Feature: Durable Stream Resume and Reconnection for Chat Runs #51

Description

Add resilience for chat streaming so users can recover cleanly across refreshes/reconnects and continue in-flight runs without duplicated output.

Acceptance Criteria

• Refresh during an active run resumes durable stream consumption.
• Reconnection does not duplicate message chunks or final content.
• Run lifecycle state is visible (running, complete, error).
• Failed runs surface actionable retry UX.

Tasks

• Implement durable stream resume from last known cursor/offset.
• Add client-side deduplication strategy for chunk replay.
• Persist/derive run status in session/message model.
• Add UI indicators for run states and retry action.
• Add tests for reconnect + dedupe scenarios.

Tracer Bullet Reference

Follows project chat streaming tracer bullet.

Additional Context

Use SolidType durable stream event schema and conventions.