Move src/shared/ipc/errors.ts to src/shared/ipc/errors/index.ts so each migrated domain can host its own error-code map as a sibling errors/<domain>.ts — value-importable by both processes and zod-free. The @shared/ipc/errors barrel path is unchanged, so every importer and test resolves identically (typecheck + IPC tests green).
Document the IpcErrorCode usage convention that previously lived only in code comments: the framework-code single source of truth, the open (string & {}) tail for domain codes, where domain codes belong (errors/, not schemas/, since the renderer may only import type from schemas), and why they are imported directly rather than aggregated through a barrel.
Make the IpcApi docs explicit about three things surfaced in review:
- overview: Why Narrow the Surface (before/after + the type/cheat-sheet/audit wins), Direction Cheat Sheet (IpcRoute vs IpcEventName + out-of-scope), and No One-Way R->M Primitive (every R->M is invoke/handle; void still round-trips).
- migration guide: Escape Hatch criteria (direction gate then frequency) with Tab_MoveWindow as the sole qualifying carve-out, its two hard conditions (still gated, still documented), and scope discipline for the sibling one-off channels; add Tab_MoveWindow to the Not In Scope table.
- README + usage: navigation pointers and the R->M / M->R high-frequency asymmetry (M->R stays via class B, R->M may escape).
