test: add missing model and error code test coverage

Sources/XCDocs/Models/DocumentationEntry.swift

@@ -33,4 +33,13 @@ public struct DocumentationEntry: Codable, Hashable, Identifiable, Sendable {
         self.title = title
         self.content = content
     }
+
+    public init(from decoder: any Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        self.id = try container.decode(String.self, forKey: .id)
+        self.framework = try container.decodeIfPresent(String.self, forKey: .framework)
+        self.kind = try? container.decodeIfPresent(DocumentationKind.self, forKey: .kind)
+        self.title = try container.decodeIfPresent(String.self, forKey: .title)
+        self.content = try container.decodeIfPresent(String.self, forKey: .content)
+    }
 }

Tests/XCDocsTests/BridgeErrorTests.swift

@@ -25,7 +25,7 @@ struct BridgeErrorTests {
     func formatsDescriptionForAllErrorCodes() {
         let codes: [BridgeErrorCode] = [
             .frameworkUnavailable, .classUnavailable, .selectorUnavailable, .assetNotFound, .invalidResponse,
-            .invalidEmbedding, .operationFailed, .searchFailed, .timeout,
+            .invalidEmbedding, .operationFailed, .invalidScore, .searchFailed, .timeout,
         ]
 
         for code in codes {

Tests/XCDocsTests/ModelTests.swift

@@ -39,6 +39,24 @@ struct ModelTests {
         guard #available(macOS 26, *) else { return }
         assertStableIdentities()
     }
+
+    @Test
+    func documentationEntryDecodesUnknownKindAsNil() throws {
+        guard #available(macOS 26, *) else { return }
+        try assertUnknownKindDecodesAsNil()
+    }
+
+    @Test
+    func searchResultWithNaNScoreThrowsOnJSONEncode() throws {
+        guard #available(macOS 26, *) else { return }
+        assertNaNScoreThrowsOnEncode()
+    }
+
+    @Test
+    func searchResultWithInfinityScoreThrowsOnJSONEncode() throws {
+        guard #available(macOS 26, *) else { return }
+        assertInfinityScoreThrowsOnEncode()
+    }
 }
 
 @available(macOS 26, *)
@@ -147,6 +165,33 @@ private func assertStableIdentities() {
     #expect(result.id == entry.id)
 }
 
+@available(macOS 26, *)
+private func assertUnknownKindDecodesAsNil() throws {
+    let json = """
+        {"id":"/doc/X","framework":null,"kind":"unknownKind","title":null,"content":null}
+        """
+    let entry = try JSONDecoder().decode(DocumentationEntry.self, from: Data(json.utf8))
+    #expect(entry.kind == nil)
+}
+
+@available(macOS 26, *)
+private func assertNaNScoreThrowsOnEncode() {
+    let result = SearchResult(
+        score: .nan,
+        entry: DocumentationEntry(id: "/doc/X", framework: nil, kind: nil, title: nil, content: nil)
+    )
+    #expect(throws: EncodingError.self) { try JSONEncoder().encode(result) }
+}
+
+@available(macOS 26, *)
+private func assertInfinityScoreThrowsOnEncode() {
+    let result = SearchResult(
+        score: .infinity,
+        entry: DocumentationEntry(id: "/doc/X", framework: nil, kind: nil, title: nil, content: nil)
+    )
+    #expect(throws: EncodingError.self) { try JSONEncoder().encode(result) }
+}
+
 private func assertRoundTrip<T: Codable & Equatable>(_ value: T) throws {
     let data = try JSONEncoder().encode(value)
     let decoded = try JSONDecoder().decode(T.self, from: data)