B6: one-source skills/agents + cross-runtime compiler

[aarontrowbridge]

What to build

One-source skills/agents + compiler (author-once, run in both runtimes): a single agent .md per agent compiled to CC (tools:/disallowed-tools:, model: sonnet) and opencode (permission: ruleset, provider/model string) variants; one neutral-body skills tree; the W-7 lint gates both. Depth policy maps for free (no task/Agent grant ⇒ flat in both). (Spec spec-20260708-112732 §7.1–7.2.)

Acceptance criteria

• one agent .md source compiles to valid CC + opencode agent configs
• one skills tree with runtime-neutral bodies passes the lint for both runtimes
• flat-by-default enforced; a task grant without a justifying annotation hard-fails the lint

Blocked by

• Blocked by B0 (decision, Jack): ratify depth-1 redesign gates G-1/G-8/G-9 #107 (B0 ratification, G-8)
• Blocked by 0.1c — amico-validate CLI + CI fast-tier schema gate (closes #17) #30 (A2 — surface: tags the compiler consumes)

Provenance

Design spec (Aaron's vault): spec-20260708-112732; plan plan-20260708-214610 (slice B6, cross-track dep on A2).

[aarontrowbridge]

HELD for amico#183. B6's agent-compiler (one agent .md → CC + opencode variants) consumes the agent defs being restructured in amico#183; building against the current format now would conflict with that open migration. The skills-side prerequisites are done (A1 lint, A2 surface: tags, A3/A4 tiering all merged). Resume once #183 lands and the target agent-def layout is settled.