[masaok]

Why

The engine has to exist as packages a command-line tool and a worker can run, separate from the Next.js app. This adds the workspace and the first package, which every later package depends on: the shape of a cost line, the shape of a finding and the money math.

Scope

• pnpm-workspace.yaml gains packages/*. The app stays at the repository root.
• packages/core (@costexplorer/core, private for now):
  • costRecordSchema, the subset of the FinOps FOCUS columns the analyzers will use, in camelCase.
  • findingSchema and Finding, the public contract from the plan, with rankFindings and totalMonthlySavingUsd.
  • sumUsd, monthlyFromHourly, floorToCents and HOURS_PER_MONTH.
• Vitest runs packages/*/src/**/*.test.ts inside pnpm test and fails under 90% coverage.
• pnpm typecheck also runs each package's own tsc. Packages use tsconfig.packages.json, which allows only syntax Node can run without a build.
• Lint rejects react, react-dom and next imports in every package except a future packages/ui.
• README.md, CONTRIBUTING.md, the guardrails table and the audit are updated.

Stacked on #2. Merge #1 and #2 first.

Tradeoffs

Three things in the plan were left out on purpose. Each has a row under "Not adopted" in docs/engineering-practices.md saying when to adopt it.

• Turborepo. The gate takes about 15 seconds.
• Changesets. Nothing is published yet. It belongs with the npm release.
• Moving the app to apps/web. It rewrites every check, the feature map and the agent instructions, and no engine code needs it.

AGENTS.md does not mention packages/ yet. That file changes only in a pull request of its own, so it is a follow-up.

Savings are ranked by dollars alone. Whether confidence should affect the order is a product call, left for review.

Verification

VERIFIED. pnpm verify on Node 24.21.0.

$ next typegen && tsc --noEmit && pnpm -r typecheck
✓ Types generated successfully
$ eslint --max-warnings 0
All matched files use Prettier code style!
PASS feature-map (2 surfaces in code, 2 rows)
PASS docs-links (30 relative links in 11 markdown files)
PASS versions (Node 24, 2 workflow files)
ℹ tests 13
ℹ pass 13
ℹ fail 0
 Test Files  3 passed (3)
      Tests  19 passed (19)
Statements   : 100% ( 26/26 )
Branches     : 100% ( 9/9 )
Functions    : 100% ( 10/10 )
Lines        : 100% ( 22/22 )
✓ Compiled successfully
PASS GET / 200, text "To get started, edit the"
PASS GET /favicon.ico 200, type "image/x-icon"
2 surfaces requested, 0 failures

Each new check was watched failing:

• Coverage: ERROR: Coverage for branches (88.88%) does not meet global threshold (90%) with one comparator branch untested.
• Package typecheck: src/zz.ts(1,14): error TS2322: Type 'string' is not assignable to type 'number'. with a bad file added and removed.
• The framework-import rule has a test in scripts/checks/lint-boundaries.test.mjs.

https://claude.ai/code/session_01WTtRZcdke1yYdYUAanaf7V

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Project	Deployment	Actions	Updated
costexplorer	Ready	Preview	Oct 2, 2026 12:03am UTC

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