GeezerVison

Stacked on #29890.

ContextUsageIndicator accepted usage: AgentContextUsage | null and read every field with usage?.. Inside the indicator, null and {} render the same thing: every field is missing. The indicator is hidden when AgentChatInput gets no contextUsage prop, and that stays true.

• ChatPageContent now always builds one usage object: { ...rawUsage, compressionThreshold, context: chatContext }. Before, it passed null when there was no usage and no pinned context. In that case the new object only adds compressionThreshold, and the indicator only shows it when a percentage exists. A percentage needs usedTokens and contextLimitTokens, and neither is set in that case, so the output is the same.
• AgentChatInputProps.contextUsage is now AgentContextUsage (optional, no null), and ContextUsageIndicator.usage is now required and non-null. This replaces 14 usage?. reads with usage..
• The NoUsage story arg is now {} instead of null.

ChatPageContent is the only production caller that passes contextUsage. The other AgentChatInput callers leave it out, so the indicator stays hidden for them.

Verified: pnpm lint:types, check, lint:oxlint, lint:compiler, lint:knip, pnpm test src/pages/AgentsPage, and pnpm test:storybook for ContextUsageIndicator, AgentChatInput, ChatPageContent, AgentChatPage and AgentChatPageView stories.

Part of the AgentsPage nullability cleanup; see #29888 for the methodology.

This PR was generated by Coder Agents on behalf of @DanielleMaywood.