ADR-003: No Global Singleton for Application

Status: Active Date: 2026-05-01

Context

Many frameworks provide a global App variable or package-level init functions. This pattern is convenient but creates hidden state, complicates parallel test execution, and makes dependency tracing implicit.

Decision

app.Application is instance-scoped:

• NewApplication() always creates a new isolated instance.
• No package-global App variable.
• All dependencies (config, validator) are provided by the caller via explicit methods.
• Logger caches, route registrations, and runtime state are isolated per instance.

Consequences

• Multiple Application instances can coexist in the same process (e.g. integration tests).
• No hidden state between tests.
• Callers must wire dependencies explicitly — this is intentional.
• More verbose bootstrap code at the cost of clarity and testability.