M7: edit grouped Thai text while preserving source formatting

Add:
- Prepare supported Form placements as original page operators through the
  existing-text UI and text_prepare, with shared-form isolation and undo/redo.
- Repair narrowly identified Thai exporter maps on copied page fonts, recording
  repairs without changing the embedded source glyph programs.

Change:
- Reuse legacy Thai Regular/Bold glyph codes and same-face punctuation subsets;
  retain point size, spacing, horizontal scale, rise, colour and paint settings.
- Keep cross-family Thai replacement explicit and write matching bundled Thai
  subsets through the existing bounded outline path rather than static embedding.
- Keep replacement-only menu choices out of the source-font preview atlas so
  opening an ordinary paragraph does not wait an extra frame for unused fonts.
- Refuse unsafe compositing, tagged or malformed groups, and missing contextual
  glyphs without losing the user's document or changing other placements.

Chores:
- Document the editing limits and headless workflow; keep text-edit parity partial.

Builds on dekkeng's Thai fallback work in #2811 (fba0a29a) and mtlcl410's Form
Ungroup implementation in #3067 (6eafca9c), adapted to the current module layout.
The Ungroup menu and older UI font-priority changes are not included.

Refs #3185, #2964 and #2142. Synthetic regressions cover source-font preservation,
shared forms, unsafe refusals, layout, undo/redo, rendering and save/reopen.

Validation: library suites 1,675 passed; automation integration 331 passed;
document-font integration 2 passed; editor flows 248 passed. Existing ignored
tests remain. Formatting, scoped strict Clippy, layers, assets, parity and wasm
checks passed. The unchanged opacity regression failed before the choice-only
atlas correction and passed afterwards.

