feat: tosc sections page for song build

Add SECTIONS (page 4): 8 slot launch+save buttons, PREV/NEXT nav,
/scene/state receive on the GROUP so sections.lua colors slots
(green=current, blue=filled, dark=empty). Update pager to 4 pages,
add 4 new tests (26 pass), rebuild dist/av-live-control.tosc.

touchosc/gen/layout.py

@@ -317,6 +317,62 @@ def seq_page():
     return page
 
 
+# ---------------------------------------------------------------------------
+# Page 4 — SECTIONS
+# ---------------------------------------------------------------------------
+
+def sections_page():
+    """Page 4: 8 section slots (launch + save), prev/next nav, SC scene feedback.
+
+    The GROUP carries sections.lua and a /scene/state receive message so that
+    onReceiveOSC fires on the GROUP and can color the slot buttons.
+    """
+    page = s.node(
+        "GROUP",
+        [
+            s.prop("name", "SECTIONS", "s"),
+            s.frame(0, 0, *CANVAS),
+            s.script(_lua("sections.lua")),
+        ],
+        messages=[
+            s.osc("/scene/state", [s.val()], send=0, receive=1, feedback=1),
+        ],
+    )
+    ch = page.find("children")
+
+    ch.append(label("SECTIONS", 10, 8, 200, 30))
+
+    gx = 10
+    bw = 138
+    gap = 10
+    step = bw + gap          # 148 px per column
+
+    launch_y, launch_h = 46, 140
+    save_y, save_h = 196, 60
+
+    for i in range(8):
+        x = gx + i * step
+        # Launch button: name=slot{i} so sections.lua can findByName("slot"..i)
+        ch.append(s.node(
+            "BUTTON",
+            [s.prop("name", f"slot{i}", "s"), s.frame(x, launch_y, bw, launch_h)],
+            messages=[s.osc("/scene/launch", [s.consti(i)])],
+        ))
+        # Save button
+        ch.append(s.node(
+            "BUTTON",
+            [s.prop("name", f"S{i + 1}", "s"), s.frame(x, save_y, bw, save_h)],
+            messages=[s.osc("/scene/save", [s.consti(i)])],
+        ))
+
+    # Nav buttons
+    nav_y, nav_h = 272, 80
+    ch.append(button("< PREV", "/scene/prev", 10, nav_y, 200, nav_h, args=[s.vali()]))
+    ch.append(button("NEXT >", "/scene/next", 220, nav_y, 200, nav_h, args=[s.vali()]))
+
+    return page
+
+
 # ---------------------------------------------------------------------------
 # Pager + root
 # ---------------------------------------------------------------------------
@@ -335,6 +391,6 @@ def build():
     root = s.node(
         "GROUP",
         [s.prop("name", "av-live-control", "s"), s.frame(0, 0, *CANVAS)],
-        children=[pager([live_page(), fx_page(), seq_page()])],
+        children=[pager([live_page(), fx_page(), seq_page(), sections_page()])],
     )
     return root

touchosc/gen/lua/sections.lua

@@ -0,0 +1,23 @@
+-- SECTIONS GROUP: color the 8 launch slot buttons from /scene/state.
+-- API verified on GrosMac at fidelity gate.
+-- /scene/state <cur:int> <fill0:int> ... <fill7:int>
+-- cur=-1 means no active section; fillN=1 means slot N is saved.
+function onReceiveOSC(message, connections)
+  local path = message[1]
+  if path ~= "/scene/state" then return end
+  local args = message[2]
+  local cur = math.floor((args[1] and tonumber(args[1].value)) or -1)
+  for i = 0, 7 do
+    local fill = math.floor((args[i + 2] and tonumber(args[i + 2].value)) or 0)
+    local slot = self:findByName("slot" .. i, true)
+    if slot then
+      if i == cur then
+        slot.color = Color(0.27, 0.8, 0.4, 1)        -- current (green)
+      elseif fill == 1 then
+        slot.color = Color(0.2, 0.4, 0.8, 1)          -- filled (blue)
+      else
+        slot.color = Color(0.15, 0.15, 0.15, 1)       -- empty (dark)
+      end
+    end
+  end
+end

touchosc/tests/test_layout.py

@@ -23,7 +23,7 @@ def _addr_list(el):
 # Root / pager
 # ---------------------------------------------------------------------------
 
