Implement session cache upgrade phase 1 foundation

AGENTS.md

@@ -6,10 +6,20 @@ Native macOS SwiftUI app for local LLMs on Apple Silicon via MLX. Provides a cha
 
 **Always use `./build.sh` to build the project** — never call `xcodebuild` directly. The script runs xcodegen first (to pick up new/removed files) and uses the correct scheme, destination, and build directory.
 
+**Always use `./test.sh` to run tests** — it regenerates the Xcode project first and runs the shared `MLXServer` test scheme so test runs are reproducible.
+
+Tests are required for finished work when the change is reasonably testable.
+Relevant tests must exist and must pass before work is considered complete.
+
+Pre-existing errors don't exist: every error is your responsibility and you have to fix it before claiming you are done.
+
 ```bash
 # Build (requires xcodegen: brew install xcodegen)
 ./build.sh
 
+# Test
+./test.sh
+
 # Run
 open "build/Debug/MLX Server.app"
 ```

MLXServer.xcodeproj/project.pbxproj

@@ -25,12 +25,15 @@
 		5946258F1DE88CE904584E0B /* ContentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 944C699FBB76C734C9DF2F2E /* ContentView.swift */; };
 		5C1E8FE1C521914CEF98D3AA /* ChatMessagesView.swift in Sources */ = {isa = PBXBuildFile; fileRef = DB1A5E8B1C9F2BC4D262C53A /* ChatMessagesView.swift */; };
 		621B7E4382199AC1378F5F9C /* StatusBarView.swift in Sources */ = {isa = PBXBuildFile; fileRef = B0EAB35D7130D56B9E7484BA /* StatusBarView.swift */; };
+		67262C5E24739F1FE0011439 /* StreamingSSEEncoder.swift in Sources */ = {isa = PBXBuildFile; fileRef = 615F8A7C9ABCADEB215D31BD /* StreamingSSEEncoder.swift */; };
 		6828CCA8B78AB40906F87CAB /* LocalModelResolver.swift in Sources */ = {isa = PBXBuildFile; fileRef = D733A0D1D4AC25DDDA6C8684 /* LocalModelResolver.swift */; };
 		7CD765C1E2F9F4D7504C8D09 /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = B629DA084A9A40E54F8EA5FA /* Assets.xcassets */; };
 		80646C5066BF79BC76E1D9D7 /* ModelConfig.swift in Sources */ = {isa = PBXBuildFile; fileRef = 38DFC212AF4359A45FBE22BA /* ModelConfig.swift */; };
 		84D32315B418B5243E017350 /* ToolPromptBuilder.swift in Sources */ = {isa = PBXBuildFile; fileRef = 16AE82A64D1D07AE3CD8D33A /* ToolPromptBuilder.swift */; };
 		85FB1EB49D76A9F21E181346 /* ChatScene.swift in Sources */ = {isa = PBXBuildFile; fileRef = C04EE8E6418EC6E9B66999B0 /* ChatScene.swift */; };
 		945474365D0B3E961811909A /* MLXVLM in Frameworks */ = {isa = PBXBuildFile; productRef = D5E8E1C2DD8D8AABB4306193 /* MLXVLM */; };
+		962083CCCC4AC848E0BBBC99 /* CancellationTokenTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = FEFF6168B2283FEC87B4BB8C /* CancellationTokenTests.swift */; };
+		A146BBA70CFBEC505BDCDF0D /* ImageDecoder.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7C1A89C076E717F87A60397D /* ImageDecoder.swift */; };
 		B13FFE238613BFBFC72E0CC8 /* ChatDocumentMigration.swift in Sources */ = {isa = PBXBuildFile; fileRef = 24E29065DD29C17D20B0400D /* ChatDocumentMigration.swift */; };
 		B1D9BC407DB7DB1489230C20 /* MonitorView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4239CFF94B819C35A8D4D617 /* MonitorView.swift */; };
 		B5AA6E3B4BE21676226B342B /* ChatViewModel.swift in Sources */ = {isa = PBXBuildFile; fileRef = B8BD93859F0291F1A3E09DA5 /* ChatViewModel.swift */; };
@@ -42,12 +45,25 @@
 		D666A311788375E8A061C832 /* SettingsView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 4147321383E94E9F17A0154E /* SettingsView.swift */; };
 		D96DDE66F76FDDA642629E17 /* APIModels.swift in Sources */ = {isa = PBXBuildFile; fileRef = F1A52E2C9964ADA9D841A89B /* APIModels.swift */; };
 		DF5C525DBD2E3153256951C1 /* SceneManagementWindow.swift in Sources */ = {isa = PBXBuildFile; fileRef = BA1592FD260014C4FBDB6995 /* SceneManagementWindow.swift */; };
+		E199D0BB09B61AC128AB093A /* CancellationToken.swift in Sources */ = {isa = PBXBuildFile; fileRef = 3489501F2F8E1BA382347CFA /* CancellationToken.swift */; };
+		E92B6656C251EDA246B8F582 /* ImageDecoderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = E4573DC9314915F4C7963B4E /* ImageDecoderTests.swift */; };
 		F141B91A64F7DAD73CE2910A /* ConversationSessionCache.swift in Sources */ = {isa = PBXBuildFile; fileRef = FFBB16D3AF2E61D001FD6051 /* ConversationSessionCache.swift */; };
 		F546CE5955ED253D8A793D5E /* MarkdownUI in Frameworks */ = {isa = PBXBuildFile; productRef = A98257123539E9E738213BFA /* MarkdownUI */; };
 		FAF7D4714AC6D02674920208 /* ChatMessage.swift in Sources */ = {isa = PBXBuildFile; fileRef = A4B359324B5FD8D106C74338 /* ChatMessage.swift */; };
 		FCD48F8C132A2B830A15EEB4 /* MLXLLM in Frameworks */ = {isa = PBXBuildFile; productRef = 3F5A4AC6DBAF7CA686ECA74E /* MLXLLM */; };
+		FE4405F66873C75CD6FA19A5 /* StreamingSSEEncoderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 49C383DD5224F3420EB98DB2 /* StreamingSSEEncoderTests.swift */; };
 /* End PBXBuildFile section */
 
