Interoperability

Citadel accepts a standard external SKILL.md with the portable name and description frontmatter fields. The compatibility proof copies the source unchanged into isolated Claude Code and Codex discovery trees, verifies the copied digest, routes an explicit invocation, executes a deterministic instruction contract, records local-only telemetry, emits a Citadel handoff, and removes the temporary runtime tree.

Reproduce the proof

node scripts/generate-distribution-metadata.js --check
node scripts/test-ecosystem-compat.js

The fixture at scripts/fixtures/ecosystem/anthropics-template-skill/ is the unmodified Anthropic Agent Skills template. Its provenance record includes the public source URL, repository ref, license basis, retrieval date, and SHA-256 digest. The digest identifies the tested bytes and the fixture is pinned to Anthropic's immutable commit 9d2f1ae187231d8199c64b5b762e1bdf2244733d; a GitHub contents lookup at that commit returned blob 50a4f9b104357d96361e257adb70454604cd15c0, whose UTF-8 bytes match the recorded SHA-256. The Apache-2.0 label is inferred for this non-document template from the primary repository README's licensing statement; no root license file was verified.

Security boundary

• Source and destination paths must remain inside real, non-symlink roots.
• Tests block Node HTTP, HTTPS, TCP, and fetch; the proof needs no network.
• Telemetry stores request and source digests, never prompt contents or secrets.
• The fixture source is read-only by contract and re-hashed after execution.
• Cleanup removes the entire temporary runtime tree; only proof telemetry and the handoff remain in the caller-owned evidence directory.

What this proves

The local Claude Code skill-directory contract and Citadel's Codex projection contract both pass. Immutable upstream provenance is locally verified. Remote distribution proof is limited to the verified ClaudePluginHub publisher listing and the hosted HOL scanner; neither is treated as third-party runtime adoption or usage.

Live registry inspection (2026-07-11)

• ClaudePluginHub indexes sethgammon/citadel as version 1.1.0, attributes it to SethGammon, and exposes 49 skills, 7 agents, 1 hook group, and 2 MCP servers. On 2026-07-11 the SethGammon GitHub identity claimed the personal-repository match; the page now states “You own this plugin” and exposes publisher management controls. Its install count is zero, so verification and indexing are not install or runtime proof.
• HOL's former citadel/citadel plugin-profile URL now returns 404. The current HOL registry indexes agents and skills rather than maintaining the old plugin publisher pages. Citadel's relevant current HOL proof is therefore the hosted plugin-scanner check, which passes on PR #181; the removed legacy profile is not a release gate.

Together these surfaces prove current Claude publisher identity, metadata discovery, and HOL scanner acceptance. They do not prove installs, successful user tasks, or retention.