fix(git): distinguish missing default branch from SSH key misconfig

The FS git clone path mapped any JGit TransportException to INVALID_GIT_SSH_CONFIGURATION (AE-GIT-4032), so importing/connecting a repo with no default branch showed a misleading "SSH key misconfiguration" error even when the SSH key was valid. JGit throws "Remote branch 'HEAD' not found in upstream origin" in that case.

Add AppsmithError GIT_DEFAULT_BRANCH_NOT_FOUND (AE-GIT-4052) with an actionable message and route that case to it in both fetchRemoteRepository overloads. No frontend change needed: the deploy-key step already renders non-4032 backend messages generically.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: sebastianiv21

app/server/appsmith-server/src/main/java/com/appsmith/server/exceptions/AppsmithError.java

@@ -370,6 +370,15 @@ public enum AppsmithError {
             "SSH key not configured",
             ErrorType.GIT_CONFIGURATION_ERROR,
             ErrorReferenceDocUrl.GIT_DEPLOY_KEY.getDocUrl()),
+    GIT_DEFAULT_BRANCH_NOT_FOUND(
+            400,
+            AppsmithErrorCode.GIT_DEFAULT_BRANCH_NOT_FOUND.getCode(),
+            "Couldn''t find a default branch in the remote repository. Set a default branch (for example main or master) "
+                    + "in your Git provider''s repository settings, then try again.",
+            AppsmithErrorAction.DEFAULT,
+            "No default branch found",
+            ErrorType.GIT_CONFIGURATION_ERROR,
+            null),
     INVALID_GIT_REPO(
             400,
             AppsmithErrorCode.INVALID_GIT_REPO.getCode(),

app/server/appsmith-server/src/main/java/com/appsmith/server/exceptions/AppsmithErrorCode.java

@@ -96,6 +96,7 @@ public enum AppsmithErrorCode {
     GIT_UPSTREAM_CHANGES("AE-GIT-4048", "Git upstream changes"),
     INVALID_GIT_SSH_URL("AE-GIT-4050", "Invalid git ssh url"),
     REPOSITORY_NOT_FOUND("AE-GIT-4051", "Repository not found"),
+    GIT_DEFAULT_BRANCH_NOT_FOUND("AE-GIT-4052", "Git default branch not found"),
     GIT_FILE_SYSTEM_ERROR("AE-GIT-5013", "Git file system error"),
     GIT_EXECUTION_TIMEOUT("AE-GIT-5014", "Git execution timeout"),
     GIT_GENERIC_ERROR("AE-GIT-5016", "Git generic error"),

app/server/appsmith-server/src/main/java/com/appsmith/server/git/fs/GitFSServiceCEImpl.java

@@ -153,6 +153,22 @@ public Boolean isGitAuthInvalid(GitAuth gitAuth) {
         return !StringUtils.hasText(gitAuth.getPrivateKey()) || !StringUtils.hasText(gitAuth.getPublicKey());
     }
 
