feat: add Codex and OpenCode routers with multi-provider support and updated configurations

demos/llm_routing/opencode_router/README.md

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+# OpenCode Router - Multi-Model Access with Intelligent Routing
+
+Plano extends OpenCode to access multiple LLM providers through a single interface and route coding requests to the best configured model.
+
+## Benefits
+
+- **Single Interface**: Use OpenCode while routing through Plano
+- **Task-Aware Routing**: Route requests based on coding task intent
+- **Provider Flexibility**: Mix OpenAI, Anthropic, and local models behind one endpoint
+- **Routing Transparency**: Inspect exactly which model served each request
+
+## How It Works
+
+Plano sits between OpenCode and configured providers:
+
+```text
+Your Request -> OpenCode -> Plano -> Selected Model -> Response
+```
+
+## Quick Start
+
+### Prerequisites
+
+- OpenCode CLI installed and available on your `PATH` (`opencode` command)
+- Docker running
+
+### 1) Enter this demo directory
+
+```bash
+cd demos/llm_routing/opencode_router
+```
+
+### 2) Set API keys
+
+```bash
+export OPENAI_API_KEY="your-openai-key-here"
+export ANTHROPIC_API_KEY="your-anthropic-key-here"
+```
+
+### 3) Start Plano
+
+```bash
+# Install with uv (recommended)
+uv tool install planoai
+planoai up
+
+# Or if already installed with uv
+uvx planoai up
+```
+
+### 4) Launch OpenCode through Plano
+
+```bash
+planoai cli-agent opencode
+# Or if installed with uv:
+uvx planoai cli-agent opencode
+```
+
+The OpenCode launcher integration configures:
+
+```bash
+OPENAI_BASE_URL=http://127.0.0.1:12000/v1
+OPENAI_API_KEY=test
+```
+
+If `arch.opencode.default` exists in `model_aliases`, `planoai cli-agent opencode` exports:
+
+```bash
+OPENAI_MODEL=<target-from-arch.opencode.default>
+```
+
+## Monitor Routing Decisions
+
+In a second terminal:
+
+```bash
+sh pretty_model_resolution.sh
+```
+
+This prints `MODEL_RESOLUTION` lines so you can see request model -> resolved model mappings in real time.
+
+## Advanced Usage
+
+### Override OpenCode model for a session
+
+```bash
+planoai cli-agent opencode --settings='{"OPENCODE_MODEL":"openai/gpt-4.1-2025-04-14"}'
+```
+
+### Context window guidance
+
+OpenCode works best with a large context window. Use models/configuration that support at least 64k context when possible.
+
+## Notes
+
+- Plano's `default: true` model is only used when a client request does not specify a model.
+- If OpenCode sends an explicit model in requests, aliasing/routing rules decide the final upstream model.