framework tools/git: strict value guards + provider-failure normalization family-wide (codex blockers on PR #1464)

- Value guards now reject option-like values: --anything always, and
  single-dash flag shapes (-h, -i). Previously -b --help consumed
  --help as the body and performed the write (codex example:
  issue-close -i --help proceeding to 'Closed GitHub issue #--help').
  Multi-char dash-leading text (-start of a list) stays a legal value.
- Every remaining direct provider exec (gh/tea/CMD arrays across
  issue-create/edit/assign/list/view, milestone-*, pr-create/edit,
  pr-close, issue-close/reopen) wrapped with rc capture and normalized
  to exit 1 with a stderr message — provider exit 2 no longer collides
  with the reserved usage-error status.
- All 16 usage-contract suites gained option-like and short-flag arms
  (16/16 green). Existing suites re-verified; test-pr-edit and
  test-issue-create-interactive-auth fail identically with these
  changes stashed (environment-coupled, not regressions; documented).

packages/mosaic/framework/tools/git/issue-comment.sh

@@ -46,7 +46,7 @@ usage_error() {
 while [[ $# -gt 0 ]]; do
     case $1 in
         -i|--issue)
-            [[ $# -ge 2 ]] || usage_error "option $1 requires a value"
+            [[ $# -ge 2 && "$2" != --* && ! "$2" =~ ^-[a-zA-Z]$ ]] || usage_error "option $1 requires a value (option-like values are rejected)"
             ISSUE_NUMBER="$2"
             shift 2
             ;;
@@ -54,12 +54,12 @@ while [[ $# -gt 0 ]]; do
             # R1 (2026-08-28): --body is the canonical flag, matching
             # issue-create/issue-edit/pr-create/pr-edit; -c/--comment stays a
             # backward-compatible alias.
-            [[ $# -ge 2 ]] || usage_error "option $1 requires a value"
+            [[ $# -ge 2 && "$2" != --* && ! "$2" =~ ^-[a-zA-Z]$ ]] || usage_error "option $1 requires a value (option-like values are rejected)"
             COMMENT="$2"
             shift 2
             ;;
         -l|--login)
-            [[ $# -ge 2 ]] || usage_error "option $1 requires a value"
+            [[ $# -ge 2 && "$2" != --* && ! "$2" =~ ^-[a-zA-Z]$ ]] || usage_error "option $1 requires a value (option-like values are rejected)"
             LOGIN_OVERRIDE="$2"
             shift 2
             ;;