[htcom-code]

Fixes #89, Fixes #90

What

#90 — coded tool errors no longer put their problem detail in structuredContent.
A stable-code error (McpToolResult.error(ErrorCode, …)) now carries its RFC 9457 problem in the result
_meta under org.htcom.protean/problem (new constant McpToolResult.PROBLEM_META_KEY), merged with any
_meta the tool attached. structuredContent carries only what the tool itself returns.

#89 — protean.list_runtimes declares runtimes[].scope as ["string","null"].

Why

• The MCP spec (2025-11-25 and 2026-07-28) says that when an outputSchema is declared, "Servers MUST provide
  structured results that conform to this schema" — with no exemption for isError results. The problem
  object never matches a tool's success schema, so every built-in tool that declares an outputSchema was
  emitting non-conforming error results (e.g. scope_list with auto-provision off, patch_module on an
  unknown module).
• This is not theoretical for a library that cannot choose its clients: @modelcontextprotocol/sdk 1.32.2
  (TypeScript SDK 1.x) validates structuredContent whenever it is present, regardless of isError, and
  replaces the actionable error with Structured content does not match the tool's output schema.
  (@modelcontextprotocol/client 2.x and the Python SDK skip validation on errors.)
• list_runtimes returns scope: null whenever auto-provision is off (the default), so every default-install
  result violated its schema, and with protean.mcp.strict-schema=true the call failed outright with
  OUTPUT_SCHEMA_VIOLATION.

Compatibility

Wire change for MCP clients: read an error's stable code from _meta["org.htcom.protean/problem"].code
instead of structuredContent.code. The [CODE]-prefixed text content, success results, and JSON-RPC
protocol errors (error.data) are unchanged. The Java API only gains a constant. Recorded under
Changed in CHANGELOG.md / CHANGELOG.ko.md.

Tests

• New McpOutputSchemaConformanceTest.error_results_never_carry_a_nonconforming_structured_content sweeps
  every tool that declares an outputSchema with error-provoking arguments and asserts no non-conforming
  structuredContent plus a coded problem in _meta. A floor (named tools + ≥10 exercised) keeps it from
  passing vacuously — missing-argument calls are JSON-RPC protocol errors, not tool results, so they
  exercise nothing.
• New: strict-mode list_runtimes with a null scope; gated scope_list reports STATE_CONFLICT in _meta;
  list_runtimes added to the real-output conformance check; tool _meta + problem merge (tool's object
  not mutated).
• Nine existing error assertions moved from structuredContent to _meta.
• Transport level: McpHttpControllerTest.coded_tool_error_over_http_carries_its_problem_in_meta POSTs
  scope_list to /platform/mcp and asserts the wire shape (_meta problem, no structuredContent) — the
  dispatcher-level tests above never touched the HTTP serialization. Fails against main's dispatcher.
• Red check: reverting only McpDispatcher and ListRuntimesTool makes all six new/changed tests fail; the
  sweep independently catches patch_module, not only scope_list.
• ./gradlew check passes locally (603 tests).
• Live, :examples:quickstart:runMcp (in-process, fresh store): gate-fail deploy → _meta problem
  GATE_FAILED/gate=tests, no structuredContent; config.set with an unknown key → INVALID_ARGUMENT with
  outcomes; scope_list → STATE_CONFLICT; list_runtimes → scope: null, no error.

Not in this PR

• The Go (protego) and Rust (protrus) ports replicate the old shape; handed off to their own repos to follow
  this contract after merge.
• The java_mcp scenario runbooks name the old location in two expected values; handed off, to apply after
  merge.

Docs

docs/guide/08-mcp-integration.md (+ko): new Tool errors section with the result shape; the outputSchema
validation section notes that a custom tool attaching structuredContent to an error must keep it conformant.