chore: add AGENTS.md to guide AI-assisted contributions

AGENTS.md

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+# OpenTelemetry Python
+
+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 the core OpenTelemetry Python API, SDK, and related packages.
+
+## General Rules and Guidelines
+
+The OpenTelemetry community has broader guidance on GenAI contributions at
+https://github.com/open-telemetry/community/blob/main/policies/genai.md — please read it before
+contributing.
+
+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
+
+- `opentelemetry-api/` - the OpenTelemetry API package
+- `opentelemetry-sdk/` - the OpenTelemetry SDK package
+- `opentelemetry-semantic-conventions/` - semantic conventions
+- `opentelemetry-proto/` / `opentelemetry-proto-json/` - protobuf definitions and generated code
+- `exporter/` - exporters (OTLP, Prometheus, Zipkin, etc.)
+- `propagator/` - context propagators (B3, Jaeger)
+- `shim/` - compatibility shims (OpenTracing, OpenCensus)
+
+Each package lives under its own directory with a `pyproject.toml` and `tests/`.
+
+## 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
+uv run tox -e py312-test-opentelemetry-sdk
+
+# Type check
+uv run tox -e lint-opentelemetry-sdk
+```
+
+## 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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+See [AGENTS.md](AGENTS.md).