feat(recipes): reconnect suggestions, undo, and base-model family tolerance

Enhance the deleted-LoRA reconnect flow in the recipe modal:

- Suggest local reconnect candidates when the panel opens, ranked by
  identity (same hash / same CivitAI version) then filename/name
  similarity, with a hard filter on confident base-model mismatches;
  the input gets a Combobox backed by the same endpoint as you type.
- Snapshot the pre-reconnect entry and offer a permanent restore:
  reconnected entries show an undo icon at the right end of the info
  row, with the original filename in the tooltip.
- Relax the manual reconnect base-model guard to a three-tier check:
  exact/unknown labels pass silently, same-architecture families
  (e.g. Pony <-> Illustrious) pass with a warning toast, and only
  cross-architecture mismatches stay hard-rejected.

py/routes/handlers/recipe_handlers.py

@@ -113,6 +113,8 @@ class RecipeHandlerSet:
             "update_recipe": self.management.update_recipe,
             "record_recipe_open": self.management.record_recipe_open,
             "reconnect_lora": self.management.reconnect_lora,
+            "restore_lora": self.management.restore_lora,
+            "get_reconnect_suggestions": self.management.get_reconnect_suggestions,
             "mark_lora_hash_invalid": self.management.mark_lora_hash_invalid,
             "find_duplicates": self.query.find_duplicates,
             "move_recipes_bulk": self.management.move_recipes_bulk,
@@ -1593,6 +1595,65 @@ class RecipeManagementHandler:
             self._logger.error("Error reconnecting LoRA: %s", exc, exc_info=True)
             return web.json_response({"error": str(exc)}, status=500)
 
+    async def restore_lora(self, request: web.Request) -> web.Response:
+        try:
+            await self._ensure_dependencies_ready()
+            recipe_scanner = self._recipe_scanner_getter()
+            if recipe_scanner is None:
+                raise RuntimeError("Recipe scanner unavailable")
+
+            data = await request.json()
+            for field in ("recipe_id", "lora_index"):
+                if field not in data:
+                    raise RecipeValidationError(f"Missing required field: {field}")
+
+            result = await self._persistence_service.restore_lora(
+                recipe_scanner=recipe_scanner,
+                recipe_id=data["recipe_id"],
+                lora_index=int(data["lora_index"]),
+            )
+            return web.json_response(result.payload, status=result.status)
+        except RecipeValidationError as exc:
+            return web.json_response({"error": str(exc)}, status=400)
+        except RecipeNotFoundError as exc:
+            return web.json_response({"error": str(exc)}, status=404)
+        except Exception as exc:
+            self._logger.error("Error restoring LoRA: %s", exc, exc_info=True)
+            return web.json_response({"error": str(exc)}, status=500)
+
+    async def get_reconnect_suggestions(self, request: web.Request) -> web.Response:
+        try:
+            await self._ensure_dependencies_ready()
+            recipe_scanner = self._recipe_scanner_getter()
+            if recipe_scanner is None:
+                raise RuntimeError("Recipe scanner unavailable")
+
+            recipe_id = request.match_info.get("recipe_id")
+            lora_index_raw = request.match_info.get("lora_index")
+            if not recipe_id or lora_index_raw is None:
+                raise RecipeValidationError("recipe_id and lora_index are required")
+            try:
+                lora_index = int(lora_index_raw)
+            except (TypeError, ValueError):
+                raise RecipeValidationError("lora_index must be an integer")
+
+            result = await self._persistence_service.get_reconnect_suggestions(
+                recipe_scanner=recipe_scanner,
+                recipe_id=recipe_id,
+                lora_index=lora_index,
+                query=request.query.get("query") or None,
+            )
+            return web.json_response(result.payload, status=result.status)
+        except RecipeValidationError as exc:
+            return web.json_response({"error": str(exc)}, status=400)
+        except RecipeNotFoundError as exc:
+            return web.json_response({"error": str(exc)}, status=404)
+        except Exception as exc:
+            self._logger.error(
+                "Error suggesting reconnect candidates: %s", exc, exc_info=True
+            )
+            return web.json_response({"error": str(exc)}, status=500)
+
     async def mark_lora_hash_invalid(self, request: web.Request) -> web.Response:
         try:
             await self._ensure_dependencies_ready()

