fix(download): compare size estimates at each quality tier

docs/EXTENSION_DEVELOPMENT.md

@@ -173,15 +173,19 @@ for custom IDs without resolving streams or triggering verification:
 - For compressed lossless audio, supply `bitDepth` and `sampleRate` in Hz.
   `channels` defaults to 2. Do not use this model for uncompressed PCM.
 - Set `isMaximum: true` for a lossless tier that can return lower quality. Its
-  estimate spans CD quality through the declared maximum. A capped bitrate
-  alone cannot supply a useful range and is shown as unavailable.
+  estimate uses the declared depth/rate and explicitly labels that assumption
+  (for example, “≈ 171.4 MB if 24-bit/192kHz”). It does not predict which quality
+  the provider will actually return. A capped bitrate alone remains unavailable.
 - Omitted parameters remain unknown. Older extensions retain estimates for
   the picker's legacy `LOSSLESS`, `HI_RES`, and `HI_RES_LOSSLESS` tiers and
   explicit codec/bitrate IDs or labels such as `opus_256` or `Opus 256kbps`.
   Generic `best`, `high`, `low`, and spatial tiers need explicit parameters.
 
 Lossy estimates use duration × bitrate / 8. Lossless estimates use a rough
-50–80% of uncompressed PCM size; this is a heuristic, not a guaranteed range.
+65% of uncompressed PCM size at the declared quality. This is a comparison
+heuristic, not measured compression for the recording or a guaranteed size.
+Do not combine a CD-quality minimum with a hi-res maximum: that range hides
+the distinction between tiers and provides little useful size information.
 Estimates exclude artwork, tags, and container overhead. They describe the
 selected quality before automatic conversion, with a separate converted-size
 estimate when enabled. Fallback quality and intermediate transfers can change