From 266c0864fe3129a1545b7f5246271e3666dd3d52 Mon Sep 17 00:00:00 2001
From: Rudy Celekli <47457359+rudycelekli@users.noreply.github.com>
Date: Wed, 30 Sep 2026 21:38:48 -0400
Subject: [PATCH] fix(lint): reject unsupported folded YAML frontmatter

Signed-off-by: Rudy Celekli <47457359+rudycelekli@users.noreply.github.com>
---
 .github/workflows/lint-agents.yml  |  4 ++++
 scripts/lint-agents.sh             |  9 +++++++++
 scripts/test-folded-frontmatter.sh | 17 +++++++++++++++++
 3 files changed, 30 insertions(+)
 create mode 100755 scripts/test-folded-frontmatter.sh

diff --git a/.github/workflows/lint-agents.yml b/.github/workflows/lint-agents.yml
index c253839d..7eea6dfc 100644
--- a/.github/workflows/lint-agents.yml
+++ b/.github/workflows/lint-agents.yml
@@ -104,3 +104,7 @@ jobs:
         run: |
           chmod +x scripts/lint-agents.sh
           ./scripts/lint-agents.sh
+
+      - name: Reject folded frontmatter fixtures
+        if: steps.rules.outputs.changed == 'true'
+        run: bash scripts/test-folded-frontmatter.sh
diff --git a/scripts/lint-agents.sh b/scripts/lint-agents.sh
index 442e6e31..15358839 100755
--- a/scripts/lint-agents.sh
+++ b/scripts/lint-agents.sh
@@ -112,6 +112,15 @@ lint_file() {
     return
   fi
 
+  # The lightweight converters read plain or quoted scalar fields. A folded
+  # block otherwise passes presence checks but leaks its YAML indicator into
+  # the generated value.
+  if grep -qE '^[[:space:]]*[[:alnum:]_-]+:[[:space:]]*>([-+][1-9]?|[1-9][-+]?)?([[:space:]]+#.*)?[[:space:]]*$' <<<"$frontmatter"; then
+    echo "ERROR $file: folded YAML frontmatter is unsupported — use a single-line scalar"
+    errors=$((errors + 1))
+    return
+  fi
+
   # 2. Check required frontmatter fields
   for field in "${REQUIRED_FRONTMATTER[@]}"; do
     if ! grep -qE -- "^${field}:" <<<"$frontmatter"; then
diff --git a/scripts/test-folded-frontmatter.sh b/scripts/test-folded-frontmatter.sh
new file mode 100755
index 00000000..04cdb176
--- /dev/null
+++ b/scripts/test-folded-frontmatter.sh
@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+set -euo pipefail
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+scratch="$(mktemp -d)"
+trap 'rm -rf "$scratch"' EXIT
+for indicator in '>' '>-' '>+' '>2' '>2-' '>-2' '>+2' '>2+ # comment'; do
+  printf '%s\n' '---' 'name: Example Agent' "description: $indicator" '  First line' '  Second line' 'color: blue' '---' '## Identity' '## Core Mission' '## Critical Rules' > "$scratch/agent.md"
+  if bash "$SCRIPT_DIR/lint-agents.sh" "$scratch/agent.md" > "$scratch/result.log" 2>&1; then
+    echo "FAIL: linter accepted folded frontmatter $indicator" >&2; exit 1
+  fi
+  grep -q 'folded YAML frontmatter is unsupported' "$scratch/result.log"
+done
+for description in '"A > B"' "'A > B'" 'Ordinary description'; do
+  printf '%s\n' '---' 'name: Example Agent' "description: $description" 'color: blue' '---' '## Identity' '## Core Mission' '## Critical Rules' '> Body quotation' > "$scratch/agent.md"
+  bash "$SCRIPT_DIR/lint-agents.sh" "$scratch/agent.md" > "$scratch/result.log" 2>&1
+done
+echo 'PASS: folded frontmatter is rejected while quoted scalars and body quotations pass'