+    /**
+     * JGit throws a TransportException with message "Remote branch ''HEAD'' not found in upstream origin"
+     * when the remote repo has no checkout-able default branch. That is not an SSH problem, so we detect it
+     * here to avoid the misleading "SSH key misconfiguration" error.
+     */
+    static boolean isRemoteDefaultBranchMissing(Throwable error) {
+        for (Throwable t = error; t != null; t = t.getCause()) {
+            String msg = t.getMessage();
+            if (msg != null && msg.toLowerCase().contains("not found in upstream")) {
+                log.debug("Remote clone failed: repository has no default branch. JGit message: {}", msg);
+                return true;
+            }
+        }
+        return false;
+    }
+
     public Mono<String> fetchRemoteRepository(
             GitConnectDTO gitConnectDTO, GitAuth gitAuth, ArtifactJsonTransformationDTO jsonTransformationDTO) {
         String workspaceId = jsonTransformationDTO.getWorkspaceId();
@@ -176,8 +192,10 @@ public Mono<String> fetchRemoteRepository(
                             .then(commonGitFileUtils.deleteLocalRepo(temporaryStorage))
                             .flatMap(isDeleted -> {
                                 if (error instanceof TransportException) {
-                                    return Mono.error(
-                                            new AppsmithException(AppsmithError.INVALID_GIT_SSH_CONFIGURATION));
+                                    AppsmithError transportError = isRemoteDefaultBranchMissing(error)
+                                            ? AppsmithError.GIT_DEFAULT_BRANCH_NOT_FOUND
+                                            : AppsmithError.INVALID_GIT_SSH_CONFIGURATION;
+                                    return Mono.error(new AppsmithException(transportError));
                                 } else if (error instanceof InvalidRemoteException) {
                                     return Mono.error(
                                             new AppsmithException(AppsmithError.INVALID_PARAMETER, "remote url"));
@@ -260,7 +278,9 @@ public Mono<String> fetchRemoteRepository(
                     AppsmithException appsmithException;
 
                     if (error instanceof TransportException) {
-                        appsmithException = new AppsmithException(AppsmithError.INVALID_GIT_SSH_CONFIGURATION);
+                        appsmithException = isRemoteDefaultBranchMissing(error)
+                                ? new AppsmithException(AppsmithError.GIT_DEFAULT_BRANCH_NOT_FOUND)
+                                : new AppsmithException(AppsmithError.INVALID_GIT_SSH_CONFIGURATION);
                     } else if (error instanceof InvalidRemoteException) {
                         appsmithException = new AppsmithException(AppsmithError.INVALID_PARAMETER, "remote url");
                     } else if (error instanceof TimeoutException) {

app/server/appsmith-server/src/test/java/com/appsmith/server/git/fs/GitFSServiceCEImplTest.java

@@ -0,0 +1,46 @@
+package com.appsmith.server.git.fs;
+
+import org.eclipse.jgit.api.errors.TransportException;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class GitFSServiceCEImplTest {
+
+    @Test
+    void isRemoteDefaultBranchMissing_returnsTrue_forJGitNoDefaultBranchMessage() {
+        Throwable error = new TransportException("Remote branch 'HEAD' not found in upstream origin");
+        assertThat(GitFSServiceCEImpl.isRemoteDefaultBranchMissing(error)).isTrue();
+    }
+
+    @Test
+    void isRemoteDefaultBranchMissing_returnsTrue_whenMessageIsInCausalChain() {
+        Throwable cause = new TransportException("Remote branch 'HEAD' not found in upstream origin");
+        Throwable error = new RuntimeException("clone failed", cause);
+        assertThat(GitFSServiceCEImpl.isRemoteDefaultBranchMissing(error)).isTrue();
+    }
+
+    @Test
+    void isRemoteDefaultBranchMissing_returnsFalse_forAuthFailure() {
+        Throwable error = new TransportException("Auth fail");
+        assertThat(GitFSServiceCEImpl.isRemoteDefaultBranchMissing(error)).isFalse();
+    }
+
+    @Test
+    void isRemoteDefaultBranchMissing_returnsFalse_forNullMessage() {
+        Throwable error = new RuntimeException();
+        assertThat(GitFSServiceCEImpl.isRemoteDefaultBranchMissing(error)).isFalse();
+    }
+
+    @Test
+    void isRemoteDefaultBranchMissing_isCaseInsensitive() {
+        Throwable error = new TransportException("Remote branch 'HEAD' NOT FOUND IN UPSTREAM origin");
+        assertThat(GitFSServiceCEImpl.isRemoteDefaultBranchMissing(error)).isTrue();
+    }
+
+    @Test
+    void isRemoteDefaultBranchMissing_returnsFalse_forOtherNotFoundMessage() {
+        Throwable error = new TransportException("Repository not found");
+        assertThat(GitFSServiceCEImpl.isRemoteDefaultBranchMissing(error)).isFalse();
+    }
+}