test: remove retired runtime guards

[chubes4]

Summary

• Remove migration-era negative fragment lists, blacklists, and absence assertions from the Docs Agent package validator.
• Keep direct current-contract coverage for portable recipes, native package identity/tools/write gates, the exact WP Codebox v0.12.21 call and release ref, runtime sources, credentials, artifacts, publication outputs, and lane behavior.
• Retain publication-tool safety and local-path/privacy checks.

Source relationship and scope

• Source relationship: existing runner recipe, native package spec, reusable workflow, and WP Codebox producer-contract assertions already define the current behavior.
• Change kind: test-only cleanup. No runtime, workflow, dependency, package, or documentation behavior changed.
• Boundedness: the deleted checks only encoded retired Data Machine, Homeboy Extensions, Codebox-wrapper, bundle/ref, runtime-envelope, and compatibility-input history; current-contract and security discriminators remain.

Tests

1. WP_CODEBOX_DIR=<pinned v0.12.21 checkout> php tests/validate-wp-codebox-run-agent-task-contract.php
2. AGENTS_API_DIR=<pinned 78e2dd409010f98fa4d26cdd72572117384ab18d checkout> php tests/native-agent-import.php
3. php tests/validate-docs-agent-packages.php
4. php tests/validate-external-native-package-sources.php
5. php tests/repair-docs-links-smoke.php
6. git diff --check

Compatibility impact

No consumer or runtime compatibility impact. The tests now describe the present portable/native runner contract directly instead of rejecting retired implementation vocabulary.

Closes #144.
Hosted proof: 29473678677.

AI disclosure

Executor: OpenCode AI agent (OpenAI gpt-5.6-terra).
Orchestration: OpenAI gpt-5.6-sol.