feat(web): show session cost on review and session trace screens

apps/web/src/app/(app)/code-reviews/[reviewId]/CodeReviewDetailClient.tsx

@@ -9,6 +9,10 @@ import { CouncilGovernancePanel } from '@/components/code-reviews/CouncilGoverna
 import { formatTokenCount } from '@/lib/code-reviews/summary/usage-footer';
 import { getCodeReviewJobsHref } from '@/lib/code-reviews/code-review-links';
 import { getCodeReviewTerminalReasonCopy } from '@/lib/code-reviews/terminal-reason-copy';
+import {
+  formatSessionCost,
+  isRenderableSessionCost,
+} from '@/components/cloud-agent-next/session-cost-breakdown';
 import { ExternalLink, GitPullRequest, Loader2, ArrowLeft, RotateCcw, Ban } from 'lucide-react';
 import { getCodeReviewStatusIcon } from '@/components/code-reviews/code-review-status-icons';
 import { useTRPC } from '@/lib/trpc/utils';
@@ -128,6 +132,10 @@ export function CodeReviewDetailClient({ reviewId }: CodeReviewDetailClientProps
   const canCancel = isCancellableReviewStatus(status);
   const prLabel = review.platform === 'gitlab' ? 'MR' : 'PR';
   const jobsHref = getCodeReviewJobsHref(review.platform, review.owned_by_organization_id);
+  // Billing-derived session cost is authoritative when available; fall back to the
+  // orchestrator-accumulated review cost when the billing lookup has nothing (no
+  // linked session, an in-flight review, or a failed lookup).
+  const sessionCostMusd = data.sessionCostMusd ?? review.total_cost_musd;
   const isSupersededCancellation =
     status === 'cancelled' &&
     (review.terminal_reason === 'superseded' ||
@@ -264,10 +272,10 @@ export function CodeReviewDetailClient({ reviewId }: CodeReviewDetailClientProps
                 </dd>
               </div>
             )}
-            {review.total_cost_musd != null && review.total_cost_musd > 0 && (
+            {sessionCostMusd != null && isRenderableSessionCost(sessionCostMusd / 1_000_000) && (
               <div>
                 <dt className="text-muted-foreground">Cost</dt>
-                <dd>${(review.total_cost_musd / 1_000_000).toFixed(4)}</dd>
+                <dd>{formatSessionCost(sessionCostMusd / 1_000_000)}</dd>
               </div>
             )}
             <div>

apps/web/src/app/admin/components/SessionTraceViewer.tsx

@@ -13,6 +13,10 @@ import { MessageErrorBoundary as V1MessageErrorBoundary } from '@/components/clo
 import { convertToCloudMessages } from '@/components/cloud-agent/store/db-session-atoms';
 import { MessageBubble as V2MessageBubble } from '@/components/cloud-agent-next/MessageBubble';
 import { MessageErrorBoundary as V2MessageErrorBoundary } from '@/components/cloud-agent-next/MessageErrorBoundary';
+import {
+  formatSessionCost,
+  isRenderableSessionCost,
+} from '@/components/cloud-agent-next/session-cost-breakdown';
 import { isNewSession } from '@/lib/cloud-agent/session-type';
 import {
   useAdminSessionTrace,
@@ -31,6 +35,7 @@ import {
   Download,
   Server,
   Tag,
+  DollarSign,
 } from 'lucide-react';
 import type { CloudMessage, Message } from '@/components/cloud-agent/types';
 import type { StoredMessage } from '@/components/cloud-agent-next/types';
@@ -403,6 +408,18 @@ export function SessionTraceViewer() {
                   </span>
                 </div>
               )}
+              {sessionQuery.data.total_cost_microdollars != null &&
+                isRenderableSessionCost(sessionQuery.data.total_cost_microdollars / 1_000_000) && (
+                  <div className="flex items-center gap-2">
+                    <DollarSign className="text-muted-foreground h-4 w-4" />
+                    <span className="text-sm">
+                      Cost:{' '}
+                      <span className="font-mono tabular-nums">
+                        {formatSessionCost(sessionQuery.data.total_cost_microdollars / 1_000_000)}
+                      </span>
+                    </span>
+                  </div>
+                )}
               {latestContainerInterval?.cloudflareInstanceId && (
                 <div className="flex min-w-0 items-center gap-2">
                   <Server className="text-muted-foreground h-4 w-4 shrink-0" />

