refactor(sync): remove legacy conflict resolution strategies

Remove the unused "local_wins" strategy and ConflictResolverOptions
interface from ConflictResolver. The CRDT-based conflict resolution
now always uses Automerge merge with server_wins fallback when CRDT
data is unavailable. This simplifies the codebase by removing
configuration options that were never used in production.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

4 files changed, 63 insertions, 197 deletions

diff --git a/src/client/sync/conflict.test.ts b/src/client/sync/conflict.test.ts
index 6cef6b0..3fe8b67 100644
--- a/src/client/sync/conflict.test.ts
+++ b/src/client/sync/conflict.test.ts
@@ -150,7 +150,7 @@ describe("ConflictResolver", () => {
 	});
 
 	describe("resolveDeckConflict", () => {
-		it("should use server data with server_wins strategy", async () => {
+		it("should use server data when no CRDT data available", async () => {
 			const localDeck = await localDeckRepository.create({
 				userId: "user-1",
 				name: "Local Name",
@@ -170,7 +170,7 @@ describe("ConflictResolver", () => {
 				syncVersion: 5,
 			};
 
-			const resolver = new ConflictResolver({ strategy: "server_wins" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveDeckConflict(localDeck, serverDeck);
 
 			expect(result.resolution).toBe("server_wins");
@@ -181,39 +181,10 @@ describe("ConflictResolver", () => {
 			expect(updatedDeck?.newCardsPerDay).toBe(20);
 			expect(updatedDeck?._synced).toBe(true);
 		});
-
-		it("should keep local data with local_wins strategy", async () => {
-			const localDeck = await localDeckRepository.create({
-				userId: "user-1",
-				name: "Local Name",
-				description: "Local description",
-				newCardsPerDay: 10,
-			});
-
-			const serverDeck = {
-				id: localDeck.id,
-				userId: "user-1",
-				name: "Server Name",
-				description: "Server description",
-				newCardsPerDay: 20,
-				createdAt: new Date("2024-01-01"),
-				updatedAt: new Date("2024-01-03"),
-				deletedAt: null,
-				syncVersion: 5,
-			};
-
-			const resolver = new ConflictResolver({ strategy: "local_wins" });
-			const result = await resolver.resolveDeckConflict(localDeck, serverDeck);
-
-			expect(result.resolution).toBe("local_wins");
-
-			const updatedDeck = await localDeckRepository.findById(localDeck.id);
-			expect(updatedDeck?.name).toBe("Local Name");
-		});
 	});
 
 	describe("resolveCardConflict", () => {
-		it("should use server data with server_wins strategy", async () => {
+		it("should use server data when no CRDT data available", async () => {
 			const deck = await localDeckRepository.create({
 				userId: "user-1",
 				name: "Test Deck",
@@ -251,7 +222,7 @@ describe("ConflictResolver", () => {
 				syncVersion: 3,
 			};
 
-			const resolver = new ConflictResolver({ strategy: "server_wins" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveCardConflict(localCard, serverCard);
 
 			expect(result.resolution).toBe("server_wins");
@@ -261,53 +232,6 @@ describe("ConflictResolver", () => {
 			expect(updatedCard?.back).toBe("Server Answer");
 			expect(updatedCard?._synced).toBe(true);
 		});
-
-		it("should keep local data with local_wins strategy", async () => {
-			const deck = await localDeckRepository.create({
-				userId: "user-1",
-				name: "Test Deck",
-				description: null,
-				newCardsPerDay: 20,
-			});
-
-			const localCard = await localCardRepository.create({
-				deckId: deck.id,
-				noteId: "test-note-id",
-				isReversed: false,
-				front: "Local Question",
-				back: "Local Answer",
-			});
-
-			const serverCard = {
-				id: localCard.id,
-				deckId: deck.id,
-				noteId: "test-note-id",
-				isReversed: false,
-				front: "Server Question",
-				back: "Server Answer",
-				state: CardState.New,
-				due: new Date(),
-				stability: 0,
-				difficulty: 0,
-				elapsedDays: 0,
-				scheduledDays: 0,
-				reps: 0,
-				lapses: 0,
-				lastReview: null,
-				createdAt: new Date(),
-				updatedAt: new Date(),
-				deletedAt: null,
-				syncVersion: 3,
-			};
-
-			const resolver = new ConflictResolver({ strategy: "local_wins" });
-			const result = await resolver.resolveCardConflict(localCard, serverCard);
-
-			expect(result.resolution).toBe("local_wins");
-
-			const updatedCard = await localCardRepository.findById(localCard.id);
-			expect(updatedCard?.front).toBe("Local Question");
-		});
 	});
 
