Run the CLI update check in non-interactive shells so agents see it

crates-cli/yaak-cli/skills/use-yaak/SKILL.md

@@ -170,3 +170,6 @@ check the status.
 5. Never write a real secret into an environment variable on the user's behalf.
    Reference one and let them fill in the value.
 6. Verify what you built by sending it, and report the real HTTP status.
+7. If the CLI warns on stderr that a newer version is available, offer to run
+   the upgrade command it prints, then re-run `yaak agent install` so this
+   skill updates too.

crates-cli/yaak-cli/src/version_check.rs

@@ -47,6 +47,8 @@ struct VersionCheckRequest<'a> {
     install_source: String,
     platform: &'a str,
     arch: &'a str,
+    // False when stdout is piped, e.g. a coding agent driving the CLI
+    interactive: bool,
 }
 
 pub async fn maybe_check_for_updates() {
@@ -102,11 +104,7 @@ fn should_skip_check() -> bool {
         return true;
     }
 
-    if std::env::var("CI").is_ok() {
+    std::env::var("CI").is_ok()
-        return true;
-    }
-
-    !std::io::stdout().is_terminal()
 }
 
 async fn fetch_version_check() -> Option<VersionCheckResponse> {
@@ -118,6 +116,7 @@ async fn fetch_version_check() -> Option<VersionCheckResponse> {
         install_source: install_source(),
         platform: std::env::consts::OS,
         arch: std::env::consts::ARCH,
+        interactive: std::io::stdout().is_terminal(),
     };
 
     let client = yaak_api_client(ApiClientKind::Cli, current_version).ok()?;