docs: document re-entrancy and integration constraints

[siphonite]

Summary

Documents what FIRST v0.1 does NOT support, so users don't infer guarantees that don't exist.

Changes

docs/limitations.md

Add new "Integration Constraints (v0.1)" section:

• One first::test() per #[test]
• Async tests not supported
• Not thread-safe
• No nested workspaces

src/lib.rs

Add limitations summary to crate documentation.

Verification

• cargo fmt -- --check ✅
• cargo clippy -- -D warnings ✅
• cargo test --doc ✅

Closes #18

[gemini-code-assist]

Summary of Changes

Hello @siphonite, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the documentation for the FIRST testing framework by clearly outlining its current limitations and integration constraints for version 0.1. The primary goal is to prevent users from inferring unsupported guarantees, thereby improving the clarity and robustness of the framework's usage guidelines. This ensures that developers understand the specific scenarios where FIRST can and cannot be effectively applied, particularly concerning re-entrancy, asynchronous testing, thread safety, and workspace management.

Highlights

• Integration Constraints Documentation: Added a new, comprehensive section to docs/limitations.md detailing integration constraints for FIRST v0.1, clarifying supported and unsupported usage patterns with rationales.
• Crate-Level Limitations Summary: Updated the src/lib.rs crate documentation to include a high-level summary of key limitations, directing users to the detailed docs/limitations.md for more information.
• Specific Limitations Clarified: Explicitly documented that first::test() should be used once per #[test], async tests are not supported, the framework is not thread-safe, and nested workspaces are not managed by FIRST.

Changelog

• docs/limitations.md
  • Introduced a new section titled "Integration Constraints (v0.1)".
  • Detailed specific patterns for first::test() usage, async test support, thread safety, and nested workspaces.
  • Provided clear "Supported" (✅) and "Undefined/Not supported" (❌) statuses for each pattern, along with rationales for the limitations.
• src/lib.rs
  • Added a new "Limitations (v0.1)" section to the crate-level documentation.
  • Listed key limitations including: one first::test() per #[test], no async tests, not thread-safe, and no nested workspaces.
  • Included a reference to docs/limitations.md for complete details on these limitations.

Activity

• No human activity (comments, reviews, etc.) has been recorded on this pull request since its creation.

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[gemini-code-assist]

Code Review

This pull request adds important documentation regarding the limitations and integration constraints of the FIRST framework. The changes are clear and add value by setting correct user expectations. I've provided a couple of minor suggestions to improve the consistency and completeness of the new documentation.

[gemini-code-assist]

This section is missing a rationale, unlike the other sections under 'Integration Constraints'. Adding a rationale would improve clarity for users and maintain consistency in the document. The limitation seems to be due to global state like environment variables and a fixed temporary directory.

Suggested change

	### No Nested Workspaces
	| Pattern | Status |
	|---------|--------|
	| User-managed dirs inside `env.path()` | ✅ Supported |
	| Expecting FIRST to manage nested isolation | ❌ Not supported |
	### No Nested Workspaces
	| Pattern | Status |
	|---------|--------|
	| User-managed dirs inside `env.path()` | ✅ Supported |
	| Expecting FIRST to manage nested isolation | ❌ Not supported |
	**Rationale**: FIRST relies on global resources like environment variables and a fixed base directory (`/tmp/first`) for orchestration. Nested test environments would conflict over these resources, leading to undefined behavior.