canvy: a pan lands on a hive rect and relocates the whole subtree — and the accident pins every auto-laid cell forever

[mmeyerlein]

Observed on a live display, reconstructed from the stored positions afterwards.

What happened

On a dense picture there is almost no empty background left: hive rects carry pointer-events: all and the outermost hive covers nearly the whole stage. A drag that was meant as a pan grabbed the outermost hive instead and moved it — measured afterwards as a uniform shift of every stored node position by the same vector (here: −541, −179). Combined with #414 (the burst of per-member writes drops frames), the person doing it does not even see a clean result: the picture half-follows, snaps around, and settles wrong.

The second half is worse than the first

A hive drag writes x/y into every member, including the ones that had no stored position. From that moment those cells are hand-placed as far as saved_positions is concerned — the flow layout will never touch them again, and there is no way to un-pin: object.update merges per key and cannot remove one. Recovery meant deleting the node objects outright so the next tick recreates them without positions. An accidental gesture should not need surgery to undo.

Also downstream of the same accident: the auto-laid cells of a sibling hive (grown later, settled against the pre-accident picture) ended up overlapping the shifted hand-placed cells — 12 node-node overlaps on a 59-cell colony. In an overlap the topmost box eats the pointer, so grabbing 'the node I see' moves a different one: reported as "I move a node and it springs back".

Directions, for a ruling

1. Make the group drag deliberate. A hive moves only by its label (or with a modifier held); a drag starting on a hive's fill pans the camera. The label is small and unambiguous; the fill is what a pan naturally lands on.
2. Make it undoable. Either an explicit un-pin (an editable-prop delete, or a canvy gesture that clears x/y), or make the group drag write one record instead of pinning every member — though the per-member record is exactly what GH canvy: adding a cell moves every hand-placed hive, because a hive anchor is a delta against the computed layout #170 chose, so this arm reopens that ruling and needs care.
3. Optionally: treat members that had no stored position specially on a group drag — move them provisionally but do not write them, so the accident stays shallow.

(1) plus an un-pin from (2) looks like the honest pair; (3) is cheap but makes a group drag's result depend on invisible state.

[mmeyerlein]

Direction 1 landed in 1b05f75f (canvy@2.1.2): a hive moves by its label only — a drag starting on a fill pans the camera. Verified with real pointer events on a live display: fill-drag pans and writes nothing, label-drag moves the group, node drags are unaffected. The client test suite covers both gestures.

Still open — the reason this stays open: the un-pin half. A group drag still writes x/y into members that had no stored position, and object.update cannot remove a prop, so recovery from an unwanted pin still means deleting the object and letting the next tick recreate it. Wants either an editable-prop delete or ruling arm (3).

[mmeyerlein]

Shipped in 0.24.0 (canvy 2.1.8/2.1.9): pinning is now its own declared, editable prop — a drag sets it once, the detail panel's 'release to the layout' clears it, and the auto layout takes the cell back. Backwards compatible by rule (no key ⇒ pinned); the 1.x position replay pins what it replays. The original accident (a pan relocating the whole subtree) was already removed by the 2.1.6 gesture model.