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002. Immutable State Management
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Status
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Accepted

Context
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Application frameworks must manage global state including configuration,
platform directories, distribution information, and resource handles. Mutable
global state creates thread safety issues, debugging complexity, and unexpected
side effects.

Python's dataclass system provides immutable patterns, and accretive data
structures offer append-only dictionary implementations. The framework needs
predictable state management that supports concurrent access patterns.

Decision
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Use immutable dataclasses for all application state management. The ``Globals``
dataclass contains all framework state as immutable fields. Configuration is
stored as accretive dictionary objects that are immutable after assignment.
State updates create new instances rather than modifying existing ones.

Alternatives
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**Mutable global state with locking**
  - Rejected: Would require complex locking strategies and error-prone thread safety
  - Rejected: Would create debugging difficulties and unpredictable behavior

**Traditional singleton patterns**
  - Rejected: Would prevent testing with different configurations
  - Rejected: Would create hidden dependencies and coupling

**Context manager state isolation**
  - Rejected: Would complicate API and require complex context propagation
  - Considered but rejected due to integration complexity with CLI patterns

Consequences
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**Positive**
  - Thread safety guaranteed without explicit locking
  - Predictable behavior and easier debugging
  - State updates are explicit and traceable
  - Testing isolation through independent state instances
  - Clear dependency injection patterns

**Negative**
  - Slight memory overhead from creating new instances for updates
  - Learning curve for developers expecting mutable global state
  - Requires careful design of state update patterns

**Neutral**
  - Aligns with functional programming principles increasingly common in Python
  - Immutable patterns becoming standard in modern application frameworks