Zoom and fit-to-view in the node editor

CLAUDE.md

@@ -32,7 +32,7 @@ This is the **ktsu ImGui Suite**, a collection of .NET libraries for building De
 - **ImGui.Color** (`ktsu.ImGui.Color`) - Bridge between `ktsu.Semantics.Color` and ImGui. Colors are held as the semantic `Color` (linear) and `Srgb` types and converted only at the ImGui seam: `ColorImGuiExtensions` (`ToImColor`/`FromImColor`, `ToImGuiVector4`, `ToImGuiU32`) and `SrgbImGuiExtensions` (`Srgb` → `ImColor`/`ImGuiVector4`/`ImU32`, packed directly with no linear round-trip). The `ImColor` and `Srgb` `ToImGuiU32` apply the global style alpha like `ImGui.GetColorU32`; the linear `Color.ToImGuiU32` is a pure pack matching `ColorConvertFloat4ToU32`. `ImColor` extension operations: adjustments (lighten/darken, saturate/desaturate, hue offset, grayscale, invert, alpha), analysis (relative luminance, contrast ratio, perceptual distance), and contrast heuristics (`MostReadableTextColor`, `AdjustForSufficientContrast`). All color math delegates to `ktsu.Semantics.Color`. (There is no `ImColor` factory class — construct via `Color`/`Srgb` and convert.)
 - **ImGui.Styler** (`ktsu.ImGui.Styler`) - Theming system with 50+ built-in themes, scoped styling, Button.Alignment, Text.Color semantic colors, Indent utilities, Alignment helpers, theme-aware color palette (`Palette`, e.g. `Palette.Basic.Red`, `Palette.Semantic.Error`), and interactive theme browser. Color construction and manipulation live in `ImGui.Color`.
 - **NodeGraph** (`ktsu.NodeGraph`) - UI-agnostic attribute-based node graph metadata: `[Node]`, `[InputPin]`, `[OutputPin]`, `[NodeExecute]`, `[NodeBehavior]`, pin type utilities
-- **ImGui.NodeEditor** (`ktsu.ImGui.NodeEditor`) - ImNodes-based visual node editor with `NodeEditorEngine`, `AttributeBasedNodeFactory`, physics-based layout, `NodeEditorRenderer`, `NodeEditorInputHandler`
+- **ImGui.NodeEditor** (`ktsu.ImGui.NodeEditor`) - ImNodes-based visual node editor with `NodeEditorEngine`, `AttributeBasedNodeFactory`, physics-based layout, `NodeEditorRenderer`, `NodeEditorInputHandler`. ImNodes has no zoom of its own, so `NodeEditorRenderer.Zoom` supplies one and `FitToView` centres a graph and picks the zoom it fits at; the engine's positions and sizes stay at their own scale throughout, since that is the space the layout's lengths are measured in
 - **ImGui.Markdown** (`ktsu.ImGui.Markdown`) - CommonMark markdown renderer built on Markdig (pipe tables, task lists, autolinks), layered on `ImGui.Color` only, with no dependency on `ImGui.App`. Static `ImGuiMarkdown.Render(string, MarkdownConfig?)` parses with an internal source-keyed cache; `MarkdownDocument` parses once for hot render paths. `MarkdownConfig` exposes `FontResolver`, `OnLinkClicked`, `ImageResolver`, `HeadingScales`, `WrapWidth`, `ListIndentPixels`, `ParagraphSpacingPixels`, and `LinkColor`. Heading sizes derive from the live font size, so DPI and `ImGuiApp.GlobalScale` are respected automatically. Bold/italic use real glyphs when the host app registers named font variants via `FontResolver`, otherwise faux styling (faux-bold double-draw, faux-italic renders upright). Fenced and indented code blocks go to `MarkdownConfig.CodeBlockRenderer` (`Action<string?, string>?` — the fence's info string and the block text) when one is supplied, which takes over drawing *and* reserving the block's layout space; `ImGui.SyntaxHighlighting` plugs into it, and neither library references the other. v1 has no built-in code-block syntax highlighting, no async remote image download, and renders HTML as escaped text.
 - **SyntaxHighlighting** (`ktsu.SyntaxHighlighting`) - Renderer-agnostic tokenizing: no ImGui, no graphics API, no third-party parser, so it can move to its own repository unchanged. `SyntaxHighlighter.Highlight(code, language, tabWidth)` returns the classified `HighlightedLine`/`HighlightedToken` runs; `SyntaxHighlighter.HighlightCached` goes through a bounded cache keyed by source, language and tab width; `HighlightedCode` tokenizes once for hot render paths. Languages are data (`LanguageDefinition`: line/block comment, string, keyword, type, constant, operator, identifier and embedded-language rules) held in `LanguageRegistry`, which resolves names and aliases case-insensitively and falls back to plain text for unknown names rather than throwing. Fifteen built-ins in `BuiltInLanguages`: text, csharp, c, cpp, javascript, typescript, python, json, yaml, xml, html, css, sql, shell, lua. Two tokenizers back them — the general `CodeTokenizer`, and `MarkupTokenizer` for definitions with `IsMarkup` (XML/HTML), which classify structurally rather than by keyword. `SyntaxTheme` holds one `ktsu.Semantics.Color.Color` per `TokenKind`, with `Dark`/`Light` built in and `Background`/`Plain`/`LineNumber` left unset for the host to fill. Comments and strings are searched for an embedded language; see [Embedded languages](#embedded-languages) below. Highlighting is lexical.
 - **ImGui.SyntaxHighlighting** (`ktsu.ImGui.SyntaxHighlighting`) - The Dear ImGui drawing layer over `ktsu.SyntaxHighlighting`, layered on `ImGui.Color` only, with no dependency on `ImGui.App`. Static `ImGuiSyntaxHighlighting.Render(code, language, SyntaxHighlightConfig?)` tokenizes through the shared cache and draws; `Render(HighlightedCode, config)` draws pre-tokenized code, and `HighlightedCodeExtensions` re-adds `code.Render(config)` as an extension since the tokenized type itself knows nothing about ImGui. `Highlight` forwards to `SyntaxHighlighter.Highlight`. Leaving `SyntaxHighlightConfig.Theme` null picks between `SyntaxTheme.Dark`/`Light` per frame from the window background's luminance, and unset `Background`/`Plain`/`LineNumber` come from `FrameBg`/`Text`/`TextDisabled`. Code is never wrapped, and there is no scrolling, selection or editing. `ImGui.Markdown`'s `CodeBlockRenderer` plugs into this, and neither library references the other.
@@ -345,9 +345,14 @@ The node graph system follows a clean separation of concerns:
 - **ImGui.NodeEditor**: Renders and interacts with the graph using ImNodes. Split into:
   - `NodeEditorEngine` - Business logic (nodes, links, physics)
   - `AttributeBasedNodeFactory` - Creates nodes from attribute-decorated types
-  - `NodeEditorRenderer` - Pure ImNodes rendering
+  - `NodeEditorRenderer` - Pure ImNodes rendering, and the view: `Zoom` and `FitToView`
   - `NodeEditorInputHandler` - Input event processing
 
+  The renderer writes each node's position into ImNodes on the frame it draws it, so the view is
+  made of node positions rather than of panning: a pan is undone as soon as it is read back, which
+  is why `FitToView` moves the nodes. Zoom is applied on the way into ImNodes and undone on the way
+  back out, so nothing zoomed ever reaches the engine.
+
 ### Key Technical Details
 
 - **PID frame limiter** with auto-tuning (Coarse/Fine/Precision phases)