Fixes #5433. Make View.Draw self-draw context flow explicit

[harder]

Summary

• Fixes Follow up #5431: make View.Draw self-draw context flow explicit #5433

Makes the View.Draw (...) self-draw flow explicit so the _localDrawContext lifecycle is owned in one place instead of being spread across three hand-aligned if (needsDrawSelf) blocks. Pure refactor — no rendering, ordering, or invalidation behavior changes.

Split from #4973; follow-up to #5431 (#5358), which introduced the needsDrawSelf / _localDrawContext mechanism and explicitly deferred this cleanup.

Background

PR #5431 fixed the child-only redraw fan-out from #5358 by capturing needsDrawSelf = NeedsDraw before DoDrawAdornments escalates NeedsDrawRect, then gating the self-content draw on it. That fix is correct, but its implementation spread the per-view _localDrawContext lifecycle across three separate if (needsDrawSelf) blocks in View.Draw (...):

1. recreate _localDrawContext,
2. SetAttributeForRole + DoClearViewport,
3. (after DoDrawSubViews) DoDrawText + DoDrawContent into _localDrawContext, then merge into the shared context.

_localDrawContext is consumed later in DoDrawComplete for TransparentMouse CachedDrawnRegion hit-testing. The subtle invariants — recreate only on self-redraw, preserve across child-only passes, consume in DoDrawComplete — were split across distant blocks, so a future edit could easily reset or split the lifecycle at the wrong point and reintroduce the #5431 review regression (TransparentMouseParent_ChildOnlyDirty_PreservesCachedDrawnRegion).

Changes

• View.Drawing.cs — new private DrawSelfContent (DrawContext sharedContext) that owns the entire _localDrawContext lifecycle for a self-redraw pass: (re)create it, draw Text and Content into it, then merge its region into the shared context. Draw (...) now calls this once, gated on needsDrawSelf, after SubViews.
• View.Drawing.cs — Draw (...) no longer creates _localDrawContext alongside the viewport clear. DoClearViewport writes only the shared context, so the local context isn't needed until DrawSelfContent; moving creation there keeps create → populate → merge in one place. The remaining "clear self viewport" block carries a comment explaining that self-draw is intentionally split around DoDrawSubViews to preserve order.
• View.Drawing.cs — _localDrawContext field gains an authoritative <remarks> documenting the lifecycle: recreated only on self-redraw passes (in DrawSelfContent), left untouched on child-only passes so DoDrawComplete keeps a valid CachedDrawnRegion.

Draw order is unchanged: Clear (self) → SubViews → flush _lastClearedViewport → Text/Content (self).

Side effect: removes a warning

Collapsing _localDrawContext's creation and use into one method lets nullable flow analysis prove it non-null, removing the pre-existing CS8602 (Dereference of a possibly null reference) warning at the old context.AddDrawnRegion (_localDrawContext.GetDrawnRegion ()) site.

Testing

• dotnet build --no-restore — 0 warnings, 0 errors (and removes one pre-existing warning, per above).
• dotnet test --project Tests/UnitTestsParallelizable --no-build — 17260 pass / 17 pre-existing skips.
  • Contract/regression coverage stays green: SubViewOnlyRedrawTests (incl. TransparentMouseParent_ChildOnlyDirty_PreservesCachedDrawnRegion), RegionAwareClearViewportTests, NeedsDrawTests.

No new tests: this is a behavior-preserving refactor whose contract is already pinned by the #5431 tests above. Coverage is maintained.

Acceptance criteria mapping

AC	Coverage
1. self-draw as one explicit unit	DrawSelfContent owns the _localDrawContext create/populate/merge; the clear half is a single documented block whose split from content is explained.
2. recreate _localDrawContext only on self-redraw	creation lives inside DrawSelfContent, called only when needsDrawSelf.
3. preserve prior context on child-only passes	DrawSelfContent not called when needsDrawSelf is false; field left untouched (documented on the field).
4. draw order unchanged	Clear → SubViews → Text → Content preserved.

To pull down this PR locally

git remote add copilot git@github.com:harder/Terminal.Gui.git
git fetch copilot fix-5433-explicit-self-draw-context
git checkout copilot/fix-5433-explicit-self-draw-context

[Copilot]

Pull request overview

This PR refactors View.Draw so the self-draw context lifecycle is centralized and easier to reason about, preserving the redraw behavior introduced by #5431 while reducing future regression risk.

Changes:

• Moves _localDrawContext creation/use/merge into a new DrawSelfContent helper.
• Keeps the self-clear phase separate to preserve draw order: clear → SubViews → self text/content.
• Adds documentation for the _localDrawContext lifecycle and a planning note for #5433.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Terminal.Gui/ViewBase/View.Drawing.cs	Centralizes self-content drawing and _localDrawContext lifecycle while preserving existing draw order and child-only redraw behavior.
plans/5433-explicit-self-draw-context.md	Documents the issue, intended refactor, verification expectations, and acceptance criteria mapping.

[tig]

Nice that collapsing it kills the CS8602 instead of forgiving it. The field remarks documenting “preserve on child-only passes” is the bit that stops someone re-breaking TransparentMouse later.

This is hero work and I love your methodical approach!