DOC-6758 (4.13) Added attachment resolution behaviour update for 4.13… (#2381)

* DOC-6758 (4.13) Added attachment resolution behaviour update for 4.13 ENT and OS

* DOC-6758 - added that default is set

Author: paulmoloneyr3

content/en/platform/corda/4.13/community/get-started/tutorials/supplementary-tutorials/tutorial-attachments.md

@@ -132,6 +132,37 @@ and which are shared explicitly. These are useful for attaching and signing audi
 that isn’t used as part of the contract logic.
 {{< /note >}}
 
+## How attachments are resolved
+
+When building a transaction, Corda automatically tries to resolve any missing class or contract by finding a suitable attachment, using the following order of priority:
+
+1. **Installed CorDapps first:** Corda searches the locally installed CorDapps directories first for a matching attachment.
+2. **Optional database fallback:** If no installed CorDapp is found, and database fallback is enabled (by default, this is enabled), then Corda will search the attachment store (trusted uploaders only). To enable or disable database fallback, use the `net.corda.node.transactionbuilder.missingClassDbSearchDisabled` option; see [Attachment resolution configuration properties]({{< relref "#attachment-resolution-configuration-properties" >}}).
+3. **Legacy CorDapps:** Legacy contracts are only resolved using the `legacy-contracts` CorDapps folder; Corda never falls back to the database.
+4. **Compatibility filtering:** Attachments with an incompatible Kotlin version are excluded.
+
+Prior to version 4.12, only the database option was used; this behavior can be restored using the `net.corda.node.transactionbuilder.installedFirstSearchDisabled` option; see [Attachment resolution configuration properties]({{< relref "#attachment-resolution-configuration-properties" >}}).
+
+### Deterministic attachment selection
+
+If multiple attachments match, Corda uses deterministic ordering to ensure all nodes pick the same attachment.
+Attachments are sorted by:
+
+1. Version (descending)
+2. Insertion date (descending) (for database attachments)
+3. ID (ascending) (for installed attachments)
+
+This prevents runtime-dependent selection and ensures identical transaction builds across the network.
+
+### Attachment resolution configuration properties
+
+The following system properties control the lookup logic:
+
+| Property                                                                | Default Value | Description                                                                            |
+|-------------------------------------------------------------------------|---------------|----------------------------------------------------------------------------------------|
+| net.corda.node.transactionbuilder.missingClassDbSearchDisabled          | false         | If true, disables database fallback — only installed CorDapps are searched.            |
+| net.corda.node.transactionbuilder.installedFirstSearchDisabled          | false         | If true, restores the database-only lookup behavior used in versions prior to 4.12).   |
+
 ## Example
 
 Here is a simple example of how to attach a file to a transaction and send it to the counterparty. The full code for this demo can be found in the [Kotlin](https://github.com/corda/samples-kotlin/tree/release/4.13/Features/attachment-sendfile) and [Java](https://github.com/corda/samples-java/tree/release/4.13/Features/attachment-sendfile) sample repositories.

content/en/platform/corda/4.13/enterprise/get-started/tutorials/supplementary-tutorials/tutorial-attachments.md

@@ -132,6 +132,37 @@ and which are shared explicitly. These are useful for attaching and signing audi
 that isn’t used as part of the contract logic.
 {{< /note >}}
 
+## How attachments are resolved
+
+When building a transaction, Corda automatically tries to resolve any missing class or contract by finding a suitable attachment, using the following order of priority:
+
+1. **Installed CorDapps first:** Corda searches the locally installed CorDapps directories first for a matching attachment.
+2. **Optional database fallback:** If no installed CorDapp is found, and database fallback is enabled, then Corda will search the attachment store (trusted uploaders only). To enable or disable database fallback, use the `net.corda.node.transactionbuilder.missingClassDbSearchDisabled` option; see [Attachment resolution configuration properties]({{< relref "#attachment-resolution-configuration-properties" >}}).
+3. **Legacy CorDapps:** Legacy contracts are only resolved using the `legacy-contracts` CorDapps folder; Corda never falls back to the database.
+4. **Compatibility filtering:** Attachments with an incompatible Kotlin version are excluded.
+
+Prior to version 4.12, only the database option was used; this behavior can be restored using the `net.corda.node.transactionbuilder.installedFirstSearchDisabled` option; see [Attachment resolution configuration properties]({{< relref "#attachment-resolution-configuration-properties" >}}).
+
+### Deterministic attachment selection
+
+If multiple attachments match, Corda uses deterministic ordering to ensure all nodes pick the same attachment.
+Attachments are sorted by:
+
+1. Version (descending)
+2. Insertion date (descending) (for database attachments)
+3. ID (ascending) (for installed attachments)
+
+This prevents runtime-dependent selection and ensures identical transaction builds across the network.
+
+### Attachment resolution configuration properties
+
+The following system properties control the lookup logic:
+
+| Property                                                                | Default Value | Description                                                                            |
+|-------------------------------------------------------------------------|---------------|----------------------------------------------------------------------------------------|
+| net.corda.node.transactionbuilder.missingClassDbSearchDisabled          | false         | If true, disables database fallback — only installed CorDapps are searched.            |
+| net.corda.node.transactionbuilder.installedFirstSearchDisabled          | false         | If true, restores the database-only lookup behavior used in versions prior to 4.12).   |
+
 ## Example
 
 Here is a simple example of how to attach a file to a transaction and send it to the counterparty. The full code for this demo can be found in the [Kotlin](https://github.com/corda/samples-kotlin/tree/release/4.13/Features/attachment-sendfile) and [Java](https://github.com/corda/samples-java/tree/release/4.13/Features/attachment-sendfile) sample repositories.