feat(dashboard): go-to-definition, Ctrl+Click, and find-usages panel

`F12` jumps the cursor to the declaration of the identifier under the
caret; `Shift+F12` opens a CodeMirror panel listing every range that
resolves to the same declaration (declaration site plus all usages),
with line-number snippets that click to jump. `Ctrl+Click` (Cmd+Click
on macOS) on an identifier is wired to the same goto path. `Esc`
closes the panel.

All three features read from `rhaiAnalysisField`, so they automatically
follow the cached parse + symbol table. The panel's styling lives in a
CodeMirror `baseTheme` keyed to the dashboard's slate palette.

Bundle delta: +3 KB raw, +1 KB gzipped.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dashboard/src/lib/rhai-mode.ts

@@ -16,8 +16,9 @@
 
 import { StreamLanguage, LanguageSupport } from '@codemirror/language';
 import { autocompletion, type CompletionContext, type CompletionResult } from '@codemirror/autocomplete';
-import { StateField, type Extension } from '@codemirror/state';
-import { parse, buildSymbolTable, type ParseResult, type SymbolTable } from './rhai';
+import { EditorSelection, StateEffect, StateField, type Extension } from '@codemirror/state';
+import { EditorView, keymap, showPanel, type Panel } from '@codemirror/view';
+import { parse, buildSymbolTable, type ParseResult, type Range, type SymbolTable } from './rhai';
 
 // Keywords that drive control flow (`if`, `for`, ...) — these get the
 // `controlKeyword` tag so the theme can color them distinctly from
@@ -396,9 +397,203 @@ export function scopeCompletionSource(context: CompletionContext): CompletionRes
 	};
 }
 
