The loader's rate was a number that was never true

[dhobi]

Dust's fuse measured its transfer rate per completed file, on the arrival that completed it — and the first thing it fetches is a film. recent got one sample carrying the file's whole size, the window it divided by floored at 0.25 s, and 13 MB / 0.25 s is 52 MB/s. The caption showed some tens of MB/s for one tick and then held that figure, unchanged, for the minute the next film spent arriving.

The bar had the same problem from the same cause: it counts fetches, Dust's boot is fourteen of them, so on a slow connection it sat at one mark for minutes.

Why

The store never streamed. HostFiles.load has always promised that onBytes "reports each chunk where the source streams", and taoot/src/files.ts does exactly that. DustFiles buffered the whole body and reported it once, so both the rate and the bar were drawn from an event that fires fourteen times a boot.

What changed

dust/src/files.ts

• reads the body chunk by chunk, like its Titanic sibling, with the same arrayBuffer() fallback where a response has no body;
• keeps the manifest's byte sizes — it was throwing the values away and keeping only the keys;
• partialProgress(): how far the in-flight fetches have got, in whole-file units;
• a joiner on a shared fetch still gets its single total report, as before.

dust/src/main.ts — one meter for the whole loader, fed by every byte the page pulls (the head phase's own two fetches included), read on a 250 ms ticker over a 3 s window:

• no number until the window is wide enough to divide by;
• the rate only while bytes are arriving — when the wire goes quiet the caption falls back to what the loader was saying, because a rate that outlives its transfer is the misleading part;
• · 8.4 MB so far beside it, a fact that cannot go stale;
• the bar counts completed fetches plus the fraction of those in flight, and the head phase's two fetches move it as they arrive.

Measured, not argued

Throttled via CDP:

	before	after
caption at 300 KB/s	one wrong figure, then frozen	300 KB/s · 5.4 MB so far, ticking
bar over the first 30 s	stuck at 16%	13% → 59%, continuous
full boot at 4 MB/s	—	100% / "ready", no page errors

tsc --noEmit clean · npm test 534/534.

One thing the honest counter surfaces: a cold Dust boot moves ~95 MB (the intro films plus town.set). That is not new, it was just never visible.

🤖 Generated with Claude Code