feat(update-checker): surface update notice to non-TTY/agent runs

- drop the CI / non-TTY early-return so agents see "Update available" too
- widen check interval 4h→24h; stay silent inside the window (no per-command repeat)
- remove orphan isCI() helper (zero callers)
- versioning.md: drop the now-false "banner suppressed under agent" rationale

Author: XXPermanentXX

packages/core/src/utils/env.ts

@@ -1,7 +1,6 @@
 export { generateFilename } from "./filename.ts";
 export { resolveOutputDir } from "./output-dir.ts";
 export { maskToken } from "./token.ts";
-export { isCI } from "./env.ts";
 export { stripUndefined } from "./object.ts";
 export {
   parseBooleanValue,

packages/core/src/utils/index.ts

@@ -7,7 +7,7 @@ export const NPM_REGISTRY = "https://registry.npmjs.org";
 export const NPM_PACKAGE = "bailian-cli";
 
 const STATE_FILE = () => join(getConfigDir(), "update-state.json");
-const CHECK_INTERVAL_MS = 4 * 60 * 60 * 1000; // 4h
+const CHECK_INTERVAL_MS = 24 * 60 * 60 * 1000; // 24h
 const FETCH_TIMEOUT_MS = 3000;
 
 /**
@@ -77,19 +77,13 @@ export async function checkForUpdate(
   currentVersion: string,
   npmPackage: string = NPM_PACKAGE,
 ): Promise<void> {
-  // Skip in CI / non-TTY environments
-  if (process.env.CI || !process.stderr.isTTY) return;
-
   const state = readState();
   const now = Date.now();
 
-  // Throttle: skip if checked within the last 4 hours
-  if (state && now - state.lastChecked < CHECK_INTERVAL_MS) {
-    if (state.latestVersion && isNewerVersion(state.latestVersion, currentVersion)) {
-      pendingNotification = state.latestVersion;
-    }
-    return;
-  }
+  // Inside the throttle window (CHECK_INTERVAL_MS since the last fetch): no
+  // network call and no notice. The state file is global, so the notice fires at
+  // most once per window across all processes/sessions — not once per command.
+  if (state && now - state.lastChecked < CHECK_INTERVAL_MS) return;
 
   const latest = await fetchLatestVersion(FETCH_TIMEOUT_MS, npmPackage);
   if (!latest) return;

packages/runtime/src/utils/update-checker.ts

@@ -3,11 +3,6 @@
 > Hand-maintained. Lives in `assets/` (not auto-generated from `catalog.ts`).
 > Entry point: [SKILL.md → Version & updates](../SKILL.md#version--updates-agent--do-first).
 
-**Why this matters for agents:** when `bl` runs interactively it prints an
-`Update available` banner. That banner is **suppressed when `bl` is piped by an
-agent** (non-TTY stderr), so the user never learns their `bl` is outdated. The
-agent must take over that responsibility.
-
 ## Agent pre-flight checklist (MANDATORY)
 
 **Do NOT run any `bl` command until you complete this checklist.** Run it **once per session**, before the first `bl` command. Cache the result — do not re-check before every command.