+// ---------------------------------------------------------------------------
+// Go-to-definition, Ctrl/Cmd+Click, find-usages
+// ---------------------------------------------------------------------------
+
+interface UsagesPanelState {
+	name: string;
+	ranges: Range[];
+}
+
+const setUsagesPanel = StateEffect.define<UsagesPanelState | null>();
+
+const usagesPanelField = StateField.define<UsagesPanelState | null>({
+	create: () => null,
+	update(value, tr) {
+		for (const e of tr.effects) if (e.is(setUsagesPanel)) return e.value;
+		return value;
+	},
+	provide: (f) => showPanel.from(f, (value) => (value ? buildUsagesPanel : null))
+});
+
+function buildUsagesPanel(view: EditorView): Panel {
+	const state = view.state.field(usagesPanelField);
+	const dom = document.createElement('div');
+	dom.className = 'cm-rhai-usages';
+
+	const head = document.createElement('div');
+	head.className = 'cm-rhai-usages-head';
+	const count = state ? state.ranges.length : 0;
+	const label = document.createElement('span');
+	label.textContent = `${count} occurrence${count === 1 ? '' : 's'} of "${state?.name ?? ''}"`;
+	head.appendChild(label);
+	const close = document.createElement('button');
+	close.type = 'button';
+	close.textContent = '×';
+	close.title = 'Close (Esc)';
+	close.onclick = () => {
+		view.dispatch({ effects: setUsagesPanel.of(null) });
+		view.focus();
+	};
+	head.appendChild(close);
+	dom.appendChild(head);
+
+	if (state) {
+		for (const r of state.ranges) {
+			const line = view.state.doc.lineAt(r.start);
+			const row = document.createElement('button');
+			row.type = 'button';
+			row.className = 'cm-rhai-usages-row';
+			const num = document.createElement('span');
+			num.className = 'cm-rhai-usages-line';
+			num.textContent = String(line.number);
+			const snip = document.createElement('span');
+			snip.className = 'cm-rhai-usages-snip';
+			snip.textContent = line.text.trim();
+			row.appendChild(num);
+			row.appendChild(snip);
+			row.onclick = () => {
+				view.dispatch({
+					selection: EditorSelection.cursor(r.start),
+					scrollIntoView: true
+				});
+				view.focus();
+			};
+			dom.appendChild(row);
+		}
+	}
+
+	return { dom, top: false };
+}
+
+const usagesPanelTheme = EditorView.baseTheme({
+	'.cm-rhai-usages': {
+		background: '#0f172a',
+		color: '#e2e8f0',
+		borderTop: '1px solid #334155',
+		padding: '0.4rem 0.5rem',
+		maxHeight: '180px',
+		overflowY: 'auto',
+		fontSize: '0.85rem'
+	},
+	'.cm-rhai-usages-head': {
+		display: 'flex',
+		justifyContent: 'space-between',
+		alignItems: 'center',
+		color: '#94a3b8',
+		marginBottom: '0.25rem'
+	},
+	'.cm-rhai-usages-head button': {
+		background: 'transparent',
+		color: '#94a3b8',
+		border: 'none',
+		fontSize: '1rem',
+		cursor: 'pointer',
+		padding: '0 0.4rem'
+	},
+	'.cm-rhai-usages-row': {
+		display: 'flex',
+		gap: '0.5rem',
+		alignItems: 'baseline',
+		width: '100%',
+		background: 'transparent',
+		color: '#e2e8f0',
+		border: 'none',
+		textAlign: 'left',
+		padding: '0.15rem 0.25rem',
+		cursor: 'pointer',
+		fontFamily: 'inherit',
+		fontSize: 'inherit',
+		borderRadius: '0.25rem'
+	},
+	'.cm-rhai-usages-row:hover': {
+		background: '#1e293b'
+	},
+	'.cm-rhai-usages-line': {
+		color: '#64748b',
+		minWidth: '2.5rem',
+		flexShrink: 0
+	},
+	'.cm-rhai-usages-snip': {
+		fontFamily:
+			'ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace',
+		whiteSpace: 'nowrap',
+		overflow: 'hidden',
+		textOverflow: 'ellipsis'
+	}
+});
+
+function declAtCursor(view: EditorView, pos: number) {
+	const analysis = view.state.field(rhaiAnalysisField, false);
+	if (!analysis) return null;
+	return analysis.table.declOfUsageAt(pos);
+}
+
+export function gotoDefinition(view: EditorView): boolean {
+	const pos = view.state.selection.main.head;
+	const decl = declAtCursor(view, pos);
+	if (!decl) return false;
+	view.dispatch({
+		selection: EditorSelection.cursor(decl.nameRange.start),
+		scrollIntoView: true
+	});
+	return true;
+}
+
+export function findUsages(view: EditorView): boolean {
+	const pos = view.state.selection.main.head;
+	const analysis = view.state.field(rhaiAnalysisField, false);
+	if (!analysis) return false;
+	const decl = analysis.table.declOfUsageAt(pos);
+	if (!decl) return false;
+	view.dispatch({
+		effects: setUsagesPanel.of({
+			name: decl.name,
+			ranges: analysis.table.usagesOf(decl)
+		})
+	});
+	return true;
+}
+
+function closeUsagesPanel(view: EditorView): boolean {
+	if (!view.state.field(usagesPanelField, false)) return false;
+	view.dispatch({ effects: setUsagesPanel.of(null) });
+	return true;
+}
+
+const rhaiKeymap = keymap.of([
+	{ key: 'F12', run: gotoDefinition },
+	{ key: 'Shift-F12', run: findUsages },
+	{ key: 'Escape', run: closeUsagesPanel }
+]);
+
+// Ctrl+Click (Cmd+Click on macOS) on an identifier → jump to its decl.
+// Returning `true` suppresses CodeMirror's default selection behavior so
+// the click doesn't simultaneously place the caret at the click site.
+const ctrlClickHandler = EditorView.domEventHandlers({
+	mousedown(event, view) {
+		if (!(event.metaKey || event.ctrlKey) || event.button !== 0) return false;
+		const pos = view.posAtCoords({ x: event.clientX, y: event.clientY });
+		if (pos == null) return false;
+		const decl = declAtCursor(view, pos);
+		if (!decl) return false;
+		view.dispatch({
+			selection: EditorSelection.cursor(decl.nameRange.start),
+			scrollIntoView: true
+		});
+		event.preventDefault();
+		return true;
+	}
+});
+
 export function rhai(): LanguageSupport {
 	const extensions: Extension[] = [
 		rhaiAnalysisField,
+		usagesPanelField,
+		usagesPanelTheme,
+		rhaiKeymap,
+		ctrlClickHandler,
 		autocompletion({ override: [scopeCompletionSource, rhaiCompletions] })
 	];
 	return new LanguageSupport(rhaiLanguage, extensions);