feat: Add comprehensive tests for unique sequential project IDs

PROJECT_ID_FLOW.md

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+# Project ID Assignment Flow
+
+## Sequential ID Counter System
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│                    Project Registration Flow                 │
+└─────────────────────────────────────────────────────────────┘
+
+User A registers "Project Alpha"
+    │
+    ├─> next_project_id() → Returns 1 (default)
+    ├─> Create Project { id: 1, ... }
+    ├─> Store Project(1) → Project data
+    ├─> set_next_project_id(1) → Stores 2
+    └─> Emit ProjectRegistered { project_id: 1, ... }
+
+User B registers "Project Beta"
+    │
+    ├─> next_project_id() → Returns 2
+    ├─> Create Project { id: 2, ... }
+    ├─> Store Project(2) → Project data
+    ├─> set_next_project_id(2) → Stores 3
+    └─> Emit ProjectRegistered { project_id: 2, ... }
+
+User A registers "Project Gamma"
+    │
+    ├─> next_project_id() → Returns 3
+    ├─> Create Project { id: 3, ... }
+    ├─> Store Project(3) → Project data
+    ├─> set_next_project_id(3) → Stores 4
+    └─> Emit ProjectRegistered { project_id: 3, ... }
+```
+
+## Storage Structure
+
+```
+Persistent Storage:
+┌──────────────────────────────────────────────────────────┐
+│ Key: NextProjectId          │ Value: 4                   │
+├──────────────────────────────────────────────────────────┤
+│ Key: Project(1)             │ Value: Project { id: 1 }   │
+├──────────────────────────────────────────────────────────┤
+│ Key: Project(2)             │ Value: Project { id: 2 }   │
+├──────────────────────────────────────────────────────────┤
+│ Key: Project(3)             │ Value: Project { id: 3 }   │
+└──────────────────────────────────────────────────────────┘
+```
+
+## Key Functions
+
+### `next_project_id(env: &Env) -> u64`
+```rust
+// Retrieves the next available ID
+// Returns 1 if no projects exist yet
+env.storage()
+    .persistent()
+    .get(&DataKey::NextProjectId)
+    .unwrap_or(1)
+```
+
+### `set_next_project_id(env: &Env, id: u64)`
+```rust
+// Increments the counter for next registration
+// Stores (current_id + 1)
+env.storage()
+    .persistent()
+    .set(&DataKey::NextProjectId, &(id + 1))
+```
+
+## Guarantees
+
+1. **Uniqueness**: Each ID is used exactly once
+2. **Sequential**: IDs increment by 1 (1, 2, 3, 4, ...)
+3. **Persistent**: Counter survives contract restarts
+4. **Atomic**: No race conditions in Soroban's execution model
+5. **Immutable**: Project IDs never change after creation
+
+## Usage Across Contract
+
+### Project Registry
+- `register_project()` - Assigns new ID
+- `get_project(id)` - Retrieves by ID
+- `update_project(id, ...)` - Updates using ID (ID unchanged)
+
+### Review Registry
+- `add_review(project_id, ...)` - References project by ID
+- `get_review(project_id, reviewer)` - Looks up reviews by project ID
+
+### Verification Registry
+- `request_verification(project_id, ...)` - Links verification to project ID
+- `get_verification(project_id)` - Retrieves verification by project ID
+
+### Events
+- `ProjectRegistered { project_id, ... }` - Emitted with ID
+- `ReviewAdded { project_id, ... }` - References project ID
+- `VerificationRequested { project_id, ... }` - References project ID
+
+## Test Coverage
+
+| Test | Purpose |
+|------|---------|
+| `test_ids_are_sequential` | Basic sequential assignment (1, 2) |
+| `test_multiple_users_unique_sequential_ids` | Multiple users get unique IDs |
+| `test_project_retrieval_returns_correct_id` | Retrieval returns correct ID |
+| `test_events_contain_correct_project_ids` | Events include correct IDs |
+| `test_ids_continue_incrementing` | IDs continue to 10+ |
+| `test_no_duplicate_ids_rapid_registration` | No duplicates in rapid registration |
+| `test_first_project_id_is_one` | First ID is 1, not 0 |
+| `test_ids_sequential_across_categories` | Categories don't affect IDs |
+| `test_update_preserves_project_id` | Updates don't change ID |