parity/acrobat-features.toml

@@ -1894,9 +1894,9 @@ tier = "P0"
 milestone = "M7"
 status = "partial"
 commands = ["edit.edit_text"]
-tools = ["text_lines", "text_paragraphs", "text_edit", "text_edit_layout", "text_font_files", "text_font_import", "text_fonts"]
-evidence = ["crates/edit/src/tests.rs::paragraphs_are_found_and_rewrapped", "crates/edit/src/tests.rs::text_lines_are_found_and_replaced_in_place", "crates/ui-egui/tests/it/editing.rs::editing_existing_text_in_place", "crates/automation/tests/it/automation.rs::editing_existing_text_through_tools", "crates/edit/src/tests.rs::a_line_whose_operator_starts_the_next_stream_can_be_edited", "crates/automation/tests/it/automation.rs::a_line_split_across_content_streams_is_listed_and_edited", "crates/ui-egui/tests/it/editing.rs::selected_text_formatting_keeps_the_rest_of_the_paragraph_and_reopens", "crates/edit/src/tests.rs::marked_paragraph_boundaries_and_cross_stream_transforms_survive_rewrite", "crates/automation/tests/it/automation.rs::explicit_font_and_disjoint_ranges_save_reopen_through_tools", "crates/edit/src/tests.rs::disjoint_style_ranges_preserve_unselected_runs_and_validate_utf8_atomically", "crates/engine/tests/it/document_fonts.rs::opentype_cff_document_font_preserves_program_codes_and_rendering_after_reopen", "crates/ui-egui/tests/it/editing.rs::cropped_images_do_not_intercept_text_and_stay_inside_each_page", "crates/automation/tests/it/automation.rs::clipped_image_bounds_and_text_edit_save_reopen_through_tools", "crates/edit/src/tests.rs::mixed_styles_and_matrix_sizes_form_visual_regions_without_merging_columns", "crates/edit/src/tests.rs::rich_region_edits_preserve_styles_positions_and_delete_all_runs_after_reopen", "crates/ui-egui/tests/it/editing.rs::one_editor_contains_mixed_styles_and_visual_rows", "crates/ui-egui/tests/it/editing.rs::inline_editor_preserves_source_font_and_previews_live_bounds", "crates/fonts/src/pdf/tests.rs::mac_subset_cmap_uses_pdf_unicode_without_changing_source_program", "crates/automation/tests/it/automation.rs::mixed_visual_region_edit_preview_save_reopen_and_undo_through_tools", "crates/ui-egui/tests/it/ui.rs::the_edit_tab_turns_on_edit_text_and_images", "crates/ui-egui/tests/it/editing.rs::the_caret_on_a_small_row_is_as_tall_as_that_row", "crates/edit/src/tests.rs::uzbek_and_kazakh_cyrillic_use_the_bundled_latin_face", "crates/automation/tests/it/automation.rs::editing_uzbek_and_kazakh_cyrillic_through_tools", "crates/edit/src/tests.rs::styled_paragraph_batches_cyrillic_without_changing_source_fonts", "crates/edit/src/tests.rs::styled_paragraph_over_240_fallback_glyphs_splits_and_refuses_atomically", "crates/edit/src/tests.rs::styled_fallback_batches_keep_face_choices_and_range_styles", "crates/edit/src/tests.rs::styled_fallback_shards_keep_text_advances_and_alignment", "crates/edit/src/tests.rs::styled_fallback_budget_is_enforced_before_objects_are_written", "crates/edit/src/tests.rs::styled_fallback_same_base_font_and_character_keep_both_weights", "crates/automation/tests/it/automation.rs::styled_cyrillic_fallback_is_batched_through_tools_and_reopen", "crates/ui-egui/tests/it/editing.rs::escape_in_an_open_paragraph_selects_its_box_for_delete"]
-notes = "The Edit tab turns Edit text & images on at once, as in Acrobat (leaving the tab puts the tool down and applies an edit in progress); Esc in an open paragraph leaves its text and selects its box, so Delete removes it (the unapplied draft is discarded); click a paragraph box and retype it in place (font reused or Helvetica substituted, colour and spacing kept, rewrapped); a page's /Contents pieces are parsed joined, so a line whose operands and operator sit in different pieces is listed and edited (lines and paragraphs still don't join across pieces; Edit image still parses each piece alone); drag a box to move it or its right-edge handle to rewrap it (edit.text-move-resize); per-character formatting changes are next Since #1116: mixed-style visual regions retain source rows, subset encodings, colour and baseline anchors in one textless-background editor. Explicit paragraph/heading scopes constrain grouping; compatible graphics planes permit cross-stream regions. Full matching document fonts complete absent subset glyphs; installed/file selection, TrueType/OpenType-CFF embedding and disjoint UTF-8 range styles have save/reopen coverage. Single-face OpenType shaping/bidi retains logical text through ToUnicode/ActualText. Replacement text the paragraph's font can't show takes the craft-fonts Japanese faces when they draw all of it (Uzbek қ, Kazakh ә are in none of them), else the bundled Inter face, so those letters write in every build (#2593). Legacy non-SFNT preview, mixed-font/style contextual runs, full structure-tree preservation and author intent in untagged PDFs remain limited; Styled-path outline fallback batches by actual face with 240 glyphs per font and preserves source styles; adjacent equal-font/style characters form runs. At most 15360 distinct fallback glyphs per styled paragraph; missing glyphs are refused before fallback objects are written. Glyph coverage, mixed contextual shaping, single-style fallback and stale-font cleanup are unchanged; see docs/editing-existing-text.md"
+tools = ["text_prepare", "text_lines", "text_paragraphs", "text_edit", "text_edit_layout", "text_font_files", "text_font_import", "text_fonts"]
