Problem

The new headless owner test in packages/slate/test/headless-contract.ts needed to import slate-history and slate-hyperscript by package name to prove real workspace headless composition.

Under Yarn PnP, that failed immediately.

Symptoms

• Error: Your application tried to access slate-history, but it isn't declared in your dependencies
• the test was correct, but the package graph was not

What Didn't Work

• assuming the root workspace or the other package's own dependencies were enough
• relying on package-name imports without declaring them in packages/slate/package.json

Solution

Declare the cross-package workspace dependencies on the package that owns the test:

"devDependencies": {
  "@babel/runtime": "^7.23.2",
  "slate-history": "workspace:*",
  "slate-hyperscript": "workspace:*"
}

Then rerun yarn install so PnP updates the dependency graph before running the proof command again.

Why This Works

The test is proving package-split usage from packages/slate.

Under PnP, package-name imports are only sound when the importing package declares them. Workspace root entries help source resolution after a package is allowed to load, but they do not bypass the dependency contract itself.

Prevention

• If a package-owned proof imports another workspace package by name, declare that workspace package in the importing package's dependencies or devDependencies.
• Do not confuse source-resolvable root entries with permission to import.
• When a new workspace proof suddenly fails under PnP before any behavior runs, check the package graph first.