🎮 The Next Input — Issue #055

The AI That Patches Your Code

In partnership with

⚡ The Briefing — 60 sec

🛠️ The Playbook — Autonomous Code Review & Patch Factory (GPT-5 Codex + Agent-3)

Mission Stand up a guard-railed, end-to-end pipeline where GPT-5 Codex proposes patches, Replit Agent-3 executes structured refactors, and human reviewers ship with confidence.
Difficulty Advanced | Build time 2–3 hours (pilot)
ROI Teams save ≈ 12–18 h/week on maintenance, repetitive refactors, and “nits”—while improving defect catch-rate.

0) Why now

With GPT-5 Codex reasoning over repos and Agent-3 executing repeatable editor flows, we can reliably automate the 80% of changes that are boring but error-prone: log hardening, null checks, unsafe API migrations, dependency bumps, and test scaffolding. Success = automation does the grind, humans handle design.

1) Reference Architecture

Layer

Tooling

Purpose

Trigger

GitHub Actions / Cron

Nightly or on-PR label auto-review

Static Checks

Semgrep / CodeQL / SonarQube

Produce concrete findings w/ locations

Planner (LLM)

GPT-5 Codex

Turn findings → stepwise patch plan per file

Executor

Replit Agent-3

Apply edits via reproducible “flows” (safe transforms)

Tests

Pytest/Jest/Vitest + Coverage

Run focused suites; capture failures

Gate

PR bot + Policy Rules

Require ✅ on tests + style + risk score

Human Checkpoint

CODEOWNERS

Final sign-off on medium/high-risk diffs

2) End-to-End Workflow

  1. Trigger:

    • Label a PR auto-review or run nightly on main.

  2. Harvest Signals:

    • Run Semgrep/CodeQL; export findings JSON (rule_id, path, line, message).

  3. Plan (GPT-5 Codex):

    • Prompt converts findings → Patch Plan with scoped edits: file, region, rationale, tests to add/modify.

  4. Execute (Agent-3):

    • For each step, Agent-3 runs an editor flow (structured commands): insert guard, rename API call, add unit test skeleton, update import.

  5. Test & Lint:

    • Run impacted tests; compute diff coverage; auto-fix lint/format.

  6. Risk Score & PR:

    • Score = change size + file criticality + test pass + rule severity.

    • If Score ≤ threshold → open PR with checklist & artifacts; else mark Needs Human with a summary.

  7. Human Review (required):

    • CODEOWNERS must approve; bot blocks merge on failing checks.

  8. Learn:

    • If reviewer edits, feed delta back into a small “patterns” file to improve future plans.

3) Prompts (drop-in)

A) Planner Prompt — GPT-5 Codex

SYSTEM: You are a senior software engineer generating SAFE patch plans.
INPUTS:
- Findings (JSON array): [{rule_id, path, start_line, end_line, message, severity}]
- Code excerpts (for each finding, +/- 30 lines)
- Repo guidelines: language, style, test framework, logging policy

TASK:
For each finding, propose a MINIMAL patch plan:
[
  {
    "path": "src/api/user.ts",
    "intent": "Add null guard on user.id before logging",
    "edits": [
      {"type":"insert_before","line":42,"code":"if (!user?.id) { return next(new BadRequest('missing id')); }"}
    ],
    "tests": [
      {"path":"tests/api/user.spec.ts","intent":"Add case for missing id -> 400"}
    ],
    "risk": "low",
    "rationale": "Semgrep rule X123 (PII logging) fired at L45; guard prevents unsafe log."
  }
]
RULES:
- No wide refactors; prefer surgical edits.
- Always propose at least one test change when logic shifts.
- Never change public API signatures without 'high' risk tag.

B) Executor Prompt — Replit Agent-3

SYSTEM: You are Agent-3 applying a structured plan. 
For each plan.edits[]:
- open(path) 
- apply exact change at indicated lines 
- run formatter ("npm run fmt" or "black")
- if tests specified, scaffold file if missing with minimal passing stub.

On failure: revert file and emit "needs_human" with reason.

C) PR Body Template

## Auto Patch Summary
- Findings addressed: {n}
- Risk score: {score} (low/med/high)
- Tests: {added}/{modified}; Coverage Δ: {delta}%
- Rules: {rule_ids}

### Reviewer Checklist
- [ ] Logic change verified
- [ ] Tests sufficiently cover fix
- [ ] Naming & style conform

4) Guardrails & Policy

  • Scope Control: deny edits outside src/ unless rule explicitly targets config/migrations.

  • Data Safety: block any addition of secrets/PII to logs; enforce logger.safe() wrapper.

  • Risk Thresholds:

    • Low: auto-PR.

    • Medium: PR + second reviewer.

    • High: require team lead + run full test matrix.

  • Kill-Switch: label no-bots on a PR or path to skip agents entirely.

5) Pilot: 90-Minute Rollout

  1. Pick one repo + 3 Semgrep rules (e.g., PII logging, insecure random, missing awaits).

  2. Wire GitHub Action → harvest findings JSON → call Planner (GPT-5 Codex) → Agent-3 execution on a branch.

  3. Run impacted tests; open first PR; capture baseline metrics (review time, diff size).

  4. Iterate thresholds based on reviewer feedback; add 1–2 rules per week.

6) Metrics that Matter

  • MTTR for “nit” fixes (hours → minutes).

  • % Findings auto-remediated (target > 50% of low-risk rules).

  • Diff coverage (not just repo-wide).

  • Rework rate (how often humans rewrite bot patches).

  • Lead time to merge for bot PRs vs human-only PRs.

Pro tip: Start with harmless refactors (format, dead code, null guards). Earn trust, then expand to migrations and security hardening.

🎯 The Arsenal — Tools & Prompts

Asset

What it does

Link

Semgrep

Fast static analysis with CI JSON output

https://semgrep.dev

CodeQL

Vulnerability queries at scale

https://codeql.github.com

Replit Agent-3

Autonomous editor-flow executor

https://blog.replit.com/introducing-agent-3-our-most-autonomous-agent-yet

GitHub Actions

Wire triggers & artifacts

https://github.com/features/actions

Prompt · “Patch Plan → PR”

Convert plan to reviewer-friendly PR text

Summarise the patch plan into a PR body with: files changed, rationale per finding, risk score, tests added, and a reviewer checklist.

💡 Free Office Hours

Need help piloting a patch factory or tuning guardrails?
Book a free 15-minute Office Hours slot—no sales pitch, just workflows solved.

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🕹️ Game Over

Automate one low-risk refactor tonight—tomorrow’s PR queue will breathe.
Share your win; you could headline Issue #056.

Aaron
Automating the boring. Amplifying the brilliant.

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