feat: add opencode compatibility layer (#68)

research/opencode-tmux-test.md

@@ -0,0 +1,54 @@
+# OpenCode TUI Test Plan (Tmux)
+
+This plan captures OpenCode TUI output and sends input via tmux so we can validate `/opencode` end-to-end.
+
+## Prereqs
+- `opencode` installed and on PATH.
+- `tmux` installed (e.g., `/home/linuxbrew/.linuxbrew/bin/tmux`).
+- Local sandbox-agent binary built.
+
+## Environment
+- `SANDBOX_AGENT_LOG_DIR=/path` to set server log dir
+- `SANDBOX_AGENT_LOG_STDOUT=1` to keep logs on stdout/stderr
+- `SANDBOX_AGENT_LOG_HTTP=0` to disable request logs
+- `SANDBOX_AGENT_LOG_HTTP_HEADERS=1` to include request headers (Authorization redacted)
+- `RUST_LOG=...` for trace filtering
+
+## Steps
+1. Build and run the server using the local binary:
+   ```bash
+   SANDBOX_AGENT_SKIP_INSPECTOR=1 cargo build -p sandbox-agent
+   SANDBOX_AGENT_LOG_HTTP_HEADERS=1 ./target/debug/sandbox-agent server \
+     --host 127.0.0.1 --port 2468 --token "$TOKEN"
+   ```
+2. Create a session via the OpenCode API:
+   ```bash
+   SESSION_JSON=$(curl -sS -H "Authorization: Bearer $TOKEN" \
+     -H "Content-Type: application/json" \
+     -d '{}' \
+     http://127.0.0.1:2468/opencode/session)
+   SESSION_ID=$(node -e "const v=JSON.parse(process.env.SESSION_JSON||'{}');process.stdout.write(v.id||'');")
+   ```
+3. Start the OpenCode TUI in tmux:
+   ```bash
+   tmux new-session -d -s opencode \
+     "opencode attach http://127.0.0.1:2468/opencode --session $SESSION_ID --password $TOKEN"
+   ```
+4. Send a prompt:
+   ```bash
+   tmux send-keys -t opencode:0.0 "hello" C-m
+   ```
+5. Capture output:
+   ```bash
+   tmux capture-pane -pt opencode:0.0 -S -200 > /tmp/opencode-screen.txt
+   ```
+6. Inspect server logs for requests:
+   ```bash
+   tail -n 200 ~/.local/share/sandbox-agent/logs/log-$(date +%m-%d-%y)
+   ```
+7. Repeat after adjusting `/opencode` stubs until the TUI displays responses.
+
+## Notes
+- Tmux captures terminal output only. GUI outputs require screenshots or logs.
+- If OpenCode connects to another host/port, logs will show no requests.
+- If the prompt stays in the input box, use `C-m` to submit (plain `Enter` may not trigger send in tmux).