Neutralize runtime tool policy vocabulary

[chubes4]

Summary

• Emit neutral canonical environment and capability_scope fields in agents-api/runtime-tool-policy/v1 policy entries.
• Keep execution_location and transport_visibility for compatibility while marking them in legacy_fields.
• Replace Codebox/sandbox-oriented fixtures and docs wording with runtime-local/delegated-runtime terminology.

Tests

• php tests/runtime-tool-policy-smoke.php
• php tests/run-result-envelope-smoke.php
• php tests/agents-chat-ability-smoke.php
• php tests/no-product-imports-smoke.php

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 via OpenCode
• Used for: Implementing the runtime policy vocabulary cleanup, updating tests/docs, and running targeted verification.