p0 line landing: coord board/roll + wrapper usage contract + dispatch layer (successor to #1467) (#1468)

Co-authored-by: orch-01 <[email protected]>

packages/mosaic/framework/tools/git/pr-create.sh

@@ -135,37 +135,51 @@ Examples:
     $(basename "$0") -i 42 -b "Implements the feature described in #42"
     $(basename "$0") -t "WIP: New feature" --draft
 EOF
-    exit "${1:-1}"
+    exit "${1:-2}"
+}
+
+# Usage-error contract (R4, 2026-08-28): usage errors print to STDERR and exit 2,
+# distinct from provider, credential, and verification failures (exit 1).
+usage_error() {
+    echo "Error: $*" >&2
+    usage >&2
 }
 
 # Parse arguments
 while [[ $# -gt 0 ]]; do
     case $1 in
         -t|--title)
+            [[ $# -ge 2 && "$2" != - && "$2" != --* && ! "$2" =~ ^-[[:alnum:]] ]] || usage_error "option $1 requires a value (option-like values are rejected; bare - is reserved)"
             TITLE="$2"
             shift 2
             ;;
         -b|--body)
+            [[ $# -ge 2 && "$2" != - && "$2" != --* && ! "$2" =~ ^-[[:alnum:]] ]] || usage_error "option $1 requires a value (option-like values are rejected; bare - is reserved)"
             BODY="$2"
             shift 2
             ;;
         -B|--base)
+            [[ $# -ge 2 && "$2" != - && "$2" != --* && ! "$2" =~ ^-[[:alnum:]] ]] || usage_error "option $1 requires a value (option-like values are rejected; bare - is reserved)"
             BASE_BRANCH="$2"
             shift 2
             ;;
         -H|--head)
+            [[ $# -ge 2 && "$2" != - && "$2" != --* && ! "$2" =~ ^-[[:alnum:]] ]] || usage_error "option $1 requires a value (option-like values are rejected; bare - is reserved)"
             HEAD_BRANCH="$2"
             shift 2
             ;;
         -l|--labels)
+            [[ $# -ge 2 && "$2" != - && "$2" != --* && ! "$2" =~ ^-[[:alnum:]] ]] || usage_error "option $1 requires a value (option-like values are rejected; bare - is reserved)"
             LABELS="$2"
             shift 2
             ;;
         -m|--milestone)
+            [[ $# -ge 2 && "$2" != - && "$2" != --* && ! "$2" =~ ^-[[:alnum:]] ]] || usage_error "option $1 requires a value (option-like values are rejected; bare - is reserved)"
             MILESTONE="$2"
             shift 2
             ;;
         -i|--issue)
+            [[ $# -ge 2 && "$2" != - && "$2" != --* && ! "$2" =~ ^-[[:alnum:]] ]] || usage_error "option $1 requires a value (option-like values are rejected; bare - is reserved)"
             ISSUE="$2"
             shift 2
             ;;
@@ -266,7 +280,9 @@ case "$PLATFORM" in
         [[ -n "$LABELS" ]] && CMD+=(--label "$LABELS")
         [[ -n "$MILESTONE" ]] && CMD+=(--milestone "$MILESTONE")
         [[ "$DRAFT" == true ]] && CMD+=(--draft)
-        "${CMD[@]}"
+        prov_rc=0
+        "${CMD[@]}" || prov_rc=$?
+        [[ "$prov_rc" -eq 0 ]] || { echo "Error: provider command failed (exit ${prov_rc}; provider failure, not a usage error)" >&2; exit 1; }
         ;;
     gitea)
         # tea pull create syntax. Always pass --repo because tea repo inference