 	describe("resolveConflicts", () => {
@@ -372,7 +296,7 @@ describe("ConflictResolver", () => {
 				...createEmptyPullResult(6),
 			};
 
-			const resolver = new ConflictResolver({ strategy: "server_wins" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveConflicts(pushResult, pullResult);
 
 			expect(result.decks).toHaveLength(2);
@@ -441,7 +365,7 @@ describe("ConflictResolver", () => {
 				...createEmptyPullResult(3),
 			};
 
-			const resolver = new ConflictResolver({ strategy: "server_wins" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveConflicts(pushResult, pullResult);
 
 			expect(result.cards).toHaveLength(1);
@@ -485,7 +409,7 @@ describe("ConflictResolver", () => {
 				...createEmptyPullResult(1),
 			};
 
-			const resolver = new ConflictResolver({ strategy: "server_wins" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveConflicts(pushResult, pullResult);
 
 			expect(result.decks).toHaveLength(1);
@@ -522,7 +446,7 @@ describe("ConflictResolver", () => {
 				...createEmptyPullResult(0),
 			};
 
-			const resolver = new ConflictResolver({ strategy: "server_wins" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveConflicts(pushResult, pullResult);
 
 			// No resolution since server doesn't have the item
@@ -533,7 +457,7 @@ describe("ConflictResolver", () => {
 			expect(localDeck?.name).toBe("Local Only Deck");
 		});
 
-		it("should default to crdt strategy", async () => {
+		it("should use CRDT strategy by default", async () => {
 			const deck = await localDeckRepository.create({
 				userId: "user-1",
 				name: "Local Name",
@@ -647,7 +571,7 @@ describe("ConflictResolver", () => {
 				],
 			};
 
-			const resolver = new ConflictResolver({ strategy: "crdt" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveConflicts(pushResult, pullResult);
 
 			expect(result.decks).toHaveLength(1);
@@ -708,7 +632,7 @@ describe("ConflictResolver", () => {
 				],
 			};
 
-			const resolver = new ConflictResolver({ strategy: "crdt" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveConflicts(pushResult, pullResult);
 
 			// Should still resolve using fallback
@@ -759,7 +683,7 @@ describe("ConflictResolver", () => {
 				...createEmptyPullResult(5),
 			};
 
-			const resolver = new ConflictResolver({ strategy: "crdt" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveConflicts(pushResult, pullResult);
 
 			expect(result.decks).toHaveLength(1);
@@ -822,7 +746,7 @@ describe("ConflictResolver", () => {
 				],
 			};
 
-			const resolver = new ConflictResolver({ strategy: "crdt" });
+			const resolver = new ConflictResolver();
 			const result = await resolver.resolveConflicts(pushResult, pullResult);
 
 			expect(result.decks).toHaveLength(1);
diff --git a/src/client/sync/conflict.ts b/src/client/sync/conflict.ts
index 88b5bfe..be767dc 100644
--- a/src/client/sync/conflict.ts
+++ b/src/client/sync/conflict.ts
@@ -41,7 +41,7 @@ import type { SyncPushResult } from "./push";
  */
 export interface ConflictResolutionItem {
 	id: string;
-	resolution: "server_wins" | "local_wins";
+	resolution: "server_wins";
 }
 
