Files
kebab/tasks/p3/p3-1-embedder-trait.md
kb bc1b3147cd refactor(spec): cleanup pass over component specs
Address 8 issues found in spec audit (post PR #2):

1. §refs label: distinguish design vs report sections in p3-1 / p3-2 / p4-2 /
   p9-1 / p9-5 contract_sections (e.g., "report §11.2 Ollama" not "§11.2").
2. mock feature gate: gate MockEmbedder (p3-1) and MockLanguageModel (p4-1)
   behind `mock` cargo feature, default OFF; add CI symbol-scan as DoD item.
3. Warning type unification: p1-2 frontmatter now emits
   `kb_parse_types::Warning` (matches p1-3 / p1-4); drops crate-internal type.
4. p4-3 streaming thread: explicitly single-threaded inside RagPipeline::ask;
   collection + sink.send share the calling thread, no race. UI concurrency
   is callers responsibility (TUI worker thread pattern in p9-3).
5. p6-2 tesseract version: noted that `tesseract` 0.13 has no stable Rust
   `version()` accessor; use TessVersion FFI or shell-out + cache approach.
6. p9-* App struct extensions: introduce `kb_tui::{Library,Search,Ask,Inspect}State`
   slots in p9-1 forward-decl form; p9-2/3/4 fill bodies in their own crate
   without editing `App`. Parallel-safety contract added.
7. p3-3 cosine score: shift `(sim+1)/2` instead of clamp; preserve ranking
   signal between unrelated and opposite vectors. Clamp reserved for NaN.
8. fixtures/ root: p0-1 DoD now creates all fixture subdirs with .gitkeep so
   downstream tasks have a stable target path.
2026-04-27 23:38:13 +00:00

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Markdown

---
phase: P3
component: kb-embed (trait crate)
task_id: p3-1
title: "Embedder trait + EmbeddingInput/Kind validation"
status: planned
depends_on: [p0-1]
unblocks: [p3-2, p3-3, p3-4]
contract_source: ../../docs/superpowers/specs/2026-04-27-kb-final-form-design.md
contract_sections: [design §3.7 SearchHit.embedding_model, design §7.1 EmbeddingInput/Kind, design §7.2 Embedder, report §11 LLM/embedding split]
---
# p3-1 — Embedder trait crate
## Goal
Provide the `kb-embed` crate that re-exports `Embedder` trait, `EmbeddingInput`/`EmbeddingKind`, and offers a mock implementation for downstream tests. This task is **trait-only**; concrete adapters live in p3-2.
## Why now / why this size
Concrete adapters (fastembed, ollama-embed, candle) need a stable trait surface. Owning the trait + a mock implementation in a tiny crate keeps `kb-store-vector` and `kb-search` testable without touching real models.
## Allowed dependencies
- `kb-core`
- `kb-config`
- `serde`
- `thiserror`
- `tracing`
- `[features] mock = []` — opt-in feature flag exposing `MockEmbedder`. Default OFF. Release builds (omit `--features mock`) compile `MockEmbedder` out entirely.
## Forbidden dependencies
- `fastembed`, `ort`, `tokenizers`, `kb-source-fs`, `kb-parse-md`, `kb-normalize`, `kb-chunk`, `kb-store-*`, `kb-search`, `kb-llm*`, `kb-rag`, `kb-tui`, `kb-desktop`
## Inputs
| input | type | source |
|-------|------|--------|
| `EmbeddingInput` | `kb_core::EmbeddingInput<'_>` | callers (parser-side or query-side) |
| model identity | `(EmbeddingModelId, EmbeddingVersion, dimensions)` | adapter at construction |
## Outputs
| output | type | downstream |
|--------|------|------------|
| `Vec<Vec<f32>>` | row-aligned with input | `kb-store-vector`, `kb-search` (vector mode) |
## Public surface (signatures only — no new types)
```rust
pub use kb_core::{EmbeddingInput, EmbeddingKind, EmbeddingModelId, EmbeddingVersion, Embedder};
/// Test-only mock that produces deterministic vectors. Compiled only when `mock` feature is on.
#[cfg(feature = "mock")]
pub struct MockEmbedder { /* internal: model_id, dims, seed */ }
#[cfg(feature = "mock")]
impl MockEmbedder {
pub fn new(model_id: kb_core::EmbeddingModelId, version: kb_core::EmbeddingVersion, dimensions: usize) -> Self;
}
#[cfg(feature = "mock")]
impl kb_core::Embedder for MockEmbedder { /* per §7.2 */ }
```
## Behavior contract
- `MockEmbedder::embed` produces vectors deterministically from `(text, kind)`: e.g., `vector[i] = hash_to_unit_float(text, kind, i, seed)` so two identical inputs produce identical vectors and different inputs produce nearly-orthogonal vectors. Used by downstream tests.
- `MockEmbedder` must respect `EmbeddingKind::Document` vs `Query` — different prefix mixed into the hash so query embeddings differ from document embeddings of the same text (mirrors real e5 behavior).
- `dimensions()` returns the value passed at construction; callers must trust it.
- Real adapters (p3-2) MUST NOT implement `Embedder` here.
- The crate may expose a tiny helper `pub fn assert_vector_shape(vecs: &[Vec<f32>], expected_dims: usize)` for downstream tests.
## Storage / wire effects
- None.
## Test plan
| kind | description | fixture / data |
|------|-------------|----------------|
| unit | trait dyn dispatch via `Box<dyn Embedder>` works | inline |
| unit | `MockEmbedder` produces identical vector for identical input | inline |
| unit | `EmbeddingKind::Document` vs `Query` for same text yield different vectors | inline |
| unit | dimensions match construction-time value | inline |
| contract | property test: 100 random inputs, each vector has length == dimensions, all finite floats | inline (proptest) |
All tests under `cargo test -p kb-embed`.
## Definition of Done
- [ ] `cargo check -p kb-embed` passes
- [ ] `cargo test -p kb-embed` passes
- [ ] No external embedding dep present
- [ ] PR links design §7.2 Embedder, §11
## Out of scope
- Real adapter (`kb-embed-local` is p3-2).
- Reranker traits (P+).
## Risks / notes
- `MockEmbedder` is gated by `mock` feature (default OFF). Downstream tests opt in via `[dev-dependencies] kb-embed = { path = "...", features = ["mock"] }`. CI build of release binary (`cargo build --release` without `--features mock`) MUST NOT include `MockEmbedder` symbol — verifiable via `cargo bloat` or `nm` symbol scan.
- Trait re-exports keep the call site stable even if `kb-core` reorganizes; downstream crates should `use kb_embed::Embedder` rather than `use kb_core::Embedder`.