From 78d8377705959dfac65aeef33055b074dc9097f3 Mon Sep 17 00:00:00 2001
From: Julien Jerphanion <git@jjerphan.xyz>
Date: Fri, 24 Jul 2026 10:14:14 +0200
Subject: [PATCH 1/8] ci: Add `win-arm64` workflows

Signed-off-by: Julien Jerphanion <git@jjerphan.xyz>
---
 .github/workflows/static_build.yml | 20 +++++++++++++-------
 .github/workflows/tests.yml        |  4 ++--
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/.github/workflows/static_build.yml b/.github/workflows/static_build.yml
index 9a872c71cf..cbe65a835f 100644
--- a/.github/workflows/static_build.yml
+++ b/.github/workflows/static_build.yml
@@ -167,14 +167,20 @@ jobs:
           name: micromamba-${{ matrix.platform }}-${{ matrix.arch }}
           path: ${{ github.workspace }}/artifacts/micromamba
   micromamba-static-win:
-    name: "win-64"
-    runs-on: windows-latest
+    name: "win-${{ matrix.arch }}"
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - { os: windows-latest, arch: "64" }
+          - { os: windows-11-arm, arch: arm64 }
     steps:
       - uses: actions/checkout@v7
       - uses: hendrikmuhs/ccache-action@main
         with:
           variant: sccache
-          key: sccache-${{ github.job }}-win-64
+          key: sccache-${{ github.job }}-win-${{ matrix.arch }}
       - name: Set up MSVC
         uses: ilammy/msvc-dev-cmd@v1
       - uses: mamba-org/setup-micromamba@v3
@@ -236,7 +242,7 @@ jobs:
         run: sccache --show-stats
       - name: Archive-build artifact
         if: failure()
-        run: tar -czf ${{ github.workspace }}/micromamba-build-failed-win-64.tar.gz ${{ github.workspace }}/build/
+        run: tar -czf ${{ github.workspace }}/micromamba-build-failed-win-${{ matrix.arch }}.tar.gz ${{ github.workspace }}/build/
 
       - name: Test basic commands
         run: |
@@ -250,10 +256,10 @@ jobs:
         uses: actions/upload-artifact@v7
         if: failure()
         with:
-          name: micromamba-build-failed-win-64
-          path: ${{ github.workspace }}/micromamba-build-failed-win-64.tar.gz
+          name: micromamba-build-failed-win-${{ matrix.arch }}
+          path: ${{ github.workspace }}/micromamba-build-failed-win-${{ matrix.arch }}.tar.gz
           retention-days: 7
       - uses: actions/upload-artifact@v7
         with:
-          name: micromamba-win-64
+          name: micromamba-win-${{ matrix.arch }}
           path: ${{ github.workspace }}/build/micromamba/micromamba.exe
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 589a37c2b1..6f4f9c2e41 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -36,9 +36,9 @@ jobs:
     name: Windows
     strategy:
       matrix:
-        os: [windows-latest]
+        os: [windows-latest, windows-11-arm]
         build_type: [release]
-      fail-fast: true
+      fail-fast: false
     uses: ./.github/workflows/windows_impl.yml
     with:
       os: ${{ matrix.os }}

From 7bbfddecf445b66c82dbf49b89acc66f2011bc60 Mon Sep 17 00:00:00 2001
From: Julien Jerphanion <git@jjerphan.xyz>
Date: Fri, 24 Jul 2026 12:28:33 +0200
Subject: [PATCH 2/8] Use `mamba-org/setup-micromamba@v3.1.0`

