[DOCS] Add note on building EMT images with older tags

docs/developer-guide/get-started/emt-build-and-deploy.md

@@ -24,13 +24,17 @@ If you want to create your own custom standalone node, follow the instructions b
 the Edge Microvisor from scratch. If you wish to use the default, non-real-time image of Edge Microvisor
 skip to [Create a bootable USB installer](#2-create-a-bootable-usb-installer).
 
-1. Clone the stable branch of edge-microvisor-toolkit repository:
+All available image configurations are stored in JSON files, located in the `imageconfigs` folder.
+If you want to configure any additional kernel command line arguments, follow the instructions in
+[Architecture Overview](../emt-architecture-overview.md#kernel-command-line).
+For example, to build a RAW image without real-time extensions, use `edge-image.json`.
 
-   Check the [tags](https://github.com/open-edge-platform/edge-microvisor-toolkit/tags) for
-   the `<stable_tag_name>`.
+### 1A. Build from the latest branch
+
+1. Clone the edge-microvisor-toolkit repository:
 
    ```bash
-   git clone https://github.com/open-edge-platform/edge-microvisor-toolkit --branch=<stable_tag_name>
+   git clone https://github.com/open-edge-platform/edge-microvisor-toolkit
    ```
 
 2. Navigate to the `edge-microvisor-toolkit` directory:
@@ -82,17 +86,101 @@ skip to [Create a bootable USB installer](#2-create-a-bootable-usb-installer).
 
 7. Build the toolkit image:
 
-   All available image configurations are stored in JSON files, located in the `imageconfigs` folder. If you want to configure any additional kernel command line arguments, follow the instructions in [Architecture Overview](../emt-architecture-overview.md#kernel-command-line).
-   For example, to build a RAW image without real-time extensions, use `edge-image.json` and run
-   the following command:
+   > **IMPORTANT**: Add the `REBUILD_PACKAGES=n` parameter only for the latest tags,
+   > as the build process uses prebuilt RPMs - downloads the latest available packages
+   > from the RPM repository.
 
    ```bash
    sudo make image -j8 REBUILD_TOOLS=y REBUILD_PACKAGES=n CONFIG_FILE=./imageconfigs/edge-image.json
    ```
 
-   The built image will be located in its separate directory under  `edge-microvisor-toolkit/out/images/`.
+### 1B. Build from a release tag
+
+1. Clone the release branch of edge-microvisor-toolkit repository:
+
+   Check the [tags](https://github.com/open-edge-platform/edge-microvisor-toolkit/tags) for
+   the `<release_tag_name>`. For example,
+   [3.0.20250718](https://github.com/open-edge-platform/edge-microvisor-toolkit/releases/tag/3.0.20250718).
+
+   ```bash
+   git clone https://github.com/open-edge-platform/edge-microvisor-toolkit --branch=3.0.20250718
+   ```
+
+2. Navigate to the `edge-microvisor-toolkit` directory:
+
+   ```bash
+   cd edge-microvisor-toolkit
+   ```
+
+3. Install prerequisites:
+
+   > **Note:** Requirements for building the toolchain were validated on Ubuntu 22.04 host.
+
+   ```bash
+   # Install required dependencies.
+   sudo ./toolkit/docs/building/prerequisites-ubuntu.sh
+
+   # Also supported:
+   #    make -C toolkit install-prereqs
+
+   # Fix go 1.21 link
+   sudo ln -vsf /usr/lib/go-1.23/bin/go /usr/bin/go
+   sudo ln -vsf /usr/lib/go-1.23/bin/gofmt /usr/bin/gofmt
+
+   # Install and configure Docker.
+   curl -fsSL https://get.docker.com -o get-docker.sh
+   sudo sh get-docker.sh
+   sudo usermod -aG docker $USER
+   ```
+
+   **You will need to log out and log back in** for user changes to take effect.
+
+4. Navigate to the `toolkit` subdirectory.
+
+   ```bash
+   cd ./toolkit
+   ```
+
+5. Rebuild the toolchain.
+
+   ```bash
+   sudo make toolchain \
+       PACKAGE_URL_LIST="" \
+       REPO_LIST="" \
+       DISABLE_UPSTREAM_REPOS=y \
+       REBUILD_TOOLCHAIN=y \
+       REBUILD_TOOLS=y
+   ```
+
+6. Customize the toolkit image.
+
+   You can include additional components to your toolkit image by adding RPM packages.
+   For more details, see
+   [Customize Your Edge Microvisor Toolkit Image](./emt-building-howto.md#customize-your-edge-microvisor-toolkit-image).
+
+7. Rebuild RPM packages.
+
+   ```bash
+   # Rebuild packages/RPMs local toolchain
+   sudo make build-packages REBUILD_TOOLS=y VALIDATE_TOOLCHAIN_GPG=n
+   ```
+
+7. Build the toolkit image:
+
+   > **IMPORTANT**: To create an image with an older tag, like
+   > [3.0.20250718](https://github.com/open-edge-platform/edge-microvisor-toolkit/releases/tag/3.0.20250718),
+   > make sure to build it **without** the `REBUILD_PACKAGES=n` option to
+   > perform a full local rebuild.
+   >
+   > Keep in mind, that it will take time (~18 hours on a machine with a 20+ core CPU).
+
+   ```bash
+   sudo make image -j8 REBUILD_TOOLS=y VALIDATE_TOOLCHAIN_GPG=n CONFIG_FILE=./imageconfigs/edge-image.json
+   ```
+
+The built image will be located in its separate directory under  `edge-microvisor-toolkit/out/images/`.
 
