Archon 0.9.0 stops workflow nodes inheriting MCP servers — every Box loses its tracker/docs/design access on upgrade

The break

Archon 0.9.0 (upstream #2535): "Claude workflow nodes no longer inherit ambient skills and MCP servers." Measured against the four installed Boxes on 2026-08-25 (the /archon-upgrade proof run's hand-executed supplement — the one BREAKS-US row in a table of ADOPT 3 · DEFER 1 · VERIFY-ONLY 9 · BREAKS-US 1):

• No Box declares mcp: on any node — grep -E '^\s*(mcp|skills|settingSources):' across all four returns nothing.
• Yet .archon/unic-dlc.config.yaml declares docs.access.mcp and design.access.mcp, and the Box prompts route nodes through "§ Access names the MCP server or skill that serves this tracker" (unic-dlc-pr-review.yaml:116, :567; unic-dlc-explore.yaml:371).

On 0.9.0 those servers silently stop reaching workflow nodes: every tracker call, docs read and design read inside a run fails or degrades, with config and prompts still pointing at servers the node can no longer see.

The half that does NOT break

The ambient-skills half is VERIFY-ONLY here: Boxes read Methods as files (Read .archon/methods/<name>/SKILL.md, literal path, explicit not-found stop), never through the Skill tool.

Consequence, until fixed

Adopting Archon 0.9.0 is gated on this ticket. Upgrading first silently removes the configured MCP servers from every node that needs them. Note the tap trap: brew upgrade archon today lands 0.8.0 (tap lags the CLI's 0.9.0 notice), so the break is one release further out — but 0.8.0's release notes are empty, so nothing about it is classified either.

Acceptance criteria

• Each Box node that composes an MCP server declares what 0.9.0 requires (mcp: — exact key per Archon's 0.9.0 docs, verified not assumed), or the plugin records a deliberate alternative.
• The plugin's stated Archon floor/compatibility note says which Archon versions the shipped Boxes are valid for.
• Verified by a run in a Consumer on the new Archon before this ticket closes — a grep is not the proof, a run is.

Context

• Whether the config's access.mcp values can drive the node declarations (config-parameterised mcp:) is a design question for the fix, not decided here.
• Source: /archon-upgrade first proof run, DXP-DesignSystem, 2026-08-25. Related: #423 (the command could not produce this table itself), #424, #422.

Start with .archon/unic-dlc.config.yaml and the node definitions in unic-dlc-pr-review.yaml (including lines 116 and 567) and unic-dlc-explore.yaml (line 371). Compare their access configuration with Archon 0.9.0's documented node requirements, then run an affected Box in a Consumer on the new Archon; done means MCP access works and the plugin states its supported Archon versions.