Preview rich-text editor: open with drag-selection preserved (bd-abo9m23f)

[cscheid]

Summary

In q2 preview --allow-edit (and hub-client's format: q2-preview), a mouse drag inside a single block now opens the rich-text editor with the dragged selection recreated — direction-aware, so a right-to-left drag keeps its focus at the release end — instead of a bare caret at the mouse-release point. This makes the selection-driven toolbar (bold, italic, link, …) immediately usable after a drag: drag, click B, done.

A drag whose selection spans multiple blocks no longer activates an editor at all. Previously the release block opened with a caret and the DOM swap destroyed the user's selection — breaking plain copy gestures.

Mechanism

Extends the bd-q9lyghv2 caret-at-click coordinate bridge from a single point to an anchor/head pair (same geometric premise: the editor renders the same visual text in the same measured box, so viewport coords captured before the DOM swap land on the same glyphs after it):

• dragSelectionCapture.ts (new): classifyOpenSelection classifies the DOM selection at the activate() chokepoint into caret / range / suppress, using direction-aware selection endpoints (anchor/focus, not the normalized range) and ownerDocument-relative lookups (iframe-safe).
• pendingClickCoordsRef → pendingOpenSelectionRef with a union payload; read-once-and-clear semantics at editor mount unchanged (self-heal remounts still fall back to end-of-block).
• placeSelectionFromDrag: replays both endpoints through posAtCoords and applies TextSelection.between(resolve(anchor), resolve(head)) — direction preserved, endpoints nudged to valid text positions.
• Mount fallback chain: range → caret at head (release point) → focus('end').

Keyboard and touch activation are untouched (no click coords → no classification).

Tests

• 9 unit tests for the capture classification (contained/backward/cross-block/collapsed/no-rects/invalid-offset).
• 5 unit tests for the replay against a real EditorState (direction preserved; misses and degenerate same-pos return false).
• Hover + editor integration tests extended: range payload stash, suppression (mouse-only — keyboard with a live selection still opens), read-once consume, fallback chain.
• New Playwright e2e (q2-preview-spa/e2e/drag-selection-open.spec.ts) driving real trusted mouse drags against the real q2 binary: forward drag (editor selection equals the selection recorded at pointerup), backward drag stays backward, cross-block drag opens nothing and preserves the selection. 3/3 passed.
• Manually verified end-to-end with q2 preview --allow-edit: drag-selecting "quick brown fox jumps over the lazy" opens the editor with that exact selection highlighted; toolbar Bold produces <strong> around exactly that range.
• cargo xtask verify green (the previously-failing changelog Q-2-17 WASM test passes after rebasing onto fix(hub-client): unbreak main — escape lone tilde in changelog (bd-q5o7ekzn) #381's fix).

Plan/design record: claude-notes/plans/2026-07-07-preview-drag-selection-into-richtext.md (strand bd-abo9m23f).

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