fix: do not override Ollama model num_ctx configuration

The native Ollama handler was explicitly setting num_ctx to modelInfo.contextWindow,
which overrode any user-configured num_ctx value in their Ollama model configuration.
This caused issues for users who had specifically configured their models with custom
context sizes to fit within their available memory.

This fix removes the num_ctx override, allowing Ollama to use the model's configured
value as intended.

Fixes #7159

Author: roomote

src/api/providers/__tests__/native-ollama.spec.ts

@@ -122,6 +122,69 @@ describe("NativeOllamaHandler", () => {
 		})
 	})
 
+	describe("num_ctx handling", () => {
+		it("should not override num_ctx in createMessage", async () => {
+			// Mock the chat response
+			mockChat.mockImplementation(async function* () {
+				yield {
+					message: { content: "Test response" },
+					eval_count: 1,
+					prompt_eval_count: 1,
+				}
+			})
+
+			const systemPrompt = "You are a helpful assistant"
+			const messages = [{ role: "user" as const, content: "Test" }]
+
+			const stream = handler.createMessage(systemPrompt, messages)
+
+			// Consume the stream
+			for await (const _ of stream) {
+				// Just consume
+			}
+
+			// Verify that num_ctx was NOT set in the options
+			expect(mockChat).toHaveBeenCalledWith(
+				expect.objectContaining({
+					model: "llama2",
+					messages: expect.any(Array),
+					stream: true,
+					options: expect.objectContaining({
+						temperature: 0,
+					}),
+				}),
+			)
+
+			// Specifically check that num_ctx is not in the options
+			const callArgs = mockChat.mock.calls[0][0]
+			expect(callArgs.options).not.toHaveProperty("num_ctx")
+		})
+
+		it("should not override num_ctx in completePrompt", async () => {
+			mockChat.mockResolvedValue({
+				message: { content: "Test response" },
+			})
+
+			await handler.completePrompt("Test prompt")
+
+			// Verify that num_ctx was NOT set in the options
+			expect(mockChat).toHaveBeenCalledWith(
+				expect.objectContaining({
+					model: "llama2",
+					messages: expect.any(Array),
+					stream: false,
+					options: expect.objectContaining({
+						temperature: 0,
+					}),
+				}),
+			)
+
+			// Specifically check that num_ctx is not in the options
+			const callArgs = mockChat.mock.calls[0][0]
+			expect(callArgs.options).not.toHaveProperty("num_ctx")
+		})
+	})
+
 	describe("error handling", () => {
 		it("should handle connection refused errors", async () => {
 			const error = new Error("ECONNREFUSED") as any

src/api/providers/native-ollama.ts

@@ -181,7 +181,7 @@ export class NativeOllamaHandler extends BaseProvider implements SingleCompletio
 				messages: ollamaMessages,
 				stream: true,
 				options: {
-					num_ctx: modelInfo.contextWindow,
+					// Don't override num_ctx - let Ollama use the model's configured value
 					temperature: this.options.modelTemperature ?? (useR1Format ? DEEP_SEEK_DEFAULT_TEMPERATURE : 0),
 				},
 			})
@@ -270,6 +270,7 @@ export class NativeOllamaHandler extends BaseProvider implements SingleCompletio
 				messages: [{ role: "user", content: prompt }],
 				stream: false,
 				options: {
+					// Don't override num_ctx - let Ollama use the model's configured value
 					temperature: this.options.modelTemperature ?? (useR1Format ? DEEP_SEEK_DEFAULT_TEMPERATURE : 0),
 				},
 			})