+/* Begin PBXContainerItemProxy section */
+		9F9E4F692B655CD8CE88479C /* PBXContainerItemProxy */ = {
+			isa = PBXContainerItemProxy;
+			containerPortal = 938BC479816FCA8527B731F9 /* Project object */;
+			proxyType = 1;
+			remoteGlobalIDString = BCD7107EE884C9B2F4C2C40E;
+			remoteInfo = MLXServer;
+		};
+/* End PBXContainerItemProxy section */
+
 /* Begin PBXFileReference section */
 		0F03A123A8908714A89315FE /* SceneCommands.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SceneCommands.swift; sourceTree = "<group>"; };
 		145B888FBDD4F931512C5473 /* Preferences.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Preferences.swift; sourceTree = "<group>"; };
@@ -56,6 +72,7 @@
 		24E29065DD29C17D20B0400D /* ChatDocumentMigration.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatDocumentMigration.swift; sourceTree = "<group>"; };
 		2DC8C86D397B1FCA08E07CBD /* DownloadModalView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DownloadModalView.swift; sourceTree = "<group>"; };
 		2E2FCA55CEBEBCED78D9479A /* SaveChatCommands.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SaveChatCommands.swift; sourceTree = "<group>"; };
+		3489501F2F8E1BA382347CFA /* CancellationToken.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CancellationToken.swift; sourceTree = "<group>"; };
 		37FEB592E5E717F817B03151 /* SceneManagementView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SceneManagementView.swift; sourceTree = "<group>"; };
 		386CD08DC6338F42460DFBE2 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist; path = Info.plist; sourceTree = "<group>"; };
 		38DFC212AF4359A45FBE22BA /* ModelConfig.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ModelConfig.swift; sourceTree = "<group>"; };
@@ -63,8 +80,11 @@
 		3D08828E16B17EF02C14243E /* APIServer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = APIServer.swift; sourceTree = "<group>"; };
 		4147321383E94E9F17A0154E /* SettingsView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SettingsView.swift; sourceTree = "<group>"; };
 		4239CFF94B819C35A8D4D617 /* MonitorView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MonitorView.swift; sourceTree = "<group>"; };
+		49C383DD5224F3420EB98DB2 /* StreamingSSEEncoderTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StreamingSSEEncoderTests.swift; sourceTree = "<group>"; };
+		615F8A7C9ABCADEB215D31BD /* StreamingSSEEncoder.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StreamingSSEEncoder.swift; sourceTree = "<group>"; };
 		6B3AA91D2C7842D7366F9A41 /* ChatDocumentPackage.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatDocumentPackage.swift; sourceTree = "<group>"; };
 		6EE59189918D06B8D2F588FC /* MLXServer.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = MLXServer.app; sourceTree = BUILT_PRODUCTS_DIR; };
+		7C1A89C076E717F87A60397D /* ImageDecoder.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ImageDecoder.swift; sourceTree = "<group>"; };
 		922CBDC9206737BD04AF2874 /* ModelManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ModelManager.swift; sourceTree = "<group>"; };
 		944C699FBB76C734C9DF2F2E /* ContentView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ContentView.swift; sourceTree = "<group>"; };
 		A4B359324B5FD8D106C74338 /* ChatMessage.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatMessage.swift; sourceTree = "<group>"; };
@@ -82,10 +102,13 @@
 		D7C9BAD674E29688ACE53B0B /* ChatExporter.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatExporter.swift; sourceTree = "<group>"; };
 		DB1A5E8B1C9F2BC4D262C53A /* ChatMessagesView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatMessagesView.swift; sourceTree = "<group>"; };
 		E35452B166893B25E765FF70 /* InferenceStats.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InferenceStats.swift; sourceTree = "<group>"; };
+		E4573DC9314915F4C7963B4E /* ImageDecoderTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ImageDecoderTests.swift; sourceTree = "<group>"; };
 		E5E6AD02CDF23BDAB64700A7 /* ChatInputView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatInputView.swift; sourceTree = "<group>"; };
 		E73B165A1822729C907791AE /* ToolCallParser.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ToolCallParser.swift; sourceTree = "<group>"; };
 		EF518FEBF3A38E830E3CE1A5 /* FocusedValues.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FocusedValues.swift; sourceTree = "<group>"; };
 		F1A52E2C9964ADA9D841A89B /* APIModels.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = APIModels.swift; sourceTree = "<group>"; };
+		F4CE2D594F7433C76169151A /* MLXServerTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = MLXServerTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
+		FEFF6168B2283FEC87B4BB8C /* CancellationTokenTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CancellationTokenTests.swift; sourceTree = "<group>"; };
 		FFBB16D3AF2E61D001FD6051 /* ConversationSessionCache.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ConversationSessionCache.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
@@ -104,6 +127,14 @@
 /* End PBXFrameworksBuildPhase section */
 
