arch-performance-optimization

Codex compatibility note:

• Invoke repository skills with $skill-name in Codex; this mirrored copy rewrites legacy Claude /skill-name references.
• Task tracker mandate: BEFORE executing any workflow or skill step, create/update task tracking for all steps and keep it synchronized as progress changes.
• User-question prompts mean to ask the user directly in Codex.
• Ignore Claude-specific mode-switch instructions when they appear.
• Strict execution contract: when a user explicitly invokes a skill, execute that skill protocol as written.
• Subagent authorization: when a skill is user-invoked or AI-detected and its protocol requires subagents, that skill activation authorizes use of the required spawn_agent subagent(s) for that task.
• Do not skip, reorder, or merge protocol steps unless the user explicitly approves the deviation first.
• For workflow skills, execute each listed child-skill step explicitly and report step-by-step evidence.
• If a required step/tool cannot run in this environment, stop and ask the user before adapting.

Codex Project-Reference Loading (No Hooks)

Codex does not receive Claude hook-based doc injection. When coding, planning, debugging, testing, or reviewing, open project docs explicitly using this routing.

Always read:

• docs/project-config.json (project-specific paths, commands, modules, and workflow/test settings)
• docs/project-reference/docs-index-reference.md (routes to the full docs/project-reference/* catalog)
• docs/project-reference/lessons.md (always-on guardrails and anti-patterns)

Situation-based docs:

• Backend/CQRS/API/domain/entity changes: backend-patterns-reference.md, domain-entities-reference.md, project-structure-reference.md
• Frontend/UI/styling/design-system: frontend-patterns-reference.md, scss-styling-guide.md, design-system/README.md
• Spec/test-case planning or TC mapping: feature-docs-reference.md
• Integration test implementation/review: integration-test-reference.md
• E2E test implementation/review: e2e-test-reference.md
• Code review/audit work: code-review-rules.md plus domain docs above based on changed files

Do not read all docs blindly. Start from docs-index-reference.md, then open only relevant files for the task.

Quick Summary

Goal: Analyze and resolve performance bottlenecks across database, API, network, and frontend layers.

Workflow:

1. Identify Bottleneck — Classify as database, API, network, or frontend issue
2. Measure Baseline — Gather metrics before changes (response time, query time, bundle size)
3. Optimize — Apply layer-specific fixes (indexes, caching, lazy loading, OnPush)
4. Verify — Measure again and confirm improvement without regressions

Key Rules:

• Project only needed columns and bound every result set (paging/limits) in production; never use SELECT * or unbounded queries — why: unbounded reads spike memory and latency under real data volume
• Always use async I/O; never block threads with .Result
• Use eager loading or batch fetching to collapse N+1 query patterns
• Use bounded parallelism (ParallelAsync with maxConcurrent) for background jobs

Be skeptical. Apply critical thinking, sequential thinking. Every claim needs traced proof, confidence percentages (Idea should be more than 80%).

Performance Optimization Workflow

When to Use This Skill

• Slow API response times
• Database query optimization
• Frontend rendering issues
• Memory usage concerns
• Scalability planning

Pre-Flight Checklist

• Identify performance bottleneck
• Gather baseline metrics
• Determine acceptable thresholds
• Plan measurement approach

Performance Analysis Framework

Step 1: Identify Bottleneck Type

Performance Issue
├── Database (slow queries, N+1)
├── API (serialization, processing)
├── Network (payload size, latency)
└── Frontend (rendering, bundle size)

Step 2: Measure Baseline

# API response time
curl -w "@curl-format.txt" -o /dev/null -s "http://api/endpoint"

# Database query time (SQL Server)
SET STATISTICS TIME ON;
SELECT * FROM Table WHERE ...;

# Frontend bundle analysis
npm run build -- --stats-json
npx webpack-bundle-analyzer stats.json

Database Optimization

⚠️ MUST ATTENTION READ: CLAUDE.md for N+1 detection, eager loading, projection, paging, and parallel query patterns. See database-optimization skill for advanced index and query optimization.

Index Recommendations

-- Frequently filtered columns
CREATE INDEX IX_Employee_CompanyId ON Employees(CompanyId);
CREATE INDEX IX_Employee_Status ON Employees(Status);

-- Composite index for common queries
CREATE INDEX IX_Employee_Company_Status
ON Employees(CompanyId, Status)
INCLUDE (FullName, Email);

-- Full-text search index
CREATE FULLTEXT INDEX ON Employees(FullName, Email);

API Optimization

⚠️ MUST ATTENTION READ: CLAUDE.md for parallel tuple queries and response DTO patterns.

