deepseek-harness/packages/boot/app-boot/README.md

description, kind

description	kind
Shared Loader boot support for dsh profiles and the temporary Python SDK runtime: environment layers, patches, diagnostics, and configuration preview.	package-library

@deepseek-ai/dsh-app-boot

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Summary

dsh-app-boot is the shared Loader boot library behind dsh profiles, including the CLI packaged by the Python runtime wheel. It loads environment layers, composes profile bundles and patches, boots every plugin, and returns the running app or identifies the failed plugin and cause. Product applications use the dsh launcher instead of publishing separate bins; direct-config helpers remain only for lower-level embedders and tests. You can preview the effective configuration before booting, select live or startup-only patch application per profile, and let a terminal-owning app restore its terminal before a fatal exit.

Table of Contents

• Use this package
• Understand the implementation
• Further Exploration
• Model Experience
• Known Limitations and Deferred Work
• Dev Note

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Use this package

Starting an app with this package is a small, explicit entry point: you give it a config file and it runs the whole boot. This section covers what you can do and what you get; the helper calls behind each outcome are documented in the folded implementation section.

When to use it

Use it when implementing the shared dsh launcher or embedding its lower-level boot helpers. Product features belong in profile bundles instead of new application bins; code that only adds plugins to an already-running app mounts those plugins directly.

Starting the app

You give your entry point a config file, and the process starts the whole app: it loads your environment layers, applies patches and profiles, boots every plugin, and returns once the app is running. In replay mode it boots the sibling cordis.snapshot.yml instead, so a recorded session reproduces identically. The smallest entry point is two calls:

installFailLoud('dsh')
const ctx = await boot('dsh', resolveConfigPath(argv[2], process.env.DSH_SNAPSHOT))

With that entry point, success looks like a running app with every plugin active; failure is never silent — one labelled line names the failing plugin and the stage, and the process exits nonzero. The app context is torn down before the error is reported, so nothing keeps running half-started.

Profiles

A profile is how one dsh installation ships different app surfaces: web, headless, acp, sdk, and sdk-minimal start distinct compositions from the same launcher. A profile lives at $DSH_HOME/profiles/<name> and combines installable bundles, its own cordis.patch.yml, and patchReload: live | startup; omitted reload policy keeps the historical live default for custom profiles. The shipped web template uses live reload, while the other shipped templates apply patches only at startup. sdk-minimal names only its standalone bundle; the other templates retain base-plus-mode stacks. dsh plugin creates custom profiles, and a missing bundle or one without a patch declaration fails startup loudly.

Your machine-local preferences also live in the Harness home:

• .env — your ordinary environment layers: the invoking directory's file outranks the Harness-home file, and both sit below the inherited environment. Variables that decide how the process starts (PATH, proxies, DSH_*, XDG_* and similar) are rejected from files: export them instead. For a non-product bin that just wants one directory's .env, a missing file is fine and an unloadable one prints one labelled warning line.
• cordis.patch.yml — your tweak layer, applied after every bundle layer (per-profile first, then the home-level file, which therefore outranks it): replace one entry's whole config (restating the fields you keep), insert new entries, or interpolate !!js expressions at boot. A patch naming an entry that does not exist prints a stderr warning; an empty or comments-only file fails boot — disable the layer with [] instead.

Profiles with patchReload: live watch both user patch files: a valid edit recomposes without restart, while a rejected edit leaves the last good app running. A startup profile installs neither those watchers nor the launcher's watch-only HMR fallback.

Previewing the effective configuration

Before you boot, you can print the exact configuration the app will mount: the dump shows the composed entry list with !!js expressions verbatim, grouped under comments naming each source file and the patch layers that changed it, as one loadable YAML document. Patches that match no row are reported with their layer label; a missing, unparsable, or invalid config fails the dump.

What you see when startup fails

Startup failure is a single labelled line plus a nonzero exit — never a silent hang or a raw stack dump. The message names the failing plugin; a plugin that threw keeps its original error, and an entry that never started is reported with the services it was waiting for.

If your app owns the terminal, it can hand the terminal back before the process exits, so your shell is never left in raw mode. The handoff is bounded: a stuck cleanup delays the fatal exit but never cancels it.

Telling the agent where the harness lives

When your app boots a model-backed agent, you can tell the agent where the DSH implementation checkout lives: it learns that path and that it must not infer the working directory from it — it should use pwd. The instruction appears once near the top of the system prompt. Apps without a system prompt service skip it; in development, reloading the system prompt drops it until the next boot.

