fix(watch-pr): report a gh that cannot start as a status-query blocker

pstack/skills/poteto-mode/scripts/watch-pr/github.test.ts

@@ -495,4 +495,25 @@ printf '%s\\n' '[{"number":42,"headRefName":"feature","baseRefName":"main","isCr
     }
   });
 
+  it("reports a gh that cannot start as a query failure", () => {
+    const directory = mkdtempSync(join(tmpdir(), "watch-pr-no-gh-"));
+    try {
+      const program = `import { GhGitHubReader, WatcherQueryError } from ${JSON.stringify(import.meta.dir + "/github.ts")};
+        try {
+          await new GhGitHubReader().pullRequest({ owner: "owner", repo: "repo", number: 42 });
+        } catch (error) {
+          console.log(JSON.stringify(error instanceof WatcherQueryError ? error.failure.kind : String(error)));
+        }`;
+      const child = spawnSync(process.execPath, ["-e", program], {
+        encoding: "utf8", timeout: 2000,
+        env: { ...process.env, PATH: directory },
+      });
+      expect(child.error).toBeUndefined();
+      expect(child.status).toBe(0);
+      expect(JSON.parse(child.stdout)).toBe("command-exit");
+    } finally {
+      rmSync(directory, { recursive: true, force: true });
+    }
+  });
+
 });

pstack/skills/poteto-mode/scripts/watch-pr/github.ts

@@ -30,10 +30,20 @@ export class ChecksUnavailable extends WatcherQueryError {
 const firstLine = (value: string): string =>
   value.trim().split(/\r?\n/, 1)[0]?.slice(0, 240) ?? "";
 function run(argv: readonly [string, ...string[]]): Promise<CommandResult> {
-  return new Promise((resolve, reject) => {
-    const child = spawn(argv[0], argv.slice(1), {
-      stdio: ["ignore", "pipe", "pipe"],
-    });
+  return new Promise((resolve) => {
+    // A command that cannot start fails like one that exits nonzero; Bun
+    // throws here while Node emits "error".
+    const failed = (error: unknown) =>
+      resolve({ code: -1, stdout: "", stderr: String(error) });
+    let child;
+    try {
+      child = spawn(argv[0], argv.slice(1), {
+        stdio: ["ignore", "pipe", "pipe"],
+      });
+    } catch (error) {
+      failed(error);
+      return;
+    }
     let stdout = "";
     let stderr = "";
     child.stdout.setEncoding("utf8");
@@ -44,7 +54,7 @@ function run(argv: readonly [string, ...string[]]): Promise<CommandResult> {
     child.stderr.on("data", (chunk: string) => {
       stderr += chunk;
     });
-    child.on("error", reject);
+    child.on("error", failed);
     child.on("close", (code) => resolve({ code: code ?? -1, stdout, stderr }));
   });
 }