fix(postcode-search): classify RH (HMO) family as addable residential

7 Leyton Avenue (UPRN 100031252876) came back from OS Places as RH03
("HMO Not Further Divided") and rendered as "Non-residential", so it
couldn't be added from the postcode-search "add properties" journey.

classifyOsCode decided "residential?" purely on an RD prefix, dropping the
whole RH (HMO) family — even though RD07 (the RD-family HMO code) was
already mapped to House. Extend the residential check to RH and map
RH01/RH02/RH03 to House (built form unknowable), consistent with RD07.

Updates ADR-0007's enumerated mapping table to stay truthful.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/adr/0007-postcode-search-creates-properties.md

@@ -35,9 +35,13 @@ modelling exists.
   distinguishable.
 - **Deterministic mapping** (fixed table, tested): RD02→House+Detached,
   RD03→House+Semi-Detached, RD04→House (Mid/End unknowable — no built form),
-  RD06→Flat, RD07→House. Every other code maps nothing; `Unknown` is never
+  RD06→Flat, RD07→House, RH01/RH02/RH03→House (the dedicated HMO family, built
+  form unknowable). Every other code maps nothing; `Unknown` is never
   written (absence, not noise) — preserving the finaliser's invariant. The
   backend's predict-EPC service consumes these for archetype matching.
+- **Addable codes**: the RD (dwelling) family except RD10 (institutions), plus
+  the RH (HMO) family. All other codes — commercial, institutional, land — are
+  not addable and render "Non-residential".
 - **Read-through cache** on the existing `postcode_search` jsonb table:
   serve when fresher than 30 days, else refresh from OS Places and upsert.
 

src/lib/postcodeSearch/model.test.ts

@@ -20,6 +20,13 @@ describe("classifyOsCode", () => {
     expect(classifyOsCode("RD07")).toEqual({ selectable: true, propertyType: "House", builtForm: null });
   });
 
+  it("maps the RH (HMO) family to House, like RD07", () => {
+    // e.g. UPRN 100031252876, 7 Leyton Avenue — RH03 must not read as non-residential.
+    expect(classifyOsCode("RH01")).toEqual({ selectable: true, propertyType: "House", builtForm: null });
+    expect(classifyOsCode("RH02")).toEqual({ selectable: true, propertyType: "House", builtForm: null });
+    expect(classifyOsCode("RH03")).toEqual({ selectable: true, propertyType: "House", builtForm: null });
+  });
+
   it("keeps other residential codes selectable but writes no facts — never Unknown", () => {
     for (const code of ["RD", "RD01", "RD08"]) {
       expect(classifyOsCode(code)).toEqual({ selectable: true, propertyType: null, builtForm: null });
@@ -63,6 +70,21 @@ describe("toAddressCandidates", () => {
     expect(out[1]).toMatchObject({ uprn: "101", selectable: false });
   });
 
+  it("classifies an RH03 HMO as a selectable House, not Non-residential", () => {
+    // Regression: 7 Leyton Avenue (UPRN 100031252876) came back RH03 ("HMO Not
+    // Further Divided") on a street of RD02/RD03 houses and rendered as
+    // "Non-residential", so it couldn't be added.
+    const hmo = [
+      { DPA: { UPRN: "100031252876", ADDRESS: "7, LEYTON AVENUE, SUTTON-IN-ASHFIELD, NG17 3BD",
+               POSTCODE: "NG17 3BD", CLASSIFICATION_CODE: "RH03", LAT: 53.1352313, LNG: -1.2522665 } },
+    ];
+    const out = toAddressCandidates(hmo as never, "NG17 3BD");
+    expect(out[0]).toMatchObject({
+      uprn: "100031252876", address: "7, Leyton Avenue, Sutton-In-Ashfield",
+      classificationCode: "RH03", selectable: true, propertyType: "House", builtForm: null,
+    });
+  });
+
   it("orders addresses numerically, so Flat 2 comes before Flat 10", () => {
     const flats = [
       { DPA: { UPRN: "1", ADDRESS: "FLAT 10, BIRCH COURT, M20 4TF", CLASSIFICATION_CODE: "RD06" } },
@@ -102,6 +124,18 @@ describe("buildWritePlan", () => {
       { component: "built_form_type", value: "Detached", originalDescription: "RD02", buildingPart: 0 },
     ]);
   });
+  it("writes a House property_type override for an RH03 HMO, keyed to the OS code", () => {
+    const plan = buildWritePlan(
+      { uprn: "100031252876", address: "7, Leyton Avenue, Sutton-In-Ashfield", postcode: "NG17 3BD",
+        classificationCode: "RH03", lat: 53.1352313, lng: -1.2522665, selectable: true,
+        propertyType: "House", builtForm: null },
+      geo,
+    );
+    // HMO built form is unknowable, so only the property_type fact is written.
+    expect(plan.overrides).toEqual([
+      { component: "property_type", value: "House", originalDescription: "RH03", buildingPart: 0 },
+    ]);
+  });
   it("writes no overrides when the code maps nothing — never Unknown", () => {
     const plan = buildWritePlan(
       { uprn: "200", address: "Birch Court", postcode: "M20 4UD", classificationCode: "RD",

src/lib/postcodeSearch/model.ts

@@ -28,7 +28,11 @@ const OS_CODE_FACTS: Record<string, { propertyType: string; builtForm: string |
   RD03: { propertyType: "House", builtForm: "Semi-Detached" },
   RD04: { propertyType: "House", builtForm: null }, // terraced — mid/end unknowable
   RD06: { propertyType: "Flat", builtForm: null },
-  RD07: { propertyType: "House", builtForm: null }, // HMO
+  RD07: { propertyType: "House", builtForm: null }, // HMO (RD-family code)
+  // RH is the dedicated HMO family; treat as House like RD07, built form unknowable.
+  RH01: { propertyType: "House", builtForm: null }, // HMO parent
+  RH02: { propertyType: "House", builtForm: null }, // HMO bedsit / non-self-contained
+  RH03: { propertyType: "House", builtForm: null }, // HMO not further divided
 };
 
 const CACHE_MAX_AGE_MS = 30 * 24 * 60 * 60 * 1000;
@@ -181,7 +185,10 @@ export function cacheAgeDays(fetchedAt: Date, now: Date): number {
 export function classifyOsCode(code: string | null): OsClassification {
   if (!code) return { selectable: false, propertyType: null, builtForm: null };
   const c = code.trim().toUpperCase();
-  const residential = c === "RD" || (c.startsWith("RD") && c !== "RD10");
+  // Addable dwellings: the RD (dwelling) family except RD10 (institutions),
+  // plus the RH (HMO) family. Everything else — commercial, institutional,
+  // land — is not addable.
+  const residential = (c.startsWith("RD") && c !== "RD10") || c.startsWith("RH");
   if (!residential) return { selectable: false, propertyType: null, builtForm: null };
   const facts = OS_CODE_FACTS[c];
   return {