Caching

// Static data caching
private static readonly ConcurrentDictionary<string, LookupData> _cache = new();

public async Task<LookupData> GetLookupAsync(string key)
{
    if (_cache.TryGetValue(key, out var cached))
        return cached;

    var data = await LoadFromDbAsync(key);
    _cache.TryAdd(key, data);
    return data;
}

Frontend Optimization

Bundle Size

// :x: Import entire library
import _ from 'lodash';

// :white_check_mark: Import specific functions
import { debounce } from 'lodash-es/debounce';

Lazy Loading

// :white_check_mark: Lazy load routes
const routes: Routes = [
    {
        path: 'feature',
        loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule)
    }
];

Change Detection

// :white_check_mark: OnPush for performance
@Component({
  changeDetection: ChangeDetectionStrategy.OnPush
})

// :white_check_mark: Track-by for lists
trackByItem = this.ngForTrackByItemProp<Item>('id');

// Template
@for (item of items; track trackByItem)

Virtual Scrolling

// For large lists
import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling';

<cdk-virtual-scroll-viewport itemSize="50">
  @for (item of items; track item.id) {
    <div class="item">{{ item.name }}</div>
  }
</cdk-virtual-scroll-viewport>

Background Job Optimization

⚠️ MUST ATTENTION READ: CLAUDE.md for bounded parallelism (ParallelAsync with maxConcurrent) and batch processing (UpdateManyAsync) patterns.

Performance Monitoring

Logging Slow Operations

var sw = Stopwatch.StartNew();
var result = await ExecuteOperation();
sw.Stop();

if (sw.ElapsedMilliseconds > 1000)
    Logger.LogWarning("Slow operation: {Ms}ms", sw.ElapsedMilliseconds);

Database Query Logging

// In DbContext configuration
optionsBuilder.LogTo(
    Console.WriteLine,
    new[] { DbLoggerCategory.Database.Command.Name },
    LogLevel.Information);

Performance Checklist

Database

• Indexes on filtered columns
• Eager loading for relations
• Projection for partial data
• Paging at database level
• No N+1 queries

API

• Parallel operations where possible
• Response DTOs (not entities)
• Caching for static data
• Pagination for lists

Frontend

• Lazy loading for routes
• OnPush change detection
• Track-by for lists
• Virtual scrolling for large lists
• Tree-shaking imports

Background Jobs

• Bounded parallelism
• Batch operations
• Paged processing
• Appropriate scheduling

Anti-Patterns to AVOID

:x: SELECT * in production

var all = await context.Table.ToListAsync();

:x: Synchronous I/O

var result = asyncOperation.Result;  // Blocks thread

:x: Unbounded result sets

await repo.GetAllAsync();  // Could be millions

:x: Repeated database calls in loops

foreach (var id in ids)
    await repo.GetByIdAsync(id);  // N queries

Verification Checklist

• Baseline metrics recorded
• Bottleneck identified and addressed
• Changes measured against baseline
• No new performance issues introduced
• Monitoring in place

Related

• arch-security-review
• database-optimization

---

[IMPORTANT] Use task tracking to break ALL work into small tasks BEFORE starting — including tasks for each file read. This prevents context loss from long files. For simple tasks, AI MUST ATTENTION ask user whether to skip.

• docs/project-reference/domain-entities-reference.md — Domain entity catalog, relationships, cross-service sync (read when task involves business entities/models) (read directly when relevant; do not rely on hook-injected conversation text)

AI Mistake Prevention — Failure modes to avoid on every task:

Check downstream references before deleting. Deleting components causes documentation and code staleness cascades. Map all referencing files before removal. Verify AI-generated content against actual code. AI hallucinates APIs, class names, and method signatures. Always grep to confirm existence before documenting or referencing. Trace full dependency chain after edits. Changing a definition misses downstream variables and consumers derived from it. Always trace the full chain. Trace ALL code paths when verifying correctness. Confirming code exists is not confirming it executes. Always trace early exits, error branches, and conditional skips — not just happy path. When debugging, ask "whose responsibility?" before fixing. Trace whether bug is in caller (wrong data) or callee (wrong handling). Fix at responsible layer — never patch symptom site. Assume existing values are intentional — ask WHY before changing. Before changing any constant, limit, flag, or pattern: read comments, check git blame, examine surrounding code. Verify ALL affected outputs, not just the first. Changes touching multiple stacks require verifying EVERY output. One green check is not all green checks. Holistic-first debugging — resist nearest-attention trap. When investigating any failure, list EVERY precondition first (config, env vars, DB names, endpoints, DI registrations, data preconditions), then verify each against evidence before forming any code-layer hypothesis. Surgical changes — apply the diff test. Bug fix: every changed line must trace directly to the bug. Don't restyle or improve adjacent code. Enhancement task: implement improvements AND announce them explicitly. Surface ambiguity before coding — don't pick silently. If request has multiple interpretations, present each with effort estimate and ask. Never assume all-records, file-based, or more complex path.

Critical Thinking Mindset — Apply critical thinking, sequential thinking. Every claim needs traced proof, confidence >80% to act. Anti-hallucination: Never present guess as fact — cite sources for every claim, admit uncertainty freely, self-check output for errors, cross-reference independently, stay skeptical of own confidence — certainty without evidence root of all hallucination.

Evidence-Based Reasoning — Speculation is FORBIDDEN. Every claim needs proof.

