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feat: support the Skills extension (SEP-2640) with digest verification

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Adds detection, enumeration, and conformance checking for the Skills
extension (`io.modelcontextprotocol/skills`) — phases 1 and 2 of #2234,
which is everything its Acceptance list names.

Skills is a *server*-declared extension, read off the connecting server's
`capabilities.extensions`, so it is deliberately absent from
`ADVERTISABLE_EXTENSIONS` — that registry is what the Inspector advertises
and the user toggles, and an entry there would be a meaningless toggle.

`skills/list` and `skills/get` are consumer-owned extension methods that
neither era codec defines, so the SDK's era gate skips them and they go out
as ordinary `client.request` calls with explicit result schemas. The
raw-wire channel modern `tasks/*` needs is not used, and the Skills tab is
not era-gated: a legacy-era server that declares the extension is serving it.

The checks are the point, not the list view. `core/mcp/skills.ts` reports
each obligation SEP-2640 states — the name/path invariant, the digest
format, the 512-entry and 16 MiB limits, and `resources: "dynamic"`, which
means integrity cannot be verified at all. Digest verification hashes the
fetched bytes with WebCrypto and returns a mismatch with both digests
attached rather than throwing, because showing a mismatch loudly is the
whole value proposition.

Files are fetched on demand: SEP-2640 is explicit that a `resources/read`
of a `SKILL.md` is not a load and confers no standing, so none of the SEP's
host machinery is implemented.

The `skills-http` fixture serves four skills over two pages, three of them
deliberately non-conforming — without those the verification code is
untestable.

Phase 3 (CLI, TUI, `resources/directory/read`, paged mode) is #2248.

Closes #2234

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018kfrH3uRNUM4JAk1reKtyY
Signed-off-by: cliffhall <cliff@futurescale.com>
This commit is contained in:
cliffhall 2026-09-04 20:01:13 -04:00
commit 63623b754b
1 changed files with 3684 additions and 4 deletions
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31
test-servers/src/composable-test-server.ts
View file

@ -49,6 +49,7 @@ import {
createModernTaskTools,
wireModernTaskHandlers,
} from "./modern-tasks.js";
import { SKILLS_EXTENSION_KEY, wireSkillsHandlers } from "./skills.js";
/**
* MCP Apps extension id. Hardcoded for the same reason the Inspector's
@ -556,6 +557,12 @@ export interface ServerConfig {
* `modern: true`. See `modern-tasks.ts`.
*/
tasksExtension?: boolean;
/**
* Advertise the Skills extension (SEP-2640) and serve `skills/list` /
* `skills/get` plus the `skill://` files those entries name. The fixture set
* deliberately includes non-conforming skills — see `skills.ts`.
*/
skills?: { directoryRead?: boolean };
/**
* Advertise the MCP Apps `io.modelcontextprotocol/ui` extension with the
* nested `elicitation` setting — the server-side half of the app-rendered
@ -824,6 +831,23 @@ export function createMcpServer(config: ServerConfig): McpServer {
};
}
// Skills extension (SEP-2640): a server-declared extension, advertised with
// its one sub-option. `directoryRead` is opt-in per config so a client can be
// exercised against both a server that offers `resources/directory/read` and
// one that does not.
if (config.skills) {
capabilities.extensions = {
...(capabilities.extensions ?? {}),
[SKILLS_EXTENSION_KEY]: {
...(config.skills.directoryRead ? { directoryRead: true } : {}),
},
};
// Skill files are fetched through ordinary `resources/read`, so the
// resources capability has to be advertised even when the config registers
// no ordinary resources of its own.
capabilities.resources = capabilities.resources ?? {};
}
// MCP Apps app-rendered elicitation (#1854): the server-side half of the
// negotiation, on the same extension the Apps work already uses.
if (config.appElicitation) {
@ -1503,6 +1527,13 @@ export function createMcpServer(config: ServerConfig): McpServer {
wireModernTaskHandlers(mcpServer, modernTaskRuntime);
}
// Skills extension (SEP-2640): raw skills/list + skills/get, and the
// `skill://` half of resources/read. Wired after the SDK's own handlers so
// the resources/read wrapper can delegate non-skill URIs to them.
if (config.skills) {
wireSkillsHandlers(mcpServer);
}
// Extension-gated tools (#1739): start each gated tool disabled, then enable
// it on `initialized` iff the connected client declared its extension.
if (config.extensionGatedTools) {