diff --git a/lib/python/base_cli/app.py b/lib/python/base_cli/app.py
index 8cb595a..6bf303a 100644
--- a/lib/python/base_cli/app.py
+++ b/lib/python/base_cli/app.py
@@ -2876,7 +2876,16 @@ def run_app(
             invocation_token = _INVOCATION_ARGV.set(invocation_argv)
             try:
                 bypass_token = _INVOCATION_MAIN_BYPASS.set(command)
-                output_capture = io.StringIO() if state.json_output else None
+                # A configured JSON option may be enabled by any Click-supported
+                # source (for example ``default_map`` or a combined short flag),
+                # so raw argv cannot determine capture eligibility.  Buffer the
+                # command whenever JSON mode exists and let the parsed lifecycle
+                # value decide whether to emit an envelope or replay human text.
+                output_capture = (
+                    io.StringIO()
+                    if app.lifecycle_options.json is not None
+                    else None
+                )
                 try:
                     if output_capture is None:
                         result = command.main(
diff --git a/tests/test_json_contracts.py b/tests/test_json_contracts.py
index 712de65..729c31d 100644
--- a/tests/test_json_contracts.py
+++ b/tests/test_json_contracts.py
@@ -189,6 +189,54 @@ def main(ctx: base_cli.Context) -> None:
         self.assertEqual(envelope["type"], "success")
         self.assertEqual(envelope["details"]["stdout"], "hello from env\n")
 
+    def test_json_mode_captures_combined_short_flags(self) -> None:
+        app = base_cli.App(
+            name="json-combined-short",
+            log_to_file=False,
+            lifecycle_options=base_cli.LifecycleOptions(
+                json=base_cli.LifecycleOption("--json", "-j"),
+            ),
+        )
+
+        @app.command()
+        @base_cli.option("-x", is_flag=True)
+        def main(ctx: base_cli.Context, x: bool) -> None:
+            del ctx, x
+            print("hello from combined flags")
+
+        with tempfile.TemporaryDirectory() as home:
+            result = base_cli.testing.invoke(app, ["-xj"], home=Path(home))
+
+        self.assertEqual(result.exit_code, 0, result.output)
+        envelope = json.loads(result.stdout)
+        self.assertEqual(envelope["type"], "success")
+        self.assertEqual(
+            envelope["details"]["stdout"],
+            "hello from combined flags\n",
+        )
+
+    def test_json_mode_captures_default_map_values(self) -> None:
+        app = base_cli.App(
+            name="json-default-map",
+            log_to_file=False,
+            lifecycle_options=base_cli.LifecycleOptions(
+                json=base_cli.LifecycleOption("--json"),
+            ),
+        )
+
+        @app.command(context_settings={"default_map": {"json": True}})
+        def main(ctx: base_cli.Context) -> None:
+            del ctx
+            print("hello from default map")
+
+        with tempfile.TemporaryDirectory() as home:
+            result = base_cli.testing.invoke(app, [], home=Path(home))
+
+        self.assertEqual(result.exit_code, 0, result.output)
+        envelope = json.loads(result.stdout)
+        self.assertEqual(envelope["type"], "success")
+        self.assertEqual(envelope["details"]["stdout"], "hello from default map\n")
+
     def test_json_mode_is_opt_in_and_human_output_remains_unchanged(self) -> None:
         app = base_cli.App(name="human-default", log_to_file=False)