doc: note architecture completeness in README

Ollie's core is feature-complete. Every capability (browser automation,
audio, RAG, scheduling, databases, external services) is achievable by
writing a tool. There are no architectural gaps — missing features are
missing tools.

README.md

@@ -81,6 +81,19 @@ session/
             └── proc/       detached process output
 ```
 
+## Architecture completeness
+
+Ollie's core architecture is complete. Every capability — browser automation, audio processing, RAG, scheduled tasks, database access, external service integrations — is achievable by writing a tool. The runtime provides:
+
+- **Multi-modal tool results**: Tools return structured JSON with text and image content blocks
+- **Multi-modal message handling**: Backends handle images in both directions
+- **Arbitrary tool complexity**: Tools are executables that can spawn browsers, call APIs, run ML models
+- **Long-running operations**: Background processes and sub-agents for parallel/delegated work
+- **External triggers**: The 9P namespace is writable — cron, systemd, or scripts can prompt agents
+- **Local embeddings**: The `embedding.Model` infrastructure exists for semantic operations
+
+There are no architectural gaps. Missing features are missing tools.
+
 ## Providers, tools, and security
 
 `session/new` accepts `name`, `remote`, `workflow`, `cwd`, and `yolo=true` key/value fields. Session-level `yolo` is persisted and applies to local or remote toolsrv startup; it disables native Landlock enforcement for explicit development use. Normal tools use the configured native Landlock policy, while approved escape requests go through the bypass broker.