`create_agent` should support bounded forced retry after tool invocation validation errors

### Privileged issue - [x] I am a LangChain maintainer, or was asked directly by a LangChain maintainer to create an issue here. ### Issue Content Deep Agents issue langchain-ai/deepagents#947 reports a failure mode where a model emits a malformed client-side tool call, `ToolNode` correctly converts the resulting Pydantic validation failure into an error `ToolMessage`, but the next model turn is allowed to answer in plain text instead of being forced to retry the corrected tool call. Example failures from the downstream report: - `task` called without required `subagent_type` - filesystem tools called with `path` instead of schema field `file_path` Current flow: 1. The model emits a tool call with invalid args. 2. `ToolNode._execute_tool_sync` / `_execute_tool_async` catches `ValidationError` and wraps it in `ToolInvocationError`. 3. The default tool error handler converts that into a `ToolMessage(status="error")` with text like `Please fix the error and try again.` 4. The agent loop sends that observation back to the model. 5. The model may respond with plain text containing corrected JSON rather than making the corrected tool call. 6. Because the response has no tool calls, it is treated as the final answer and leaks incorrect implementation details to the user. This is not about failing to detect validation errors — `ToolInvocationError` already provides the right retryable signal. The missing behavior is an agent-loop policy for retryable tool invocation/schema failures. Potential design: - Preserve or expose structured information that a prior tool error was a `ToolInvocationError` wrapping a Pydantic validation failure, rather than requiring consumers to parse `ToolMessage.content`. - Add an opt-in or default bounded retry path in `create_agent` that, after a retryable tool invocation validation failure, forces the next model call to use the same tool via `ModelRequest.tool_choice` / `bind_tools(..., tool_choice=...)`. - Track a retry budget to avoid loops. - …