IPFS Cost Estimation in Confirm/Execute Flow

[tcsenpai]

Implement custom_charges mechanism in the confirm/execute two-step transaction flow to allow users to see IPFS costs before transaction execution.

Overview

Users currently cannot see how much an IPFS operation will cost before it executes. This epic adds a custom_charges field to transactions that:

1. Client includes cost estimate in tx.content BEFORE signing
2. Node validates the estimate during confirmTx
3. Node returns actual cost breakdown in ValidityData
4. User reviews and approves before broadcastTx
5. Execution charges actual cost (≤ signed max)

Key Principle

Transaction is NEVER modified by the node - client signs the max cost they agree to pay.

Affected Repositories

• Node (/home/tcsenpai/kynesys/node): Validation, cost calculation, ValidityData enrichment
• SDK (../sdks): Types, estimation helpers, transaction building

Reference

See Serena memory: ipfs_custom_charges_implementation.md