inspector/core/mcp/skillsSchemas.ts

/**
 * Skills extension wire schemas — SEP-2640 (`io.modelcontextprotocol/skills`).
 *
 * There is no `@modelcontextprotocol/ext-skills` package (404 on npm) and the
 * SDK's era codecs define none of these methods, so the Inspector drives them
 * as ordinary `client.request(…, ResultSchema)` calls with the explicit result
 * schemas below. That is exactly what the SDK prescribes for a consumer-owned
 * extension method: `Protocol._assertOutboundRequestInEra` only fires for names
 * one of the era codecs knows, so `skills/list` and `skills/get` are era-blind
 * and go out unchanged on both the 2025- and 2026-era legs. The raw-wire escape
 * hatch that modern `tasks/*` needs is deliberately NOT used here — `tasks/*`
 * are spec names the 2026 codec deleted, which is a different problem.
 *
 * **This module is the whole wire surface.** SEP-2640 is Accepted, so the method
 * names and the entry shape are settled, but the skill *format* is delegated to
 * the independently-versioned Agent Skills specification and the SEP leaves the
 * `skills/get` caching attributes (SEP-2549 `ttlMs` / `cacheScope`) open. Keeping
 * every wire type here makes a spec revision a single-file edit (#2234).
 *
 * Schemas are deliberately permissive (`looseObject`, and a `digest` typed as a
 * plain string rather than a hex-constrained one) so a non-conforming server is
 * *surfaced* rather than rejected — the Inspector is a conformance tool, and a
 * malformed digest is a finding to report, not a parse error to swallow. The
 * structural checks live in `skills.ts`.
 */

import { z } from "zod/v4";

/** SEP-2133 extension identifier for the Skills extension (SEP-2640). */
export const SKILLS_EXTENSION_KEY = "io.modelcontextprotocol/skills";

/** The `skills/list` JSON-RPC method name. */
export const SKILLS_LIST_METHOD = "skills/list";

/** The `skills/get` JSON-RPC method name. */
export const SKILLS_GET_METHOD = "skills/get";

/**
 * The `resources/directory/read` method name, gated on the server declaring
 * `directoryRead: true` in its extension advertisement. Declared here so the
 * one wire-surface module names every method the extension defines, even though
 * the Inspector does not call it yet (phase 3 of #2234).
 */
export const RESOURCES_DIRECTORY_READ_METHOD = "resources/directory/read";

/** `mimeType` marking a resource as a directory rather than a file. */
export const DIRECTORY_MIME_TYPE = "inode/directory";

/**
 * The literal `resources` value meaning "this skill's file set is generated and
 * cannot be enumerated". Integrity verification is impossible for such a skill,
 * which is why it is a reported finding rather than a silent absence.
 */
export const DYNAMIC_RESOURCES = "dynamic";

/**
 * The verbatim YAML frontmatter of a `SKILL.md`, expressed as JSON. `name` and
 * `description` are the two fields SEP-2640 requires; everything else the Agent
 * Skills format defines passes through untouched, since that format versions
 * independently of this extension.
 */
export const SkillFrontmatterSchema = z.looseObject({
  name: z.string().optional(),
  description: z.string().optional(),
});

export type SkillFrontmatter = z.infer<typeof SkillFrontmatterSchema>;

/**
 * One file in a skill's manifest. `digest` is `sha256:` + 64 lowercase hex per
 * the SEP, but it is typed as a bare string so a server that gets the format
 * wrong still parses and can be *reported* — see `checkSkillConformance`.
 */
export const SkillResourceSchema = z.looseObject({
  uri: z.string(),
  digest: z.string().optional(),
  size: z.number().optional(),
});

export type SkillResource = z.infer<typeof SkillResourceSchema>;

/**
 * A skill entry as returned by `skills/list` and `skills/get`. `resources` is
 * either the full file manifest or the literal `"dynamic"`; the union is
 * preserved on the type rather than normalized away, because which one a server
 * sent is itself the finding.
 */
export const SkillEntrySchema = z.looseObject({
  uri: z.string(),
  frontmatter: SkillFrontmatterSchema,
  resources: z.union([
    z.literal(DYNAMIC_RESOURCES),
    z.array(SkillResourceSchema),
  ]),
});

export type SkillEntry = z.infer<typeof SkillEntrySchema>;

/** `skills/list` result: a page of entries plus the opaque cursor. */
export const ListSkillsResultSchema = z.looseObject({
  skills: z.array(SkillEntrySchema),
  nextCursor: z.string().optional(),
});

export type ListSkillsResult = z.infer<typeof ListSkillsResultSchema>;

/**
 * The envelope form of a `skills/get` result: the entry wrapped under `skill`.
 */
const GetSkillEnvelopeSchema = z.looseObject({ skill: SkillEntrySchema });

/**
 * Collapse either accepted `skills/get` shape to the entry it carries.
 *
 * Written as a parse rather than an `in` check because both accepted shapes are
 * loose objects — they carry an index signature, so `"skill" in result` narrows
 * nothing and would leave the extracted value `unknown`. Parsing the envelope
 * is what proves its `skill` really is an entry, with no cast anywhere.
 */
export function normalizeGetSkillResult(result: unknown): SkillEntry {
  const enveloped = GetSkillEnvelopeSchema.safeParse(result);
  return enveloped.success
    ? enveloped.data.skill
    : SkillEntrySchema.parse(result);
}

/**
 * `skills/get` result, normalized to the entry.
 *
 * ⚠️ The SEP settles the *entry* shape but not the envelope this result wraps it
 * in, so both plausible forms are accepted: `{ skill: <entry> }` and the entry
 * returned inline at the top level. Being permissive here costs nothing (the
 * two are structurally distinguishable — an inline entry carries `uri` and
 * `frontmatter`, the envelope carries neither) and spares a server author a
 * failure whose cause is a spec ambiguity rather than their code. The transform
 * means every caller receives the entry and none of them branches.
 */
export const GetSkillResultSchema = z
  .union([GetSkillEnvelopeSchema, SkillEntrySchema])
  .transform(normalizeGetSkillResult);

export type GetSkillResult = SkillEntry;

/**
 * ⚠️ **No `resources/directory/read` result schema here yet, on purpose.**
 *
 * The method name and the directory MIME type above are stated in SEP-2640;
 * the shape of the result it returns is not something this PR verified against
 * the normative text, and the Inspector does not call the method (phase 3,
 * #2248). Declaring a guessed schema would put an unverified claim in the one
 * module that is supposed to be the authority on the wire format — and one
 * nothing exercises, so it could be wrong indefinitely without failing
 * anything. Phase 3 adds it against the spec, alongside the call that uses it.
 */