[mike-doctorina]

Split out of #27 — it has nothing to do with the selection chrome that PR is about, and nothing inside the package calls it.

What

The renderer has no maxLines and is not gaining one. A host that wants a collapsed preview needs to know where the Nth visual text line ends, so it can size a clipped box without cutting a line in half.

final clamp = clampMarkdownToLines(
  markdown: model,
  theme: theme,
  maxWidth: constraints.maxWidth,
  maxLines: 6,
);
// clamp.height        — full content height
// clamp.clampedHeight — ends on a line boundary
// clamp.overflows     — whether the budget left content out

Counting comes from the new MarkdownPainter.textLineBottoms() (@meta.internal):

• runs that share a bottom edge — a table row's cells, a bullet and its first line — count as one line;
• blocks with no text of their own (MD$Spacer, MD$Divider) add height without spending the budget, so a clamp never ends on trailing blank space.

Why it is its own PR

grep -rn "clampMarkdownToLines\|textLineBottoms\|MarkdownLineClamp" lib/ example/lib finds only the definitions. Zero callers in the package, zero in the example — the only thing that ever exercised the line-counting heuristic was its own unit tests, so it deserves its own read rather than riding along in an 8k-line selection PR.

Cost

It is a full layout per call on a throwaway painter. Documented as such; callers must cache and must not call it from build on every frame.

Tests

12 cases in test/line_clamp/line_clamp_test.dart, wired into test/unit_test.dart: budget not exceeded, cut lands on the last allowed line, soft-wrapped paragraph, list items, blank lines and dividers adding height without spending the budget, zero and negative budgets, empty document, table rows, a quote with a nested fence, and a zero measuring width.

flutter test test/unit_test.dart → 990 passed. dart analyze --fatal-infos --fatal-warnings lib/ test/ → clean.

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Credit: the original implementation is @itsezlife's, from #27. It is split out here unchanged in substance; the commit is under my name only because the branch was assembled from that PR — the work is theirs.