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/threads.py

@@ -103,18 +103,25 @@ async def _wait_for_post_complete(tab, timeout=30.0):
 
 
 async def check_login(cdp_client):
-    tab, reused = await cdp_client.get_or_open_tab(S["url"], "threads.com")
+    tab, reused = await cdp_client.get_or_open_tab(S["url"], "threads.com", activate=False)
     if reused:
         await tab.eval("window.onbeforeunload = null")
         await tab.navigate(S["url"])
-    await asyncio.sleep(4)
     if await tab.exists(S["login_marker"]):
         return False
-    return await tab.eval(
-        "!!(document.querySelector('[placeholder=\"What\\'s new?\"]')"
-        " || [...document.querySelectorAll('span,div')]"
-        ".find(e => e.innerText && e.innerText.trim() === 'What\\'s new?'))"
+    # JS state, not the "What's new?" composer: that composer never mounts in a
+    # backgrounded tab, so a signed-in account read as signed out (measured
+    # 2026-09-12 — DOM signal False while the session cookie was right there).
+    # Threads runs on the Instagram session, hence ds_user_id.
+    state = await tab.eval(
+        "(() => { const m = document.cookie.match(/(?:^|;\\s*)ds_user_id=(\\d+)/);"
+        " return m ? 'in:' + m[1] : (document.cookie ? 'out' : 'unavailable'); })()"
     )
+    if state.startswith("in:"):
+        return True
+    if state == "out":
+        return False
+    raise CDPError("threads: no cookies readable on threads.com — cannot tell signed-in from signed-out")
 
 
 async def get_notifications(cdp_client, count=10):