Context Engine ADR set
Three canonical ADRs that pin the Context Engine's retrieval, graph, and inference-hosting decisions so sibling build stories cite stable doctrine instead of an unmerged RFD note.
What this Story is
Story-2054 is row CE-22 of the founder-redlined Context Engine execution manifest (pramaan-functions docs/notes/rfd-context-engine.md ยง14.3). It lands the ADR set in pramaan-docs and updates both ADR registries. No code, no schema, no board mutation.
Why it matters
The Context Engine build (Epics #2049 / #2050) fans out across functions, infra, and agents lanes. Those stories must cite settled decisions with pramaan-docs ADR-NNN grammar. Until these ADRs merge, the only record of the retrieval posture, the Neptune supersession, and the Bedrock-region carve-out is a repo-local RFD note in another repo — not citable doctrine.
Each ADR records a founder-locked decision (designed around, not relitigated), so all three land as accepted.
The three decisions
| ADR | Decision | Prior-ADR relation |
|---|---|---|
ADR-155 |
pgvector + FTS hybrid (RRF → rerank → top-k) in the one RDS Postgres is the retrieval system of record at pilot scale (~2M chunks / ~400 matters). OpenSearch is a documented scale trigger only, built nowhere. | extends ADR-003; settles the dead ADR-032 → OpenSearch drift; answers Spike-1551. |
ADR-156 |
Neptune is the graph of record for Context Engine assertions, contradictions, and chronology (edges live only on Neptune; relational context.assertions is the trust/tenancy projection; no-RLS tenancy supplied by a mandatory scoped helper + VPC + IAM). |
scoped supersession of ADR-069 — ADR-069's Neptune-exclusion still holds for agent runtime state (chat/runs/traces stay Postgres). |
ADR-157 |
Embeddings (cohere.embed-v4) and reranking (Cohere Rerank 3.5) run on Bedrock in-account, cross-region to one pinned region (us-east-1), ids + dimension + region in config per ADR-151. Generative inference stays OpenRouter-ZDR. Voyage direct-API is a double-gated contingency only. |
scoped amendment to ADR-116 / ADR-120 (reconciled with ADR-122); ZDR floor preserved; does not reintroduce ADR-113's Bedrock generative matrix. |
What changed
| File | Change |
|---|---|
docs/decisions/adrs/ADR-155-context-engine-retrieval-posture-pgvector-fts-system-of-record.md | New ADR: retrieval posture. |
docs/decisions/adrs/ADR-156-neptune-graph-of-record-context-engine.md | New ADR: Neptune graph of record (scoped supersession of ADR-069). |
docs/decisions/adrs/ADR-157-context-engine-embeddings-rerank-bedrock-pinned-region.md | New ADR: Bedrock embeddings/rerank, one pinned region (scoped amendment to ADR-116/120). |
docs/decisions/adrs/ADR-REGISTRY.md | Three new rows appended to the Active ADRs table. |
docs/decisions/adrs/adr-registry.json | Three new routing entries (additive; 154 insertions, 0 deletions). |
docs/walkthroughs/story-2054-walkthrough.html | This walkthrough, required for the Story PR. |
Not in scope
No edits to the accepted ADR-069/116/120 files (supersession/amendment is recorded in the new ADRs per repo danger-zone doctrine; the ADR-154/ADR-123 precedent). No code, migrations, Terraform, or agent config — those are the functions/infra/agents CE-* stories. No Project #2 board mutation. The CE-4 retrieval-eval verdict is noted as a follow-up input to ADR-157, not decided here.