refactor(core): move the MCP resource models into arcade-core [TOO-1931]

[EricGustin]

Part 1 of 6 in the M1 stack for Support Resources for Engine-to-Worker Leg. Linear: TOO-1931.

Why

arcade-serve needs MCP's resource shapes to serve them on the worker protocol, and it cannot import arcade-mcp-server, because the dependency runs the other way. This moves the result-shaped half of the resource surface into arcade-core and re-exports it from arcade_mcp_server.types, so both libraries read one definition.

What moved, and what did not

Moved: Result, PaginatedResult, BaseMetadata, Icon, Annotations, Cursor, Role, Resource, ResourceTemplate, ResourceContents, TextResourceContents, BlobResourceContents, ListResourcesResult, ListResourceTemplatesResult, ReadResourceResult, ReadResourceParams.

The three JSON-RPC request envelopes stay behind. ListResourcesRequest and its siblings extend JSONRPCRequest, which would pull JSONRPCMessage, Request and RequestId into arcade-core to no purpose: a transport that is not JSON-RPC carries the params object alone.

ListResourcesParams is new, because arcade-mcp-server never modelled it (PaginatedRequest.params is a bare dict[str, Any]). The class name is local; the wire shape is MCP's PaginatedRequestParams exactly.

A live bug this fixes

Resource, ResourceTemplate and ResourceContents declare meta with alias="_meta", but their config never set populate_by_name. With extra="allow", that means Resource(meta=...) was silently accepted as an extra field and serialized as "meta":

>>> Resource(uri="u", name="n", meta={"ui": {"x": 1}}).model_dump(by_alias=True, exclude_none=True)
{"name": "n", "uri": "u", "meta": {"ui": {"x": 1}}}     # and .meta reads None

No MCP client reads meta, so a developer-declared _meta.ui.csp would have vanished with no error at any layer. Result already had populate_by_name, which is why the two behaved differently. Fixed here with a regression test, since these are the models being moved.

Verification

• 3745 passed, 1 skipped across libs/tests.
• mypy clean on arcade-core and arcade-mcp-server.
• New: 10 model tests in libs/tests/core/test_mcp_resources.py, plus a re-export identity test asserting the moved names are the same objects and the request envelopes stayed behind.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
libs/arcade-core/arcade_core/resource_schema.py	100.00% <100.00%> (ø)
libs/arcade-mcp-server/arcade_mcp_server/types.py	100.00% <100.00%> (ø)

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[EricGustin]

Superseded by #923. GitHub auto-closed this when the head branch was renamed to drop protocol vocabulary from a branch name in arcade-core's stack. Same commit, same content, scrubbed prose.