Add structured content to the Rust weather server and client and update to v3

[olaservo]

Updates the Rust examples to rmcp 3.1 (lockfiles at 3.1.2) and protocol revision 2026-07-28, and gives both tools a declared output_schema with matching structured_content.

get_alerts declares Vec<Alert>, so it answers with a top-level JSON array. Before 2026-07-28 an output schema had to be object-rooted, so a tool returning a list had to invent a key to hang it off. get_forecast returns an object, for contrast.

This supersedes #143, which bumped rmcp 0.3 → 1.4 and failed CI because the 0.3 #[tool] macro API doesn't survive the jump. The rewrite was required either way, so the bump is folded in and taken to 3.1.

An rmcp bug this PR found, now fixed upstream

For most of this PR's life list_tools was hand-written here, purely because #[tool_handler] generated one hardcoding ttl_ms: None, cache_scope: None — both required on a paginated result at 2026-07-28 (SEP-2549), so a strict client rejected the response outright.

Filed as rust-sdk#1114, fixed by #1120, released in rmcp 3.1.1. The override is gone and the server is back on the plain #[tool_handler] path. That's why the lockfiles are at 3.1.2 — anyone pinned below 3.1.1 still needs the workaround.

get_info also now sets server_info: ServerInfo::default() reports rmcp's own crate name, so the server was identifying itself as rmcp/3.1.0 instead of weather/1.0.0 like the other four.

Also

• Error paths return a tool-level error — a tool declaring an output_schema MUST return conforming structured content.
• The client compiles every declared schema at connect and validates results (the spec's client-side SHOULD). rmcp doesn't do this and its docs point at the jsonschema crate, which is the one new dependency here.
• content goes to the model, structured_content is used as data.
• A missing .env is no longer fatal, and the key is checked after connecting — matching Python and TypeScript.
• Model identifier moves to claude-sonnet-5, replacing an identifier past end of life.

One caveat

rmcp sends an array-rooted schema as written rather than projecting it down the way TypeScript does, so a 2025-11-25 client rejects the tool list. Use an object root if you need to serve both eras. The README says so.

Verification

A real get_alerts("TX") call against live NWS, captured off the raw wire with no SDK on the client side: outputSchema.type = "array", resultType: "complete", ttlMs: 0 and cacheScope: "public" (emitted by the macro — nothing here sets them), structuredContent an 8-item array, content one block of prose. server/discover returns versions through 2026-07-28 and serverInfo weather/1.0.0.

If you probe server/discover by hand, it must carry the _meta keys the revision requires (io.modelcontextprotocol/protocolVersion and io.modelcontextprotocol/clientCapabilities) — without them rmcp's stdio server answers nothing at all, which is rust-sdk#1157, not anything about this example.

One of a set, one PR per language: #164 (Python, merged), #165 (TypeScript), #166 (Go), #167 (Rust); #163 was the shared test prerequisite and has merged. Ruby is not in the set — the mcp gem never emits the mandatory resultType, so a spec-strict client rejects every response. That needs an upstream fix.

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[Copilot]

Pull request overview

Updates the Rust MCP weather examples (server + client) to rmcp 3.0.0-beta.2 and the 2026-07-28 protocol semantics by declaring tool output_schema and returning matching structured_content (including an array-rooted schema for get_alerts), with the Rust client additionally compiling and validating each declared output schema at connect time.

Changes:

• Weather server: add explicit structured output types (Alert, Forecast) and return dual-channel tool results (content + structured_content) with declared output_schema.
• Weather server: implement a custom list_tools to include required pagination metadata fields (ttl_ms, cache_scope) for the newer revision expectations.
• Rust client: compile each tool’s declared outputSchema using jsonschema and validate non-error tool results; make .env optional and check ANTHROPIC_API_KEY after connecting.

Reviewed changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
weather-server-rust/src/main.rs	Adds structured output types, dual-channel tool results, output schemas, and a custom list_tools; updates transport usage.
weather-server-rust/README.md	Documents structured output behavior and the array-rooted schema caveat for older clients.
weather-server-rust/Cargo.toml	Bumps rmcp to 3.0.0-beta.2 (and retains required deps for new code paths).
weather-server-rust/Cargo.lock	Lockfile updates for the rmcp upgrade.
mcp-client-rust/src/main.rs	Adds output-schema compilation + validation, routes content vs structured_content, and makes .env optional with deferred API-key checking.
mcp-client-rust/README.md	Documents the client’s structured output validation behavior.
mcp-client-rust/Cargo.toml	Adds jsonschema and bumps rmcp to 3.0.0-beta.2.
mcp-client-rust/Cargo.lock	Lockfile updates for the rmcp upgrade and new dependency.

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[olaservo]

The self is load-bearing, so this one stays as written.

schemars' derive macro expands to schemars::-qualified paths, so the module name has to be in scope wherever #[derive(JsonSchema)] is used — which is five types in this file. Importing JsonSchema alone brings the trait but not the path root.

Tested rather than argued: rewriting the import as schemars::JsonSchema and rebuilding gives 20 errors, all error[E0433]: cannot find module or crate \schemars` in this scope, one per derive site. cargo buildon the file as it stands is clean with no unused-import warning, which is the compiler agreeing thatself` is used.