fix: write transcript completion marker last

Package.swift

@@ -28,5 +28,9 @@ let package = Package(
                 ]),
             ]
         ),
+        .testTarget(
+            name: "quillTests",
+            dependencies: ["quill"]
+        ),
     ]
 )

Sources/quill/Transcription/TranscriptionCoordinator.swift

@@ -231,7 +231,7 @@ private struct SessionMeta {
 
 /// Canonical transcript. Property names are the JSON schema — this struct
 /// exists to be serialized.
-private struct Transcript: Codable {
+struct Transcript: Codable {
     struct Segment: Codable {
         let speaker: String
         let start_ms: Int
@@ -244,16 +244,19 @@ private struct Transcript: Codable {
     let created_at: String
     let segments: [Segment]
 
-    /// Write transcript.json and render transcript.md. Both writes are atomic
-    /// (temp file + rename), so a partially written transcript never exists on
-    /// disk — resumePending treats presence of transcript.json as "done".
+    /// Render transcript.md, then write transcript.json as the completion
+    /// marker. Both writes are atomic (temp file + rename), and writing JSON
+    /// last ensures resumePending retries if either artifact fails.
     func write(to dir: URL) throws {
         let encoder = JSONEncoder()
         encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
-        try encoder.encode(self)
-            .write(to: dir.appendingPathComponent("transcript.json"), options: .atomic)
-        try Data(rendered(title: dir.lastPathComponent).utf8)
+        let json = try encoder.encode(self)
+        let markdown = Data(rendered(title: dir.lastPathComponent).utf8)
+
+        try markdown
             .write(to: dir.appendingPathComponent("transcript.md"), options: .atomic)
+        try json
+            .write(to: dir.appendingPathComponent("transcript.json"), options: .atomic)
     }
 
     private func rendered(title: String) -> String {

Tests/quillTests/Transcription/TranscriptTests.swift

@@ -0,0 +1,40 @@
+import Foundation
+import Testing
+
+@testable import quill
+
+struct TranscriptTests {
+    @Test("A failed Markdown write does not leave the completion marker")
+    func failedMarkdownWriteDoesNotLeaveCompletionMarker() throws {
+        let fileManager = FileManager.default
+        let session = fileManager.temporaryDirectory
+            .appendingPathComponent("quill-\(UUID().uuidString)", isDirectory: true)
+        try fileManager.createDirectory(at: session, withIntermediateDirectories: true)
+        defer { try? fileManager.removeItem(at: session) }
+
+        try fileManager.createDirectory(
+            at: session.appendingPathComponent("transcript.md", isDirectory: true),
+            withIntermediateDirectories: true
+        )
+
+        let transcript = Transcript(
+            engine: "parakeet",
+            model: "test-model",
+            created_at: "2026-07-28T00:00:00Z",
+            segments: []
+        )
+
+        do {
+            try transcript.write(to: session)
+            Issue.record("Expected writing transcript.md over a directory to fail.")
+        } catch {
+            // Expected: transcript.md is a directory.
+        }
+
+        let completionMarker = session.appendingPathComponent("transcript.json")
+        #expect(
+            fileManager.fileExists(atPath: completionMarker.path) == false,
+            "A failed transcript.md write must leave the session pending."
+        )
+    }
+}