feat: cross-encoder reranker for recipe suggestions (kiwi#117)

Integrates cf-core reranker into the L1/L2 recipe engine. Paid+ tier
gets a BGE cross-encoder pass over the top-20 FTS candidates, scoring
each recipe against the user's full context: pantry state, dietary
constraints, allergies, expiry urgency, style preference, and effort
preference. Free tier keeps the existing overlap sort unchanged.

- New app/services/recipe/reranker.py: build_query, build_candidate_string,
  rerank_suggestions with tier gate (_RERANKER_TIERS) and graceful fallback
- rerank_score field added to RecipeSuggestion (None on free tier, float on paid+)
- recipe_engine.py: single call after candidate assembly, before final sort;
  hard_day_mode tier grouping preserved as primary sort when reranker active
- Fix pre-existing circular import in app/services/__init__.py (eager import
  of ReceiptService triggered store.py → services → receipt_service → store)
- 27 unit tests (mock backend, no model weights) + 2 engine-level tier tests;
  325 tests passing, no regressions

app/models/schemas/recipe.py

@@ -43,6 +43,7 @@ class RecipeSuggestion(BaseModel):
     source_url: str | None = None
     complexity: str | None = None  # 'easy' | 'moderate' | 'involved'
     estimated_time_min: int | None = None  # derived from step count + method signals
+    rerank_score: float | None = None  # cross-encoder relevance score (paid+ only, None for free tier)
 
 
 class GroceryLink(BaseModel):

app/services/__init__.py

@@ -3,6 +3,11 @@
 Business logic services for Kiwi.
 """
 
-from app.services.receipt_service import ReceiptService
+__all__ = ["ReceiptService"]
 
-__all__ = ["ReceiptService"]
+
+def __getattr__(name: str):
+    if name == "ReceiptService":
+        from app.services.receipt_service import ReceiptService
+        return ReceiptService
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

app/services/recipe/recipe_engine.py

@@ -26,6 +26,7 @@ from app.services.recipe.grocery_links import GroceryLinkBuilder
 from app.services.recipe.substitution_engine import SubstitutionEngine
 from app.services.recipe.sensory import SensoryExclude, build_sensory_exclude, passes_sensory_filter
 from app.services.recipe.time_effort import parse_time_effort
+from app.services.recipe.reranker import rerank_suggestions
 
 _LEFTOVER_DAILY_MAX_FREE = 5
 
@@ -880,11 +881,21 @@ class RecipeEngine:
                 estimated_time_min=row_time_min,
             ))
 
-        # Sort corpus results — assembly templates are now served from a dedicated tab.
-        # Hard day mode: primary sort by tier (0=premade, 1=simple, 2=moderate),
-        # then by match_count within each tier.
-        # Normal mode: sort by match_count descending.
-        if req.hard_day_mode and hard_day_tier_map:
+        # Sort corpus results.
+        # Paid+ tier: cross-encoder reranker orders by full pantry + dietary fit.
+        # Free tier (or reranker failure): overlap sort with hard_day_mode tier grouping.
+        reranked = rerank_suggestions(req, suggestions)
+        if reranked is not None:
+            # Reranker provided relevance order. In hard_day_mode, still respect
+            # tier grouping as primary sort; reranker order applies within each tier.
+            if req.hard_day_mode and hard_day_tier_map:
+                suggestions = sorted(
+                    reranked,
+                    key=lambda s: hard_day_tier_map.get(s.id, 1),
+                )
+            else:
+                suggestions = reranked
+        elif req.hard_day_mode and hard_day_tier_map:
             suggestions = sorted(
                 suggestions,
                 key=lambda s: (hard_day_tier_map.get(s.id, 1), -s.match_count),

