Add the opencode Harness (OpenCode) #439

Parent

#432

What to build

harness opencode runs a Command's sessions on OpenCode, with MiMo-V2.6-Pro, or any other Model the user's OpenCode providers route, wherever the other Harnesses can be chosen, including [harness.opencode] and Setup. It reuses three earlier pieces: the instruction-file fallback link (agy), skill-tool loading and the read after exit (Muse), and the tree-stop.

Facts: the harness candidates research note, §6. Flags and environment: ADR 0013.

Acceptance criteria

• Each session runs opencode run --standalone --format json --auto, with the prompt on stdin, never as an argument, and OPENCODE_DISABLE_AUTOUPDATE=1. The same applies to every Resume and to the check.

• The Model and Effort are passed as -m <provider>/<model>#<effort>.

• Before any work, the Model and Effort are checked with a minimal standalone test call. A provider.no-route error is reported as a bad Model or Effort. Setup checks its answer the same way and proposes no default Model.

• The Factory skills are linked into .agents/skills/. The prompt tells the model to load the skill with its skill tool, and a warning is written when the stream has no tool_use of the skill tool for that skill.

• When the worktree root has CLAUDE.md and no AGENTS.md, AGENTS.md is linked to CLAUDE.md there and kept out of git.

• Once the session exits, opencode session export --standalone <id> is read:

  • an outcome of failed fails the session whatever the exit code;
  • the final message is the last assistant message's last text part;
  • the usage is the sum over the assistant messages.

  When the export fails, the final message falls back to the stream's last text and no usage is shown.

• The session id comes from the stream. A Resume runs -s <id>, only ever with an id read from the stream.

• Interrupting a Run stops the session and its shell command, and nothing is left running.

• A fake opencode in the test harness reads its prompt from stdin, sometimes drops its last step_finish, and answers session export. A sessions scenario test covers the above, including an exported outcome of failed with exit 0.

• The docs list OpenCode: it never reads CLAUDE.md or ~/.claude/, --standalone adds 2–3 s per session, and it takes the Model id from the user's provider config.

Blocked by

• Stop the whole process tree for every Harness #435
• Add the agy Harness (Antigravity CLI) #436
• Add the muse Harness (Muse Code) #438