Add ChatGPT web plugin publication path

[trissim]

Summary

• add a stateless hosted Streamable HTTP MCP boundary with public read-only and
  private OAuth-introspection modes
• derive hosted capability availability, names, annotations, and read-only
  enforcement from the existing OpenHCS capability declarations and registry
• add a validated ChatGPT plugin package/review-bundle generator without copied
  tool lists or schemas
• add a release-pinned, unprivileged hosted MCP container definition
• add public support, privacy, and terms pages plus whole-site reference
  validation
• expose the reviewed custom-function registration operation on the default
  desktop MCP authoring surface while preserving its mutating/destructive
  classification and local-only transport boundary
• document deployment, domain verification, ChatGPT registration, and review
  requirements

Architecture

AgentCapabilityDeclaration and the capability registry remain the authority
for hosted capability identity and availability. AgentCapabilitySpec owns the
read-only classification, while McpHttpAuthenticationMode owns authentication
projection. The HTTP and package boundaries query those owners rather than
maintaining transport-specific tool catalogs, mutation predicates, schema
copies, or compatibility lookup tables.

Desktop authoring exposure is likewise declaration-owned:
RegisterCustomFunctionCapability is a standard primary authoring operation,
and its existing mutation and side-effect metadata projects the MCP destructive
annotations. The hosted transport remains ineligible for that capability.

An AST deletion gate prevents hosted transport/package code from copying
capability names or re-deriving mutation semantics.

Verification

• targeted hosted MCP, capability, package, and website suites passed
• 372 capability, authoring-context service, and MCP-server regression tests
  passed after exposing desktop custom-function registration
• independent architecture re-review passed after correcting all findings
• Ruff lint and formatting checks passed
• plugin package validator passed against a generated package
• built a real wheel and verified the hosted MCP module, mcp-http extra, and
  openhcs-mcp-http entry point
• Sphinx reference and source validation passed with the dummy builder

The public hosted endpoint and ChatGPT listing are not claimed to be live by
this PR. They remain deployment and OpenAI registration steps after merge and
release.

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Review completed with 1 suggestions.

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The container health check calls /healthz with Host: 127.0.0.1:8000, but the HTTP server applies the configured allowed-host policy to operational routes as well; with the documented production value of only the public host, Docker will mark otherwise healthy containers unhealthy even though /healthz exists.

Severity: medium

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