fix: locate the Devin CLI on Windows

KNOWN_BINS only listed Unix/macOS paths, and whichDevin() always shelled
out to /usr/bin/which. On Windows neither resolves, so the provider could
not find `devin.exe` even when it was installed and on PATH. The model
catalog therefore never loaded and the provider silently fell back to the
four hard-coded FALLBACK_MODELS entries.

- Probe the documented Windows install locations (%LOCALAPPDATA%\devin\
  cli\bin\devin.exe, the Devin Desktop bundled CLI for both per-user and
  machine-wide installs, plus two fallbacks).
- Build the candidate list lazily so a DEVIN_CLI value set after module
  load is still honoured.
- Use `where` instead of /usr/bin/which on Windows, and accept multiple
  result lines, since `where` prints one path per line.

All existing Unix/macOS paths are preserved.

Tested on Windows 11, Node 24.5.0, pi 0.87.1, Devin CLI 3000.11.3:
`pi --list-models devin` goes from 4 models to 52 with DEVIN_CLI unset.
`tsc --noEmit` and the existing test suite both pass.

src/cli.ts

@@ -6,20 +6,38 @@ import { promisify } from "node:util";
 
 const execFileAsync = promisify(execFile);
 
-const KNOWN_BINS = [
+function candidateBins(): string[] {
+  const localAppData = process.env.LOCALAPPDATA ?? join(homedir(), "AppData/Local");
+  return [
+    // Explicit override always wins. Read lazily so a value set after module
+    // load (e.g. by the host process) is still honoured.
     process.env.DEVIN_CLI,
+    // ── Windows ──────────────────────────────────────────────────────────
+    // Official installer location (%LOCALAPPDATA%\devin\cli\bin\devin.exe)
+    join(localAppData, "devin/cli/bin/devin.exe"),
+    // Devin Desktop (Windsurf-based) bundled CLI, per-user install
+    join(localAppData, "Programs/Devin/resources/app/extensions/windsurf/devin/bin/devin.exe"),
+    // Devin Desktop bundled CLI, machine-wide install
+    process.env.ProgramFiles &&
+      join(process.env.ProgramFiles, "Devin/resources/app/extensions/windsurf/devin/bin/devin.exe"),
+    // Set by the official Windows installer when it completes normally.
+    process.env.LOCALAPPDATA && join(process.env.LOCALAPPDATA, "devin/bin/devin.exe"),
+    // Manual fallback for installs that could not finish while Devin was running.
+    join(homedir(), ".devin-cli/devin.exe"),
+    // ── Unix / macOS ─────────────────────────────────────────────────────
     join(homedir(), ".local/bin/devin"),
     join(homedir(), ".devin/bin/devin"),
     "/opt/homebrew/bin/devin",
     "/usr/local/bin/devin",
     "/Applications/Devin.app/Contents/Resources/app/extensions/windsurf/devin/bin/devin",
   ].filter((p): p is string => Boolean(p));
+}
 
 let cachedBin: string | null | undefined;
 
 export function findDevinBin(): string | null {
   if (cachedBin !== undefined) return cachedBin;
-  for (const bin of KNOWN_BINS) {
+  for (const bin of candidateBins()) {
     if (existsSync(bin)) {
       cachedBin = bin;
       return bin;
@@ -36,16 +54,25 @@ export function clearDevinBinCache(): void {
 export async function whichDevin(): Promise<string | null> {
   const known = findDevinBin();
   if (known) return known;
+  // Windows has no `which`; use `where` and probe the returned paths directly.
+  const isWindows = process.platform === "win32";
+  const locator = isWindows ? "where" : "/usr/bin/which";
+  const candidates = isWindows ? ["devin.exe", "devin.cmd", "devin"] : ["devin"];
+  for (const candidate of candidates) {
     try {
-    const { stdout } = await execFileAsync("/usr/bin/which", ["devin"], { timeout: 5_000 });
-    const path = stdout.trim();
+      const { stdout } = await execFileAsync(locator, [candidate], { timeout: 5_000 });
+      // `where` may return several lines; take the first existing one.
+      for (const line of stdout.split(/\r?\n/)) {
+        const path = line.trim();
         if (path && existsSync(path)) {
           cachedBin = path;
           return path;
         }
+      }
     } catch {
       // not on PATH
     }
+  }
   return null;
 }