DeepSeek Harness SDK is a plugin-based agent harness on vendored Cordis: **everything is a plugin**. Read [docs/architecture.md](docs/architecture.md) before changing `packages/`; follow [docs/AGENTS.md](docs/AGENTS.md) for documentation.
**Remove this section at the first tagged release.** With no external consumers, prefer the correct foundation over compatibility shims: rename or repackage freely and update every reference together. Backends reject old on-disk formats. SQLite uses monotonic `SCHEMA_VERSION`; `dsh-session` keeps `SESSION_FORMAT_VERSION` at `0` with no compatibility promise.
When required `gh`, `pnpm`, build, test, or generator commands fail because the agent sandbox blocks credentials, network, IPC, file watching, or nested `sandbox-exec`, retry unchanged with the narrowest host escalation before diagnosing authentication or project failure. Require sandbox evidence; never bypass genuine test failures or the product sandbox under test.
Run narrow checks during implementation and this CI-equivalent sequence before marking a PR ready. Fresh worktrees need `pnpm run build` before publint and NodeNext inspect `lib/`:
Real-API tests and demos read `DEEPSEEK_API_KEY`, optional `DEEPSEEK_BASE_URL`, and root `.env`. cordis.yml allows `!!js` (never `!js`) only under plugin `config`; Loader metadata is static, so conditional composition uses overlays ([primer](docs/cordis-primer.md#loader-configuration)). Never commit credentials. CI e2e skips without a key; [testing.md](docs/testing.md) owns key policy.
- Every npm package is `@deepseek-ai/dsh-<name>`; vendored packages keep upstream names and are `private: true`. `cordis` is a peerDependency (+ dev) of every harness package.
- ESM everywhere (`"type": "module"`). Cross-package imports use package names; in-package relative imports include `.ts`. CI subprocesses that boot examples or Cordis configs run built `lib/` under plain Node; only explicit source-path regressions use tsx ([testing policy](docs/testing.md#test-subprocess-launch-modes)).
- **Runtime invariants assert owned relationships.** Check authoritative event streams or mutable data, not service or method presence, plugin metadata or effects, or fixed pure examples. If a package has no plausible relationship, an explained empty companion is correct ([package contract](packages/AGENTS.md)).
- **Typed events use declaration merging** and merge-extensible maps. Event JSDoc needs `@mode` and payload `@param`; scoped keys absent from payloads need `@dshScopeScan unsupported`. Public service methods document parameters and non-void returns.
- **Waterfall listeners MUST call `next()`** to delegate; returning without it is the veto ([semantics](docs/cordis-primer.md#cordis-waterfall-semantics)).
- **Model-visible ⟺ logged**: anything that reaches a model request must be reconstructable from the session log; a new model-visible input requires a session event.
- **Explicit > implicit at package seams**: defaulting is an explicit `resolve(request): Spec` step in the owning implementation, never a hidden `?? default` inside `run()` (the `dsh-bash` request/spec split is the template).
- **No hardcoded tunables in plugins**: deployment-varying choices are validated `Config` fields changeable from cordis.yml; a `DEFAULT_*` constant or test seam is not configurability. Protocol constants, external specs, and security invariants stay fixed.
- **Trust TypeScript at typed same-process seams.** Do not add runtime validation, fallback behavior, or hostile-input tests solely for values the static interface requires; validate at parser/config, queued, model/tool JSON, durable/file, worker, process, and wire boundaries.
- **Every non-trivial change MUST include at least one Agent Note in the same PR.** Update the owning note or add one, validate its premises against code, and exempt only mechanical/local edits ([scope](.agents/notes/README.md#when-to-write-one)).
- **Testing policy** — [docs/testing.md](docs/testing.md). Every non-trivial model- or human-visible change adds or updates a keyless snapshot through a real runnable example in the same PR; package tests, e2e-only assertions, and mock-only fixtures do not substitute for the assembled application transcript. Fixtures must replay on macOS/Linux; fix fixtures, not normalizers.
- **A tool's ACP render intent is part of its design**, decided up front (`generic`/`terminal`/`diff`, `locations`); presentation methods are pure functions of `args` ([cookbook](docs/cookbook/adding-a-tool.md)).
- **Plan unit, e2e, and snapshot coverage** for new seams, lifecycle shapes, and transcript surfaces; missing snapshot-harness support is part of the implementation, not deferred follow-up.
- **Keep PRs coherent and merge with merge commits.** Split an independently meaningful feature or design decision into a separate or stacked PR when combining it obscures ownership, intent, or verification. Never squash/rebase or rewrite pushed branches; put a review fix on its introducing PR, then merge down the stack ([guide](docs/cookbook/responding-to-pr-review-on-a-stack.md)).
Everything compiles under `strict: true` with `noImplicitAny`; every remaining `any` explains why a narrower type is infeasible. Every module and export has concise JSDoc for its non-obvious contract; function-like exports include `@param`/`@returns`, as enforced by `verify-export-jsdoc`. Heritage-declared members, plugin-protocol slots, and constructors keep their docs at the declaring seam, protocol, or class.
Comments and docs preserve complete contracts and non-obvious orientation, not reasoning transcripts. Do not narrate control flow or tests, preserve review history, or restate code. Keep factual clauses affecting behavior, failure, timing, ownership, or safe use; link aggressively to owning rationale. Use [dsh-prose-standard](.agents/skills/dsh-prose-standard/SKILL.md) for prose decisions. Wire mechanically checkable invariants into an executed top-level gate and prove each new or changed acceptance path rejects an invalid case. Use narrow justified exceptions instead of disabling a rule globally.
Docs accompany every code change: update affected README/JSDoc contracts together; update both sides of a bilingual pair and re-record it ([i18n contract](docs/i18n/README.md)). Current-state prose, one physical line per paragraph, one home per fact, and word budgets live in [docs/AGENTS.md](docs/AGENTS.md).
`CLAUDE.md` symlinks `AGENTS.md` at root, `packages/`, and `examples/`; edit the real file. Keep each rule self-contained while linking high-level docs. Condense when clarity survives; raise a `verify-doc-budgets` ceiling when the contract genuinely needs more space.
`vendor/` packages are pinned source copies (manifest with upstream SHAs in [vendor/README.md](vendor/README.md)). Update via the sync procedure there; re-apply or retire the logged local modifications; rerun `pnpm run test && pnpm run build`.
