# M2.1 — Embeddings client

| Field | Value |
|---|---|
| Phase | M2 — Projections |
| Size | S — under 1 day |
| Status | ✅ Done |
| Flags | — |
| Spec | inlined below |
| Blocks | M1.1 |

## Goal

Turn text into 768-dim vectors, batched, against the gateway's TEI endpoint.

## Facts (inlined — no spec read needed)

```
POST /v1/embeddings
{"model":"nomic-ai/nomic-embed-text-v2-moe","input":["..."]}
-> {"object":"list","data":[{"embedding":[...768 floats...]}],"usage":{...}}
```

**768 dimensions**, probed and confirmed. It is the `vector(768)` in the schema
and in the HNSW index; a model swap is a schema migration, not a config change.

**Batch limit is 32.** Verified: 1200 inputs returned
`{"message":"batch size 1200 > maximum allowed batch size 32","code":413}`.
Chunk the input list accordingly.

This route currently has **no auth** — no `konghq.com/plugins` annotation, so
`model-key-auth` never attaches. Send the `apikey` header anyway: the route
should be fixed, and a client that only works while auth is broken breaks when
it is fixed.

Bodies here are large (many texts × long strings) and the Kong buffer is 16m, so
batching also keeps requests well inside it.

## Steps

1. `EmbeddingsClient::embed(texts: &[String]) -> Result<Vec<Vec<f32>>>` in `mem-llm`.
2. Split into batches of ≤32, preserving input order in the output.
3. Assert every returned vector is exactly 768 long; a mismatch is an error
   naming the model, not a silent pad or truncate.
4. Reuse M1.1's client config: `apikey` header, retry on 5xx only, generous
   timeout.
5. `embed_one` convenience wrapper.

## Acceptance

- 100 texts return 100 vectors in input order.
- Every vector is 768-dim.
- A dimension mismatch errors loudly.

## Verify

**Harness:** `wiremock` offline, one `#[ignore]` live test.

**Integration test** — `tests/it_embeddings.rs`:
1. `a1_batches_at_32` — 100 inputs produce exactly 4 requests.
2. `a2_order_preserved` — mock returns identifiable vectors; assert output order
   matches input order across batch boundaries.
3. `a3_dimension_asserted` — mock returns a 512-dim vector; assert an error
   naming the model.
4. `a4_apikey_sent` — assert the header is present even though the route does not
   require it.
5. `a5_live_dims` — `#[ignore]`; real gateway, assert 768.

**Command:** `cargo test -p mem-llm embeddings` (add `-- --ignored` for a5)

**False pass:**
- Testing with ≤32 inputs. The batching path never runs and order-across-batches
  — the thing most likely to be wrong — is never exercised.
- Trusting the response order within a batch without asserting it. Assertion 2
  must use distinguishable vectors, not a length check.

## Traps

- Hardcoding 768 in three places. Put it in one constant that the schema
  migration also references, so a model change is one edit and one migration.
- Assuming no auth is needed because it currently works without a key. That route
  is missing its plugin annotation, which is a bug scheduled to be fixed.

---

Background: [DESIGN.md](../DESIGN.md) — Verified facts, pgvector