app/services/recipe/reranker.py

@@ -0,0 +1,175 @@
+"""
+Reranker integration for recipe suggestions.
+
+Wraps circuitforge_core.reranker to score recipe candidates against a
+natural-language query built from the user's pantry, constraints, and
+preferences. Paid+ tier only; free tier returns None (caller keeps
+existing sort). All exceptions are caught and logged — the reranker
+must never break recipe suggestions.
+
+Environment:
+    CF_RERANKER_MOCK=1  — force mock backend (tests, no model required)
+"""
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass, field
+
+from app.models.schemas.recipe import RecipeRequest, RecipeSuggestion
+
+log = logging.getLogger(__name__)
+
+# Tiers that get reranker access.
+_RERANKER_TIERS: frozenset[str] = frozenset({"paid", "premium", "local"})
+
+# Minimum candidates worth reranking — below this the cross-encoder
+# overhead is not justified and the overlap sort is fine.
+_MIN_CANDIDATES: int = 3
+
+
+@dataclass(frozen=True)
+class RerankerInput:
+    """Intermediate representation passed to the reranker."""
+    query: str
+    candidates: list[str]
+    suggestion_ids: list[int]  # parallel to candidates, for re-mapping
+
+
+# ── Query builder ─────────────────────────────────────────────────────────────
+
+def build_query(req: RecipeRequest) -> str:
+    """Build a natural-language query string from the recipe request.
+
+    Encodes the user's full context so the cross-encoder can score
+    relevance, dietary fit, and expiry urgency in a single pass.
+    Only non-empty segments are included.
+    """
+    parts: list[str] = []
+
+    if req.pantry_items:
+        parts.append(f"Recipe using: {', '.join(req.pantry_items)}")
+
+    if req.exclude_ingredients:
+        parts.append(f"Avoid: {', '.join(req.exclude_ingredients)}")
+
+    if req.allergies:
+        parts.append(f"Allergies: {', '.join(req.allergies)}")
+
+    if req.constraints:
+        parts.append(f"Dietary: {', '.join(req.constraints)}")
+
+    if req.category:
+        parts.append(f"Category: {req.category}")
+
+    if req.style_id:
+        parts.append(f"Style: {req.style_id}")
+
+    if req.complexity_filter:
+        parts.append(f"Prefer: {req.complexity_filter}")
+
+    if req.hard_day_mode:
+        parts.append("Prefer: easy, minimal effort")
+
+    # Secondary pantry items carry a state label (e.g. "stale", "overripe")
+    # that helps the reranker favour recipes suited to those specific states.
+    if req.secondary_pantry_items:
+        expiry_parts = [f"{name} ({state})" for name, state in req.secondary_pantry_items.items()]
+        parts.append(f"Use soon: {', '.join(expiry_parts)}")
+    elif req.expiry_first:
+        parts.append("Prefer: recipes that use expiring items first")
+
+    return ". ".join(parts) + "." if parts else "Recipe."
+
+
+# ── Candidate builder ─────────────────────────────────────────────────────────
+
+def build_candidate_string(suggestion: RecipeSuggestion) -> str:
+    """Build a candidate string for a single recipe suggestion.
+
+    Format: "{title}. Ingredients: {comma-joined ingredients}"
+    Matched ingredients appear before missing ones.
+    Directions excluded to stay within BGE's 512-token window.
+    """
+    ingredients = suggestion.matched_ingredients + suggestion.missing_ingredients
+    if not ingredients:
+        return suggestion.title
+    return f"{suggestion.title}. Ingredients: {', '.join(ingredients)}"
+
+
+# ── Input assembler ───────────────────────────────────────────────────────────
+
+def build_reranker_input(
+    req: RecipeRequest,
+    suggestions: list[RecipeSuggestion],
+) -> RerankerInput:
+    """Assemble query and candidate strings for the reranker."""
+    query = build_query(req)
+    candidates: list[str] = []
+    ids: list[int] = []
+    for s in suggestions:
+        candidates.append(build_candidate_string(s))
+        ids.append(s.id)
+    return RerankerInput(query=query, candidates=candidates, suggestion_ids=ids)
+
+
+# ── cf-core seam (isolated for monkeypatching in tests) ──────────────────────
+
+def _do_rerank(query: str, candidates: list[str], top_n: int = 0):
+    """Thin wrapper around cf-core rerank(). Extracted so tests can patch it."""
+    from circuitforge_core.reranker import rerank
+    return rerank(query, candidates, top_n=top_n)
+
+
+# ── Public entry point ────────────────────────────────────────────────────────
+
+def rerank_suggestions(
+    req: RecipeRequest,
+    suggestions: list[RecipeSuggestion],
+) -> list[RecipeSuggestion] | None:
+    """Rerank suggestions using the cf-core cross-encoder.
+
+    Returns a reordered list with rerank_score populated, or None when:
+    - Tier is not paid+ (free tier keeps overlap sort)
+    - Fewer than _MIN_CANDIDATES suggestions (not worth the overhead)
+    - Any exception is raised (graceful fallback to existing sort)
+
+    The caller should treat None as "keep existing sort order".
+    Original suggestions are never mutated.
+    """
+    if req.tier not in _RERANKER_TIERS:
+        return None
+
+    if len(suggestions) < _MIN_CANDIDATES:
+        return None
+
+    try:
+        rinput = build_reranker_input(req, suggestions)
+        results = _do_rerank(rinput.query, rinput.candidates, top_n=0)
+
+        # Map reranked results back to RecipeSuggestion objects using the
+        # candidate string as key (build_candidate_string is deterministic).
+        candidate_map: dict[str, RecipeSuggestion] = {
+            build_candidate_string(s): s for s in suggestions
+        }
+
+        reranked: list[RecipeSuggestion] = []
+        for rr in results:
+            suggestion = candidate_map.get(rr.candidate)
+            if suggestion is not None:
+                reranked.append(suggestion.model_copy(
+                    update={"rerank_score": round(float(rr.score), 4)}
+                ))
+
+        if len(reranked) < len(suggestions):
+            log.warning(
+                "Reranker lost %d/%d suggestions during mapping, falling back",
+                len(suggestions) - len(reranked),
+                len(suggestions),
+            )
+            return None
+
+        return reranked
+
+    except Exception:
+        log.exception("Reranker failed, falling back to overlap sort")
+        return None

