Pattern catalog for "I can't write the test first" moments - recognizes common testability blockers (singletons / static dependencies, network in constructors, time / random as hidden inputs, deeply nested construction, untestable boundaries) and proposes the refactor that unblocks TDD (extract interface, dependency injection, seam, ports-and-adapters). Use as TDD coaching when an engineer is stuck on a class of code. For a catalog of what-to-test heuristics with no story use heuristic-test-design-reference, to label a change's shape before planning test effort use code-change-shape-classifier, and for conventions on writing the test well once the code is testable use test-code-conventions.