The editor lands where the preview does, and the outline follows from the same line

[PathGao]

What this is

Follow-up to #748, which I pushed to that branch after it had been merged, so it never landed. Two things found testing the split-view jump on a build (ref #744).

Mechanism

Where a click lands. The preview puts the clicked heading just under its top edge; the editor centred it. With scroll sync off the two panes showed different places (with it on, the editor's scroll then dragged the preview into agreement, which is why it looked fine there). The editor now reveals the heading near its top too (revealLineNearTop, a gap of five lines or 20% of the viewport). The context menu's Edit keeps centring: revealSourceRange takes a placement, and only the outline asks for top.

Following the editor. The outline was one entry behind whenever a heading was the first line on screen: it was handed Monaco's top line, the one the viewport cuts in half. It now gets the line the tab records as its reading position, through tabAnchorForEditorTopLine — the one crossing from a Monaco top line into the outline's numbering, the same one editorReadingPosition uses. The preview side already fed the outline from its anchor line; now both panes do.

Scope

The second half of #744, "scrolling the editor does not move the outline highlight", was checked on a build and is not broken: the highlight follows the editor's scroll with sync off and on. It follows the scroll position, not the caret. Not changed.

At the exact boundary the two panes can disagree by one entry (the preview's anchor is 60px down, the editor's two lines down); whichever scrolled last wins. Inherent to two anchors, unchanged.

The source assertions in jumpToSelectedFragment.test.ts and tocFollowsEditor.test.ts are updated to the new contract; the latter's conversion fixture now pins the anchor-line case (top line one short of a heading → the heading's entry), which fails against the old toRendererLine(position.line).

Verification

npm run check       830 files, 0 errors
npm test            1028 pass
npm run test:vitest 434 pass

On a build, driven by script: click an entry with sync off → editor at the heading (selected, five lines from the top), preview at the heading. Wheel-scroll the editor with sync off → outline follows while the preview stays; with sync on → preview follows, outline agrees. Caret walked across a heading without scrolling → outline unchanged.