SCG + Ollama both (macOS26 and macOS15)

Sources/SwiftCommitGen/CommitGenOptions.swift

@@ -21,6 +21,7 @@ struct CommitGenOptions {
     case detailed
 
     #if canImport(FoundationModels)
+      @available(macOS 26.0, *)
       var promptRepresentation: Prompt {
         Prompt { styleGuidance }
       }

Sources/SwiftCommitGen/CommitGenTool.swift

@@ -72,7 +72,11 @@ struct CommitGenTool {
         self.llmClient = OllamaClient(configuration: config)
       #if canImport(FoundationModels)
         case .foundationModels:
-          self.llmClient = FoundationModelsClient()
+          if #available(macOS 26.0, *) {
+            self.llmClient = FoundationModelsClient()
+          } else {
+            fatalError("FoundationModels backend requires macOS 26.0 or newer")
+          }
       #else
         case .foundationModels:
           fatalError("FoundationModels is not available on this platform")

Sources/SwiftCommitGen/Core/BatchCombinationPromptBuilder.swift

@@ -57,43 +57,22 @@ struct BatchCombinationPromptBuilder {
       "Produce one final commit subject (<= 50 characters) and an optional body that summarizes the full change set. Avoid repeating the batch headings—present the combined commit message only."
     )
 
-    #if canImport(FoundationModels)
-      let userPrompt = Prompt {
-        for line in userLines {
-          line
-        }
-      }
-
-      let systemPrompt = Instructions {
-        """
-        You are an AI assistant merging multiple partial commit drafts into a single, well-structured commit message. 
-        Preserve all important intent from the inputs, avoid redundancy, and keep the final subject concise (<= 50 characters). 
-        The title should succinctly describe the change in a specific and informative manner.
-        Provide an optional body only when useful for additional context. 
-        If a body is present, it should describe the _purpose_ of the change, not just _what_ was changed: focus on the reasoning behind the changes rather than a file-by-file summary.
-
-        Be clear and concise, but do not omit critical information.
-        """
-        ""
-        metadata.style.styleGuidance
-      }
-    #else
-      let userPrompt = PromptContent(userLines.joined(separator: "\n"))
+    // Always use PromptContent - LLM client will convert if needed
+    let userPrompt = PromptContent(userLines.joined(separator: "\n"))
 
-      let systemPrompt = PromptContent(
-        """
-        You are an AI assistant merging multiple partial commit drafts into a single, well-structured commit message. 
-        Preserve all important intent from the inputs, avoid redundancy, and keep the final subject concise (<= 50 characters). 
-        The title should succinctly describe the change in a specific and informative manner.
-        Provide an optional body only when useful for additional context. 
-        If a body is present, it should describe the _purpose_ of the change, not just _what_ was changed: focus on the reasoning behind the changes rather than a file-by-file summary.
+    let systemPrompt = PromptContent(
+      """
+      You are an AI assistant merging multiple partial commit drafts into a single, well-structured commit message. 
+      Preserve all important intent from the inputs, avoid redundancy, and keep the final subject concise (<= 50 characters). 
+      The title should succinctly describe the change in a specific and informative manner.
+      Provide an optional body only when useful for additional context. 
+      If a body is present, it should describe the _purpose_ of the change, not just _what_ was changed: focus on the reasoning behind the changes rather than a file-by-file summary.
 
-        Be clear and concise, but do not omit critical information.
+      Be clear and concise, but do not omit critical information.
 
-        \(metadata.style.styleGuidance)
-        """
-      )
-    #endif
+      \(metadata.style.styleGuidance)
+      """
+    )
 
     let characterCount = userLines.reduce(0) { $0 + $1.count + 1 }
     let estimatedTokens = PromptDiagnostics.tokenEstimate(forCharacterCount: characterCount)

Sources/SwiftCommitGen/Core/CommitGenError.swift

@@ -9,6 +9,7 @@ enum CommitGenError: Error {
   case modelTimedOut(timeout: TimeInterval)
   case modelGenerationFailed(message: String)
   case llmRequestFailed(reason: String)
+  case invalidBackend(String)
   case notImplemented
 }
 
@@ -33,6 +34,8 @@ extension CommitGenError: LocalizedError {
       message
     case .llmRequestFailed(let reason):
       "LLM request failed: \(reason)"
+    case .invalidBackend(let message):
+      message
     case .notImplemented:
       "Commit generation is not implemented yet; future phases will add this capability."
     }

Sources/SwiftCommitGen/Core/DiffSummarizer.swift

@@ -53,6 +53,7 @@ struct ChangeSummary: Hashable, Codable {
     }
 
     #if canImport(FoundationModels)
+      @available(macOS 26.0, *)
       var promptRepresentation: Prompt {
         Prompt {
           for line in promptLines() {
@@ -198,6 +199,7 @@ struct ChangeSummary: Hashable, Codable {
   }
 
   #if canImport(FoundationModels)
+    @available(macOS 26.0, *)
     var promptRepresentation: Prompt {
       Prompt {
         for line in promptLines() {

Sources/SwiftCommitGen/Core/LLMClient.swift

@@ -9,25 +9,9 @@ protocol LLMClient {
   func generateCommitDraft(from prompt: PromptPackage) async throws -> LLMGenerationResult
 }
 
