fix(claude): pass only transcript entries to the rewind session store

The session store parsed each transcript line and cast it to a session
entry without checking it. Keep only JSON objects with a string type, and
cover transcripts with non-entry lines in the real-SDK rewind test.

packages/server/src/server/agent/providers/claude/rewind.test.ts

@@ -103,9 +103,15 @@ interface TranscriptLine {
   text: string;
 }
 
-function writeTranscript(transcriptPath: string, sessionId: string, lines: TranscriptLine[]): void {
-  const entries = lines.map(({ type, uuid, parentUuid, text }) =>
-    JSON.stringify({
+function writeTranscript(
+  transcriptPath: string,
+  sessionId: string,
+  lines: Array<TranscriptLine | string>,
+): void {
+  const entries = lines.map((line) => {
+    if (typeof line === "string") return line;
+    const { type, uuid, parentUuid, text } = line;
+    return JSON.stringify({
       type,
       uuid,
       parentUuid,
@@ -113,8 +119,8 @@ function writeTranscript(transcriptPath: string, sessionId: string, lines: Trans
       cwd: "/repo",
       timestamp: new Date().toISOString(),
       message: { role: type, content: text },
-    }),
-  );
+    });
+  });
   writeFileSync(transcriptPath, `${entries.join("\n")}\n`, "utf8");
 }
 
@@ -175,4 +181,40 @@ describe("Claude rewind against the Claude SDK", () => {
       "first reply",
     ]);
   });
+
+  test("skips transcript lines that are not entries when forking", async () => {
+    tempRoot = mkdtempSync(path.join(tmpdir(), "claude-rewind-config-dir-"));
+    delete process.env.CLAUDE_CONFIG_DIR;
+    const projectDir = path.join(tempRoot, "custom-claude-dir", "projects", "-repo");
+    mkdirSync(projectDir, { recursive: true });
+    const sessionId = randomUUID();
+    const firstUser = randomUUID();
+    const firstReply = randomUUID();
+    const transcriptPath = path.join(projectDir, `${sessionId}.jsonl`);
+    writeTranscript(transcriptPath, sessionId, [
+      "null",
+      { type: "user", uuid: firstUser, parentUuid: null, text: "first" },
+      "[1, 2]",
+      '"text"',
+      "{}",
+      { type: "assistant", uuid: firstReply, parentUuid: firstUser, text: "first reply" },
+      { type: "user", uuid: randomUUID(), parentUuid: firstReply, text: "second" },
+    ]);
+    let currentSessionId = sessionId;
+
+    await revertClaudeConversation({
+      sdk: realClaudeRewindSdk,
+      sessionId,
+      transcriptPath,
+      messageId: firstReply,
+      setSessionId: (nextSessionId) => {
+        currentSessionId = nextSessionId;
+      },
+    });
+
+    expect(readMessageTexts(path.join(projectDir, `${currentSessionId}.jsonl`))).toEqual([
+      "first",
+      "first reply",
+    ]);
+  });
 });

packages/server/src/server/agent/providers/claude/rewind.ts

@@ -49,15 +49,27 @@ function parseTranscriptEntries(text: string): SessionStoreEntry[] {
   const entries: SessionStoreEntry[] = [];
   for (const line of text.split("\n")) {
     if (!line.trim()) continue;
+    let parsed: unknown;
     try {
-      entries.push(JSON.parse(line) as SessionStoreEntry);
+      parsed = JSON.parse(line);
     } catch {
       // Skip a line that is not JSON, as the SDK's own transcript reader does.
+      continue;
     }
+    if (isSessionStoreEntry(parsed)) entries.push(parsed);
   }
   return entries;
 }
 
+function isSessionStoreEntry(value: unknown): value is SessionStoreEntry {
+  return (
+    typeof value === "object" &&
+    value !== null &&
+    !Array.isArray(value) &&
+    typeof (value as { type?: unknown }).type === "string"
+  );
+}
+
 export async function revertClaudeConversation(input: {
   sdk: ClaudeRewindSdk;
   sessionId: string | null;