docs: clarify universal schema support vs native agent capabilities

README.md

@@ -17,7 +17,9 @@
 
 [Documentation](https://sandboxagent.dev/docs) — [Discord](https://rivet.dev/discord)
 
-## Agent Compatibility
+## Universal Schema Support
+
+Which agent features are normalized into the universal event schema. All agents have full native capabilities; this shows what's exposed via the API.
 
 | Feature | [Claude Code](https://docs.anthropic.com/en/docs/agents-and-tools/claude-code/overview) | [Codex](https://github.com/openai/codex) | [OpenCode](https://github.com/opencode-ai/opencode) | [Amp](https://ampcode.com) |
 |---------|:-----------:|:-----:|:--------:|:---:|
@@ -25,17 +27,20 @@
 | Text Messages | ✓ | ✓ | ✓ | ✓ |
 | Tool Calls | ✓ | ✓ | ✓ | ✓ |
 | Tool Results | ✓ | ✓ | ✓ | ✓ |
-| Questions (HITL) | ✓ | | ✓ | |
-| Permissions (HITL) | ✓ | | ✓ | |
-| Images | | ✓ | ✓ | |
-| File Attachments | | ✓ | ✓ | |
-| Session Lifecycle | | ✓ | ✓ | |
-| Error Events | | ✓ | ✓ | ✓ |
-| Reasoning/Thinking | | ✓ | | |
-| Command Execution | | ✓ | | |
-| File Changes | | ✓ | | |
-| MCP Tools | | ✓ | | |
-| Streaming Deltas | ✓ | ✓ | ✓ | |
+| Questions (HITL) | ✓ | ○ | ✓ | ○ |
+| Permissions (HITL) | ✓ | ○ | ✓ | ○ |
+| Images | ○ | ✓ | ✓ | ○ |
+| File Attachments | ○ | ✓ | ✓ | ○ |
+| Session Lifecycle | ○ | ✓ | ✓ | ○ |
+| Error Events | ○ | ✓ | ✓ | ✓ |
+| Reasoning/Thinking | ○ | ✓ | | |
+| Command Execution | ○ | ✓ | | |
+| File Changes | ○ | ✓ | | |
+| MCP Tools | ○ | ✓ | | |
+| Streaming Deltas | ✓ | ✓ | ✓ | ○ |
+
+- ✓ = Supported in universal schema
+- ○ = Supported by agent, schema support in progress
 
 Want support for another agent? [Open an issue](https://github.com/rivet-dev/sandbox-agent/issues/new) to request it.