fix(exec): suppress fish startup config in fallback shell

src/agents/shell-utils.test.ts

@@ -68,7 +68,7 @@ describe("getShellConfig", () => {
     process.env.PATH = "";
     const { shell, args } = getShellConfig();
     expect(shell).toBe("/usr/bin/fish");
-    expect(args).toEqual(["-c"]);
+    expect(args).toEqual(["--no-config", "-c"]);
   });
 
   it("uses zsh no-rc mode to avoid startup-file env overrides", () => {

src/agents/shell-utils.ts

@@ -50,6 +50,9 @@ function resolvePosixShellArgs(shellPath: string): string[] {
   if (shellName === "bash") {
     return ["--noprofile", "--norc", "-c"];
   }
+  if (shellName === "fish") {
+    return ["--no-config", "-c"];
+  }
   return ["-c"];
 }