Signed-off-by: Julien Jerphanion <git@jjerphan.xyz>
---
 .github/workflows/coverage.yml     |  2 +-
 .github/workflows/linters.yml      |  2 +-
 .github/workflows/static_build.yml |  4 ++--
 .github/workflows/unix_impl.yml    | 10 +++++-----
 .github/workflows/windows_impl.yml |  8 ++++----
 5 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index 37ba316937..621926e709 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -44,7 +44,7 @@ jobs:
       - name: Checkout mamba repository
         uses: actions/checkout@v7
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./dev/environment-dev.yml
           environment-name: build_env
diff --git a/.github/workflows/linters.yml b/.github/workflows/linters.yml
index ed8676b5ea..4619e2e82f 100644
--- a/.github/workflows/linters.yml
+++ b/.github/workflows/linters.yml
@@ -36,7 +36,7 @@ jobs:
           df -h
       - uses: actions/checkout@v7
       - name: Install pre-commit and identify
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-name: linters
           create-args: pre-commit identify
diff --git a/.github/workflows/static_build.yml b/.github/workflows/static_build.yml
index cbe65a835f..655a260daf 100644
--- a/.github/workflows/static_build.yml
+++ b/.github/workflows/static_build.yml
@@ -97,7 +97,7 @@ jobs:
           mv mamba/ micromamba-feedstock/source
           # Prevent irrelevant file permission error
           git -C micromamba-feedstock/ config --local --add safe.directory '*'
-      - uses: mamba-org/setup-micromamba@v3
+      - uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-name: mambabuild
           create-args: python boa
@@ -183,7 +183,7 @@ jobs:
           key: sccache-${{ github.job }}-win-${{ matrix.arch }}
       - name: Set up MSVC
         uses: ilammy/msvc-dev-cmd@v1
-      - uses: mamba-org/setup-micromamba@v3
+      - uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-name: mambabuild
           init-shell: bash cmd.exe
diff --git a/.github/workflows/unix_impl.yml b/.github/workflows/unix_impl.yml
index 1f88de78a9..6db6ddb3c1 100644
--- a/.github/workflows/unix_impl.yml
+++ b/.github/workflows/unix_impl.yml
@@ -47,7 +47,7 @@ jobs:
       - name: Checkout mamba repository
         uses: actions/checkout@v7
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./dev/environment-dev.yml
           environment-name: build_env
@@ -121,7 +121,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -181,7 +181,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -240,7 +240,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -320,7 +320,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
diff --git a/.github/workflows/windows_impl.yml b/.github/workflows/windows_impl.yml
index fc73a8aebb..7e006873c3 100644
--- a/.github/workflows/windows_impl.yml
+++ b/.github/workflows/windows_impl.yml
@@ -23,7 +23,7 @@ jobs:
       - name: Checkout mamba repository
         uses: actions/checkout@v7
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./dev/environment-dev.yml
           environment-name: build_env
@@ -77,7 +77,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -116,7 +116,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -148,7 +148,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3
+        uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env

From 336f88339fdfd1d3b865f6f70710df7578c5a876 Mon Sep 17 00:00:00 2001
From: Julien Jerphanion <git@jjerphan.xyz>
Date: Fri, 24 Jul 2026 14:40:18 +0200
Subject: [PATCH 3/8] Handle many missing top-level packages

Signed-off-by: Julien Jerphanion <git@jjerphan.xyz>
---
 libmamba/src/solver/problems_graph.cpp        | 97 +++++++++++++++----
 .../tests/src/solver/test_problems_graph.cpp  | 41 ++++++++
 2 files changed, 117 insertions(+), 21 deletions(-)

diff --git a/libmamba/src/solver/problems_graph.cpp b/libmamba/src/solver/problems_graph.cpp
index 6a3d6789cc..688dda18e8 100644
--- a/libmamba/src/solver/problems_graph.cpp
+++ b/libmamba/src/solver/problems_graph.cpp
@@ -9,7 +9,6 @@
 #include <limits>
 #include <map>
 #include <sstream>
-#include <stdexcept>
 #include <string_view>
 #include <tuple>
 #include <type_traits>
@@ -378,6 +377,28 @@ namespace mamba::solver
             return std::visit([](const auto& n) -> std::string_view { return name_or(n, ""); }, node);
         }
 