tests/services/recipe/test_recipe_engine.py

@@ -170,3 +170,37 @@ def test_within_time_over_limit_fails():
     from app.services.recipe.recipe_engine import _within_time
     steps = ["brown onions for 15 minutes", "simmer for 30 minutes"]
     assert _within_time(steps, max_total_min=30) is False
+
+
+# ── Reranker tier-gating tests ────────────────────────────────────────────────
+
+def test_paid_tier_suggest_populates_rerank_score(store_with_recipes, monkeypatch):
+    """Paid tier: at least one suggestion should have rerank_score populated."""
+    monkeypatch.setenv("CF_RERANKER_MOCK", "1")
+    try:
+        from circuitforge_core.reranker import reset_reranker
+        reset_reranker()
+    except ImportError:
+        pytest.skip("cf-core reranker not installed")
+
+    from app.services.recipe.recipe_engine import RecipeEngine
+    from app.models.schemas.recipe import RecipeRequest
+    engine = RecipeEngine(store_with_recipes)
+    req = RecipeRequest(pantry_items=["butter", "parmesan", "pasta"], level=1, tier="paid")
+    result = engine.suggest(req)
+    # Need at least _MIN_CANDIDATES for reranker to fire
+    from app.services.recipe.reranker import _MIN_CANDIDATES
+    if len(result.suggestions) >= _MIN_CANDIDATES:
+        assert any(s.rerank_score is not None for s in result.suggestions)
+
+    reset_reranker()
+
+
+def test_free_tier_suggest_has_no_rerank_score(store_with_recipes):
+    """Free tier: rerank_score must be None on all suggestions."""
+    from app.services.recipe.recipe_engine import RecipeEngine
+    from app.models.schemas.recipe import RecipeRequest
+    engine = RecipeEngine(store_with_recipes)
+    req = RecipeRequest(pantry_items=["butter", "parmesan"], level=1, tier="free")
+    result = engine.suggest(req)
+    assert all(s.rerank_score is None for s in result.suggestions)

