feat: add explicit image return codecs and quality controls

docs/serverless-media.md

@@ -1,6 +1,6 @@
 # Typed serverless media (PR2)
 
-`comfy-media-v1` adds typed, lossless list results for `IMAGE`, `AUDIO`, `MASK`,
+`comfy-media-v1` adds typed list results, exact by default, for `IMAGE`, `AUDIO`, `MASK`,
 `STRING`, and native ComfyUI `VIDEO`. It is an **explicit endpoint profile**, not
 an automatically detected capability. Omitting `media_profile` still selects
 `legacy-image-v1`; existing image collectors and handlers keep their old contract.
@@ -44,6 +44,32 @@ sockets. Different items may have different valid shapes or audio sample rates.
 The entire remote response is validated and decoded before any of its results
 are delivered; missing, duplicate, mismatched, or corrupt results fail collection.
 
+## Image return format and quality
+
+`transfer_format` defaults to **`exact`** and `transfer_quality` to **90**.
+These controls affect **remote IMAGE returns only**, not master-local images,
+uploaded inputs, MASK, AUDIO, STRING or native VIDEO values.
+
+- `exact`: preserve floating-point dtype and values, with no image quantization.
+- `legacy_png`, `png`, `ffv1`: lossless **8-bit image pixels**, not exact float
+  tensors. Image values are clipped to [0,1] and quantized as in the existing
+  Collector. `legacy_png` uses PNG without compression; `png` compresses it.
+- `jpeg`, `webp`: lossy still-image compression.
+- `h264`, `h265`, `av1`: lossy video encoding of each IMAGE tensor's frame batch.
+  This does not transcode the native `video` socket or combine separate list items.
+- Quality 1–100 affects lossy formats only, using the existing Collector's
+  quality-to-CRF mapping for video. Dimensions, frame order and channel count
+  are preserved; alpha is carried separately where needed, not silently dropped.
+
+Both master and endpoint must have this bridge revision for compressed image
+returns. Pillow handles still formats and CPU/software PyAV encoders handle video;
+unavailable codecs fail clearly rather than silently changing the selection.
+Compression can reduce result egress and inline response size, but does not relax
+encoded/decoded byte budgets or the input request limit. Compressed IMAGE batches
+are capped at 240 frames and 8192 pixels per dimension, with a conservative
+256 MiB aggregate decode budget (including codec scratch and alpha). The original Collector's
+settings, default and fallback behavior are unchanged.
+
 ## Inputs and fidelity
 
 Automatic local-file transfer supports stock `LoadImage`, plus explicit stock