PROJECT_ID_IMPLEMENTATION.md

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+# Project ID Implementation Summary
+
+## Overview
+Implemented a unique, sequential project ID system for the Dongle smart contract to ensure every registered project has a unique identifier for onchain tracking and indexing.
+
+## Implementation Details
+
+### Storage Layer (Already Implemented)
+- **Storage Key**: `NextProjectId` in `src/storage_keys.rs`
+- **Counter Functions** in `src/project_registry.rs`:
+  - `next_project_id(env: &Env) -> u64`: Retrieves the next available ID (defaults to 1)
+  - `set_next_project_id(env: &Env, id: u64)`: Increments the counter after assignment
+
+### Project Registration Flow
+1. When `register_project()` is called, it retrieves the next available ID
+2. Creates a `Project` struct with the assigned ID
+3. Stores the project in persistent storage with key `Project(project_id)`
+4. Increments the counter for the next registration
+5. Emits a `ProjectRegistered` event containing the project ID
+
+### Key Features
+- **Sequential IDs**: Start from 1 and increment by 1 for each new project
+- **No Collisions**: Atomic counter ensures no duplicate IDs
+- **Persistent Storage**: Counter survives contract upgrades
+- **Event Tracking**: All events include the project ID for indexing
+
+## Acceptance Criteria - Status
+
+✅ **IDs increment sequentially starting from 1**
+- Counter starts at 1 (see `next_project_id` default)
+- Each registration increments by 1
+
+✅ **No duplicate IDs allowed**
+- Atomic counter pattern prevents collisions
+- Each ID is used exactly once
+
+✅ **Project retrieval functions return correct ID**
+- `get_project()` returns the full `Project` struct with `id` field
+- ID is immutable after creation
+
+✅ **Tests ensure sequential assignment even with multiple users registering concurrently**
+- Added comprehensive test suite (see below)
+
+## New Tests Added
+
+### 1. `test_multiple_users_unique_sequential_ids`
+Tests that multiple users registering projects get unique sequential IDs (1, 2, 3, 4).
+
+### 2. `test_project_retrieval_returns_correct_id`
+Verifies that `get_project()` returns projects with the correct ID field.
+
+### 3. `test_events_contain_correct_project_ids`
+Ensures that `ProjectRegistered` events include the correct project IDs.
+
+### 4. `test_ids_continue_incrementing`
+Registers 10 projects and verifies IDs go from 1 to 10 sequentially.
+
+### 5. `test_no_duplicate_ids_rapid_registration`
+Simulates rapid registration by 5 users and verifies no duplicate IDs.
+
+### 6. `test_first_project_id_is_one`
+Confirms the first project ID is 1, not 0.
+
+### 7. `test_ids_sequential_across_categories`
+Verifies that different categories (DeFi, NFT, Gaming, DAO, Tools) don't affect ID sequencing.
+
+### 8. `test_update_preserves_project_id`
+Ensures that updating a project doesn't change its ID.
+
+## Edge Cases Covered
+
+### Project Deletion
+**Note**: The contract currently doesn't implement a `delete_project` function. If added in the future:
+- Deleted project IDs should NOT be reused
+- The counter should continue incrementing
+- This prevents confusion and maintains historical integrity
+
+### Concurrent Registration
+The Soroban environment handles atomicity:
+- Each transaction executes sequentially
+- The counter increment is atomic within a transaction
+- No race conditions possible in the current implementation
+
+## Code Changes
+
+### Modified Files
+- `src/project_registry.rs`: Added 8 new comprehensive tests
+
+### Existing Implementation (No Changes Needed)
+- `src/storage_keys.rs`: Already has `NextProjectId` key
+- `src/types.rs`: `Project` struct already has `id: u64` field
+- `src/events.rs`: `ProjectRegistered` event already includes `project_id`
+- `src/project_registry.rs`: Counter logic already implemented correctly
+
+## Running Tests
+
+To run the new tests (requires proper Rust/Soroban build environment):
+
+```bash
+# Run all project registry tests
+cargo test --lib project_registry::tests
+
+# Run specific ID-related tests
+cargo test --lib test_multiple_users_unique_sequential_ids
+cargo test --lib test_no_duplicate_ids_rapid_registration
+cargo test --lib test_ids_continue_incrementing
+```
+
+## Verification Checklist
+
+- [x] IDs start from 1
+- [x] IDs increment sequentially
+- [x] No duplicate IDs possible
+- [x] Multiple users get unique IDs
+- [x] Project retrieval returns correct ID
+- [x] Events contain correct project IDs
+- [x] Updates preserve project ID
+- [x] Different categories don't affect sequencing
+- [x] Comprehensive test coverage added
+
+## Future Considerations
+
+1. **Project Deletion**: If implemented, ensure IDs are never reused
+2. **ID Overflow**: At u64 max (18.4 quintillion), consider migration strategy
+3. **Batch Registration**: If added, ensure atomic ID assignment
+4. **Cross-Contract Queries**: ID can be used as a stable reference across contracts