obs(transcription): log initial_prompt presence at WhisperRsBackend boundary

crates/transcription/Cargo.toml

@@ -25,3 +25,6 @@ whisper-rs = { version = "0.16", default-features = false, features = ["vulkan"]
 # Direct whisper-rs backend (WhisperRsBackend): thread pool sizing + typed errors.
 num_cpus = "1"
 thiserror = "2"
+
+# Structured logging at backend boundaries (observability for initial_prompt flow).
+tracing = "0.1"

crates/transcription/src/whisper_rs_backend.rs

@@ -44,6 +44,12 @@ impl WhisperRsBackend {
         samples: &[f32],
         options: &TranscriptionOptions,
     ) -> Result<Vec<Segment>, WhisperBackendError> {
+        tracing::info!(
+            language = ?options.language,
+            has_initial_prompt = options.initial_prompt.as_deref().map(|p| !p.is_empty()).unwrap_or(false),
+            "WhisperRsBackend::transcribe_sync entering"
+        );
+
         let mut state = self
             .ctx
             .create_state()