tests/services/recipe/test_reranker.py

@@ -0,0 +1,287 @@
+"""
+Tests for app.services.recipe.reranker.
+
+All tests use CF_RERANKER_MOCK=1 -- no model weights required.
+The mock reranker scores by Jaccard similarity of query tokens vs candidate
+tokens, which is deterministic and fast.
+"""
+import os
+import pytest
+
+
+# ── Fixtures ──────────────────────────────────────────────────────────────────
+
+@pytest.fixture(autouse=True)
+def mock_reranker(monkeypatch):
+    """Force mock backend and reset the cf-core singleton before/after each test."""
+    monkeypatch.setenv("CF_RERANKER_MOCK", "1")
+    try:
+        from circuitforge_core.reranker import reset_reranker
+        reset_reranker()
+        yield
+        reset_reranker()
+    except ImportError:
+        yield
+
+
+def _make_request(**kwargs):
+    from app.models.schemas.recipe import RecipeRequest
+    defaults = dict(pantry_items=["chicken", "rice"], tier="paid")
+    defaults.update(kwargs)
+    return RecipeRequest(**defaults)
+
+
+def _make_suggestion(id: int, title: str, matched: list[str], missing: list[str] | None = None, match_count: int | None = None):
+    from app.models.schemas.recipe import RecipeSuggestion
+    mi = missing or []
+    return RecipeSuggestion(
+        id=id,
+        title=title,
+        match_count=match_count if match_count is not None else len(matched),
+        matched_ingredients=matched,
+        missing_ingredients=mi,
+    )
+
+
+# ── TestBuildQuery ────────────────────────────────────────────────────────────
+
+class TestBuildQuery:
+    def test_basic_pantry(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(pantry_items=["chicken", "rice", "broccoli"])
+        query = build_query(req)
+        assert "chicken" in query
+        assert "rice" in query
+        assert "broccoli" in query
+
+    def test_exclude_ingredients_included(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(exclude_ingredients=["cilantro", "fish sauce"])
+        query = build_query(req)
+        assert "cilantro" in query
+        assert "fish sauce" in query
+
+    def test_allergies_separate_from_exclude(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(allergies=["shellfish"], exclude_ingredients=["cilantro"])
+        query = build_query(req)
+        # Both should appear, and they should be in separate labeled segments
+        assert "shellfish" in query
+        assert "cilantro" in query
+        allergy_pos = query.index("shellfish")
+        exclude_pos = query.index("cilantro")
+        assert allergy_pos != exclude_pos
+
+    def test_allergies_labeled_separately(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(allergies=["peanuts"], exclude_ingredients=[])
+        query = build_query(req)
+        assert "Allergies" in query or "allerg" in query.lower()
+
+    def test_constraints_included(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(constraints=["gluten-free", "dairy-free"])
+        query = build_query(req)
+        assert "gluten-free" in query
+        assert "dairy-free" in query
+
+    def test_category_included(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(category="Soup")
+        query = build_query(req)
+        assert "Soup" in query
+
+    def test_complexity_filter_included(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(complexity_filter="easy")
+        query = build_query(req)
+        assert "easy" in query
+
+    def test_hard_day_mode_signal(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(hard_day_mode=True)
+        query = build_query(req)
+        assert "easy" in query.lower() or "minimal" in query.lower() or "effort" in query.lower()
+
+    def test_secondary_pantry_items_expiry(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(secondary_pantry_items={"bread": "stale", "banana": "overripe"})
+        query = build_query(req)
+        assert "bread" in query
+        assert "banana" in query
+        # State labels add specificity for the cross-encoder
