refactor: remove END_DEMO directive, auto-calculate from sequences

Remove END_DEMO keyword from timeline format. Demo duration now
calculated from max effect end time across all sequences. Sort
sequences by start time at compile time for deterministic ordering.

Changes:
- seq_compiler.py: Auto-calculate duration, sort sequences
- seq_compiler.cc: Remove END_DEMO parsing, sort by start time
- workspaces/test/timeline.seq: Remove END_DEMO directive
- Generated timeline.cc: Duration now 40.0f (was hardcoded)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

3 files changed, 27 insertions, 15 deletions

diff --git a/tools/seq_compiler.cc b/tools/seq_compiler.cc
index 5804031..462bdba 100644
--- a/tools/seq_compiler.cc
+++ b/tools/seq_compiler.cc
@@ -703,17 +703,7 @@ int main(int argc, char* argv[]) {
     std::string command;
     ss >> command;
 
-    if (command == "END_DEMO") {
-      std::string end_time;
-      if (!(ss >> end_time)) {
-        std::cerr << "Error line " << line_num
-                  << ": END_DEMO requires <time>\n";
-        return 1;
-      }
-      // Convert beat notation to time
-      demo_end_time = convert_to_time(end_time, bpm);
-      std::cout << "Demo end time: " << demo_end_time << "s\n";
-    } else if (command == "SEQUENCE") {
+    if (command == "SEQUENCE") {
       std::string start, priority;
       if (!(ss >> start >> priority)) {
         std::cerr << "Error line " << line_num
@@ -855,9 +845,23 @@ int main(int argc, char* argv[]) {
     }
   }
 
-  // Sort sequences by priority
+  // Calculate demo end time from maximum effect end time
+  float max_end_time = 0.0f;
+  for (const auto& seq : sequences) {
+    float seq_start = std::stof(seq.start_time);
+    for (const auto& eff : seq.effects) {
+      max_end_time = std::max(max_end_time, seq_start + std::stof(eff.end));
+    }
+  }
+  demo_end_time = std::to_string(max_end_time);
+  std::cout << "Demo end time (calculated): " << demo_end_time << "s\n";
+
+  // Sort sequences by start time (primary) then priority (secondary)
   std::sort(sequences.begin(), sequences.end(),
             [](const SequenceEntry& a, const SequenceEntry& b) {
+              float a_start = std::stof(a.start_time);
+              float b_start = std::stof(b.start_time);
+              if (a_start != b_start) return a_start < b_start;
               return std::stoi(a.priority) < std::stoi(b.priority);
             });
 
diff --git a/tools/seq_compiler.py b/tools/seq_compiler.py
index 3b8d126..70faf5b 100755
--- a/tools/seq_compiler.py
+++ b/tools/seq_compiler.py
@@ -446,6 +446,16 @@ def main():
         print("Error: No sequences found in input file", file=sys.stderr)
         sys.exit(1)
 
+    # Sort sequences by start time
+    sequences.sort(key=lambda s: s.start_time)
+
+    # Calculate demo duration from max effect end time (absolute time)
+    demo_duration = 0.0
+    for seq in sequences:
+        for effect in seq.effects:
+            # Effect times are relative to sequence start
+            demo_duration = max(demo_duration, seq.start_time + effect.end)
+
     # Process each sequence
     all_cpp = '''// Generated by seq_compiler.py
 // DO NOT EDIT
@@ -523,7 +533,7 @@ void RenderTimeline(WGPUCommandEncoder encoder, float time, int width, int heigh
 }
 
 float GetDemoDuration() {
-    return 40.0f;  // TODO: Calculate from sequences
+    return ''' + f'{demo_duration:.1f}f' + ''';
 }
 
 // Surface-based rendering with framebuffers
diff --git a/workspaces/test/timeline.seq b/workspaces/test/timeline.seq
index c4aba02..d4b0004 100644
--- a/workspaces/test/timeline.seq
+++ b/workspaces/test/timeline.seq
@@ -5,5 +5,3 @@
 SEQUENCE 0.0 0 "MainLoop"
 EFFECT + Flash source -> flash_out 0.0 16.0
 EFFECT + PeakMeter flash_out -> sink 0.0 16.0
-
-END_DEMO 32.0