merge: origin/main into next for the 0.0.50 integration line

next carries 108 commits main lacks; main carries 23 next lacks, including
the MOSAIC_GIT_IDENTITY work that per-agent git credentials depend on.
Neither stream alone can ship 0.0.50: next drops identity, main drops
everything since the split.

Conflicts and how they were settled:
- packages/mosaic/package.json test:framework-shell -- union. Neither side
  removed an entry; next added 6, main added 8, one shared. 50 total.
- framework/tools/git/pr-merge.sh -- next's form. It permits base 'main' or
  'next'; main's permits 'main' only, and the release line targets next.
- framework/tools/git/test-ci-queue-wait-tristate.sh -- both sides appended
  to the same region (next: merge-readiness assertions; main: a real-clock
  watchdog control). Kept both.
- docs/SITEMAP.md -- both sides appended distinct sections. Kept both.

tools/install.sh

@@ -405,13 +405,17 @@ ensure_monorepo() {
     exit 1
   fi
 
-  # Gitea archives extract to <repo-name>/ inside the work dir
-  EXTRACTED_DIR="$(find "$WORK_DIR" -maxdepth 1 -mindepth 1 -type d | head -1)"
-  if [[ -z "$EXTRACTED_DIR" ]] || [[ ! -d "$EXTRACTED_DIR" ]]; then
-    fail "Could not locate extracted source in archive."
+  # Gitea archives extract to exactly one <repo-name>/ inside the work dir.
+  # Read the complete population so a malformed multi-root archive reaches the
+  # named diagnostic instead of aborting on an upstream SIGPIPE under pipefail.
+  local -a extracted_dirs=()
+  mapfile -d '' -t extracted_dirs < <(find "$WORK_DIR" -maxdepth 1 -mindepth 1 -type d -print0)
+  if [[ "${#extracted_dirs[@]}" -ne 1 ]] || [[ ! -d "${extracted_dirs[0]:-}" ]]; then
+    fail "Could not locate exactly one extracted source directory in archive."
     ls -la "$WORK_DIR" >&2
     exit 1
   fi
+  EXTRACTED_DIR="${extracted_dirs[0]}"
 }
 
 # Build @mosaicstack/mosaic + @mosaicstack/gateway from source and install both