feat: render build mode with looped heartbeat + red pulse

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

render.py

@@ -2,7 +2,8 @@ import base64
 import html
 from pathlib import Path
 
-from sting import chime_wav_bytes, sting_wav_bytes
+from sting import (chime_wav_bytes, flatline_wav_bytes, heartbeat_wav_bytes,
+                   sigh_wav_bytes, sting_wav_bytes)
 
 _PLACEHOLDER = "...nothing yet. tell me something true."
 
@@ -44,6 +45,9 @@ _IMG = {name: _load_image(name)
 
 _STING = base64.b64encode(sting_wav_bytes()).decode()
 _CHIMES = [base64.b64encode(chime_wav_bytes(i)).decode() for i in range(3)]
+_HEARTBEAT = base64.b64encode(heartbeat_wav_bytes()).decode()
+_SIGH = base64.b64encode(sigh_wav_bytes()).decode()
+_FLATLINE = base64.b64encode(flatline_wav_bytes()).decode()
 
 
 def _src(name: str) -> str:
@@ -79,7 +83,23 @@ def render_entity(affinity: int, mode: str = "idle", seq: int = 0) -> str:
 
     ghost = ""
     tint = ""
-    if mode == "rage":
+    if mode == "build":
+        # finale suspense bed: the child stays the materialized smudge while a
+        # heartbeat loops and a red pulse throbs. The HTML is byte-identical
+        # across recital steps, so Gradio doesn't remount it and the looped
+        # <audio> plays continuously (no JS) until the climax swaps the mode.
+        figure = (
+            '<div class="entity-figure">'
+            f'<img class="entity-img" src="{_src("base")}" style="{look}">'
+            "</div>"
+        )
+        flash = ""
+        tint = '<div class="entity-redpulse"></div>'
+        ghost = (
+            f'<audio autoplay loop src="data:audio/wav;base64,{_HEARTBEAT}">'
+            "</audio>"
+        )
+    elif mode == "rage":
         figure = (
             '<div class="entity-figure">'
             f'<img class="entity-img entity-rage" src="{_src("rage")}" '

tests/test_render.py

@@ -255,3 +255,16 @@ class TestReplyChime:
     def test_frenzy_keeps_only_the_sting(self):
         out = render_entity(12, "frenzy")
         assert out.count("<audio autoplay") == 1
+
+
+class TestBuildMode:
+    def test_build_loops_the_heartbeat_and_not_the_chime(self):
+        html = render_entity(50, "build", seq=4)
+        assert "<audio autoplay loop" in html          # heartbeat bed loops
+        assert "entity-redpulse" in html               # red suspense pulse
+        # the per-turn music-box chime must NOT play during a finale build
+        assert html.count("<audio") == 1
+
+    def test_build_keeps_the_child_visible(self):
+        html = render_entity(50, "build", seq=4)
+        assert "entity-img" in html