 /* Begin PBXGroup section */
+		03BB61C0F16FAD47436AA178 /* MLXServerTests */ = {
+			isa = PBXGroup;
+			children = (
+				154AF0C071A7DC02EB5F6F49 /* Server */,
+			);
+			path = MLXServerTests;
+			sourceTree = "<group>";
+		};
 		05B1BAE308E64D2FB2E73823 /* Utilities */ = {
 			isa = PBXGroup;
 			children = (
@@ -126,10 +157,21 @@
 			path = Documents;
 			sourceTree = "<group>";
 		};
+		154AF0C071A7DC02EB5F6F49 /* Server */ = {
+			isa = PBXGroup;
+			children = (
+				FEFF6168B2283FEC87B4BB8C /* CancellationTokenTests.swift */,
+				E4573DC9314915F4C7963B4E /* ImageDecoderTests.swift */,
+				49C383DD5224F3420EB98DB2 /* StreamingSSEEncoderTests.swift */,
+			);
+			path = Server;
+			sourceTree = "<group>";
+		};
 		652987C2A419DBFC79E32CDE /* Products */ = {
 			isa = PBXGroup;
 			children = (
 				6EE59189918D06B8D2F588FC /* MLXServer.app */,
+				F4CE2D594F7433C76169151A /* MLXServerTests.xctest */,
 			);
 			name = Products;
 			sourceTree = "<group>";
@@ -205,7 +247,10 @@
 			children = (
 				F1A52E2C9964ADA9D841A89B /* APIModels.swift */,
 				3D08828E16B17EF02C14243E /* APIServer.swift */,
+				3489501F2F8E1BA382347CFA /* CancellationToken.swift */,
 				FFBB16D3AF2E61D001FD6051 /* ConversationSessionCache.swift */,
+				7C1A89C076E717F87A60397D /* ImageDecoder.swift */,
+				615F8A7C9ABCADEB215D31BD /* StreamingSSEEncoder.swift */,
 				E73B165A1822729C907791AE /* ToolCallParser.swift */,
 				16AE82A64D1D07AE3CD8D33A /* ToolPromptBuilder.swift */,
 			);
@@ -216,6 +261,7 @@
 			isa = PBXGroup;
 			children = (
 				6816BF8EF7C92384DD7C9177 /* MLXServer */,
+				03BB61C0F16FAD47436AA178 /* MLXServerTests */,
 				652987C2A419DBFC79E32CDE /* Products */,
 			);
 			sourceTree = "<group>";
@@ -246,6 +292,24 @@
 			productReference = 6EE59189918D06B8D2F588FC /* MLXServer.app */;
 			productType = "com.apple.product-type.application";
 		};
+		CE11F8C258BB944F38A5840D /* MLXServerTests */ = {
+			isa = PBXNativeTarget;
+			buildConfigurationList = A2168D037766ED36A199C6F7 /* Build configuration list for PBXNativeTarget "MLXServerTests" */;
+			buildPhases = (
+				6DEBF8BBA4F6DB333E0C55B0 /* Sources */,
+			);
+			buildRules = (
+			);
+			dependencies = (
+				8870DD8F1917C831FD4FD595 /* PBXTargetDependency */,
+			);
+			name = MLXServerTests;
+			packageProductDependencies = (
+			);
+			productName = MLXServerTests;
+			productReference = F4CE2D594F7433C76169151A /* MLXServerTests.xctest */;
+			productType = "com.apple.product-type.bundle.unit-test";
+		};
 /* End PBXNativeTarget section */
 
