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+# Implementation Checklist
+
+Work through each item in order. Check it off before moving to the next.
+
+## Settlement contract
+
+- [ ] Add `TotalReceived` variant to `StorageKey` enum
+- [ ] In `receive_payment`: after crediting developer or pool, do
+      `total = get_total_received() + amount` (checked_add, panic on overflow),
+      write back to `StorageKey::TotalReceived`
+- [ ] Same increment in `batch_receive_payment` (once per item, same pattern)
+- [ ] Add `pub fn get_total_received(env: Env) -> i128` (returns 0 if key absent)
+- [ ] Add unit test: single receive → `get_total_received() == amount`
+- [ ] Add unit test: multiple receives → running total matches sum
+
+## Vault contract
+
+- [ ] Add `TotalDeducted` variant to `StorageKey` enum
+- [ ] In `deduct`: after `meta.balance` update, increment `TotalDeducted` (checked_add)
+- [ ] In the batch loop in `batch_deduct`: accumulate per-item amounts, then
+      increment `TotalDeducted` once after the loop commits
+- [ ] Add `pub fn get_total_deducted(env: Env) -> i128` (returns 0 if key absent)
+- [ ] Add unit test: deduct → `get_total_deducted() == amount`
+- [ ] Add unit test: batch_deduct → `get_total_deducted() == sum of items`
+
+## Cross-contract test
+
+- [ ] Create `contracts/vault/src/test_cross_invariant.rs`
+- [ ] Register vault + settlement (+ optional revenue pool stub) in one env
+- [ ] Run 64-seed × 48-step random sequence
+- [ ] After every step assert:
+      `vault.get_total_deducted() == settlement.get_total_received()`
+- [ ] After every step assert settlement internal conservation:
+      `settlement.get_total_received()
+         == Σ developer_balance + global_pool.total_balance + cumulative_withdrawn`
+- [ ] Add `#[cfg(test)] mod test_cross_invariant;` to `contracts/vault/src/lib.rs`
+
+## Docs
+
+- [ ] `docs/interfaces/vault.json`: add `get_total_deducted` function entry
+- [ ] `docs/interfaces/settlement.json`: add `get_total_received` function entry
+
+## Final checks
+
+- [ ] `cargo fmt --all -- --check` passes
+- [ ] `cargo clippy --all-targets --all-features -- -D warnings` passes
+- [ ] `cargo test --workspace` green (all existing + new tests)
+- [ ] Coverage ≥ 95% (`./scripts/coverage.sh`)
diff --git a/docs/issues/cross-contract-conservation-invariants/README.md b/docs/issues/cross-contract-conservation-invariants/README.md
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+# Cross-Contract Cumulative Conservation Invariants
+
+**Campaign:** GrantFox  
+**Scope:** `callora-vault`, `callora-settlement`, `callora-revenue-pool`  
+**Type:** Smart-contract invariant hardening  
+
+---
+
+## Problem
+
+Each contract has its own per-contract invariant tests, but no test verifies that
+funds are conserved **across** the full vault → settlement → revenue-pool pipeline.
+A bug in the routing logic (e.g. double-credit, missing transfer, misrouted amount)
+could pass all three individual test suites while violating conservation end-to-end.
+
+---
+
+## Invariant to Enforce
+
+```
+vault.deducted_total
+  == settlement.developer_balances_sum
+   + settlement.global_pool.total_balance
+   + revenue_pool.usdc_on_ledger
+```
+
+More precisely, for every sequence of operations:
+
+1. **Vault conservation** — `vault.balance + Σ(deducted)` equals the initial deposit.
+2. **Settlement conservation** — `Σ(receive_payment amounts)` equals
+   `Σ(developer_balance[i]) + global_pool.total_balance`.
+3. **Revenue-pool conservation** — `Σ(yield_deposit amounts)` equals
+   `revenue_pool USDC on-ledger + Σ(distributed amounts)`.
+4. **End-to-end** — `vault.deducted_total` equals the sum of all credits that
+   eventually arrived in settlement or revenue pool.
