fix(DockView): stop sibling blanking on any exit-maximize

[zhaijunlei955]

Issues

close #1045

Two fixes around the onlyWhenVisible renderer and visibility transitions.

1. Active panel resets to the first / blanks after becoming visible

Problem: Activate a non-first panel in a group, switch to another view (so this
DockView's container is hidden), refresh, then switch back — the group's active
panel snaps to the first one and its content goes blank (tab titles remain).

Cause: setWidth's tab-overflow fallback force-activated group.panels[0]
whenever the visible tab strip had no active tab. On becoming visible after a
hidden init the group expands through narrow widths and transiently overflows the
active tab into the dropdown → reads as "no active tab" → wrong switch + churn.

Fix: Only re-pick the active tab on a real shrink (header width strictly drops,
never the transient expand), switching before the active tab is tucked away. The
remaining fallback fires only when the group genuinely has no active panel.

2. Blank DockView when a group is removed/moved/added/hidden while maximized

Problem: With a grid group maximized, closing all its panels (or otherwise
removing/moving/adding/hiding a group) leaves the whole DockView blank.

Cause: The core exits maximize on its own for those operations
(gridview.removeView/setViewVisible/moveView/addView), but without the
maximizing flag the onlyWhenVisible handler moves the restored siblings'
content into the template → blank. Earlier fixes (e.g. #1025) only set the flag on
the toggle-button and save paths.

Fix: A single guard wraps the core's exitMaximizedView so every exit-maximize
carries the maximizing flag, covering all paths at once.

Summary by Sourcery

Guard DockView maximize exits and refine active-panel selection during tab overflow handling to prevent panels and views from becoming blank after visibility or layout changes.

Bug Fixes:

• Ensure exiting a maximized grid view always carries the maximizing flag so sibling groups restore their content instead of rendering blank when groups are added, removed, moved, or hidden.
• Adjust tab overflow handling to only reselect the first panel on genuine header width shrink and when a group has no active panel, preventing active panels from resetting or going blank after visibility transitions.

[bb-auto]

Thanks for your PR, @zhaijunlei955. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[sourcery-ai]

Reviewer's Guide

Adds a guard to ensure all maximize exits carry the maximizing flag, and refines tab overflow handling so active panels are only reset on genuine header width shrinks and only when a group truly has no active panel, preventing blank DockView content on visibility/maximize transitions.

Sequence diagram for guarded maximize exit behavior

sequenceDiagram
    participant Dockview
    participant Gridview
    participant DockviewParams as DockviewParams

    Dockview->>Dockview: cerateDockview
    Dockview->>Dockview: guardMaximizeExit
    Dockview->>Gridview: wrap exitMaximizedView

    Gridview->>Gridview: exitMaximizedView
    Gridview->>DockviewParams: set maximizing = true
    Gridview->>Gridview: original exitMaximizedView
    Gridview->>DockviewParams: restore maximizing

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Flow diagram for setWidth active panel handling on shrink

flowchart TD
    A[setWidth] --> B[find group for header]
    B --> C[update _lastHeaderWidth]
    C --> D{voidWidth == 0?}
    D -->|no| H
    D -->|yes| E{tabs > 1?}
    E -->|no| H
    E -->|yes| F{shrinking and active tab would overflow?}
    F -->|yes| G[call group.panels_0_.api.setActive]
    F -->|no| H[adjust tabs into dropdown]
    H --> I{group.activePanel exists?}
    I -->|no| J[call group.panels_0_.api.setActive]
    I -->|yes| K[keep current active panel]

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File-Level Changes

Change	Details	Files
Guard all gridview maximize exits so the maximizing flag is set consistently, preventing blank restored siblings when leaving maximized state via core operations.	Introduce a guardMaximizeExit wrapper that patches the gridview prototype’s exitMaximizedView method once per prototype. Within the wrapper, locate the associated DockView accessor, temporarily set params.maximizing = true for the duration of exitMaximizedView, and restore the previous value afterward. Wire guardMaximizeExit into DockView initialization alongside the existing collapsed-proportions guard.	src/components/BootstrapBlazor.DockView/wwwroot/js/dockview-utils.js
Tighten tab header width handling so the active panel is only re-picked on actual shrinks and only when there is no active panel, avoiding unwanted switches and blank content after hidden views become visible.	Track the last known header width per group (_lastHeaderWidth) and compute a shrinking flag when the header width strictly decreases. On shrink with overflow, proactively activate the first panel if the currently active tab would overflow into the dropdown, switching before it is hidden. Replace the prior "no active tab in visible strip" fallback with a simpler check that the group exists and has no activePanel, then activate the first panel as a true fallback. Ensure the early return when there is only one tab remains and reuse the computed group object throughout setWidth.	src/components/BootstrapBlazor.DockView/wwwroot/js/dockview-utils.js

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[sourcery-ai]

Hey - I've left some high level feedback:

• In guardMaximizeExit, consider defensively checking that proto.exitMaximizedView exists before wrapping it so the guard degrades gracefully if the underlying gridview implementation changes.
• The _lastHeaderWidth state is being attached ad hoc to the group object; it may be safer to centralize this tracking (or ensure it’s cleared on group disposal) to avoid stale width data if groups/headers are recycled.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `guardMaximizeExit`, consider defensively checking that `proto.exitMaximizedView` exists before wrapping it so the guard degrades gracefully if the underlying gridview implementation changes.
- The `_lastHeaderWidth` state is being attached ad hoc to the group object; it may be safer to centralize this tracking (or ensure it’s cleared on group disposal) to avoid stale width data if groups/headers are recycled.

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