diff --git a/apps/web/src/components/ChatView.browser.tsx b/apps/web/src/components/ChatView.browser.tsx
index 3bad1c2e59..f127047b71 100644
--- a/apps/web/src/components/ChatView.browser.tsx
+++ b/apps/web/src/components/ChatView.browser.tsx
@@ -3581,6 +3581,98 @@ describe("ChatView timeline estimator parity (full app)", () => {
     }
   });
 
+  it("creates a fresh worktree draft from an existing worktree thread when the default mode is worktree", async () => {
+    const mounted = await mountChatView({
+      viewport: DEFAULT_VIEWPORT,
+      snapshot: {
+        ...createSnapshotForTargetUser({
+          targetMessageId: "msg-user-new-thread-worktree-default-test" as MessageId,
+          targetText: "new thread worktree default test",
+        }),
+        threads: createSnapshotForTargetUser({
+          targetMessageId: "msg-user-new-thread-worktree-default-test" as MessageId,
+          targetText: "new thread worktree default test",
+        }).threads.map((thread) =>
+          thread.id === THREAD_ID
+            ? Object.assign({}, thread, {
+                branch: "feature/existing",
+                worktreePath: "/repo/.t3/worktrees/existing",
+              })
+            : thread,
+        ),
+      },
+      configureFixture: (nextFixture) => {
+        nextFixture.serverConfig = {
+          ...nextFixture.serverConfig,
+          settings: {
+            ...nextFixture.serverConfig.settings,
+            defaultThreadEnvMode: "worktree",
+          },
+        };
+      },
+    });
+
+    try {
+      const newThreadButton = page.getByTestId("new-thread-button");
+      await expect.element(newThreadButton).toBeInTheDocument();
+
+      await newThreadButton.click();
+
+      const newThreadPath = await waitForURL(
+        mounted.router,
+        (path) => UUID_ROUTE_RE.test(path),
+        "Route should change to a new draft thread.",
+      );
+      const newDraftId = draftIdFromPath(newThreadPath);
+
+      expect(useComposerDraftStore.getState().getDraftSession(newDraftId)).toMatchObject({
+        envMode: "worktree",
+        worktreePath: null,
+      });
+    } finally {
+      await mounted.cleanup();
+    }
+  });
+
+  it("creates a new draft instead of reusing a promoting draft thread", async () => {
+    const mounted = await mountChatView({
+      viewport: DEFAULT_VIEWPORT,
+      snapshot: createSnapshotForTargetUser({
+        targetMessageId: "msg-user-promoting-draft-new-thread-test" as MessageId,
+        targetText: "promoting draft new thread test",
+      }),
+    });
+
+    try {
+      const newThreadButton = page.getByTestId("new-thread-button");
+      await expect.element(newThreadButton).toBeInTheDocument();
+
+      await newThreadButton.click();
+
+      const firstDraftPath = await waitForURL(
+        mounted.router,
+        (path) => UUID_ROUTE_RE.test(path),
+        "Route should change to the first draft thread.",
+      );
+      const firstDraftId = draftIdFromPath(firstDraftPath);
+      const firstThreadId = draftThreadIdFor(firstDraftId);
+
+      await materializePromotedDraftThreadViaDomainEvent(firstThreadId);
+      expect(mounted.router.state.location.pathname).toBe(firstDraftPath);
+
+      await newThreadButton.click();
+
+      const secondDraftPath = await waitForURL(
+        mounted.router,
+        (path) => UUID_ROUTE_RE.test(path) && path !== firstDraftPath,
+        "Route should change to a second draft thread instead of reusing the promoting draft.",
+      );
+      expect(draftIdFromPath(secondDraftPath)).not.toBe(firstDraftId);
+    } finally {
+      await mounted.cleanup();
+    }
+  });
+
   it("snapshots sticky codex settings into a new draft thread", async () => {
     useComposerDraftStore.setState({
