feat(app): update token counts and context fill after every step

- Set context tokens per-step in recordStepUsage instead of waiting
  for turn completion; each step re-sends the full conversation so
  the reported usage monotonically increases
- Add UsageUpdatedEvent to trigger a TUI re-render after each step
  so the status bar reflects updated tokens, cost, and context %
  even during gaps between streaming chunks
- Update test to expect per-step context token updates

internal/app/app.go

@@ -923,7 +923,7 @@ func (a *App) subscribeSDKEvents(sendFn func(tea.Msg), stepUsageSeen *atomic.Boo
 		case kit.SteerConsumedEvent:
 			sendFn(SteerConsumedEvent{})
 		case kit.StepUsageEvent:
-			a.recordStepUsage(ev, stepUsageSeen)
+			a.recordStepUsage(ev, stepUsageSeen, sendFn)
 		case kit.PasswordPromptEvent:
 			// Convert SDK PasswordPromptEvent to app PasswordPromptEvent
 			// The TUI will handle this and send the response back
@@ -1241,7 +1241,16 @@ func (a *App) PrintBlockFromExtension(opts extensions.PrintBlockOpts) {
 // recordStepUsage applies token/cost usage reported for a completed step.
 // Step usage events arrive even when a turn is later cancelled, so this keeps
 // the usage widget accurate on all stop paths.
-func (a *App) recordStepUsage(ev kit.StepUsageEvent, stepUsageSeen *atomic.Bool) {
+//
+// Both session totals (cost, token counts) and the context window fill level
+// are updated here so the status bar reflects progress after every LLM call,
+// not just at the end of the full turn. Context fill monotonically increases
+// across steps because each step re-sends the entire conversation plus any
+// new tool results, so the numbers only go up.
+//
+// sendFn is called with a UsageUpdatedEvent to trigger a TUI re-render so
+// the updated values are visible immediately.
+func (a *App) recordStepUsage(ev kit.StepUsageEvent, stepUsageSeen *atomic.Bool, sendFn func(tea.Msg)) {
 	hasUsage := ev.InputTokens > 0 || ev.OutputTokens > 0 || ev.CacheReadTokens > 0 || ev.CacheWriteTokens > 0
 	if a.opts.Debug {
 		log.Printf("[DEBUG] recordStepUsage: hasUsage=%v input=%d output=%d cacheRead=%d cacheWrite=%d",
@@ -1262,11 +1271,21 @@ func (a *App) recordStepUsage(ev kit.StepUsageEvent, stepUsageSeen *atomic.Bool)
 		int(ev.CacheReadTokens),
 		int(ev.CacheWriteTokens),
 	)
-	// NOTE: We do NOT call SetContextTokens here. Context fill is set once
-	// at turn completion via updateUsageFromTurnResult, which sums all token
-	// categories (Input + CacheRead + CacheCreate + Output) from FinalUsage.
-	// Per-step context tokens would cause the display to jump around during
-	// multi-step tool calls.
+	// Update context window fill from this step's usage. Each step sends
+	// the full conversation to the LLM, so the reported token counts
+	// represent the actual context utilization at that point.
+	contextFill := int(ev.InputTokens) + int(ev.CacheReadTokens) + int(ev.CacheWriteTokens) + int(ev.OutputTokens)
+	if contextFill > 0 {
+		if a.opts.Debug {
+			log.Printf("[DEBUG] recordStepUsage: SetContextTokens=%d (Input=%d + CacheRead=%d + CacheWrite=%d + Output=%d)",
+				contextFill, ev.InputTokens, ev.CacheReadTokens, ev.CacheWriteTokens, ev.OutputTokens)
+		}
+		a.opts.UsageTracker.SetContextTokens(contextFill)
+	}
+	// Notify the TUI so it re-renders the status bar with updated values.
+	if sendFn != nil {
+		sendFn(UsageUpdatedEvent{})
+	}
 }
 
 // updateUsageFromTurnResult records token usage from an SDK TurnResult into the

internal/app/app_test.go

@@ -534,9 +534,9 @@ func TestQueueLength_reflects(t *testing.T) {
 }
 
 // TestRecordStepUsage_updatesTracker verifies that per-step usage updates are
-// recorded immediately for cost tracking. Context tokens are NOT updated here
-// (only via updateUsageFromTurnResult) to avoid display jumps during multi-step
-// tool calls.
+// recorded immediately for cost tracking. Context tokens are also updated so
+// the status bar reflects context fill after every LLM call in a multi-step
+// turn, not just at the end.
 func TestRecordStepUsage_updatesTracker(t *testing.T) {
 	usage := &usageUpdaterStub{}
 	app := New(Options{UsageTracker: usage}, nil)
@@ -547,7 +547,7 @@ func TestRecordStepUsage_updatesTracker(t *testing.T) {
 		OutputTokens:     45,
 		CacheReadTokens:  5,
 		CacheWriteTokens: 2,
-	}, nil)
+	}, nil, nil)
 
 	usage.mu.Lock()
 	defer usage.mu.Unlock()
@@ -559,9 +559,13 @@ func TestRecordStepUsage_updatesTracker(t *testing.T) {
 		t.Fatalf("unexpected usage update payload: in=%d out=%d cache_read=%d cache_write=%d",
 			usage.lastUpdateInput, usage.lastUpdateOutput, usage.lastUpdateCacheRead, usage.lastUpdateCacheWrite)
 	}
-	// Context tokens should NOT be updated by recordStepUsage (only by updateUsageFromTurnResult)
-	if usage.contextCalls != 0 {
-		t.Fatalf("expected 0 context token updates from recordStepUsage, got %d", usage.contextCalls)
+	// Context tokens should now be updated per-step (Input + CacheRead + CacheWrite + Output).
+	if usage.contextCalls != 1 {
+		t.Fatalf("expected 1 context token update from recordStepUsage, got %d", usage.contextCalls)
+	}
+	expectedContext := 120 + 45 + 5 + 2
+	if usage.lastContextTokens != expectedContext {
+		t.Fatalf("expected context tokens %d, got %d", expectedContext, usage.lastContextTokens)
 	}
 }
 

internal/app/events.go

@@ -210,6 +210,12 @@ type ModelChangedEvent struct {
 	ModelName string
 }
 
+// UsageUpdatedEvent is sent after each completed LLM step to notify the TUI
+// that token counts and costs have changed. The UsageTracker is updated
+// in-place before this event is sent; the TUI just needs to re-render to
+// reflect the new values in the status bar.
+type UsageUpdatedEvent struct{}
+
 // WidgetUpdateEvent is sent when an extension adds, updates, or removes a
 // widget via ctx.SetWidget or ctx.RemoveWidget. The TUI re-reads widget state
 // from its WidgetProvider on the next render cycle.

internal/ui/model.go

@@ -2076,6 +2076,12 @@ func (m *AppModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		m.providerName = msg.ProviderName
 		m.modelName = msg.ModelName
 
+	case app.UsageUpdatedEvent:
+		// Token usage was updated after a completed LLM step. No state
+		// changes needed — the UsageTracker was already mutated in-place.
+		// Returning from Update() triggers View() which re-renders the
+		// status bar with the latest token counts, cost, and context %.
+
 	case app.WidgetUpdateEvent:
 		// Extension widget changed — recalculate height distribution so the
 		// stream region accounts for widget space. View() will read the