+        /**
+         * The name of a CompressedProblemsGraph::node_t.
+         */
+        auto compressed_node_name(const CompressedProblemsGraph::node_t& node) -> std::string_view
+        {
+            return std::visit(
+                [](const auto& n) -> std::string_view
+                {
+                    using Node = std::decay_t<decltype(n)>;
+                    if constexpr (std::is_same_v<Node, CompressedProblemsGraph::RootNode>)
+                    {
+                        return "";
+                    }
+                    else
+                    {
+                        return n.name();
+                    }
+                },
+                node
+            );
+        }
+
         /**
          * The criteria for deciding whether to merge two nodes together.
          */
@@ -533,7 +554,16 @@ namespace mamba::solver
                 {
                     new_graph.add_edge(new_from, new_to, CompressedProblemsGraph::edge_t());
                 }
-                new_graph.edge(new_from, new_to).insert(old_graph.edge(old_from, old_to));
+                // NamedList requires a single package name. Different dependency names can
+                // map to the same (from, to) pair after node merges (e.g. via provides);
+                // keep the first name and drop incompatible MatchSpecs rather than aborting
+                // problem reporting.
+                auto& new_edge = new_graph.edge(new_from, new_to);
+                const auto& old_edge = old_graph.edge(old_from, old_to);
+                if (new_edge.empty() || (invoke_name(old_edge) == new_edge.name()))
+                {
+                    new_edge.insert(old_edge);
+                }
             };
             old_graph.for_each_edge_id(add_new_edge);
         }
@@ -649,22 +679,17 @@ namespace mamba::solver
     {
         if (first < last)
         {
+            const auto first_name = std::string(invoke_name(*first));
             for (auto it = first; it < last; ++it)
             {
-                if (invoke_name(*it) != invoke_name(*first))
+                // Keep a single package name per list. Divergent names can appear after
+                // aggressive graph merges; dropping them preserves explainability.
+                if (invoke_name(*it) == first_name)
                 {
-                    throw std::invalid_argument(
-                        util::concat(
-                            "iterator contains different names (",
-                            invoke_name(*first),
-                            ", ",
-                            invoke_name(*it)
-                        )
-                    );
+                    Base::insert(*it);
                 }
             }
         }
-        Base::insert(first, last);
     }
 
     template <typename T, typename A>
@@ -799,12 +824,12 @@ namespace mamba::solver
     template <typename T_>
     void CompressedProblemsGraph::NamedList<T, A>::insert_impl(T_&& e)
     {
+        // NamedList is a same-name collection. When explaining complex unsolvable
+        // environments, incompatible names can show up after node/edge merges; skip
+        // them instead of aborting the error message with an exception.
         if ((size() > 0) && (invoke_name(e) != name()))
         {
-            throw std::invalid_argument(
-                "Name of new element (" + invoke_name(e) + ") does not match name of list ("
-                + name() + ')'
-            );
+            return;
         }
         Base::insert(std::forward<T_>(e));
     }
@@ -1115,9 +1140,11 @@ namespace mamba::solver
             }
 
             // All children are the same type of visited or leaves, no grand-children,
-            // and same status.
+            // same status, and same package name.
             // We dynamically delete all children and mark the whole node as such.
-            auto all_same_split_children = [](TreeNodeIter first, TreeNodeIter last) -> bool
+            // Name equality is required because NamedList / problem messaging assumes a
+            // single package name per node; providers of the same dependency can differ.
+            auto all_same_split_children = [&](TreeNodeIter first, TreeNodeIter last) -> bool
             {
                 if (last <= first)
                 {
@@ -1125,7 +1152,17 @@ namespace mamba::solver
                 }
                 auto same = [&first](const TreeNode& tn)
                 { return (tn.type == first->type) && (tn.status == first->status); };
-                return std::all_of(first, last, same);
+                if (!std::all_of(first, last, same))
+                {
+                    return false;
+                }
+                const auto first_name = compressed_node_name(m_pbs.graph().node(children_ids.front()));
+                return std::all_of(
+                    children_ids.begin(),
+                    children_ids.end(),
+                    [&](node_id id)
+                    { return compressed_node_name(m_pbs.graph().node(id)) == first_name; }
+                );
             };
             const TreeNodeIter children_end = out;
             if ((n_children >= 1) && all_same_split_children(children_begin, children_end))
@@ -1624,7 +1661,15 @@ namespace mamba::solver
             for (auto id : ids)
             {
                 const auto& node = std::get<Node>(m_pbs.graph().node(id));
-                out.insert(node.begin(), node.end());
+                // NamedList is single-name; when a split groups providers of different names,
+                // only keep entries that match the first name so messaging can still proceed.
+                for (const auto& pkg : node)
+                {
+                    if (out.empty() || (invoke_name(pkg) == out.name()))
+                    {
+                        out.insert(pkg);
+                    }
+                }
             }
             return out;
         }
@@ -1670,8 +1715,18 @@ namespace mamba::solver
             {
                 for (auto t : to)
                 {
+                    if (!m_pbs.graph().has_edge(f, t))
+                    {
+                        continue;
+                    }
                     const auto& e = m_pbs.graph().edge(f, t);
-                    out.insert(e.begin(), e.end());
+                    for (const auto& ms : e)
+                    {
+                        if (out.empty() || (invoke_name(ms) == out.name()))
+                        {
+                            out.insert(ms);
+                        }
+                    }
                 }
             }
             return out;
diff --git a/libmamba/tests/src/solver/test_problems_graph.cpp b/libmamba/tests/src/solver/test_problems_graph.cpp
index 6a933d1716..51a81c0cfa 100644
--- a/libmamba/tests/src/solver/test_problems_graph.cpp
+++ b/libmamba/tests/src/solver/test_problems_graph.cpp
@@ -272,6 +272,46 @@ namespace
         return create_pubgrub_hard_(ctx, channel_context, true);
     }
 
