docs: add AGENTS.md, STYLEGUIDE.md, agent-assisted contribution (#114)

[lipikaramaswamy]

Summary

• Add AGENTS.md — architecture overview, pipeline diagrams, and structural invariants for agents working in
  the codebase.
• Add STYLEGUIDE.md — code conventions ruff and ty cannot enforce (Pydantic vs dataclass, error handling,
  column-name constants, prompt construction).
• Add CLAUDE.md — 3-line redirect to AGENTS.md so Claude Code picks it up.
• Add an "Agent-Assisted Development" subsection to CONTRIBUTING.md establishing the
  plans/<issue-number>/<short-name>.md convention for non-trivial changes.
• Ignore .claude/worktrees/ (Claude Code session worktrees).

Filed #148 as a follow-up for three pre-existing column-name string-literal violations in
llm_replace_workflow.py:53-55 that the new STYLEGUIDE rule covers.

Closes #114.

Test plan

• CI passes (format-check, mkdocs build --strict)
• Reviewer can navigate the AGENTS.md ↔ STYLEGUIDE.md ↔ CONTRIBUTING.md cross-links
• git check-ignore .claude/worktrees/foo returns the path (worktrees properly ignored)

[greptile-apps]

Greptile Summary

This PR adds developer-facing documentation — AGENTS.md, STYLEGUIDE.md, CLAUDE.md, and an "Agent-Assisted Development" subsection in CONTRIBUTING.md — to guide both human contributors and coding agents through the project's architecture, conventions, and structural invariants. It also adds .claude/worktrees/ to .gitignore.

• AGENTS.md documents the three-module layout, both pipeline diagrams (replace and rewrite modes), core concepts, NDD adapter contract, prompt conventions, and structural invariants for agents working in the codebase.
• STYLEGUIDE.md codifies conventions that static analysis cannot enforce: Pydantic-vs-dataclass selection, error handling patterns, column-name constants, prompt construction, and annotation requirements.
• CONTRIBUTING.md adds the plans/<issue-number>/<short-name>.md convention requiring a design-review PR before non-trivial implementation work.

Confidence Score: 5/5

This PR adds only documentation and a .gitignore entry — no production code is changed, so there is no risk to runtime behavior.

All five files are documentation or configuration. The cross-links between AGENTS.md, STYLEGUIDE.md, and CONTRIBUTING.md are internally consistent, the pipeline diagrams match the described module boundaries, and the structural invariants align across all three guides. The .gitignore addition is a single, correct path entry.

No files require special attention.

Important Files Changed

Filename	Overview
AGENTS.md	New file — architecture overview, pipeline ASCII diagrams, invariants, and NDD adapter contract for agent-assisted development. Cross-links are accurate; structural invariants are consistent with STYLEGUIDE.md.
STYLEGUIDE.md	New file — code conventions covering Pydantic/dataclass usage, error handling, column constants, prompt construction, type annotations, and code organization. Well structured; cross-links to AGENTS.md and CONTRIBUTING.md are correct.
CLAUDE.md	New 3-line file that redirects Claude Code to AGENTS.md via the @AGENTS.md file-import syntax. Minimal and correct.
CONTRIBUTING.md	Adds "Agent-Assisted Development" subsection establishing the plans/<issue-number>/<short-name>.md convention and requiring agents to read AGENTS.md/STYLEGUIDE.md before non-trivial changes.
.gitignore	Adds .claude/worktrees/ ignore entry to exclude Claude Code session worktrees from version control.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["CLAUDE.md\n(Claude Code entry point)"] -->|"@AGENTS.md"| B["AGENTS.md\nArchitecture + Invariants"]
    B -->|cross-link| C["STYLEGUIDE.md\nCode Conventions"]
    B -->|cross-link| D["CONTRIBUTING.md\nWorkflow + Agent-Assisted Dev"]
    C -->|cross-link| B
    C -->|cross-link| D
    D -->|cross-link| B
    D -->|cross-link| C
    D --> E["plans/issue/name.md\nDesign review PRs"]
    F[".gitignore"] -->|ignores| G[".claude/worktrees/\nSession worktrees"]

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_{Reviews (5): Last reviewed commit: "docs: clarify TYPE_CHECKING guidance and..." | Re-trigger Greptile}

[greptile-apps]

TYPE_CHECKING guidance may mislead agents into wrong pandas placement

The example puts pandas inside a TYPE_CHECKING block, and the very next sentence says "only import it at the top level where it is actually needed at runtime." An agent reading these two adjacent statements could interpret "use TYPE_CHECKING blocks for heavy libraries" as universal advice and wrap every pandas import in TYPE_CHECKING — even in workflow files that use DataFrames at runtime — causing NameError at execution time. The intent is that TYPE_CHECKING is for type-hint-only imports, while runtime pandas usage always goes at the top level. Splitting these into two clearly labelled scenarios (type-hint-only vs. runtime-needed) would prevent the misreading.

[greptile-apps]

Minor naming inconsistency: AGENTS.md calls the library "DataDesigner" while STYLEGUIDE.md calls it "NeMo Data Designer". Both point to the same URL, but an agent doing a grep for one spelling will miss the other. Aligning to the same display name avoids confusion.

Suggested change

	NeMo Anonymizer wraps [NeMo Data Designer](https://github.com/NVIDIA-NeMo/DataDesigner) (NDD) for LLM column generation. References to NDD below mean that library.
	NeMo Anonymizer wraps [DataDesigner](https://github.com/NVIDIA-NeMo/DataDesigner) (NDD) for LLM column generation. References to NDD below mean that library.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!