diff --git a/.claude/hooks/auto_fix_diagnostics.py b/.claude/hooks/auto_fix_diagnostics.py
index 306fabc5..1ed056be 100644
--- a/.claude/hooks/auto_fix_diagnostics.py
+++ b/.claude/hooks/auto_fix_diagnostics.py
@@ -1,21 +1,22 @@
 #!/usr/bin/env python3
 """
-PostToolUse Auto-fix Hook — Detects type errors and surfaces them for fixing.
+PostToolUse Auto-fix Hook — Detects errors and surfaces them for fixing.
 
 Two-hook system:
-  PostToolUse (this file) → runs pyright on edited file, saves errors to state
+  PostToolUse (this file) → runs pyright + ruff on edited file, saves errors to state
   PreToolUse (pre_edit_gate.py) → blocks edits to OTHER files until errors fixed
 
 Key behaviors:
-- Runs py_compile (syntax), ruff (lint), pyright (type errors) on edited file
+- Runs py_compile (syntax), ruff lint+format, pyright (type errors) on edited file
 - Runs seedgo checklist for AIPass standards
-- Saves type errors to state file for PreToolUse gate
+- Saves ruff lint AND pyright errors to state file for PreToolUse gate (hard block)
 - Surfaces ALL errors in additionalContext so Claude sees them
-- Smart batching per-file
 
-Version: 5.1.0
+Version: 5.2.0
 
 CHANGELOG:
+  - v5.2.0 (2026-04-20): Save ruff lint errors to state file for hard-block enforcement.
+                          Pre-edit gate now blocks on F401/lint just like type errors.
   - v5.1.0 (2026-04-19): Added ruff format --check to surface format drift.
   - v5.0.0 (2026-03-17): Replaced mcp__ide__getDiagnostics with direct pyright.
                           Added state file for PreToolUse gate integration.
@@ -145,6 +146,36 @@ def run_python_checks(file_path: str) -> list[str]:
     return errors
 
 
+
+def run_ruff_lint_structured(file_path: str) -> list[dict]:
+    """Run ruff check and return structured violations for the state file.
+
+    Returns list of {line, message} dicts — same format as pyright errors.
+    Only non-empty when ruff finds real violations (not format drift).
+    """
+    if '/.claude/hooks/' in file_path:
+        return []
+    try:
+        result = subprocess.run(
+            ["ruff", "check", "--select=E,F,W", "--output-format=json", file_path],
+            capture_output=True, text=True, timeout=10
+        )
+        if not result.stdout.strip():
+            return []
+        violations = json.loads(result.stdout)
+        if not isinstance(violations, list):
+            return []
+        errors = []
+        for v in violations[:10]:
+            line = v.get("location", {}).get("row", 0)
+            code = v.get("code", "?")
+            message = v.get("message", "unknown")[:100]
+            errors.append({"line": line, "message": f"{code}: {message}"})
+        return errors
+    except (FileNotFoundError, json.JSONDecodeError, subprocess.TimeoutExpired, Exception):
+        return []
+
+
 def run_pyright_check(file_path: str) -> list[dict]:
     """Run pyright on a single file. Returns list of error dicts."""
     # Skip hook files - they don't follow project standards
@@ -322,8 +353,9 @@ def main():
             for te in type_errors:
                 errors.append(f"TYPE: L{te['line']}: {te['message']}")
 
-            # Save type errors to state file for PreToolUse gate
-            save_diagnostics_state(file_path, type_errors)
+            # Save ruff lint + type errors to state file for PreToolUse gate (hard block)
+            ruff_lint_errors = run_ruff_lint_structured(file_path)
+            save_diagnostics_state(file_path, ruff_lint_errors + type_errors)
 
         elif file_path.endswith(".json"):
             file_type = "JSON"
diff --git a/src/aipass/seedgo/apps/handlers/aipass_standards/ruff_check.py b/src/aipass/seedgo/apps/handlers/aipass_standards/ruff_check.py
index f7bf01da..cdcc45c6 100644
--- a/src/aipass/seedgo/apps/handlers/aipass_standards/ruff_check.py
+++ b/src/aipass/seedgo/apps/handlers/aipass_standards/ruff_check.py
@@ -1,20 +1,24 @@
 # =================== AIPass ====================
 # Name: ruff_check.py
 # Description: Ruff Linter Standards Checker Handler
-# Version: 1.0.0
+# Version: 1.1.0
 # Created: 2026-04-16
-# Modified: 2026-04-16
+# Modified: 2026-04-20
 # =============================================
 
 """
 Ruff Linter Standards Checker Handler
 
-Runs ruff against a branch's apps/ directory and scores based on violation
-count. Prevents ruff debt from silently re-accumulating after a cleanup.
+Two modes:
+- check_branch(): runs ruff across entire apps/ tree (used by audit pipeline,
+  AUDIT_SCOPE = branch_level, ADVISORY = always-passes)
+- check_module(): runs ruff on a single file (used by checklist/per-file hooks,
+  returns passed=False on violations so subagent_stop_gate can block)
 
-AUDIT_SCOPE: branch_level — runs once per branch, ruff walks the tree.
-ADVISORY: surfaces violations and score but always passes overall.
-          Promote to required once all branches are clean.
+AUDIT_SCOPE: branch_level — audit pipeline uses check_branch() once per branch.
+  Checkers that also implement check_module() are eligible for per-file checklist runs.
+ADVISORY: check_branch() surfaces violations but always passes (advisory score).
+          check_module() returns passed=False so checklist/hooks can block.
 """
 
 import json
@@ -95,6 +99,123 @@ def _score_from_count(count: int) -> int:
     return 25
 