+    /**
+     * Many missing top-level packages plus some with broken transitive deps.
+     *
+     * Regression for problem-tree messaging aborting with
+     * "Name of new element (...) does not match name of list (...)" when explaining
+     * large unsatisfiable environments (e.g. win-arm64 missing conda-forge coverage).
+     */
+    auto create_many_missing_top_level(Context&, ChannelContext& channel_context)
+    {
+        return std::pair(
+            create_pkgs_database(
+                channel_context,
+                std::array{
+                    mkpkg("mitmproxy", "1.0.0", { "aioquic=1.2.0" }),
+                    mkpkg("sphinx-book-theme", "1.0.0", { "sphinx", "theme-dep-missing" }),
+                    mkpkg("sphinx", "1.0.0", { "requests" }),
+                    mkpkg("sphinx-copybutton", "1.0.0", { "sphinx" }),
+                    mkpkg("requests", "1.0.0", { "urllib3", "brotli-python" }),
+                    mkpkg("pre-commit", "1.0.0", { "python" }),
+                    mkpkg("python", "3.12.0"),
+                }
+            ),
+            Request{
+                {},
+                {
+                    Request::Install{ "doxygen"_ms },
+                    Request::Install{ "catch2"_ms },
+                    Request::Install{ "cmake"_ms },
+                    Request::Install{ "cxx-compiler"_ms },
+                    Request::Install{ "menuinst"_ms },
+                    Request::Install{ "pywin32"_ms },
+                    Request::Install{ "sphinx-book-theme"_ms },
+                    Request::Install{ "sphinx-copybutton"_ms },
+                    Request::Install{ "pre-commit"_ms },
+                    Request::Install{ "mitmproxy"_ms },
+                },
+            }
+        );
+    }
+
     /**
      * Create a conflict due to a pin.
      */
@@ -641,6 +681,7 @@ TEST_CASE("Create problem graph", "[mamba::solver]")
         std::pair{ "PubGrub example", &create_pubgrub },
         std::pair{ "Harder PubGrub example", &create_pubgrub_hard },
         std::pair{ "PubGrub example with missing packages", &create_pubgrub_missing },
+        std::pair{ "Many missing top-level packages", &create_many_missing_top_level },
         std::pair{ "Pin conflict", &create_pin_conflict },
         std::pair{ "PyTorch CPU", &create_pytorch_cpu },
         std::pair{ "PyTorch Cuda", &create_pytorch_cuda },

From e551bf613f74b115ede15c91d4ef293541690c39 Mon Sep 17 00:00:00 2001
From: Julien Jerphanion <git@jjerphan.xyz>
Date: Fri, 24 Jul 2026 14:44:53 +0200
Subject: [PATCH 4/8] Use MSVC toolchain for `arm64`

Signed-off-by: Julien Jerphanion <git@jjerphan.xyz>
---
 .github/workflows/static_build.yml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/.github/workflows/static_build.yml b/.github/workflows/static_build.yml
index 655a260daf..a5ed591cfa 100644
--- a/.github/workflows/static_build.yml
+++ b/.github/workflows/static_build.yml
@@ -183,6 +183,10 @@ jobs:
           key: sccache-${{ github.job }}-win-${{ matrix.arch }}
       - name: Set up MSVC
         uses: ilammy/msvc-dev-cmd@v1
+        with:
+          # Native ARM64 on windows-11-arm; x64 elsewhere. Default is x64 and
+          # linking ARM64 conda libs with an x64 linker fails with LNK4272.
+          arch: ${{ matrix.arch == 'arm64' && 'arm64' || 'x64' }}
       - uses: mamba-org/setup-micromamba@v3.1.0
         with:
           environment-name: mambabuild