+        assert "stale" in query or "overripe" in query
+
+    def test_expiry_first_without_secondary(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(expiry_first=True, secondary_pantry_items={})
+        query = build_query(req)
+        assert "expir" in query.lower()
+
+    def test_style_id_included(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(style_id="mediterranean")
+        query = build_query(req)
+        assert "mediterranean" in query.lower()
+
+    def test_empty_pantry_returns_fallback(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(pantry_items=[])
+        query = build_query(req)
+        assert len(query) > 0  # never empty string
+
+    def test_no_duplicate_separators(self):
+        from app.services.recipe.reranker import build_query
+        req = _make_request(
+            pantry_items=["egg"],
+            allergies=["nuts"],
+            constraints=["vegan"],
+            complexity_filter="easy",
+        )
+        query = build_query(req)
+        assert ".." not in query  # no doubled periods from empty segments
+
+
+# ── TestBuildCandidateString ──────────────────────────────────────────────────
+
+class TestBuildCandidateString:
+    def test_title_and_ingredients(self):
+        from app.services.recipe.reranker import build_candidate_string
+        s = _make_suggestion(1, "Chicken Fried Rice", ["chicken", "rice"], ["soy sauce"])
+        candidate = build_candidate_string(s)
+        assert candidate.startswith("Chicken Fried Rice")
+        assert "chicken" in candidate
+        assert "rice" in candidate
+        assert "soy sauce" in candidate
+
+    def test_title_only_when_no_ingredients(self):
+        from app.services.recipe.reranker import build_candidate_string
+        s = _make_suggestion(2, "Mystery Dish", [], [])
+        candidate = build_candidate_string(s)
+        assert candidate == "Mystery Dish"
+        assert "Ingredients:" not in candidate
+
+    def test_matched_before_missing(self):
+        from app.services.recipe.reranker import build_candidate_string
+        s = _make_suggestion(3, "Pasta Dish", ["pasta", "butter"], ["parmesan", "cream"])
+        candidate = build_candidate_string(s)
+        pasta_pos = candidate.index("pasta")
+        parmesan_pos = candidate.index("parmesan")
+        assert pasta_pos < parmesan_pos
+
+
+# ── TestBuildRerankerInput ────────────────────────────────────────────────────
+
+class TestBuildRerankerInput:
+    def test_parallel_ids_and_candidates(self):
+        from app.services.recipe.reranker import build_reranker_input
+        req = _make_request()
+        suggestions = [
+            _make_suggestion(10, "Recipe A", ["chicken"]),
+            _make_suggestion(20, "Recipe B", ["rice"]),
+            _make_suggestion(30, "Recipe C", ["broccoli"]),
+        ]
+        rinput = build_reranker_input(req, suggestions)
+        assert len(rinput.candidates) == 3
+        assert len(rinput.suggestion_ids) == 3
+        assert rinput.suggestion_ids == [10, 20, 30]
+
+    def test_query_matches_build_query(self):
+        from app.services.recipe.reranker import build_reranker_input, build_query
+        req = _make_request(pantry_items=["egg", "cheese"], constraints=["vegetarian"])
+        suggestions = [_make_suggestion(1, "Omelette", ["egg", "cheese"])]
+        rinput = build_reranker_input(req, suggestions)
+        assert rinput.query == build_query(req)
+
+
+# ── TestRerankSuggestions ─────────────────────────────────────────────────────
+
+class TestRerankSuggestions:
+    def test_free_tier_returns_none(self):
+        from app.services.recipe.reranker import rerank_suggestions
+        req = _make_request(tier="free")
+        suggestions = [_make_suggestion(i, f"Recipe {i}", ["chicken"]) for i in range(5)]
+        result = rerank_suggestions(req, suggestions)
+        assert result is None
+
+    def test_paid_tier_returns_reranked_list(self):
+        from app.services.recipe.reranker import rerank_suggestions