py/routes/recipe_route_registrar.py

@@ -49,6 +49,12 @@ ROUTE_DEFINITIONS: tuple[RouteDefinition, ...] = (
     RouteDefinition("POST", "/api/lm/recipe/move", "move_recipe"),
     RouteDefinition("POST", "/api/lm/recipes/move-bulk", "move_recipes_bulk"),
     RouteDefinition("POST", "/api/lm/recipe/lora/reconnect", "reconnect_lora"),
+    RouteDefinition("POST", "/api/lm/recipe/lora/restore", "restore_lora"),
+    RouteDefinition(
+        "GET",
+        "/api/lm/recipe/{recipe_id}/lora/{lora_index}/reconnect-suggestions",
+        "get_reconnect_suggestions",
+    ),
     RouteDefinition(
         "POST", "/api/lm/recipe/lora/mark-hash-invalid", "mark_lora_hash_invalid"
     ),

py/services/recipe_scanner.py

@@ -5,6 +5,8 @@
 from __future__ import annotations
 
 import asyncio
+import copy
+import difflib
 import json
 import logging
 import os
@@ -244,6 +246,188 @@ class RecipeScanner:
             self._local_filename_cache_versions = versions
             return cache
 
+    @staticmethod
+    def _strip_weight_extension(name: str) -> str:
+        """Strip a known weight-file extension, preserving the original case."""
+        lower = name.lower()
+        for ext in sorted(WEIGHT_FILE_EXTENSIONS, key=len, reverse=True):
+            if lower.endswith(ext):
+                return name[: -len(ext)]
+        return name
+
+    async def suggest_reconnect_candidates(
+        self,
+        *,
+        entry: dict[str, Any],
+        recipe_base_model: Optional[str],
+        query: Optional[str] = None,
+        limit: int = 5,
+    ) -> list[dict[str, Any]]:
+        """Rank local LoRAs as reconnect candidates for a broken recipe entry.
+
+        Identity signals (same hash / same CivitAI model version) outrank
+        similarity signals (filename / model name fuzzy match). A confident
+        base-model mismatch (both sides known and different) is a hard
+        rejection here. This is deliberately stricter than reconnect itself,
+        which tolerates same-architecture-family labels (Pony ↔ Illustrious):
+        suggestions trade recall for a noise-free list, and the input box
+        remains available for deliberate cross-family picks. Unknown on
+        either side stays eligible, matching ``find_matching_models``.
+        When ``query`` is given
+        (search-as-you-type), identity signals are skipped and both
+        similarity signals score against the query, with a substring hit
+        (query of 3+ chars) flooring that signal's ratio at 0.8.
+
+        The name-similarity threshold (0.65) is stricter than the filename
+        one (0.55): long generic names share tokens like "style"/"pony" and
+        score deceptively high (measured 0.638 for unrelated models), while
+        filenames are the authoritative match key and get more slack.
+        """
+        if limit <= 0 or not isinstance(entry, dict):
+            return []
+
+        lora_scanner = self._lora_scanner
+        if lora_scanner is None:
+            return []
+
+        data = await lora_scanner.get_cached_data()
+        recipe_bm = (recipe_base_model or "").strip().casefold()
+
+        def _base_model_known_mismatch(item: dict[str, Any]) -> bool:
+            """Confident mismatch only — unknown on either side stays eligible."""
+            if not recipe_bm or recipe_bm == "unknown":
+                return False
+            item_bm = (item.get("base_model") or "").strip().casefold()
+            return bool(item_bm) and item_bm != "unknown" and item_bm != recipe_bm
+
+        def _base_model_adjustment(item: dict[str, Any]) -> float:
+            # Mismatches are already filtered out; this only boosts known-equal.
+            if not recipe_bm or recipe_bm == "unknown":
+                return 0.0
+            item_bm = (item.get("base_model") or "").strip().casefold()
+            return 0.1 if item_bm == recipe_bm else 0.0
+
+        pool: list[dict[str, Any]] = []
+        for item in getattr(data, "raw_data", None) or []:
+            if not isinstance(item, dict):
+                continue
+            # Items without a sha256 (pending/failed downloads) leave the
+            # entry without a usable hash — same rule as the filename cache.
+            if not (item.get("sha256") or "").strip():
+                continue
+            if not self._is_type_compatible(item, is_checkpoint=False):
+                continue
+            if _base_model_known_mismatch(item):
+                continue
+            pool.append(item)
+        if not pool:
+            return []
+
+        # Basename collision counts decide whether target_name needs the
+        # folder-relative path to resolve uniquely in find_matching_models.
+        basename_counts: dict[str, int] = {}
+        for item in pool:
