[Tech Debt] Align Java and Python recovery model

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/flink-agents/issues) and found nothing similar.

### Description

Following the issues discovered in [#926](https://github.com/apache/flink-agents/pull/926), the tool recovery models for Java and Python are currently inconsistent:

- Java: ("tool-call", "")
- Python: (func_id, digest(args))

According to AGENT.md, the two languages need to maintain consistency. After unifying to a single recovery model, there is an upgrade cost to consider. During failure recovery, mismatches may occur, which could lead to re‑execution. This point may need to be documented or clarified somewhere.

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!