+        req = _make_request(tier="paid", pantry_items=["chicken", "rice"])
+        suggestions = [
+            _make_suggestion(1, "Chicken Fried Rice", ["chicken", "rice"]),
+            _make_suggestion(2, "Chocolate Cake", ["flour", "sugar", "cocoa"]),
+            _make_suggestion(3, "Chicken Soup", ["chicken", "broth"]),
+        ]
+        result = rerank_suggestions(req, suggestions)
+        assert result is not None
+        assert len(result) == len(suggestions)
+
+    def test_rerank_score_is_populated(self):
+        from app.services.recipe.reranker import rerank_suggestions
+        req = _make_request(tier="paid")
+        suggestions = [_make_suggestion(i, f"Recipe {i}", ["chicken"]) for i in range(4)]
+        result = rerank_suggestions(req, suggestions)
+        assert result is not None
+        assert all(s.rerank_score is not None for s in result)
+        assert all(isinstance(s.rerank_score, float) for s in result)
+
+    def test_too_few_candidates_returns_none(self):
+        from app.services.recipe.reranker import rerank_suggestions, _MIN_CANDIDATES
+        req = _make_request(tier="paid")
+        suggestions = [_make_suggestion(i, f"Recipe {i}", ["chicken"]) for i in range(_MIN_CANDIDATES - 1)]
+        result = rerank_suggestions(req, suggestions)
+        assert result is None
+
+    def test_premium_tier_gets_reranker(self):
+        from app.services.recipe.reranker import rerank_suggestions
+        req = _make_request(tier="premium")
+        suggestions = [_make_suggestion(i, f"Recipe {i}", ["chicken"]) for i in range(4)]
+        result = rerank_suggestions(req, suggestions)
+        assert result is not None
+
+    def test_local_tier_gets_reranker(self):
+        from app.services.recipe.reranker import rerank_suggestions
+        req = _make_request(tier="local")
+        suggestions = [_make_suggestion(i, f"Recipe {i}", ["chicken"]) for i in range(4)]
+        result = rerank_suggestions(req, suggestions)
+        assert result is not None
+
+    def test_preserves_all_suggestion_fields(self):
+        from app.services.recipe.reranker import rerank_suggestions
+        req = _make_request(tier="paid")
+        original = _make_suggestion(
+            id=42,
+            title="Garlic Butter Pasta",
+            matched=["pasta", "butter", "garlic"],
+            missing=["parmesan"],
+            match_count=3,
+        )
+        result = rerank_suggestions(req, [original, original, original, original])
+        assert result is not None
+        found = next((s for s in result if s.id == 42), None)
+        assert found is not None
+        assert found.title == "Garlic Butter Pasta"
+        assert found.matched_ingredients == ["pasta", "butter", "garlic"]
+        assert found.missing_ingredients == ["parmesan"]
+        assert found.match_count == 3
+
+    def test_graceful_fallback_on_exception(self, monkeypatch):
+        from app.services.recipe.reranker import rerank_suggestions
+        # Simulate reranker raising at runtime
+        import app.services.recipe.reranker as reranker_mod
+        def _boom(query, candidates, top_n=0):
+            raise RuntimeError("model exploded")
+        monkeypatch.setattr(reranker_mod, "_do_rerank", _boom)
+        req = _make_request(tier="paid")
+        suggestions = [_make_suggestion(i, f"Recipe {i}", ["chicken"]) for i in range(4)]
+        result = rerank_suggestions(req, suggestions)
+        assert result is None
+
+    def test_original_suggestions_not_mutated(self):
+        from app.services.recipe.reranker import rerank_suggestions
+        req = _make_request(tier="paid")
+        suggestions = [_make_suggestion(i, f"Recipe {i}", ["chicken"]) for i in range(4)]
+        originals = [s.model_copy() for s in suggestions]
+        rerank_suggestions(req, suggestions)
+        for original, after in zip(originals, suggestions):
+            assert original.rerank_score == after.rerank_score  # None == None (no mutation)