+evidence = ["crates/edit/src/tests.rs::editing_legacy_thai_keeps_the_embedded_face_weight_size_spacing_and_paint_after_reopen", "crates/fonts/src/pdf/tests.rs::composite_subset_without_cmap_uses_pdf_glyph_ids_in_editor_and_shaper_without_replacing_the_program", "crates/automation/tests/it/automation.rs::grouped_existing_thai_body_edits_saves_reopens_and_undo_restores_original_glyphs", "crates/edit/src/tests.rs::grouped_text_preparation_keeps_unsafe_compositing_paths_and_malformed_forms_intact", "crates/automation/tests/it/automation.rs::explicit_bundled_thai_font_choice_layout_edit_undo_and_reopen", "crates/edit/src/tests.rs::existing_thai_subset_uses_shaped_matching_face_without_embedding_variable_font", "crates/edit/src/tests.rs::paragraphs_are_found_and_rewrapped", "crates/edit/src/tests.rs::text_lines_are_found_and_replaced_in_place", "crates/ui-egui/tests/it/editing.rs::editing_existing_text_in_place", "crates/automation/tests/it/automation.rs::editing_existing_text_through_tools", "crates/edit/src/tests.rs::a_line_whose_operator_starts_the_next_stream_can_be_edited", "crates/automation/tests/it/automation.rs::a_line_split_across_content_streams_is_listed_and_edited", "crates/ui-egui/tests/it/editing.rs::selected_text_formatting_keeps_the_rest_of_the_paragraph_and_reopens", "crates/edit/src/tests.rs::marked_paragraph_boundaries_and_cross_stream_transforms_survive_rewrite", "crates/automation/tests/it/automation.rs::explicit_font_and_disjoint_ranges_save_reopen_through_tools", "crates/edit/src/tests.rs::disjoint_style_ranges_preserve_unselected_runs_and_validate_utf8_atomically", "crates/engine/tests/it/document_fonts.rs::opentype_cff_document_font_preserves_program_codes_and_rendering_after_reopen", "crates/ui-egui/tests/it/editing.rs::cropped_images_do_not_intercept_text_and_stay_inside_each_page", "crates/automation/tests/it/automation.rs::clipped_image_bounds_and_text_edit_save_reopen_through_tools", "crates/edit/src/tests.rs::mixed_styles_and_matrix_sizes_form_visual_regions_without_merging_columns", "crates/edit/src/tests.rs::rich_region_edits_preserve_styles_positions_and_delete_all_runs_after_reopen", "crates/ui-egui/tests/it/editing.rs::one_editor_contains_mixed_styles_and_visual_rows", "crates/ui-egui/tests/it/editing.rs::inline_editor_preserves_source_font_and_previews_live_bounds", "crates/fonts/src/pdf/tests.rs::mac_subset_cmap_uses_pdf_unicode_without_changing_source_program", "crates/automation/tests/it/automation.rs::mixed_visual_region_edit_preview_save_reopen_and_undo_through_tools", "crates/ui-egui/tests/it/ui.rs::the_edit_tab_turns_on_edit_text_and_images", "crates/ui-egui/tests/it/editing.rs::the_caret_on_a_small_row_is_as_tall_as_that_row", "crates/edit/src/tests.rs::uzbek_and_kazakh_cyrillic_use_the_bundled_latin_face", "crates/automation/tests/it/automation.rs::editing_uzbek_and_kazakh_cyrillic_through_tools", "crates/edit/src/tests.rs::styled_paragraph_batches_cyrillic_without_changing_source_fonts", "crates/edit/src/tests.rs::styled_paragraph_over_240_fallback_glyphs_splits_and_refuses_atomically", "crates/edit/src/tests.rs::styled_fallback_batches_keep_face_choices_and_range_styles", "crates/edit/src/tests.rs::styled_fallback_shards_keep_text_advances_and_alignment", "crates/edit/src/tests.rs::styled_fallback_budget_is_enforced_before_objects_are_written", "crates/edit/src/tests.rs::styled_fallback_same_base_font_and_character_keep_both_weights", "crates/automation/tests/it/automation.rs::styled_cyrillic_fallback_is_batched_through_tools_and_reopen", "crates/ui-egui/tests/it/editing.rs::escape_in_an_open_paragraph_selects_its_box_for_delete"]
+notes = "Supported grouped Forms are prepared on entering Edit text, or via text_prepare, so their existing source glyphs can be edited directly. Unsafe groups remain intact. Narrow legacy THSarabunPSK character-map recovery is recorded. Legacy Thai source editing reuses original font programs, positional glyphs and same-face subsets, preserving Regular/Bold, point size, spacing and paint. A different Thai family requires explicit selection; the Noto replacement is Regular only; mixed contextual style runs remain limited. The Edit tab turns Edit text & images on at once, as in Acrobat (leaving the tab puts the tool down and applies an edit in progress); Esc in an open paragraph leaves its text and selects its box, so Delete removes it (the unapplied draft is discarded); click a paragraph box and retype it in place (font reused or Helvetica substituted, colour and spacing kept, rewrapped); a page's /Contents pieces are parsed joined, so a line whose operands and operator sit in different pieces is listed and edited (lines and paragraphs still don't join across pieces; Edit image still parses each piece alone); drag a box to move it or its right-edge handle to rewrap it (edit.text-move-resize); per-character formatting changes are next Since #1116: mixed-style visual regions retain source rows, subset encodings, colour and baseline anchors in one textless-background editor. Explicit paragraph/heading scopes constrain grouping; compatible graphics planes permit cross-stream regions. Full matching document fonts complete absent subset glyphs; installed/file selection, TrueType/OpenType-CFF embedding and disjoint UTF-8 range styles have save/reopen coverage. Single-face OpenType shaping/bidi retains logical text through ToUnicode/ActualText. Replacement text the paragraph's font can't show takes the craft-fonts Japanese faces when they draw all of it (Uzbek қ, Kazakh ә are in none of them), else the bundled Inter face, so those letters write in every build (#2593). Legacy non-SFNT preview, mixed-font/style contextual runs, full structure-tree preservation and author intent in untagged PDFs remain limited; Styled-path outline fallback batches by actual face with 240 glyphs per font and preserves source styles; adjacent equal-font/style characters form runs. At most 15360 distinct fallback glyphs per styled paragraph; missing glyphs are refused before fallback objects are written. Glyph coverage, mixed contextual shaping, single-style fallback and stale-font cleanup are unchanged; see docs/editing-existing-text.md"
 
 [[feature]]
 id = "edit.text-reflow"