test(ra_e2e): MCP resources (list_resources, read_resource, subscribe/unsubscribe) have no e2e coverage

[bug-ops]

Description

PR #124 added MCP resources support (LSP diagnostics exposed as MCP resources via lsp-diagnostics:// URIs). The McpClient test helper and the ra_e2e_suite do not exercise any of the four resource operations: list_resources, read_resource, subscribe, unsubscribe.

This means the entire resources feature path — `server.rs:list_resources`, `server.rs:read_resource`, `bridge/resources.rs`, push notification on diagnostics change — has no end-to-end test coverage.

Reproduction Steps

1. Inspect crates/mcpls-core/tests/e2e/mcp_client.rs — no list_resources or read_resource methods exist.
2. Search tests/ra_e2e.rs for "resources" — no hits.
3. Run cargo test --workspace --all-features --test ra_e2e -- --ignored — passes but never exercises resources.

Expected Behavior

ra_e2e_suite should include sub-cases that:

1. Call list_resources after opening a file and verify lsp-diagnostics:// URIs are returned.
2. Call read_resource with a valid URI and verify diagnostic content is returned.
3. Call subscribe and unsubscribe and verify no errors.

McpClient should grow list_resources() and read_resource(uri) helper methods.

Actual Behavior

None of the above is exercised. A bug in list_resources, read_resource, or the subscription pipeline would go undetected by the test suite.

Environment

• Version: HEAD 0f40608
• Features: all-features

Logs / Evidence

grep -n "list_resources\|read_resource" crates/mcpls-core/tests/e2e/mcp_client.rs → empty
grep -n "resources" crates/mcpls-core/tests/ra_e2e.rs → empty