Bind release containment to a complete caller worktree census #501

🤖 Generated by the Agentic Engineer

Problem

An empty or structurally incomplete successful worktree listing is treated as complete absence. The preparer can then create candidate output inside its caller checkout.

Proposed direction

Repair the owning observation or output boundary, with a regression that fails on current main before changing the implementation. Preserve the existing conservative behavior and public interface.

Acceptance criteria

• Require a structurally complete census with the actual caller worktree represented before concluding containment.
• Reject empty, missing-worktree, duplicate and unterminated observations before candidate output exists.
• Preserve legitimate linked, detached and path-with-newline worktree controls.

Size: S/M. Part of #101.