fix(wgpu): reset gpu_ready on close + re-init (use-after-free guard)

[apotema]

Addresses the gemini High on #426. gpu_ready stayed true after closeWindow freed the GPU resources (sprite buffers/pipeline → null), so a stray endDrawing/ensureSurface after close — or a re-init whose initGpu fails — would pass the if (!gpu_ready) return guard and touch freed handles (panic / UB). Reset to false in closeWindow (authoritative: resources freed) and at the top of initWindow (initGpu sets it true on success, so a failed re-init stays not-ready). Completes the re-init state hygiene from #425. wgpu example builds (macOS Metal).

Summary by CodeRabbit

• Bug Fixes
  • Improved window lifecycle handling to avoid rendering with partially initialized or already released GPU resources.
  • Ensured graphics state is reset when the window is initialized or closed, reducing the chance of crashes or invalid drawing after failed setup or shutdown.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 6d9e6621-b986-425c-b457-3a6b9a1d0fa1

📥 Commits

Reviewing files that changed from the base of the PR and between e5c2815 and 8165238.

📒 Files selected for processing (1)

• backends/wgpu/src/window.zig

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📝 Walkthrough

Walkthrough

In backends/wgpu/src/window.zig, gpu_ready is now explicitly set to false at two points: during initWindow state reset (before initGpu() runs) and at the end of closeWindow after GPU resources are released and GLFW is terminated.

Changes

gpu_ready lifecycle management

Layer / File(s)	Summary
gpu_ready guards in init and close backends/wgpu/src/window.zig	Sets gpu_ready = false on initWindow state reset and after GPU teardown in closeWindow to prevent rendering against uninitialized or freed GPU handles.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A flag set false, a guard in place,
No freed GPU shall render's grace.
Init resets, close does too,
The rabbit hops and sees it through!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main fix: resetting gpu_ready on close and re-init to prevent use-after-free.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/wgpu-gpu-ready-reset

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[gemini-code-assist]

Code Review

This pull request updates backends/wgpu/src/window.zig to set gpu_ready = false during window initialization and closure to prevent drawing calls on freed handles. The reviewer noted that setting gpu_ready = false at the end of closeWindow() creates a vulnerability where re-entrant events or callbacks could access partially freed resources, and recommended moving this assignment to the beginning of the function.

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[gemini-code-assist]

Setting gpu_ready = false at the very end of closeWindow() leaves a window of vulnerability. During the release of GPU resources and GLFW termination, callbacks or re-entrant events could be triggered. If these callbacks attempt to draw or update the surface, they will see gpu_ready as true while resources are partially freed, leading to undefined behavior or panics.

It is much safer to set gpu_ready = false at the very beginning of closeWindow() (before releasing any resources) to immediately gate any re-entrant calls. Please move this assignment and its comment to the top of the closeWindow() function.