fix(coding-agent): remove process-cwd tool singletons and use tool-name allowlists

- switch SDK/CLI tool selection to name-based allowlists
- apply allowlists across built-in, extension, and SDK tools
- remove ambient process.cwd defaults from core tooling and resource helpers
- update tests, examples, and TUI callers for explicit cwd plumbing
- add regression coverage for extension tool filtering

closes #3452
closes #2835

packages/coding-agent/src/core/system-prompt.ts

@@ -16,8 +16,8 @@ export interface BuildSystemPromptOptions {
 	promptGuidelines?: string[];
 	/** Text to append to system prompt. */
 	appendSystemPrompt?: string;
-	/** Working directory. Default: process.cwd() */
-	cwd?: string;
+	/** Working directory. */
+	cwd: string;
 	/** Pre-loaded context files. */
 	contextFiles?: Array<{ path: string; content: string }>;
 	/** Pre-loaded skills. */
@@ -25,7 +25,7 @@ export interface BuildSystemPromptOptions {
 }
 
 /** Build the system prompt with tools, guidelines, and context */
-export function buildSystemPrompt(options: BuildSystemPromptOptions = {}): string {
+export function buildSystemPrompt(options: BuildSystemPromptOptions): string {
 	const {
 		customPrompt,
 		selectedTools,
@@ -36,7 +36,7 @@ export function buildSystemPrompt(options: BuildSystemPromptOptions = {}): strin
 		contextFiles: providedContextFiles,
 		skills: providedSkills,
 	} = options;
-	const resolvedCwd = cwd ?? process.cwd();
+	const resolvedCwd = cwd;
 	const promptCwd = resolvedCwd.replace(/\\/g, "/");
 
 	const now = new Date();