 /**
@@ -57,19 +57,6 @@ export interface ConflictResolutionResult {
 }
 
 /**
- * Options for conflict resolver
- */
-export interface ConflictResolverOptions {
-	/**
-	 * Strategy for resolving conflicts
-	 * - "crdt": Use Automerge CRDT merge for conflict-free resolution (default)
-	 * - "server_wins": Always use server data (fallback when no CRDT data)
-	 * - "local_wins": Always use local data
-	 */
-	strategy?: "crdt" | "server_wins" | "local_wins";
-}
-
-/**
  * CRDT merge result with entity data
  */
 interface CrdtMergeConflictResult<T> {
@@ -203,17 +190,11 @@ function serverNoteFieldValueToLocal(
  * Handles conflicts reported by the server during push operations.
  * When a conflict occurs (server has newer data), this resolver:
  * 1. Identifies conflicting items from push result
- * 2. Uses Automerge CRDT merge for conflict-free resolution (default)
+ * 2. Uses Automerge CRDT merge for conflict-free resolution
  * 3. Falls back to server_wins when CRDT data is unavailable
  * 4. Updates local database accordingly
  */
 export class ConflictResolver {
-	private strategy: "crdt" | "server_wins" | "local_wins";
-
-	constructor(options: ConflictResolverOptions = {}) {
-		this.strategy = options.strategy ?? "crdt";
-	}
-
 	/**
 	 * Check if there are conflicts in push result
 	 */
@@ -243,15 +224,15 @@ export class ConflictResolver {
 	}
 
 	/**
-	 * Resolve deck conflict using configured strategy
+	 * Resolve deck conflict using CRDT merge with server_wins fallback
 	 */
 	async resolveDeckConflict(
 		localDeck: LocalDeck,
 		serverDeck: ServerDeck,
 		serverCrdtBinary?: Uint8Array,
 	): Promise<ConflictResolutionItem> {
-		// Try CRDT merge first if strategy is "crdt" and we have CRDT data
-		if (this.strategy === "crdt" && serverCrdtBinary) {
+		// Try CRDT merge first if we have CRDT data
+		if (serverCrdtBinary) {
 			const mergeResult = await this.mergeDeckWithCrdt(
 				localDeck,
 				serverCrdtBinary,
@@ -273,18 +254,11 @@ export class ConflictResolver {
 			}
 		}
 
-		// Fallback strategy when CRDT merge is not available
-		const resolution =
-			this.strategy === "local_wins" ? "local_wins" : "server_wins";
-
-		if (resolution === "server_wins") {
-			// Update local with server data
-			const localData = serverDeckToLocal(serverDeck);
-			await localDeckRepository.upsertFromServer(localData);
-		}
-		// If local_wins, we keep local data and it will be pushed again next sync
+		// Fallback to server_wins when CRDT merge is not available
+		const localData = serverDeckToLocal(serverDeck);
+		await localDeckRepository.upsertFromServer(localData);
 
-		return { id: localDeck.id, resolution };
+		return { id: localDeck.id, resolution: "server_wins" };
 	}
 
 	/**
@@ -327,15 +301,15 @@ export class ConflictResolver {
 	}
 
 	/**
-	 * Resolve card conflict using configured strategy
+	 * Resolve card conflict using CRDT merge with server_wins fallback
 	 */
 	async resolveCardConflict(
 		localCard: LocalCard,
 		serverCard: ServerCard,
 		serverCrdtBinary?: Uint8Array,
 	): Promise<ConflictResolutionItem> {
-		// Try CRDT merge first if strategy is "crdt" and we have CRDT data
-		if (this.strategy === "crdt" && serverCrdtBinary) {
+		// Try CRDT merge first if we have CRDT data
+		if (serverCrdtBinary) {
 			const mergeResult = await this.mergeCardWithCrdt(
 				localCard,
 				serverCrdtBinary,
@@ -356,18 +330,11 @@ export class ConflictResolver {
 			}
 		}
 
-		// Fallback strategy when CRDT merge is not available
-		const resolution =
-			this.strategy === "local_wins" ? "local_wins" : "server_wins";
+		// Fallback to server_wins when CRDT merge is not available
+		const localData = serverCardToLocal(serverCard);
+		await localCardRepository.upsertFromServer(localData);
 
-		if (resolution === "server_wins") {
-			// Update local with server data
-			const localData = serverCardToLocal(serverCard);
-			await localCardRepository.upsertFromServer(localData);
-		}
-		// If local_wins, we keep local data and it will be pushed again next sync
-
-		return { id: localCard.id, resolution };
+		return { id: localCard.id, resolution: "server_wins" };
 	}
 
