chore: import upstream snapshot with attribution

AGENTS.md

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+# Haystack Guidelines for AI Agents
+
+## Environment
+
+Haystack uses **Hatch** for environment and dependency management.
+
+Do not run `python` or `pip` directly.
+
+Before running code on this project, you must be able to run `hatch --version` and get a correct output.
+
+If not, ask the user where Hatch is or if they want to install it. For installation instructions, refer to https://hatch.pypa.io/latest/install/#installation.
+
+### Run scripts with test dependencies
+
+hatch -e test run python SCRIPT.py
+
+### Open a shell with test dependencies
+
+hatch -e test shell
+
+### Install temporary dependencies (for experiments only)
+
+uv pip install PACKAGE
+
+### Delete the environment
+
+hatch env prune
+
+## Tests
+
+Tests run via Hatch and support pytest arguments.
+
+Prefer running tests on a specific module or using `-k`, since the full suite is large.
+
+### Run unit tests
+
+hatch run test:unit
+
+### Run integration tests
+
+hatch run test:integration
+
+## Quality Checks
+
+### Type checking with mypy
+hatch run test:types
+
+To fix type issues, avoid `type: ignore`, casts, or assertions when possible. If they are necessary, explain why.
+
+### Format and lint
+hatch run fmt
+
+## Release Notes
+
+Every user-facing PR (not docs, not CI) must include a release note:
+
+hatch run release-note SHORT_DESCRIPTION
+
+Edit the generated file in `releasenotes/notes/`. Release notes use reStructuredText formatting; see the [release notes section in CONTRIBUTING.md](CONTRIBUTING.md#release-notes) for details.