/compact extension command collides with pi's built-in (dropped from autocomplete)

Running `loom` (0.4.0, pinned to `@earendil-works/pi-coding-agent@0.78.1`) now prints this on startup:

```
[Extension issues]
path (temp) .../extensions/loom
Extension command '/compact' conflicts with built-in interactive command. Skipping in autocomplete.
```

We register our own `/compact` in `extensions/loom/index.ts` (around line 264), and it's not just a passthrough -- it adds Galaxy-aware behavior:

- a default summary instruction that preserves the analysis plan, decisions, and Galaxy invocation state while dropping verbose tool output (the notebook is the durable record)
- `/compact ` to steer the summary
- a concurrency guard so a second compaction doesn't orphan the first
- before/after token notifications

At some point pi gained its own built-in `/compact`, so the two collide and ours gets dropped from autocomplete.

The open question is what actually runs when you type `/compact` -- pi's built-in, or our registered handler? If the built-in shadows ours at dispatch (not just in autocomplete), we silently lose the Galaxy-aware compaction, which is the whole reason ours exists. If our handler still runs and only the autocomplete entry is suppressed, it's cosmetic and we just want to quiet the warning.

Options once we know which it is:
- dispatch is shadowed -> rename ours (`/loom-compact`?) or have pi allow an extension to override the built-in
- dispatch still hits ours -> suppress the startup warning for this known case
- pi's built-in now does enough -> drop ours and fold the Galaxy summary instructions in elsewhere

First step is just confirming dispatch precedence against pi 0.78.1.