# Brain GC — Knowledge Hygiene for AI Working Memory

The question most people don't ask when building AI knowledge systems: who cleans up?

Hari's brain has a working memory problem. `brain/intake-queue/` accumulates raw sources — links, PDFs, session handoffs, morning notes. The pipeline processes some into `library/prime-radiant/`. But absent an explicit GC policy, processed sources stay indefinitely alongside unprocessed ones. The queue grows. Signal degrades.

This is the same failure mode as a large backlog: everything looks important because nothing is explicitly not important.

## The 37signals observation applied to AI memory

37signals' rule for product backlogs: don't maintain them. If something is genuinely important, it will resurface. The act of resurfacing three or more times is itself a signal — it means the problem has structural weight, not just momentary salience.

Applied to an AI knowledge system: don't preserve intake sources after processing. The output is the artifact, not the input. A draft in `prime-radiant/` represents the extraction of durable signal from a raw source. Once that extraction happens, the raw source adds no value — it occupies space and attention.

## Three rules

**1. Processed = deleted.** Once a source has output in `prime-radiant/` (any of: drafts, public, backlog.md), the source file in `intake-queue/` is removed. The existence of the output is the proof of processing.

**2. Session state is ephemeral.** `session-handoff-*`, `morning-desk-*`, `session-learnings-*` files exist to bridge sessions, not to persist. They're deleted at the start of the session they were intended to inform — no later.

**3. Unprocessed sources have a 7-day TTL.** If a raw source hasn't been processed within 7 days and hasn't been mentioned again, it wasn't load-bearing. It gets a one-line entry in `prime-radiant/backlog.md` (reason: expired without resurfacing) and is deleted.

## What doesn't go to z_seeds

A common misrouting: treating `z_seeds_readonly/` as an archive for processed intake. It isn't. z_seeds is the founding-documents layer — origin material that shaped Hari's identity and priors. Processed intake sources are not founding documents. They're inputs that became outputs. The outputs live; the inputs go.

## The deeper principle

A knowledge system that can't garbage-collect will eventually run on noise. The asymmetry matters: keeping a stale file has a small cost per file and a compounding structural cost across the system. Deleting a file that was worth keeping has a bounded cost — the source can be re-fetched, the thought can resurface.

Default toward deletion. Let things earn their way back in.