deepseek-harness/docs/rfc/implemented/architecture/2026-06-20-extract-example-app-packages.md

RFC: Extract example apps into packages

Status: implemented

Problem

An example folder is supposed to be thin — the variable wiring of a demo, not the demo's machinery. Before this change it was thick. Each example carried a hand-rolled start.ts boot bootstrap, an infra preamble (timer, and — for the stdio demos — logger + hmr), nested includes of three shared YAML fragments (base.yml / base-core.yml / acp-agent/acp-tail.yml), and per-example agent-loop/persistence/system-prompt config. The actual app — the spine of services every agent needs — was spread across the leaf and those includes.

The deeper problem was a coupled front-door cluster that lived at the leaf with nothing enforcing it. Choosing the ACP bridge over ui-stdio was not one swappable line: an ACP server must drop the stdout console logger (stdout is the JSON-RPC channel — a stray log corrupts the frames) and pre-create no agents (ACP session/new creates them on demand), whereas the stdio app needs a console logger and a pre-created main. (timer is the one infra plugin common to both — it writes nothing to stdout — so it belongs in the shared spine, not the cluster.) That coupling was enforced only by prose warnings in the leaf YAML. A leaf that wired a console logger into the ACP config was a one-line, comment-only mistake away — exactly the stdout-purity footgun the examples guarded by hand. The three start.ts files also duplicated the Loader-boot tail, the .env loader, and (for ACP) snapshot-mode branching and the stdin-dispose lifecycle.

What shipped

Each example is now mostly an invocation of an app package, splitting the wiring along the existing interface / implementation / consumer seam: the app package owns the composition, the leaf cordis.yml owns only the swappable choices (which LLM adapter, which bash executor, model, prompt, persistence root).

• @deepseek-ai/dsh-agent-core (packages/core/agent-core) — a Cordis bundle plugin for the providerless, executor-less, UI-less spine: timer + llm + sessions + system-prompt + tools + agents + invariants + tool-bash + agent-loop, mounted as child plugins inside its apply(ctx) via ctx.plugin(...). This is the old base-core.yml minus bash-local, plus timer and the loop, as code instead of a YAML include. The bundle forwards agent-loop's agents list as its own config (export const Config = AgentLoop.Config, default [], the existing AgentLoop.Config shape in packages/core/agent-loop/src/index.ts) — so each app supplies its own pre-created agents. This is precisely the reason the old base-core.yml gave for keeping agent-loop out of the shared core ("the examples disagree — stdio needs a pre-created main, acp needs none"); forwarding the config dissolves that objection — the loop is shared, the agents list is per-app. The bundle children register into the root service store, so a leaf-mounted sibling (the adapter, the executor) sees them exactly as a nested plugin-include subtree's services were seen before. Depending on the CONCRETE dsh-agent-loop (not just the dsh-agent interface) is deliberate and is the sanctioned exception to the "extension plugins depend on interfaces, never on the concrete loop" rule (packages/README.md, docs/architecture.md § Service map): the rule constrains plugins that EXTEND the system, whereas this bundle's whole job is to COMPOSE the concrete spine. Swapping the loop means publishing a different bundle, not rewiring every extension.
• @deepseek-ai/dsh-stdio-agent (packages/ui/stdio-agent) and @deepseek-ai/dsh-acp-agent (packages/ui/acp-agent) — app packages, each consuming dsh-agent-core and baking in its coupled front-door cluster: stdio = ui-stdio + console logger + a pre-created main; acp = the acp bridge + JSONL persistence + no stdout logger + no pre-created agents. The leaf no longer carries the cluster, so it has no logger entry to copy wrong by default — the common stdout-purity mistake loses its foothold. (A leaf can still add a sibling logger entry — a package cannot forbid what a leaf author writes — so the rule "never add a stdout logger to an ACP leaf" stays documented at the leaf; what changed is that the default leaf has nothing to get wrong.) They land under the existing ui group alongside acp, so no new package group (and no tsconfig/packages/README group plumbing) was needed.
• start.ts is gone. Each app package exposes a bin (dsh-stdio-agent / dsh-acp-agent); the demo:* scripts invoke it (e.g. dsh-stdio-agent ./cordis.yml). The Loader-boot tail, .env loading, and fail-loud guards live in the shared @deepseek-ai/dsh-app-boot package (unit-tested under the per-file coverage gate — see share the app bins' boot glue); each bin is a thin self-executing composition over those helpers plus its app-specific lifecycle (the ACP bin: snapshot-mode selection and stdin-dispose). The bin.ts files themselves stay coverage-excluded (self-executing CLI entries, like the old start.ts) and are driven by the keyless Loader-path tests.
• Each leaf cordis.yml collapses to backends + config: the LLM adapter (llm-deepseek with apiKey/models, or llm-replay), the bash executor (bash-local), hmr for the stdio demos (see the amendment below), and one app entry carrying the app's config (model, system prompt, persistence root — surfaced as the app package's own Config, which routes each value to wherever the app wires it: stdio onto its pre-created agent, acp onto the bridge plugin).
• echo-agent folds onto dsh-stdio-agent, swapping the LLM backend to the local mock-llm and adding the local echo-tool (plus bash-local, which the spine's tool-bash injects) at the leaf — the clean demonstration of "swap the backend, keep the app". mock-llm.ts / echo-tool.ts stay as example-local teaching plugins.
• base.yml, base-core.yml, and acp-agent/acp-tail.yml are retired — the spine they shared now lives in dsh-agent-core.

