feat: add microcompact_boundary event handling in web UI

Adds support for Claude Code's microcompact_boundary system message type to display context microcompaction events with token savings information in the chat UI. Shows a package icon with formatted token count (e.g., "Context compacted (saved 32K tokens)"). close #108

web/src/chat/normalizeAgent.ts

@@ -246,6 +246,23 @@ export function normalizeAgentRecord(
                 meta
             }
         }
+        if (data.type === 'system' && data.subtype === 'microcompact_boundary') {
+            const metadata = isObject(data.microcompactMetadata) ? data.microcompactMetadata : null
+            return {
+                id: messageId,
+                localId,
+                createdAt,
+                role: 'event',
+                content: {
+                    type: 'microcompact',
+                    trigger: asString(metadata?.trigger) ?? 'auto',
+                    preTokens: asNumber(metadata?.preTokens) ?? 0,
+                    tokensSaved: asNumber(metadata?.tokensSaved) ?? 0
+                },
+                isSidechain: false,
+                meta
+            }
+        }
         return null
     }
 

web/src/chat/presentation.ts

@@ -58,6 +58,11 @@ export function getEventPresentation(event: AgentEvent): EventPresentation {
         const ms = typeof event.durationMs === 'number' ? event.durationMs : 0
         return { icon: '⏱️', text: `Turn: ${formatDuration(ms)}` }
     }
+    if (event.type === 'microcompact') {
+        const saved = typeof event.tokensSaved === 'number' ? event.tokensSaved : 0
+        const formatted = saved >= 1000 ? `${Math.round(saved / 1000)}K` : String(saved)
+        return { icon: '📦', text: `Context compacted (saved ${formatted} tokens)` }
+    }
     try {
         return { icon: null, text: JSON.stringify(event) }
     } catch {

web/src/chat/types.ts

@@ -16,6 +16,7 @@ export type AgentEvent =
     | { type: 'ready' }
     | { type: 'api-error'; retryAttempt: number; maxRetries: number; error: unknown }
     | { type: 'turn-duration'; durationMs: number }
+    | { type: 'microcompact'; trigger: string; preTokens: number; tokensSaved: number }
     | ({ type: string } & Record<string, unknown>)
 
 export type ToolResultPermission = {