diff --git a/apps/mobile/src/features/threads/new-task-flow-provider.tsx b/apps/mobile/src/features/threads/new-task-flow-provider.tsx
index ee2bde9d971..682a47901e0 100644
--- a/apps/mobile/src/features/threads/new-task-flow-provider.tsx
+++ b/apps/mobile/src/features/threads/new-task-flow-provider.tsx
@@ -348,7 +348,10 @@ export function NewTaskFlowProvider(props: React.PropsWithChildren) {
   const workspaceMode = selectedProjectDraft.workspaceSelection?.mode ?? "local";
   const selectedBranchName = selectedProjectDraft.workspaceSelection?.branch ?? null;
   const selectedWorktreePath = selectedProjectDraft.workspaceSelection?.worktreePath ?? null;
-  const startFromOrigin = selectedProjectDraft.workspaceSelection?.startFromOrigin ?? false;
+  const startFromOrigin =
+    selectedProjectDraft.workspaceSelection?.startFromOrigin ??
+    selectedEnvironmentServerConfig?.settings.newWorktreesStartFromOrigin ??
+    true;
   const runtimeMode = selectedProjectDraft.runtimeMode ?? DEFAULT_RUNTIME_MODE;
   const interactionMode = selectedProjectDraft.interactionMode ?? DEFAULT_PROVIDER_INTERACTION_MODE;
 
@@ -598,8 +601,8 @@ export function NewTaskFlowProvider(props: React.PropsWithChildren) {
       return;
     }
     const preferredBranch =
-      availableBranches.find((branch) => branch.current) ??
       availableBranches.find((branch) => branch.isDefault) ??
+      availableBranches.find((branch) => branch.current) ??
       null;
     if (preferredBranch) {
       selectBranch(preferredBranch);
diff --git a/apps/server/src/vcs/GitVcsDriverCore.test.ts b/apps/server/src/vcs/GitVcsDriverCore.test.ts
index dc58fc2543c..655dfea568c 100644
--- a/apps/server/src/vcs/GitVcsDriverCore.test.ts
+++ b/apps/server/src/vcs/GitVcsDriverCore.test.ts
@@ -523,6 +523,26 @@ it.layer(TestLayer)("GitVcsDriver core integration", (it) => {
       }),
     );
 
+    it.effect("marks the origin default ref as default when no local copy exists", () =>
+      Effect.gen(function* () {
+        const cwd = yield* makeTmpDir();
+        const remote = yield* makeTmpDir("git-vcs-driver-remote-");
+        const { initialBranch } = yield* initRepoWithCommit(cwd);
+        yield* git(remote, ["init", "--bare"]);
+        yield* git(cwd, ["remote", "add", "origin", remote]);
+        yield* git(cwd, ["push", "-u", "origin", initialBranch]);
+        yield* git(cwd, ["remote", "set-head", "origin", initialBranch]);
+        yield* git(cwd, ["checkout", "-b", "feature/only-local"]);
+        yield* git(cwd, ["branch", "-D", initialBranch]);
+        const driver = yield* GitVcsDriver.GitVcsDriver;
+
+        const refs = yield* driver.listRefs({ cwd });
+        const remoteDefault = refs.refs.find((ref) => ref.name === `origin/${initialBranch}`);
+        assert.equal(remoteDefault?.isRemote, true);
+        assert.equal(remoteDefault?.isDefault, true);
+      }),
+    );
+
     it.effect("creates, checks out, renames, and lists refs", () =>
       Effect.gen(function* () {
         const cwd = yield* makeTmpDir();
diff --git a/apps/server/src/vcs/GitVcsDriverCore.ts b/apps/server/src/vcs/GitVcsDriverCore.ts
index a406cbce549..0140a25d6f4 100644
--- a/apps/server/src/vcs/GitVcsDriverCore.ts
+++ b/apps/server/src/vcs/GitVcsDriverCore.ts
@@ -2202,7 +2202,12 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
                 name: refName.name,
                 current: false,
                 isRemote: true,
-                isDefault: false,
+                // origin/HEAD's target is the repo default even when no local
+                // copy of the default branch exists.
+                isDefault:
+                  defaultBranch !== null &&
+                  parsedRemoteRef?.remoteName === "origin" &&
+                  parsedRemoteRef.branchName === defaultBranch,
                 worktreePath: null,
               };
               if (parsedRemoteRef) {
diff --git a/apps/web/src/components/BranchToolbarBranchSelector.tsx b/apps/web/src/components/BranchToolbarBranchSelector.tsx
index e2ee24c3608..67ae3a8187d 100644
--- a/apps/web/src/components/BranchToolbarBranchSelector.tsx
+++ b/apps/web/src/components/BranchToolbarBranchSelector.tsx
@@ -422,17 +422,32 @@ export function BranchToolbarBranchSelector({
     });
   };
 
