move out into write module #25

Task: Pull filesystem I/O out of the generate-template core

Repo: LLazyEmail/generate-template
Goal: Core engine is catalog + render + payload → HTML. Disk is an adapter. run({ templateId, payload }) must not touch fs.

Why

The public contract is already GenerateRequest / GenerateResult. Filesystem leftover from the old in-app script still lives in the engine:

• listTemplateFiles() scans templatesDir
• payload.ts probes dataDir / {slug}.data.js / require()
• render/file-adapter.ts writes temp files and spawnSyncs Node
• CLI existsSyncs catalog file entries
• Defaults still assume src/templates and src/data

Writers already go through markup-generator. Reads should follow the same split.

Out of scope

• Do not add HTTP/Express
• Do not publish to npmjs
• Do not merge markup-generator into this package
• Do not keep file + exportName on the default path

Target shape

src/
  engine/          createGenerator, run, render  (no node:fs)
  catalog/         find / slug / ids
  persist/         Writer → markup-generator only
  adapters/
    payload-files.ts    dataPath json / *.data.js
    file-renderer.ts    spawn path, opt-in
    list-files.ts       directory scan for CLI --list
  cli.ts           uses adapters, not the engine internals

Steps

1. Audit every fs, path.resolve(process.cwd()), createRequire, spawnSync, os.tmpdir() import. Table: file, API, required or adapter.
2. Engine rule: TemplateGenerator.render / run / loadPayload (default) use only:
   • catalog
   • injected render
   • explicit payload or samplePayloads or config.loadPayload
   • no templatesDir / dataDir unless an adapter is registered
3. Move payload file loading to adapters/payload-files.ts. Wire it only when dataPath is set or useDataFiles: true. Default: missing payload → NO_PAYLOAD, do not existsSync(dataDir).
4. Move listTemplateFiles off the class public API used by other repos, or keep it as listTemplateFiles(dir) on the CLI adapter. Engine lists catalog ids, not directories.
5. Keep file-spawn in adapters/file-renderer.ts. Still gated by allowFileTemplates. Engine must not import spawnSync.
6. CLI may import adapters. --list uses list-files. --data= uses payload-files. Generate still goes through run().
7. Defaults: stop inventing src/templates and src/data when config omits them. outDir stays 'generated' only for writes.
8. Tests
   • engine test with no temp dirs and no fs mock required for run({ templateId, payload })
   • payload-files adapter tests isolated
   • file-renderer tests stay behind the flag
   • sandbox keeps injected render + run({ write }) — that write path is markup-generator, allowed
9. Docs: MIGRATION.md + README: “pass payload or loadPayload; do not rely on src/data/*.data.js unless you opt into the adapter.”

Done when

• rg "node:fs|spawnSync|createRequire" src only hits src/adapters/ and src/cli.ts
• run({ templateId, payload }) works in a process with no project src/templates or src/data
• CI + npm run sandbox still produce HTML
• Sibling note: if anyone used {slug}.data.js auto-load, they pass payload or enable the payload-files adapter

Suggested split

• PR A: stop default dataDir probe; require explicit payload / sample / hook
• PR B: move listTemplateFiles to CLI adapter
• PR C: isolate file-spawn so generator.ts / render.ts have no fs