Reorganize along Problem / Proposal / High-level API / Detailed design /
Roadmap / FAQ / Prior art / Alternatives / Acceptance / Risks. The
product survey and Pi failure shapes move to Prior art; user-facing
behavior (walkthrough, cordis.yml config, stdio, ACP, ctx.modes) gets
its own High-level API section; FAQ collects behavioral clarifications
of the chosen design, disjoint from Alternatives (rejected designs) and
Risks (accepted costs). The zh counterpart and its pairing metadata are
removed; the RFC is English-only (not in the required-pairs manifest).
A folded mode name the current config no longer defines behaves as default
plus one boundary notice naming the dropped definition — set()'s loud
validation covers only the write path.
kingwl