[nicoburns]

LLM Contributions: Written by Devin (Cognition AI) under direction of @nicoburns.

#48 rebased onto the break-spaces branch (#38 / upstream linebender#820, at f76e660), plus one extra commit so the flat scan keeps its speed with linebender#820's soft_line_break rule. Stacked on #38; supersedes #48.

Corpus benchmark (250 KB real text, calculate_content_widths, CPU-pinned, interleaved, n=12 x 3; widths-result identical):

build	median ms	min ms
v0.11.0	0.67–0.68	0.66
main (3fdcdca)	1.14–1.15	1.12
linebender#820 branch (f76e660)	1.35–1.37	1.31
linebender#820 + #48 rebased naively (calling soft_line_break per atom)	1.28–1.32	1.27
this PR	0.81–0.82	0.78

Commit 1 — engine: ShapedClusterFlags has 5 free bits; they now hold the first character's Boundary (2 bits) and Whitespace (3 bits, all 8 variants), set in process_shaped_clusters::flush. Additive API on ShapedCluster: boundary_before(), whitespace(), char_len(). ShapedCluster stays 20 bytes. (Message mentions the layout use; that's commit 2.)

Commit 2 — layout (+ flag round-trip test): for runs without letter/word spacing, calculate_content_widths scans shaped_clusters directly instead of atoms_start(): break/newline checks only on atom-start clusters (i == 0 || is_grapheme_start(), with skip_atom for a Newline atom's continuation clusters), hanging accumulator updated per cluster (if cluster_hangs { += advance } else { = 0 }, equivalent to atom_hanging_advance when there are no gaps), whitespace_hangs(first char, style) checked before char_len() == 1 so letters never load chars_range. Runs with spacing keep the atom loop.

Commit 3 — break-spaces in the flat scan: soft_line_break() reads characters[index-1] and characters[index] (plus their styles) per atom, which is what made the naive rebase lose most of the gain. The flat scan now evaluates the same rule from the cached flags: boundary_before() == Line && !is_break_space_class(whitespace, style) || is_break_space(characters[start-1]), and only does that (and the characters[start-1] load) when some style in the layout uses BreakSpaces (any_break_spaces, computed once per call); otherwise it's just boundary_before() == Line. is_break_space is split into is_break_space_class(whitespace, style) + the existing character-based wrapper.

Changelog: None

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/2564f38c1f574d04ac6e9a57a7284d93
Open in Devin Desktop: https://dioxus.staging.devinenterprise.com/desktop/session/2564f38c1f574d04ac6e9a57a7284d93?variant=devin-insiders

[staging-devin-ai-integration]

I'll fix CI failures and address comments from users with write access that start with 'DevinAI' or '@devin'.

• Disable automatic comment, CI, and merge conflict monitoring