Add Rust-extension state-machine guidance

[leynos]

Summary

• add the state-machine modelling guidance to generated AGENTS.md files when
  use_rust enables the Rust extension
• distinguish caller-driven typestate from parser-, frame-, socket-, channel-,
  and scheduler-driven runtime ADTs
• require state owners to encapsulate correlated transitions and mandatory
  finalization
• preserve ordinary booleans for independent observations
• add a regression test proving the wording appears in Rust-enabled renders and
  remains absent from Python-only renders

Scope

The guidance sits entirely inside the existing {% if use_rust %} block. Pure
Python projects therefore retain their current generated instructions.

Validation

• reviewed the two-file branch diff and conditional placement through the
  GitHub connector
• added a parameterized render test for both use_rust = false and
  use_rust = true
• no local repository checkout was available in this session; draft PR CI should
  run the parent-template test, lint, type-check, Markdown, and spelling gates

Summary by Sourcery

Guide Rust-enabled projects toward explicit, well-encapsulated state-machine designs in generated AGENTS.md files.

New Features:

• Add Rust-extension guidance for modelling state machines, choosing between typestate and runtime ADTs, encapsulating transitions and finalization, and retaining independent booleans.

Enhancements:

• Scope the new guidance to generated AGENTS.md files for Rust-enabled projects while preserving Python-only output.

Tests:

• Add parameterized render coverage confirming the guidance appears only when the Rust extension is enabled.

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[sourcery-ai]

Reviewer's Guide

The PR extends the Rust-only section of the AGENTS.md template with guidance for modelling state machines, choosing caller-driven typestate versus runtime ADTs, and encapsulating transitions and cleanup. A parameterized render test verifies that all guidance appears when use_rust is enabled and remains absent for Python-only projects.

Flow diagram for Rust-only state-machine guidance rendering

flowchart TD
    Render[Render AGENTS.md template] --> RustCheck{use_rust enabled?}
    RustCheck -->|yes| Guidance[Include state-machine modelling guidance]
    RustCheck -->|no| PythonOnly[Retain Python-only instructions]
    Guidance --> Typestate[Choose caller-driven typestate when applicable]
    Guidance --> RuntimeADT[Choose runtime ADT for parser, frame, socket, channel, or scheduler transitions]
    Guidance --> Encapsulation[Encapsulate correlated transitions and finalization]
    Guidance --> Booleans[Keep independent observations as booleans]

Loading

File-Level Changes

Change	Details	Files
Add Rust-specific state-machine modelling guidance to the generated agent instructions.	Explain when to use enums, typestate, runtime ADTs, or runtime stacks based on transition ownership. Require state owners to encapsulate correlated transitions and mandatory cleanup. Clarify that independent observations should remain booleans.	template/AGENTS.md.jinja
Verify the guidance is rendered only for Rust-enabled projects.	Add a parameterized Copier render test covering both Rust-enabled and Python-only configurations. Assert each guidance fragment is present or absent according to the use_rust setting.	tests/test_agents_state_machine_guidance.py

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