docs(discovery): rename Catalog Entry mediaType field to type (ADR 0014) (#32)

## What

Adapts the **MCP Catalog Entry** in `docs/discovery.md` to [AI Catalog
PR #37](https://github.com/Agent-Card/ai-catalog/pull/37) / ADR 0014,
which renames the `CatalogEntry.mediaType` member to **`type`** and
reframes its description as an open-text *type identifier* rather than a
strict IANA media type.

Changes (docs-only, `docs/discovery.md`):

- Renames the `mediaType` member to `type` in the Catalog Entry table.
- Updates the member description to mirror ADR 0014: "An identifier
specifying the type of the referenced artifact."
- Updates the `type` key in all four example catalog entries.
- Updates the client-validation prose (`type` set to … / "ignore entries
with unrecognized types").

## Rebase / conflict resolution

This branch was rebased onto the current `main` to resolve a merge
conflict in `docs/discovery.md`. The conflict came from changes that
landed on `main` after this branch was cut:

- **#31** — `urn:air:` identifier adaptation (ADR 0015). **Preserved.**
- **#39 / #14** — removal of the `displayName` field from MCP Catalog
entries. **Preserved** — this PR does **not** reintroduce `displayName`;
it only renames the field `mediaType` → `type` on top of main's current
structure.

The resolved diff is exactly the `mediaType` → `type` rename (table row,
four examples, validation prose) applied on top of main — nothing from
either side's intent was dropped.

## Scope decision — value deliberately kept as
`application/mcp-server-card+json`

This PR renames the **field only**. The value stays
`application/mcp-server-card+json` and is **not** changed to ADR 0014's
known-type `application/mcp-server+json`. Rationale:

- ADR 0014 explicitly makes `type` an **open-text** format ("any string
value is accepted"); `application/mcp-server+json` is a non-binding
"known type," and ecosystem types are "governed externally" (i.e., by
MCP). So keeping a more precise MCP-governed value is compatible with
ADR 0014, not a contradiction.
- This repo **deliberately** chose `application/mcp-server-card+json`
over `application/mcp-server+json` (issue #9 / PR #18) to avoid
colliding with the MCP Registry's `server.json` concept — a distinction
the README documents in "Relationship to the MCP Registry."

**Flag for maintainers:** AI Catalog's ADR 0014 known-types list uses
`application/mcp-server+json` for MCP. Whether this repo should also
adopt that value (reversing issue #9 / PR #18 and re-introducing the
`server.json` naming collision) is a separate, more consequential
decision and is intentionally **out of scope** here. Happy to file a
cross-repo issue if maintainers want to pursue it.

## What is intentionally NOT changed

- The **Server Card document's own HTTP media type** (`Accept` /
`Content-Type` negotiation, the reserved `/server-card` location prose).
That is a genuine IANA media type, not the renamed catalog field, and
ADR 0014 does not touch it.
- `schema.ts` / `schema.json` — the Server Card schema has no
`mediaType`/`type` member; this convention lives only in the discovery
doc.

## Verification

- [x] Rebased onto latest `main`; merge conflict in `docs/discovery.md`
resolved, preserving both #31 (`urn:air:`) and #39 (`displayName`
removal). PR now reports `MERGEABLE`.
- [x] `npm run check` — `schema.json` up to date, `tsc --noEmit` clean
- [x] `npm run validate` — all 7 examples pass
- [x] `npm run format:check` — `docs/discovery.md` clean, including
markdown table re-alignment
- [x] Verified zero `mediaType` field tokens remain (`git grep
mediaType` → no matches)
- [x] Verified the Server Card HTTP media-type prose was left intact (no
over-reach)
- [x] **CI green** — `build`, `Analyze (actions)`, and `CodeQL` all pass
on the rebased head
([run](https://github.com/modelcontextprotocol/experimental-ext-server-card/actions/runs/29278815978))
- [x] Independent fresh-eyes subagent review: **APPROVE** (rename
complete & correct; no `displayName` reintroduced; value unchanged;
Server Card media-type prose intact; no stray `mediaType`; no conflict
markers)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: tadasant <bob@tadasant.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/discovery.md

@@ -50,11 +50,11 @@ An MCP Catalog document is a JSON object that MUST contain the following members
 
 Each entry in the `entries` array describes a single MCP server and MUST contain:
 
-| Member       | Type   | Required | Description                                                                           |
+| Member       | Type   | Required | Description                                                                                              |
-| :----------- | :----- | :------- | :------------------------------------------------------------------------------------ |
+| :----------- | :----- | :------- | :------------------------------------------------------------------------------------------------------- |
-| `identifier` | string | Yes      | A logical discovery URN for this server (e.g., `urn:air:example.com:weather`)         |
+| `identifier` | string | Yes      | A logical discovery URN for this server (e.g., `urn:air:example.com:weather`)                            |
-| `mediaType`  | string | Yes      | The media type of the referenced artifact. MUST be `application/mcp-server-card+json` |
+| `type`       | string | Yes      | An identifier specifying the type of the referenced artifact. MUST be `application/mcp-server-card+json` |
-| `url`        | string | Yes      | URL where the full [Server Card](#mcp-server-cards) can be retrieved                  |
+| `url`        | string | Yes      | URL where the full [Server Card](#mcp-server-cards) can be retrieved                                     |
 
 An MCP Catalog entry carries no human-readable-name field. Every entry references a
 [Server Card](#mcp-server-cards), and the Server Card's `title` is the source of truth for
@@ -100,7 +100,7 @@ A domain hosting a single MCP server:
   "entries": [
     {
       "identifier": "urn:air:example.com:weather",
-      "mediaType": "application/mcp-server-card+json",
+      "type": "application/mcp-server-card+json",
       "url": "https://example.com/mcp/server-card"
     }
   ]
@@ -117,17 +117,17 @@ A domain hosting several MCP servers, each with its own server card:
   "entries": [
     {
       "identifier": "urn:air:acme.com:code-review",
-      "mediaType": "application/mcp-server-card+json",
+      "type": "application/mcp-server-card+json",
       "url": "https://acme.com/code-review/server-card"
     },
     {
       "identifier": "urn:air:acme.com:docs-search",
-      "mediaType": "application/mcp-server-card+json",
+      "type": "application/mcp-server-card+json",
       "url": "https://acme.com/docs-search/server-card"
     },
     {
       "identifier": "urn:air:acme.com:ci-cd",
-      "mediaType": "application/mcp-server-card+json",
+      "type": "application/mcp-server-card+json",
       "url": "https://acme.com/ci-cd/server-card"
     }
   ]
@@ -155,8 +155,8 @@ flowchart TD
    [Server Card Location](#server-card-location))
 4. Use the server card metadata to configure and establish an MCP connection
 
-Clients SHOULD validate that each entry has `mediaType` set to `application/mcp-server-card+json`
+Clients SHOULD validate that each entry has `type` set to `application/mcp-server-card+json`
-and ignore entries with unrecognized media types.
+and ignore entries with unrecognized types.
 
 ## MCP Server Cards