Summary

Fixes #89662 where the context usage indicator in the webchat UI disappears after sending a message and does not reappear until page refresh.

The root cause was in getContextNoticeViewModel() which returned null when totalTokensFresh was false, completely hiding the indicator even when valid (but potentially stale) token counts were available. This created a poor user experience where users lost visibility into their context usage during normal conversation flow.

This PR reorders the validation logic to check data availability before freshness, ensuring that imperfect information is shown rather than no information at all.

Fixes #89662

Real behavior proof

Behavior addressed: Context indicator disappearing after message send, requiring page refresh to restore visibility.

After-fix evidence:

✅ All 13 unit tests passing covering:

• Fresh vs stale data handling
• Low vs high usage scenarios
• Edge cases (zero tokens, NaN, negative values)
• Warning threshold enforcement
• Compaction recommendation logic

Key test validating the fix:

it("should render indicator with stale but valid low-usage data (FIX #89662)", () => {
  const session = { totalTokens: 18000, totalTokensFresh: false, contextTokens: 180000 };
  const result = getContextNoticeViewModel(session, null);
  expect(result).not.toBeNull(); // BEFORE FIX: would be null
  expect(result!.pct).toBe(10);
});

Git stats:

 ui/src/ui/chat/context-notice.ts      | 21 ++++++++++++++++-----
 ui/src/ui/chat/context-notice.test.ts | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 5 deletions(-)

Observed result after the fix:
Context indicator remains visible after message send, showing token usage percentage even when data may be slightly stale. Users no longer need to refresh the page to restore visibility.

Tests and validation

Risk checklist

Did user-visible behavior change? Yes - indicator now stays visible with stale data instead of disappearing.

Did config, environment, or migration behavior change? No.

Did security, auth, secrets, network, or tool execution behavior change? No.

Highest-risk area: Users might see slightly outdated token counts. Mitigated by: gateway periodic refresh, manual refresh option, conservative compaction recommendations.

Current review state

What is the next action? Maintainer review requested. CI validation pending.