perf-hotpath-guard - SKILL.md Agent Skill

name: perf-hotpath-guard description: | INTERNAL DEV WORKFLOW for WpfHexEditor — Claude self-invokes after editing C# in render/layout/scroll hot paths (HexEditor/, CodeEditor/Rendering, Viewport, GlyphRun, Renderer, ScrollHandler*, OnRender, MeasureOverride, ArrangeOverride) to detect allocations and patterns that cause jank or GC pressure. Skip on: tests, mocks, designer files, non-render code in non-hot directories.

perf-hotpath-guard (internal)

Catches perf anti-patterns from project history (jank, GC pressure in render loops). Memory anchors: adr_006_zoom_rendering, adr_hexeditor_viewport_race, bug_drag_scroll_fix, feedback_wordwrap_column, bug_doc_editor_caret_hittest.

When I invoke

Trigger: .cs edits matching ANY of:

Path under HexEditor/ or CodeEditor/Rendering
Filename contains Viewport, GlyphRun, Renderer, ScrollHandler
Edit modifies OnRender, MeasureOverride, or ArrangeOverride

Skip if path contains Test, Mock, *.Designer.cs, *.g.cs, *.g.i.cs.

Pipeline

scripts/hotpath-scan.ps1 -Files <paths> (applies rules inside hot-method bodies only) → HotPath: <n> issues or OK.

9 rules

See references/perf-rules.md for regex + rationale.

Rule	Anchor
`alloc-in-render`	GC pressure/jank
`linq-in-hot`	allocations + delegate creation
`string-concat-loop`	O(n²) allocations
`boxing`	struct→object passing
`dispatcher-cosmetic`	`feedback_wordwrap_column` anti-pattern
`formatted-text-recreate`	`bug_doc_editor_caret_hittest`
`glyph-run-recreate`	render cost without pool
`findvisualchild-render`	O(n) tree walk every frame
`regex-in-render`	compile cost on hot path

Hot methods (from references/hot-methods.md): OnRender, MeasureOverride, ArrangeOverride, OnPreviewMouseMove, OnScrollChanged, Render*/Draw*/Paint* in renderer files, any method preceded by // HOT. Exclude with // COLD.

Output

HotPath: 2 issues
  HexLineRenderer.cs:142  alloc-in-render         OnRender -> new SolidColorBrush(...)
  TextViewport.cs:88      formatted-text-recreate OnRender -> new FormattedText(...)

Suppress: // alloc-ok: <reason> (alloc-in-render), // COLD (exclude method), // HOT-EXCEPTION: <note> (document legitimate exception). Static analysis only — no runtime profiling, no code rewrite.