Fast-suite threshold failures belong in *.slow spec files

Problem

GitHub Actions failed pnpm check on PR #4902, but the failing specs were not logically broken. The CI log showed the real issue:

• packages/ai/src/react/ai-chat/hooks/useAIChatEditor.spec.tsx
• packages/ai/src/react/ai-chat/hooks/useEditorChat.spec.tsx
• packages/ai/src/react/ai-chat/utils/getLastAssistantMessage.spec.ts
• packages/ai/src/react/ai-chat/utils/submitAIChat.spec.ts

Each one tripped the fast-suite runtime threshold on GitHub runners.

Root cause

This repo treats *.spec.ts[x] as the fast lane and *.slow.ts[x] as the slow lane. Those four AI chat specs had become slow enough that CI started rejecting them, even though they still passed.

The misleading part is that the failure lands inside pnpm check, so it smells like a generic CI or typecheck problem until you read the test:slowest output.

Fix

Move the offenders into the slow lane without changing their assertions:

useAIChatEditor.spec.tsx -> useAIChatEditor.slow.tsx
useEditorChat.spec.tsx -> useEditorChat.slow.tsx
getLastAssistantMessage.spec.ts -> getLastAssistantMessage.slow.ts
submitAIChat.spec.ts -> submitAIChat.slow.ts

That keeps the fast lane honest and lets pnpm check pass on GitHub runners.

Verification

These checks passed after the rename:

bun test ./packages/ai/src/react/ai-chat/hooks/useAIChatEditor.slow.tsx
bun test ./packages/ai/src/react/ai-chat/hooks/useEditorChat.slow.tsx
bun test ./packages/ai/src/react/ai-chat/utils/getLastAssistantMessage.slow.ts
bun test ./packages/ai/src/react/ai-chat/utils/submitAIChat.slow.ts
pnpm install
pnpm turbo build --filter=./packages/ai
pnpm turbo typecheck --filter=./packages/ai
pnpm lint:fix
pnpm check

Prevention

When CI says Fast-suite threshold exceeded, do not waste time treating it like a logic regression.

Read the test:slowest output first. If the spec is just too heavy for the fast lane, rename it to *.slow.ts[x] and keep moving. The bug is usually the file lane, not the assertions.