feat(ui): wire lyrics tab + cross-tab use-in-generate handoff (m4)

app.py

@@ -261,6 +261,50 @@ def on_extend_click(
         raise gr.Error(str(e)) from e
 
 
+def on_draft_lyrics(
+    brief: str,
+    structure: str,
+    language: str,
+    tone: str,
+    verse_lines: float,
+    chorus_lines: float,
+    bridge_lines: float,
+    rhyme: str,
+    temperature: float,
+    top_p: float,
+    top_k: float,
+    max_new_tokens: float,
+    seed,
+    progress=gr.Progress(track_tqdm=True),  # noqa: B008
+):
+    """Lyrics-mode click. Calls ``modes.lyrics(...)`` directly — no ACE-Step
+    pipeline is touched. Qwen 2.5 7B is its own lazy singleton inside
+    ``lyrics_lm``; the first click triggers a ~4 GB MLX download (cached
+    afterwards) and ~30 s warm-up before the draft appears.
+    """
+    try:
+        return modes.lyrics(
+            get_backend(),
+            params={
+                "brief": brief,
+                "structure": structure,
+                "language": language,
+                "tone": tone,
+                "verse_lines": int(verse_lines),
+                "chorus_lines": int(chorus_lines),
+                "bridge_lines": int(bridge_lines),
+                "rhyme": rhyme,
+                "temperature": float(temperature),
+                "top_p": float(top_p),
+                "top_k": int(top_k),
+                "max_new_tokens": int(max_new_tokens),
+                "seed": int(seed) if seed is not None else None,
+            },
+        )
+    except ValueError as e:
+        raise gr.Error(str(e)) from e
+
+
 def on_edit_click(
     source_audio,
     sub_mode: str,
@@ -513,7 +557,35 @@ def build_app() -> gr.Blocks:
                         outputs=[e["output_audio"], e["output_meta"]],
                     )
                 with gr.Group(visible=False, elem_classes=["ams-tab-pane"]) as pane_lyrics:
-                    gr.Markdown("### ✍️ Lyrics\n\nPlaceholder — implemented in M4.")
+                    lyr = ui.build_lyrics_tab()
+                    lyr["draft_btn"].click(
+                        fn=on_draft_lyrics,
+                        inputs=[
+                            lyr["brief"],
+                            lyr["structure"],
+                            lyr["language"],
+                            lyr["tone"],
+                            lyr["verse_lines"],
+                            lyr["chorus_lines"],
+                            lyr["bridge_lines"],
+                            lyr["rhyme"],
+                            lyr["temperature"],
+                            lyr["top_p"],
+                            lyr["top_k"],
+                            lyr["max_new_tokens"],
+                            lyr["seed"],
+                        ],
+                        outputs=[lyr["lyrics_output"], lyr["meta_output"]],
+                    )
+                    # Cross-tab "Use these in Generate" — pipes the drafted
+                    # text straight into the Generate tab's lyrics textbox.
+                    # Both panes were declared inside the same gr.Blocks
+                    # context so referencing g["lyrics"] across panes works.
+                    lyr["use_in_generate_btn"].click(
+                        fn=lambda txt: txt,
+                        inputs=[lyr["lyrics_output"]],
+                        outputs=[g["lyrics"]],
+                    )
 
         panes = [pane_generate, pane_cover, pane_extend, pane_edit, pane_lyrics]
 

theme.py

@@ -861,6 +861,59 @@ main, .contain {{
   padding:0 12px 12px 12px !important;
 }}
 
+/* ============================================================
+ * Lyrics tab (M4)
+ * Mono draft textbox + secondary "Use in Generate" CTA. The LM-params
+ * accordion reuses the same chrome as the LoRA + experimental
+ * accordions so the bordered section header reads consistently.
+ * ============================================================ */
+.ams-content .ams-lyrics-output textarea {{
+  font-family: {FONT_MONO} !important;
+  font-size: 12px !important;
+  line-height: 1.6 !important;
+  min-height: 280px !important;
+  background:{SURFACE_STRONG} !important;
+  border:1px solid {BORDER} !important;
+  color:{INK} !important;
+}}
+.ams-content .ams-lyrics-output textarea::placeholder {{
+  font-style: italic;
+}}
+.ams-content .ams-lyrics-use-btn {{
+  margin-top: 6px !important;
+}}
+.ams-content .ams-lm-accordion {{
+  border:1px solid {BORDER} !important;
+  border-radius:3px !important;
+  background:{SURFACE_STRONG} !important;
+  margin-top:10px !important;
+  padding:0 !important;
+}}
+.ams-content .ams-lm-accordion > .label-wrap,
+.ams-content .ams-lm-accordion summary,
+.ams-content .ams-lm-accordion > button {{
+  font-family: {FONT_MONO} !important;
+  font-size:10px !important;
+  letter-spacing:0.08em !important;
+  text-transform:uppercase !important;
+  color:{INK_MUTED} !important;
+  padding:10px 12px !important;
+  background:transparent !important;
+  border:none !important;
+}}
+.ams-content .ams-lm-accordion > .label-wrap span,
+.ams-content .ams-lm-accordion summary span,
+.ams-content .ams-lm-accordion > button span {{
+  color:{INK_MUTED} !important;
+  font-family: {FONT_MONO} !important;
+  font-size:10px !important;
+  letter-spacing:0.08em !important;
+  text-transform:uppercase !important;
+}}
+.ams-content .ams-lm-accordion > div:not(.label-wrap):not(summary) {{
+  padding:0 12px 12px 12px !important;
+}}
+
 /* Hide Gradio footer + the floating "Use via API" / settings panel */
 footer {{ display:none !important; }}
 .show-api {{ display:none !important; }}

