diff --git a/crates/git-credential-nostr/src/lib.rs b/crates/git-credential-nostr/src/lib.rs
index b51443600d..b791649e93 100644
--- a/crates/git-credential-nostr/src/lib.rs
+++ b/crates/git-credential-nostr/src/lib.rs
@@ -158,6 +158,13 @@ pub fn run() -> i32 {
     let req = parse_stdin();
 
     if !req.has_authtype_capability {
+        if std::env::var("BUZZ_NOSTR_GIT_AUTH_REQUIRED").as_deref() == Ok("1") {
+            eprintln!(
+                "error: Nostr git authentication requires Git 2.46 or newer \
+                 (credential authtype support)"
+            );
+            return 1;
+        }
         println!();
         let _ = io::stdout().flush();
         return 0;
diff --git a/crates/git-credential-nostr/tests/integration.rs b/crates/git-credential-nostr/tests/integration.rs
index 6697b45f39..99745bccb8 100644
--- a/crates/git-credential-nostr/tests/integration.rs
+++ b/crates/git-credential-nostr/tests/integration.rs
@@ -21,6 +21,7 @@ fn run_helper(input: &str, env_vars: &[(&str, &str)]) -> std::process::Output {
         .current_dir(std::env::temp_dir())
         .env_remove("NOSTR_PRIVATE_KEY")
         .env_remove("BUZZ_AUTH_TAG")
+        .env_remove("BUZZ_NOSTR_GIT_AUTH_REQUIRED")
         .env_remove("GIT_CONFIG_COUNT")
         // Prevent git config on the test machine from supplying credentials.
         .env("GIT_CONFIG_GLOBAL", "/dev/null")
@@ -183,9 +184,10 @@ fn malformed_nip_oa_auth_tag_fails_closed() {
     assert!(!String::from_utf8_lossy(&out.stdout).contains("credential="));
 }
 
-/// Old git (no `capability[]=authtype` in input) → empty line on stdout, exit 0.
+/// A globally configured helper must still decline silently for old Git when
+/// Buzz has not marked the operation as requiring Nostr authentication.
 #[test]
-fn old_git_no_authtype_capability() {
+fn old_git_without_buzz_requirement_declines_silently() {
     let input = "protocol=https\n\
                  host=relay.example.com\n\
                  path=git/owner/repo.git/info/refs\n\
@@ -213,6 +215,34 @@ fn old_git_no_authtype_capability() {
     );
 }
 
+/// Buzz explicitly supplies a Nostr key for relay git operations. If Git is
+/// too old to support `authtype`, fail with the real requirement instead of
+/// silently falling through to Git's misleading username prompt.
+#[test]
+fn old_git_with_buzz_requirement_reports_minimum_version() {
+    let input = "protocol=https\n\
+                 host=relay.example.com\n\
+                 path=git/owner/repo.git/info/refs\n\
+                 \n";
+
+    let nsec = fresh_nsec();
+    let out = run_helper(
+        input,
+        &[
+            ("NOSTR_PRIVATE_KEY", &nsec),
+            ("BUZZ_NOSTR_GIT_AUTH_REQUIRED", "1"),
+        ],
+    );
+
+    assert_eq!(out.status.code(), Some(1));
+    let stderr = String::from_utf8_lossy(&out.stderr);
+    assert!(
+        stderr.contains("Git 2.46 or newer"),
+        "expected minimum Git version diagnostic, got:\n{stderr}"
+    );
+    assert!(!String::from_utf8_lossy(&out.stdout).contains("credential="));
+}
+
 /// No key configured at all → exit 1, stderr mentions "no nostr key configured".
 #[test]
 fn missing_key() {
diff --git a/desktop/src-tauri/src/commands/project_git_exec.rs b/desktop/src-tauri/src/commands/project_git_exec.rs
index 3f16c0fba9..bca00b0313 100644
--- a/desktop/src-tauri/src/commands/project_git_exec.rs
+++ b/desktop/src-tauri/src/commands/project_git_exec.rs
@@ -172,6 +172,9 @@ fn configure_git_auth(command: &mut Command, auth: &GitAuthConfig, needs_credent
             return apply_git_config(command, &entries);
         };
         command.env("NOSTR_PRIVATE_KEY", &auth.nsec);
+        // Git before 2.46 never advertises credential authtype support, so let
+        // the helper surface Buzz's actual minimum-version requirement.
+        command.env("BUZZ_NOSTR_GIT_AUTH_REQUIRED", "1");
         entries.push(("credential.helper", cred_helper.display().to_string()));
         entries.push(("credential.useHttpPath", "true".to_string()));
     }
@@ -315,8 +318,8 @@ fn validate_clone_url_against_relay(clone_url: &str, relay_base: &str) -> Result
 #[cfg(test)]
 mod tests {
     use super::{
-        clean_branch, clean_target_ref, git_needs_credentials, git_subcommand, validate_clone_url,
-        validate_clone_url_against_relay,
+        clean_branch, clean_target_ref, configure_git_auth, git_needs_credentials, git_subcommand,
+        validate_clone_url, validate_clone_url_against_relay, GitAuthConfig,
     };
 
     #[test]
@@ -350,6 +353,25 @@ mod tests {
         assert!(!git_needs_credentials(&["rev-parse", "HEAD"]));
     }
 
+    #[test]
+    fn remote_git_marks_nostr_auth_as_required() {
+        let auth = GitAuthConfig {
+            git_path: "git".into(),
+            credential_helper: Some("git-credential-nostr".into()),
+            nsec: "nsec1test".into(),
+            allow_file_transport: false,
+        };
+        let mut command = std::process::Command::new("git");
+
+        configure_git_auth(&mut command, &auth, true);
+
+        let required = command
+            .get_envs()
+            .find_map(|(key, value)| (key == "BUZZ_NOSTR_GIT_AUTH_REQUIRED").then_some(value))
+            .flatten();
+        assert_eq!(required, Some(std::ffi::OsStr::new("1")));
+    }
+
     #[test]
     fn clean_branch_accepts_plain_and_prefixed_names() {
         assert_eq!(