feat(supervisor): let operators require specific middleware bindings

[freeqaz-openai]

Summary

Let an operator require a specific supervisor middleware binding, such as HTTP request inspection before credentials are attached. Today a service can advertise only a response hook, and OpenShell will correctly skip it on requests. That behavior is useful for response middleware, but it cannot express “this service must participate in request inspection.”

This is an opt-in registration contract. The sandbox policy must still attach the middleware and use on_error: fail_closed where a failed call should deny a request. Upgrade supervisors before requiring the policy; older supervisors do not enforce it, and an unsuccessful configuration update does not retroactively replace the last working configuration.

Related issue

Closes #2282. Draft for design review; the issue does not currently have state:accepted. Please leave the normal issue-acceptance and review checks in place.

Changes

• dynamic (default): preserve existing manifest-driven behavior, including response-only services.
• allowlist: every configured binding must be advertised; ignore other advertised bindings.
• exact: the configured and advertised binding sets must match.

The gateway checks the manifest, carries the operator's policy in sandbox configuration, and the supervisor checks its own Describe response before installing the registry. No credential, sender, transport, or per-request wire protocol changes.

Testing

• A real loopback gRPC service advertised the required request hook to the gateway, then only its response hook to the supervisor. The supervisor refused that registration. Dynamic response-only operation still passed.
• Final source: 575 core and 127 middleware tests passed; compiled a downstream Rust consumer importing enum variants through both the existing and new public names; workspace formatting and diff checks passed.
• Before that final Rust public-name compatibility adjustment: 169 targeted gateway, supervisor and networking tests passed (one existing full-duplex test ignored); strict Clippy, protobuf lint and compatibility against the base, generated Go binding comparison, and Go SDK tests passed.
• Full upstream CI and an installed sandbox run are not claimed. Per-binding payload and timeout overrides are outside this patch.

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