v0.4: background reads, JS-state login signals, blind sleeps dropped

get_or_open_tab(activate=True) — added, not replaced. Read paths pass
activate=False; post flows keep the foreground for dialogs and file inputs.

check_login moved off DOM signals onto session state: fb c_user, ig/threads
ds_user_id, twitter twid, yt ytcfg.LOGGED_IN. Three platforms were reporting
OUT on a signed-in account because their composer never mounts in a hidden
tab. The fixed sleep(4)/sleep(5) before each check goes with them — every
signal reads present the moment navigate() returns.

Unreadable cookies raise instead of returning False: "cannot tell" is not
"signed out". tiktok untouched and still activated — it reported
visibilityState "visible" from a sibling-activated tab, so it has never been
read from a genuine background.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

platforms/tiktok.py

@@ -120,6 +120,13 @@ async def _wait_for_success(tab, timeout=120.0):
 
 
 async def check_login(cdp_client):
+    # The only platform still activated for a login check. TikTok could not be
+    # backgrounded on 2026-09-12: a sibling tab in the *same* window was
+    # activated (Browser.getWindowForTarget agreed on windowId) and TikTok still
+    # reported visibilityState "visible" — own window, or it overrides the
+    # property to keep video playing. Its DOM signal has never lied, but it has
+    # never been read from a genuine background either. Three states, not two:
+    # this stays foreground until there is evidence, not until it looks fine.
     tab, reused = await cdp_client.get_or_open_tab(S["url"], "tiktok.com")
     if reused:
         await tab.eval("window.onbeforeunload = null")