Disable Generate button and show busy label during generation

Prevents double-clicking Generate from firing overlapping requests on
the same slot, and gives clearer feedback that a job is in flight.
Wired via .then() (not .success()) on all three tabs so the button
re-enables even if the generate call raises.

app.py

@@ -2537,6 +2537,20 @@ def _update_slot_visibility(n):
     return [gr.update(visible=(i < n)) for i in range(MAX_SLOTS)]
 
 
+def _btn_generating():
+    """Disable a Generate button and show a busy label. Chained as the first
+    .click() step so it fires immediately, before the (possibly slow) generate
+    call starts."""
+    return gr.update(value="Generating…", interactive=False)
+
+
+def _btn_ready():
+    """Re-enable a Generate button. Chained via .then() (not .success()) so it
+    always runs — even if an earlier step in the chain raised — otherwise a
+    crashed generation would leave the button stuck disabled."""
+    return gr.update(value="Generate", interactive=True)
+
+
 # ================================================================== #
 #                       GRADIO UI                                     #
 # ================================================================== #
@@ -3042,6 +3056,10 @@ with gr.Blocks(title="Generate Audio for Video", css=_SLOT_CSS, js=_GLOBAL_JS) a
             # Split group visibility into a separate .then() to avoid Gradio 5 SSR
             # "Too many arguments" caused by including gr.Group in mixed output lists.
             (taro_btn.click(
+                fn=_btn_generating,
+                inputs=None,
+                outputs=[taro_btn],
+            ).then(
                 fn=_run_taro,
                 inputs=[taro_video, taro_seed, taro_cfg, taro_steps, taro_mode,
                         taro_cf_dur, taro_cf_db, taro_samples],
@@ -3050,6 +3068,10 @@ with gr.Blocks(title="Generate Audio for Video", css=_SLOT_CSS, js=_GLOBAL_JS) a
                 fn=_update_slot_visibility,
                 inputs=[taro_samples],
                 outputs=taro_slot_grps,
+            ).then(
+                fn=_btn_ready,
+                inputs=None,
+                outputs=[taro_btn],
             ))
 
             # Per-slot regen handlers — JS calls /gradio_api/queue/join with
@@ -3098,6 +3120,10 @@ with gr.Blocks(title="Generate Audio for Video", css=_SLOT_CSS, js=_GLOBAL_JS) a
                 return _unpack_outputs(flat, n, "mma")
 
             (mma_btn.click(
+                fn=_btn_generating,
+                inputs=None,
+                outputs=[mma_btn],
+            ).then(
                 fn=_run_mmaudio,
                 inputs=[mma_video, mma_prompt, mma_neg, mma_seed,
                         mma_cfg, mma_steps, mma_cf_dur, mma_cf_db, mma_samples],
@@ -3106,6 +3132,10 @@ with gr.Blocks(title="Generate Audio for Video", css=_SLOT_CSS, js=_GLOBAL_JS) a
                 fn=_update_slot_visibility,
                 inputs=[mma_samples],
                 outputs=mma_slot_grps,
+            ).then(
+                fn=_btn_ready,
+                inputs=None,
+                outputs=[mma_btn],
             ))
 
             mma_regen_btns = _register_regen_handlers(
@@ -3153,6 +3183,10 @@ with gr.Blocks(title="Generate Audio for Video", css=_SLOT_CSS, js=_GLOBAL_JS) a
                 return _unpack_outputs(flat, n, "hf")
 
             (hf_btn.click(
+                fn=_btn_generating,
+                inputs=None,
+                outputs=[hf_btn],
+            ).then(
                 fn=_run_hunyuan,
                 inputs=[hf_video, hf_prompt, hf_neg, hf_seed,
                         hf_guidance, hf_steps, hf_size, hf_cf_dur, hf_cf_db, hf_samples],
@@ -3161,6 +3195,10 @@ with gr.Blocks(title="Generate Audio for Video", css=_SLOT_CSS, js=_GLOBAL_JS) a
                 fn=_update_slot_visibility,
                 inputs=[hf_samples],
                 outputs=hf_slot_grps,
+            ).then(
+                fn=_btn_ready,
+                inputs=None,
+                outputs=[hf_btn],
             ))
 
             hf_regen_btns = _register_regen_handlers(