 
+def _find_ruff_bypass_from_file(file_path: str) -> list:
+    """Walk up from file_path to find .seedgo/ruff_bypass.json at the branch root."""
+    fp = Path(file_path).resolve()
+    for parent in list(fp.parents):
+        candidate = parent / ".seedgo" / "ruff_bypass.json"
+        if candidate.exists():
+            try:
+                data = json.loads(candidate.read_text(encoding="utf-8"))
+                return data if isinstance(data, list) else []
+            except Exception as exc:
+                logger.warning("Failed to load ruff_bypass.json at %s: %s", candidate, exc)
+                return []
+        if (parent / ".git").exists():
+            break
+    return []
+
+
+def check_module(module_path: str, bypass_rules: list | None = None) -> Dict:
+    """Run ruff check on a single file.
+
+    Used by checklist mode and subagent_stop_gate for per-file enforcement.
+    Returns passed=False when violations exist so hooks can block.
+
+    Args:
+        module_path: Absolute path to the Python file to check.
+        bypass_rules: Standard bypass rules from .seedgo/bypass.json
+
+    Returns:
+        dict with passed, checks, score, standard keys.
+    """
+    fp = Path(module_path)
+
+    if is_bypassed(module_path, "ruff_check", bypass_rules=bypass_rules):
+        return {
+            "passed": True,
+            "checks": [{"name": "Ruff check", "passed": True, "message": "Standard bypassed via .seedgo/bypass.json"}],
+            "score": 100,
+            "standard": "RUFF_CHECK",
+        }
+
+    if shutil.which("ruff") is None:
+        return {
+            "passed": True,
+            "checks": [{"name": "Ruff check", "passed": True, "message": "ruff not installed — check skipped"}],
+            "score": 100,
+            "standard": "RUFF_CHECK",
+        }
+
+    ruff_bypass = _find_ruff_bypass_from_file(module_path)
+
+    try:
+        proc = subprocess.run(
+            ["ruff", "check", str(fp), "--output-format=json"],
+            capture_output=True,
+            text=True,
+            timeout=15,
+        )
+    except subprocess.TimeoutExpired:
+        logger.warning("ruff check_module timed out on %s", module_path)
+        return {
+            "passed": True,
+            "checks": [{"name": "Ruff check", "passed": True, "message": "ruff check timed out — skipped"}],
+            "score": 100,
+            "standard": "RUFF_CHECK",
+        }
+    except Exception as exc:
+        logger.warning("ruff check_module failed on %s: %s", module_path, exc)
+        return {
+            "passed": True,
+            "checks": [{"name": "Ruff check", "passed": True, "message": f"ruff error — skipped: {exc}"}],
+            "score": 100,
+            "standard": "RUFF_CHECK",
+        }
+
+    violations: list = []
+    if proc.stdout.strip():
+        try:
+            violations = json.loads(proc.stdout)
+            if not isinstance(violations, list):
+                violations = []
+        except (json.JSONDecodeError, ValueError) as exc:
+            logger.warning("ruff JSON parse failed for %s: %s", module_path, exc)
+            violations = []
+
+    active = [v for v in violations if not _is_ruff_bypassed(v, ruff_bypass)]
+    count = len(active)
+
+    if count == 0:
+        json_handler.log_operation(
+            "check_completed",
+            {"file": module_path, "score": 100, "standard": "ruff_check"},
+        )
+        return {
+            "passed": True,
+            "checks": [{"name": "Ruff check", "passed": True, "message": "No ruff violations found"}],
+            "score": 100,
+            "standard": "RUFF_CHECK",
+        }
+
+    top = active[:5]
+    msgs = [f"{v.get('code', '?')} L{v.get('location', {}).get('row', '?')}: {v.get('message', '?')[:80]}" for v in top]
+    suffix = f" (and {count - 5} more)" if count > 5 else ""
+    detail = f"{count} violation(s) — " + "; ".join(msgs) + suffix
+
+    json_handler.log_operation(
+        "check_completed",
+        {"file": module_path, "score": 0, "standard": "ruff_check", "violations": count},
+    )
+
+    return {
+        "passed": False,
+        "checks": [{"name": "Ruff check", "passed": False, "message": detail}],
+        "score": 0,
+        "standard": "RUFF_CHECK",
+    }
+
+
 def check_branch(branch_path: str, bypass_rules: list | None = None) -> Dict:
     """Run ruff against the branch and score based on violation count.
 
diff --git a/src/aipass/seedgo/apps/modules/checklist.py b/src/aipass/seedgo/apps/modules/checklist.py
index 67973b0e..807b9e9a 100644
--- a/src/aipass/seedgo/apps/modules/checklist.py
+++ b/src/aipass/seedgo/apps/modules/checklist.py
@@ -86,13 +86,15 @@ def _is_applicable(checker, file_path: str) -> bool:
     Rules based on AUDIT_SCOPE:
       - "entry_point" (default) -> only apps/{name}.py files
       - "all_files"             -> any .py file
-      - "branch_level"          -> not applicable to single-file checks
+      - "branch_level"          -> normally skipped, but eligible if checker
+                                   also implements check_module() for per-file use
     """
     scope = getattr(checker, "AUDIT_SCOPE", "entry_point")
 
-    # Branch-level checkers need a branch path, not a single file
+    # Branch-level checkers skip per-file runs UNLESS they also implement
+    # check_module() for targeted single-file validation (e.g., ruff_check)
     if scope == "branch_level":
-        return False
+        return hasattr(checker, "check_module") and file_path.endswith(".py")
 
     # Only check_module() capable checkers
     if not hasattr(checker, "check_module"):