TIL : one AGENTS.md per subdirectory replaces repeated instructions

OpenCode (and most agents) reads CLAUDE.md or AGENTS.md files by walking up the directory tree from the active file. A file at src/Service/AGENTS.md is read on top of the root file when the agent works in that directory.

myproject/
├── AGENTS.md           ← project-wide conventions
├── src/
│   ├── Service/
│   │   └── AGENTS.md   ← Symfony service-specific conventions
│   └── ApiResource/
│       └── AGENTS.md   ← API Platform conventions
└── tests/
    └── AGENTS.md       ← PHPUnit test conventions

# src/Service/AGENTS.md

- Services are final by default
- Constructor injection only (no setter injection)
- No business logic in the constructor
- Public methods over 20 lines should be split

In practice, this avoids repeating each layer’s conventions in every prompt. The agent knows them as soon as it opens a file in that directory.