 /* Begin PBXProject section */
@@ -276,6 +340,7 @@
 			projectRoot = "";
 			targets = (
 				BCD7107EE884C9B2F4C2C40E /* MLXServer */,
+				CE11F8C258BB944F38A5840D /* MLXServerTests */,
 			);
 		};
 /* End PBXProject section */
@@ -292,12 +357,23 @@
 /* End PBXResourcesBuildPhase section */
 
 /* Begin PBXSourcesBuildPhase section */
+		6DEBF8BBA4F6DB333E0C55B0 /* Sources */ = {
+			isa = PBXSourcesBuildPhase;
+			buildActionMask = 2147483647;
+			files = (
+				962083CCCC4AC848E0BBBC99 /* CancellationTokenTests.swift in Sources */,
+				E92B6656C251EDA246B8F582 /* ImageDecoderTests.swift in Sources */,
+				FE4405F66873C75CD6FA19A5 /* StreamingSSEEncoderTests.swift in Sources */,
+			);
+			runOnlyForDeploymentPostprocessing = 0;
+		};
 		BC03844286F51DFAEF96B823 /* Sources */ = {
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
 				D96DDE66F76FDDA642629E17 /* APIModels.swift in Sources */,
 				50DD129CCF2843482DEC3B96 /* APIServer.swift in Sources */,
+				E199D0BB09B61AC128AB093A /* CancellationToken.swift in Sources */,
 				2E3A02DF9C6A5109E532D5E2 /* ChatDocumentController.swift in Sources */,
 				1A8833E3CCD3289C95E282A2 /* ChatDocumentManifest.swift in Sources */,
 				B13FFE238613BFBFC72E0CC8 /* ChatDocumentMigration.swift in Sources */,
@@ -312,6 +388,7 @@
 				F141B91A64F7DAD73CE2910A /* ConversationSessionCache.swift in Sources */,
 				C07A377244DCD67F4FE709FE /* DownloadModalView.swift in Sources */,
 				4DC033E45880B2948B47DEB1 /* FocusedValues.swift in Sources */,
+				A146BBA70CFBEC505BDCDF0D /* ImageDecoder.swift in Sources */,
 				2D08769282BD71C170DB0943 /* InferenceStats.swift in Sources */,
 				6828CCA8B78AB40906F87CAB /* LocalModelResolver.swift in Sources */,
 				50B6861FF8610B3ED4FFAD9D /* MLXServerApp.swift in Sources */,
@@ -328,6 +405,7 @@
 				CFEE79815DFB80E51FE3745A /* SceneStore.swift in Sources */,
 				D666A311788375E8A061C832 /* SettingsView.swift in Sources */,
 				621B7E4382199AC1378F5F9C /* StatusBarView.swift in Sources */,
+				67262C5E24739F1FE0011439 /* StreamingSSEEncoder.swift in Sources */,
 				189362AAE2CDE5D4B3428334 /* ToolCallParser.swift in Sources */,
 				84D32315B418B5243E017350 /* ToolPromptBuilder.swift in Sources */,
 			);
@@ -335,7 +413,49 @@
 		};
 /* End PBXSourcesBuildPhase section */
 
