collab: Defer account age check to POST /completion endpoint (#26956)

This PR defers the account age check to the `POST /completion` endpoint
instead of doing it when an LLM token is generated.

This will allow us to lift the account age restriction for using Edit
Prediction.

Note: We're still temporarily performing the account age check when
issuing the LLM token until this change is deployed and the LLM tokens
have had a chance to cycle.

Release Notes:

- N/A

crates/collab/src/llm.rs

@@ -5,6 +5,7 @@ mod token;
 use crate::api::events::SnowflakeRow;
 use crate::api::CloudflareIpCountryHeader;
 use crate::build_kinesis_client;
+use crate::rpc::MIN_ACCOUNT_AGE_FOR_LLM_USE;
 use crate::{db::UserId, executor::Executor, Cents, Config, Error, Result};
 use anyhow::{anyhow, Context as _};
 use authorization::authorize_access_to_language_model;
@@ -217,6 +218,15 @@ async fn perform_completion(
         params.model,
     );
 
+    let bypass_account_age_check = claims.has_llm_subscription || claims.bypass_account_age_check;
+    if !bypass_account_age_check {
+        if let Some(account_created_at) = claims.account_created_at {
+            if Utc::now().naive_utc() - account_created_at < MIN_ACCOUNT_AGE_FOR_LLM_USE {
+                Err(anyhow!("account too young"))?
+            }
+        }
+    }
+
     authorize_access_to_language_model(
         &state.config,
         &claims,