 40 frames was laid out over 2,126,762 bytes of text while the frames were measured, and is now laid out over 21,035 (`thread::tests::many_frames_measure_about_the_text_they_take`). Type on a path, Shrink Text to Fit, lines aligned other than to the top, and a frame whose share ends in the story's last paragraph are still measured with the whole rest.
+  When a story flows through threaded area type, each frame is measured with the whole paragraphs of the story that it needs and a few more, not with the whole rest of the story, and it keeps the same text as before. A story of 1,500 one-line paragraphs (55,892 bytes) through 40 frames was laid out over 2,126,762 bytes of text while the frames were measured, and is now laid out over 21,035 (`thread::tests::many_frames_measure_about_the_text_they_take`). Area type with its lines aligned to the center, the bottom or justified vertically, and type on a path whose first paragraph is aligned Left, Justify Left or Auto, are measured the same way: the same story through 40 area frames aligned to the center was laid out over 2,126,762 bytes and is now laid out over 21,035, and through 40 paths aligned Left over 2,135,202 bytes and now over 20,583 (same test). Shrink Text to Fit, Dynamic Text, Optical Margin Alignment and Roman Hanging Punctuation on a path, a path aligned another way, horizontal type on a path whose first paragraph is set right to left or with right-to-left text in the rest of the story, and a frame whose share ends in the story's last paragraph are still measured with the whole rest.
   A paragraph that continues from one threaded frame into the next has its first-line indent and bullet or number in the frame where it starts; in the next frame its first line starts where its wrapped lines start. In frames that are no longer threaded, copies of a frame and point type converted from one, the first paragraph has its indent and bullet or number again.
   In threaded text, a paragraph format given to the empty paragraph after a frame's last paragraph break stays after the story flows again, in that frame and in the frames the paragraph continues into, unless the same edit also formats the next frame's first paragraph, whose format then applies (VectorCraft's own rule; `thread::tests::restyled_empty_last_paragraph_wins_over_unedited_next_frame`, `cmd::threads::tests::editing_a_frames_empty_last_paragraph_survives_thread_reflow`).
   Type › Convert To Point Type on a frame of threaded text makes point type of the text that frame holds and takes it out of the thread; the story flows through the other frames without that text, so each character is in the document once.