Add AGENTS.md

AGENTS.md

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+# AGENTS.md
+
+Guidance for coding agents working in this repository.
+
+## Project overview
+
+This is a test fixture repository, not a real project. Its README states that it
+exists to exercise Sourcegraph batch changes. It contains only Markdown files
+plus a placeholder CI workflow — there is no application code.
+
+Some files exist specifically to test text-handling edge cases: `TRAILING.md`
+and `NONTRAILING.md` differ in whether the file ends with a trailing newline.
+
+## Repository layout
+
+Flat, single level — there are no source directories.
+
+| Path | Purpose |
+| --- | --- |
+| `README.md` | Placeholder; states the repo is for testing batch changes |
+| `CONTRIBUTING.md` | Heading only, no content |
+| `CHANGELOG.md` | Single trivial entry |
+| `ANOTHER.md`, `RANDOM.md`, `TESTING.md`, `TESTINGGG.md` | Placeholder Markdown |
+| `TRAILING.md`, `NONTRAILING.md` | Fixtures for trailing-newline behavior |
+| `.github/workflows/blank.yml` | Unmodified GitHub Actions starter template |
+| `.gitignore` | Ignores `.DS_Store` and `.env` |
+
+## Setup, build, test, lint
+
+There is nothing to set up, build, test, or lint. The repository has no package
+manager manifest, no Makefile, and no linter configuration. Do not add build
+tooling unless a task explicitly asks for it.
+
+`.github/workflows/blank.yml` is the default GitHub Actions starter workflow; it
+echoes a greeting and validates nothing. A green CI run here does not mean a
+change is correct.
+
+## Conventions
+
+- Content is plain Markdown. No style guide or linter is enforced.
+- No formatter runs over this repository, so avoid reflowing or reformatting
+  files you were not asked to change.
+
+## Gotchas
+
+- Preserve each file's existing trailing-newline state. `TRAILING.md` and
+  `NONTRAILING.md` are fixtures for exactly this; normalizing them defeats their
+  purpose.
+- Scope edits narrowly. Because the files are near-identical placeholder text, a
+  broad find-and-replace can easily touch fixtures a task did not intend to
+  modify.
+- Treat this repository as disposable test data. Do not rely on anything here as
+  an example of production conventions.