fix(onboarding): validates upstream repo existence on manual add

- adds GET /repos/{owner}/{repo} check on manual upstream entry
- 404 shows "Repository not found", disables input during check
- enables "Finish Setup" when upstream repos selected (no org repos)
- updates button repo count to include upstream repos

Author: wgordon17

src/app/components/onboarding/OnboardingWizard.tsx

@@ -127,12 +127,12 @@ export default function OnboardingWizard() {
             <button
               type="button"
               onClick={handleFinish}
-              disabled={selectedRepos().length === 0}
+              disabled={selectedRepos().length === 0 && upstreamRepos().length === 0}
               class="btn btn-primary"
             >
-              {selectedRepos().length === 0
+              {selectedRepos().length + upstreamRepos().length === 0
                 ? "Finish Setup"
-                : `Finish Setup (${selectedRepos().length} ${selectedRepos().length === 1 ? "repo" : "repos"})`}
+                : `Finish Setup (${selectedRepos().length + upstreamRepos().length} ${selectedRepos().length + upstreamRepos().length === 1 ? "repo" : "repos"})`}
             </button>
           </div>
         </Show>

src/app/components/onboarding/RepoSelector.tsx

@@ -45,6 +45,7 @@ export default function RepoSelector(props: RepoSelectorProps) {
   const [discoveringUpstream, setDiscoveringUpstream] = createSignal(false);
   const [discoveryCapped, setDiscoveryCapped] = createSignal(false);
   const [manualEntry, setManualEntry] = createSignal("");
+  const [validatingManual, setValidatingManual] = createSignal(false);
   const [manualEntryError, setManualEntryError] = createSignal<string | null>(null);
 
   // Initialize org states and fetch repos on mount / when selectedOrgs change
@@ -320,7 +321,7 @@ export default function RepoSelector(props: RepoSelectorProps) {
     }
   }
 
-  function handleManualAdd() {
+  async function handleManualAdd() {
     const raw = manualEntry().trim();
     if (!raw) return;
     if (!VALID_REPO_NAME.test(raw)) {
@@ -344,14 +345,38 @@ export default function RepoSelector(props: RepoSelectorProps) {
       return;
     }
 
+    const client = getClient();
+    if (!client) {
+      setManualEntryError("Not connected — try again");
+      return;
+    }
+
+    setValidatingManual(true);
+    setManualEntryError(null);
+    try {
+      await client.request("GET /repos/{owner}/{repo}", { owner, repo: name });
+    } catch (err) {
+      const status = typeof err === "object" && err !== null && "status" in err
+        ? (err as { status: number }).status
+        : null;
+      if (status === 404) {
+        setManualEntryError("Repository not found");
+      } else {
+        setManualEntryError("Could not verify repository — try again");
+      }
+      return;
+    } finally {
+      setValidatingManual(false);
+    }
+
     const newRepo: RepoRef = { owner, name, fullName };
     props.onUpstreamChange?.([...(props.upstreamRepos ?? []), newRepo]);
     setManualEntry("");
     setManualEntryError(null);
   }
 
   function handleManualKeyDown(e: KeyboardEvent) {
-    if (e.key === "Enter") handleManualAdd();
+    if (e.key === "Enter") void handleManualAdd();
   }
 
   // Manually-added upstream repos not in the discovered list
@@ -554,15 +579,17 @@ export default function RepoSelector(props: RepoSelectorProps) {
                 setManualEntryError(null);
               }}
               onKeyDown={handleManualKeyDown}
+              disabled={validatingManual()}
               class="input input-sm flex-1"
               aria-label="Add upstream repo manually"
             />
             <button
               type="button"
-              onClick={handleManualAdd}
+              onClick={() => void handleManualAdd()}
+              disabled={validatingManual()}
               class="btn btn-sm btn-outline"
             >
-              Add
+              {validatingManual() ? "Checking..." : "Add"}
             </button>
           </div>
           <Show when={manualEntryError()}>

tests/components/onboarding/RepoSelector.test.tsx

@@ -4,8 +4,9 @@ import userEvent from "@testing-library/user-event";
 import type { RepoRef, RepoEntry } from "../../../src/app/services/api";
 
 // Mock getClient before importing component
+const mockRequest = vi.fn().mockResolvedValue({ data: {} });
 vi.mock("../../../src/app/services/github", () => ({
-  getClient: () => ({}),
+  getClient: () => ({ request: mockRequest }),
 }));
 
 vi.mock("../../../src/app/stores/auth", () => ({
@@ -379,6 +380,7 @@ describe("RepoSelector — upstream discovery", () => {
     vi.restoreAllMocks();
     vi.mocked(api.fetchRepos).mockResolvedValue(myorgRepos);
     vi.mocked(api.discoverUpstreamRepos).mockResolvedValue([]);
+    mockRequest.mockReset().mockResolvedValue({ data: {} });
   });
 
   it("does not call discoverUpstreamRepos when showUpstreamDiscovery is false (default)", async () => {
@@ -661,4 +663,30 @@ describe("RepoSelector — upstream discovery", () => {
 
     screen.getByText(/already discovered/i);
   });
+
+  it("manual entry: shows error when repo does not exist (404)", async () => {
+    const user = userEvent.setup();
+    mockRequest.mockRejectedValue(Object.assign(new Error("Not Found"), { status: 404 }));
+
+    render(() => (
+      <RepoSelector
+        selectedOrgs={["myorg"]}
+        selected={[]}
+        onChange={vi.fn()}
+        showUpstreamDiscovery={true}
+        upstreamRepos={[]}
+        onUpstreamChange={vi.fn()}
+      />
+    ));
+
+    await waitFor(() => screen.getByText("Upstream Repositories"));
+
+    const input = screen.getByRole("textbox", { name: /add upstream repo/i });
+    await user.type(input, "nonexistent-org/no-repo");
+    await user.click(screen.getByRole("button", { name: /^Add$/ }));
+
+    await waitFor(() => {
+      screen.getByText(/repository not found/i);
+    });
+  });
 });