+/* Begin PBXTargetDependency section */
+		8870DD8F1917C831FD4FD595 /* PBXTargetDependency */ = {
+			isa = PBXTargetDependency;
+			target = BCD7107EE884C9B2F4C2C40E /* MLXServer */;
+			targetProxy = 9F9E4F692B655CD8CE88479C /* PBXContainerItemProxy */;
+		};
+/* End PBXTargetDependency section */
+
 /* Begin XCBuildConfiguration section */
+		18921C5B777D8B7FEF662D6F /* Release */ = {
+			isa = XCBuildConfiguration;
+			buildSettings = {
+				BUNDLE_LOADER = "$(TEST_HOST)";
+				COMBINE_HIDPI_IMAGES = YES;
+				GENERATE_INFOPLIST_FILE = YES;
+				LD_RUNPATH_SEARCH_PATHS = (
+					"$(inherited)",
+					"@executable_path/../Frameworks",
+					"@loader_path/../Frameworks",
+				);
+				PRODUCT_BUNDLE_IDENTIFIER = com.mlxserver.MLXServerTests;
+				SDKROOT = macosx;
+				TEST_HOST = "$(BUILT_PRODUCTS_DIR)/MLX Server.app/Contents/MacOS/MLX Server";
+			};
+			name = Release;
+		};
+		2B83417701A93BF554428C56 /* Debug */ = {
+			isa = XCBuildConfiguration;
+			buildSettings = {
+				BUNDLE_LOADER = "$(TEST_HOST)";
+				COMBINE_HIDPI_IMAGES = YES;
+				GENERATE_INFOPLIST_FILE = YES;
+				LD_RUNPATH_SEARCH_PATHS = (
+					"$(inherited)",
+					"@executable_path/../Frameworks",
+					"@loader_path/../Frameworks",
+				);
+				PRODUCT_BUNDLE_IDENTIFIER = com.mlxserver.MLXServerTests;
+				SDKROOT = macosx;
+				TEST_HOST = "$(BUILT_PRODUCTS_DIR)/MLX Server.app/Contents/MacOS/MLX Server";
+			};
+			name = Debug;
+		};
 		6C0C08FC4653A138A768ECF0 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
@@ -524,6 +644,15 @@
 			defaultConfigurationIsVisible = 0;
 			defaultConfigurationName = Debug;
 		};
+		A2168D037766ED36A199C6F7 /* Build configuration list for PBXNativeTarget "MLXServerTests" */ = {
+			isa = XCConfigurationList;
+			buildConfigurations = (
+				2B83417701A93BF554428C56 /* Debug */,
+				18921C5B777D8B7FEF662D6F /* Release */,
+			);
+			defaultConfigurationIsVisible = 0;
+			defaultConfigurationName = Debug;
+		};
 /* End XCConfigurationList section */
 
 /* Begin XCRemoteSwiftPackageReference section */

MLXServer.xcodeproj/xcshareddata/xcschemes/MLXServer.xcscheme

@@ -0,0 +1,116 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "1640"
+   version = "1.7">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES"
+      runPostActionsOnFailure = "NO">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "BCD7107EE884C9B2F4C2C40E"
+               BuildableName = "MLXServer.app"
+               BlueprintName = "MLXServer"
+               ReferencedContainer = "container:MLXServer.xcodeproj">
+            </BuildableReference>
+         </BuildActionEntry>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "NO"
+            buildForProfiling = "NO"
+            buildForArchiving = "NO"
+            buildForAnalyzing = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "CE11F8C258BB944F38A5840D"
+               BuildableName = "MLXServerTests.xctest"
+               BlueprintName = "MLXServerTests"
+               ReferencedContainer = "container:MLXServer.xcodeproj">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      onlyGenerateCoverageForSpecifiedTargets = "NO">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "BCD7107EE884C9B2F4C2C40E"
+            BuildableName = "MLXServer.app"
+            BlueprintName = "MLXServer"
+            ReferencedContainer = "container:MLXServer.xcodeproj">
+         </BuildableReference>
+      </MacroExpansion>
+      <Testables>
+         <TestableReference
+            skipped = "NO"
+            parallelizable = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "CE11F8C258BB944F38A5840D"
+               BuildableName = "MLXServerTests.xctest"
+               BlueprintName = "MLXServerTests"
+               ReferencedContainer = "container:MLXServer.xcodeproj">
+            </BuildableReference>
+         </TestableReference>
+      </Testables>
+      <CommandLineArguments>
+      </CommandLineArguments>
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+      <BuildableProductRunnable
+         runnableDebuggingMode = "0">
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "BCD7107EE884C9B2F4C2C40E"
+            BuildableName = "MLXServer.app"
+            BlueprintName = "MLXServer"
+            ReferencedContainer = "container:MLXServer.xcodeproj">
+         </BuildableReference>
+      </BuildableProductRunnable>
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <BuildableProductRunnable
+         runnableDebuggingMode = "0">
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "BCD7107EE884C9B2F4C2C40E"
+            BuildableName = "MLXServer.app"
+            BlueprintName = "MLXServer"
+            ReferencedContainer = "container:MLXServer.xcodeproj">
+         </BuildableReference>
+      </BuildableProductRunnable>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>

MLXServer/ContentView.swift

@@ -15,6 +15,10 @@ struct ContentView: View {
     @State private var documentErrorMessage: String?
     @State private var exportErrorMessage: String?
 