-def test_root_has_pager_with_three_pages(tmp_path):
+def test_root_has_pager_with_four_pages(tmp_path):
     root = layout.build()
     out = tmp_path / "full.tosc"
     schema.write_tosc(root, str(out))
@@ -31,7 +31,7 @@ def test_root_has_pager_with_three_pages(tmp_path):
     pager = parsed.find(".//node[@type='PAGER']")
     assert pager is not None, "PAGER node not found"
     pages = pager.findall("children/node[@type='GROUP']")
-    assert len(pages) == 3, f"expected 3 pages, got {len(pages)}"
+    assert len(pages) == 4, f"expected 4 pages, got {len(pages)}"
 
 
 def test_sixteen_patterns():
@@ -322,3 +322,72 @@ def test_live_page_pad_groups_carry_armed_receive():
             f"pad GROUP '{grp_name}' must have exactly 1 /armed/* receive msg "
             f"on the GROUP itself, got {len(armed_msgs)}"
         )
+
+
+# ---------------------------------------------------------------------------
+# Page 4 — SECTIONS
+# ---------------------------------------------------------------------------
+
+def test_sections_page_launch_buttons():
+    """SECTIONS page: 8 /scene/launch messages with CONSTANT/INTEGER args 0..7."""
+    page = layout.sections_page()
+    launch_args = []
+    for osc_el in page.findall(".//messages/osc"):
+        path_val = osc_el.find("path/partial/value")
+        if path_val is not None and path_val.text == "/scene/launch":
+            for part in osc_el.findall("arguments/partial"):
+                typ = part.find("type")
+                conv = part.find("conversion")
+                val = part.find("value")
+                if typ is not None and conv is not None and val is not None:
+                    launch_args.append((typ.text, conv.text, val.text))
+    assert len(launch_args) == 8, f"expected 8 /scene/launch arg partials, got {len(launch_args)}"
+    for typ, conv, _ in launch_args:
+        assert typ == "CONSTANT", f"launch arg type must be CONSTANT, got {typ}"
+        assert conv == "INTEGER", f"launch arg conversion must be INTEGER, got {conv}"
+    vals = {v for _, _, v in launch_args}
+    assert vals == {"0", "1", "2", "3", "4", "5", "6", "7"}, (
+        f"expected launch values 0..7, got {vals}"
+    )
+
+
+def test_sections_page_save_buttons():
+    """SECTIONS page: 8 /scene/save messages with CONSTANT/INTEGER args 0..7."""
+    page = layout.sections_page()
+    save_args = []
+    for osc_el in page.findall(".//messages/osc"):
+        path_val = osc_el.find("path/partial/value")
+        if path_val is not None and path_val.text == "/scene/save":
+            for part in osc_el.findall("arguments/partial"):
+                typ = part.find("type")
+                conv = part.find("conversion")
+                val = part.find("value")
+                if typ is not None and conv is not None and val is not None:
+                    save_args.append((typ.text, conv.text, val.text))
+    assert len(save_args) == 8, f"expected 8 /scene/save arg partials, got {len(save_args)}"
+    for typ, conv, _ in save_args:
+        assert typ == "CONSTANT", f"save arg type must be CONSTANT, got {typ}"
+        assert conv == "INTEGER", f"save arg conversion must be INTEGER, got {conv}"
+
+
+def test_sections_page_nav_buttons():
+    """SECTIONS page: /scene/prev and /scene/next present."""
+    page = layout.sections_page()
+    addrs = _addrs(page)
+    assert "/scene/prev" in addrs, "/scene/prev not found on SECTIONS page"
+    assert "/scene/next" in addrs, "/scene/next not found on SECTIONS page"
+
+
+def test_sections_page_state_receive_on_group():
+    """SECTIONS GROUP itself must carry /scene/state receive so sections.lua fires."""
+    page = layout.sections_page()
+    # Direct messages/osc on the top-level GROUP (not descendants)
+    state_msgs = [
+        osc_el for osc_el in page.findall("messages/osc")
+        if osc_el.get("receive") == "1"
+        and osc_el.find("path/partial/value") is not None
+        and osc_el.find("path/partial/value").text == "/scene/state"
+    ]
+    assert len(state_msgs) == 1, (
+        f"SECTIONS GROUP must have exactly 1 /scene/state receive msg, got {len(state_msgs)}"
+    )