+            key = self._normalize_filename_key(item.get("file_name") or "")
+            if key:
+                basename_counts[key] = basename_counts.get(key, 0) + 1
+
+        best: dict[str, dict[str, Any]] = {}
+
+        def _consider(item: dict[str, Any], score: float, reason: str) -> None:
+            key = item.get("file_path") or item.get("file_name") or ""
+            if not key:
+                return
+            current = best.get(key)
+            if current is None or score > current["score"]:
+                best[key] = {"item": item, "score": score, "reason": reason}
+
+        query_text = (query or "").strip()
+
+        if not query_text:
+            entry_hash = (entry.get("hash") or "").lower()
+            if entry_hash:
+                hash_cache = await self.build_local_hash_cache()
+                hit = hash_cache.get(entry_hash)
+                if (
+                    isinstance(hit, dict)
+                    and (hit.get("sha256") or "").strip()
+                    and self._is_type_compatible(hit, is_checkpoint=False)
+                    and not _base_model_known_mismatch(hit)
+                ):
+                    _consider(hit, 1.0 + _base_model_adjustment(hit), "same_hash")
+
+            version_id = entry.get("modelVersionId") or entry.get("id")
+            if version_id is not None:
+                hit = self._get_lora_from_version_index(str(version_id))
+                if (
+                    isinstance(hit, dict)
+                    and (hit.get("sha256") or "").strip()
+                    and not _base_model_known_mismatch(hit)
+                ):
+                    _consider(hit, 0.95 + _base_model_adjustment(hit), "same_version")
+
+        filename_source = query_text or (entry.get("file_name") or "")
+        name_source = query_text or (entry.get("modelName") or "")
+        norm_filename_source = self._normalize_filename_key(filename_source)
+        name_source_cf = name_source.casefold()
+        # Substring hits floor the similarity ratio, but only for meaningful
+        # queries — a 1-2 character query is a substring of nearly every
+        # filename and would flood the suggestions with noise.
+        substring_floor = len(query_text) >= 3
+
+        for item in pool:
+            adjustment = _base_model_adjustment(item)
+
+            item_filename = self._normalize_filename_key(item.get("file_name") or "")
+            if norm_filename_source and item_filename:
+                ratio = difflib.SequenceMatcher(
+                    None, norm_filename_source, item_filename
+                ).ratio()
+                if substring_floor and norm_filename_source in item_filename:
+                    ratio = max(ratio, 0.8)
+                if ratio >= 0.55:
+                    _consider(
+                        item, 0.5 + 0.4 * ratio + adjustment, "similar_filename"
+                    )
+
+            item_name = (item.get("model_name") or "").casefold()
+            if name_source_cf and item_name:
+                ratio = difflib.SequenceMatcher(
+                    None, name_source_cf, item_name
+                ).ratio()
+                if substring_floor and name_source_cf in item_name:
+                    ratio = max(ratio, 0.8)
+                if ratio >= 0.65:
+                    _consider(item, 0.4 + 0.35 * ratio + adjustment, "similar_name")
+
+        suggestions = []
+        for record in best.values():
+            item = record["item"]
+            file_name = item.get("file_name") or ""
+            stem = self._strip_weight_extension(file_name)
+            folder = (item.get("folder") or "").replace("\\", "/").strip("/")
+            norm_key = self._normalize_filename_key(file_name)
+            if norm_key and basename_counts.get(norm_key, 0) > 1 and folder:
+                target_name = f"{folder}/{stem}"
+            else:
+                target_name = stem
+            suggestions.append(
+                {
+                    "file_name": file_name,
+                    "file_path": item.get("file_path") or "",
+                    "model_name": item.get("model_name") or "",
+                    "base_model": item.get("base_model") or "",
+                    "preview_url": item.get("preview_url") or "",
+                    "hash": (item.get("sha256") or "").lower(),
+                    "score": round(record["score"], 3),
+                    "match_reason": record["reason"],
+                    "target_name": target_name,
+                }
+            )
+
+        suggestions.sort(key=lambda s: (-s["score"], s["file_name"].lower()))
+        return suggestions[:limit]
+
     def _is_rematch_candidate(self, entry: dict[str, Any]) -> bool:
         """Return True when a recipe entry is eligible for local re-matching.
 