-#if canImport(FoundationModels)
-  @Generable(description: "A commit for changes made in a git repository.")
-#endif
 /// Model representation for the subject/body pair returned by the language model.
 struct CommitDraft: Hashable, Codable, Sendable {
-  #if canImport(FoundationModels)
-    @Guide(
-      description:
-        "The title of a commit. It should be no longer than 50 characters and should summarize the contents of the changeset for other developers reading the commit history. It should describe WHAT was changed."
-    )
-  #endif
   var subject: String
-
-  #if canImport(FoundationModels)
-    @Guide(
-      description:
-        "A detailed description of the the purposes of the changes. It should describe WHY the changes were made."
-    )
-  #endif
   var body: String?
 
   init(subject: String = "", body: String? = nil) {
@@ -77,6 +61,35 @@ struct CommitDraft: Hashable, Codable, Sendable {
   }
 }
 
+#if canImport(FoundationModels)
+  @available(macOS 26.0, *)
+  extension CommitDraft: Generable {
+    static var generationSchema: GenerationSchema {
+      GenerationSchema(
+        type: Self.self,
+        description: "A commit for changes made in a git repository.",
+        properties: [
+          .init(name: "subject", type: String.self),
+          .init(name: "body", type: String?.self),
+        ]
+      )
+    }
+
+    init(_ content: GeneratedContent) throws {
+      self.subject = try content.value(forProperty: "subject")
+      self.body = try content.value(forProperty: "body")
+    }
+
+    var generatedContent: GeneratedContent {
+      var props: [(String, any ConvertibleToGeneratedContent)] = [("subject", subject)]
+      if let body = body {
+        props.append(("body", body))
+      }
+      return GeneratedContent(properties: props, uniquingKeysWith: { _, second in second })
+    }
+  }
+#endif
+
 /// Wraps a generated draft alongside diagnostics gathered during inference.
 struct LLMGenerationResult: Sendable {
   var draft: CommitDraft
@@ -85,6 +98,7 @@ struct LLMGenerationResult: Sendable {
 
 #if canImport(FoundationModels)
   /// Concrete LLM client backed by Apple's FoundationModels framework.
+  @available(macOS 26.0, *)
   struct FoundationModelsClient: LLMClient {
     /// Controls retry behavior and timeouts for generation requests.
     struct Configuration {
@@ -125,17 +139,26 @@ struct LLMGenerationResult: Sendable {
         throw CommitGenError.modelUnavailable(reason: reason)
       }
 
+      // Convert PromptContent to FoundationModels types
+      guard let systemPromptContent = prompt.systemPrompt as? PromptContent,
+        let userPromptContent = prompt.userPrompt as? PromptContent
+      else {
+        throw CommitGenError.invalidBackend(
+          "FoundationModels backend expected PromptContent but received: System: \(type(of: prompt.systemPrompt)), User: \(type(of: prompt.userPrompt))"
+        )
+      }
+
       let session = LanguageModelSession(
         model: model,
-        instructions: prompt.systemPrompt
+        instructions: { Instructions { systemPromptContent.content } }
       )
 
       var diagnostics = prompt.diagnostics
       let response = try await session.respond(
         generating: CommitDraft.self,
         options: generationOptions
       ) {
-        prompt.userPrompt
+        Prompt { userPromptContent.content }
       }
 
       let usage = analyzeTranscriptEntries(response.transcriptEntries)
@@ -279,16 +302,39 @@ struct OllamaClient: LLMClient {
     request.httpMethod = "POST"
     request.setValue("application/json", forHTTPHeaderField: "Content-Type")
 
+    // Extract string content from prompts
+    #if canImport(FoundationModels)
+      // When FoundationModels is available, prompts could be either PromptContent or FoundationModels types
+      // depending on macOS version and runtime availability
+      let systemContent: String
+      let userContent: String
+
+      if let systemPromptContent = prompt.systemPrompt as? PromptContent,
+        let userPromptContent = prompt.userPrompt as? PromptContent
+      {
+        systemContent = systemPromptContent.content
+        userContent = userPromptContent.content
+      } else {
+        // This should not happen if the builder correctly uses PromptContent for non-macOS 26+ systems
+        throw CommitGenError.invalidBackend(
+          "Ollama backend requires PromptContent, but received FoundationModels types (System: \(type(of: prompt.systemPrompt)), User: \(type(of: prompt.userPrompt))). Use FoundationModels backend instead."
+        )
+      }
+    #else
+      let systemContent = prompt.systemPrompt.content
+      let userContent = prompt.userPrompt.content
+    #endif
+
     // Structure the messages properly
     let messages: [[String: String]] = [
       [
         "role": "system",
-        "content": prompt.systemPrompt.content,
+        "content": systemContent,
       ],
       [
         "role": "user",
         "content": """
-        \(prompt.userPrompt.content)
+        \(userContent)
 
         IMPORTANT: You must respond with ONLY valid JSON in this exact format, with no additional text before or after:
         {
@@ -314,8 +360,8 @@ struct OllamaClient: LLMClient {
 
     // Log the request if verbose logging is enabled
     configuration.logger?.debug {
-      let systemPreview = prompt.systemPrompt.content.prefix(200)
-      let userPreview = prompt.userPrompt.content.prefix(800)
+      let systemPreview = systemContent.prefix(200)
+      let userPreview = userContent.prefix(800)
       return """
         📤 Ollama Request to \(configuration.model):
         ┌─ System Prompt (first 200 chars):
@@ -367,7 +413,7 @@ struct OllamaClient: LLMClient {
       promptTokens = promptEvalCount
     } else {
       promptTokens = PromptDiagnostics.tokenEstimate(
-        forCharacterCount: prompt.systemPrompt.content.count + prompt.userPrompt.content.count
+        forCharacterCount: systemContent.count + userContent.count
       )
     }