Add Devin CLI as a selectable agent backend in plan2code-loop

Upstream replaced GitHub Copilot CLI with Devin; Plan2Code keeps both, so
Claude Code, Copilot CLI and Devin are all selectable and existing Copilot
selections keep working.

AI Assisted

plan2code-loop/src/agents/devin-cli.ts

@@ -0,0 +1,81 @@
+import type { Agent, AgentConfig, AgentExecutionOptions, AgentExecutionResult } from './types.js';
+import { executeCommand } from '../utils/process.js';
+import { writeFileSync, unlinkSync } from 'fs';
+import { join } from 'path';
+import { tmpdir } from 'os';
+
+const devinCliConfig: AgentConfig = {
+  name: 'devin-cli',
+  displayName: 'Devin CLI',
+  command: 'devin',
+  models: [
+    { value: 'default', label: 'Default (use Devin config)' },
+  ],
+  defaultModel: 'default',
+  flags: {
+    prompt: '--print',
+    promptFile: '--prompt-file',
+    model: '--model',
+    skipPermissions: '--permission-mode',
+  },
+};
+
+class DevinCliAgent implements Agent {
+  readonly config = devinCliConfig;
+
+  async execute(options: AgentExecutionOptions): Promise<AgentExecutionResult> {
+    // Devin CLI takes the prompt via --prompt-file rather than stdin
+    const tempFile = join(tmpdir(), `plan2code-prompt-${Date.now()}.txt`);
+    writeFileSync(tempFile, options.prompt, 'utf-8');
+
+    try {
+      const args: string[] = [
+        this.config.flags.prompt,                 // --print for non-interactive mode
+        this.config.flags.promptFile!, tempFile,   // --prompt-file <path>
+        this.config.flags.skipPermissions, 'dangerous', // --permission-mode dangerous (auto-approve all tools)
+      ];
+
+      // Only add --model if not using default
+      if (options.model && options.model !== 'default') {
+        args.push(this.config.flags.model, options.model);
+      }
+
+      const result = await executeCommand({
+        command: this.config.command,
+        args,
+        cwd: options.cwd,
+        timeout: options.timeout,
+        signal: options.signal,
+      });
+
+      return {
+        stdout: result.stdout,
+        stderr: result.stderr,
+        exitCode: result.exitCode,
+        timedOut: result.timedOut,
+        cancelled: result.cancelled,
+        duration: result.duration,
+      };
+    } finally {
+      // Clean up temp file
+      try {
+        unlinkSync(tempFile);
+      } catch {
+        // Ignore cleanup errors
+      }
+    }
+  }
+
+  async isAvailable(): Promise<boolean> {
+    // Run devin --version to verify it's actually installed and working
+    const result = await executeCommand({
+      command: this.config.command,
+      args: ['--version'],
+      cwd: process.cwd(),
+      timeout: 5000,
+    });
+    return result.exitCode === 0;
+  }
+}
+
+export const devinCliAgent = new DevinCliAgent();