fix(framework/tools): wrapper body-safety + login-resolution hardening (#559, #560)

#559 — Markdown body safety / eval removal:
- Add test-issue-create-body-safety.sh: feeds a hostile Markdown body
  ($(...), backticks, quotes, $vars, pipes) through issue-create.sh and
  asserts no command substitution runs and the body reaches tea verbatim.
- Convert issue-comment.sh from unquoted $(get_gitea_repo_args) word-splitting
  to an argv array with an explicit loud login-resolution error.
- Confirmed: zero eval usages remain across tools/git/*.sh; the other
  body-carrying wrappers (issue-create, pr-create, issue-edit, issue-assign)
  already use argv arrays.

#560 — host-derived Gitea login + loud failure:
- detect-platform.sh: add print_gitea_login_diagnostic and emit it on the
  get_gitea_login_for_host failure path (stderr only) — names the unresolved
  host, lists available tea logins, and gives the GITEA_LOGIN override +
  tea-login-add fix. Replaces the previous silent failure.
- Extend test-gitea-login-resolution.sh: assert the diagnostic fires and lists
  logins, login is derived from origin host for both mosaicstack and usc (scoped
  second tea mock), and a valid GITEA_LOGIN override is honored.

Also gitignore the .mosaic-test-work/ shell-harness scratch dir.
Scope: wrapper surface only. All wrapper test harnesses pass locally.

packages/mosaic/framework/tools/git/test-issue-create-body-safety.sh

@@ -0,0 +1,102 @@
+#!/usr/bin/env bash
+# Regression harness for issue-create.sh Markdown-body safety (#559).
+#
+# Guards against reintroduction of eval-based command construction. The wrapper
+# builds its tea/gh invocation as an argv array, so a body containing command
+# substitution ($(...)), backticks, quotes, and dollar signs MUST reach tea
+# verbatim and MUST NOT be shell-evaluated. This test asserts both:
+#   1. No command-substitution side effect (an injected `touch SENTINEL` never runs).
+#   2. The --description value tea receives is byte-for-byte the original body.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+WORK_DIR="${MOSAIC_TEST_WORK_DIR:-$PWD/.mosaic-test-work/issue-create-body-safety}"
+REPO_DIR="$WORK_DIR/repo"
+BIN_DIR="$WORK_DIR/bin"
+SENTINEL="$WORK_DIR/INJECTION_SENTINEL"
+BODY_FILE="$WORK_DIR/body.txt"
+RECEIVED_FILE="$WORK_DIR/received-description.txt"
+
+rm -rf "$WORK_DIR"
+mkdir -p "$REPO_DIR" "$BIN_DIR"
+
+git -C "$REPO_DIR" init -q
+git -C "$REPO_DIR" remote add origin https://git.mosaicstack.dev/mosaicstack/stack.git
+
+# Hostile Markdown body. The unquoted heredoc expands $SENTINEL (a real path we
+# want embedded) but every shell metacharacter we care about is backslash-escaped
+# so the TEST shell writes them literally into the file — the bytes the wrapper
+# must then preserve.
+cat > "$BODY_FILE" <<EOF
+# Release notes
+
+Inline code: \`rm -rf /\` must stay literal.
+Command sub attempt: \$(touch $SENTINEL)
+Backtick cmd attempt: \`touch $SENTINEL\`
+Dollars: \$HOME \${PATH} \$5.00 and 100% done
+Quotes: "double" and 'single' and \`mixed\`
+Trailing pipe-ish: foo | bar && baz ; qux
+EOF
+
+BODY="$(cat "$BODY_FILE")"
+
+# Mock tea: resolve a mosaicstack login, then capture the --description verbatim.
+cat > "$BIN_DIR/tea" <<'SH'
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ "$*" == "login list --output json" ]]; then
+    cat <<'JSON'
+[
+  {"name":"mosaicstack","url":"https://git.mosaicstack.dev","user":"jason.woltje"}
+]
+JSON
+    exit 0
+fi
+
+if [[ "${1:-}" == "issue" && "${2:-}" == "create" ]]; then
+    desc=""
+    while [[ $# -gt 0 ]]; do
+        case "$1" in
+            --description) desc="$2"; shift 2 ;;
+            *) shift ;;
+        esac
+    done
+    printf '%s' "$desc" > "$MOSAIC_TEST_RECEIVED"
+    echo "#1 created"
+    exit 0
+fi
+
+exit 0
+SH
+chmod +x "$BIN_DIR/tea"
+
+(
+    cd "$REPO_DIR"
+    PATH="$BIN_DIR:$PATH" \
+    MOSAIC_TEST_RECEIVED="$RECEIVED_FILE" \
+    "$SCRIPT_DIR/issue-create.sh" -t "Body safety test" -b "$BODY"
+) >/dev/null
+
+# 1. No command substitution executed anywhere in the pipeline.
+if [[ -e "$SENTINEL" ]]; then
+    echo "FAIL: injected command substitution executed (sentinel file created): $SENTINEL" >&2
+    exit 1
+fi
+
+# 2. tea actually received the body (issue create path taken, not silently dropped).
+if [[ ! -f "$RECEIVED_FILE" ]]; then
+    echo "FAIL: tea issue create was never invoked with a --description" >&2
+    exit 1
+fi
+
+# 3. The description tea received is byte-for-byte the original body.
+if [[ "$(cat "$RECEIVED_FILE")" != "$BODY" ]]; then
+    echo "FAIL: body was not preserved verbatim through issue-create.sh" >&2
+    echo "--- expected ---" >&2; printf '%s\n' "$BODY" >&2
+    echo "--- received ---" >&2; cat "$RECEIVED_FILE" >&2
+    exit 1
+fi
+
+echo "issue-create.sh Markdown body-safety regression harness passed"