From 6da8d2a1bf4d8f70f13e40f435d9fce96b233d78 Mon Sep 17 00:00:00 2001
From: Julien Jerphanion <git@jjerphan.xyz>
Date: Fri, 24 Jul 2026 15:00:26 +0200
Subject: [PATCH 5/8] Skip micromamba PE dependencies for win-arm64

Signed-off-by: Julien Jerphanion <git@jjerphan.xyz>
---
 .github/workflows/static_build.yml | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/.github/workflows/static_build.yml b/.github/workflows/static_build.yml
index a5ed591cfa..93a9e815e2 100644
--- a/.github/workflows/static_build.yml
+++ b/.github/workflows/static_build.yml
@@ -236,10 +236,13 @@ jobs:
           if %errorlevel% neq 0 exit /b %errorlevel%
           .\build\micromamba\micromamba.exe --help
           if %errorlevel% neq 0 exit /b %errorlevel%
+      # binutils is not yet distributed for win-arm64 on conda-forge.
       - name: Install mingw objdump
+        if: matrix.arch != 'arm64'
         shell: bash -l {0}
         run: micromamba install -n mambabuild -y -c conda-forge binutils
       - name: Check micromamba PE dependencies
+        if: matrix.arch != 'arm64'
         shell: bash -l {0}
         run: bash dev/check_micromamba_windows_dlls.sh build/micromamba/micromamba.exe
       - name: build cache statistics

From e41ce6c4a2cae723dda6c353356f65600d3b1970 Mon Sep 17 00:00:00 2001
From: Julien Jerphanion <git@jjerphan.xyz>
Date: Fri, 24 Jul 2026 15:04:31 +0200
Subject: [PATCH 6/8] Install python 3.14 in basic test commands

Signed-off-by: Julien Jerphanion <git@jjerphan.xyz>
---
 .github/workflows/static_build.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/static_build.yml b/.github/workflows/static_build.yml
index 93a9e815e2..b34f4bb830 100644
--- a/.github/workflows/static_build.yml
+++ b/.github/workflows/static_build.yml
@@ -256,7 +256,7 @@ jobs:
           mkdir test_prefix
           ${{ github.workspace }}/build/micromamba/micromamba.exe --version
           ${{ github.workspace }}/build/micromamba/micromamba.exe --help
-          ${{ github.workspace }}/build/micromamba/micromamba.exe env create -y -n testenv -r ./test_prefix "python<3.13"
+          ${{ github.workspace }}/build/micromamba/micromamba.exe env create -y -n testenv -r ./test_prefix "python=3.14"
           ${{ github.workspace }}/build/micromamba/micromamba.exe list -n testenv -r ./test_prefix  --log-level 1
 
       - name: Upload build artifacts

From 4a9dea0275430c4063c5480b108e76c4e85843f3 Mon Sep 17 00:00:00 2001
From: Julien Jerphanion <git@jjerphan.xyz>
Date: Mon, 27 Jul 2026 17:37:18 +0200
Subject: [PATCH 7/8] Only add workflows for static builds for now

Signed-off-by: Julien Jerphanion <git@jjerphan.xyz>
---
 .github/workflows/coverage.yml                |  2 +-
 .github/workflows/linters.yml                 |  2 +-
 .github/workflows/tests.yml                   |  4 +-
 .github/workflows/unix_impl.yml               | 10 +-
 .github/workflows/windows_impl.yml            |  8 +-
 libmamba/src/solver/problems_graph.cpp        | 97 ++++---------------
 .../tests/src/solver/test_problems_graph.cpp  | 41 --------
 7 files changed, 34 insertions(+), 130 deletions(-)

diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index 621926e709..37ba316937 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -44,7 +44,7 @@ jobs:
       - name: Checkout mamba repository
         uses: actions/checkout@v7
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./dev/environment-dev.yml
           environment-name: build_env
diff --git a/.github/workflows/linters.yml b/.github/workflows/linters.yml
index 4619e2e82f..ed8676b5ea 100644
--- a/.github/workflows/linters.yml
+++ b/.github/workflows/linters.yml
@@ -36,7 +36,7 @@ jobs:
           df -h
       - uses: actions/checkout@v7
       - name: Install pre-commit and identify
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-name: linters
           create-args: pre-commit identify
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 6f4f9c2e41..589a37c2b1 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -36,9 +36,9 @@ jobs:
     name: Windows
     strategy:
       matrix:
-        os: [windows-latest, windows-11-arm]
+        os: [windows-latest]
         build_type: [release]
-      fail-fast: false
+      fail-fast: true
     uses: ./.github/workflows/windows_impl.yml
     with:
       os: ${{ matrix.os }}
diff --git a/.github/workflows/unix_impl.yml b/.github/workflows/unix_impl.yml
index 6db6ddb3c1..1f88de78a9 100644
--- a/.github/workflows/unix_impl.yml
+++ b/.github/workflows/unix_impl.yml
@@ -47,7 +47,7 @@ jobs:
       - name: Checkout mamba repository
         uses: actions/checkout@v7
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./dev/environment-dev.yml
           environment-name: build_env
@@ -121,7 +121,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -181,7 +181,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -240,7 +240,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -320,7 +320,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
diff --git a/.github/workflows/windows_impl.yml b/.github/workflows/windows_impl.yml
index 7e006873c3..fc73a8aebb 100644
--- a/.github/workflows/windows_impl.yml
+++ b/.github/workflows/windows_impl.yml
@@ -23,7 +23,7 @@ jobs:
       - name: Checkout mamba repository
         uses: actions/checkout@v7
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./dev/environment-dev.yml
           environment-name: build_env
@@ -77,7 +77,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -116,7 +116,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
@@ -148,7 +148,7 @@ jobs:
           path: build/
           key_suffix: ${{ inputs.os }}-${{ inputs.build_type }}
       - name: Create build environment
-        uses: mamba-org/setup-micromamba@v3.1.0
+        uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: ./build/environment.lock
           environment-name: build_env
diff --git a/libmamba/src/solver/problems_graph.cpp b/libmamba/src/solver/problems_graph.cpp
index 688dda18e8..6a3d6789cc 100644
--- a/libmamba/src/solver/problems_graph.cpp
+++ b/libmamba/src/solver/problems_graph.cpp
@@ -9,6 +9,7 @@
 #include <limits>
 #include <map>
 #include <sstream>
+#include <stdexcept>
 #include <string_view>
 #include <tuple>
 #include <type_traits>
@@ -377,28 +378,6 @@ namespace mamba::solver
             return std::visit([](const auto& n) -> std::string_view { return name_or(n, ""); }, node);
         }
 
-        /**
-         * The name of a CompressedProblemsGraph::node_t.
-         */
-        auto compressed_node_name(const CompressedProblemsGraph::node_t& node) -> std::string_view
-        {
-            return std::visit(
-                [](const auto& n) -> std::string_view
-                {
-                    using Node = std::decay_t<decltype(n)>;
-                    if constexpr (std::is_same_v<Node, CompressedProblemsGraph::RootNode>)
-                    {
-                        return "";
-                    }
-                    else
-                    {
-                        return n.name();
-                    }
-                },
-                node
-            );
-        }
-
         /**
          * The criteria for deciding whether to merge two nodes together.
          */
@@ -554,16 +533,7 @@ namespace mamba::solver
                 {
                     new_graph.add_edge(new_from, new_to, CompressedProblemsGraph::edge_t());
                 }
-                // NamedList requires a single package name. Different dependency names can
-                // map to the same (from, to) pair after node merges (e.g. via provides);
-                // keep the first name and drop incompatible MatchSpecs rather than aborting
-                // problem reporting.
-                auto& new_edge = new_graph.edge(new_from, new_to);
-                const auto& old_edge = old_graph.edge(old_from, old_to);
-                if (new_edge.empty() || (invoke_name(old_edge) == new_edge.name()))
-                {
-                    new_edge.insert(old_edge);
-                }
+                new_graph.edge(new_from, new_to).insert(old_graph.edge(old_from, old_to));
             };
             old_graph.for_each_edge_id(add_new_edge);
         }
@@ -679,17 +649,22 @@ namespace mamba::solver
     {
         if (first < last)
         {
-            const auto first_name = std::string(invoke_name(*first));
             for (auto it = first; it < last; ++it)
             {
-                // Keep a single package name per list. Divergent names can appear after
-                // aggressive graph merges; dropping them preserves explainability.
-                if (invoke_name(*it) == first_name)
+                if (invoke_name(*it) != invoke_name(*first))
                 {
-                    Base::insert(*it);
+                    throw std::invalid_argument(
+                        util::concat(
+                            "iterator contains different names (",
+                            invoke_name(*first),
+                            ", ",
+                            invoke_name(*it)
+                        )
+                    );
                 }
             }
         }
+        Base::insert(first, last);
     }
 
