Application declarations

A plugin whose MCP server fronts a desktop application declares which application that is and what the server needs of it. The core evaluates the declaration on the host and gates the server’s tools, and any skill that names the application, on the answer. The parser imports only the standard library and mibyan_platform. The vocabulary lives in mibyan_platform/declaration.py. A declaration is data plus policy, parsed from plain mappings (already-decoded YAML, JSON, a dict literal — the parser never touches a file):

from mibyan_platform import declaration

decl = declaration.parse_declaration(
    "my-server",
    raw_app={"linux": {"presence": "executable", "location": "/opt/my-app/server"}},
    raw_requires={"app": True},
    where="my-plugin/plugin.yaml",   # human label used in error messages
)
declaration.register("my-server", decl)

register(server_name, decl) stores one declaration under the configured server name in a process-local registry. Loader integration is separate work; core does not read plugin YAML automatically. An unregistered MCP server keeps its connection-only check. A skill that explicitly names an unregistered server is hidden. clear() removes every registration and is not a per-plugin unload operation. Registrations are process-wide, not profile-scoped.

`app` — how to find the application on each OS

app:
  win32:
    presence: executable
    location: "%ProgramFiles%/Vendor/Vendor App/McpServer/Server.exe"
    version: { kind: uninstall_registry, display_name_prefix: "Vendor App" }
    liveness:
      kind: server_json
      path: "%LOCALAPPDATA%/Vendor/Vendor App/McpServer/server.json"
      pid_key: pid
      url_key: http
      token_key: token
      endpoint_path: /mcp
  darwin:
    presence: bundle
    location: /Applications/Vendor.app
    version: { kind: plist }

field	type	rule	maps to `AppDef`
`<os>`	`win32` \| `darwin` \| `linux`	at least one; unknown key is an error	`AppDef.os_family`
`presence`	`executable` \| `bundle`	required per OS	`.presence`
`location`	str	required; drive-rooted (`C:\\...`) on Windows, or starting with `~` / `%VAR%` / `$VAR`; UNC paths are rejected so a presence check never touches the network; no `..` segment or URL scheme; expansion at lookup	`.location`
`version.kind`	`pe_resource` \| `plist` \| `uninstall_registry` \| `none`	default `none`; `pe_resource`/`uninstall_registry` only under `win32`, `plist` only under `darwin`	`.version_kind`
`version.display_name_prefix`	str	required when `uninstall_registry`	`.version_arg`
`liveness.kind`	`server_json` \| `none`	default `none`	`.liveness_kind`
`liveness.path`	str	required when `server_json`	`.liveness_path`
`liveness.pid_key` / `url_key` / `token_key`	str	defaults `pid` / `http` / `token`	`.liveness_*_key`
`liveness.endpoint_path`	str	default `/mcp`; the path used for `initialize`, never the one in the file	`.endpoint_path`

When requires.app is true, an OS missing from app: gives unsupported_os.

`requires` — what the server needs before it is offered

requires:
  app: true
  min_version: "2.3.0"

field	type	rule
`app`	bool	when true, `app:` must exist and the server is gated on presence
`min_version`	str	requires `app: true`; dotted numeric; every applicable `app.<os>` must declare a real `version.kind`; compared numerically per segment, non-numeric characters in a segment are dropped (`2.3.0.12594` ≥ `2.3.0`; prerelease suffixes are not ordered)

requires.app: true with no app: block is a DeclarationError.

Availability: the one evaluation every reader uses

mibyan_platform/resolver/availability.py::availability(decl) -> Availability

Availability(
  state:   available | installed_not_running | missing_app | version_too_old
         | unsupported_os | no_requirements,
  version: str | None,       # inspected, when present
  path:    str | None,       # where the app was found or looked for
  min_version: str | None,   # from requires
)

no_requirements: no requires.app; the application gate passes, but the connection check still applies.
unsupported_os: requires.app and no app.<this os> block. Zero I/O.
missing_app: locate found nothing at location.
version_too_old: the version is below the minimum or cannot be read.
available: present, version acceptable or not required.
installed_not_running: reserved vocabulary; this evaluator never produces it.

Evaluation uses locate and optional version inspection. It never probes a server, launches an application, or connects. The tool registry retains its existing availability cache.

The two gates

MCP check_fn (tools/mcp_tool_handlers.py::_make_check_fn): connection alive AND, when a declaration with requires.app is registered for the server, availability(decl).offerable. Returns a plain bool because the registry caches bool(fn()).
Skill requires_apps: frontmatter (agent/skill_utils.py::skill_matches_apps): each name resolves through declaration.lookup; an unknown name hides the skill (fail closed). Offer-time filter, like environments:.

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Application declarations

`app` — how to find the application on each OS

`requires` — what the server needs before it is offered

Availability: the one evaluation every reader uses

The two gates

​app — how to find the application on each OS

​requires — what the server needs before it is offered

​Availability: the one evaluation every reader uses

​The two gates

`app` — how to find the application on each OS

`requires` — what the server needs before it is offered

Availability: the one evaluation every reader uses

The two gates