docs: add repository agent guidance

AGENTS.md

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+# Repository guide
+
+Python 3.11 / Flask service that converts raster images to SVG using NumPy,
+OpenCV, FAISS, scikit-image and Potrace. Requests can return raw SVG or upload it
+to S3. Start with `README.md` for setup and usage.
+
+## Code map
+
+- `vectorizing/__init__.py`: app factory, request validation, cropping and API responses.
+- `vectorizing/solvers/binary/`: binary masks and tracing.
+- `vectorizing/solvers/color/`: quantization, cluster cleanup, ordered masks and tracing.
+- `vectorizing/geometry/` and `vectorizing/svg/`: path conversion, bounds and SVG serialization.
+- `vectorizing/util/`: image loading, color-mode normalization and size limits.
+- `vectorizing/server/`: environment settings, S3, logging and timing.
+- `vectorizing/tests/`: API contracts, image gallery and algorithm regressions.
+- `scripts/`: local infrastructure, dependency generation and offline comparison/benchmark tools.
+
+## Development and checks
+
+Prefer Docker Compose; it supplies Moto S3 and needs no AWS account or `.env` file.
+Run from the repository root:
+
+```sh
+docker compose up --build
+pre-commit run --all-files
+docker compose --profile testing run --build --rm test
+```
+
+For a focused test run:
+
+```sh
+docker compose --profile testing run --build --rm test \
+  python -m pytest vectorizing/tests/test_color_bitmap_rims.py
+```
+
+- The API defaults to `http://localhost:8000` in Compose.
+- Application source is copied into the image, not bind-mounted. Rebuild after edits.
+- Use `docker compose down` to stop services you started; Moto data is discarded.
+  Isolate project names and image tags when testing alongside other sessions/worktrees.
+- Native execution needs the Python dependencies and system libraries from the
+  Dockerfile/dev-container setup. Package imports require `PORT` and `S3_BUCKET`;
+  integration tests also require a distinct `S3_TEST_BUCKET` and a local S3 endpoint.
+- Preserve normal AWS behavior unless `AWS_ENDPOINT_URL` is explicitly configured.
+  Use Moto for validation, not live buckets.
+- CI runs the pre-commit hooks with Python 3.11 and the Compose test command.
+
+## Output and behavior contracts
+
+- Keep smooth anti-aliasing and transparent exteriors. Do not hide seams with SVG
+  strokes or `shape-rendering="crispEdges"`, or reduce normal tracing quality.
+- Color masks use bounded overlaps, not full underpainting. The current rim is
+  two processed-image pixels; zoom enlarges it and very thin features may remain
+  covered. Do not promise universally exact holes and seam-free rendering.
+- Preserve palette/centroid ordering, dtypes and overflow behavior, connectivity,
+  and independent mask storage when optimizing arrays. Rim conversion runs forward
+  because the next mask must still be cumulative.
+- Preserve public defaults, response/error shapes, return containers, SVG paint
+  order and numeric formatting during refactors or performance work.
+- Image readers currently wrap all loading failures, including interrupts, and URL
+  downloads have no timeout. These are tested legacy contracts, not recommendations;
+  change them deliberately with updated tests, never incidentally during lint cleanup.
+- Comments and docstrings should explain behavior and invariants, not edit history.
+
+## Regression evidence
+
+- Add focused tests for changed behavior. Keep reference implementations independent
+  of the optimized code they check.
+- The gallery can auto-create missing PNG baselines. A newly seeded baseline does
+  **not** prove equivalence; do not delete or replace baselines just to make tests pass.
+- For output-preserving changes, capture before editing (or use a trusted baseline
+  checkout), then compare SVG bytes, RGBA pixels, palettes, dimensions and bounds
+  with `scripts/vectorization_outputs.py`. See the README for commands.
+- For layer/geometry changes, check layer deletion, zero alpha and half opacity,
+  transparent backgrounds and thin features, including `aftermath.png`. An assembled
+  render alone cannot establish editability.
+- Use `scripts/benchmark_vectorization.py` for measured performance claims. Retain
+  raw samples, check equivalent outputs, and report runtime/hardware context. Its
+  timing excludes input decoding, HTTP/S3 and rasterization; process peak RSS includes
+  startup and warmups. Local results are not production or concurrent-load guarantees.
+
+## Style, dependencies and artifacts
+
+- Follow `.pre-commit-config.yaml` and `pyproject.toml`: Black, 88 columns, isort,
+  annotations and NumPy-style docstrings. Avoid broad lint suppressions and keep
+  correctness/security checks enabled. Passing lint is not a static-type-check claim.
+- Prefer existing dependencies. Edit `requirements/prod.in` or `requirements/dev.in`,
+  then use `scripts/compile_requirements.sh` and `scripts/compile_envs.sh` when dependency
+  updates are needed. The latter requires the configured Conda `dev` environment.
+  Keep system dependency setup consistent with `scripts/install_system_dependencies.sh`
+  and the Dockerfile.
+- Keep generated captures, benchmarks, investigations and scratch source under `.user/`
+  or temporary directories, not tracked code. `.user/` is excluded from Git and Docker.
+  Historical notes there may be stale; verify them against current source.
+- Keep visual evidence local unless upload is explicitly requested. Never include
+  credentials in reports or commits.
+
+## Pull requests
+
+Keep descriptions short and plain-language. Fetch `.github/pull_request_template.md`
+from the `Kittl/.github` repository rather than inventing a replacement.
+Leave owner attestations unchecked without explicit approval. Do not add agent/tool
+badges. After addressing human review feedback, reply but leave the thread open
+unless the user explicitly asks to resolve it; uncertain reviewer identity counts
+as human.