feat(dashboard): hand-rolled Rhai parser + symbol table + Vitest

Foundation for upcoming editor features (scope-aware autocomplete,
goto-def / find-usages, source formatter). Hand-rolled recursive
descent in TypeScript with Pratt precedence climbing for expressions,
error-tolerant so partial trees stay usable while the user is typing.
Symbol table walks the AST to produce per-scope declarations, usage
sites, and object-literal field maps. Vitest added as a dev-only
runner; no editor wiring in this commit.

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

dashboard/src/lib/rhai/ast.ts

@@ -0,0 +1,275 @@
+// AST node definitions for the dashboard's hand-rolled Rhai parser.
+//
+// Every node carries `start` / `end` byte offsets into the source so the
+// editor features (autocomplete, goto-def, find-usages, format) can map
+// between positions in the document and nodes in the tree.
+//
+// The shape mirrors the Rhai book grammar (https://rhai.rs/book/language/)
+// but simplified: type annotations are absent (Rhai is dynamic), and
+// statement-vs-expression duality is collapsed by letting `if` / `switch` /
+// block expressions appear in both positions (an `ExprStmt` wrapper turns
+// any expression into a statement).
+
+export interface Range {
+	start: number;
+	end: number;
+}
+
+// ---------------------------------------------------------------------------
+// Comments — captured by the lexer with their positions and re-emitted by
+// the formatter. Kept off the AST tree so they don't clutter walkers.
+// ---------------------------------------------------------------------------
+
+export interface Comment extends Range {
+	kind: 'LineComment' | 'BlockComment';
+	text: string;
+}
+
+// ---------------------------------------------------------------------------
+// Statements
+// ---------------------------------------------------------------------------
+
+export type Stmt =
+	| LetStmt
+	| ConstStmt
+	| FnDecl
+	| ExprStmt
+	| ReturnStmt
+	| WhileStmt
+	| LoopStmt
+	| ForStmt
+	| BreakStmt
+	| ContinueStmt
+	| TryStmt;
+
+export interface LetStmt extends Range {
+	kind: 'Let';
+	name: string;
+	nameRange: Range;
+	init: Expr | null;
+}
+
+export interface ConstStmt extends Range {
+	kind: 'Const';
+	name: string;
+	nameRange: Range;
+	init: Expr | null;
+}
+
+export interface Param extends Range {
+	name: string;
+}
+
+export interface FnDecl extends Range {
+	kind: 'FnDecl';
+	name: string;
+	nameRange: Range;
+	params: Param[];
+	body: BlockExpr;
+}
+
+export interface ExprStmt extends Range {
+	kind: 'ExprStmt';
+	expr: Expr;
+	// Whether the statement is terminated with `;`. Block-form expressions
+	// (`if`/`switch`/`{...}`) don't require it; everything else does.
+	semi: boolean;
+}
+
+export interface ReturnStmt extends Range {
+	kind: 'Return';
+	value: Expr | null;
+}
+
+export interface WhileStmt extends Range {
+	kind: 'While';
+	cond: Expr;
+	body: BlockExpr;
+}
+
+export interface LoopStmt extends Range {
+	kind: 'Loop';
+	body: BlockExpr;
+}
+
+export interface ForStmt extends Range {
+	kind: 'For';
+	varName: string;
+	varRange: Range;
+	iter: Expr;
+	body: BlockExpr;
+}
+
+export interface BreakStmt extends Range {
+	kind: 'Break';
+}
+
+export interface ContinueStmt extends Range {
+	kind: 'Continue';
+}
+
+export interface TryStmt extends Range {
+	kind: 'Try';
+	body: BlockExpr;
+	catchVar: string | null;
+	catchVarRange: Range | null;
+	handler: BlockExpr;
+}
+
+// ---------------------------------------------------------------------------
+// Expressions
+// ---------------------------------------------------------------------------
+
+export type Expr =
+	| IdentExpr
+	| NumberExpr
+	| StringExpr
+	| BoolExpr
+	| NullExpr
+	| CallExpr
+	| MemberExpr
+	| IndexExpr
+	| UnaryExpr
+	| BinaryExpr
+	| AssignExpr
+	| ParenExpr
+	| ObjectMapExpr
+	| ArrayExpr
+	| FnExpr
+	| IfExpr
+	| SwitchExpr
+	| BlockExpr;
+
+export interface IdentExpr extends Range {
+	kind: 'Ident';
+	name: string;
+}
+
+export interface NumberExpr extends Range {
+	kind: 'Number';
+	raw: string;
+}
+
+export interface StringExpr extends Range {
+	kind: 'String';
+	// The surrounding quote — `"` is escape-processed, backtick is raw and
+	// may span multiple lines. We don't decode escapes; the formatter just
+	// preserves the raw text between the quotes.
+	quote: '"' | '`';
+	raw: string;
+}
+
+export interface BoolExpr extends Range {
+	kind: 'Bool';
+	value: boolean;
+}
+
+export interface NullExpr extends Range {
+	kind: 'Null';
+}
+
+export interface CallExpr extends Range {
+	kind: 'Call';
+	callee: Expr;
+	args: Expr[];
+}
+
+export interface MemberExpr extends Range {
+	kind: 'Member';
+	object: Expr;
+	property: string;
+	propertyRange: Range;
+}
+
+export interface IndexExpr extends Range {
+	kind: 'Index';
+	object: Expr;
+	index: Expr;
+}
+
+export interface UnaryExpr extends Range {
+	kind: 'Unary';
+	op: string;
+	operand: Expr;
+}
+
+export interface BinaryExpr extends Range {
+	kind: 'Binary';
+	op: string;
+	left: Expr;
+	right: Expr;
+}
+
+export interface AssignExpr extends Range {
+	kind: 'Assign';
+	op: string; // = += -= *= /= %= ??=
+	target: Expr;
+	value: Expr;
+}
+
+export interface ParenExpr extends Range {
+	kind: 'Paren';
+	expr: Expr;
+}
+
+export interface ObjectMapEntry extends Range {
+	key: string;
+	keyRange: Range;
+	value: Expr;
+}
+
+export interface ObjectMapExpr extends Range {
+	kind: 'ObjectMap';
+	entries: ObjectMapEntry[];
+}
+
+export interface ArrayExpr extends Range {
+	kind: 'Array';
+	elements: Expr[];
+}
+
+export interface FnExpr extends Range {
+	kind: 'FnExpr';
+	params: Param[];
+	body: BlockExpr;
+}
+
+export interface IfExpr extends Range {
+	kind: 'IfExpr';
+	cond: Expr;
+	then: BlockExpr;
+	// else branch: either a block or another `if` for `else if` chains.
+	else_: BlockExpr | IfExpr | null;
+}
+
+export interface SwitchArm extends Range {
+	pattern: Expr | null; // null = `_` default case
+	guard: Expr | null;
+	value: Expr;
+}
+
+export interface SwitchExpr extends Range {
+	kind: 'SwitchExpr';
+	subject: Expr;
+	arms: SwitchArm[];
+}
+
+export interface BlockExpr extends Range {
+	kind: 'BlockExpr';
+	stmts: Stmt[];
+}
+
+// ---------------------------------------------------------------------------
+// Top-level parse output
+// ---------------------------------------------------------------------------
+
+export interface ParseError extends Range {
+	message: string;
+}
+
+export interface ParseResult {
+	source: string;
+	program: BlockExpr;
+	errors: ParseError[];
+	comments: Comment[];
+}