fix(cloud-agent-next): include step and error detail in session restore failure messages

[eshurakov]

Summary

When kilo-restore-session.js fails, the structured stdout (containing step, error, and code fields) was logged locally inside the Durable Object but lost by the time the error propagated through the tRPC chain to logpush. The error message only said "Cold-start session restore failed: exit 1", making it impossible to diagnose failures from logpush alone.

This change enriches the SessionSnapshotRestoreError message at the throw site to include step and error fields extracted from the restore script's JSON stdout. The richer message flows naturally through the existing error chain (SessionSnapshotRestoreError → ExecutionError.workspaceSetupFailed → TRPCError) without any downstream changes.

Before: "Failed to prepare workspace: Cold-start session restore failed: exit 1"
After: "Failed to prepare workspace: Cold-start session restore failed: exit 1, step=import, error=kilo import failed exitCode=1"

Verification

• pnpm run typecheck — passed (tsgo + wrapper)
• pnpm run test — 642 tests passed, 25 test files
• Verified existing test assertions use substring matching (toThrow('Cold-start session restore failed')) and remain compatible with the enriched message

Visual Changes

N/A

Reviewer Notes

• Single file change: cloud-agent-next/src/session-service.ts — extends the existing stdout JSON parsing block (which already extracts code) to also extract step and error.
• No new error class fields, no changes to orchestrator/CloudAgentSession/session-execution.
• The as Record<string, unknown> cast on JSON.parse matches the existing pattern at this location.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 files)

• cloud-agent-next/src/session-service.ts