 	/**
@@ -405,15 +372,15 @@ export class ConflictResolver {
 	}
 
 	/**
-	 * Resolve note type conflict using configured strategy
+	 * Resolve note type conflict using CRDT merge with server_wins fallback
 	 */
 	async resolveNoteTypeConflict(
 		localNoteType: LocalNoteType,
 		serverNoteType: ServerNoteType,
 		serverCrdtBinary?: Uint8Array,
 	): Promise<ConflictResolutionItem> {
-		// Try CRDT merge first if strategy is "crdt" and we have CRDT data
-		if (this.strategy === "crdt" && serverCrdtBinary) {
+		// Try CRDT merge first if we have CRDT data
+		if (serverCrdtBinary) {
 			const mergeResult = await this.mergeNoteTypeWithCrdt(
 				localNoteType,
 				serverCrdtBinary,
@@ -434,16 +401,11 @@ export class ConflictResolver {
 			}
 		}
 
-		// Fallback strategy when CRDT merge is not available
-		const resolution =
-			this.strategy === "local_wins" ? "local_wins" : "server_wins";
+		// Fallback to server_wins when CRDT merge is not available
+		const localData = serverNoteTypeToLocal(serverNoteType);
+		await localNoteTypeRepository.upsertFromServer(localData);
 
-		if (resolution === "server_wins") {
-			const localData = serverNoteTypeToLocal(serverNoteType);
-			await localNoteTypeRepository.upsertFromServer(localData);
-		}
-
-		return { id: localNoteType.id, resolution };
+		return { id: localNoteType.id, resolution: "server_wins" };
 	}
 
 	/**
@@ -481,15 +443,15 @@ export class ConflictResolver {
 	}
 
 	/**
-	 * Resolve note field type conflict using configured strategy
+	 * Resolve note field type conflict using CRDT merge with server_wins fallback
 	 */
 	async resolveNoteFieldTypeConflict(
 		localFieldType: LocalNoteFieldType,
 		serverFieldType: ServerNoteFieldType,
 		serverCrdtBinary?: Uint8Array,
 	): Promise<ConflictResolutionItem> {
-		// Try CRDT merge first if strategy is "crdt" and we have CRDT data
-		if (this.strategy === "crdt" && serverCrdtBinary) {
+		// Try CRDT merge first if we have CRDT data
+		if (serverCrdtBinary) {
 			const mergeResult = await this.mergeNoteFieldTypeWithCrdt(
 				localFieldType,
 				serverCrdtBinary,
@@ -510,16 +472,11 @@ export class ConflictResolver {
 			}
 		}
 
-		// Fallback strategy when CRDT merge is not available
-		const resolution =
-			this.strategy === "local_wins" ? "local_wins" : "server_wins";
-
-		if (resolution === "server_wins") {
-			const localData = serverNoteFieldTypeToLocal(serverFieldType);
-			await localNoteFieldTypeRepository.upsertFromServer(localData);
-		}
+		// Fallback to server_wins when CRDT merge is not available
+		const localData = serverNoteFieldTypeToLocal(serverFieldType);
+		await localNoteFieldTypeRepository.upsertFromServer(localData);
 
-		return { id: localFieldType.id, resolution };
+		return { id: localFieldType.id, resolution: "server_wins" };
 	}
 
 	/**
@@ -560,15 +517,15 @@ export class ConflictResolver {
 	}
 
 	/**
-	 * Resolve note conflict using configured strategy
+	 * Resolve note conflict using CRDT merge with server_wins fallback
 	 */
 	async resolveNoteConflict(
 		localNote: LocalNote,
 		serverNote: ServerNote,
 		serverCrdtBinary?: Uint8Array,
 	): Promise<ConflictResolutionItem> {
-		// Try CRDT merge first if strategy is "crdt" and we have CRDT data
-		if (this.strategy === "crdt" && serverCrdtBinary) {
+		// Try CRDT merge first if we have CRDT data
+		if (serverCrdtBinary) {
 			const mergeResult = await this.mergeNoteWithCrdt(
 				localNote,
 				serverCrdtBinary,
@@ -589,16 +546,11 @@ export class ConflictResolver {
 			}
 		}
 
