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Plugins

A plugin in install.yaml/manifest.json is one of two kinds:

Embedded

Its full code sits inside plugins/<id>/ in the artifact, tarred/encrypted with everything else.

  • PluginRef.sha256 is required and is the hash the agent re-verifies post-extraction.
  • This is the default — simplest, self-contained, no extra network calls at deploy time.

Source-based

plugin.yaml declares a source: {url, ref, subdirectory} block (typically handed out by a marketplace/registry as a resolvable link).

  • Only non-code metadata (plugin.yaml, .env.template) ships in the artifact; the actual code is fetched from url at ref via git during the pipeline's resolve_plugins stage, merged onto that metadata.
  • PluginRef.sha256 is optional here — the packer doesn't fetch external repos at build time, so it has nothing to hash unless pinned out of band.

Use a commit SHA for ref, not a branch or tag

Only a SHA is content-addressed, so it's the only form that makes a pinned sha256 (or the absence of one) mean something — a mutable branch can change without the manifest ever noticing.

Resolution mechanism

PluginResolver (plugin_resolver.py) fetches via:

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git init + fetch --depth 1 <ref> + checkout FETCH_HEAD

This works for a branch, tag, or commit SHA alike (unlike git clone --branch, which can't target an arbitrary commit). Public and private repos are the same operation with different auth, exactly like using git from a shell:

  • SSH (git@host:org/repo.git) — authenticates via the host's own SSH agent/config; xcore-agent does nothing special.
  • HTTPS — authenticates via a per-host token from --git-token HOST=TOKEN (repeatable, on deploy/watch), spliced into the URL as https://x-access-token:<token>@host/.... No token configured for that host just means the URL is used as-is (fine for a public repo).

Plugins vs. extensions

Plugin Extension (service)
Install target plugins/<id>/ (Layout.plugin_dir) extensions/<id>/ (Layout.extension_dir)
Metadata plugin.yaml none
execution_mode: trusted signing Supported (--plugin-secret-key) Not applicable
Marketplace kind --kind plugin --kind service

A plugin and an extension may legitimately share an id — they install to different target directories — which is why scaffolded step ids distinguish them (install_<id> vs install_ext_<id>).

Environment files

A plugin may declare an optional environment: block in plugin.yaml. The write_env action (or --env-template at scaffold time) writes the required variables to the plugin's env file and validates them before the plugin is started. Missing required variables → a clear InstallError, not a silent no-op.