feat(context-window-monitor): add progressive warnings at 50%, 60%, 70%, 80%

- Replace single 70% threshold with stepped warnings
- Add ANSI color coding for visual urgency (blue → yellow → orange → red)
- Track notified thresholds per session to avoid duplicate alerts
- Each threshold triggers once with appropriate urgency level:
  - 50% INFO: checkpoint notification
  - 60% NOTICE: awareness notification
  - 70% WARNING: caution notification
  - 80% CRITICAL: urgent action needed

Author: taetaetae

src/hooks/context-window-monitor.ts

@@ -7,13 +7,59 @@ const ANTHROPIC_ACTUAL_LIMIT =
   process.env.VERTEX_ANTHROPIC_1M_CONTEXT === "true"
     ? 1_000_000
     : 200_000
-const CONTEXT_WARNING_THRESHOLD = 0.70
 
-const CONTEXT_REMINDER = `${createSystemDirective(SystemDirectiveTypes.CONTEXT_WINDOW_MONITOR)}
+const PROGRESSIVE_WARNING_THRESHOLDS = [0.50, 0.60, 0.70, 0.80] as const
+
+type ThresholdLevel = (typeof PROGRESSIVE_WARNING_THRESHOLDS)[number]
+
+const ANSI = {
+  RESET: "\x1b[0m",
+  BOLD: "\x1b[1m",
+  BLUE: "\x1b[34m",
+  YELLOW: "\x1b[33m",
+  ORANGE: "\x1b[38;5;208m",
+  RED: "\x1b[31m",
+  BG_BLUE: "\x1b[44m",
+  BG_YELLOW: "\x1b[43m",
+  BG_ORANGE: "\x1b[48;5;208m",
+  BG_RED: "\x1b[41m",
+  WHITE: "\x1b[37m",
+} as const
+
+const THRESHOLD_CONFIG: Record<ThresholdLevel, { emoji: string; urgency: string; color: string; bgColor: string }> = {
+  0.50: { emoji: "📊", urgency: "INFO", color: ANSI.BLUE, bgColor: ANSI.BG_BLUE },
+  0.60: { emoji: "📈", urgency: "NOTICE", color: ANSI.YELLOW, bgColor: ANSI.BG_YELLOW },
+  0.70: { emoji: "⚠️", urgency: "WARNING", color: ANSI.ORANGE, bgColor: ANSI.BG_ORANGE },
+  0.80: { emoji: "🚨", urgency: "CRITICAL", color: ANSI.RED, bgColor: ANSI.BG_RED },
+}
+
+function createContextReminder(threshold: ThresholdLevel): string {
+  const { emoji, urgency, color, bgColor } = THRESHOLD_CONFIG[threshold]
+  const baseReminder = createSystemDirective(SystemDirectiveTypes.CONTEXT_WINDOW_MONITOR)
+
+  const coloredHeader = `${bgColor}${ANSI.WHITE}${ANSI.BOLD} ${emoji} [${urgency}] ${ANSI.RESET}${color}`
+
+  if (threshold >= 0.80) {
+    return `${baseReminder}
+
+${coloredHeader} Context window is running LOW!
+Consider wrapping up current task or preparing for session handoff.
+Prioritize completing critical work before context limit is reached.${ANSI.RESET}`
+  }
+
+  if (threshold >= 0.70) {
+    return `${baseReminder}
+
+${coloredHeader} Context window usage is getting high.
+Continue working but be mindful of context consumption.
+Consider summarizing progress if approaching complex tasks.${ANSI.RESET}`
+  }
 
-You are using Anthropic Claude with 1M context window.
-You have plenty of context remaining - do NOT rush or skip tasks.
-Complete your work thoroughly and methodically.`
+  return `${baseReminder}
+
+${coloredHeader} Context window checkpoint.
+You have sufficient context remaining - continue working normally.${ANSI.RESET}`
+}
 
 interface AssistantMessageInfo {
   role: "assistant"
@@ -31,16 +77,14 @@ interface MessageWrapper {
 }
 
 export function createContextWindowMonitorHook(ctx: PluginInput) {
-  const remindedSessions = new Set<string>()
+  const notifiedThresholdsPerSession = new Map<string, Set<ThresholdLevel>>()
 
   const toolExecuteAfter = async (
     input: { tool: string; sessionID: string; callID: string },
     output: { title: string; output: string; metadata: unknown }
   ) => {
     const { sessionID } = input
 
-    if (remindedSessions.has(sessionID)) return
-
     try {
       const response = await ctx.client.session.messages({
         path: { id: sessionID },
@@ -57,27 +101,39 @@ export function createContextWindowMonitorHook(ctx: PluginInput) {
       const lastAssistant = assistantMessages[assistantMessages.length - 1]
       if (lastAssistant.providerID !== "anthropic") return
 
-      // Use only the last assistant message's input tokens
-      // This reflects the ACTUAL current context window usage (post-compaction)
       const lastTokens = lastAssistant.tokens
       const totalInputTokens = (lastTokens?.input ?? 0) + (lastTokens?.cache?.read ?? 0)
-
       const actualUsagePercentage = totalInputTokens / ANTHROPIC_ACTUAL_LIMIT
 
-      if (actualUsagePercentage < CONTEXT_WARNING_THRESHOLD) return
+      if (!notifiedThresholdsPerSession.has(sessionID)) {
+        notifiedThresholdsPerSession.set(sessionID, new Set())
+      }
+      const sessionNotified = notifiedThresholdsPerSession.get(sessionID)!
 
-      remindedSessions.add(sessionID)
+      let thresholdToNotify: ThresholdLevel | null = null
+      for (const threshold of PROGRESSIVE_WARNING_THRESHOLDS) {
+        if (actualUsagePercentage >= threshold && !sessionNotified.has(threshold)) {
+          thresholdToNotify = threshold
+        }
+      }
+
+      if (thresholdToNotify === null) return
 
+      sessionNotified.add(thresholdToNotify)
+
+      const { color } = THRESHOLD_CONFIG[thresholdToNotify]
       const displayUsagePercentage = totalInputTokens / ANTHROPIC_DISPLAY_LIMIT
       const usedPct = (displayUsagePercentage * 100).toFixed(1)
       const remainingPct = ((1 - displayUsagePercentage) * 100).toFixed(1)
       const usedTokens = totalInputTokens.toLocaleString()
       const limitTokens = ANTHROPIC_DISPLAY_LIMIT.toLocaleString()
 
-      output.output += `\n\n${CONTEXT_REMINDER}
-[Context Status: ${usedPct}% used (${usedTokens}/${limitTokens} tokens), ${remainingPct}% remaining]`
+      const reminder = createContextReminder(thresholdToNotify)
+
+      output.output += `\n\n${reminder}
+${color}[Context Status: ${usedPct}% used (${usedTokens}/${limitTokens} tokens), ${remainingPct}% remaining]${ANSI.RESET}`
     } catch {
-      // Graceful degradation - do not disrupt tool execution
+      // Graceful degradation
     }
   }
 
@@ -87,7 +143,7 @@ export function createContextWindowMonitorHook(ctx: PluginInput) {
     if (event.type === "session.deleted") {
       const sessionInfo = props?.info as { id?: string } | undefined
       if (sessionInfo?.id) {
-        remindedSessions.delete(sessionInfo.id)
+        notifiedThresholdsPerSession.delete(sessionInfo.id)
       }
     }
   }