feat: add Codex provider support

.env.example

@@ -2,10 +2,12 @@
 # Copy to ~/.applypilot/.env and fill in your values.
 
 # LLM Provider (pick one)
+# LLM_PROVIDER=gemini     # Explicit provider selection (gemini/openai/local/codex)
 GEMINI_API_KEY=           # Gemini 2.0 Flash (recommended, cheapest)
 # OPENAI_API_KEY=         # OpenAI (GPT-4o-mini)
 # LLM_URL=http://127.0.0.1:8080/v1  # Local LLM (llama.cpp, Ollama)
 # LLM_MODEL=              # Override model name
+# For Codex: set LLM_PROVIDER=codex and run `codex login`
 
 # Auto-Apply (optional)
 CAPSOLVER_API_KEY=        # For CAPTCHA solving during auto-apply

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to ApplyPilot will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+- **Codex provider support** - added Codex as an LLM provider option for scoring, tailoring,
+  cover letters, and apply-time automation
+
 ## [0.2.0] - 2026-02-17
 
 ### Added

src/applypilot/agent.py

@@ -0,0 +1,54 @@
+"""Helpers for selecting and launching the autonomous agent backend."""
+
+from __future__ import annotations
+
+import json
+import shutil
+from dataclasses import dataclass
+
+from applypilot import config
+
+
+@dataclass(frozen=True)
+class AgentBackend:
+    """Execution backend for the auto-apply agent."""
+
+    name: str
+    binary: str
+    model: str
+
+
+def get_agent_backend(preferred: str | None = None, model: str | None = None) -> AgentBackend:
+    """Resolve the backend and default model to use."""
+    backend = (preferred or config.get_agent_backend()).strip().lower()
+    if backend not in config.AGENT_BACKENDS:
+        backend = config.get_agent_backend()
+
+    if backend == "codex":
+        binary = shutil.which("codex") or "codex"
+        resolved_model = model or "gpt-5.4-mini"
+    else:
+        binary = shutil.which("claude") or "claude"
+        resolved_model = model or "haiku"
+
+    return AgentBackend(name=backend, binary=binary, model=resolved_model)
+
+
+def codex_login_ok() -> tuple[bool, str]:
+    """Check Codex login status."""
+    return config.codex_login_status()
+
+
+def build_playwright_override_args(cdp_port: int) -> list[str]:
+    """Build `codex exec -c` overrides for the Playwright MCP server."""
+    args = [
+        "@playwright/mcp@latest",
+        f"--cdp-endpoint=http://localhost:{cdp_port}",
+        f"--viewport-size={config.DEFAULTS['viewport']}",
+    ]
+    return [
+        "-c",
+        'mcp_servers.playwright.command="npx"',
+        "-c",
+        f"mcp_servers.playwright.args={json.dumps(args)}",
+    ]