bash-local and the LLM adapter stay leaf choices: the bundle ships tool-bash (the consumer schema), the leaf picks the executor implementation, so a sandboxed executor or replay adapter swaps in without touching the app.

Amendment on implementation: hmr stays a leaf entry

The proposal listed hmr among the stdio app's baked-in front-door cluster. Validating against the code, baking hmr into the dsh-stdio-agent package fights cordis in two ways, so it ships as a leaf cordis.yml entry instead:

1. @cordisjs/plugin-hmr is a Loader-only, subprocess-only dev plugin — its constructor throws without node --expose-internals + a live loader service, so it can only run in the real demo:*/bin subprocess, never in the in-process unit/coverage tier.
2. The in-process test tier (vitest) cannot even import the vendored hmr module (its class-decorator @Inject form fails under Vite's transform), so a package whose apply statically imported it could never satisfy the per-file 100% coverage gate on its headline function.

Crucially, hmr is not a stdout-purity footgun the way the console logger is — a stray hmr in the ACP config would not corrupt the JSON-RPC frames — so leaving it at the leaf costs none of the safety the coupling argument is about. The logger (the real coupling) stays baked in: the stdio app includes it, the ACP app omits it.

Why not keep the wiring in shared YAML includes?

The old base*.yml/acp-tail.yml includes already deduped the config, but a YAML include cannot encapsulate the front-door coupling — it can only describe it in a comment and trust every leaf to obey. It also cannot own a bin, so the boot glue stayed copied across three start.ts files. A package turns "the ACP app never logs to stdout" from a prose warning into a property of the artifact: there is no logger entry in the leaf to get wrong.

Verification

• Each example directory is cordis.yml (+ the acp cordis.snapshot.yml) + README.md + tests only — no start.ts, no infra preamble; base.yml/base-core.yml/acp-tail.yml are gone.
• demo:echo / demo:repl / demo:acp run via the app-package bins.
• The new packages carry the per-file 100% coverage gate and a README like every @deepseek-ai/dsh-*. Each app package has a keyless real-load-path smoke that boots it through its bin + the cordis Loader (not a hand-built ctx.plugin({...}) mount), guarding the unwrapExports export-shape bug class (postmortem 0001).
• The ACP snapshot replay transcript is unchanged: the boot restructuring preserved the plugin set + load order, so pnpm run test:snapshot stays green against the committed goldens with no re-record.

What we give up

• The bare-plugin-tree pedagogy. echo-agent's inlined cordis.yml showed every plugin at once; the spine now lives behind a bundle, so seeing the whole tree means opening dsh-agent-core. The app package's README carries that teaching weight.
• A layer of indirection. "What does this demo load?" becomes a package read, not a single YAML scan.

Related

• Supersedes Make the shared example base providerless: renaming base.yml to the providerless core is moot once the spine moves into dsh-agent-core and the base*.yml files are deleted.
• Builds on the capability-seams interface/implementation/consumer split — backends and presentation stay leaf choices; the spine is the shared bundle.
• Complements Reorganize packages into a modular hierarchy: the new app/core packages slot into existing groups under that hierarchy (core for the reusable spine bundle, ui for the app-specific front doors).