fix(exec): skip gateway cwd injection for remote node host

When exec runs with host=node and no explicit cwd is provided, the
gateway was injecting its own process.cwd() as the default working
directory. In cross-platform setups (e.g. Linux gateway + Windows node),
this gateway-local path does not exist on the node, causing
"SYSTEM_RUN_DENIED: approval requires an existing canonical cwd".

This change detects when no explicit workdir was provided (neither via
the tool call params.workdir nor via agent defaults.cwd) and passes
undefined instead of the gateway cwd. This lets the remote node use its
own default working directory.

Changes:
- bash-tools.exec.ts: Track whether workdir was explicitly provided;
  when host=node and no explicit workdir, pass undefined instead of
  gateway process.cwd()
- bash-tools.exec-host-node.ts: Accept workdir as string | undefined;
  only send cwd to system.run.prepare when defined
- bash-tools.exec-approval-request.ts: Accept workdir as
  string | undefined in HostExecApprovalParams

Fixes #58934

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/agents/bash-tools.exec-host-node.ts

@@ -35,7 +35,7 @@ import { listNodes, resolveNodeIdFromList } from "./tools/nodes-utils.js";
 
 export type ExecuteNodeHostCommandParams = {
   command: string;
-  workdir: string;
+  workdir: string | undefined;
   env: Record<string, string>;
   requestedEnv?: Record<string, string>;
   requestedNode?: string;
@@ -108,7 +108,7 @@ export async function executeNodeHostCommand(
       params: {
         command: argv,
         rawCommand: params.command,
-        cwd: params.workdir,
+        ...(params.workdir != null ? { cwd: params.workdir } : {}),
         agentId: params.agentId,
         sessionKey: params.sessionKey,
       },
@@ -121,7 +121,7 @@ export async function executeNodeHostCommand(
   }
   const runArgv = prepared.plan.argv;
   const runRawCommand = prepared.plan.commandText;
-  const runCwd = prepared.plan.cwd ?? params.workdir;
+  const runCwd = prepared.plan.cwd ?? params.workdir ?? undefined;
   const runAgentId = prepared.plan.agentId ?? params.agentId;
   const runSessionKey = prepared.plan.sessionKey ?? params.sessionKey;
 
@@ -453,3 +453,4 @@ export async function executeNodeHostCommand(
     } satisfies ExecToolDetails,
   };
 }
+