Large language model agents increasingly externalize procedural knowledge into reusable skills: invocable code, natural-language procedures, SKILL.md packages, graphs, or parametric adapters. This externalization turns adaptation into a new learning problem. The agent does not only update its prompt or weights; it updates a library of artifacts that changes what future policies can retrieve, compose, execute, and trust. This survey studies the rapidly growing 2023-2026 literature on dynamic or self-evolving skill systems and argues that such systems are best understood as lifecycle-managed, verified, evolving artifact stores for LLM agents. We extend the options-based skill formalism to a seven-tuple that makes edits, admission verification, and provenance explicit, and we lift it to library-level dynamics driven by a ten-operator algebra (Add, Refine, Merge, Split, Prune, Distill, Abstract, Compose, Rewrite, Rerank). Using this formalism, we organize a 94-paper modern audit set of dynamic-skill and boundary/context papers around a skill lifecycle: evidence acquisition, proposal, verification/admission, organization, retrieval/composition, maintenance/repair, distillation/portability, and governance. The resulting taxonomy separates artifact families, update loci, assurance models, storage topologies, maintenance regimes, and governance maturity without reducing the field to a list of systems. We then synthesize the mechanisms that make lifecycle-managed stores improve: edit repertoires, admission gates, storage/retrieval structure, and fast-slow update clocks. The most consistent evidence is that admission and repair matter more than raw skill count, verifier quality is often load-bearing in skill-aware RL, flat retrieval degrades in the moderate-library-size regime, and benchmarks still under-report library trajectories. We close with a research agenda for compositional verifiers, maintenance schedules, registry-scale retrieval, cross-library portability, provenance, and lifecycle-aware evaluation.