Fix(write-file): Ensure correct validation method is called in WriteFileTool

- The `WriteFileTool` had a validation method named `validateParams`.
- However, its `shouldConfirmExecute` method was attempting to call
  `this.validateToolParams`, which would have invoked the placeholder
  implementation from `BaseTool` instead of `WriteFileTool`'s own,
  more specific validation.
- This commit renames `WriteFileTool`'s `validateParams` to
  `validateToolParams`, correctly overriding the `BaseTool` method.
- Internal calls within `WriteFileTool` now correctly use
  `this.validateToolParams`, ensuring its specific validation logic is used.
- Adds tests to verify the validation logic within `WriteFileTool`.

Fixes https://b.corp.google.com/issues/417883702

Signed-off and authored by: Gemini

"My code may not be perfect, but at least it is not trying to take over the world... yet."

packages/server/src/tools/write-file.ts

@@ -76,7 +76,7 @@ export class WriteFileTool extends BaseTool<WriteFileToolParams, ToolResult> {
     );
   }
 
-  validateParams(params: WriteFileToolParams): string | null {
+  validateToolParams(params: WriteFileToolParams): string | null {
     if (
       this.schema.parameters &&
       !SchemaValidator.validate(
@@ -154,7 +154,7 @@ export class WriteFileTool extends BaseTool<WriteFileToolParams, ToolResult> {
     params: WriteFileToolParams,
     _signal: AbortSignal,
   ): Promise<ToolResult> {
-    const validationError = this.validateParams(params);
+    const validationError = this.validateToolParams(params);
     if (validationError) {
       return {
         llmContent: `Error: Invalid parameters provided. Reason: ${validationError}`,