diff --git a/apps/server/src/provider/Layers/ClaudeCodeAdapter.test.ts b/apps/server/src/provider/Layers/ClaudeCodeAdapter.test.ts
index 68bc0f7d1edccdcf5d48d3ab3945c1d207c5c9e5..21b3254b6d63546c63f9350aa54b67e11d7496f6 100644
--- a/apps/server/src/provider/Layers/ClaudeCodeAdapter.test.ts
+++ b/apps/server/src/provider/Layers/ClaudeCodeAdapter.test.ts
@@ -386,7 +386,7 @@ describe("ClaudeCodeAdapterLive", () => {
         provider: "claudeCode",
         resumeCursor: {
           threadId: "resume-thread-1",
-          resume: "resume-session-1",
+          resume: "550e8400-e29b-41d4-a716-446655440000",
           resumeSessionAt: "assistant-99",
           turnCount: 3,
         },
@@ -395,13 +395,13 @@ describe("ClaudeCodeAdapterLive", () => {
       assert.equal(session.threadId, "resume-thread-1");
       assert.deepEqual(session.resumeCursor, {
         threadId: "resume-thread-1",
-        resume: "resume-session-1",
+        resume: "550e8400-e29b-41d4-a716-446655440000",
         resumeSessionAt: "assistant-99",
         turnCount: 3,
       });
 
       const createInput = harness.getLastCreateQueryInput();
-      assert.equal(createInput?.options.resume, "resume-session-1");
+      assert.equal(createInput?.options.resume, "550e8400-e29b-41d4-a716-446655440000");
       assert.equal(createInput?.options.resumeSessionAt, "assistant-99");
     }).pipe(
       Effect.provideService(Random.Random, makeDeterministicRandomService()),
@@ -409,6 +409,28 @@ describe("ClaudeCodeAdapterLive", () => {
     );
   });
 
+  it.effect("does not synthesize resume session id from generated thread ids", () => {
+    const harness = makeHarness();
+    return Effect.gen(function* () {
+      const adapter = yield* ClaudeCodeAdapter;
+
+      const session = yield* adapter.startSession({
+        provider: "claudeCode",
+      });
+
+      assert.equal(
+        "resume" in (session.resumeCursor as Record<string, unknown>),
+        false,
+      );
+
+      const createInput = harness.getLastCreateQueryInput();
+      assert.equal(createInput?.options.resume, undefined);
+    }).pipe(
+      Effect.provideService(Random.Random, makeDeterministicRandomService()),
+      Effect.provide(harness.layer),
+    );
+  });
+
   it.effect("supports rollbackThread by trimming in-memory turns and preserving earlier turns", () => {
     const harness = makeHarness();
     return Effect.gen(function* () {
diff --git a/apps/server/src/provider/Layers/ClaudeCodeAdapter.ts b/apps/server/src/provider/Layers/ClaudeCodeAdapter.ts
index 7ea84f9bda7d99756e1837a4eb0bbb384d6dec7d..6975b5ee7a67d4fcc1f64aed2740018ea374b8f8 100644
--- a/apps/server/src/provider/Layers/ClaudeCodeAdapter.ts
+++ b/apps/server/src/provider/Layers/ClaudeCodeAdapter.ts
@@ -88,6 +88,7 @@ interface ClaudeSessionContext {
   readonly promptQueue: Queue.Queue<PromptQueueItem>;
   readonly query: ClaudeQueryRuntime;
   readonly startedAt: string;
+  resumeSessionId: string | undefined;
   readonly pendingApprovals: Map<ApprovalRequestId, PendingApproval>;
   readonly turns: Array<{
     id: ReturnType<typeof ProviderTurnId.makeUnsafe>;
@@ -115,6 +116,12 @@ export interface ClaudeCodeAdapterLiveOptions {
   }) => ClaudeQueryRuntime;
 }
 
+function isUuid(value: string): boolean {
+  return /^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i.test(
+    value,
+  );
+}
+
 function toMessage(cause: unknown, fallback: string): string {
   if (cause instanceof Error && cause.message.length > 0) {
     return cause.message;
@@ -148,12 +155,13 @@ function readClaudeResumeState(resumeCursor: unknown): ClaudeResumeState | undef
   };
 
   const threadId = typeof cursor.threadId === "string" ? cursor.threadId : undefined;
-  const resume =
+  const resumeCandidate =
     typeof cursor.resume === "string"
       ? cursor.resume
       : typeof cursor.sessionId === "string"
         ? cursor.sessionId
         : undefined;
+  const resume = resumeCandidate && isUuid(resumeCandidate) ? resumeCandidate : undefined;
   const resumeSessionAt =
     typeof cursor.resumeSessionAt === "string" ? cursor.resumeSessionAt : undefined;
   const turnCountValue = typeof cursor.turnCount === "number" ? cursor.turnCount : undefined;
@@ -351,7 +359,7 @@ function makeClaudeCodeAdapter(options?: ClaudeCodeAdapterLiveOptions) {
 
         const resumeCursor = {
           threadId,
-          resume: threadId,
+          ...(context.resumeSessionId ? { resume: context.resumeSessionId } : {}),
           ...(context.lastAssistantUuid ? { resumeSessionAt: context.lastAssistantUuid } : {}),
           turnCount: context.turns.length,
         };
@@ -369,6 +377,7 @@ function makeClaudeCodeAdapter(options?: ClaudeCodeAdapterLiveOptions) {
     ): Effect.Effect<void> =>
       Effect.gen(function* () {
         const nextThreadId = ProviderThreadId.makeUnsafe(message.session_id);
+        context.resumeSessionId = message.session_id;
         const changed = context.session.threadId !== nextThreadId;
 
         if (changed) {
@@ -935,7 +944,7 @@ function makeClaudeCodeAdapter(options?: ClaudeCodeAdapterLiveOptions) {
           threadId,
           resumeCursor: {
             threadId,
-            resume: resumeState?.resume ?? threadId,
+            ...(resumeState?.resume ? { resume: resumeState.resume } : {}),
             ...(resumeState?.resumeSessionAt
               ? { resumeSessionAt: resumeState.resumeSessionAt }
               : {}),
@@ -950,6 +959,7 @@ function makeClaudeCodeAdapter(options?: ClaudeCodeAdapterLiveOptions) {
           promptQueue,
           query: queryRuntime,
           startedAt,
+          resumeSessionId: resumeState?.resume,
           pendingApprovals,
           turns: [],
           inFlightTools,