+    private var isRunningTests: Bool {
+        ProcessInfo.processInfo.environment["XCTestConfigurationFilePath"] != nil
+    }
+
     var body: some View {
         exportedContent
     }
@@ -30,11 +34,11 @@ struct ContentView: View {
                         delegate.chatViewModel = vm
                     }
                     // Auto-start API server if configured
-                    if Preferences.apiAutoStart {
+                    if Preferences.apiAutoStart && !isRunningTests {
                         vm.startAPIServer()
                     }
                     // Restore autosaved session if no document is being opened
-                    if !documentController.hasPendingOpenRequests {
+                    if !documentController.hasPendingOpenRequests && !isRunningTests {
                         Task {
                             await vm.restoreFromAutosave()
                         }

MLXServer/Server/APIServer.swift

@@ -1,4 +1,3 @@
-import AppKit
 import Foundation
 import MLXLMCommon
 import Network
@@ -288,7 +287,7 @@ final class APIServer {
             var messageImages: [UserInput.Image] = []
             var messageImageBytes = 0
             for urlString in imageURLs {
-                if let decoded = decodeBase64Image(urlString) {
+                if let decoded = ImageDecoder.decode(urlString) {
                     messageImages.append(decoded.image)
                     messageImageBytes += decoded.estimatedBytes
                 }
@@ -448,28 +447,6 @@ final class APIServer {
         modelManager.touchActivity()
     }
 
-    /// Decode a base64 data URI (data:image/png;base64,...) into a UserInput.Image.
-    private func decodeBase64Image(_ urlString: String) -> DecodedImage? {
-        // Handle data URIs: data:image/png;base64,<data>
-        let base64String: String
-        if urlString.hasPrefix("data:") {
-            guard let commaIndex = urlString.firstIndex(of: ",") else { return nil }
-            base64String = String(urlString[urlString.index(after: commaIndex)...])
-        } else {
-            // Could be a plain base64 string
-            base64String = urlString
-        }
-
-        guard let data = Data(base64Encoded: base64String),
-              let nsImage = NSImage(data: data),
-              let cgImage = nsImage.cgImage(forProposedRect: nil, context: nil, hints: nil) else {
-            return nil
-        }
-
-                let estimatedBytes = max(data.count, cgImage.width * cgImage.height * 4)
-                return DecodedImage(image: .ciImage(CIImage(cgImage: cgImage)), estimatedBytes: estimatedBytes)
-    }
-
     // MARK: - Non-streaming response
 
     private func handleNonStreamingResponse(
@@ -887,11 +864,6 @@ final class APIServer {
     }
 }
 
-private struct DecodedImage {
-    let image: UserInput.Image
-    let estimatedBytes: Int
-}
-
 // MARK: - HTTP request parser
 
 private struct HTTPRequest {

MLXServer/Server/CancellationToken.swift

@@ -0,0 +1,14 @@
+import os
+
+/// Thread-safe cancellation flag for cooperative stream shutdown.
+final class CancellationToken: @unchecked Sendable {
+    private let lock = OSAllocatedUnfairLock(initialState: false)
+
+    var isCancelled: Bool {
+        lock.withLock { $0 }
+    }
+
+    func cancel() {
+        lock.withLock { $0 = true }
+    }
+}

MLXServer/Server/ImageDecoder.swift

@@ -0,0 +1,31 @@
+import AppKit
+import CoreImage
+import Foundation
+import MLXLMCommon
+
+/// Extracted from APIServer — decodes data URIs to UserInput.Image.
+enum ImageDecoder {
+    struct DecodedImage {
+        let image: UserInput.Image
+        let estimatedBytes: Int
+    }
+
+    static func decode(_ urlString: String) -> DecodedImage? {
+        let base64String: String
+        if urlString.hasPrefix("data:") {
+            guard let commaIndex = urlString.firstIndex(of: ",") else { return nil }
+            base64String = String(urlString[urlString.index(after: commaIndex)...])
+        } else {
+            base64String = urlString
+        }
+
+        guard let data = Data(base64Encoded: base64String),
+              let nsImage = NSImage(data: data),
+              let cgImage = nsImage.cgImage(forProposedRect: nil, context: nil, hints: nil) else {
+            return nil
+        }
+
+        let estimatedBytes = max(data.count, cgImage.width * cgImage.height * 4)
+        return DecodedImage(image: .ciImage(CIImage(cgImage: cgImage)), estimatedBytes: estimatedBytes)
+    }
+}

