…round-trip

Implements the full table pipeline for issue #1317, designed so the model can
be swapped for the native NSTextBlock/NSTextTable/NSTextTableBlock classes
when they arrive in UIKit with iOS 27:

Model
- Extend TextBlock (DTTextBlock) to the full NSTextBlock API: six dimensions
  with absolute/percentage value types, per-layer/per-edge widths, per-edge
  border colors and vertical alignment. The existing padding/backgroundColor
  convenience API keeps working; NSCoding stays readable by older versions.
- Add TextTable and TextTableBlock mirroring their NS counterparts with
  identical enum raw values (verified against AppKit by parity tests).
- TextTable/TextTableBlock compare by identity like the NS classes. This is
  load-bearing: Foundation uniques value-equal attribute dictionaries across
  attributed strings, so value equality bled shared instances between
  documents (covered by a concurrency stress test).
- TextBlockConverter converts DT <-> NS losslessly on macOS, preserving
  instance identity; it is the swap point for iOS 27.
- Border styles (solid/dashed/dotted/double) as a documented DT extension;
  NSTextBlock only models width and color.

Parsing
- table/tr/td/th/thead/tbody/tfoot/caption/col(group) produce the exact
  structure the macOS HTML importer produces (verified structurally against
  the live system importer): one paragraph run per cell, shared table and
  cell block instances, outermost-first nesting, no placeholder blocks for
  rowspan-covered positions, caption as centered paragraph outside the grid.
- Maps colspan/rowspan, cellpadding/cellspacing, border, bgcolor on
  table/row/cell, valign, col widths, and CSS: per-edge borders with styles,
  1-4 value border lists, thin/medium/thick, padding, width/min/max-width
  (percentages preserved), vertical-align, border-collapse, empty-cells,
  table-layout.

Layout
- CoreTextLayoutFrame lays out tables as grids: automatic column sizing
  (explicit widths win, natural widths propagate recursively out of nested
  tables, leftover width goes to flexible columns), fixed layout, rowspan-
  aware row heights, vertical alignment including true first-baseline
  alignment per the NSTextBlock documentation, justified cell text, and
  recursive nested tables. Flow continues below the table.
- Backgrounds and per-edge borders draw from grid-computed cell frames in
  correct stacking order; dashed/dotted/double styles render.
- border-collapse resolves boundaries to the wider border so collapsed
  tables draw a single-line grid (pixel-verified).
- Block-run grouping switched from isEqual to instance identity, matching
  the system semantics; CoreTextParagraphStyle.textBlocks is now typed.

Writing & SwiftUI
- HTMLWriter emits table/tr/td with colspan/rowspan and inline CSS for
  widths, backgrounds, borders (incl. styles), padding and vertical-align;
  structure and styling round-trip through the parser, nested tables incl.
- DTTextBlocksKey is a typed [TextBlock] AttributedString key; tables keep
  shared-instance identity through AttributedString and back.

Docs, demo and verification
- DocC article documents the empirically determined macOS representation
  (reproducible dump tool in Tools/TableInvestigation) and the DT layer.
- Four demo app pages: Tables, Alignment, Widths, Borders.
- 296 tests in 30 suites on macOS, 288 in 29 on the iOS simulator; render
  previews are written as PNGs on both platforms for visual inspection.
- Fixes a pre-existing test race that mutated the shared default stylesheet.

Closes #1317 except the iOS 27 SDK hookup, which waits on the SDK.

Co-Authored-By: Claude Fable 5 <[email protected]>

The table layout path consumed the entire table range without checking the
frame's maximum Y, so visibleStringRange() reported clipped rows as fitted
and continuation frames skipped them.

Tables now consume only the leading rows that fit within the frame: the
consumed range is cut at the first cell of the first excluded row, the
partial table draws without a bottom edge, and the remaining rows lay out
as a grid in the continuation frame. A table that does not fit at all moves
entirely to the next frame, and a frame that starts with a table taller
than itself still consumes the first row so pagination always progresses
(mirroring how a single oversized line behaves).

Addresses the review feedback on PR #1318.

Co-Authored-By: Claude Fable 5 <[email protected]>

The Swift workflow still only triggered on the v2 branch, a leftover from
the Swift migration that was merged into develop with #1316 — so pushes to
develop and PRs targeting it ran no CI at all.

Co-Authored-By: Claude Fable 5 <[email protected]>

Restate @unchecked Sendable on TextTable and TextTableBlock (required for
subclasses of a Sendable class) and move TextBlock's conformance onto the
class declaration. Check the header font through the NSAttributedString
conversion instead of the typed font subscript, whose NSFont/UIFont value
type has an unavailable Sendable conformance.