ui.py

@@ -418,3 +418,137 @@ def build_edit_tab() -> dict[str, gr.components.Component]:
             _build_output_panel(components)
 
     return components
+
+
+def build_lyrics_tab() -> dict[str, gr.components.Component]:
+    """Lyrics tab body: Qwen 2.5 7B drafts structurally-tagged lyrics.
+
+    Compact 2-column row: form on the left (brief / structure / language /
+    line counts / tone / rhyme + collapsed LM-params accordion), output on
+    the right (read-only multi-line textbox + ``Use these in Generate``
+    cross-tab CTA + bordered JSON metadata panel).
+
+    The output textbox carries ``elem_classes=["ams-lyrics-output"]`` so
+    the Brutalist Mono treatment in ``theme.CSS`` (mono font, 12 px,
+    280 px min-height) applies. The "Use in Generate" button is tagged
+    ``ams-lyrics-use-btn`` so it gets a small top margin instead of
+    sitting flush against the textbox.
+
+    Does NOT include the LoRA accordion — Qwen-7B has no LoRA picker and
+    the audio-mode LoRA semantics don't apply here.
+    """
+    c: dict[str, gr.components.Component] = {}
+    with gr.Row():
+        # --- FORM column (left) ---
+        with gr.Column(scale=12):
+            c["brief"] = gr.Textbox(
+                label="Brief",
+                lines=4,
+                placeholder=("Describe the song. Tone, mood, references, specific images, lines to avoid…"),
+            )
+            with gr.Row():
+                c["structure"] = gr.Textbox(
+                    label="Structure",
+                    value="intro, verse, chorus, verse, chorus, bridge, chorus, outro",
+                )
+                c["language"] = gr.Dropdown(
+                    choices=["en", "zh", "ja", "ko", "es", "fr", "de"],
+                    value="en",
+                    label="Language",
+                )
+            with gr.Row():
+                c["verse_lines"] = gr.Slider(
+                    minimum=2,
+                    maximum=10,
+                    value=6,
+                    step=1,
+                    label="Verse lines",
+                )
+                c["chorus_lines"] = gr.Slider(
+                    minimum=2,
+                    maximum=8,
+                    value=4,
+                    step=1,
+                    label="Chorus lines",
+                )
+                c["bridge_lines"] = gr.Slider(
+                    minimum=1,
+                    maximum=6,
+                    value=2,
+                    step=1,
+                    label="Bridge lines",
+                )
+            c["tone"] = gr.Textbox(
+                label="Tone / mood",
+                placeholder="euphoric, hypnotic, transcendent, not cheesy",
+            )
+            c["rhyme"] = gr.Radio(
+                choices=["strict", "loose", "none"],
+                value="loose",
+                label="Rhyme",
+            )
+            with gr.Accordion(
+                "LM parameters",
+                open=False,
+                elem_classes=["ams-lm-accordion"],
+            ):
+                c["temperature"] = gr.Slider(
+                    minimum=0.0,
+                    maximum=2.0,
+                    value=0.85,
+                    step=0.05,
+                    label="Temperature",
+                )
+                c["top_p"] = gr.Slider(
+                    minimum=0.0,
+                    maximum=1.0,
+                    value=0.9,
+                    step=0.05,
+                    label="Top-p",
+                )
+                c["top_k"] = gr.Slider(
+                    minimum=0,
+                    maximum=200,
+                    value=40,
+                    step=1,
+                    label="Top-k",
+                )
+                c["max_new_tokens"] = gr.Slider(
+                    minimum=100,
+                    maximum=2000,
+                    value=600,
+                    step=50,
+                    label="Max new tokens",
+                )
+                c["seed"] = gr.Number(
+                    value=42,
+                    precision=0,
+                    label="Seed",
+                )
+            c["draft_btn"] = gr.Button(
+                "▶ Draft lyrics",
+                variant="primary",
+            )
+
+        # --- OUTPUT column (right) ---
+        with gr.Column(scale=10):
+            # NOTE: gr.Textbox in Gradio 6.14 doesn't accept ``show_copy_button``
+            # (the kwarg landed in a later 6.x). The Brutalist Mono textbox already
+            # exposes a native selection + browser copy via Cmd-A / Cmd-C; the
+            # copy-button affordance is therefore a no-op miss here.
+            c["lyrics_output"] = gr.Textbox(
+                label="Draft",
+                lines=14,
+                interactive=False,
+                elem_classes=["ams-lyrics-output"],
+            )
+            c["use_in_generate_btn"] = gr.Button(
+                "↑ Use these in Generate",
+                variant="primary",
+                elem_classes=["ams-lyrics-use-btn"],
+            )
+            c["meta_output"] = gr.JSON(
+                label="Metadata",
+                elem_classes=["ams-out", "ams-out-meta"],
+            )
+    return c