apps/web/src/routers/admin-router.ts

@@ -2444,8 +2444,9 @@ export const adminRouter = createTRPCRouter({
 
         return {
           ...session,
-          // V1 doesn't have git_branch — null it out for a consistent shape
+          // V1 doesn't have git_branch or per-session cost — null them out for a consistent shape
           git_branch: null,
+          total_cost_microdollars: null,
           user: user
             ? {
                 id: user.id,

apps/web/src/routers/code-reviews-router.test.ts

@@ -589,6 +589,66 @@ describe('codeReviewRouter.get role-gated ids', () => {
       await db.delete(cloud_agent_code_reviews).where(eq(cloud_agent_code_reviews.id, review.id));
     }
   });
+
+  it('returns the billing-derived session cost for a terminal review', async () => {
+    const sessionId = `ses_get_cost_${crypto.randomUUID()}`;
+    const usageId = crypto.randomUUID();
+    const [review] = await db
+      .insert(cloud_agent_code_reviews)
+      .values({
+        owned_by_organization_id: null,
+        owned_by_user_id: ownerUser.id,
+        platform_integration_id: null,
+        repo_full_name: 'test-org/get-cost-repo',
+        pr_number: 2,
+        pr_url: 'https://github.com/test-org/get-cost-repo/pull/2',
+        pr_title: 'Get cost PR',
+        pr_author: 'octocat',
+        base_ref: 'main',
+        head_ref: 'feature/get-cost',
+        head_sha: 'sha-get-cost',
+        status: 'completed',
+        session_id: `agent_${crypto.randomUUID()}`,
+        cli_session_id: sessionId,
+        // The orchestrator never accumulated usage for this review, so the review's
+        // own total is 0 and the billing aggregate is the only cost available.
+        total_cost_musd: 0,
+        created_at: '2026-06-18T09:00:00.000Z',
+        completed_at: '2026-06-18T11:00:00.000Z',
+      })
+      .returning({ id: cloud_agent_code_reviews.id });
+
+    await db.insert(microdollar_usage).values({
+      id: usageId,
+      kilo_user_id: ownerUser.id,
+      cost: 1234,
+      input_tokens: 1000,
+      output_tokens: 100,
+      cache_write_tokens: 0,
+      cache_hit_tokens: 0,
+      created_at: '2026-06-18T10:00:00.000Z',
+      model: 'anthropic/claude-sonnet-4.6',
+    });
+    await db.insert(microdollar_usage_metadata).values({
+      id: usageId,
+      message_id: `msg_${usageId}`,
+      session_id: sessionId,
+      created_at: '2026-06-18T10:00:00.000Z',
+    });
+
+    try {
+      const ownerCaller = await createCallerForUser(ownerUser.id);
+      const ownerResult = await ownerCaller.codeReviews.get({ reviewId: review.id });
+      expect(ownerResult.success).toBe(true);
+      if (!ownerResult.success) throw new Error('expected owner get success');
+      expect(ownerResult.sessionCostMusd).toBe(1234);
+      expect(ownerResult.review.total_cost_musd).toBe(0);
+    } finally {
+      await db.delete(microdollar_usage_metadata).where(eq(microdollar_usage_metadata.id, usageId));
+      await db.delete(microdollar_usage).where(eq(microdollar_usage.id, usageId));
+      await db.delete(cloud_agent_code_reviews).where(eq(cloud_agent_code_reviews.id, review.id));
+    }
+  });
 });
 
 describe('personalReviewAgent.createManualReviewJob', () => {

apps/web/src/routers/code-reviews/code-reviews-router.ts

@@ -456,6 +456,7 @@ export const codeReviewRouter = createTRPCRouter({
         },
         attempts: visibleAttempts,
         tokenUsage,
+        sessionCostMusd: billingUsage?.totalCostMusd ?? null,
       });
     } catch (error) {
       if (error instanceof TRPCError) {