fix(metrics): show turn/step metrics for compacted conversations

Compacted conversations start with a system summary (role: "system")
instead of a user message (role: "user"). The interleaveTurnMetrics
function only detected segments by role === "user", so compacted
conversations got zero segments and no metrics were emitted.

Fix: when no user messages are found but metrics entries exist, treat
the entire transcript as one segment. This places turn-metrics at the
end and anchors step-metrics to any tool-batch groups by stepId.

686 tests green.

1 files changed, 9 insertions, 1 deletions

diff --git a/src/core/metrics/place.ts b/src/core/metrics/place.ts
index 47d3c5f..0048fa0 100644
--- a/src/core/metrics/place.ts
+++ b/src/core/metrics/place.ts
@@ -64,7 +64,15 @@ export function interleaveTurnMetrics(
 		}
 	}
 
-	const T = segmentStarts.length;
+	let T = segmentStarts.length;
+
+	// No user messages — e.g. a compacted conversation whose history starts
+	// with a system summary. Treat the entire transcript as one segment so
+	// turn/step metrics can still be placed.
+	if (T === 0 && entries.length > 0) {
+		segmentStarts.push(0);
+		T = 1;
+	}
 
 	if (T === 0) {
 		return groups.map((g) => ({ kind: "group" as const, group: g }));