@@ -3677,6 +3861,13 @@ class RecipeScanner:
                 raise RecipeNotFoundError("LoRA index out of range in recipe")
 
             lora_entry = loras[lora_index]
+            # Snapshot the pre-update state so the association can be restored
+            # later (undo reconnect). Never nest snapshots.
+            snapshot = {
+                key: copy.deepcopy(value)
+                for key, value in lora_entry.items()
+                if key != "reconnectSnapshot"
+            }
             lora_entry["isDeleted"] = False
             lora_entry["hashInvalid"] = False
             lora_entry["exclude"] = False
@@ -3695,6 +3886,8 @@ class RecipeScanner:
                     lora_entry["modelVersionName"] = civitai_info.get("name", "")
                     lora_entry["modelVersionId"] = civitai_info.get("id")
 
+            lora_entry["reconnectSnapshot"] = snapshot
+
             from ..utils.utils import calculate_recipe_fingerprint
 
             recipe_data["fingerprint"] = calculate_recipe_fingerprint(
@@ -3730,6 +3923,68 @@ class RecipeScanner:
         updated_lora = self._enrich_lora_entry(updated_lora)
         return recipe_data, updated_lora
 
+    async def restore_lora_entry(
+        self,
+        recipe_id: str,
+        lora_index: int,
+    ) -> Tuple[Dict[str, Any], Dict[str, Any]]:
+        """Restore a LoRA entry to its pre-reconnect snapshot.
+
+        Reverses :meth:`update_lora_entry`: the entry saved under
+        ``reconnectSnapshot`` becomes the entry again and the snapshot is
+        dropped. Returns the updated recipe data and the restored LoRA
+        metadata.
+        """
+
+        recipe_json_path = await self.get_recipe_json_path(recipe_id)
+        if not recipe_json_path or not os.path.exists(recipe_json_path):
+            raise RecipeNotFoundError("Recipe not found")
+
+        async with self._mutation_lock:
+            with open(recipe_json_path, "r", encoding="utf-8") as file_obj:
+                recipe_data = json.load(file_obj)
+
+            loras = recipe_data.get("loras", [])
+            if lora_index < 0 or lora_index >= len(loras):
+                raise RecipeNotFoundError("LoRA index out of range in recipe")
+
+            snapshot = loras[lora_index].get("reconnectSnapshot")
+            if not isinstance(snapshot, dict):
+                raise RecipeValidationError(
+                    "LoRA entry has no reconnect snapshot to restore"
+                )
+
+            restored_entry = copy.deepcopy(snapshot)
+            restored_entry.pop("reconnectSnapshot", None)
+            loras[lora_index] = restored_entry
+
+            from ..utils.utils import calculate_recipe_fingerprint
+
+            recipe_data["fingerprint"] = calculate_recipe_fingerprint(
+                recipe_data.get("loras", [])
+            )
+            recipe_data["modified"] = time.time()
+
+            with open(recipe_json_path, "w", encoding="utf-8") as file_obj:
+                json.dump(recipe_data, file_obj, indent=4, ensure_ascii=False)
+
+        cache = await self.get_cached_data()
+        replaced = await cache.replace_recipe(recipe_id, recipe_data, resort=False)
+        if not replaced:
+            await cache.add_recipe(recipe_data, resort=False)
+        self._schedule_resort()
+
+        # Update FTS index
+        self._update_fts_index_for_recipe(recipe_data, "update")
+
+        # Update persistent SQLite cache
+        if self._persistent_cache:
+            self._persistent_cache.update_recipe(recipe_data, recipe_json_path)
+            self._json_path_map[recipe_id] = recipe_json_path
+
+        restored_lora = self._enrich_lora_entry(dict(restored_entry))
+        return recipe_data, restored_lora
+
     async def set_lora_entry_hash_invalid(
         self,
         recipe_id: str,

py/services/recipes/persistence_service.py

@@ -13,6 +13,11 @@ from typing import Any, Awaitable, Dict, Iterable, Optional, cast
 
 from ...config import config
 from ...recipes.constants import GEN_PARAM_KEYS
+from ...utils.base_model import (
+    RELATION_COMPATIBLE,
+    RELATION_INCOMPATIBLE,
+    base_model_relation,
+)
 from ...utils.utils import calculate_recipe_fingerprint
 from ..pending_delete_service import get_pending_delete_service
 from .errors import RecipeNotFoundError, RecipeValidationError
@@ -430,20 +435,31 @@ class RecipePersistenceService:
         with open(recipe_path, "r", encoding="utf-8") as file_obj:
             recipe_base_model = json.load(file_obj).get("base_model", "")
 
