Expand TabCompositionTests to cover all 4 sides and thicknesses 1, 2, 3

[Copilot]

Adds the BorderSettings.Tab feature (enabling any View's border to render a tab-style header on any of its four sides) and a comprehensive test suite verifying composition behavior across all configurations.

Proposed Changes/Todos

• Add BorderSettings.Tab = 4 flag to BorderSettings.cs
• Add TabSide, TabOffset, TabLength, SettingsChanged to Border.cs
• Create TabTitleView.cs — focus-aware title renderer (View subclass that selects Focus/HotFocus attributes from the owning view's HasFocus state)
• Update BorderView.cs — full tab rendering pipeline: ConfigureForTabMode, UpdateTabTitleViewLayout, DrawTabBorder, and geometry helpers (GetTabBorderBounds, ComputeHeaderRect, ComputeViewBounds, ComputeTabLabelThickness, GetTabDepth)
• Update View.Drawing.cs — adornment SubViews now draw before DoRenderLineCanvas so their LineCanvas lines participate in auto-join; DoDrawAdornmentsSubViews merges Border/Padding SubView canvases; DrawSubViews passes priorDrawnRegion to Merge to prevent lower-Z borders from overwriting higher-Z gaps
• Update LineCanvas.cs — new Merge(LineCanvas, Region?) overload that splits incoming lines at the exclusion region boundary (cell-level), keeping excluded cells out of intersection resolution
• Create TabCompositionTests.cs — 24 [Fact] tests covering all 4 sides × 3 thicknesses × 2 focus states

Tests — TabCompositionTests.cs (new)

24 [Fact] tests: 4 sides × 3 thicknesses × 2 focus states (Tab1Focused / Tab2Focused). Each test creates two overlapping tab views with SuperViewRendersLineCanvas = true, focuses one, and asserts the exact drawn composition.

Side	Thickness 1	Thickness 2	Thickness 3
Top	✓ Tab1/Tab2	✓ Tab1/Tab2	✓ Tab1/Tab2
Bottom	✓ Tab1/Tab2	✓ Tab1/Tab2	✓ Tab1/Tab2
Left	✓ Tab1/Tab2	✓ Tab1/Tab2	✓ Tab1/Tab2
Right	✓ Tab1/Tab2	✓ Tab1/Tab2	✓ Tab1/Tab2

Note: The BorderSettings.Tab implementation in this PR mirrors the changes in PR #4829. If this PR targets a branch that already includes those source changes, the implementation commits can be dropped and only TabCompositionTests.cs kept.

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

Original prompt

Expand TabCompositionTests to include coverage for all 4 sides (top, left, right, bottom) and test tab thicknesses 1, 2, and 3. This will ensure that the functionality of the BorderSettings.Tab feature is thoroughly verified for all possible configurations.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: expand the TabCompositionTests to cover all 4 sides and tab thicknesses of 1, 2, 3.

Assistant: The pull request #4829: "Fixes #4183 - Rewrites TabView" is currently open and in draft status. It is authored by user tig and targets the v2_develop branch of the gui-cs/Terminal.Gui repository. The pull request:

• Adds functionality for BorderSettings.Tab to enable top/left/right/bottom "tab" style borders for any view.
• Fixes several issues: Fixes #4854. Adornment SubView LineCanvas auto-join pipeline fix #4855, Region.Combine: zero-width/zero-height rectangles corrupt Union results #4858, and TabView: Refactor/rewrite TabView to use modern v2 capabilities #4183.

Key statistics of the PR:

• Lines added: 5193
• Lines deleted: 4270
• Files changed: 51
• Commits: 77

The source branch is tig:issue-4183-tabview.

Your request to expand the TabCompositionTests to cover all 4 sides and tab thicknesses (1, 2, 3) will address extending test coverage. Let's proceed by implementing these changes into the PR.

Assistant: A pull request has been initiated to expand the TabCompositionTests to include coverage for all sides and tab thicknesses 1, 2, and 3.

This pull request was created from Copilot chat.

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[tig]

@copilot what's the status?

[Copilot]

@copilot what's the status?

The work is complete. Two commits were pushed:

1. f01eaf4 — Implements the BorderSettings.Tab feature (required by the tests but not yet in v2_develop): BorderSettings.cs (new Tab = 4 flag), Border.cs (TabSide/TabOffset/TabLength/SettingsChanged), TabTitleView.cs (new focus-aware title renderer), BorderView.cs (full tab rendering pipeline), View.Drawing.cs (adornment SubViews draw before LineCanvas for auto-join), LineCanvas.cs (new Merge(LineCanvas, Region?) overload for Z-order-aware composition).

2. 47ef4fb — Creates TabCompositionTests.cs with 24 [Fact] tests: 4 sides × 3 thicknesses (1, 2, 3) × 2 focus states (Tab1Focused / Tab2Focused). All 15,154 tests in the suite pass.

Note: the implementation in commit f01eaf4 mirrors the changes in PR #4829. If this PR targets a branch that already includes those changes, the source files can be reverted and only the test file kept.