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/agent-session-runtime.ts

@@ -133,9 +133,6 @@ export class AgentSessionRuntime {
 	}
 
 	private apply(result: CreateAgentSessionRuntimeResult): void {
-		if (process.cwd() !== result.services.cwd) {
-			process.chdir(result.services.cwd);
-		}
 		this._session = result.session;
 		this._services = result.services;
 		this._diagnostics = result.diagnostics;
@@ -346,9 +343,6 @@ export async function createAgentSessionRuntime(
 ): Promise<AgentSessionRuntime> {
 	assertSessionCwdExists(options.sessionManager, options.cwd);
 	const result = await createRuntime(options);
-	if (process.cwd() !== result.services.cwd) {
-		process.chdir(result.services.cwd);
-	}
 	return new AgentSessionRuntime(
 		result.session,
 		result.services,