D55 — Agents also materialized on OpenCode, via frontmatter translation

Context. D48 materializes kind: agent only on claude — but OpenCode has its own native subagents (.opencode/agent/<nome>.md, singular dir, incompatible frontmatter: description + mode: subagent, name from the filename).

Decision. destDir maps agent×opencode → .opencode/agent/<nome>.md (codex/kiro remain unsupported). The content is not copied verbatim: translateAgentForProvider (a pure function, called by Apply before writing) extracts description from the source Claude frontmatter and emits a minimal OpenCode frontmatter + verbatim body. Claude-only fields that cannot be mapped reliably (tools, model, name) are dropped, not guessed. ContentHash remains that of the source (unchanged): translation happens only at write time, never in the hash computation — drift detection stays agnostic to the destination provider. Rationale. The translation lives in Apply (client-side), not in the manifest, the same architectural choice as D48. Dropping unmappable fields avoids silently wrong behavior on an artifact that drives an agent's behavior. Discarded alternatives. Mapping tools/model with a best-effort heuristic: syntax and names diverge enough to make any automatic mapping fragile and silently incorrect. Details: docs/sync.md §Agents and hooks, docs/interoperability.md §Provider capability matrix.