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, 8 insertions, 9 deletions

diff --git a/src/features/chat/ui.test.ts b/src/features/chat/ui.test.ts
index 9568813..bea5e77 100644
--- a/src/features/chat/ui.test.ts
+++ b/src/features/chat/ui.test.ts
@@ -373,8 +373,8 @@ describe("ChatView", () => {
     expect(screen.getByText("Hi")).toBeInTheDocument();
     expect(screen.getByText("Hello!")).toBeInTheDocument();
     expect(screen.getByText(/step 1/)).toBeInTheDocument();
-    expect(screen.getAllByText(/150 tok/)).toHaveLength(2);
-    expect(screen.getByText(/turn 1 · 150 tok \(100 in \/ 50 out\)/)).toBeInTheDocument();
+    expect(screen.getByText(/step 1 · 100 in \/ 50 out/)).toBeInTheDocument();
+    expect(screen.getByText(/turn 1 · 50 tok out · 100 in/)).toBeInTheDocument();
     expect(screen.getByText(/1\.2s/)).toBeInTheDocument();
   });
 
@@ -478,11 +478,11 @@ describe("ChatView", () => {
 
     // Both step-metrics and turn-metrics render
     expect(screen.getByText(/step 1/)).toBeInTheDocument();
-    expect(screen.getByText(/turn 1 · 100 tok/)).toBeInTheDocument();
+    expect(screen.getByText(/turn 1 · 20 tok out/)).toBeInTheDocument();
 
     // They are in separate elements (different rows)
-    const stepEl = screen.getByText(/step 1 · 100 tok/).closest("div");
-    const turnEl = screen.getByText(/turn 1 · 100 tok/).closest("div");
+    const stepEl = screen.getByText(/step 1 · 80 in \/ 20 out/).closest("div");
+    const turnEl = screen.getByText(/turn 1 · 20 tok out/).closest("div");
     expect(stepEl).not.toBe(turnEl);
   });
 
@@ -554,9 +554,9 @@ describe("ChatView", () => {
 
     // Step metrics rendered
     expect(screen.getByText(/step 1/)).toBeInTheDocument();
-    expect(screen.getAllByText(/15 tok/)).toHaveLength(2);
+    expect(screen.getByText(/step 1 · 10 in \/ 5 out/)).toBeInTheDocument();
     // Turn metrics rendered
-    expect(screen.getByText(/turn 1 · 15 tok \(10 in \/ 5 out\)/)).toBeInTheDocument();
+    expect(screen.getByText(/turn 1 · 5 tok out · 10 in/)).toBeInTheDocument();
     // No "null" or "undefined" in the DOM
     expect(screen.queryByText("null")).toBeNull();
     expect(screen.queryByText("undefined")).toBeNull();
@@ -602,8 +602,7 @@ describe("ChatView", () => {
     render(ChatView, { props: { chunks, turnMetrics } });
 
     // Step metrics should render
-    expect(screen.getByText(/step 1/)).toBeInTheDocument();
-    expect(screen.getByText(/150 tok/)).toBeInTheDocument();
+    expect(screen.getByText(/step 1 · 100 in \/ 50 out/)).toBeInTheDocument();
 
     // Turn total should NOT render (total is null — turn still in progress)
     expect(screen.queryByText(/^turn/)).toBeNull();