chore: changeset for context-usage breakdown

Author: kevin-dp

.changeset/context-usage-breakdown.md

@@ -0,0 +1,13 @@
+---
+'@electric-ax/agents-runtime': minor
+'@electric-ax/agents-server-ui': patch
+---
+
+Context-usage indicator: a circular ring gauge plus a hover breakdown popover
+showing how the prompt decomposes across system prompt, tools, messages, and
+free space (à la Claude Code's `/context`). The runtime now persists an
+approximate `context_breakdown` of the stable request parts (system + tools) on
+each step alongside the cache-inclusive total, and exports new
+`computeContextBreakdown` / `parseContextBreakdown` helpers from the client
+entry; the UI derives the "messages" bucket as the real remainder so the
+segments always sum to the gauge.