Implemented Soroban stream storage, events, and errors

.gitignore

@@ -6,3 +6,6 @@ target
 coverage
 *.log
 *.sh
+
+# Soroban test runner — auto-generated, never commit
+**/test_snapshots/

contracts/stream_contract/src/errors.rs

@@ -0,0 +1,28 @@
+use soroban_sdk::contracterror;
+
+/// Exhaustive error surface for `StreamContract`.
+///
+/// Each variant maps to a unique u32 so that clients and indexers can
+/// distinguish failures without parsing error messages.
+#[contracterror]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum StreamError {
+    /// Amount is zero, negative, or otherwise out of range.
+    InvalidAmount = 1,
+    /// No stream exists for the supplied ID.
+    StreamNotFound = 2,
+    /// Caller is not authorised to perform this action on the stream.
+    Unauthorized = 3,
+    /// Operation requires an active stream, but the stream is inactive.
+    StreamInactive = 4,
+    /// `initialize` has already been called; cannot re-initialize.
+    AlreadyInitialized = 5,
+    /// Caller is not the protocol admin.
+    NotAdmin = 6,
+    /// Supplied fee rate exceeds the platform maximum (1 000 bps).
+    InvalidFeeRate = 7,
+    /// Protocol config has not been initialized yet.
+    NotInitialized = 8,
+    /// Duration supplied to `create_stream` is zero.
+    InvalidDuration = 9,
+}

contracts/stream_contract/src/events.rs

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+use soroban_sdk::{contracttype, Address};
+
+/// Emitted when a new stream is created.
+///
+/// Topic: `("stream_created", stream_id)`
+#[contracttype]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct StreamCreatedEvent {
+    pub stream_id: u64,
+    pub sender: Address,
+    pub recipient: Address,
+    /// Net rate per second after protocol fee deduction.
+    pub rate_per_second: i128,
+    pub token_address: Address,
+    /// Net deposited amount after protocol fee deduction.
+    pub deposited_amount: i128,
+    pub start_time: u64,
+}
+
+/// Emitted when a sender tops up an active stream.
+///
+/// Topic: `("stream_topped_up", stream_id)`
+#[contracttype]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct StreamToppedUpEvent {
+    pub stream_id: u64,
+    pub sender: Address,
+    /// Net top-up amount credited to the stream (after protocol fee).
+    pub amount: i128,
+    /// Total deposited amount on the stream after this top-up.
+    pub new_deposited_amount: i128,
+}
+
+/// Emitted when the recipient withdraws accrued tokens.
+///
+/// Topic: `("tokens_withdrawn", stream_id)`
+#[contracttype]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct TokensWithdrawnEvent {
+    pub stream_id: u64,
+    pub recipient: Address,
+    pub amount: i128,
+    pub timestamp: u64,
+}
+
+/// Emitted when a sender cancels an active stream.
+///
+/// Topic: `("stream_cancelled", stream_id)`
+#[contracttype]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct StreamCancelledEvent {
+    pub stream_id: u64,
+    pub sender: Address,
+    pub recipient: Address,
+    /// Total amount withdrawn by the recipient up to cancellation.
+    pub amount_withdrawn: i128,
+    /// Unspent amount (deposited - withdrawn) returned to sender.
+    pub refunded_amount: i128,
+}
+
+/// Emitted when a protocol fee is collected during create or top-up.
+///
+/// Topic: `("fee_collected", stream_id)`
+#[contracttype]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct FeeCollectedEvent {
+    pub stream_id: u64,
+    pub treasury: Address,
+    pub fee_amount: i128,
+    pub token: Address,
+}