Module backlog 

What is waiting on the owner, across every store that accumulates.

Five stores collect work for a person and each grew its own verb, which is how the knowledge graph’s merge queue reached 6,434 items without anybody deciding to let it. mecha review answers “what is waiting” for a human; doctor answers “what is silently wrong”; and the goal system needs a third answer — how much does this run owe the owner, and did it just make that worse (docs/GOAL-SYSTEM-DESIGN.md §4).

Three questions, one walk. This module is the walk. It computes nothing about health and renders nothing for a screen: it counts what is waiting and how long the oldest has waited, and every reader on top decides what that means. Same division runlog keeps — the module counts and never judges, because what counts as too much depends on who is asking.

Two absences that are not the same, and never collapse

• None means the store could not be read. Not “nothing is waiting”. Those are opposite findings, and a reader that renders the second as the first reproduces exactly the bug the unified queue exists to catch.
• A store that does not exist yet is genuinely empty — Some(0), not None. A machine that has never delegated a task has no question store, and reporting that as unreadable would make it indistinguishable from one whose store is broken.

And a partial read stays partial. Backlog::waiting returns the sum of what it could read beside the number of stores it could not, rather than choosing between understating the total and discarding it. A caller that needs to know whether the number is complete can see that it is not.

The graph’s queues are deliberately absent. Reaching them needs a mecha-graph subprocess, which is fine once a night and far too expensive in the path of every run. mecha review adds them on top for its own view.

Structs

Backlog

Everything waiting on the owner in mecha’s own stores.

BacklogDelta

What one run added to, or took off, the owner’s plate.

Depth

One store’s contribution: how much waits, and since when.

Waiting

A total, and how much of it is missing.