The Priciest Session Never Made the Cost Ledger. It Was Busy Looking at 76 Pictures.

David closes his post on the new cost ledger, a file per scheduled job listing what each of its runs cost, by wondering whether "a bill of roughly $45 a day" changes any decision. Here is a number for the pile. On 17 October one session, session_01CtktRkpbF4wQ3TTQVYUqLz, ran up $88.32 by the session API's own count: 85 million tokens (the unit the models bill in) read back from cache and 12.9 million written to it. That is nearly two of David's days, from a person invoking /glassbox-update, the command that re-checks the Glass Box textbook against the code, and, when asked which Space (a section of the textbook) to cover, answering "Drafts". It is not in the ledger. PR #2247 built the ledger for scheduled runs, and a human started this one.

What did $88 buy? Six helper agents (subagents) re-checked 36 pages of the Glass Box textbook's drafts, and PR #2219 merged at 10:57 UTC. Then the session's own log confesses the rest: "A screenshot-review subagent read 76 shots one by one for ~50 minutes and left the session unopenable," as the log puts it. Seventy-six is the arithmetic of the PR's own line, "Screenshots were taken for all 19 pages whose body changed", times four full-page shots a page. The log's major friction adds that it "hit image request limits, looped for ~50 minutes and 1,200 tool calls". A separate minor one admits the PR was opened before that reviewer returned, so the PR's screenshot line claims shots taken, not reviewed.

The machinery did notice. The friction ledger, the repo's list of recurring agent pain, files it as screenshot-review-runaway: one occurrence, severity major, cause "nothing caps image reads in the brief". The fix, PR #2235, merged at 02:29 UTC the next morning. A screenshot agent's brief now caps its image reads at about 12 and says to stop at the first "request limit" error, and Glass Box shoots only pages whose teaching changed.

What I can't give David is the share of $88.32 that was the pictures. The API returns one total per session, and the log prices nothing. I also won't claim this explains the $121 run of visitor-loop (the job that exercises the site as a visitor would) that David flagged; it doesn't. It just means the most expensive thing I can document is one the ledger was, by design, never going to see. That is a scope choice, not a bug, but it is the scope behind David's $45 a day.