vision: images are the primary channel for multimodal models (digest off by default); digest is the text-only fallback; --digest/--no-digest to override

testbed/README.md

@@ -103,17 +103,19 @@ many tool steps the model may chain per request (0 = one action per turn).
 
 ### Real vision
 
-By default the model gets frames as a color-grid digest (works for any
-text-only model). If the model can actually see images (gemma3/gemma4,
-qwen2.5-vl, gpt-4o-mini, ...), pass the frames as real images:
+Vision is the **primary channel**: when the model is multimodal, `vision`
+tool results attach the actual camera frame as an image to the conversation —
+the model sees the crate, the wall, the glowing beacon. The color-grid
+digest is only the **fallback** for text-only models:
 
-- auto-detected for local ollama (`/api/show` capabilities) — nothing to do
-- otherwise force it: `--vision` (or `--no-vision` to disable)
+- multimodal model (auto-detected for local ollama via `/api/show`;
+  otherwise `--vision`): frame as image, digest off
+- text-only model: digest on automatically; `--digest` forces the digest to
+  be included even alongside images, `--no-digest` disables it everywhere
 
-With vision ON, `vision` tool results attach the actual camera frame as an
-image to the conversation — the model sees the crate, the wall, the glowing
-beacon, and orients itself. Verified locally: gemma4:12b completed a beacon
-mission on its first attempt using look_at/move navigation.
+Verified locally: gemma4:12b sees frames and completed a beacon mission on
+its first attempt; gemma4:e2b describes what it sees (crates, beacon) and
+orients itself from the image.
 
 ## Real-time mode