-   For more information about specific building parameters, refer to [this article](https://github.com/open-edge-platform/edge-microvisor-toolkit/blob/3.0/toolkit/docs/building/building.md#local-build-variables).
+For more information about specific building parameters, refer to [this article](https://github.com/open-edge-platform/edge-microvisor-toolkit/blob/3.0/toolkit/docs/building/building.md#local-build-variables).
 
 ## 2. Create a bootable USB installer
 

docs/developer-guide/get-started/emt-building-howto.md

@@ -23,31 +23,49 @@ of the resulting image, such as:
 Before you can build OS images you need to build the toolchain and make sure to
 [**install pre-requisites (Ubuntu)**](https://github.com/open-edge-platform/edge-microvisor-toolkit/blob/3.0/toolkit/docs/building/prerequisites-ubuntu.md).
 
-> **Note:**
-  Use the *stable* tag instead of *latest* for building the OS images with prebuilt packages.
-  This is the recommended approach, as building the **entire toolchain** may take a lot of
-  time. Adding the `REBUILD_TOOLCHAIN=y` parameter to the `make` command rebuilds
-  the entire toolchain.
-
-
 ### Clone the Edge Microvisor Toolkit repository
 
-Checkout the stable branch of the repository. See the
+Checkout the release tag of the repository. See the
 [tags](https://github.com/open-edge-platform/edge-microvisor-toolkit/tags) for
-`<stable_tag_name>`.
+`<release_tag_name>`. For example,
+[3.0.20250718](https://github.com/open-edge-platform/edge-microvisor-toolkit/releases/tag/3.0.20250718).
 
 ```bash
-git clone https://github.com/open-edge-platform/edge-microvisor-toolkit --branch=<stable_tag_name>
+git clone https://github.com/open-edge-platform/edge-microvisor-toolkit --branch=3.0.20250718
 ```
 
 ### Build the tools
 
-Navigate to the `edge-microvisor-toolkit/toolkit` directory and build the toolchain.
+1. Navigate to the `edge-microvisor-toolkit/toolkit` directory and build the toolchain.
+
+   ```bash
+   cd edge-microvisor-toolkit/toolkit
+   sudo make toolchain \
+       PACKAGE_URL_LIST="" \
+       REPO_LIST="" \
+       DISABLE_UPSTREAM_REPOS=y \
+       REBUILD_TOOLCHAIN=y \
+       REBUILD_TOOLS=y
+   ```
+
+   > **Note:**
+   > Building the **entire toolchain** may take a lot of time. Adding the
+   > `REBUILD_TOOLCHAIN=y` parameter to the `make` command rebuilds
+   > the entire toolchain.
 
-```bash
-cd edge-microvisor-toolkit/toolkit
-sudo make toolchain REBUILD_TOOLS=y
-```
+
+2. Customize the toolkit image.
+
+   You can include additional components to your toolkit image by adding RPM packages.
+   For more details, see
+   [Customize Your Edge Microvisor Toolkit Image](#customize-your-edge-microvisor-toolkit-image).
+
+3. Rebuild RPM packages.
+
+   ```bash
+   # Rebuild packages/RPMs local toolchain
+   sudo make build-packages REBUILD_TOOLS=y VALIDATE_TOOLCHAIN_GPG=n
+   ```
 
 ## Build the Edge Microvisor Toolkit Image
 
@@ -75,25 +93,37 @@ microvisor/
 Different image types can be built by using different JSON config files and parameters.
 You can find more information about specific parameters in the [build variables](https://github.com/open-edge-platform/edge-microvisor-toolkit/blob/3.0/toolkit/docs/building/building.md#local-build-variables) section.
 
+**IMPORTANT**: To create an image from an older tag, for example the
+[3.0.20250718](https://github.com/open-edge-platform/edge-microvisor-toolkit/releases/tag/3.0.20250718)
+release tag, make sure to build it **without** the `REBUILD_PACKAGES=n` option.
+Otherwise, the build process will download the latest available RPMs,
+which do not match those included in the older tag. It will cause a mismatch
+between versions of installed RPMS in the image and the available SPECs in
+Edge Microvisor Toolkit code.
+
 To build an ISO image, run the following command:
 
 ```bash
-sudo make iso -j8 REBUILD_TOOLS=y REBUILD_PACKAGES=n CONFIG_FILE=./imageconfigs/full.json
+sudo make iso -j8 REBUILD_TOOLS=y CONFIG_FILE=./imageconfigs/full.json
 ```
 
 To build a RAW image without real-time extensions, run the following command:
 
 
 ```bash
-sudo make image -j8 REBUILD_TOOLS=y REBUILD_PACKAGES=n CONFIG_FILE=./imageconfigs/edge-image.json
+sudo make image -j8 REBUILD_TOOLS=y CONFIG_FILE=./imageconfigs/edge-image.json
 ```
 
 To build a RAW image with real-time extensions, use the following command:
 
 ```bash
-sudo make image -j8 REBUILD_TOOLS=y REBUILD_PACKAGES=n CONFIG_FILE=./imageconfigs/edge-image-rt.json
+sudo make image -j8 REBUILD_TOOLS=y CONFIG_FILE=./imageconfigs/edge-image-rt.json
 ```
 
+Keep in mind, that building without `REBUILD_PACKAGES=n` will perform a full
+rebuild based on the tag and take time (~18 hours on a machine with
+a 20+ core CPU).
+
 ## Customize Your Edge Microvisor Toolkit Image
 
 To add packages to the default image, you can define your own `packagelist.json` file, pointing to RPMs that should be included in the image.