Adds matrix indexer as its own row in the §1 component table and a
new §3.4 with port plan. Distinct from vectord (substrate); lives at
internal/matrix/ + gateway /v1/matrix/*.
Five components in dependency order: corpus builders → multi-corpus
retrieve+merge → relevance filter → strong-model downgrade gate →
learning-loop integration.
Locks in the framing J flagged 2026-04-29: in Rust the matrix indexer
was emergent across mode.rs + build_*_corpus.ts + observer /relevance,
and earlier port-planning reduced it to "we have vectord." The SPEC
now names it explicitly so the port preserves the multi-corpus
retrieval shape AND the learning loop, not just the HNSW substrate.
Sharding-by-id was investigated as a throughput fix and rejected —
corpus-as-shard at the matrix layer is the existing retrieval shape
and parallelizes Adds for free.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
71b35fb85e