Context resets to 0% after abort

[dnouri]

Problem

After aborting a streaming response with C-c C-k, the context percentage in the header line resets to 0%, even though context was consumed before the abort.

Reference behavior

The TUI skips aborted messages when tracking usage:

// compaction.ts, line 91
function getAssistantUsage(msg: AgentMessage): Usage | undefined {
  if (msg.role === "assistant" && "usage" in msg) {
    const assistantMsg = msg as AssistantMessage;
    if (assistantMsg.stopReason !== "aborted" && assistantMsg.stopReason !== "error" && assistantMsg.usage) {
      return assistantMsg.usage;
    }
  }
  return undefined;
}

Only successful completions (end_turn, tool_use) update the context display.

Current behavior

Usage is captured from any assistant message, including aborted ones:

("message_end"
 (let ((message (plist-get event :message)))
   (when (equal (plist-get message :role) "assistant")
     (setq pi--last-usage (plist-get message :usage)))))  ; captures even aborted

When aborted, usage may be nil or incomplete, causing the header to show 0%.

Suggested fix

Only update pi--last-usage for successful completions:

(when (and (equal (plist-get message :role) "assistant")
           (member (plist-get message :stopReason) '("end_turn" "tool_use"))
           (plist-get message :usage))
  (setq pi--last-usage (plist-get message :usage)))

[dnouri]

Investigation Findings

Root Cause

The issue occurs when aborting before the message_start event is received. The usage object exists but has all zeros (initial values), causing 0% context display.

Reference Implementation Analysis

The TUI has two different approaches:

Purpose	Location	Approach
Display context %	footer.ts	Skip aborted only
Compaction calculation	compaction.ts	Skip aborted + error

This is intentional: display can show error data (context was consumed), but automated decisions should be conservative.

Correction to Original Bug Report

The suggested fix used Anthropic API terminology (end_turn, tool_use), but the agent uses normalized terminology (stop, toolUse). Also, the inclusion approach would incorrectly exclude length (max tokens) which has valid usage data.

Correct Fix

Match footer.ts - use exclusion approach, only skip aborted:

(when (and (equal (plist-get message :role) "assistant")
           (not (equal (plist-get message :stopReason) "aborted"))
           (plist-get message :usage))
  (setq pi--last-usage (plist-get message :usage)))