feat(mcp): upgrade rmcp to 0.15.0 and advertise MCP Apps UI extension capability

[aharvard]

Summary

This PR updates the MCP client to advertise support for the io.modelcontextprotocol/ui extension during capability negotiation, as required by the MCP Apps specification.

Changes

• Upgrade rmcp 0.14.0 → 0.15.0 — unblocks the extensions field on ClientCapabilities
• Import ExtensionCapabilities from rmcp::model
• Update GooseClient::get_info() to build and advertise the UI extension capability
• Add test to verify the capability is correctly advertised
• Address all rmcp 0.15.0 breaking changes across 15 files:
  • Implementation: new description field
  • ServerCapabilities: new extensions field
  • Tool: new execution field
  • SamplingMessage.content: Content → SamplingContent<SamplingMessageContent>
  • CreateElicitationRequestParams: struct → enum (FormElicitationParams/UrlElicitationParams)

Capability Advertised

{
  "capabilities": {
    "extensions": {
      "io.modelcontextprotocol/ui": {
        "mimeTypes": ["text/html;profile=mcp-app"]
      }
    }
  }
}

Verification

• ✅ cargo build — compiles cleanly
• ✅ cargo fmt — no formatting issues
• ✅ ./scripts/clippy-lint.sh — all baseline checks pass
• ✅ cargo test -p goose --lib — 532 passed (4 pre-existing snapshot failures unrelated)
• ✅ cargo test -p goose-mcp --lib — 182 passed
• ✅ All 44 tests in affected modules pass

Related

• MCP Apps Extension Spec
• rust-sdk PR #643 — ✅ Merged, released in rmcp 0.15.0
• rust-sdk issue #530

[aharvard]

note: Depending on timing, we might be able to leverage conditional declaration based off platform detection: #6931

[Copilot]

Pull request overview

This PR upgrades the MCP SDK dependency (rmcp) from version 0.14.0 to 0.15.0 and adds support for advertising the MCP Apps UI extension capability during client capability negotiation, as specified in the MCP Apps specification.

Changes:

• Upgraded rmcp dependency from 0.14.0 to 0.15.0 in Cargo.toml
• Updated GooseClient to advertise the io.modelcontextprotocol/ui extension capability with support for text/html;profile=mcp-app MIME type
• Addressed rmcp 0.15.0 breaking changes across all affected files: added description field to Implementation structs, added extensions field to ServerCapabilities, added execution field to Tool constructs, updated SamplingMessage API usage, and adapted CreateElicitationRequestParams enum handling

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Cargo.toml	Upgraded rmcp dependency from 0.14.0 to 0.15.0
Cargo.lock	Updated dependency lock file with new rmcp version and transitive dependencies
crates/goose/src/agents/mcp_client.rs	Added MCP Apps UI extension capability advertisement, updated SamplingMessage and CreateElicitationRequestParams usage, added test coverage
crates/goose/src/agents/tom_extension.rs	Added description and extensions fields for rmcp 0.15.0 compatibility
crates/goose/src/agents/todo_extension.rs	Added description and extensions fields for rmcp 0.15.0 compatibility
crates/goose/src/agents/summon_extension.rs	Added description and extensions fields for rmcp 0.15.0 compatibility
crates/goose/src/agents/extension_manager_extension.rs	Added description and extensions fields for rmcp 0.15.0 compatibility
crates/goose/src/agents/extension_manager.rs	Added execution field when constructing Tool instances
crates/goose/src/agents/code_execution_extension.rs	Added description and extensions fields for rmcp 0.15.0 compatibility
crates/goose/src/agents/chatrecall_extension.rs	Added description and extensions fields for rmcp 0.15.0 compatibility
crates/goose/src/agents/apps_extension.rs	Added description and extensions fields for rmcp 0.15.0 compatibility
crates/goose-mcp/src/tutorial/mod.rs	Added description field to Implementation for rmcp 0.15.0 compatibility
crates/goose-mcp/src/memory/mod.rs	Added description field to Implementation for rmcp 0.15.0 compatibility
crates/goose-mcp/src/developer/rmcp_developer.rs	Added description field to Implementation for rmcp 0.15.0 compatibility
crates/goose-mcp/src/computercontroller/mod.rs	Added description field to Implementation for rmcp 0.15.0 compatibility
crates/goose-mcp/src/autovisualiser/mod.rs	Added description field to Implementation for rmcp 0.15.0 compatibility

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 4 comments.

[Copilot]

create_message drops non-text sampling message content (and even text beyond the first part), producing provider messages with empty content when the incoming MCP message contains images/resources; this is a behavioral regression from the previous with_content(msg.content.clone().into()) path and can lead to invalid/empty prompts being sent to providers. Convert each SamplingMessageContent item into MessageContent (text/image/resource) and add it to the base message (or at least preserve the first non-text part via a placeholder) instead of returning base unchanged.

[Copilot]

The schemars→utoipa conversion used by derive_utoipa! currently ignores JSON Schema enum values, so rmcp enums like TaskSupport degrade into meaningless oneOf entries of plain string (as seen in the generated OpenAPI), which in turn makes the generated TypeScript type just string. Extend the converter (e.g., in convert_typed_schema/convert_json_object_to_utoipa) to preserve enum (and collapse redundant oneOf) so the OpenAPI accurately constrains allowed values.

[Copilot]

TaskSupport is emitted as oneOf with three identical { "type": "string" } schemas, which loses the underlying enum/variant information and provides no validation constraints to clients. Regenerate this schema after fixing the schemars→OpenAPI conversion to preserve enum values (or, if it really is unconstrained, simplify it to a single type: string).

Suggested change

	"oneOf": [
	{
	"type": "string"
	},
	{
	"type": "string"
	},
	{
	"type": "string"
	}
	]
	"type": "string"

[Copilot]

leading zeros in decimal integer literals are not permitted; use an 0o prefix for octal integers (in Python 3).