Build fails on fresh clone: tsdown cannot load tsdown.config.ts because "unrun" is not installed

[thrasher824]

Description

Following the README's from-source setup:

pnpm install
pnpm run build

pnpm run build fails at the tsdown step with:

ERROR  Error: Failed to import module "unrun". Please ensure it is installed.
    at importWithError (.../node_modules/tsdown/dist/general-Cp4NiJNK.mjs:42:9)
    at async unrunImport (.../node_modules/tsdown/dist/options-DWGUHu4D.mjs:696:20)
    at async loadConfigFile (.../node_modules/tsdown/dist/options-DWGUHu4D.mjs:604:19)
    ...
[ELIFECYCLE] Command failed with exit code 1.

Root cause

tsdown 0.22.2 loads tsdown.config.ts through a config loader. With the default --config-loader auto, on a runtime without native TS support it resolves to the unrun loader:

const autoLoader = isBun || nativeTS && isSupported ? "native" : "unrun";

unrun is declared by tsdown as an optional peerDependency ("unrun": "*"), so pnpm does not install it automatically. The repository's root devDependencies includes tsdown's other optional peers (tsx, publint, ...) but is missing unrun — so a fresh clone cannot build.

Steps to reproduce

1. git clone https://github.com/deepseek-ai/deepseek-harness.git
2. cd deepseek-harness
3. pnpm install (pnpm@11.7.0, matches packageManager)
4. pnpm run build → fails in tsdown

Environment

• OS: Windows 10
• Node: v22.17.1 (also below the repo's engines: ^22.19.0 || >=24.0.0)
• pnpm: 11.7.0

Suggested fix

Add "unrun" to the root devDependencies (e.g. "unrun": "^0.3.1"), alongside the other tsdown optional peers already present.

Workaround

Set NODE_OPTIONS=--experimental-strip-types so tsdown falls back to its native loader, or upgrade Node to >= 22.18 where native TS support is enabled by default.