-        target_lora = await recipe_scanner.get_local_lora(target_name, recipe_base_model)
-        if not target_lora:
-            matches = await recipe_scanner.find_local_loras_by_name(target_name)
-            if len(matches) > 1:
-                raise RecipeValidationError(
-                    f"Multiple local LoRAs match '{target_name}'; "
-                    "include the folder path to disambiguate"
-                )
-            if len(matches) == 1:
-                raise RecipeValidationError(
-                    f"Local LoRA '{target_name}' has a different base model than the recipe"
-                )
+        matches = await recipe_scanner.find_local_loras_by_name(target_name)
+        if not matches:
             raise RecipeNotFoundError(f"Local LoRA not found with name: {target_name}")
 
+        # Three-tier base-model guard: exact/unknown labels pass silently;
+        # labels from the same architecture family (e.g. Pony ↔ Illustrious)
+        # pass but are reported so the UI can warn; confident architecture
+        # mismatches stay hard-rejected because they can never load.
+        eligible: list[tuple[dict, str]] = []
+        for match in matches:
+            relation = base_model_relation(recipe_base_model, match.get("base_model"))
+            if relation != RELATION_INCOMPATIBLE:
+                eligible.append((match, relation))
+
+        if not eligible:
+            raise RecipeValidationError(
+                f"Local LoRA '{target_name}' has a different base model than the recipe"
+            )
+        if len(eligible) > 1:
+            raise RecipeValidationError(
+                f"Multiple local LoRAs match '{target_name}'; "
+                "include the folder path to disambiguate"
+            )
+        target_lora, target_relation = eligible[0]
+
         recipe_data, updated_lora = await recipe_scanner.update_lora_entry(
             recipe_id,
             lora_index,
@@ -451,6 +467,43 @@ class RecipePersistenceService:
             target_lora=target_lora,
         )
 
+        image_path = recipe_data.get("file_path")
+        if image_path and os.path.exists(image_path):
+            self._exif_utils.append_recipe_metadata(image_path, recipe_data)
+
+        matching_recipes = []
+        if "fingerprint" in recipe_data:
+            matching_recipes = await recipe_scanner.find_recipes_by_fingerprint(recipe_data["fingerprint"])
+            if recipe_id in matching_recipes:
+                matching_recipes.remove(recipe_id)
+
+        payload: dict[str, Any] = {
+            "success": True,
+            "recipe_id": recipe_id,
+            "updated_lora": updated_lora,
+            "matching_recipes": matching_recipes,
+        }
+        if target_relation == RELATION_COMPATIBLE:
+            # Structured data, not prose — the frontend localizes the warning.
+            payload["base_model_mismatch"] = {
+                "recipe_base_model": recipe_base_model,
+                "lora_base_model": target_lora.get("base_model") or "",
+            }
+        return PersistenceResult(payload)
+
+    async def restore_lora(
+        self,
+        *,
+        recipe_scanner,
+        recipe_id: str,
+        lora_index: int,
+    ) -> PersistenceResult:
+        """Restore a LoRA entry to the state captured before its reconnect."""
+
+        recipe_data, updated_lora = await recipe_scanner.restore_lora_entry(
+            recipe_id, lora_index
+        )
+
         image_path = recipe_data.get("file_path")
         if image_path and os.path.exists(image_path):
             self._exif_utils.append_recipe_metadata(image_path, recipe_data)
@@ -470,6 +523,35 @@ class RecipePersistenceService:
             }
         )
 
+    async def get_reconnect_suggestions(
+        self,
+        *,
+        recipe_scanner,
+        recipe_id: str,
+        lora_index: int,
+        query: str | None = None,
+    ) -> PersistenceResult:
+        """Return ranked local LoRA candidates for reconnecting a recipe entry."""
+
+        recipe_path = await recipe_scanner.get_recipe_json_path(recipe_id)
+        if not recipe_path or not os.path.exists(recipe_path):
+            raise RecipeNotFoundError("Recipe not found")
+
+        with open(recipe_path, "r", encoding="utf-8") as file_obj:
+            recipe_data = json.load(file_obj)
+
+        loras = recipe_data.get("loras") or []
+        if lora_index < 0 or lora_index >= len(loras):
+            raise RecipeValidationError(f"Invalid lora_index: {lora_index}")
+
+        suggestions = await recipe_scanner.suggest_reconnect_candidates(
+            entry=loras[lora_index],
+            recipe_base_model=recipe_data.get("base_model"),
+            query=query,
+        )
+
+        return PersistenceResult({"success": True, "suggestions": suggestions})
+
     async def mark_lora_hash_invalid(
         self,
         *,

