perf: parallelize LLM call detail and errors queries (#2561)

## Summary
- Runs `llm_calls.findUnique` and `optimization_errors.findMany` in
parallel via `Promise.all`
- Both queries use `params.id` directly — no data dependency between
them
- Page load time reduced from sum to max of both queries

## Evidence
- Proof doc: `js/cf-webapp/proof/17-parallel-llm-call-detail.md`

## Test plan
- [ ] `bash
js/cf-webapp/proof/reproducers/17-parallel-llm-call-detail.sh` — 5/5
checks pass
- [ ] LLM call detail page renders correctly with error list

js/cf-webapp/proof/17-parallel-llm-call-detail.md

@@ -0,0 +1,37 @@
+# Proof 17: Parallelize LLM Call Detail + Errors Queries
+
+## What Changed
+In `src/app/observability/llm-call/[id]/page.tsx`, two sequential Prisma queries are now parallel:
+1. `llm_calls.findUnique` — fetches the LLM call record
+2. `optimization_errors.findMany` — fetches related errors
+
+Both use `params.id` and are independent, so they run in `Promise.all`.
+
+## Why
+The queries have no data dependency — both use the route param `id` directly. Running them sequentially means the page waits for the first query to complete before starting the second.
+
+**Before**: Total time = llmCall query + errors query
+**After**: Total time = max(llmCall query, errors query)
+
+## Evidence
+
+### Before (sequential)
+```typescript
+const llmCall = await prisma.llm_calls.findUnique({ where: { id: params.id } })
+// ...
+const relatedErrors = await prisma.optimization_errors.findMany({ where: { llm_call_id: params.id }, ... })
+```
+
+### After (parallel)
+```typescript
+const [llmCall, relatedErrors] = await Promise.all([
+  prisma.llm_calls.findUnique({ where: { id: params.id } }),
+  prisma.optimization_errors.findMany({ where: { llm_call_id: params.id }, orderBy: { created_at: "desc" } }),
+])
+```
+
+## How to Verify
+```bash
+cd js/cf-webapp
+bash proof/reproducers/17-parallel-llm-call-detail.sh
+```

js/cf-webapp/proof/reproducers/17-parallel-llm-call-detail.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# Proof reproducer for commit 17: parallelize LLM call detail queries
+set -euo pipefail
+
+PASS=0
+FAIL=0
+TOTAL=0
+
+check() {
+  local desc="$1"; shift
+  TOTAL=$((TOTAL + 1))
+  if "$@" >/dev/null 2>&1; then
+    echo "  PASS: $desc"
+    PASS=$((PASS + 1))
+  else
+    echo "  FAIL: $desc"
+    FAIL=$((FAIL + 1))
+  fi
+}
+
+check_not() {
+  local desc="$1"; shift
+  TOTAL=$((TOTAL + 1))
+  if "$@" >/dev/null 2>&1; then
+    echo "  FAIL: $desc"
+    FAIL=$((FAIL + 1))
+  else
+    echo "  PASS: $desc"
+    PASS=$((PASS + 1))
+  fi
+}
+
+LLM_PAGE="src/app/observability/llm-call/[id]/page.tsx"
+
+echo "=== Proof 17: parallelize LLM call detail queries ==="
+echo ""
+
+echo "--- Parallelization checks ---"
+check "Promise.all used" \
+  grep -q 'Promise.all' "$LLM_PAGE"
+
+check "llmCall and relatedErrors destructured from Promise.all" \
+  grep -q '\[llmCall, relatedErrors\].*await Promise.all' "$LLM_PAGE"
+
+check "llm_calls.findUnique in Promise.all" \
+  grep -q 'llm_calls.findUnique' "$LLM_PAGE"
+
+check "optimization_errors.findMany in Promise.all" \
+  grep -q 'optimization_errors.findMany' "$LLM_PAGE"
+
+echo ""
+echo "--- Sequential pattern removed ---"
+check_not "no standalone relatedErrors assignment after llmCall" \
+  grep -q 'const relatedErrors = await prisma' "$LLM_PAGE"
+
+echo ""
+echo "=== Results: $PASS/$TOTAL passed, $FAIL failed ==="
+[ "$FAIL" -eq 0 ] && echo "ALL CHECKS PASSED" || echo "SOME CHECKS FAILED"
+exit "$FAIL"

js/cf-webapp/src/app/observability/llm-call/[id]/page.tsx

@@ -31,21 +31,21 @@ export async function generateMetadata(props: LLMCallDetailPageProps): Promise<M
 
 export default async function LLMCallDetailPage(props: LLMCallDetailPageProps) {
   const params = await props.params;
-  // Fetch LLM call details
-  const llmCall = await prisma.llm_calls.findUnique({
-    where: { id: params.id },
-  })
+  // Fetch LLM call details and related errors in parallel
+  const [llmCall, relatedErrors] = await Promise.all([
+    prisma.llm_calls.findUnique({
+      where: { id: params.id },
+    }),
+    prisma.optimization_errors.findMany({
+      where: { llm_call_id: params.id },
+      orderBy: { created_at: "desc" },
+    }),
+  ])
 
   if (!llmCall) {
     notFound()
   }
 
-  // Fetch related errors
-  const relatedErrors = await prisma.optimization_errors.findMany({
-    where: { llm_call_id: params.id },
-    orderBy: { created_at: "desc" },
-  })
-
   return (
     <div className="container mx-auto px-4 py-8">
       {/* Header */}