feat(core): LayoutPriority.Fill — one view/group fills, siblings stay fixed

[mathuo]

Summary

Adds LayoutPriority.Fill so a view (standalone gridview) or group (dockview) absorbs all surplus/deficit space while its siblings keep their fixed sizes — the common "central content fills, side/bottom panels stay put" layout that the existing proportional priorities (Low/High/Normal) can't express.

Closes #1378.

Motivation

Today every priority participates in proportional redistribution, so resizing the window / adding / removing a panel rescales every view. Consumers end up fighting this with manual setSize calls on every layout change. Fill solves it declaratively: designate one leaf as the filler and the rest hold their size.

What's included

Engine ( standalone gridview + splitview)

• LayoutPriority.Fill — a fill view absorbs surplus/deficit in layout/relayout/distributeEmptySpace; siblings are held fixed.
• Multiple fill views split the surplus equally (spilling to siblings only once a fill hits a min/max).
• A hidden fill view can't absorb, so the layout falls back to normal proportional distribution.
• BranchNode propagates Fill up the grid tree (highest precedence), so it works in nested layouts.
• Runtime priority setter on GridviewPanel triggers a full relayout so propagation up the branch tree takes effect.

Dockview (group-level)

• Set at creation: api.addGroup({ priority: LayoutPriority.Fill }).
• Set at runtime: group.api.priority = LayoutPriority.Fill.
• Serialized on the group and restored on load (toJSON/fromJSON).
• Priority is a group concept in dockview (the group is the grid leaf; tabs share one box), not per-panel.

Backwards compatibility

Fully backwards compatible. Every behaviour change is gated on a fill view being present, so existing layouts and serialized state are unchanged. The serialized priority key only appears when a group opts in; older payloads simply omit it and load unchanged.

Tests

• splitview: single-fill absorb (grow/shrink/add/remove), equal multi-fill split, Fill-beats-High, vertical orientation.
• gridview: priority round-trips through toJSON/fromJSON.
• dockview: addGroup({ priority }) + round-trip persistence, runtime group.api.priority, and a behavioural test (three groups; middle set to Fill; only it resizes while siblings stay fixed).

dockview-core: 1082/1082 green, tsc clean.

🤖 Generated with Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
86.5% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud