[Snapshots] PK snapshot: In-run reconnect/resume (cursor + backoff)

[kvch]

Type: AFK

Parent

#601

What to build

Per-sub-range in-memory cursor; on transient/connection errors, reconnect and resume from the cursor using pkg/backoff; data/logic errors fail the sub-range fast.

Requirements

• Dropping the connection mid-walk completes the snapshot correctly
• A constraint/type error fails fast without retry

Depends on

• [Snapshots] PK snapshot: Sub-range execution model #937 — Sub-range execution model