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Understand the implementation

Implementation internals — click to expand

This section explains how the outcomes above are realized and points at the code that realizes them; everything here is developer-facing and not needed to use the package.

Design notes

• Channel-neutral library. The package carries no loader hooks and no dev-mode surface; the dsh app owns its Node source-launch hook and consumes these helpers for the boot sequence, and built consumers use plain Node package resolution.
• Two Loader builtins. mountRootInclude registers cordis:include and cordis:group as Loader builtins: a group row gives one isolate realm to a provider and its consumers together, and an agent preset outside this workspace cannot resolve @deepseek-ai/cordis-plugin-group by name. Both load through the ambient module pipeline rather than the included tree's own specifier resolution.
• Profile module fallback. Bare plugin specifiers resolve through the Loader from the config directory. Plain Node maintains one symlink per package in the installation dependency closure. A packaged executable instead reads each installed export map with Node ESM conditions and writes real proxy packages that re-export virtual module URLs, because an operating-system symlink cannot enter pkg's /snapshot tree. Missing exports stay unavailable, malformed maps fail startup, and a cross-process writer lock replaces stale entries without exposing partial proxies.
• One rejection checkpoint. assertEntriesActivated keeps the exact reasons it folds into the boot diagnostic visible through the next process rejection checkpoint, so installFailLoud coalesces Loader's duplicate notification while unrelated unhandled rejections remain fatal.
• Two-stage failure labels. boot() distinguishes host preparation failed — prepare threw before any config-tree entry mounted — from plugin tree failed to load, and appends the deepest plugin error's stack so the startup diagnostic preserves the original activation error instead of only the wrap chain.

Helper behavior

The exports each own one stage of the boot: config resolution and snapshot replay, layered environment loading, fail-loud reporting, activation auditing, patch parsing, root-include mounting, config dump rendering, live patch watching, profile composition, and the harness-source section. Per-export contracts live in the code, not this README — see src/index.ts and src/profile.ts.

Source map

File	Role
src/index.ts	Boot helpers: config resolution, environment loading, fail-loud guard, activation audit, patch parsing, config dump, harness-source section
src/profile.ts	Profile discovery, initialization, bundle resolution, module fallback
src/invariant.ts	Invariant companion (no runtime invariant; boundary and replay tests cover the protocol mapping)

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Further Exploration

Read these pages when the package-level contract is not enough. They move from the shared boot mechanics to the composition model and the decision evidence behind it.

• Cordis primer — Loader, !!js config expressions, and include/group semantics.
• dsh app — the dsh bin that consumes these helpers.
• dsh-cmdline — the launcher-to-app command-line handoff the bins use.
• Profile bundles — installable patch layers composed into dsh --profile.
• dsh-home-paths — the Harness-home resolver (resolveDshHome).
• Configuration source ownership — why a discovered file may not decide bootstrap behavior.
• Profile plugin bundles — the profile and bundle composition design.

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Model Experience

Indirectly, through the loaded plugin tree, which alone contributes model context; the one export that adds model-visible text, addHarnessSourceSection, does so only when a consumer calls it after boot.

KV Cache effect

Boot itself invalidates nothing in the request prefix. A consumer that calls addHarnessSourceSection places one short line near the system prompt's head, before per-request content, so it does not invalidate the cache across turns; any other request-prefix change is owned by the named consumer.

Known Limitations and Deferred Work

These limits describe when this boot library is a poor fit or needs special care. They are current package constraints, not a task backlog.

• Bare package specifiers depend on Loader internals — production bins need Loader's optional native helper; an in-process caller without it must use resolvable relative/file specifiers or provide its own module-resolution hook.
• Snapshot replay swapping is basename-specific — only a config ending in cordis.yml or cordis.yaml maps to the sibling cordis.snapshot.yml; custom config names require caller-managed selection.
• Environment discovery is launch-scoped — loadLayeredEnv reads only the invocation directory and Harness home once; it does not search parents or follow a workspace selected later. loadEnv remains the one-directory helper for non-product bins.
• A user patch replaces the whole matched config — an id-targeted patch does not deep-merge, so a profile override restates the bundle fields it keeps.

Dev Note

Working context for maintainers — click to expand

This Dev Note is working context for maintainers: open design questions and directions that are not decided. It is explicitly non-authoritative — shipped behavior, limits, and accepted rationale live in the sections above, the package code, and the linked Agent Notes.

Open: config dump stability

renderConfigDump output is a loadable YAML document whose # == provenance comments and !!js-verbatim rendering serve the --dump-config diagnostic. Nothing promises byte stability across package versions; decide whether the dump becomes a serialization contract before anything consumes it programmatically.