Status line `used_percentage` does not reflect actual context window usage

[cmanfre4]

Describe the bug

Status line used_percentage does not reflect actual context window usage

The context_window.used_percentage field in the status line JSON does not match the context utilization reported by /context.

Observed behavior

• used_percentage starts at 0% on session start or resume, regardless of existing context
• It grows disproportionately to actual context usage reported by /context until it maxes out at 100%
• /context reports stable, plausible values throughout (e.g. ~20-22%)

Point in session	Status line used_percentage	/context
After resume, before first message	0%	~20%
After first post-resume message	16%	~20%
After several more exchanges	100%	22%

Affected version

v1.0.3

Steps to reproduce the behavior

1. Configure the status line script in ~/.copilot/config.json (see example below)
2. Enable the experimental status line feature: run /experimental on and restart Copilot CLI
3. Start a new session and exchange several messages
4. Compare the status line's reported percentage with /context output
5. Continue exchanging messages and observe the status line percentage grow while /context remains stable
6. Exit and resume session.
7. Status line percentage resets to 0.
8. Repeat Steps 3, 4, and 5.

Minimal script to reproduce -- displays used_percentage as reported in the status line JSON:

#!/usr/bin/env bash
input=$(cat)
used=$(echo "$input" | jq -r '.context_window.used_percentage // "n/a"')
echo "ctx: ${used}%"

Config in ~/.copilot/config.json:

{
  "status_line": {
    "type": "command",
    "command": "/absolute/path/to/statusline.sh"
  }
}

Expected behavior

used_percentage should reflect the same context window utilization as /context

Additional context

• Copilot CLI v1.0.3
• macOS 15 (Darwin 24.6.0)
• Status line feature enabled via /experimental on