chore: automates session tracing context

[rchardx]

Description

Removes manual session identifiers from phase scopes so they resolve from contextvars. Introduces a decorator to register sessions per sample when a task is active and applies it to rollout workflows to streamline tracing. Refreshes profiling guidance and tests to match the new implicit session workflow.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not
  work as expected)
• Documentation update
• Code refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Checklist

• I have read the Contributing Guide
• I have run formatting tools (pre-commit or manual)
• I have run relevant unit tests and they pass
• I have added tests for new functionality
• I have updated documentation if needed
• My branch is up to date with main
• This PR introduces breaking changes (if yes, fill out details below)
• If this PR changes documentation, I have built and previewed it locally with
  jb build docs
• No critical issues raised by AI reviewers (/gemini review)

Breaking Change Details (if applicable):

Additional Context

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[gemini-code-assist]

Summary of Changes

Hello @rchardx, 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 refactors the performance tracing mechanism to automate the management of session identifiers. By leveraging Python's contextvars, it eliminates the need for manual session_id passing in tracing functions and context managers. This change simplifies the API for developers, making it easier to integrate session tracing into workflows, particularly for individual samples within a larger task, without altering core functionality.

Highlights

• Automated Session Tracing Context: Manual session identifiers have been removed from phase scopes, allowing them to resolve implicitly from contextvars.
• New session_context Decorator: A new decorator, session_context, has been introduced to automatically register sessions per sample when a task is active, streamlining tracing workflows.
• Simplified Tracing API: The trace_session_phase and atrace_session_phase context managers no longer require explicit session_id arguments, fetching it automatically from the context.
• Updated Rollout Workflows: Rollout workflows (rlvr.py, vision_rlvr.py) now utilize the session_context decorator on their _collect_samples methods, simplifying session management.
• Documentation and Test Refresh: Profiling guidance and tests have been updated to align with the new implicit session workflow, ensuring clarity and correctness.

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[gemini-code-assist]

Code Review

This pull request introduces a significant improvement to the session tracing mechanism by automating context management with contextvars. The new @session_context decorator and the updated trace_session_phase/atrace_session_phase functions greatly simplify the tracing API, removing the need for manual session ID propagation. The changes are well-implemented across the tracer utility, workflow files, and documentation. My review includes a couple of minor suggestions to improve code clarity in the updated tests by removing redundant try...finally blocks.

[Copilot]

Pull Request Overview

This PR streamlines session tracing by automating context management for session identifiers. The changes eliminate manual session registration code in workflow methods, replacing it with a new @session_context() decorator that automatically handles session creation and context population from the active task. This reduces boilerplate and makes the tracing API more intuitive.

• Introduced session_context() decorator to automatically register sessions per sample invocation
• Simplified atrace_session_phase() and trace_session_phase() APIs to no longer require explicit session_id parameters
• Updated rollout workflows (RLVRWorkflow and VisionRLVRWorkflow) to use the new decorator-based approach

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
areal/utils/perf_tracer.py	Added session_context() decorator factory and updated phase tracing context managers to automatically retrieve session_id from context
areal/workflow/rlvr.py	Applied @session_context() decorator to _collect_samples method and removed manual session registration code
areal/workflow/vision_rlvr.py	Applied @session_context() decorator to _collect_samples method and removed manual session registration code
areal/tests/test_perf_tracer.py	Updated tests to use new API where phase context managers no longer require session_id parameter
docs/best_practices/perf_profiling.md	Refreshed documentation with examples of the new decorator-based workflow and updated API signatures

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[rchardx]

/gemini review

[gemini-code-assist]

Code Review

This pull request is a well-executed refactoring that automates session tracing context using contextvars. The introduction of the @session_context decorator is a significant improvement, as it removes boilerplate code from workflows and makes the tracing mechanism more implicit and easier to use. The changes are applied consistently, and the updates to tests and documentation are thorough and clear. Overall, this is a great enhancement to the codebase's maintainability. I have a couple of minor suggestions to improve docstring consistency.

[Copilot]

Pull Request Overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

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[garrett4wade]

LGTM