# m6p5 — Query Composition + SUGGEST Autocomplete (✅ COMPLETE 2026-02-23)

Phase spec and acceptance criteria: [ROADMAP · Milestone 6 · Phase 5](../ROADMAP.md).
Milestone index: [README.md](README.md). Backfilled record.

## What shipped

1. **`WithinScope` on SEARCH** (`tidal/src/query/search/types.rs:33-44`) — five
   variants, exactly as specified:

   | Variant | Candidate set |
   |---------|---------------|
   | `Trending { window_hours }` | items above the velocity threshold in the window, from the global ledger |
   | `CohortTrending { cohort, window_hours }` | same, scoped to a defined cohort (m6p1) |
   | `Following` | items from creators the querying user follows; requires `for_user` |
   | `Category { name }` | items matching the category metadata value |
   | `Collection { id }` | items in the collection's bitmap (m6p4) |

   The scope resolves to a `RoaringBitmap` applied *before* candidate scoring, so
   it reaches both retrieval arms: a post-filter for Tantivy BM25 and a predicate
   callback for the USearch ANN search. Scoping before scoring is the point —
   scoping after would rank the wrong universe and then discard the answer.
2. **`db.suggest()`** (`tidal/src/query/suggest.rs`,
   `tidal/src/db/query_ops.rs`). Prefix autocomplete over terms extracted from
   item titles at write time, updated incrementally on
   `write_item_with_metadata`; an empty prefix returns trending search terms by
   recent query frequency, counted on each `db.search()` call.

## Evidence

- `tidal/tests/m6p5_scope.rs` — 13 `#[test]` functions: each `WithinScope`
  variant independently, the composition case (search within cohort trending),
  and SUGGEST with both a prefix and an empty prefix.
- `tidal/src/query/search/types/tests.rs` — `WithinScope` unit coverage.

## Dependencies this phase actually had

`CohortTrending` needs m6p1's cohort ledger and `Collection` needs m6p4's
collection bitmap, so despite the ROADMAP DAG showing phases 1–4 as broadly
parallel, m6p5 was genuinely gated on both.

## Note on the "< 50 ms SEARCH / < 20 ms SUGGEST" criteria

Marked `[x]` with no recorded measurement in `docs/`. Functional behaviour is
proven by `m6p5_scope.rs`; the two latency figures are not evidenced.