> ## Documentation Index
> Fetch the complete documentation index at: https://docs.tac.build/llms.txt
> Use this file to discover all available pages before exploring further.

# Transaction Lifecycle

> Complete journey of cross-chain transactions from user initiation to final execution and confirmation

The transaction lifecycle in TAC represents the complete journey of a cross-chain operation from initial user action to final confirmation. Understanding this lifecycle helps developers build better applications, implement proper status tracking, and troubleshoot issues effectively.

## Transaction Type

Three transation types are supported:

<Columns cols={3}>
  <Card title="TON->TAC->TON" icon="circle-arrow-right">
    Swaps, adding and removing liquidity,
    withdrawing from dApp
  </Card>

  <Card title="TON->TAC" icon="circle-arrow-right">
    Depositing to dApp, bridging assets
  </Card>

  <Card title="TAC->TON" icon="circle-arrow-right">
    Bridging assets
  </Card>
</Columns>

## Stage Progression

Cross-chain transactions progress through specific stages that can be monitored and tracked for status updates.
Below is an example for **TON->TAC** transaction type:

<Steps>
  <Step title="Collected in TAC" icon="scan-eye">
    * **Detection**: Sequencers detect the cross-chain event and store transaction details in their local databases for validation.

    * **Validation**: Each sequencer independently validates the transaction parameters, asset transfers, and user authorization.
  </Step>

  <Step title="Included in TAC consensus" icon="handshake">
    * **Merkle Tree Formation**: Sequencers compile validated transactions into Merkle trees at the end of each epoch period.

    * **Consensus**: Sequencer groups work to achieve 3/5 internal agreement on their Merkle tree root hashes and executor selection.

    * **Network Submission**: Successfully agreed-upon tree is submitted to TAC EVM.
  </Step>

  <Step title="Executed in TAC" icon="circle-check">
    * **Detection**: Selected executor detects the submitted on-chain Merkle Tree root.

    * **Verification**: Selected executor verifies the root against the transaction info from its internal database.

    * **Asset Operations**: Required token minting or unlocking operations are performed.

    * **Proxy Call**: The EVM proxy contract is called with properly formatted parameters and bridged assets.

    * **Execution**: Proxy forwards formatted parameters and bridged assets to the target EVM dApp contract.
  </Step>
</Steps>

For the **TAC->TON** transaction type, the above stages are mirrored.

For operations that send results back to TON (**TON->TAC->TON** transaction type) the flow continues:

<Steps>
  <Step title="Collected in TON" icon="scan-eye">
    * **Return Message Creation**: dApp on EVM side creates return messages containing results or assets to send back to TON and sends them back to Proxy.

    * **Proxy Call**: Proxy forwards the message and assets to the EVM Cross-Chain Layer contract.

    * **Detection**: The same sequencer network detects return messages and begins validation for the reverse journey.
  </Step>

  <Step title="Included in TON consensus" icon="handshake">
    * **Consensus**: Return messages go through the same consensus process as initial messages.

    * **Network Submission**: Successfully agreed-upon tree is submitted to TON.
  </Step>

  <Step title="Executed in TON" icon="circle-check">
    * **Detection**: Selected executor detects the submitted on-chain Merkle Tree root.

    * **Verification**: Selected executor verifies the root against the transaction info from its internal database.

    * **Asset Operations**: Required token minting or unlocking operations are performed.

    * **Execution**: Return messages are executed on TON, delivering results or assets back to the original user.
  </Step>
</Steps>

## Simplified Operation Status

You don’t need to know the exact flow an operation goes through.
If you only want to know whether it is already executed or still being processed,
use the [simplified statuses](https://github.com/TacBuild/tac-sdk/blob/main/docs/sdks/operation_tracker.md#getsimplifiedoperationstatus) from the TAC SDK.

<Tabs>
  <Tab title="Operation ID Not Found">
    The transaction has been sent and is being processed by the TON Adapter (sequencer network).
  </Tab>

  <Tab title="Pending">
    The transaction is in progress.
  </Tab>

  <Tab title="Successful">
    Everything is fine!
  </Tab>

  <Tab title="Failed">
    The transaction on TAC EVM failed, and there were no attached assets to roll back.
  </Tab>

  <Tab title="Rollback">
    The transaction on TAC EVM failed, and the assets locked on TON were refunded to the original owner.
  </Tab>

  <Tab title="Insufficient Fee">
    This usually happens when manually customizing transaction fees using SDK. In most cases, the default fee is enough.
  </Tab>
</Tabs>

## Monitoring and Debugging

### Real-Time Monitoring

Applications can implement real-time monitoring features from **TAC SDK** to provide users with live updates via [`startTracking`](https://github.com/TacBuild/tac-sdk/blob/main/docs/sdks/utilities.md#starttracking) feature:

```javascript theme={null}
const transactionLinker = await tacSdk.sendCrossChainTransaction(
  evmProxyMsg, // What to call on EVM
  sender, // TON wallet
  assets // Tokens to bridge
);
await tacSdk.startTracking(transactionLinker);
```

### Debugging Transactions

* **Status**: Status info and error message if any. Learn more in SDK's docs [related section](https://github.com/TacBuild/tac-sdk/blob/main/docs/sdks/operation_tracker.md#getsimplifiedoperationstatus).

* **Stage Profiling**: Detailed info about every stage. Learn more in SDK's docs [related section](https://github.com/TacBuild/tac-sdk/blob/main/docs/sdks/operation_tracker.md#getstageprofiling).