fix: Add retry logic for Bun socket connection errors

[konard]

Summary

Adds automatic retry logic for socket connection errors that occur due to Bun's known 10-second idle timeout issue in Bun.serve() contexts.

Problem

When using the agent CLI with streaming API providers (e.g., opencode/grok-code), connections frequently fail after approximately 10-12 seconds with:

Error: The socket connection was closed unexpectedly. For more information, pass `verbose: true` in the second argument to fetch()

This is a known Bun limitation (oven-sh/bun#14439) where the default idleTimeout of 10 seconds causes long-running streaming connections to be dropped.

Solution

1. New Error Type: Added SocketConnectionError in message-v2.ts that is always marked as retryable
2. Error Detection: Updated fromError() to detect socket errors by message pattern
3. Retry Logic: Enhanced processor.ts to retry socket errors up to 3 times
4. Backoff Strategy: Uses exponential backoff (1s → 2s → 4s) specific to socket errors

Changes

• js/src/session/message-v2.ts - Add SocketConnectionError type and detection logic
• js/src/session/processor.ts - Add retry handling for socket connection errors
• js/src/session/retry.ts - Add socket-specific retry configuration and delay function
• js/tests/socket-retry.test.js - Unit tests for socket error detection and retry logic
• docs/case-studies/issue-109/ - Case study documentation with timeline and analysis
• js/experiments/socket-error-simulation.ts - Experiment script to verify fix behavior

Test Plan

• Unit tests pass (bun test tests/socket-retry.test.js)
• Lint checks pass (bun run lint)
• Format checks pass (bun run format:check)
• Experiment script validates error detection and retry delays

References

• Fixes Socket connection closed unexpectedly during streaming API responses with Bun #109
• oven-sh/bun#14439 - Bun idle timeout issue
• link-assistant/hive-mind#1098 - Original report with full case study

[konard]

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