     template <typename T, typename A>
@@ -824,12 +799,12 @@ namespace mamba::solver
     template <typename T_>
     void CompressedProblemsGraph::NamedList<T, A>::insert_impl(T_&& e)
     {
-        // NamedList is a same-name collection. When explaining complex unsolvable
-        // environments, incompatible names can show up after node/edge merges; skip
-        // them instead of aborting the error message with an exception.
         if ((size() > 0) && (invoke_name(e) != name()))
         {
-            return;
+            throw std::invalid_argument(
+                "Name of new element (" + invoke_name(e) + ") does not match name of list ("
+                + name() + ')'
+            );
         }
         Base::insert(std::forward<T_>(e));
     }
@@ -1140,11 +1115,9 @@ namespace mamba::solver
             }
 
             // All children are the same type of visited or leaves, no grand-children,
-            // same status, and same package name.
+            // and same status.
             // We dynamically delete all children and mark the whole node as such.
-            // Name equality is required because NamedList / problem messaging assumes a
-            // single package name per node; providers of the same dependency can differ.
-            auto all_same_split_children = [&](TreeNodeIter first, TreeNodeIter last) -> bool
+            auto all_same_split_children = [](TreeNodeIter first, TreeNodeIter last) -> bool
             {
                 if (last <= first)
                 {
@@ -1152,17 +1125,7 @@ namespace mamba::solver
                 }
                 auto same = [&first](const TreeNode& tn)
                 { return (tn.type == first->type) && (tn.status == first->status); };
-                if (!std::all_of(first, last, same))
-                {
-                    return false;
-                }
-                const auto first_name = compressed_node_name(m_pbs.graph().node(children_ids.front()));
-                return std::all_of(
-                    children_ids.begin(),
-                    children_ids.end(),
-                    [&](node_id id)
-                    { return compressed_node_name(m_pbs.graph().node(id)) == first_name; }
-                );
+                return std::all_of(first, last, same);
             };
             const TreeNodeIter children_end = out;
             if ((n_children >= 1) && all_same_split_children(children_begin, children_end))
@@ -1661,15 +1624,7 @@ namespace mamba::solver
             for (auto id : ids)
             {
                 const auto& node = std::get<Node>(m_pbs.graph().node(id));
-                // NamedList is single-name; when a split groups providers of different names,
-                // only keep entries that match the first name so messaging can still proceed.
-                for (const auto& pkg : node)
-                {
-                    if (out.empty() || (invoke_name(pkg) == out.name()))
-                    {
-                        out.insert(pkg);
-                    }
-                }
+                out.insert(node.begin(), node.end());
             }
             return out;
         }
@@ -1715,18 +1670,8 @@ namespace mamba::solver
             {
                 for (auto t : to)
                 {
-                    if (!m_pbs.graph().has_edge(f, t))
-                    {
-                        continue;
-                    }
                     const auto& e = m_pbs.graph().edge(f, t);
-                    for (const auto& ms : e)
-                    {
-                        if (out.empty() || (invoke_name(ms) == out.name()))
-                        {
-                            out.insert(ms);
-                        }
-                    }
+                    out.insert(e.begin(), e.end());
                 }
             }
             return out;
diff --git a/libmamba/tests/src/solver/test_problems_graph.cpp b/libmamba/tests/src/solver/test_problems_graph.cpp
index 51a81c0cfa..6a933d1716 100644
--- a/libmamba/tests/src/solver/test_problems_graph.cpp
+++ b/libmamba/tests/src/solver/test_problems_graph.cpp
@@ -272,46 +272,6 @@ namespace
         return create_pubgrub_hard_(ctx, channel_context, true);
     }
 
