What

Implements real CSS float layout. float was parsed into DTHTMLElementFloatStyle but never used — floated images were forced to be their own block as a workaround (the old comment in TextAttachmentHTMLElement said "we don't support float yet"). Now:

• Floated images become a box at the left/right content edge and the paragraph text wraps around them, returning to full width below the float.
• Floated blocks (div, span, even table) become a column — explicit CSS width or shrink-to-fit — laid out via the existing table-cell flow, including their backgrounds, padding and nested tables.
• clear:left/right/both makes paragraphs and floats start below earlier floated content.
• HTML writer round-trip: floated attachments get a wrapping <span style="float:…">, floated block ranges become <div style="float:…;width:…px">, clear is emitted on paragraph styles.

How

• Elements emit DTFloatStyleAttribute (and DTFloatWidthAttribute for an explicit width, DTClearFloatsAttribute for clear) over their output range; the attachment workaround that forced floated images to be blocks is removed so they stay inline.
• CoreTextLayoutFrame._buildLinesWithTypesetter takes marked content out of the flow before the table check (so floated tables become columns), tracks float regions, and narrows the lines that vertically intersect them. Since a line's height is only known after typesetting, each line is re-typeset until the assumed float insets match its real vertical extent.
• Several floats on one side stack next to each other and move down when out of room; a float that does not fit a finite frame moves whole to the continuation frame (pagination); a standalone floated image absorbs its paragraph break so the flow gets no empty line.
• The float region (not the line metrics) drives the wrap, so this works on macOS too where attachments have no CT run delegate; the float line's ascent/descent are set from the attachment so its frame matches the image box on both platforms.

Notes for review

• The native AppKit HTML importer was checked for parity: it carries no float information into attributed strings (a floated img/span is merely promoted to its own paragraph; float/width on a div are dropped, clear ignored). So unlike tables/NSTextTable there was nothing native to mirror, and DT-specific attributes are the only encoding option.
• Degradation: rendering a DT string in a plain NSTextView now shows a floated image inline in its paragraph (previously: own line). The wrap itself only happens in DT's own layout engine.
• Known limits (unchanged scope): floats inside table cells are ignored, and a float marker mid-line starts wrapping on the following line instead of splitting the current line box. Width-unknown frames disable floats.
• Tests: new FloatLayoutTests suite (16 tests: attribute emission, wrap geometry left/right, side-by-side floats, shrink-to-fit, clear, frame height, pagination, writer round-trips) plus a Floats.html demo snippet. Full suite passes: 315 tests on macOS, 307 on the iOS simulator (CI-equivalent invocations).

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