v2.6.1

• [Enhancement] Speed up Contract#call by ~1.25x for minimal and ~1.4x for fully populated data: resolve rule paths with a single Hash#fetch per level instead of key? + [], inline the per-rule type dispatch into the rules loop, and compare the dig sentinel via #equal? so #== is never dispatched to the validated (user-provided) values. This is the per-message validation path in WaterDrop producers.
• [Fix] Contract#call with rule paths of 3+ keys no longer raises NoMethodError when an intermediate value is not a Hash and reports the path as missing instead, consistent with the 2-key path behavior.
• [Change] Reject reserved setting names with an ArgumentError in Configurable::Node#setting and #register: internal state names (node_name, children, nestings, compiled, configs_refs, local_defs) and the node public API names (setting, configure, to_h, deep_dup, register, compile). Previously such names silently shadowed the node own accessors, breaking deep_dup or to_h, and assignments like config.children = value corrupted the node internal state.
• [Enhancement] Skip the event name mapping hash lookup in Monitor#instrument when no namespace is used and the event id is already a String, which is the case for all events in the Karafka ecosystem (~1.2x faster dispatch on the common no-subscribers path). Symbol event ids and namespaced monitors keep going through the mapping.
• [Enhancement] Mirror config values into instance variables and use attr_reader based readers in Configurable::Node, yielding ~1.4x faster flat and ~1.6x faster nested settings reads on hot paths. @configs_refs remains the canonical store; non-identifier setting names (e.g. registered names with dashes) keep the previous hash-based accessors.
• [Enhancement] Instantiate each Configurable::Node through a per-layout anonymous subclass so the ivar-backed settings do not grow object shape variations on the shared Node class (which would degrade ivar access and trigger Ruby performance warnings). deep_dup reuses the template's subclass, so duplicated configs share object shapes.
• [Fix] Symbolize setting names at definition time (setting, same as register) and on config store writes so String setting names work end to end (accessors, #to_h, recompilation state) and cannot corrupt node internal state when matching reserved internal names (previously string-named settings were quietly broken as accessors and the store disagreed on the key type).
• [Change] Config nodes are now instances of anonymous Node subclasses: is_a?(Karafka::Core::Configurable::Node) still holds, but instance_of?(Node) is now false and node.class.name is nil.
• [Change] Assigning a setting on a frozen config node now raises FrozenError (previously the write silently mutated internal storage despite the freeze).