[tinker-cookbook] set_scope_context: add helper

[kennyyu]

This adds a helper to make it easier to set context when tracing, and changes the existing callsites to use the new helper.

[claude]

Claude finished @kennyyu's task —— View job

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Code Review Complete ✅

I've reviewed the PR that adds the set_scope_context helper function. This is a nice ergonomic improvement to the tracing utilities. Below are my findings:

Overview

The PR introduces a new helper function set_scope_context() in trace.py that simplifies setting trace context attributes. The existing callsites that were manually calling get_scope_context() and then updating attributes have been refactored to use this cleaner helper.

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✅ Strengths

1. Improved Ergonomics: The new helper reduces boilerplate from:

   context = get_scope_context()
   context.attributes["foo"] = value

   to:

   set_scope_context({"foo": value})

2. Consistent Implementation: The helper correctly uses update() to merge new attributes with existing ones, preserving any previously set values.

3. Comprehensive Refactoring: All existing callsites have been updated consistently across the codebase (checkpoint_utils.py:25, 80; distillation/train_on_policy.py:228; rl/train.py:812, 906; supervised/train.py:110, 118, 230, 290).

4. Test Coverage: The test file demonstrates both the old get_scope_context() pattern and the new set_scope_context() helper working together (test_trace.py:40).

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🔍 Observations & Minor Suggestions

1. Documentation Clarity (trace.py:410-422):

   • The docstring is concise and clear with a good example
   • Consider adding a note that set_scope_context merges with existing attributes rather than replacing them, since it uses update(). This could be helpful for users wondering what happens to previously set attributes.

   Example enhancement:

   def set_scope_context(values: dict[str, Any]) -> None:
       """Set the current scope's context. New values are merged with any existing
       attributes in the current scope.
       
       Example usage:
       
       @scope
       async def foo(step: int):
           set_scope_context({"step": step})
           set_scope_context({"extra": "value"})  # Both step and extra will be present
           await bar()
       """

2. Naming Consistency (trace.py:390-407):

   • The existing function is named get_scope_context() (returns the context object)
   • The new function is named set_scope_context() (updates attributes in the context)
   • There's a slight semantic mismatch: get_scope_context() returns a context object while set_scope_context() doesn't "set the context" but rather "updates the context attributes"
   • Consider if update_scope_context() might be more semantically accurate, though set_scope_context() is certainly shorter and clear enough in practice
   • This is a very minor naming observation and not a blocker

3. Type Safety (trace.py:419-421):

   • The assertion on line 420 is good for catching usage errors
   • The function assumes trace_context.get() will return a ScopeContext when decorated with @scope, which is correct
   • No issues here, just noting the safety check is appropriate

4. Refactoring Quality:

   • supervised/train.py:110, 118, 230, 290 - All properly refactored ✓
   • rl/train.py:812, 906 - Both uses look correct ✓
   • distillation/train_on_policy.py:228 - Proper usage ✓
   • checkpoint_utils.py:25, 80 - Clean refactoring ✓

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🎯 Test Coverage Review (test_trace.py)

The test file demonstrates both patterns:

• Line 40: Uses the new set_scope_context({"baz": "baz"}) helper
• Lines 18-20, 27-28: Uses the old get_scope_context() pattern

The test validates that attributes are correctly propagated to the trace events (lines 111-121), which confirms the helper works correctly.

Suggestion: Consider adding a test that explicitly validates the merging behavior of set_scope_context() when called multiple times in the same scope:

@scope
async def test_multiple_sets():
    set_scope_context({"first": "value1"})
    set_scope_context({"second": "value2"})
    # Both should be present in the end event

This would document and test the merge semantics.

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✅ Final Assessment

This is a clean, well-executed refactoring that improves code readability and reduces boilerplate. The implementation is correct, the refactoring is comprehensive, and the change is backward compatible (since get_scope_context() still exists for cases where direct access to the context object is needed).

Recommendation: Approve ✅

The only suggestions above are minor documentation enhancements and a potential test addition to explicitly validate merge behavior. None are blockers for merging.

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