-		// Fallback strategy when CRDT merge is not available
-		const resolution =
-			this.strategy === "local_wins" ? "local_wins" : "server_wins";
-
-		if (resolution === "server_wins") {
-			const localData = serverNoteToLocal(serverNote);
-			await localNoteRepository.upsertFromServer(localData);
-		}
+		// Fallback to server_wins when CRDT merge is not available
+		const localData = serverNoteToLocal(serverNote);
+		await localNoteRepository.upsertFromServer(localData);
 
-		return { id: localNote.id, resolution };
+		return { id: localNote.id, resolution: "server_wins" };
 	}
 
 	/**
@@ -636,15 +588,15 @@ export class ConflictResolver {
 	}
 
 	/**
-	 * Resolve note field value conflict using configured strategy
+	 * Resolve note field value conflict using CRDT merge with server_wins fallback
 	 */
 	async resolveNoteFieldValueConflict(
 		localFieldValue: LocalNoteFieldValue,
 		serverFieldValue: ServerNoteFieldValue,
 		serverCrdtBinary?: Uint8Array,
 	): Promise<ConflictResolutionItem> {
-		// Try CRDT merge first if strategy is "crdt" and we have CRDT data
-		if (this.strategy === "crdt" && serverCrdtBinary) {
+		// Try CRDT merge first if we have CRDT data
+		if (serverCrdtBinary) {
 			const mergeResult = await this.mergeNoteFieldValueWithCrdt(
 				localFieldValue,
 				serverCrdtBinary,
@@ -665,16 +617,11 @@ export class ConflictResolver {
 			}
 		}
 
-		// Fallback strategy when CRDT merge is not available
-		const resolution =
-			this.strategy === "local_wins" ? "local_wins" : "server_wins";
-
-		if (resolution === "server_wins") {
-			const localData = serverNoteFieldValueToLocal(serverFieldValue);
-			await localNoteFieldValueRepository.upsertFromServer(localData);
-		}
+		// Fallback to server_wins when CRDT merge is not available
+		const localData = serverNoteFieldValueToLocal(serverFieldValue);
+		await localNoteFieldValueRepository.upsertFromServer(localData);
 
-		return { id: localFieldValue.id, resolution };
+		return { id: localFieldValue.id, resolution: "server_wins" };
 	}
 
 	/**
@@ -900,18 +847,14 @@ export class ConflictResolver {
 }
 
 /**
- * Create a conflict resolver with the given options
+ * Create a conflict resolver
  */
-export function createConflictResolver(
-	options: ConflictResolverOptions = {},
-): ConflictResolver {
-	return new ConflictResolver(options);
+export function createConflictResolver(): ConflictResolver {
+	return new ConflictResolver();
 }
 
 /**
- * Default conflict resolver using CRDT (Automerge) strategy
+ * Default conflict resolver using CRDT (Automerge) merge
  * Falls back to server_wins when CRDT data is unavailable
  */
-export const conflictResolver = new ConflictResolver({
-	strategy: "crdt",
-});
+export const conflictResolver = new ConflictResolver();
diff --git a/src/client/sync/index.ts b/src/client/sync/index.ts
index c3ddab4..81d5f14 100644
--- a/src/client/sync/index.ts
+++ b/src/client/sync/index.ts
@@ -2,7 +2,6 @@ export {
 	type ConflictResolutionItem,
 	type ConflictResolutionResult,
 	ConflictResolver,
-	type ConflictResolverOptions,
 	conflictResolver,
 	createConflictResolver,
 } from "./conflict";
diff --git a/src/client/sync/manager.test.ts b/src/client/sync/manager.test.ts
index 0758261..8af6e6f 100644
--- a/src/client/sync/manager.test.ts
+++ b/src/client/sync/manager.test.ts
@@ -112,7 +112,7 @@ describe("SyncManager", () => {
 			...createEmptyPullResult(0),
 		} satisfies SyncPullResult);
 
-		conflictResolver = new ConflictResolver({ strategy: "server_wins" });
+		conflictResolver = new ConflictResolver();
 	});
 
 	afterEach(async () => {