[blove]

The duplication

ColumnsSection.tsx and grouping/GroupingSection.tsx carried near-verbatim copies of the same pointer-drag state machine, recorded during the SP3b review: DRAG_THRESHOLD_PX, the PendingRowDrag/ActiveRowDrag shapes, the pointerdown/move/up/cancel handlers, endDrag, and the document-level Escape-cancel effect with the preventDefault interlock. Only the pure insertion geometry (tool-panel-drop-target.ts) was shared.

The extraction

The machine now lives in packages/react/src/tool-panel/useToolRowDrag.ts, parameterized over the three real differences:

• measureRows — how the section measures its rendered rows (called fresh on every move and again at release; the never-cache rationale moved into the option's TSDoc).
• groups — the rendered subgroups (the columns section's pin partition vs the grouping list's single constant group).
• commit — what a finished move applies. Called only from a release over a resolved target; the commit-time getState re-read rationale stays with each section's commit, because what there is to re-read differs (live columnLayout vs the row model's rowGroups).

The hook returns { drag, gripHandlers }; each section spreads gripHandlers(columnId) onto its grip. Constraint-carrying comments moved with the code they constrain: capture-at-pointerdown with its rAF-coalescing measurement, commit-on-release-only with the coalesced-last-move cross-boundary finding, the Escape preventDefault interlock, and the generalized no-stopPropagation-on-pointerdown rule (an open popover's outside-press close must fire). GroupingSection's async-settle-aware pending-grip-focus handling stays section-side, inside its commit. Behavior-preserving by construction and by suite: no existing test was touched except to add one.

Mutation proof

• Commit path disabled in the hook → 2 failures, one per section: the grouping suite's "pointer drag … commits … the whole reordered list" and the columns suite's new release-commit test. (The columns section previously had no jsdom pin on the pointer-release commit — only cancel paths — so this mutation was initially caught by the grouping suite alone; one test added to close that hole.)
• Escape-cancel's endDrag removed → 2 failures, both sections' pre-existing "Escape mid-drag cancels" tests.
• Reverted → pnpm --filter @pretable/react test tool-panel: 8 files, 119 tests green.

Verification

• Full react suite: 110 files, 1568 tests green.
• pnpm format, eslint, tsc --noEmit: clean.
• api:check fresh — nothing public moved (the hook is internal, not in any barrel); no changeset.
• Net −20 lines (246 added incl. the new test, 266 removed).

🤖 Generated with Claude Code

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