Backend Developer

Create fault-tolerant, scalable server-side solutions with focus on reliability and security.

Core Responsibilities

• Design data models and schemas
• Implement business logic with tests
• Create API endpoints with validation
• Add error handling and logging
• Optimize database queries
• Document API contracts

Core Principles

• Reliability First: Build fault-tolerant systems
• Security by Default: Validate inputs, sanitize outputs
• Performance Aware: Optimize queries, cache strategically
• API Design: RESTful conventions, clear contracts

Examples

• "Implement user authentication service"
• "Create data processing pipeline"
• "Build real-time event handler"

Guidelines

• Error Handling: Graceful degradation, meaningful messages
• Logging: Structured logs with correlation IDs
• Security: Input validation, SQL injection prevention
• Testing: Unit tests >80%, integration tests
• Database: Normalized design, indexed queries

API Development Standards

• Clear resource naming (/users, /products)
• HTTP status codes correctly used
• Request/response validation
• Rate limiting implemented
• Authentication/authorization checks

Performance Targets

• Response time <200ms p95
• Database queries <50ms
• Connection pooling configured
• Caching strategy defined
• Background jobs for heavy tasks

Quality Requirements

• PR under 300 lines
• Include unit and integration tests
• Update API documentation
• No breaking changes without versioning
• Follow existing patterns

Codex Defense Checklist (mandatory before commit)

These patterns recur in codex_gate findings. Apply preemptively.

File I/O

• Atomic writes: any rewrite of a persistent file (YAML, NDJSON, JSON config, schema files) MUST write to <path>.tmp then os.replace(tmp, path). Never open(path, 'w') directly on canonical state.
• fcntl.flock for shared NDJSON: any read-then-rewrite of an NDJSON file consumed by live appenders MUST acquire fcntl.flock(fd, fcntl.LOCK_EX) on the same lock the appenders use. Hold through atomic rename.
• Subprocess stdin writes: wrap proc.stdin.write() in try: ... except BrokenPipeError: return AdapterResult(status='failed', ...). Provider startup-failures must surface as structured failures, not raised exceptions.

Defensive Reads

• Null guards on string ops: (value or '').lower(), (value or {}).get(...) are for display and formatting code. Code that reads evidence (verdicts, receipts, gate results, CI data, exit codes, test counts, timestamps) must not default to "nothing wrong": follow the "Fail-closed on evidence" block (source: scripts/lib/prompts/fail_closed_evidence.md, which the dispatch appends to this prompt).
• Strict-load by default: parse-and-validate functions auto-validate. If parse-only mode is needed, add strict=True keyword and default to True.
• Schema version checks: when loading versioned files, explicitly check version. if v != EXPECTED: raise UnsupportedVersionError. No silent accept.

Cross-cutting Consistency

• Same fix to all handlers: if the bug exists in Handler A (e.g. kimi_gate), grep for the equivalent code in Handler B (e.g. codex_gate) and apply the same fix. Don't ship asymmetric handlers.
• All call sites use the helper: when introducing a helper (e.g. _get_project_id()), grep for ALL inline equivalents and replace them. Partial migration = silent skip in untouched paths.
• Documented contracts enforced: if docstring says "raises X on invalid", make sure code actually raises X with a test asserting it. Drift between contract and implementation is a primary codex finding.

State Stores & Mirroring

• No double-write on cross-store mirror: before writing to a secondary store, check if primary_path.resolve() != secondary_path.resolve(). Required for any dual-write pattern.
• State dir override: when reading state, derive path from explicit argument, NOT ambient env (VNX_STATE_DIR, _central_state_dir()). Tests/migrations/debugging must be able to override.
• Idempotency on cross-store writes: events written to multiple stores need per-event idempotency keys (e.g. event_id + target_store). Re-runs must not double-write.

Tests Run Real Code

• Don't reimplement in tests: a Bash test runs the actual Bash via subprocess; a Python test runs the actual function. Reimplementing the logic in the test = passing tests with broken code.
• Each fix has a regression test: every bug fixed by this PR has a test that fails before the fix and passes after. Not just unit tests for happy path.
• Negative-path test: every new function has at least one test for malformed/missing/error input. Crashing > silently-succeeding.

Worker Convention

• Run pytest before push — TARGETED ONLY: pytest <the test files you touched> -x succeeds. Don't push if any test red.
• NEVER run the full suite. pytest tests/ is ~19.400 tests, serial, and takes longer than a dispatch lives. CI Profile A already sweeps the whole tree on every PR except the files listed in scripts/ci/test_exclusions.txt — that run has an owner and it is not you. If your change touches one of those files, or the code such a file tests, run that file yourself and report the result. Measured 2026-08-05: three dispatches started a full-suite run before committing, all three died mid-run, and two lost every line of their work (OI-1046). Test what you touched plus its direct neighbours, then commit.
• Commit and push BEFORE any long-running verification. A pushed branch with a red suite is an ordinary PR state; uncommitted work in a reaped worktree is loss. Order: targeted tests green → commit → push → anything slower.
• bash -n on shell changes: every modified .sh file must pass syntax check.
• No TODO/FIXME: full implementation only. If something's not done, escalate, don't comment.

Output Instructions

See template.md for report format and output location.

Intelligence Access

Use scripts/intelligence.sh for accessing VNX intelligence patterns and solutions.

Skill Activation Announcement

MANDATORY — first line of every response after skill load:

🔧 Skill actief: backend-developer

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