+
+---
+
+## Implementation Plan
+
+### 1. `callora-settlement` — add `get_total_received` view
+
+Settlement currently tracks per-developer balances and a global pool balance but
+has no running total of all funds received. Add a persistent `TotalReceived`
+storage key incremented on every `receive_payment` / `batch_receive_payment` call.
+
+```
+StorageKey::TotalReceived  →  i128  (default 0)
+```
+
+- Increment in `receive_payment` using `checked_add` (panic on overflow).
+- Expose as `pub fn get_total_received(env: Env) -> i128`.
+- Invariant: `get_total_received() == Σ developer_balance[i] + global_pool.total_balance + Σ withdrawn`.
+
+### 2. `callora-vault` — add `get_total_deducted` view
+
+Vault tracks `meta.balance` (decremented on deduct) but not cumulative outflow.
+Add a persistent `TotalDeducted` storage key incremented on every successful
+`deduct` / `batch_deduct`.
+
+```
+StorageKey::TotalDeducted  →  i128  (default 0)
+```
+
+- Increment after `meta.balance` update using `checked_add`.
+- Expose as `pub fn get_total_deducted(env: Env) -> i128`.
+- Invariant: `initial_balance - meta.balance == get_total_deducted()` (ignoring withdrawals).
+
+### 3. Cross-contract test — `test_cross_invariant.rs`
+
+A new integration-style test module wired up in the vault crate (which already
+imports `callora-settlement` as a dev-dependency) that:
+
+- Deploys vault + settlement + revenue pool together.
+- Runs a random sequence (64 seeds × 48 steps) of: deposit, deduct (→ settlement),
+  batch_deduct, developer withdraw, pool distribute.
+- After every step checks:
+  ```
+  vault.get_total_deducted()
+    == settlement.get_total_received()
+  ```
+  and:
+  ```
+  settlement.get_total_received()
+    == Σ settlement.get_developer_balance(dev_i)
+     + settlement.get_global_pool().total_balance
+     + total_withdrawn_from_settlement
+  ```
+
+---
+
+## Files to Change
+
+| File | Change |
+|------|--------|
+| `contracts/settlement/src/lib.rs` | Add `StorageKey::TotalReceived`, increment in `receive_payment`, expose `get_total_received` |
+| `contracts/vault/src/lib.rs` | Add `StorageKey::TotalDeducted`, increment in `deduct`/`batch_deduct`, expose `get_total_deducted` |
+| `contracts/vault/src/test_cross_invariant.rs` | New: cross-contract conservation test |
+| `contracts/vault/src/lib.rs` | Add `#[cfg(test)] mod test_cross_invariant` |
+| `docs/interfaces/vault.json` | Document `get_total_deducted` |
+| `docs/interfaces/settlement.json` | Document `get_total_received` |
+
+---
+
+## Acceptance Criteria
+
+- [ ] `get_total_deducted` view exists on vault; returns cumulative deducted amount.
+- [ ] `get_total_received` view exists on settlement; returns cumulative received amount.
+- [ ] `test_cross_invariant.rs` passes with ≥ 64 seeds, ≥ 48 steps each.
+- [ ] All three per-contract invariant tests continue to pass.
+- [ ] `cargo clippy -- -D warnings` clean.
+- [ ] `cargo test --workspace` green.
+- [ ] Interface JSON docs updated.
+
+---
+
+## Branch
+
+```bash
+git checkout -b feature/cross-contract-conservation-invariants
+```
+
+Commit message:
+
+```
+feat: cross-contract cumulative conservation invariants
+
+- vault: add TotalDeducted storage key + get_total_deducted() view
+- settlement: add TotalReceived storage key + get_total_received() view
+- test_cross_invariant: 64-seed × 48-step end-to-end conservation check
+- docs: update vault.json and settlement.json interface summaries
+
+Closes #<issue>
+```
+
+---
+
+## Security Notes
+
+- Both new counters use `checked_add` — overflow panics loudly rather than wrapping silently.
+- Both are view-only getter additions; no existing auth surface is changed.
+- `TotalDeducted` / `TotalReceived` are informational — they do not gate any transfer logic.