docs: add Decoding Error 1010 tutorial for Bounty #318

[a918124259a]

Summary

Complete tutorial submission for Bounty #318 — Decoding Error 1010: What 'Invalid Transaction' Actually Means.

This tutorial provides a developer-focused deep-dive into Midnight's error code system, based on analysis of the actual midnight-ledger source code. It goes beyond surface-level explanations to show the exact Rust source locations, code structures, and diagnostic steps for each error code.

Deliverables

File	Description
tutorials/decoding-error-1010/TUTORIAL.md	~2,500-word comprehensive walkthrough

Coverage

1. Error code structure: POOL_INVALID_TX = AUTHOR(1000) + 10 — how Substrate's custom error wrapping works
2. Error 139 (Transaction Builder UnknownError): SDK version mismatch, with diagnosis steps
3. Error 154 (BlockLimitExceeded): The 5-dimension cost model with actual block limits and normalization
4. Error 168 (RETIRED): Historical context
5. Error 170 (InvalidDustSpendProof): Merkle root pruning, indexer sync issues, with diagnostic fields
6. Error 186 (RETIRED — replaced by 212-218): Full sub-code mapping for effects check failures
7. Ledger cost model: All 5 dimensions with Rust source code references
8. Diagnostic toolkit: Logging, SDK version checking, indexer monitoring, cost estimation
9. Quick reference flowchart

Key Differentiators

• Source-level accuracy: Based on actual midnight-ledger Rust source (types.rs, cost_model.rs, lib.rs)
• Not generic blockchain advice: Each error maps to specific Midnight code locations
• Practical diagnostics: Real commands and code snippets for debugging
• Cost model explained: The 5-dimensional fee model with concrete block limits (200KB, 50KB, 1MB, etc.)
• Quick fix flowchart: Start-to-finish diagnostic flow

Bounty: #318 - Decoding Error 1010 Tutorial
Wallet: (Ready to provide upon acceptance)

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