Treat any change to a public interface (PDK function signatures, plugin config/schema fields, or other externally-consumed API contracts) as a compatibility commitment.

Do

• Avoid expanding public API surface unless the benefit is clear and the tradeoffs are acceptable.
• If a function signature must change, append new parameters at the end (never insert in the middle) to preserve positional-arg compatibility.
• For schema/config additions: require a compatibility plan—discussion/approval, changelog entry, and any related compatibility/removed-fields plumbing (and tests that validate the schema).

Don’t

• Don’t add new public parameters that “paint you into a corner” without a strong necessity.
• Don’t change schema semantics/config options without coordinating compatibility artifacts.

Example (signature change rule)

-- Before
function compose_tags(service_name, status, consumer_id, tags, conf) end

-- After (append new param at the end)
function compose_tags(service_name, status, consumer_id, tags, conf, route_name) end

Apply this checklist whenever a change touches externally-defined contracts: if users (or other plugins) might call it, update it with backward compatibility as the default and a documented migration/compat story.