fix(turn-metrics): exact per-turn placement via turnId, decode-only TPS, step-level retention

Placement
- Chunks carry their producing turn: StoredChunk.turnId (backend [email protected]) for
  committed rows (persisted in the IDB cache; old cached rows are upgraded on
  sync) and the live event's turnId for provisional ones (the optimistic echo is
  tagged on turn-start).
- interleaveTurnMetrics attributes every group to its turn (turnId, else the
  turn owning its stepId) and puts the turn total after the turn's LAST visible
  group. No user-message counting: sending, streaming, steering, images, errored
  turns and chat-limit unloading can no longer shift metrics between turns — at
  any point during a turn, not just after it ends. A turn cut in half by the
  chat limit keeps its total under its visible tail.
- Legacy rows (no turnId) fall back to an order-preserving, count-guarded match
  that leaves a turn blank rather than show another turn's numbers.
- A turn that errors re-syncs metrics (the backend now persists them).

TPS
- Step TPS = outputTokens / decodeMs only (no genTotalMs fallback — it includes
  time-to-first-token). Turn TPS sums tokens and decode time over timed steps
  only. Tool execution is excluded by the backend.

Display
- Retention = this turn's first-step cache reads / previous turn's last-step
  prompt (step-level; turn sums made it pin at 100%).
- Turn row shows output tokens + input processed (with cached), instead of a
  misleading 'total tok' that summed every step's full prompt.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/features/chat/ui/ChatView.svelte b/src/features/chat/ui/ChatView.svelte
index 6805b20..182b3d6 100644
--- a/src/features/chat/ui/ChatView.svelte
+++ b/src/features/chat/ui/ChatView.svelte
@@ -254,8 +254,8 @@
             {sv.label} · {sv.tokensLabel}
             {#if sv.tps}
               · {sv.tps}{/if}
-            {#if sv.genTotal}
-              · {sv.genTotal}{/if}
+            {#if sv.ttft}
+              · {sv.ttft} to first token{/if}
           </div>
         </div>
       </div>
@@ -263,12 +263,12 @@
       {@const turnView = viewTurnMetrics(row.turn, row.turnNumber)}
       {@const lastCache = viewCacheRate(row.turn.usage)}
       {@const chatCache = viewCacheRate(row.cumulativeUsage)}
-      {@const retention = viewExpectedCache(row.turn.usage, row.prevTurnUsage)}
+      {@const retention = viewExpectedCache(row.turn.steps[0]?.usage, row.prevLastStepUsage)}
       <div class="chat chat-start">
         <div class="chat-bubble w-full max-w-5xl bg-transparent p-0">
           <div class="flex flex-col gap-1 text-xs">
             <div class="opacity-70">
-              {turnView.label} · {turnView.tokensLabel} ({turnView.breakdown})
+              {turnView.label} · {turnView.tokensLabel} · {turnView.breakdown}
               {#if turnView.tps}
                 · {turnView.tps}{/if}
               {#if turnView.duration}