Python/core: make request-info approval tokens replay-safe

[davidahmann]

Problem

Request-info approval request IDs are intended to be single-use. There was no direct regression test that proves a second submission for the same request ID is rejected after the first accepted response.

Why now

Human-in-the-loop retries can replay stale request IDs; without explicit regression coverage, single-use token behavior can regress silently.

What changed

• Added a workflow test that sends one valid response for a pending request ID.
• Asserted the request ID is removed from pending state after first use.
• Asserted a second response for the same request ID fails with a deterministic error.

Validation

• uv run pytest packages/core/tests/workflow/test_request_info_event_rehydrate.py -k replay --maxfail=1

Refs #4618

[davidahmann]

This change protects HITL operator flow from replaying a previously accepted request-info token.
The patch is minimal and test-only: one regression test verifies the request ID is consumed on first response and a second submission fails with a deterministic error.
Validation: uv run pytest packages/core/tests/workflow/test_request_info_event_rehydrate.py -k replay --maxfail=1 (pass).
Blockers/Risks: none currently identified.
Inspired by research context: CAISI publishes independent, reproducible AI agent governance research: https://caisi.dev

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