feat(polish): add question guard, ABE routing, and flow trace

Harden polish so question drafts stay questions, add local density
routing with style-specific degrade, expand fun style packs, and add
end-to-end FlowTrace logging plus offline guard eval scripts.

OSGKeyboardShared/Utilities/UtteranceStreamChunker.swift

@@ -22,8 +22,20 @@ public enum UtteranceStreamChunker {
                 var chunkIndex = 0
 
                 func emit(upTo splitEnd: Int, isLast: Bool) {
-                    guard splitEnd > 0, splitEnd <= buffer.count else { return }
+                    guard splitEnd > 0, splitEnd <= buffer.count else {
+                        FlowTrace.warn(
+                            "pipeline.chunk.emitSkipped",
+                            "chunk=\(chunkIndex) splitEnd=\(splitEnd) buffered=\(buffer.count)"
+                        )
+                        return
+                    }
                     let chunkSamples = Array(buffer[..<splitEnd])
+                    FlowTrace.pipeline(
+                        "chunk.emit",
+                        "chunk=\(chunkIndex) samples=\(chunkSamples.count) "
+                            + "seconds=\(FlowTrace.seconds(samples: chunkSamples.count, sampleRate: config.sampleRate)) "
+                            + "rms=\(FlowTrace.rms(chunkSamples)) isLast=\(isLast ? 1 : 0)"
+                    )
                     continuation.yield(
                         UtteranceAudioChunk(index: chunkIndex, samples: chunkSamples, isLast: isLast)
                     )
@@ -36,9 +48,13 @@ public enum UtteranceStreamChunker {
                     }
                 }
 
+                var receivedSnapshots = 0
+                var receivedSamples = 0
                 for await snap in stream {
                     if Task.isCancelled { break }
                     guard !snap.samples.isEmpty else { continue }
+                    receivedSnapshots += 1
+                    receivedSamples += snap.samples.count
                     buffer.append(contentsOf: snap.samples)
 
                     while buffer.count >= config.maxChunkSamples(forChunkIndex: chunkIndex) {
@@ -51,10 +67,24 @@ public enum UtteranceStreamChunker {
                     }
                 }
 
+                FlowTrace.pipeline(
+                    "chunk.streamEnded",
+                    "snapshots=\(receivedSnapshots) samples=\(receivedSamples) "
+                        + "seconds=\(FlowTrace.seconds(samples: receivedSamples, sampleRate: config.sampleRate)) "
+                        + "chunksEmitted=\(chunkIndex) buffered=\(buffer.count) "
+                        + "cancelled=\(Task.isCancelled ? 1 : 0)"
+                )
+
                 if !buffer.isEmpty {
                     emit(upTo: buffer.count, isLast: true)
                 } else if chunkIndex == 0 {
-                    // Empty utterance — no chunks.
+                    // Empty utterance — no chunks. The recogniser is never
+                    // invoked, so an empty transcript here means the mic stream
+                    // itself was empty, not that recognition failed.
+                    FlowTrace.warn(
+                        "pipeline.chunk.emptyUtterance",
+                        "snapshots=\(receivedSnapshots) samples=0 chunksEmitted=0"
+                    )
                 } else {
                     // Stream ended exactly on a chunk boundary; prior emit holds
                     // all tail audio. Marker so FinalChunkRecovery paths run.