feat(cli): add fern automations list preview subcommand

[devin-ai-integration]

Description

Refs fern-api/actions#8

Adds a new fern automations list preview CLI subcommand that discovers previewable generator groups and outputs structured JSON. This replaces the client-side YAML parsing in the fern-preview GitHub Action's detect-groups.ts with a single CLI call, making the CLI the single source of truth for which generators are previewable.

Also extracts the existing fern automations list generate inline logic into a matching testable module (listGenerateCommands.ts) for consistency.

Changes Made

New: fern automations list preview

• Extracted listPreviewGroups() into packages/cli/cli/src/commands/automations/listPreviewGroups.ts
• Uses Pick<AbstractAPIWorkspace<unknown>, ...> for type-safe workspace input
• Reuses isNpmGenerator from sdk-preview/overrideOutputForPreview.ts (canonical set of supported TypeScript generators)
• Filters generators by automation.preview and isNpmGenerator
• Deduplicates to one entry per (groupName, apiName) pair (first matching generator wins)
• Supports --json flag for machine-readable output, human-readable by default
• Supports --group and --api filters (same as list generate)

Refactored: fern automations list generate

• Extracted inline logic from cli.ts into listGenerateCommands.ts (matches listPreviewGroups pattern)

• No behavioral changes — purely structural for consistency and testability

• Updated README.md generator (if applicable) — N/A, hidden subcommand

Testing

• Unit tests added/updated
  • listPreviewGroups.test.ts (21 tests): detection, filtering, deduplication, multi-API, edge cases
  • listGenerateCommands.test.ts (16 tests): command generation, skip logic, options, multi-API, edge cases
• Manual testing completed — pnpm run check (biome lint) passes, all 37 tests pass

Usage

# Human-readable output (default)
fern automations list preview

# JSON output for GitHub Actions
fern automations list preview --json

# Filter to a specific group
fern automations list preview --json --group ts-sdk

# Filter to a specific API in multi-API repos
fern automations list preview --json --api payments

JSON output:

[
  { "groupName": "ts-sdk", "apiName": null, "generator": "fernapi/fern-typescript-sdk" }
]

Human-readable output:

ts-sdk — fernapi/fern-typescript-sdk
node (api: payments) — fernapi/fern-typescript-node-sdk

Link to Devin session: https://app.devin.ai/sessions/2db06cbb70d74a77a637d0067171f482

[devin-ai-integration]

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