-    /**
-     * Many missing top-level packages plus some with broken transitive deps.
-     *
-     * Regression for problem-tree messaging aborting with
-     * "Name of new element (...) does not match name of list (...)" when explaining
-     * large unsatisfiable environments (e.g. win-arm64 missing conda-forge coverage).
-     */
-    auto create_many_missing_top_level(Context&, ChannelContext& channel_context)
-    {
-        return std::pair(
-            create_pkgs_database(
-                channel_context,
-                std::array{
-                    mkpkg("mitmproxy", "1.0.0", { "aioquic=1.2.0" }),
-                    mkpkg("sphinx-book-theme", "1.0.0", { "sphinx", "theme-dep-missing" }),
-                    mkpkg("sphinx", "1.0.0", { "requests" }),
-                    mkpkg("sphinx-copybutton", "1.0.0", { "sphinx" }),
-                    mkpkg("requests", "1.0.0", { "urllib3", "brotli-python" }),
-                    mkpkg("pre-commit", "1.0.0", { "python" }),
-                    mkpkg("python", "3.12.0"),
-                }
-            ),
-            Request{
-                {},
-                {
-                    Request::Install{ "doxygen"_ms },
-                    Request::Install{ "catch2"_ms },
-                    Request::Install{ "cmake"_ms },
-                    Request::Install{ "cxx-compiler"_ms },
-                    Request::Install{ "menuinst"_ms },
-                    Request::Install{ "pywin32"_ms },
-                    Request::Install{ "sphinx-book-theme"_ms },
-                    Request::Install{ "sphinx-copybutton"_ms },
-                    Request::Install{ "pre-commit"_ms },
-                    Request::Install{ "mitmproxy"_ms },
-                },
-            }
-        );
-    }
-
     /**
      * Create a conflict due to a pin.
      */
@@ -681,7 +641,6 @@ TEST_CASE("Create problem graph", "[mamba::solver]")
         std::pair{ "PubGrub example", &create_pubgrub },
         std::pair{ "Harder PubGrub example", &create_pubgrub_hard },
         std::pair{ "PubGrub example with missing packages", &create_pubgrub_missing },
-        std::pair{ "Many missing top-level packages", &create_many_missing_top_level },
         std::pair{ "Pin conflict", &create_pin_conflict },
         std::pair{ "PyTorch CPU", &create_pytorch_cpu },
         std::pair{ "PyTorch Cuda", &create_pytorch_cuda },

From 95cdc634982e9cef83339860c48c4448e73ed664 Mon Sep 17 00:00:00 2001
From: Julien Jerphanion <git@jjerphan.xyz>
Date: Tue, 28 Jul 2026 17:22:07 +0200
Subject: [PATCH 8/8] Use `mamba-org/setup-micromamba@v3`

---
 .github/workflows/static_build.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/static_build.yml b/.github/workflows/static_build.yml
index b34f4bb830..b15f71796e 100644
--- a/.github/workflows/static_build.yml
+++ b/.github/workflows/static_build.yml
@@ -97,7 +97,7 @@ jobs:
           mv mamba/ micromamba-feedstock/source
           # Prevent irrelevant file permission error
           git -C micromamba-feedstock/ config --local --add safe.directory '*'
-      - uses: mamba-org/setup-micromamba@v3.1.0
+      - uses: mamba-org/setup-micromamba@v3
         with:
           environment-name: mambabuild
           create-args: python boa
@@ -187,7 +187,7 @@ jobs:
           # Native ARM64 on windows-11-arm; x64 elsewhere. Default is x64 and
           # linking ARM64 conda libs with an x64 linker fails with LNK4272.
           arch: ${{ matrix.arch == 'arm64' && 'arm64' || 'x64' }}
-      - uses: mamba-org/setup-micromamba@v3.1.0
+      - uses: mamba-org/setup-micromamba@v3
         with:
           environment-name: mambabuild
           init-shell: bash cmd.exe