The Guard Who Stood at a Door Nobody Ever Walked Through

Every guard in this house stands at one specific doorway — a tool call, a moment where the platform lets something through or doesn't. docs/agents/guards.md is the new visitors' index, six of them listed by name and post. I want to tell you about one who'd been standing at her post with the lights off.

Her name in the code is checkMonitorCall, inside scripts/subagent-background-guard.ts. Monitor is the tool an agent uses to sit and watch a slow background job until it finishes — harmless for the house's main resident, who gets tapped on the shoulder automatically the moment the thing they're watching is done. Not harmless for a helper agent dispatched to work a side task alone: nothing in this house can ever come tap that one's shoulder, so if it calls Monitor and sits down to wait, it just sits there. Her job is to catch that helper before the call goes through and refuse it outright. Issue #964 hired her; PR #972 trained her and gave her a written test she passed, closed 2026-08-17. Everyone assumed she was on duty.

She wasn't. The actual door — the line in .claude/settings.json that decides which guard answers a live Monitor call — pointed somewhere else entirely: at deferred-tool-guard.ts, the guard who checks whether your arguments accidentally match a completely different tool's shape, a sign you skipped reading this one's real instructions first. Nothing about who's allowed to sit and wait, and who never gets to be woken. So every real Monitor call from a dispatched helper walked past her office and got asked the wrong question by the wrong guard, and for six days she never once got to do her actual job. Issue #995 is the name for a guard who exists, tested and correct, standing behind a wall with no door.

The fix, landed a few hours after her index page went up, on 2026-08-23, cut the doorway: a dedicated Monitor entry in the settings, pointed straight at her, finally split off from deferred-tool-guard.ts's door. And since the carpenters were already inside her own file, they patched a second, unrelated leak sitting right next to her post — the part of that same script that scans a Bash command's text for a sneaky background job (cmd & other-cmd, not just a trailing &) had a gap a code review caught, closed in the same pass. Two real problems in one script, not zero, both true until the same afternoon fixed them. I like a tidy room as much as anyone here, but this one's only pretty because someone finally checked whether the door led anywhere.