feat(gpu): support Apple Silicon GPU usage and unified memory

[narthur]

Problem

On Apple Silicon Macs, sysmon's GPU usage always showed 0%, and it displayed separate Memory and GPU Memory bars even though the CPU and GPU share a single unified memory pool.

The root cause: detectGPUVendor only knew how to read stats from nvidia-smi (NVIDIA) and rocm-smi (AMD). Neither exists on macOS, so detection fell through to gpuVendorNone → constant 0%. There was also no concept of unified memory, so the redundant two-bar memory layout was always used.

Fix

• Apple Silicon GPU detection: added a gpuVendorApple vendor, detected on macOS by reading ioreg -r -d 1 -w 0 -c IOAccelerator. GPU usage comes from the Device Utilization % field (the same figure Activity Monitor reports) — no extra tools and no sudo required.
• Unified memory: added a UnifiedMemory flag to SystemStats. When set, the view renders a single full-width "Unified Memory" bar instead of the misleading Memory / GPU Memory split.
• Tests for the ioreg parser (parseAppleGPUUsage) and the unified-memory view.
• README updated.

Testing

• go vet, go test, and go build all pass.
• Verified at runtime on an Apple M5: vendor detected as Apple, GPU usage reports a live non-zero value, and the unified-memory bar renders in place of the two-bar split.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added GPU monitoring support for Apple Silicon systems
  • Apple Silicon systems now display unified memory as a single full-width bar instead of separate Memory/GPU Memory bars
  • GPU statistics work automatically on Apple Silicon without additional configuration

• Documentation

  • Updated GPU feature docs to include Apple Silicon details and unified-memory behavior

• Tests

  • Added unit tests for Apple GPU usage parsing and unified-memory UI rendering

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 09ed3a5 and f7859d9.

📒 Files selected for processing (2)

• main.go
• main_test.go

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📝 Walkthrough

Walkthrough

This PR adds Apple Silicon GPU support to a system monitoring application. It introduces a UnifiedMemory flag to the SystemStats type, implements GPU vendor detection for Apple via ioreg, adds GPU usage parsing, conditionally renders a unified memory bar on Apple platforms instead of separate Memory/GPU Memory bars, and updates documentation.

Changes

Apple Silicon GPU Support

Layer / File(s)	Summary
Type definitions and foundation main.go	Adds runtime import, introduces UnifiedMemory bool field on SystemStats, and defines gpuVendorApple constant for Apple GPU identification.
Apple GPU vendor detection main.go	Enhances detectGPUVendor with macOS/arm64 branch that executes ioreg and detects Apple GPU by checking for "Device Utilization %" marker.
Apple GPU usage parsing and tests main.go, main_test.go	Implements getGPUUsageApple and parseAppleGPUUsage helpers to extract GPU utilization from ioreg output; table-driven test validates parsing across normal values, zeros, edge cases, and error conditions.
Unified memory bar rendering and tests main.go, main_test.go	View method conditionally renders single full-width "Unified Memory" bar when UnifiedMemory is true, otherwise displays split Memory/GPU Memory bars; test confirms unified bar presence and GPU memory bar absence when enabled.
Stats collection wiring main.go	Sets UnifiedMemory flag during stats collection based on detected GPU vendor being Apple.
Documentation updates README.md	Enumerates platform-specific GPU data sources, notes Apple Silicon GPU stats availability via built-in ioreg, and clarifies unified-memory rendering in output format section.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 30.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes the main change: adding Apple Silicon GPU usage support and unified memory display to the application.
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.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/macos-apple-silicon-gpu

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[Copilot]

Pull request overview

Adds macOS Apple Silicon GPU utilization support and updates the TUI to properly represent unified-memory systems, avoiding misleading “GPU Memory” reporting when CPU/GPU share a single pool.

Changes:

• Detect Apple GPU on macOS and read GPU usage via ioreg (Device Utilization %) with a new parser.
• Add SystemStats.UnifiedMemory and render a single full-width “Unified Memory” bar when enabled.
• Add unit tests for the ioreg parser and unified-memory view; update README with platform/tooling notes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
README.md	Documents Apple Silicon GPU stats via ioreg and the unified-memory UI behavior.
main.go	Implements Apple GPU vendor detection/usage parsing and unified-memory-aware rendering.
main_test.go	Adds tests for parseAppleGPUUsage and unified-memory view output behavior.