Storage Compaction Pass

[oyinade247]

Closes #567

File locations

File	Monorepo path
Contract source	app/contract/src/lib.rs
Cargo manifest	app/contract/Cargo.toml
Integration & regression tests	app/contract/tests/integration.rs
Criterion benchmarks	app/contract/benches/storage_bench.rs
Audit document	app/contract/STORAGE_COMPACTION.md

The two compile-time structural tests are the key regression guards: they make it impossible to accidentally re-introduce the redundant fields without a visible, intentional change.

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Semantic invariants preserved

• A username can only be claimed once ✓
• link_count is monotonically increasing and equals the next link_id ✓
• PaymentLink::creator matches UserRecord::owner at creation time ✓
• REVOKED flag is OR-ed in; no other flags are cleared ✓
• total_received accumulates correctly across multiple payments ✓
• total_links (global) matches sum of all per-user link_count values ✓

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Migration note

This is a breaking storage schema change. Existing testnet data encoded under the old String-keyed schema is not readable by the new contract. A fresh deploy to testnet is sufficient — no migration invocation is needed.

Mainnet is unaffected: X-Ray / ZK functionality went live on 22 Jan 2026 under the new schema, so no user data exists under the old one.

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Checklist

• Audit completed — all storage records reviewed for redundancy
• DataKey variants compacted (String → Symbol, sequence number inlined)
• UserRecord compacted (username dropped, link_count narrowed)
• PaymentLink compacted (username dropped, asset promoted to Symbol, booleans bitpacked)
• Benchmarks added with before/after numbers documented
• Regression tests cover all semantic behaviour
• Compile-time structural guards prevent re-introduction of dropped fields
• STORAGE_COMPACTION.md audit document committed alongside code
• No breaking change to contract public API (function signatures unchanged)

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[Cedarich]

@oyinade247 fix ci