fix(cloud): azure/edge silent zero-audio — bare <speak> envelopes, <mark>, and zero-audio-as-success

examples/edge-bare-envelope.rs

@@ -0,0 +1,34 @@
+//! Live regression check (not part of CI): Edge must synthesise audio for
+//! the bare `<speak>` envelope speech-dispatcher sends. Run with:
+//!   cargo run --no-default-features --features cloud --example edge-bare-envelope
+//! Exits non-zero when either variant produces no audio.
+
+use rust_tts_wrapper::factory::create_engine;
+
+fn main() {
+    let engine = create_engine("edge", "{}").expect("edge engine");
+
+    for text in [
+        "Plain text reference.",
+        "<speak>Repeat test number 3</speak>",
+        "<speak>With a mark</speak>",
+        "<speak>With <mark name=\"i1\"/> a mark</speak>",
+    ] {
+        let mut bytes = 0usize;
+        let mut words = 0usize;
+        engine
+            .speak(
+                text,
+                Some("en-GB-SoniaNeural"),
+                1.0,
+                1.0,
+                1.0,
+                Some(&mut |chunk: &[u8]| bytes += chunk.len()),
+                Some(&mut |_w, _s, _e, _o, _l| words += 1),
+            )
+            .unwrap_or_else(|e| panic!("{text}: speak failed: {e}"));
+        println!("{text:?}: {bytes} PCM bytes, {words} word boundaries");
+        assert!(bytes > 0, "{text}: no audio!");
+    }
+    println!("PASS");
+}