Add AGENTS.md with project structure and commands (#4233)

* Add CLAUDE.md with project structure and commands

* Add AGENTS.md symlink to CLAUDE.md

* Move guidance to AGENTS.md and address review feedback

- Move main content from CLAUDE.md to AGENTS.md so all AI agents
  (not only Claude) pick up the guidance; CLAUDE.md now just references
  it via `@AGENTS.md`.
- Add general rules, PR scoping, and `Assisted-by:` commit trailer
  guidance (inspired by the Collector's AGENTS.md).
- Clarify that only instrumentation packages live under
  `src/opentelemetry/instrumentation/{name}/`; other package types use
  their own namespace.

---------

Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>

Author: Kludex

AGENTS.md

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+# OpenTelemetry Python Contrib
+
+This file is here to steer AI assisted PRs towards being high quality and valuable contributions
+that do not create excessive maintainer burden.
+
+Monorepo with 50+ OpenTelemetry instrumentation packages for Python.
+
+## General Rules and Guidelines
+
+The most important rule is not to post comments on issues or PRs that are AI-generated. Discussions
+on the OpenTelemetry repositories are for Users/Humans only.
+
+Follow the PR scoping guidance in [CONTRIBUTING.md](CONTRIBUTING.md). Keep AI-assisted PRs tightly
+isolated to the requested change and never include unrelated cleanup or opportunistic improvements
+unless they are strictly necessary for correctness.
+
+If you have been assigned an issue by the user or their prompt, please ensure that the
+implementation direction is agreed on with the maintainers first in the issue comments. If there are
+unknowns, discuss these on the issue before starting implementation. Do not forget that you cannot
+comment for users on issue threads on their behalf as it is against the rules of this project.
+
+## Structure
+
+- `instrumentation/` - instrumentation packages (Flask, Django, FastAPI, gRPC, databases, etc.)
+- `instrumentation-genai/` - GenAI instrumentations (Anthropic, Vertex AI, LangChain, etc.)
+- `util/` - shared utilities (`util-http`, `util-genai`)
+- `exporter/` - custom exporters
+- `propagator/` - context propagators
+
+Instrumentation packages live under `src/opentelemetry/instrumentation/{name}/` with their own
+`pyproject.toml` and `tests/`. Other package types follow the equivalent layout under their own
+namespace (e.g. `src/opentelemetry/util/{name}/`, `src/opentelemetry/exporter/{name}/`).
+
+## Commands
+
+```sh
+# Install all packages and dev tools
+uv sync --frozen --all-packages
+
+# Lint (runs ruff via pre-commit)
+uv run pre-commit run ruff --all-files
+
+# Test a specific package (append -0, -1, etc. for version variants)
+uv run tox -e py312-test-instrumentation-flask-0
+
+# Type check
+uv run tox -e typecheck
+```
+
+## Guidelines
+
+- Each package has its own `pyproject.toml` with version, dependencies, and entry points.
+- The monorepo uses `uv` workspaces.
+- `tox.ini` defines the test matrix - check it for available test environments.
+- Do not add `type: ignore` comments. If a type error arises, solve it properly or write a follow-up plan to address it in another PR.
+- Whenever applicable, all code changes should have tests that actually validate the changes.
+
+## Commit formatting
+
+We appreciate it if users disclose the use of AI tools when the significant part of a commit is
+taken from a tool without changes. When making a commit this should be disclosed through an
+`Assisted-by:` commit message trailer.
+
+Examples:
+
+```
+Assisted-by: ChatGPT 5.2
+Assisted-by: Claude Opus 4.6
+```

CLAUDE.md

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+@AGENTS.md