TASK-IMP-058: ADR backfill for irreversible decisions

Summary

Backfill ADRs for irreversible calls agents keep re-litigating: own-chat, AGE removal, payload vs platform, rules_sha cone, HITL gates (R50 + batch/12d).

Problem

Strategy docs bury decisions; future agents re-propose rejected paths.

Proposed Solution

Five accepted ADRs under docs/adrs/ plus an index README; thin docs/adr/ alias pointer. Cross-link DEC rows when present; do not invent a fake ledger.

Alternatives Considered

• Only update strategy essays — rejected: not citable as ADR artefacts.
• Include RouterBackend/SSO in the same five — deferred; own-chat/AGE/payload/ rules_sha/HITL were the operator-selected set for this batch.

Success Metrics

• Index lists ≥5 new ADRs as accepted with stable filenames.

Scope

In scope: ADR bodies + index + docs/adr/ pointer. Out of scope: full DEC ledger migration.

AI Authorship Disclosure

• Session agent; HITL Stephen Cheng (session operator).

1. Description (normative)

• 1.1 MUST add ADRs for: own-chat-from-scratch; AGE removal; payload vs platform; rules_sha cone; HITL gates.
• 1.2 MUST add/update docs/adrs/README.md index linking them.
• 1.3 MUST provide docs/adr/README.md pointing at docs/adrs/ (singular path).

2. Acceptance criteria

• [x] AC 1 (traces_to: #1.1) - five ADR files exist with status: accepted
• [x] AC 2 (traces_to: #1.2, #1.3) - both README indexes present and linked

3. Edge cases

• Existing ADR-IMP-068 / ADR-OBS-003 remain; index includes them.