diag: capture real Uno failure + rmumps version on Windows

Author: bnaras

.github/workflows/diagnose-uno-windows.yml

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+name: Diagnose Uno on Windows
+
+# Throwaway diagnostic: install the DNLP stack on a Windows runner and capture
+# Uno's REAL error (verbose), plus the actual rmumps version present. Manual
+# trigger only -- not part of the publish pipeline.
+
+on:
+  workflow_dispatch:
+
+jobs:
+  diagnose:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: r-lib/actions/setup-r@v2
+        with:
+          r-version: release
+          use-public-rspm: true
+
+      - uses: r-lib/actions/setup-r-dependencies@v2
+        with:
+          packages: |
+            any::CVXR
+            any::Uno
+            any::sparsediff
+            any::rmumps
+            any::highs
+
+      - name: Run Uno diagnostic
+        run: Rscript scripts/diag_uno.R

scripts/diag_uno.R

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+# Diagnostic: capture Uno's ACTUAL failure mode on this platform.
+# Run by .github/workflows/diagnose-uno-windows.yml (workflow_dispatch only).
+
+options(warn = 1)
+
+cat("===== installed versions =====\n")
+for (p in c("rmumps", "Uno", "sparsediff", "CVXR", "highs")) {
+  v <- tryCatch(as.character(packageVersion(p)),
+                error = function(e) "NOT INSTALLED")
+  cat(sprintf("%-12s %s\n", p, v))
+}
+
+cat("\n===== rmumps loadable? =====\n")
+cat("requireNamespace('rmumps'):",
+    requireNamespace("rmumps", quietly = TRUE), "\n")
+
+library(CVXR)
+
+cat("\n===== convex solve via UNO (verbose = TRUE) =====\n")
+x <- Variable(2)
+prob <- Problem(Minimize(sum_squares(x - c(1, 2))))
+res <- tryCatch(
+  psolve(prob, nlp = TRUE, solver = "UNO", verbose = TRUE),
+  error = function(e) {
+    cat("CAUGHT ERROR:\n", conditionMessage(e), "\n")
+    NULL
+  }
+)
+cat("\n----- result -----\n")
+print(res)
+cat("\n===== done =====\n")