Update sample code for: LangGraph Tutorial: Build Stateful AI Agents in Python by martin-martin · Pull Request #784 · realpython/materials

…in Python

Refresh the LangGraph companion code for the tutorial update:
- Bump to langgraph 1.2.5, langchain-openai 1.3.2, langchain-core 1.4.7,
  pydantic 2.13.4 (regenerated requirements.txt; pyproject floors raised)
- Switch the model to gpt-5.4-nano
- Fix check_escalation_status_node to fall back to 0 when no fine is
  extracted (avoids a TypeError on notices without a max potential fine)
- Store the boolean answer.is_true in follow_ups (was storing the model object)
- Drop the unused critical_fields_missing key from the agent's initial state
- Point the README API-key link at platform.openai.com/api-keys and match
  the new tutorial title

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

The companion emails still used 2024/2025 dates while the tutorial's
examples and REPL transcripts use 2026. Update Email 0 (May 15 / June 10,
2026) and Email 3 (June 10 / August 5, 2026) so extracted dates match the
tutorial output.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>