4349 lines, 9 numbered sections per the Backend Finalization Sprint
spec: Bootstrap, Endpoint Framework, CRUD Contracts (~102 endpoints
across 20 domains), Authentication (spliced from AUTHENTICATION.md),
Security, Error Model (spliced from ERROR_CONTRACT.md), Uploads, Real
Backend Implementation Guide, Backend Checklist (34 items).
Everything traced to docs/context/BACKEND-AUDIT.md and actual current
source - proposed (unverified) paths explicitly marked as such,
everything the frontend has no opinion on marked "Requires backend
decision" rather than invented.
Archived the three docs this supersedes (BACKEND_API.md, AUTH.md,
BACKEND_API_REMAINING_WORK.md) to docs/archive/ with pointers back to
this file. AUTHENTICATION.md, ERROR_CONTRACT.md, MAINTENANCE_MODE.md
kept in place as standalone companion references (their content is
also inlined/cross-referenced here). ADMIN.md left untouched - it's a
frontend admin-UI sprint doc, not a backend spec, no overlap.
Verified via repo-wide search: no other backend/API spec docs remain
outside archive/ and this canonical file.
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