add cursor rule (#2)

Co-authored-by: David Halim <david.halim@rakuten.com>

.cursor/rules/naming-conventions.mdc

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+---
+description: Naming conventions for value mappings in the Void project
+alwaysApply: true
+---
+
+# Naming Conventions
+
+## Mapping Types: `bOfA`
+
+All types/variables that map from a value **A** to a value **B** should be named **`bOfA`**.
+
+Examples:
+- A hashmap from `toolId` to `toolName` → `toolNameOfToolId`
+- A map from `userId` to `userEmail` → `userEmailOfUserId`
+- A map from `fileUri` to `fileContent` → `fileContentOfFileUri`
+
+```typescript
+// BAD
+const toolMap: Record<string, string> = {};
+const idToName = new Map<ToolId, ToolName>();
+
+// GOOD
+const toolNameOfToolId: Record<ToolId, ToolName> = {};
+const userEmailOfUserId = new Map<UserId, Email>();
+```

.cursor/rules/scope-and-validation.mdc

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+---
+description: Scope guardrails and validation policy for the Void project
+alwaysApply: true
+---
+
+# Scope & Validation
+
+## Modification Scope
+
+**Never** modify files outside `src/vs/workbench/contrib/void` without consulting with the user first.
+
+If a change appears to require touching files in other parts of the repo (e.g. core VSCode files, build configs, other contribs), pause and ask before editing.
+
+## Validation Policy
+
+Do **not** run anything to validate your changes. This includes:
+- `npm run`, `yarn`, `pnpm` build/test/lint scripts
+- `tsc`, `eslint`, or any type-checker / linter directly
+- Launching the app
+
+Instead, **tell the user what to run** to validate the changes, e.g.:
+
+> To validate, please run `npm run watch` and reload the Extension Host window.

.cursor/rules/typescript-conventions.mdc

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+---
+description: TypeScript conventions for the Void project
+globs: **/*.ts,**/*.tsx
+alwaysApply: false
+---
+
+# TypeScript Conventions
+
+## No Unnecessary Casting
+
+Do **NOT** cast to types if not necessary. **NEVER** lazily cast to `any`. Find the correct type to apply and use it.
+
+```typescript
+// BAD
+const result = (data as any).value;
+const node = something as MyType;
+
+// GOOD
+const result: ValueType = data.value;
+// If types genuinely don't line up, fix the source type or use a type guard:
+if (isMyType(something)) {
+  const node = something;
+}
+```
+
+## Semicolons
+
+Do **not** add or remove semicolons in existing files. Follow the existing convention of the file and make the **least** number of changes.

.cursor/rules/void-context.mdc

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+---
+description: Project context for the Void repo (a VSCode fork)
+alwaysApply: true
+---
+
+# Void Project Context
+
+This is a fork of the VSCode repo called **Void**.
+
+- Most code we care about lives in `src/vs/workbench/contrib/void`.
+- You may often need to explore the full repo to find relevant parts of code.
+- Look for existing services and built-in functions you might need to reuse instead of re-implementing functionality.