MLXServer/Server/StreamingSSEEncoder.swift

@@ -0,0 +1,72 @@
+import Foundation
+
+/// Pre-computes static JSON parts for SSE streaming.
+/// Only the dynamic delta payload is serialized per token.
+struct StreamingSSEEncoder: Sendable {
+    private let requestId: String
+    private let created: Int
+    private let modelName: String
+
+    init(requestId: String, created: Int, modelName: String) {
+        self.requestId = requestId
+        self.created = created
+        self.modelName = modelName
+    }
+
+    func encodeContentDelta(_ text: String) -> Data {
+        Self.encodeChunk(
+            APIChatCompletionChunk(
+                id: requestId,
+                object: "chat.completion.chunk",
+                created: created,
+                model: modelName,
+                choices: [
+                    APIStreamChoice(
+                        index: 0,
+                        delta: APIDeltaMessage(role: nil, content: text, tool_calls: nil),
+                        finish_reason: nil
+                    )
+                ],
+                usage: nil
+            )
+        )
+    }
+
+    func encodeRoleDelta(_ role: String) -> Data {
+        Self.encodeChunk(
+            APIChatCompletionChunk(
+                id: requestId,
+                object: "chat.completion.chunk",
+                created: created,
+                model: modelName,
+                choices: [
+                    APIStreamChoice(
+                        index: 0,
+                        delta: APIDeltaMessage(role: role, content: nil, tool_calls: nil),
+                        finish_reason: nil
+                    )
+                ],
+                usage: nil
+            )
+        )
+    }
+
+    static func encodeFinalChunk(_ chunk: APIChatCompletionChunk) -> Data {
+        encodeChunk(chunk)
+    }
+
+    private static func encodeChunk(_ chunk: APIChatCompletionChunk) -> Data {
+        let encoder = JSONEncoder()
+        encoder.outputFormatting = [.sortedKeys]
+
+        guard let json = try? encoder.encode(chunk) else {
+            return Data("data: {}\n\n".utf8)
+        }
+
+        var data = Data(capacity: json.count + 8)
+        data.append(Data("data: ".utf8))
+        data.append(json)
+        data.append(Data("\n\n".utf8))
+        return data
+    }
+}

MLXServerTests/Server/CancellationTokenTests.swift

@@ -0,0 +1,18 @@
+import XCTest
+@testable import MLX_Server
+
+final class CancellationTokenTests: XCTestCase {
+    func testStartsNotCancelled() {
+        let token = CancellationToken()
+
+        XCTAssertFalse(token.isCancelled)
+    }
+
+    func testCancelSetsFlag() {
+        let token = CancellationToken()
+
+        token.cancel()
+
+        XCTAssertTrue(token.isCancelled)
+    }
+}

MLXServerTests/Server/ImageDecoderTests.swift

@@ -0,0 +1,20 @@
+import XCTest
+@testable import MLX_Server
+
+final class ImageDecoderTests: XCTestCase {
+    private let onePixelPNGBase64 = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAFgwJ/lRyXWQAAAABJRU5ErkJggg=="
+
+    func testDecodeDataURI() {
+        let image = ImageDecoder.decode("data:image/png;base64,\(onePixelPNGBase64)")
+
+        XCTAssertNotNil(image)
+        XCTAssertGreaterThanOrEqual(image?.estimatedBytes ?? 0, 4)
+    }
+
+    func testDecodePlainBase64() {
+        let image = ImageDecoder.decode(onePixelPNGBase64)
+
+        XCTAssertNotNil(image)
+        XCTAssertGreaterThanOrEqual(image?.estimatedBytes ?? 0, 4)
+    }
+}

