Fix opencode not found: symlink installer binary to /usr/local/bin

The opencode curl installer puts the binary in /root/.local/bin which
isn't on PATH for the nextjs user. Add a symlink to /usr/local/bin
after install. Also ensure /usr/local/bin is always in the PATH
passed to spawned agent processes.

apps/harness/Dockerfile

@@ -42,6 +42,8 @@ RUN apk add --no-cache git github-cli curl ca-certificates
 RUN npm install -g @anthropic-ai/claude-code @openai/codex
 RUN curl -fsSL https://opencode.ai/install | sh || \
     echo "WARN: opencode install failed, skipping"
+# Ensure opencode is on PATH (installer puts it in ~/.local/bin)
+RUN if [ -f /root/.local/bin/opencode ]; then ln -s /root/.local/bin/opencode /usr/local/bin/opencode; fi
 
 # MCP servers: Gitea (Go binary from builder stage)
 COPY --from=gitea-mcp-builder /usr/local/bin/gitea-mcp /usr/local/bin/gitea-mcp

apps/harness/src/lib/agent-env.ts

@@ -14,6 +14,12 @@ export async function buildAgentEnv(
 ): Promise<NodeJS.ProcessEnv> {
   const env: NodeJS.ProcessEnv = { ...process.env, TERM: "xterm-256color" };
 
+  // Ensure global bin paths are available (npm -g, opencode installer)
+  const path = env.PATH || "/usr/local/bin:/usr/bin:/bin";
+  if (!path.includes("/usr/local/bin")) {
+    env.PATH = `/usr/local/bin:${path}`;
+  }
+
   const providersToInject =
     config.runtime === "opencode"
       ? Object.keys(PROVIDER_ENV_VARS)