framework tools/git: R3 --body-file across all nine body/comment carriers

--body-file <path> and --body-file - (stdin) load the body/comment from
a file, killing the fragile shell-quoting class for long Markdown
(Jason remediation R3). Contract: mutually exclusive with --body
(rc 2), unreadable file rc 2 naming the path, resolution runs AFTER
parsing and BEFORE the required-value checks. Full arm set on the
issue-comment suite (file, stdin, exclusive, missing); all nine
carrier suites and the readback suite green. Mirrored to brain.

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

@@ -12,6 +12,7 @@ source "$SCRIPT_DIR/detect-platform.sh"
 # Parse arguments
 ISSUE_NUMBER=""
 COMMENT=""
+BODY_FILE=""
 
 # Usage-error contract (R4, 2026-08-28): usage errors print to STDERR and exit 2,
 # distinct from provider, credential, and verification failures (exit 1), so a
@@ -36,6 +37,12 @@ while [[ $# -gt 0 ]]; do
             COMMENT="$2"
             shift 2
             ;;
+        --body-file)
+            # R3: body from file (or '-' = stdin); mutually exclusive with --body.
+            [[ $# -ge 2 && "$2" != --* ]] || usage_error "option $1 requires a path (or - for stdin)"
+            BODY_FILE="$2"
+            shift 2
+            ;;
         -h|--help)
             echo "Usage: issue-close.sh -i <issue_number> [-b <comment>]"
             echo ""
@@ -54,6 +61,19 @@ while [[ $# -gt 0 ]]; do
     esac
 done
 
+# R3 (2026-08-29): resolve --body-file into COMMENT (file or stdin '-');
+# exclusive with an explicit --body/--comment value.
+if [[ -n "$BODY_FILE" ]]; then
+    [[ -z "$COMMENT" ]] || usage_error "--body-file and --body are mutually exclusive"
+    if [[ "$BODY_FILE" == "-" ]]; then
+        COMMENT=$(cat) || usage_error "could not read body from stdin"
+    else
+        [[ -r "$BODY_FILE" ]] || usage_error "body file not readable: $BODY_FILE"
+        COMMENT=$(cat "$BODY_FILE") || usage_error "could not read body file: $BODY_FILE"
+    fi
+fi
+
+
 if [[ -z "$ISSUE_NUMBER" ]]; then
     usage_error "issue number is required (-i/--issue)"
 fi