fix(opencode): prevent reasoning content from duplicating as assistant text

OpenCode's message.part.delta events use field="text" for all parts
including reasoning, because "text" is the property name being updated.
Track part types from message.part.updated events and use them to
correctly classify deltas for known reasoning parts.

Also set PASEO_SUPERVISED=0 in vitest setup to prevent process.send()
conflicts with vitest's fork pool.

packages/server/src/test-utils/vitest-setup.ts

@@ -7,6 +7,7 @@ const serverRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), ".
 dotenv.config({ path: path.resolve(serverRoot, ".env.test"), override: true });
 dotenv.config({ path: path.resolve(serverRoot, "../.env") });
 
+process.env.PASEO_SUPERVISED = "0";
 process.env.GIT_TERMINAL_PROMPT = "0";
 process.env.GIT_SSH_COMMAND = "ssh -oBatchMode=yes";
 process.env.SSH_ASKPASS = "/usr/bin/false";