MLXServerTests/Server/StreamingSSEEncoderTests.swift

@@ -0,0 +1,82 @@
+import XCTest
+@testable import MLX_Server
+
+final class StreamingSSEEncoderTests: XCTestCase {
+    func testEncodeContentDeltaMatchesJSONEncoderOutput() throws {
+        let encoder = StreamingSSEEncoder(requestId: "chatcmpl-test", created: 1_234_567, modelName: "qwen\"model")
+        let text = "line 1\nline 2\t\"quoted\"\\slash"
+
+        let actual = encoder.encodeContentDelta(text)
+        let expected = try baselineData(
+            for: APIChatCompletionChunk(
+                id: "chatcmpl-test",
+                object: "chat.completion.chunk",
+                created: 1_234_567,
+                model: "qwen\"model",
+                choices: [
+                    APIStreamChoice(
+                        index: 0,
+                        delta: APIDeltaMessage(role: nil, content: text, tool_calls: nil),
+                        finish_reason: nil
+                    )
+                ],
+                usage: nil
+            )
+        )
+
+        XCTAssertEqual(actual, expected)
+    }
+
+    func testEncodeRoleDeltaMatchesJSONEncoderOutput() throws {
+        let encoder = StreamingSSEEncoder(requestId: "chatcmpl-role", created: 99, modelName: "gemma")
+
+        let actual = encoder.encodeRoleDelta("assistant")
+        let expected = try baselineData(
+            for: APIChatCompletionChunk(
+                id: "chatcmpl-role",
+                object: "chat.completion.chunk",
+                created: 99,
+                model: "gemma",
+                choices: [
+                    APIStreamChoice(
+                        index: 0,
+                        delta: APIDeltaMessage(role: "assistant", content: nil, tool_calls: nil),
+                        finish_reason: nil
+                    )
+                ],
+                usage: nil
+            )
+        )
+
+        XCTAssertEqual(actual, expected)
+    }
+
+    func testEncodeFinalChunkMatchesBaseline() throws {
+        let chunk = APIChatCompletionChunk(
+            id: "chatcmpl-final",
+            object: "chat.completion.chunk",
+            created: 7,
+            model: "gemma",
+            choices: [
+                APIStreamChoice(
+                    index: 0,
+                    delta: APIDeltaMessage(role: nil, content: nil, tool_calls: nil),
+                    finish_reason: "stop"
+                )
+            ],
+            usage: APIUsageInfo(prompt_tokens: 10, completion_tokens: 3, total_tokens: 13)
+        )
+
+        XCTAssertEqual(StreamingSSEEncoder.encodeFinalChunk(chunk), try baselineData(for: chunk))
+    }
+
+    private func baselineData(for chunk: APIChatCompletionChunk) throws -> Data {
+        let encoder = JSONEncoder()
+        encoder.outputFormatting = [.sortedKeys]
+        let json = try encoder.encode(chunk)
+        var data = Data("data: ".utf8)
+        data.append(json)
+        data.append(Data("\n\n".utf8))
+        return data
+    }
+}

docs/session-cache-upgrade.md

@@ -2558,9 +2558,9 @@ Each step should be independently buildable and testable.
 
 ### Phase 1: Foundation (no behavior change yet)
 
-1. **`CancellationToken.swift`** — Standalone utility, no dependencies. Write + unit test.
+1. [x] **`CancellationToken.swift`** — Standalone utility, no dependencies. Write + unit test.
-2. **`ImageDecoder.swift`** — Extract from APIServer. Mechanical move.
+2. [x] **`ImageDecoder.swift`** — Extract from APIServer. Mechanical move.
-3. **`StreamingSSEEncoder.swift`** — Standalone, testable in isolation. Verify JSON output matches current `JSONEncoder` output.
+3. [x] **`StreamingSSEEncoder.swift`** — Standalone, testable in isolation. Verify JSON output matches current `JSONEncoder` output.
 
 ### Phase 2: Core Engine
 

project.yml

@@ -42,3 +42,25 @@ targets:
         product: MLXLMCommon
       - package: MarkdownUI
         product: MarkdownUI
+  MLXServerTests:
+    type: bundle.unit-test
+    platform: macOS
+    sources:
+      - MLXServerTests
+    settings:
+      base:
+        GENERATE_INFOPLIST_FILE: "YES"
+        TEST_HOST: "$(BUILT_PRODUCTS_DIR)/MLX Server.app/Contents/MacOS/MLX Server"
+        BUNDLE_LOADER: "$(TEST_HOST)"
+    dependencies:
+      - target: MLXServer
+
+schemes:
+  MLXServer:
+    build:
+      targets:
+        MLXServer: all
+        MLXServerTests: [test]
+    test:
+      targets:
+        - MLXServerTests

test.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+set -euo pipefail
+
+PROJECT_DIR="$(cd "$(dirname "$0")" && pwd)"
+BUILD_DIR="$PROJECT_DIR/build"
+CONFIG="${1:-Debug}"
+APP_NAME="MLX Server"
+DESTINATION="${TEST_DESTINATION:-platform=macOS,arch=arm64}"
+
+echo "==> Testing $APP_NAME ($CONFIG)"
+
+# Regenerate Xcode project from project.yml (picks up any new/removed files)
+if command -v xcodegen &>/dev/null; then
+    xcodegen generate --spec "$PROJECT_DIR/project.yml" --project "$PROJECT_DIR" 2>&1 | grep -v '^$'
+fi
+
+# Run tests — filter to test progress, app warnings, build failures, and final result
+xcodebuild \
+    -project "$PROJECT_DIR/MLXServer.xcodeproj" \
+    -scheme MLXServer \
+    -destination "$DESTINATION" \
+    -configuration "$CONFIG" \
+    SYMROOT="$BUILD_DIR" \
+    test 2>&1 | \
+    grep -E "(Test Suite|Test Case|Executed [0-9]+ tests|Testing started|Testing failed|Testing passed|error:|warning:.*MLXServer/|\*\* TEST|BUILD )"
+
+echo ""
+echo "==> Tests passed"