Task: Reconcile canonical memory with merged Go backend

Identity

Reconcile canonical .project-docs memory with the Go backend implementation merged into main by b8db39d and d0fb346.
Promote the pending promotion candidates of tasks 20260813-go-remaining-modules-7d3a9e42 and 20260814-go-remaining-integration-5e7c9a1b (Go module map and contract fixtures) into canonical architecture memory.
Repair stale canonical documents that still described the Go migration as not started.
Complete task-lifecycle housekeeping: commit the untracked record of 20260812-architecture-task-breakdown-a83f61c2, correct its Status, and release its stale ownership of main.

Record factual implementation progress; do not claim a production cutover that has not happened. ACK-001 remains the deployed truth.
Do not reverse or weaken accepted decisions (RDS-001, RDS-002, ACK-001, ADR-003).
Fill template files only from facts already present in the repository (READMEs, task records, contracts, migrations); keep unknowns explicit.
Feature task records of the source tasks stay read-only; only my own integration record and canonical documents change.

Updated current-state.md with Integrated Through entries for b8db39d, d0fb346, and f10cdd9, current focus (implemented but unrouted Go backend), next steps, open questions, and risky areas.
Updated system-overview.md, module-map.md, and data-flow.md to describe the merged Go implementation while keeping the deployed Next.js/Node topology authoritative until cutover.
Updated decision-index.md (ADR-003 row), adr-003-next-go-target.md Status, and the migration proposal implementation/canonical-promotion lines.
Appended the six Go migration tasks to task-history.md.
Updated commitments.md: marked the pre-implementation contract commitment completed and added cutover-validation and Cookie//api/v1 decision commitments.
Filled the placeholder templates project-positioning.md, business-rules.md, glossary.md, success-criteria.md, and stale-items.md missing context from repository facts.
Committed the completed record of task 20260812-architecture-task-breakdown-a83f61c2 (Status corrected to Ready for Integration) as f10cdd9 and released its stale ownership of the main worktree.

Verified merge topology: b8db39d (merge of aef5a97) and d0fb346 (merge of c1cbd78 into main at 7de3300; 219 files, +32465/-23).
Verified repository facts used in the docs: 154 Go files under backend/, 18 internal/ packages, 24 contract fixtures under contracts/, migrations 0001/0002.
check_project_docs.py passes; check_doc_drift.py --task-id 20260814-go-memory-reconcile-7f2a9c41 passes.
No application, database, test, or deployment file was changed.

Five completed Go feature worktrees remain owned and ready_for_integration; release them after their records and merges are confirmed.
Root README.md/README.zh-CN.md tech-stack sections still describe only the Next.js stack; update when the Go backend becomes deployed.
Real RDS/OSS/provider/Webhook validation and the cutover plan remain open (see commitments.md and current-state.md).

None beyond what this integration task already applied; no canonical changes remain pending from the merged Go tasks.