backend/app/api/v1/cleanup.py

@@ -67,6 +67,16 @@ async def guess_gender(
     return [GenderProposal(**r) for r in rows]
 
 
+@router.get("/{tree_id}/cleanup/gender/from-spouse", response_model=list[GenderProposal])
+async def guess_gender_from_spouse(
+    tree_id: uuid.UUID, session: SessionDep, current: CurrentUser
+) -> list[GenderProposal]:
+    """Infer a missing sex from a partner whose sex is set (opposite-sex couple)."""
+    tree = await tree_service.get_tree(session, viewer_id=current.id, tree_id=tree_id)
+    rows = await cleanup_service.guess_gender_by_spouse(session, actor=current, tree=tree)
+    return [GenderProposal(**r) for r in rows]
+
+
 @router.post("/{tree_id}/cleanup/gender", response_model=CleanupResult)
 async def apply_gender(
     tree_id: uuid.UUID, data: GenderApply, session: SessionDep, current: CurrentUser

backend/app/services/cleanup_service.py

@@ -12,8 +12,10 @@ import uuid
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from app.models.enums import RelationshipType
 from app.models.event import Event
 from app.models.person import Name, Person
+from app.models.relationship import Relationship
 from app.models.tree import Tree
 from app.models.user import User
 from app.services import gedcom, privacy
@@ -182,6 +184,52 @@ async def guess_gender_by_name(
     return out
 
 
+async def guess_gender_by_spouse(
+    session: AsyncSession, *, actor: User, tree: Tree
+) -> list[dict]:
+    """Infer the sex of a person who has none set from a partner whose sex IS set
+    (couples in a tree are opposite-sex in practice — e.g. a confirmed-male
+    husband implies a female wife). People whose known partners disagree are
+    ambiguous and skipped; the result is a preview to review, not an auto-write."""
+    await _require_editor(session, actor=actor, tree=tree)
+    persons = await _persons(session, tree.id)
+    gender = {p.id: p.gender for p in persons}
+    names = await _primary_name_by_person(session, tree.id)
+    rels = (
+        await session.execute(
+            select(Relationship).where(
+                Relationship.tree_id == tree.id,
+                Relationship.deleted_at.is_(None),
+                Relationship.type == RelationshipType.partnership,
+            )
+        )
+    ).scalars().all()
+    opp = {"male": "female", "female": "male"}
+    proposals: dict[uuid.UUID, set[str]] = {}
+    for r in rels:
+        for me_id, other_id in (
+            (r.person_from_id, r.person_to_id),
+            (r.person_to_id, r.person_from_id),
+        ):
+            if gender.get(me_id):
+                continue  # this person already has a sex
+            other_sex = str(gender.get(other_id) or "")
+            if other_sex in opp:
+                proposals.setdefault(me_id, set()).add(opp[other_sex])
+    out: list[dict] = []
+    for pid, sexes in proposals.items():
+        if len(sexes) != 1:
+            continue  # partners of differing known sex → ambiguous
+        nm = names.get(pid)
+        if nm is None:
+            continue
+        out.append(
+            {"person_id": str(pid), "name": _display(nm), "proposed_gender": next(iter(sexes))}
+        )
+    out.sort(key=lambda r: r["name"])
+    return out
+
+
 async def apply_gender(
     session: AsyncSession, *, actor: User, tree: Tree, updates: list[dict]
 ) -> int:

backend/tests/test_cleanup.py

@@ -51,6 +51,44 @@ async def test_deceased_preview_and_apply(client):
     assert old not in [r["person_id"] for r in prev2]
 
 
+async def test_gender_from_spouse_preview_and_apply(client):
+    h, tid = await _tree(client, "cl-spouse@example.com")
+    husband = (
+        await client.post(
+            f"/api/v1/trees/{tid}/persons",
+            json={"given": "Otto", "surname": "Frey", "gender": "male"},
+            headers=h,
+        )
+    ).json()["id"]
+    wife = await _person(client, h, tid, "Bea", "Frey")  # no sex
+    loner = await _person(client, h, tid, "Nyx", "Alone")  # no sex, no partner
+    await client.post(
+        f"/api/v1/trees/{tid}/relationships",
+        json={"type": "partnership", "person_from_id": husband, "person_to_id": wife},
+        headers=h,
+    )
+
+    prev = (await client.get(f"/api/v1/trees/{tid}/cleanup/gender/from-spouse", headers=h)).json()
+    by = {r["person_id"]: r["proposed_gender"] for r in prev}
+    assert by.get(wife) == "female"  # opposite of the confirmed-male husband
+    assert loner not in by  # no known-sex partner → not proposed
+    assert husband not in by  # already has a sex
+
+    r = await client.post(
+        f"/api/v1/trees/{tid}/cleanup/gender",
+        json={"updates": [{"person_id": wife, "gender": "female"}]},
+        headers=h,
+    )
+    assert r.status_code == 200 and r.json()["updated"] == 1
+    assert (
+        await client.get(f"/api/v1/trees/{tid}/persons/{wife}", headers=h)
+    ).json()["gender"] == "female"
+
+    # Once set, the wife is no longer proposed.
+    prev2 = (await client.get(f"/api/v1/trees/{tid}/cleanup/gender/from-spouse", headers=h)).json()
+    assert wife not in [r["person_id"] for r in prev2]
+
+
 GED = b"""0 HEAD
 0 @I1@ INDI
 1 NAME Josias /Moody/