Co-Authored-By: Claude Fable 5 <[email protected]>

Add HTML table support with NSTextTable-compatible model, layout and round-trip

CSS float was parsed into DTHTMLElementFloatStyle but never used; floated
images were forced to be their own block as a workaround. Floats are now
laid out for real:

- Floated content is marked with DTFloatStyleAttribute (plus
  DTFloatWidthAttribute for an explicit CSS width) and taken out of the
  normal flow during line building in CoreTextLayoutFrame.
- A floated image becomes a box at the left/right content edge; a floated
  block (div, span, table) becomes a shrink-to-fit or fixed-width column
  laid out via the table cell flow, including its backgrounds and borders.
- Text lines vertically intersecting a float region are narrowed and
  re-typeset until the assumed insets match the line's real extent;
  several floats on one side stack next to each other and move down when
  there is no room, and a float that does not fit a finite frame moves to
  the continuation frame.
- The clear property (left/right/both) makes paragraphs and floats start
  below earlier floated content, via DTClearFloatsAttribute.
- HTMLWriter round-trips floats: floated attachments get a wrapping span
  with the float style, floated block ranges become a div with float and
  width, and clear is emitted on paragraph styles.
- New Floats.html demo snippet and a FloatLayoutTests suite covering
  attribute emission, wrap geometry, side-by-side floats, shrink-to-fit,
  clear, frame height, pagination and writer round-trips.

Co-Authored-By: Claude Fable 5 <[email protected]>

Float lines inflated typesetLines.count past the strict-equality
truncation checks, so numberOfLines (and the lines-fitting retry) never
fired after a leading float. Line limits now count only lines of the
normal flow — floated content is out of the flow, like in CSS — and the
checks tolerate jumps (>= instead of ==). The lines-fitting retry also
captures the flow line count so a rebuild cannot recurse with a zero
limit when only float lines exist.

Co-Authored-By: Claude Fable 5 <[email protected]>

UIKit publishes NSTextBlock/NSTextTable/NSTextTableBlock with the iOS 27 SDK
(Xcode 27, Swift 6.4), so TextBlockConverter now compiles there too: the same
identity-preserving conversion as on macOS, plus attributed-string level
methods that move the DTTextBlocks attribute onto native
NSParagraphStyle.textBlocks (and back), so DTCoreText output can be handed
straight to TextKit. Verified on the iOS 27 simulator: TextKit 1 lays out
and renders the converted tables natively, and the system HTML reader and
writer round-trip them.

The 27 SDKs also change the AppKit text block enums from NSUInteger to
NSInteger raw types; the converter and the AppKit parity tests now bridge
raw values with numericCast so they compile with both Xcode 26 and 27.

Also routes tvOS through the UIKit branch for CSS shadow offsets, fixing
the tvOS build.

Co-Authored-By: Claude Fable 5 <[email protected]>

The macos-latest image only ships simulator runtimes for its default Xcode;
after pinning Xcode 26.0 the test job found no iOS devices at all. Download
the platform when no iPhone simulator is available before testing.

Also clarify in the UIKit parity suite why the raw-value test needs no
availability guard (the text block enums are available since iOS 6 in the
27 SDK; only the converter and per-edge accessors are 27-only).

Co-Authored-By: Claude Fable 5 <[email protected]>

Support float:left/right for images and blocks with text wrapping

Bridge text blocks and tables to the native UIKit classes on iOS 27

The parser only honored the legacy cellspacing attribute; the
border-spacing property was ignored from any source, even though
default.css declared it, and the writer never emitted cell spacing, so
it was lost on every HTML round trip.

- Parse border-spacing (one- and two-value forms) from the cascade,
  with browser precedence: border-collapse:collapse forces zero, CSS
  beats the cellspacing attribute, falling back to the 0.5pt margin
  importer default. Margins are now tracked per axis so asymmetric
  spacing lays out correctly.
- Emit border-spacing on the table tag when the cells' margins differ
  from the default, so cellspacing/border-spacing survives writing.
- Remove the dead border-spacing declaration from default.css: with
  the property now honored, the merged cascade would let it override
  every cellspacing attribute and the Apple-parity 0.5pt default.

Co-Authored-By: Claude Fable 5 <[email protected]>

Support CSS border-spacing on tables

DTCoreText only ever imported the HTMLParser module, which now lives in
its own package (Cocoanetics/XMLKit, extracted from SwiftText with
history). Depending on the HTMLParser product directly drops SwiftText,
swift-markdown and swift-cmark from the graph, and no traits are needed
anymore.

swift-docc-plugin is gone too: Swift Package Index injects the plugin
automatically when building hosted documentation (.spi.yml), Xcode
builds the DocC catalog natively, and CI never generates docs. With it
go SymbolKit and swift-argument-parser.

Resolved dependencies shrink from five packages to one: xmlkit 1.0.1.

Co-Authored-By: Claude Fable 5 <[email protected]>

Depend only on XMLKit: drop SwiftText and the DocC plugin

Point push/pull_request triggers at main. Drop the v2 trigger; that
branch no longer exists on the remote.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>