docs(tokens): document image dimension token tradeoffs

docs/reference/token-use.md

@@ -36,6 +36,12 @@ Everything the model receives counts toward the context limit:
 - Compaction summaries and pruning artifacts
 - Provider wrappers or safety headers (not visible, but still counted)
 
+For images, OpenClaw downscales transcript/tool image payloads before provider calls.
+Use `agents.defaults.imageMaxDimensionPx` (default: `1200`) to tune this:
+
+- Lower values usually reduce vision-token usage and payload size.
+- Higher values preserve more visual detail for OCR/UI-heavy screenshots.
+
 For a practical breakdown (per injected file, tools, skills, and system prompt size), use `/context list` or `/context detail`. See [Context](/concepts/context).
 
 ## How to see current token usage
@@ -106,6 +112,7 @@ agents:
 
 - Use `/compact` to summarize long sessions.
 - Trim large tool outputs in your workflows.
+- Lower `agents.defaults.imageMaxDimensionPx` for screenshot-heavy sessions.
 - Keep skill descriptions short (skill list is injected into the prompt).
 - Prefer smaller models for verbose, exploratory work.