frontend/app/trees/[id]/cleanup/page.tsx

@@ -109,6 +109,15 @@ export default function CleanupPage() {
     setGenSel(new Set((data ?? []).map((g) => g.person_id)));
   }
 
+  async function guessGenderFromSpouse() {
+    setGenMsg(null);
+    const { data } = await api.GET("/api/v1/trees/{tree_id}/cleanup/gender/from-spouse", {
+      params: { path: { tree_id: treeId } },
+    });
+    setGender(data ?? []);
+    setGenSel(new Set((data ?? []).map((g) => g.person_id)));
+  }
+
   async function applyGender() {
     const updates = (gender ?? [])
       .filter((g) => genSel.has(g.person_id))
@@ -246,10 +255,15 @@ export default function CleanupPage() {
             <Button variant="outline" onClick={guessGender}>
               Guess from first name
             </Button>
+            <Button variant="outline" onClick={guessGenderFromSpouse}>
+              Infer from spouse
+            </Button>
           </div>
           <p className="text-xs text-[var(--muted)]">
-            “Guess from first name” uses a built-in name dictionary for people with no sex set;
-            ambiguous names (Marion, Frances, …) are left for you to decide.
+            “Guess from first name” uses a built-in name dictionary for people with no sex set.
+            “Infer from spouse” sets the opposite sex for an unset partner of someone whose sex is
+            known (e.g. a confirmed-male husband ⇒ a female wife) — review before applying, since
+            it assumes opposite-sex couples.
           </p>
           {genMsg && <p className="text-sm text-bronze">{genMsg}</p>}
           {gender && (

frontend/lib/api/schema.d.ts

@@ -734,6 +734,26 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/api/v1/trees/{tree_id}/cleanup/gender/from-spouse": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        /**
+         * Guess Gender From Spouse
+         * @description Infer a missing sex from a partner whose sex is set (opposite-sex couple).
+         */
+        get: operations["guess_gender_from_spouse_api_v1_trees__tree_id__cleanup_gender_from_spouse_get"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/api/v1/trees/{tree_id}/cleanup/gender": {
         parameters: {
             query?: never;
@@ -3687,6 +3707,37 @@ export interface operations {
             };
         };
     };
+    guess_gender_from_spouse_api_v1_trees__tree_id__cleanup_gender_from_spouse_get: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path: {
+                tree_id: string;
+            };
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Successful Response */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["GenderProposal"][];
+                };
+            };
+            /** @description Validation Error */
+            422: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["HTTPValidationError"];
+                };
+            };
+        };
+    };
     apply_gender_api_v1_trees__tree_id__cleanup_gender_post: {
         parameters: {
             query?: never;

frontend/openapi.json

@@ -2915,6 +2915,54 @@
         }
       }
     },
+    "/api/v1/trees/{tree_id}/cleanup/gender/from-spouse": {
+      "get": {
+        "tags": [
+          "cleanup"
+        ],
+        "summary": "Guess Gender From Spouse",
+        "description": "Infer a missing sex from a partner whose sex is set (opposite-sex couple).",
+        "operationId": "guess_gender_from_spouse_api_v1_trees__tree_id__cleanup_gender_from_spouse_get",
+        "parameters": [
+          {
+            "name": "tree_id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string",
+              "format": "uuid",
+              "title": "Tree Id"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Successful Response",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "array",
+                  "items": {
+                    "$ref": "#/components/schemas/GenderProposal"
+                  },
+                  "title": "Response Guess Gender From Spouse Api V1 Trees  Tree Id  Cleanup Gender From Spouse Get"
+                }
+              }
+            }
+          },
+          "422": {
+            "description": "Validation Error",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/HTTPValidationError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/api/v1/trees/{tree_id}/cleanup/gender": {
       "post": {
         "tags": [