fix(sessions): scale context breakdown bar to the context window

[adboio]

Problem

The context-usage popover (opened by clicking the token percentage on a task) renders a segmented bar whose segments were scaled to the used token count rather than the model's context window. That made the bar sit partially filled with no clear meaning for the empty portion, and it never matched the % full number or the ring above it — e.g. on a 1M-context model it could read ~75% full while % full said 19%. It looked like the segments should add up to the whole context window, but they didn't.

Changes

SegmentedBar now scales each segment to size (the context window) instead of used. The filled portion equals the % full figure and the ring, and the leftover empty track genuinely reads as remaining context. Added a test asserting a 50K-of-200K segment fills a quarter of the bar.

How did you test this?

• pnpm --filter @posthog/ui exec vitest run ContextBreakdownPopover — 4 passed (including the new scaling test).

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code from a Slack thread

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