[High] ClusterState 40-field God Struct needs decomposition

[piwi3910]

Codebase Review Round 2 — Finding #10

Severity: High
Location: config.rs:85-156

Problem

ClusterState is a 40-field flat struct that serves as the central configuration object. This "God Struct" anti-pattern makes the code hard to understand, test, and extend. Tests that construct ClusterState require 47 lines of boilerplate to set all fields.

Impact

• Adding new features requires modifying a 40+ field struct
• Test setup is verbose and fragile (any new field breaks all test constructors)
• No logical grouping makes it hard to understand which fields relate to which subsystem

Fix

• Decompose into logical sub-structs: TlsConfig, RateLimitConfig, WafConfig, MeshConfig, ObservabilityConfig, etc.
• Implement Default for each sub-struct to reduce test boilerplate
• ClusterState becomes a composition of these sub-structs