fix: prioritize user-configured embedding dimension over model default

- Updated config-manager.ts to check user-configured dimension first
- Updated service-factory.ts to use the same dimension priority logic
- Fixed tests to reflect the new behavior
- Added specific test for issue #8102 scenario (1536 vs 1024)

Fixes #8102

src/services/code-index/__tests__/config-manager.spec.ts

@@ -1688,7 +1688,7 @@ describe("CodeIndexConfigManager", () => {
 				vi.clearAllMocks()
 			})
 
-			it("should return model's built-in dimension when available", async () => {
+			it("should prioritize user-configured dimension over model's built-in dimension", async () => {
 				// Mock getModelDimension to return a built-in dimension
 				mockedGetModelDimension.mockReturnValue(1536)
 
@@ -1696,7 +1696,7 @@ describe("CodeIndexConfigManager", () => {
 					codebaseIndexEnabled: true,
 					codebaseIndexEmbedderProvider: "openai",
 					codebaseIndexEmbedderModelId: "text-embedding-3-small",
-					codebaseIndexEmbedderModelDimension: 2048, // Custom dimension should be ignored
+					codebaseIndexEmbedderModelDimension: 2048, // Custom dimension should take priority
 					codebaseIndexQdrantUrl: "http://localhost:6333",
 				})
 				mockContextProxy.getSecret.mockImplementation((key: string) => {
@@ -1707,20 +1707,46 @@ describe("CodeIndexConfigManager", () => {
 				configManager = new CodeIndexConfigManager(mockContextProxy)
 				await configManager.loadConfiguration()
 
-				// Should return model's built-in dimension, not custom
+				// Should return user-configured dimension, not model's built-in
+				expect(configManager.currentModelDimension).toBe(2048)
+				// getModelDimension should not be called when custom dimension is set
+				expect(mockedGetModelDimension).not.toHaveBeenCalled()
+			})
+
+			it("should fall back to model's built-in dimension when no custom dimension is set", async () => {
+				// Mock getModelDimension to return a built-in dimension
+				mockedGetModelDimension.mockReturnValue(1536)
+
+				mockContextProxy.getGlobalState.mockReturnValue({
+					codebaseIndexEnabled: true,
+					codebaseIndexEmbedderProvider: "openai",
+					codebaseIndexEmbedderModelId: "text-embedding-3-small",
+					// No custom dimension set
+					codebaseIndexQdrantUrl: "http://localhost:6333",
+				})
+				mockContextProxy.getSecret.mockImplementation((key: string) => {
+					if (key === "codeIndexOpenAiKey") return "test-key"
+					return undefined
+				})
+
+				configManager = new CodeIndexConfigManager(mockContextProxy)
+				await configManager.loadConfiguration()
+
+				// Should fall back to model's built-in dimension
 				expect(configManager.currentModelDimension).toBe(1536)
 				expect(mockedGetModelDimension).toHaveBeenCalledWith("openai", "text-embedding-3-small")
 			})
 
-			it("should use custom dimension only when model has no built-in dimension", async () => {
-				// Mock getModelDimension to return undefined (no built-in dimension)
-				mockedGetModelDimension.mockReturnValue(undefined)
+			it("should use user-configured dimension (1536) even when model default is different (1024)", async () => {
+				// This test specifically addresses the issue reported in #8102
+				// Mock getModelDimension to return 1024 (model default)
+				mockedGetModelDimension.mockReturnValue(1024)
 
 				mockContextProxy.getGlobalState.mockReturnValue({
 					codebaseIndexEnabled: true,
 					codebaseIndexEmbedderProvider: "openai-compatible",
-					codebaseIndexEmbedderModelId: "custom-model",
-					codebaseIndexEmbedderModelDimension: 2048, // Custom dimension should be used
+					codebaseIndexEmbedderModelId: "some-model-with-1024-default",
+					codebaseIndexEmbedderModelDimension: 1536, // User explicitly sets 1536
 					codebaseIndexQdrantUrl: "http://localhost:6333",
 				})
 				mockContextProxy.getSecret.mockImplementation((key: string) => {
@@ -1731,9 +1757,10 @@ describe("CodeIndexConfigManager", () => {
 				configManager = new CodeIndexConfigManager(mockContextProxy)
 				await configManager.loadConfiguration()
 
-				// Should use custom dimension as fallback
-				expect(configManager.currentModelDimension).toBe(2048)
-				expect(mockedGetModelDimension).toHaveBeenCalledWith("openai-compatible", "custom-model")
+				// Should use user-configured dimension (1536), not model default (1024)
+				expect(configManager.currentModelDimension).toBe(1536)
+				// getModelDimension should not be called when custom dimension is set
+				expect(mockedGetModelDimension).not.toHaveBeenCalled()
 			})
 
 			it("should return undefined when neither model dimension nor custom dimension is available", async () => {

src/services/code-index/config-manager.ts

@@ -442,19 +442,17 @@ export class CodeIndexConfigManager {
 
 	/**
 	 * Gets the current model dimension being used for embeddings.
-	 * Returns the model's built-in dimension if available, otherwise falls back to custom dimension.
+	 * Returns the user-configured custom dimension if set, otherwise falls back to model's built-in dimension.
 	 */
 	public get currentModelDimension(): number | undefined {
-		// First try to get the model-specific dimension
-		const modelId = this.modelId ?? getDefaultModelId(this.embedderProvider)
-		const modelDimension = getModelDimension(this.embedderProvider, modelId)
-
-		// Only use custom dimension if model doesn't have a built-in dimension
-		if (!modelDimension && this.modelDimension && this.modelDimension > 0) {
+		// Prioritize user-configured custom dimension if explicitly set
+		if (this.modelDimension && this.modelDimension > 0) {
 			return this.modelDimension
 		}
 
-		return modelDimension
+		// Fall back to model-specific dimension from profiles
+		const modelId = this.modelId ?? getDefaultModelId(this.embedderProvider)
+		return getModelDimension(this.embedderProvider, modelId)
 	}
 
 	/**

src/services/code-index/service-factory.ts

@@ -123,12 +123,12 @@ export class CodeIndexServiceFactory {
 
 		let vectorSize: number | undefined
 
-		// First try to get the model-specific dimension from profiles
-		vectorSize = getModelDimension(provider, modelId)
-
-		// Only use manual dimension if model doesn't have a built-in dimension
-		if (!vectorSize && config.modelDimension && config.modelDimension > 0) {
+		// Prioritize user-configured custom dimension if explicitly set
+		if (config.modelDimension && config.modelDimension > 0) {
 			vectorSize = config.modelDimension
+		} else {
+			// Fall back to model-specific dimension from profiles
+			vectorSize = getModelDimension(provider, modelId)
 		}
 
 		if (vectorSize === undefined || vectorSize <= 0) {