+  // Default the worktree base to the repo default branch (origin/HEAD), only
+  // falling back to the checked-out branch when no default is known.
+  const defaultBranchName = useMemo(
+    () => refs.find((refName) => refName.isDefault)?.name ?? null,
+    [refs],
+  );
+  const worktreeBaseBranchCandidate = isInitialBranchesLoadPending
+    ? null
+    : (defaultBranchName ?? currentGitBranch);
   useEffect(() => {
     if (
       effectiveEnvMode !== "worktree" ||
       activeWorktreePath ||
       activeThreadBranch ||
-      !currentGitBranch
+      !worktreeBaseBranchCandidate
     ) {
       return;
     }
-    setThreadBranch(currentGitBranch, null);
-  }, [activeThreadBranch, activeWorktreePath, currentGitBranch, effectiveEnvMode, setThreadBranch]);
+    setThreadBranch(worktreeBaseBranchCandidate, null);
+  }, [
+    activeThreadBranch,
+    activeWorktreePath,
+    effectiveEnvMode,
+    setThreadBranch,
+    worktreeBaseBranchCandidate,
+  ]);
 
   // ---------------------------------------------------------------------------
   // Combobox / list plumbing
diff --git a/packages/contracts/src/settings.test.ts b/packages/contracts/src/settings.test.ts
index ac2d47ca336..b1db6005223 100644
--- a/packages/contracts/src/settings.test.ts
+++ b/packages/contracts/src/settings.test.ts
@@ -88,14 +88,14 @@ describe("ServerSettings.providerInstances (slice-2 invariant)", () => {
 });
 
 describe("ServerSettings worktree defaults", () => {
-  it("defaults start-from-origin off for legacy configs", () => {
-    expect(decodeServerSettings({}).newWorktreesStartFromOrigin).toBe(false);
+  it("defaults start-from-origin on for legacy configs", () => {
+    expect(decodeServerSettings({}).newWorktreesStartFromOrigin).toBe(true);
   });
 
   it("accepts start-from-origin updates", () => {
     expect(
-      decodeServerSettingsPatch({ newWorktreesStartFromOrigin: true }).newWorktreesStartFromOrigin,
-    ).toBe(true);
+      decodeServerSettingsPatch({ newWorktreesStartFromOrigin: false }).newWorktreesStartFromOrigin,
+    ).toBe(false);
   });
 });
 
diff --git a/packages/contracts/src/settings.ts b/packages/contracts/src/settings.ts
index 6ccd65533dd..e3cac17889a 100644
--- a/packages/contracts/src/settings.ts
+++ b/packages/contracts/src/settings.ts
@@ -375,7 +375,7 @@ export const ServerSettings = Schema.Struct({
     Schema.withDecodingDefault(Effect.succeed("local" as const satisfies ThreadEnvMode)),
   ),
   newWorktreesStartFromOrigin: Schema.Boolean.pipe(
-    Schema.withDecodingDefault(Effect.succeed(false)),
+    Schema.withDecodingDefault(Effect.succeed(true)),
   ),
   addProjectBaseDirectory: TrimmedString.pipe(Schema.withDecodingDefault(Effect.succeed(""))),
   textGenerationModelSelection: ModelSelection.pipe(