diff --git a/.github/scripts/prune-runner-apt-sources.sh b/.github/scripts/prune-runner-apt-sources.sh
new file mode 100755
index 00000000000..0eab0a538d3
--- /dev/null
+++ b/.github/scripts/prune-runner-apt-sources.sh
@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+#
+# GitHub's Ubuntu runner images preinstall Microsoft's apt repositories (azure-cli and the
+# packages.microsoft.com prod repo). Wails uses neither, and when that host serves a 403 for
+# them - see https://github.com/wailsapp/wails/issues/6040 - `apt-get update` fails and takes
+# the whole job down with it. Dropping the two list files makes our CI independent of it.
+#
+# Only do this on ephemeral GitHub-hosted VMs. On a self-hosted runner, or on a developer's
+# machine running these workflows locally with `act`, /etc/apt belongs to the host: deleting
+# real apt sources there is destructive and not something a CI job should do.
+set -euo pipefail
+
+if [ "${ACT:-}" = "true" ] || [ "${RUNNER_ENVIRONMENT:-}" != "github-hosted" ]; then
+	echo "Leaving apt sources untouched (ACT=${ACT:-unset}, RUNNER_ENVIRONMENT=${RUNNER_ENVIRONMENT:-unset})."
+	exit 0
+fi
+
+sudo rm -f /etc/apt/sources.list.d/microsoft-prod.list /etc/apt/sources.list.d/azure-cli.list
diff --git a/.github/workflows/build-and-test-v3.yml b/.github/workflows/build-and-test-v3.yml
index 3a8b58119f2..14fb14ff118 100644
--- a/.github/workflows/build-and-test-v3.yml
+++ b/.github/workflows/build-and-test-v3.yml
@@ -108,6 +108,8 @@ jobs:
       - name: Install linux dependencies (GTK4 default)
         if: matrix.os == 'ubuntu-latest'
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-4-dev libwebkitgtk-6.0-dev libwayland-dev build-essential pkg-config xvfb x11-xserver-utils at-spi2-core xdg-desktop-portal-gtk
 
@@ -219,6 +221,8 @@ jobs:
       - name: Install linux dependencies (GTK4 default)
         if: matrix.os == 'ubuntu-latest'
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-4-dev libwebkitgtk-6.0-dev libwayland-dev build-essential pkg-config
 
diff --git a/.github/workflows/build-and-test.yml b/.github/workflows/build-and-test.yml
index 094091d9d9c..07e0d8a0461 100644
--- a/.github/workflows/build-and-test.yml
+++ b/.github/workflows/build-and-test.yml
@@ -27,12 +27,16 @@ jobs:
       - name: Install apt packages (ubuntu-22.04)
         if: matrix.os == 'ubuntu-22.04'
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-3-dev libwebkit2gtk-4.0-dev build-essential pkg-config
 
       - name: Install apt packages (ubuntu-24.04)
         if: matrix.os == 'ubuntu-24.04'
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-3-dev libwebkit2gtk-4.1-dev build-essential pkg-config libegl1
 
@@ -130,6 +134,8 @@ jobs:
       - name: Install apt packages (ubuntu-22.04)
         if: matrix.os == 'ubuntu-22.04'
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-3-dev libwebkit2gtk-4.0-dev build-essential pkg-config
 
@@ -140,6 +146,8 @@ jobs:
       - name: Install apt packages (ubuntu-24.04)
         if: matrix.os == 'ubuntu-24.04'
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-3-dev libwebkit2gtk-4.1-dev build-essential pkg-config libegl1
 
diff --git a/.github/workflows/build-cross-image.yml b/.github/workflows/build-cross-image.yml
index 9ec25622288..6cb34c0a138 100644
--- a/.github/workflows/build-cross-image.yml
+++ b/.github/workflows/build-cross-image.yml
@@ -162,6 +162,8 @@ jobs:
 
       - name: Install Linux dev dependencies
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update
           sudo apt-get install -y libgtk-4-dev libwebkitgtk-6.0-dev libgtk-3-dev libwebkit2gtk-4.1-dev libwayland-dev
 
diff --git a/.github/workflows/cross-compile-test-v3.yml b/.github/workflows/cross-compile-test-v3.yml
index bd2c42a0a3f..fb148991bfb 100644
--- a/.github/workflows/cross-compile-test-v3.yml
+++ b/.github/workflows/cross-compile-test-v3.yml
@@ -88,6 +88,8 @@ jobs:
 
       - name: Install Linux dependencies
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-4-dev libwebkitgtk-6.0-dev libgtk-3-dev libwebkit2gtk-4.1-dev libwayland-dev build-essential pkg-config
 
diff --git a/.github/workflows/pr-master.yml b/.github/workflows/pr-master.yml
index 09bd745eb23..1bf50f8e1c1 100644
--- a/.github/workflows/pr-master.yml
+++ b/.github/workflows/pr-master.yml
@@ -68,12 +68,16 @@ jobs:
       - name: Install linux dependencies (22.04)
         if: matrix.os == 'ubuntu-22.04'
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-3-dev libwebkit2gtk-4.0-dev build-essential pkg-config
 
       - name: Install linux dependencies (24.04)
         if: matrix.os == 'ubuntu-24.04'
         run: |
+          # Drop the runner image's unused Microsoft apt repos (no-op off GitHub-hosted runners).
+          ./.github/scripts/prune-runner-apt-sources.sh
           sudo apt-get update -qq
           sudo apt-get install -y --no-install-recommends libgtk-3-dev libwebkit2gtk-4.1-dev build-essential pkg-config