py/utils/base_model.py

@@ -0,0 +1,79 @@
+"""Base-model architecture families and compatibility relations.
+
+CivitAI base-model labels describe fine-tune lineages, not architectures.
+A LoRA physically loads on any checkpoint sharing its tensor architecture,
+so e.g. Pony / Illustrious / NoobAI / SDXL 1.0 LoRAs are interchangeable
+(quality varies, but nothing breaks). Different architectures (SD 1.5 vs
+SDXL vs Flux) are guaranteed failures and must stay hard-rejected.
+
+Only families with high-confidence architecture equivalence are listed.
+Anything not in the table is treated as its own family, i.e. only an exact
+label match is accepted — unknown new labels never get wrongly waved through.
+"""
+
+from __future__ import annotations
+
+from typing import Optional
+
+# Normalized (casefolded, stripped) base-model label -> architecture family.
+_BASE_MODEL_FAMILIES = {
+    # SD 1.x — all share the original 512px latent UNet.
+    "sd 1.4": "sd1",
+    "sd 1.5": "sd1",
+    "sd 1.5 lcm": "sd1",
+    "sd 1.5 hyper": "sd1",
+    # SDXL lineage — Pony / Illustrious / NoobAI are SDXL fine-tunes.
+    # Note: Pony V7 is AuraFlow-based, NOT SDXL, so it is deliberately absent.
+    "sdxl 1.0": "sdxl",
+    "sdxl lightning": "sdxl",
+    "sdxl hyper": "sdxl",
+    "pony": "sdxl",
+    "pony diffusion": "sdxl",
+    "pony diffusion v6 xl": "sdxl",
+    "illustrious": "sdxl",
+    "illustrious 0.1": "sdxl",
+    "illustrious 1.0": "sdxl",
+    "illustrious 1.1": "sdxl",
+    "noobai": "sdxl",
+    # Flux.1 — dev/schnell/Krea share the 12B rectified-flow transformer.
+    "flux.1 d": "flux1",
+    "flux.1 s": "flux1",
+    "flux.1 krea": "flux1",
+    # SD 3.5 Large and its Turbo distill share the 8B MMDiT. SD 3 (2B) and
+    # SD 3.5 Medium (2.5B) have different shapes and stay unlisted.
+    "sd 3.5 large": "sd35-large",
+    "sd 3.5 large turbo": "sd35-large",
+}
+
+_UNKNOWN_TOKENS = {"", "unknown", "other", "none", "null"}
+
+# Relation constants returned by base_model_relation().
+RELATION_UNKNOWN = "unknown"  # at least one side has no usable label
+RELATION_SAME = "same"  # identical labels
+RELATION_COMPATIBLE = "compatible"  # different labels, same architecture family
+RELATION_INCOMPATIBLE = "incompatible"  # different labels, different/unknown family
+
+
+def _normalize(label: Optional[str]) -> str:
+    return (label or "").strip().casefold()
+
+
+def base_model_relation(a: Optional[str], b: Optional[str]) -> str:
+    """Classify how two base-model labels relate for reconnect purposes.
+
+    ``RELATION_UNKNOWN`` when either side has no usable label (callers treat
+    it as lenient-allow), ``RELATION_SAME`` for identical labels,
+    ``RELATION_COMPATIBLE`` when both labels map to the same architecture
+    family, and ``RELATION_INCOMPATIBLE`` otherwise — including when a label
+    is missing from the family table (conservative fallback).
+    """
+    na, nb = _normalize(a), _normalize(b)
+    if na in _UNKNOWN_TOKENS or nb in _UNKNOWN_TOKENS:
+        return RELATION_UNKNOWN
+    if na == nb:
+        return RELATION_SAME
+    fa = _BASE_MODEL_FAMILIES.get(na)
+    fb = _BASE_MODEL_FAMILIES.get(nb)
+    if fa is not None and fa == fb:
+        return RELATION_COMPATIBLE
+    return RELATION_INCOMPATIBLE