Add a CSpell custom-dictionary redundancy auditor

[szmyty]

Outcome

Add a maintained cspell-dicts workflow that finds custom dictionary entries already covered by active, installed, or upstream CSpell dictionaries and can remove safe duplicates without destroying formatting or comments.

A validated prototype from an interactive tooling session already established the desired command model:

cspell-dicts
cspell-dicts audit --scope active
cspell-dicts list --scope installed
cspell-dicts sync
cspell-dicts audit --scope upstream
cspell-dicts clean --dry-run
cspell-dicts clean
cspell-dicts doctor

The prototype delegated membership checks to CSpell's own trace mechanism so plain text, gzip, Hunspell, and compiled trie dictionaries could be handled consistently.

Required behavior

• Discover the effective CSpell configuration and imported configuration graph.
• Resolve dictionaryDefinitions, enabled dictionaries, and additional installed @cspell/dict-* packages.
• Support active, installed, and explicitly synchronized upstream scopes.
• Cache upstream data beneath the XDG cache root; do not write generated state into the repository.
• Report exact custom word → covering dictionary mappings.
• Preserve flagged, compound, commented, or ambiguous dictionary syntax for manual review.
• Make cleanup opt-in, confirmation-gated, backup-producing, and previewable with --dry-run.
• Preserve source formatting/comments where the configured file format permits safe surgical edits.
• Support table, JSON, CSV, TSV, Markdown, and words-only output.
• Provide a CI failure mode for duplicate custom entries.
• Redact secrets and avoid copying unrelated config contents into reports.

Acceptance criteria

• CLI has documented exit codes and stable machine-readable output.
• Config discovery handles JSON/JSONC/YAML and imported configs where CSpell supports them.
• Membership checks use CSpell-compatible semantics rather than a partial custom parser.
• Cleanup never removes ambiguous/flagged entries automatically.
• Every mutation has a dry run, explicit confirmation or --yes, timestamped backup, and atomic rewrite.
• Backup/cache locations respect XDG conventions and are surfaced by doctor.
• Tests cover comments, duplicate entries, case sensitivity, compounds, Hunspell/trie dictionaries, imported configs, missing packages, offline mode, and interrupted cleanup.
• CI fixture proves that --fail-on-duplicates behaves deterministically.
• Documentation distinguishes “recognized by an enabled dictionary” from “valid for this project's domain language.”

Provenance

Distilled from a successful repository cleanup session in which hundreds of redundant custom spellings were identified, previewed, backed up, and removed while ambiguous entries remained untouched. Repository-specific word lists and filenames are intentionally omitted.