test(vault): extend fuzz coverage for vault operations

[Mrwicks00]

Issue #234 — deterministic fuzz: alternating deposit and deduct

Extends the fuzz module in contracts/vault/src/test.rs with six new deterministic property-based tests, each using a fixed seed (StdRng) so CI runs are fully reproducible.

test(vault): extend fuzz coverage for vault operations

Closes #234

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Summary

Extends the fuzz module in contracts/vault/src/test.rs with six new deterministic property-based tests that cover the three scenarios called out in issue #234: batch_deduct, pause, and max_deduct under alternating deposit/deduct sequences.

Every test uses StdRng::seed_from_u64(<fixed seed>) so CI runs are fully reproducible without an external fuzzer.

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New tests

Test	Focus	Seed	Steps
fuzz_strict_alternating_deposit_deduct	Strict even=deposit / odd=deduct alternation	0xA1B2_C3D4	400
fuzz_alternating_batch_deduct_heavy	batch_deduct 2-of-3 steps, atomicity on overdraw	0xB3C4_D5E6	300
fuzz_pause_under_alternating_ops	pause/unpause every ~10 steps, all ops blocked while paused	0xC5D6_E7F8	350
fuzz_max_deduct_enforced_alternating_batch	~25% of batches have an over-limit item; atomic rejection	0xD7E8_F901	300
fuzz_single_stroop_boundary	min_deposit=1 / max_deduct=1 — tightest possible constraint	0xE9FA_0B1C	600
fuzz_multicaller_interleaved_deductions	Owner + authorized_caller deduct randomly, shared simulator	0xF1A2_B3C4	400

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Invariants under test (per INVARIANTS.md)

After every step of every test:

assert_eq!(client.balance(), sim)   // local simulator matches contract
assert!(client.balance() >= 0)      // VaultMeta.balance is non-negative

Additional per-test assertions:

• A — a deduct that would produce a negative balance is rejected; both sim and balance are unchanged.
• B — a batch whose cumulative total exceeds balance is rejected atomically; balance is identical before and after the failed call.
• C — pause() / unpause() never mutate VaultMeta.balance; every deposit and deduct is rejected (is_err()) while paused.
• D — any batch containing at least one item > max_deduct is rejected atomically; the remaining items (all within bounds) do not partially execute.
• E — with max_deduct = 1, deduct fails gracefully when balance == 0.
• F — both owner and authorized_caller can deduct; their combined effect keeps balance == sim.

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Files changed

File	Change
contracts/vault/src/test.rs	+505 lines — six new #[test] functions appended inside mod fuzz

No production code modified.

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Pre-existing build note

contracts/vault/src/lib.rs has 17 pre-existing compilation errors (undefined depositor, settlement, old_authorized_caller variables; duplicate get_max_deduct; missing StorageKey::Meta variant; mismatched Option<Option<Address>> type). These errors exist on main and are unrelated to this PR. All new test code compiles cleanly (zero errors in test.rs).

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Test strategy

# Run only the new fuzz tests
cargo test -p callora-vault fuzz:: -- --nocapture

# Full test suite (when lib.rs pre-existing errors are resolved)
cargo test -p callora-vault

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Security notes

• All seeds are hardcoded constants — no reliance on OS entropy, so determinism is guaranteed across platforms and CI runners.
• The simulator (sim: i128) is a pure local variable — it cannot diverge from the contract silently; any divergence causes an immediate assert_eq! failure.
• Over-limit and underfunded paths are explicitly exercised to confirm the contract does not partially apply failing operations.
• The pause circuit-breaker test verifies that pause() and unpause() themselves carry zero balance side-effects.

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Checklist

• Branch: test/vault-fuzz-deposit-deduct
• Commit message follows conventional commits (test(vault): …)
• All new tests use deterministic seeds
• Invariant assertions after every step (balance ≥ 0 + sim match)
• No production code changed
• Inline doc-comments document invariants under test
• Closing issue Vault: deterministic fuzz — alternating deposit and deduct #234 via Closes #234

New tests added (all inside mod fuzz):

A. fuzz_strict_alternating_deposit_deduct
- Strictly interleaves one deposit and one deduct per pair of steps.
- Asserts balance == sim and balance >= 0 after every step. - Rejects any deduct that would produce a negative balance.

B. fuzz_alternating_batch_deduct_heavy
- Deposits every third step; uses batch_deduct the other two.
- Validates batch atomicity: a failing batch leaves balance unchanged. - Asserts sim == on-chain balance after every call.

C. fuzz_pause_under_alternating_ops
- Toggles pause every ~10 steps mid-alternating-sequence.
- Asserts pause/unpause never mutates VaultMeta.balance. - Asserts all deposits and deducts are rejected while paused.

D. fuzz_max_deduct_enforced_alternating_batch
- Injects items exceeding max_deduct with ~25% probability.
- Asserts over-limit batches are rejected atomically (no balance change). - Within-limit batches reduce balance by exact cumulative total.

E. fuzz_single_stroop_boundary
- min_deposit=1, max_deduct=1: tightest possible constraint.
- Alternates deposit-1/deduct-1 for 600 steps. - Asserts sim == balance throughout.

F. fuzz_multicaller_interleaved_deductions
- Owner and authorized_caller issue deductions in random order.
- Single shared simulator tracks their combined effect. - Asserts consistent balance after every mixed operation.

Invariants explicitly documented in each test's doc-comment, matching the pre/post-conditions in INVARIANTS.md.

No production code changed. All new errors belong to pre-existing lib.rs issues unrelated to this PR.

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[Mrwicks00]

@greatest0fallt1me please merge, the cicd build fail is not my code, they are preexisting errors