docs: expand DEVELOPMENT.md with architecture and testing guide

[yarikoptic-gitmate]

Summary

Significantly expanded DEVELOPMENT.md with comprehensive documentation of the codebase architecture, testing infrastructure, and CI/CD setup. Also updated CLAUDE.md to redirect developers to the authoritative DEVELOPMENT.md file rather than duplicating guidance.

Key Changes

• Codebase Architecture — Added detailed directory layout with descriptions of each module (cli/, files/, metadata/, validate/, support/, tests/)
• Key Design Patterns — Documented CLI delegation, file-type hierarchy, enum-based configuration, generator-based processing, context managers, retry logic, and lazy imports
• Key Classes — Listed and described major classes (DandiAPIClient, ParsedDandiURL, DandiFile, ValidationResult, Dandiset, DandiInstance)
• Code Style Conventions — Expanded with comprehensive rules for formatting, imports, type annotations, naming, exceptions, docstrings, and CLI patterns; noted that most are enforced by pre-commit
• Pre-commit Hooks — Added section documenting the 5 hook categories and explaining the auto-fix workflow
• Test Infrastructure — New section covering pytest markers, key fixtures, test organization, pytest configuration, and CI/CD workflows
• Development Commands — Added examples for running specific tests with tox and building documentation
• Docker Compose Testing — Documented the local_dandi_api fixture and DANDI_TESTS_PULL_DOCKER_COMPOSE environment variable
• CLAUDE.md Refactor — Replaced detailed command/style duplication with a single directive to read DEVELOPMENT.md, reducing maintenance burden and ensuring single source of truth

Implementation Details

• Organized documentation hierarchically with clear section headers and subsections
• Used code blocks for directory structure and command examples
• Provided context for design decisions (e.g., why lazy imports are used)
• Included references to specific files and configuration locations
• Maintained consistency with existing documentation style

https://claude.ai/code/session_017qM7WyFgvqy5UQHEtEcHzY

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.96%. Comparing base (2b5f8ea) to head (b33cd10).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1902   +/-   ##
=======================================
  Coverage   76.96%   76.96%           
=======================================
  Files          88       88           
  Lines       12882    12882           
=======================================
  Hits         9914     9914           
  Misses       2968     2968           

Flag	Coverage Δ
unittests	76.96% <ø> (ø)

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[Copilot]

Pull request overview

This PR expands contributor-facing documentation by making DEVELOPMENT.md the single, authoritative source for architecture, testing, and CI/CD guidance, and simplifying CLAUDE.md to point developers to that guide.

Changes:

• Added detailed codebase architecture documentation (directory layout, key design patterns, key classes) to DEVELOPMENT.md
• Added expanded testing and CI/CD documentation, including fixtures, markers, and common development commands
• Refactored CLAUDE.md to remove duplicated guidance and redirect contributors to DEVELOPMENT.md

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
DEVELOPMENT.md	Major expansion of developer documentation covering architecture, testing, pre-commit, and CI/CD
CLAUDE.md	Reduced duplicated instructions and directs contributors to DEVELOPMENT.md as the source of truth

Suppressed comments (3)

DEVELOPMENT.md:107

• This refers to a “docker-compose fixture”, but the test harness uses the docker compose CLI (space) rather than the legacy docker-compose binary. Rewording avoids implying the wrong command name.

Tests that need a running archive instance use the `local_dandi_api`
docker-compose fixture.  Set `DANDI_TESTS_PULL_DOCKER_COMPOSE=""` to skip
`docker compose pull` and speed up repeated runs.

DEVELOPMENT.md:179

• AssetDirURL is listed as a ParsedDandiURL subclass, but there is no such class in dandi/dandiarchive.py (the directory-like multi-asset URL type is AssetFolderURL). This makes the architecture overview inaccurate.

- `ParsedDandiURL` (`dandiarchive.py`) — abstract base for URL parsing;
  subclasses `DandisetURL`, `SingleAssetURL`, `AssetItemURL`, `AssetDirURL`
- `DandiFile` (`files/bases.py`) — abstract base for all file types;

DEVELOPMENT.md:282

• The documented CI Python version range doesn’t match the current test matrix in .github/workflows/run-tests.yml (which includes 3.11–3.14). Updating this keeps the CI/CD documentation accurate.

- `run-tests.yml` — full test matrix: Python 3.10–3.13 × Ubuntu,
  macOS (M1 + Intel), Windows

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[github-actions]

🚀 PR was released in 0.77.0 🚀