Mutable defaults fixes

[tempusfrangit]

Python's mutable default footgun (shared mutable objects across function calls)
was not being caught in Cog runtime, leading to subtle bugs where predictors with
default=[] would share the same list instance across predictions.

Replace error-throwing validation with automatic conversion of mutable defaults
to safe default_factory implementations. This prevents the footgun while
maintaining backward compatibility and requiring no code changes.

Automatic Conversion Logic:

• Empty collections: [] → default_factory=list, {} → default_factory=dict
• Populated collections: [1,2,3] → default_factory=lambda: copy.deepcopy([1,2,3])
• Custom objects: MyObj() → default_factory=lambda: copy.deepcopy(MyObj())
• Immutable types: No conversion needed (strings, numbers, tuples, etc.)

Collection Type Support:

• Lists: list, List[T], list[T] (Python 3.9+)
• Dicts: dict, Dict[K,V], dict[K,V] (Python 3.9+)
• Sets: set, Set[T], set[T] (Python 3.9+)
• Custom objects: Any mutable object not in allowlist

Implementation:

• Use real dataclass.Field objects with proper default_factory
• Automatic conversion happens at import time in Input() function
• Runtime properly executes factories to create fresh instances per prediction
• Full isolation verified with E2E tests

Testing & Validation:

• Updated all tests to verify auto-conversion instead of error cases
• New E2E test verifies no state leakage between predictions
• Python 3.9-3.13 compatibility maintained
• Go integration tests updated for new behavior

Before (silent footgun):

def predict(self, items: List[str] = Input(default=[])) -> str:
    items.append("new")  # Modifies shared list across predictions!
    return str(items)

After (automatic fix):

  def predict(self, items: List[str] = Input(default=[])) -> str:
      items.append("new")  # Safe: auto-converted to fresh list each time
      return str(items)   # No code changes required!

Prevents mutable default footgun with zero breaking changes to existing code.

This accurately describes what we actually implemented - automatic conversion rather than validation errors.

[Copilot]

Pull Request Overview

This PR implements comprehensive mutable defaults validation for the Cog runtime to prevent Python's mutable default footgun where shared mutable objects across function calls can cause subtle bugs. The implementation adds import-time validation that hard errors on mutable defaults and suggests proper default_factory usage, with comprehensive support for all collection types in both Python 3.9+ and typing module syntax.

• Added comprehensive mutable defaults validation to the Input() function with clear error messages
• Enhanced type system to support all collection types including sets and bare types like list→List[Any]
• Implemented proper default_factory support using real dataclass.Field objects
• Fixed compatibility issues across Python versions 3.9-3.13

Reviewed Changes

Copilot reviewed 30 out of 32 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
python/coglet/api.py	Added mutable default validation and default_factory parameter to Input() function
python/coglet/adt.py	Enhanced type system for collection types and added PrimitiveType.ANY
python/coglet/schemas.py	Fixed Secret schema encoding with proper Field object handling
python/coglet/inspector.py	Enhanced Field object handling in validation and runtime execution
python/cog/coder/set_coder.py	Added new SetCoder for set type support
python/cog/coder/json_coder.py	Enhanced JsonCoder for Python 3.13 compatibility
python/cog/coder/pydantic_coder.py	Fixed BaseModelCoder for generic type compatibility
python/tests/test_input_function.py	Added comprehensive mutable defaults validation tests
python/tests/test_input_functional.py	Updated test to use default_factory instead of mutable default
python/tests/schemas/*.py	Updated all schema test files to use default_factory for mutable defaults
python/tests/runners/*.py	Added collection type test files and updated existing ones
python/tests/cases/repetition.py	Updated to use default_factory for list default
python/tests/bad_predictors/*.py	Updated test files to use default_factory for mutable defaults
internal/tests/input_defaults_test.go	Added Go integration tests for mutable default validation

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[Copilot]

Pull Request Overview

Copilot reviewed 30 out of 32 changed files in this pull request and generated 2 comments.

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[michaeldwan]

Code good, but be warned, I have less than zero experience with this aspect of python 😬

Let's talk about the question I raised about failing vs best-effort correcting.

[Copilot]

Pull Request Overview

Copilot reviewed 31 out of 33 changed files in this pull request and generated 2 comments.

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[michaeldwan]

looks good, I like the new behavior!