feat: add GitHub Copilot CLI as LLM backend

README.md

@@ -384,6 +384,33 @@ See the [Claude Code quickstart example](examples/claude_code_quickstart/) for a
 
 </details>
 
+<details>
+<summary><b>🤖 GitHub Copilot CLI (No API Key)</b></summary>
+
+Use the [GitHub Copilot CLI](https://docs.github.com/copilot/how-tos/copilot-cli) as the LLM backend — no API keys needed, authentication uses your GitHub Copilot subscription.
+
+```bash
+# Install and authenticate
+npm install -g @github/copilot
+copilot login
+```
+
+```yaml
+# config.yaml
+llm:
+  provider: "copilot_cli"
+  models:
+    - name: "claude-sonnet-4.6"
+      weight: 0.8
+      reasoning_effort: "medium"
+    - name: "gpt-5.4"
+      weight: 0.2
+```
+
+See the [Copilot CLI quickstart example](examples/copilot_cli_quickstart/) for a complete walkthrough.
+
+</details>
+
 ## Examples Gallery
 
 <div align="center">

examples/copilot_cli_quickstart/README.md

@@ -0,0 +1,82 @@
+# GitHub Copilot CLI Quickstart
+
+This example shows how to use the [GitHub Copilot CLI](https://docs.github.com/copilot/how-tos/copilot-cli) as the LLM backend for OpenEvolve. No API keys are needed — authentication uses your GitHub Copilot subscription.
+
+## Prerequisites
+
+1. **Install GitHub Copilot CLI:**
+   ```bash
+   npm install -g @github/copilot
+   ```
+
+2. **Authenticate:**
+   ```bash
+   copilot login
+   ```
+
+   For headless runs you can instead export a fine-grained personal access token with the "Copilot Requests" permission as `COPILOT_GITHUB_TOKEN`.
+
+3. **Install OpenEvolve:**
+   ```bash
+   pip install openevolve
+   ```
+
+## Run
+
+```bash
+python openevolve-run.py \
+  examples/copilot_cli_quickstart/initial_program.py \
+  examples/copilot_cli_quickstart/evaluator.py \
+  --config examples/copilot_cli_quickstart/config.yaml \
+  --iterations 50
+```
+
+## How It Works
+
+The `config.yaml` sets `provider: "copilot_cli"` which routes all LLM calls through the `copilot -p` subprocess instead of the OpenAI-compatible API. The CLI handles authentication, model selection, and billing.
+
+Because the CLI has no `--system-prompt` flag, the system message is prepended to the prompt. Each call runs with `--silent --no-color --no-ask-user --no-custom-instructions --disable-builtin-mcps` so that only the model response reaches stdout and prompts stay reproducible across machines.
+
+### Key Config Options
+
+| Field | Description | Default |
+|-------|-------------|---------|
+| `provider` | Set to `"copilot_cli"` to use the CLI backend | `"openai"` |
+| `name` | Model passed to `--model`; use `"auto"` to let Copilot choose | `"auto"` |
+| `reasoning_effort` | One of `none`, `minimal`, `low`, `medium`, `high`, `xhigh`, `max` | unset |
+| `max_ai_credits` | Per-call AI credit budget | unset |
+| `allow_all_tools` | Pre-approve the agent's tools | `false` |
+| `timeout` | CLI timeout in seconds | `300` |
+| `retries` | Number of retry attempts on failure | `3` |
+| `retry_delay` | Seconds between retries | `5` |
+
+`temperature`, `top_p` and `max_tokens` have no equivalent CLI flag and are ignored by this backend.
+
+Evolution only needs text generation, so tools are left unapproved by default. Set `allow_all_tools: true` only if you want the agent to read and write files while generating.
+
+### Ensemble Example
+
+A single provider covers every model your subscription exposes, so an ensemble can mix vendors:
+
+```yaml
+llm:
+  provider: "copilot_cli"
+  models:
+    - name: "claude-sonnet-4.6"
+      weight: 0.5
+    - name: "gpt-5.4"
+      weight: 0.3
+    - name: "gemini-3.1-pro-preview"
+      weight: 0.2
+```
+
+### Programmatic Usage
+
+You can also inject the Copilot CLI backend at runtime without modifying config files:
+
+```python
+from openevolve.llm.copilot_cli import init_copilot_cli_client
+
+for model_cfg in config.llm.models:
+    model_cfg.init_client = init_copilot_cli_client
+```

examples/copilot_cli_quickstart/config.yaml

@@ -0,0 +1,57 @@
+# Configuration for function minimization using GitHub Copilot CLI as the LLM backend.
+# No API keys needed - authentication uses `copilot login`.
+#
+# Prerequisites:
+#   1. Install GitHub Copilot CLI: npm install -g @github/copilot
+#   2. Authenticate: copilot login
+#
+# Run:
+#   python openevolve-run.py \
+#     examples/copilot_cli_quickstart/initial_program.py \
+#     examples/copilot_cli_quickstart/evaluator.py \
+#     --config examples/copilot_cli_quickstart/config.yaml \
+#     --iterations 50
+
+max_iterations: 50
+checkpoint_interval: 10
+
+llm:
+  provider: "copilot_cli"
+  models:
+    - name: "claude-sonnet-4.6"
+      weight: 0.8
+      timeout: 300
+      reasoning_effort: "medium"
+      max_ai_credits: 5.0
+    - name: "gpt-5.4"
+      weight: 0.2
+      timeout: 300
+      reasoning_effort: "low"
+      max_ai_credits: 2.0
+  retries: 3
+  retry_delay: 5
+
+prompt:
+  system_message: >
+    You are an expert programmer specializing in optimization algorithms.
+    Your task is to improve a function minimization algorithm to find the
+    global minimum of a complex function with many local minima.
+    The function is f(x, y) = sin(x) * cos(y) + sin(x*y) + (x^2 + y^2)/20.
+    Focus on improving the search_algorithm function to reliably find the
+    global minimum, escaping local minima that might trap simple algorithms.
+
+database:
+  population_size: 50
+  archive_size: 20
+  num_islands: 3
+  elite_selection_ratio: 0.2
+  exploitation_ratio: 0.7
+  similarity_threshold: 0.99
+
+evaluator:
+  timeout: 60
+  cascade_thresholds: [1.3]
+  parallel_evaluations: 3
+
+diff_based_evolution: true
+max_code_length: 20000