Pass entire transcript to Foundation Models session

Author: mattt

Sources/AnyLanguageModel/Models/SystemLanguageModel.swift

@@ -78,7 +78,7 @@
             let fmSession = FoundationModels.LanguageModelSession(
                 model: systemModel,
                 tools: session.tools.toFoundationModels(),
-                instructions: session.instructions?.toFoundationModels()
+                transcript: session.transcript.toFoundationModels(instructions: session.instructions)
             )
 
             let fmResponse = try await fmSession.respond(to: fmPrompt, options: fmOptions)
@@ -115,7 +115,7 @@
             let fmSession = FoundationModels.LanguageModelSession(
                 model: systemModel,
                 tools: session.tools.toFoundationModels(),
-                instructions: session.instructions?.toFoundationModels()
+                transcript: session.transcript.toFoundationModels(instructions: session.instructions)
             )
 
             let stream = AsyncThrowingStream<LanguageModelSession.ResponseStream<Content>.Snapshot, any Error> {
@@ -475,4 +475,77 @@
             nil
         }
     }
+
+    @available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, visionOS 26.0, *)
+    extension Transcript {
+        fileprivate func toFoundationModels(instructions: AnyLanguageModel.Instructions?) -> FoundationModels.Transcript
+        {
+            var fmEntries: [FoundationModels.Transcript.Entry] = []
+
+            // Add instructions entry if provided and not already in transcript
+            if let instructions = instructions {
+                let hasInstructions =
+                    self.first.map { entry in
+                        if case .instructions = entry { return true } else { return false }
+                    } ?? false
+
+                if !hasInstructions {
+                    let fmInstructions = FoundationModels.Transcript.Instructions(
+                        segments: [.text(.init(content: instructions.description))],
+                        toolDefinitions: []
+                    )
+                    fmEntries.append(.instructions(fmInstructions))
+                }
+            }
+
+            // Convert each entry
+            for entry in self {
+                switch entry {
+                case .instructions(let instr):
+                    let textContent = instr.segments.compactMap { segment -> String? in
+                        if case .text(let textSegment) = segment {
+                            return textSegment.content
+                        }
+                        return nil
+                    }.joined(separator: " ")
+                    let fmInstructions = FoundationModels.Transcript.Instructions(
+                        segments: [.text(.init(content: textContent))],
+                        toolDefinitions: []
+                    )
+                    fmEntries.append(.instructions(fmInstructions))
+
+                case .prompt(let prompt):
+                    let textContent = prompt.segments.compactMap { segment -> String? in
+                        if case .text(let textSegment) = segment {
+                            return textSegment.content
+                        }
+                        return nil
+                    }.joined(separator: " ")
+                    let fmPrompt = FoundationModels.Transcript.Prompt(
+                        segments: [.text(.init(content: textContent))]
+                    )
+                    fmEntries.append(.prompt(fmPrompt))
+
+                case .response(let response):
+                    let textContent = response.segments.compactMap { segment -> String? in
+                        if case .text(let textSegment) = segment {
+                            return textSegment.content
+                        }
+                        return nil
+                    }.joined(separator: " ")
+                    let fmResponse = FoundationModels.Transcript.Response(
+                        assetIDs: [],
+                        segments: [.text(.init(content: textContent))]
+                    )
+                    fmEntries.append(.response(fmResponse))
+
+                case .toolCalls, .toolOutput:
+                    // Tool calls/outputs require more complex conversion; skip for now
+                    break
+                }
+            }
+
+            return FoundationModels.Transcript(entries: fmEntries)
+        }
+    }
 #endif