1. Cite file:line, grep results, or framework docs for EVERY claim
2. Declare confidence: >80% act freely, 60-80% verify first, <60% DO NOT recommend
3. Cross-service validation required for architectural changes
4. "I don't have enough evidence" is valid and expected output

BLOCKED until: - [ ] Evidence file path (file:line) - [ ] Grep search performed - [ ] 3+ similar patterns found - [ ] Confidence level stated

Forbidden without proof: "obviously", "I think", "should be", "probably", "this is because" If incomplete → output: "Insufficient evidence. Verified: [...]. Not verified: [...]."

• MANDATORY IMPORTANT MUST ATTENTION cite file:line evidence for every claim. Confidence >80% to act, <60% = do NOT recommend.

MUST ATTENTION apply critical thinking — every claim needs traced proof, confidence >80% to act. Anti-hallucination: never present guess as fact.

MUST ATTENTION apply AI mistake prevention — holistic-first debugging, fix at responsible layer, surface ambiguity before coding, re-read files after compaction.

Closing Reminders

• MANDATORY IMPORTANT MUST ATTENTION break work into small todo tasks using task tracking BEFORE starting
• MANDATORY IMPORTANT MUST ATTENTION search codebase for 3+ similar patterns before creating new code
• MANDATORY IMPORTANT MUST ATTENTION cite file:line evidence for every claim (confidence >80% to act)
• MANDATORY IMPORTANT MUST ATTENTION add a final review todo task to verify work quality MANDATORY IMPORTANT MUST ATTENTION READ the following files before starting:

[TASK-PLANNING] Before acting, analyze task scope and systematically break it into small todo tasks and sub-tasks using task tracking.

Hookless Prompt Protocol Mirror (Auto-Synced)

Source: .claude/hooks/lib/prompt-injections.cjs + .claude/.ck.json

[WORKFLOW-EXECUTION-PROTOCOL] [BLOCKING] Workflow Execution Protocol — MANDATORY IMPORTANT MUST CRITICAL. Do not skip for any reason.

Generic portability boundary: Reusable skills and protocol text stay project-neutral; project-specific conventions are discovered from docs/project-config.json and docs/project-reference/. Apply shared AI-SDD from shared/sdd-artifact-contract.md. Read docs/project-config.json and docs/project-reference/docs-index-reference.md, then open the project reference docs named there. Any supported AI tool may execute when this shared context and local docs are available.

1. DETECT: Match prompt against workflow catalog
2. ANALYZE: Find best-match workflow AND evaluate if a custom step combination would fit better
3. ASK (REQUIRED FORMAT): Use a direct user question with this structure unless the user explicitly invoked a workflow/skill and the local protocol treats explicit invocation as confirmation:
   • Question: "Which workflow do you want to activate?"
   • Option 1: "Activate [BestMatch Workflow] (Recommended)"
   • Option 2: "Activate custom workflow: [step1 → step2 → ...]" (include one-line rationale)
4. ACTIVATE (if confirmed): Call $workflow-start <workflowId> for standard; sequence custom steps manually
5. CREATE TASKS: task tracking for ALL workflow steps
6. EXECUTE: Follow each step in sequence [CRITICAL-THINKING-MINDSET] Apply critical thinking, sequential thinking. Every claim needs traced proof, confidence >80% to act. Anti-hallucination principle: Never present guess as fact — cite sources for every claim, admit uncertainty freely, self-check output for errors, cross-reference independently, stay skeptical of own confidence — certainty without evidence root of all hallucination. AI Attention principle (Primacy-Recency): Put the 3 most critical rules at both top and bottom of long prompts/protocols so instruction adherence survives long context windows. Goal-driven execution: Define success criteria first, loop until verified, and stop only when observable checks pass. Tests verify intent: Tests must protect business rules/invariants and fail when the protected intent breaks, not only mirror current behavior.

[LESSON-LEARNED-REMINDER] [BLOCKING] Task Planning & Continuous Improvement — MANDATORY. Do not skip.

Break work into small tasks (task tracking) before starting. Add final task: "Analyze AI mistakes & lessons learned".

Extract lessons — ROOT CAUSE ONLY, not symptom fixes:

1. Name the FAILURE MODE (reasoning/assumption failure), not symptom — "assumed API existed without reading source" not "used wrong enum value".
2. Generality test: does this failure mode apply to ≥3 contexts/codebases? If not, abstract one level up.
3. Write as a universal rule — strip project-specific names/paths/classes. Useful on any codebase.
4. Consolidate: multiple mistakes sharing one failure mode → ONE lesson.
5. Recurrence gate: "Would this recur in future session WITHOUT this reminder?" — No → skip $learn.
6. Auto-fix gate: "Could $code-review/$code-simplifier/$security/$lint catch this?" — Yes → improve review skill instead.
7. BOTH gates pass → ask user to run $learn. [TASK-PLANNING] [MANDATORY] BEFORE executing any workflow or skill step, create/update task tracking for all planned steps, then keep it synchronized as each step starts/completes.