Integrate the already-merged step-limit work from develop. Only conflict was
ai-chat.service.spec.ts: both sides appended a describe block and edited the
import line. Resolved as a union — keep compactToolOutput + the assistantParts/
serializeSteps/rowToUiMessage suites (this branch) AND the prepareAgentStep
suite (develop), importing all symbols from ai-chat.service.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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