Add structured content to the Go weather server and client and update to latest SDK and protocol version

[olaservo]

Brings the Go examples onto go-sdk v1.7.0 and protocol revision 2026-07-28, and gives both tools a declared OutputSchema with matching StructuredContent.

get_alerts returns []Alert, so it answers with a top-level JSON array:

[
  { "event": "Flood Warning", "area": "La Salle County", ... },
  { "event": "Heat Advisory",  "area": "Wheeler County",  ... }
]

Through 2025-11-25 an OutputSchema 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.

Non-object output schema support (SEP-2106) landed after v1.6.1; v1.7.0 is the first stable release carrying it.

Schema declaration, and where it is left to inference

get_forecast sets no OutputSchema on the Tool — the SDK infers one from the handler's return type, which is the idiomatic Go spelling and worth showing.

get_alerts overrides it. jsonschema-go infers ["null","array"] for a slice because a nil slice marshals to null, and the handler always builds one, so the override narrows the root to "array". Re-checked against v1.7.0: rebuilding with the override removed still yields the nullable form, so it is still required.

Three structural fixes

Two build artefacts were committed by mistake in the first commit of this branch — mcp-client-go.exe and weather-server-go/weather.exe, about 14MB of binaries. Removed here; the ignore rules that keep them out come with #163, which is also what builds weather-server-go/server.

Forecast periods now have their own type. Forecast.Periods reused ForecastPeriod, the struct that decodes the NWS response, so its camelCase json tags leaked into the declared schema — temperatureUnit and detailedForecast where the other four quickstarts publish temperature_unit and detailed_forecast. Splitting out a Period output type follows what this file already does with Alert and AlertProperties: the shape NWS sends and the shape the tool publishes are different contracts. All five examples now advertise identical shapes.

The deprecated logging capability is no longer advertised. With a nil ServerOptions the SDK defaults ServerCapabilities to {"logging":{}} — "for historical reasons", per its own doc comment. This server does no logging, and logging is deprecated as of 2026-07-28 (SEP-2577), so an example for that revision should not claim it. Passing an empty Capabilities suppresses the default; tools is still inferred from the registered tools.

Other changes

Error paths return an error. A tool declaring an OutputSchema MUST return conforming structured content, so a path with no data has to fail rather than answer with a bare text result.

The client validates. It compiles every declared OutputSchema at connect time and checks results against it — the spec's client-side SHOULD. jsonschema-go is already an SDK dependency, so this adds none.

Each channel goes to its stated reader. Content is forwarded to the model; StructuredContent is used as data, reporting how many items came back.

A missing .env is no longer fatal, and ANTHROPIC_API_KEY is checked after connecting rather than before, matching the Python and TypeScript clients. That is what lets the connection be exercised without credentials.

Model identifier moves to claude-sonnet-5. The second call in the tool loop used a hardcoded ModelClaude3_7SonnetLatest while the first used the package variable; both now use the same one.

One caveat

The SDK sends an array-rooted schema as written on every connection rather than projecting it down the way the TypeScript SDK does, so a 2025-11-25 client rejects the tool list:

Invalid result for tools/list: path ["tools", 0, "outputSchema", "type"], expected "object"

Use an object root if you need to serve both eras. The README says so.

Verification

Captured off the raw wire — a real get_alerts("TX") call against live NWS data, no SDK on the client side:

server/discover -> OK, versions=["2026-07-28", ...]
                   capabilities={"tools":{"listChanged":true}}
tools/list      -> get_alerts outputSchema.type = "array"

tools/call:
  resultType: "complete"
  ttlMs: 0, cacheScope: "public"
  structuredContent: ARRAY (8 items)
  content: 2 block(s)

Two blocks because the SDK appends the serialised JSON as a backwards-compatibility fallback alongside the tool's own prose.

Related

One of a set bringing the examples onto 2026-07-28, one PR per language so the four can be compared: #164 (Python), #165 (TypeScript), #166 (Go), #167 (Rust). #163 is the shared prerequisite.

CI here is green, but on main the smoke test does not cover the Go examples at all — nothing in this diff is exercised by it, so until #163 lands this PR is verified by the raw-wire capture above rather than by CI. #163 adds the Go server to the suite and installs the Go toolchain, after which this diff is covered.

The Ruby examples are not in the set. The mcp gem 1.1.0 does now negotiate 2026-07-28, but its server never emits the resultType field that the revision makes mandatory, so a spec-strict client rejects every response including tools/list. That is an upstream fix, not something an example can work around.

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[Copilot]

Pull request overview

Updates the Go weather server and Go MCP client examples to support MCP protocol revision 2026-07-28, adding structured tool outputs and aligning dependencies with the latest Go SDK prerelease needed for non-object output schemas.

Changes:

• Weather server tools now return structured outputs (get_forecast as an object, get_alerts as a top-level JSON array) and convert prior “no data” paths into tool errors.
• Go client compiles/validates each tool’s declared outputSchema at connect time and uses StructuredContent as application data while forwarding Content to the model.
• Dependency updates to github.com/modelcontextprotocol/go-sdk v1.7.0-pre.3 and github.com/google/jsonschema-go v0.4.3.

Reviewed changes

Copilot reviewed 6 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
weather-server-go/README.md	Documents structured output behavior and protocol/client caveat for array-rooted schemas.
weather-server-go/main.go	Adds structured output types, error-on-failure behavior, and explicit array-root schema override for get_alerts.
weather-server-go/go.mod	Bumps Go SDK and pins jsonschema-go directly.
weather-server-go/go.sum	Updates dependency checksums for bumped modules.
mcp-client-go/README.md	Documents client-side schema compilation/validation and channel handling.
mcp-client-go/main.go	Adds output schema compilation + result validation and separates model-facing Content from app-facing StructuredContent.
mcp-client-go/go.mod	Bumps Go SDK and jsonschema-go versions.
mcp-client-go/go.sum	Updates dependency checksums for bumped modules.

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