fix(paper): preserve pending update flags when cell is hidden during updateViewsBatch

[Geliogabalus]

Summary

• When a mounted view became invisible during updateViewsBatch, the currentFlag (e.g. a translate flag) was discarded — only FLAG_INSERT was stored in the unmounted list via registerUnmountedView
• When the view was later re-mounted, the pending update was never applied, leaving the view in a stale state (e.g. the transform attribute retained the old position)
• Fix: move _mergeUnmountedViewScheduledUpdates(cid, currentFlag) outside the else branch so it runs for both the mounted and already-unmounted cases, consistent with how the already-unmounted path already worked

Test plan

• Run packages/joint-core tests: cd packages/joint-core && grunt test:server --file=test/jointjs/dia/Paper.js
• New test: 'propagate updates flag when the cell is hidden during the update' — moves a rect to a position that triggers unmount, then re-mounts it and checks the transform attribute reflects the new position

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes a joint.dia.Paper view-management edge case where scheduled update flags (e.g., translate/transform updates) could be lost when a view becomes hidden during updateViewsBatch, causing stale state when the view is later re-mounted.

Changes:

• Preserve pending view update flags when a mounted view is unmounted due to cellVisibility during updateViewsBatch.
• Add a regression test covering “hide during update → re-mount → ensure transform reflects the latest position”.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
packages/joint-core/src/dia/Paper.mjs	Ensures unmounted-queue scheduled flags are merged even when the view transitions from mounted → unmounted during updateViewsBatch.
packages/joint-core/test/jointjs/dia/Paper.js	Adds a QUnit test intended to reproduce and prevent the stale-transform regression.

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