       stickyModelSelectionByProvider: {
diff --git a/apps/web/src/components/Sidebar.logic.test.ts b/apps/web/src/components/Sidebar.logic.test.ts
index 35534af9f3..fb75013928 100644
--- a/apps/web/src/components/Sidebar.logic.test.ts
+++ b/apps/web/src/components/Sidebar.logic.test.ts
@@ -169,6 +169,28 @@ describe("resolveSidebarNewThreadEnvMode", () => {
 });
 
 describe("resolveSidebarNewThreadSeedContext", () => {
+  it("prefers the default worktree mode over active thread context", () => {
+    expect(
+      resolveSidebarNewThreadSeedContext({
+        projectId: "project-1",
+        defaultEnvMode: "worktree",
+        activeThread: {
+          projectId: "project-1",
+          branch: "feature/existing",
+          worktreePath: "/repo/.t3/worktrees/existing",
+        },
+        activeDraftThread: {
+          projectId: "project-1",
+          branch: "feature/draft",
+          worktreePath: "/repo/.t3/worktrees/draft",
+          envMode: "worktree",
+        },
+      }),
+    ).toEqual({
+      envMode: "worktree",
+    });
+  });
+
   it("inherits the active server thread context when creating a new thread in the same project", () => {
     expect(
       resolveSidebarNewThreadSeedContext({
diff --git a/apps/web/src/components/Sidebar.logic.ts b/apps/web/src/components/Sidebar.logic.ts
index 8c742cbe9b..67f6fa49ed 100644
--- a/apps/web/src/components/Sidebar.logic.ts
+++ b/apps/web/src/components/Sidebar.logic.ts
@@ -183,6 +183,12 @@ export function resolveSidebarNewThreadSeedContext(input: {
   worktreePath?: string | null;
   envMode: SidebarNewThreadEnvMode;
 } {
+  if (input.defaultEnvMode === "worktree") {
+    return {
+      envMode: "worktree",
+    };
+  }
+
   if (input.activeDraftThread?.projectId === input.projectId) {
     return {
       branch: input.activeDraftThread.branch,
diff --git a/apps/web/src/composerDraftStore.ts b/apps/web/src/composerDraftStore.ts
index 231cf06566..20f7cbe032 100644
--- a/apps/web/src/composerDraftStore.ts
+++ b/apps/web/src/composerDraftStore.ts
@@ -1881,13 +1881,18 @@ const composerDraftStore = create<ComposerDraftStoreState>()(
               [draftId]: nextDraftThread,
             };
             let nextDraftsByThreadKey = state.draftsByThreadKey;
+            const previousDraftThread =
+              previousThreadKeyForLogicalProject === undefined
+                ? undefined
+                : nextDraftThreadsByThreadKey[previousThreadKeyForLogicalProject];
             if (
               previousThreadKeyForLogicalProject &&
               previousThreadKeyForLogicalProject !== draftId &&
               !isComposerThreadKeyInUse(
                 nextLogicalProjectDraftThreadKeyByLogicalProjectKey,
                 previousThreadKeyForLogicalProject,
-              )
+              ) &&
+              !isDraftThreadPromoting(previousDraftThread)
             ) {
               delete nextDraftThreadsByThreadKey[previousThreadKeyForLogicalProject];
               if (state.draftsByThreadKey[previousThreadKeyForLogicalProject] !== undefined) {
diff --git a/apps/web/src/hooks/useHandleNewThread.ts b/apps/web/src/hooks/useHandleNewThread.ts
index 6856140daa..f567735691 100644
--- a/apps/web/src/hooks/useHandleNewThread.ts
+++ b/apps/web/src/hooks/useHandleNewThread.ts
@@ -87,7 +87,8 @@ function useNewThreadState() {
       if (
         latestActiveDraftThread &&
         currentRouteTarget?.kind === "draft" &&
-        latestActiveDraftThread.logicalProjectKey === logicalProjectKey
+        latestActiveDraftThread.logicalProjectKey === logicalProjectKey &&
+        latestActiveDraftThread.promotedTo == null
       ) {
         if (hasBranchOption || hasWorktreePathOption || hasEnvModeOption) {
           setDraftThreadContext(currentRouteTarget.draftId, {