Unified API error envelope + full HTTP status catalogue (401/403/404/
409/422/429/500/503, maintenance, validation, tenant-disabled,
rate-limit, expired-token, invalid-signature) with JSON examples and
current frontend reaction behavior, including two flagged pre-existing
frontend bugs (expired-token/invalid-signature body-code handling is
currently dead code - toAuthErrorShape() ignores fallbackCode for real
HTTP errors).
Maintenance-mode contract (global/per-tenant/per-module/read-only/
scheduled/feature-disable) with proposed 503 response shapes and an
explicit split between "requires backend decision" and "no frontend UI
exists yet, requires a future frontend task."
These two agents wrote their files before hitting a session usage
limit that killed the process before final report-back; content
verified complete on disk before committing.
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