diff --git a/.githooks/check_hardcoded_paths.py b/.githooks/check_hardcoded_paths.py
new file mode 100755
index 000000000..74db9621e
--- /dev/null
+++ b/.githooks/check_hardcoded_paths.py
@@ -0,0 +1,226 @@
+#!/usr/bin/env python3
+"""
+Pre-commit hook for detecting hardcoded ~/.hermes paths.
+
+This is a poka-yoke (error-proofing) measure to prevent profile isolation
+failures. All code should use get_hermes_home() from hermes_constants instead
+of hardcoding ~/.hermes or Path.home() / ".hermes".
+
+Installation:
+    git config core.hooksPath .githooks
+
+To bypass:
+    git commit --no-verify
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+import sys
+from pathlib import Path
+from typing import Iterable, List
+
+# ANSI color codes
+RED = "\033[0;31m"
+YELLOW = "\033[1;33m"
+GREEN = "\033[0;32m"
+NC = "\033[0m"
+
+
+class Finding:
+    """Represents a single hardcoded path finding."""
+
+    def __init__(self, filename: str, line: int, message: str, suggestion: str = "") -> None:
+        self.filename = filename
+        self.line = line
+        self.message = message
+        self.suggestion = suggestion
+
+    def __repr__(self) -> str:
+        return f"Finding({self.filename!r}, {self.line}, {self.message!r})"
+
+
+# ---------------------------------------------------------------------------
+# Regex patterns for hardcoded paths
+# ---------------------------------------------------------------------------
+
+# Pattern 1: Path.home() / ".hermes" or Path.home() / '.hermes'
+_RE_PATH_HOME_HERMES = re.compile(
+    r"""Path\.home\(\)\s*/\s*['"]\.hermes['"]"""
+)
+
+# Pattern 2: Path.home() / ".hermes" / something
+_RE_PATH_HOME_HERMES_SUB = re.compile(
+    r"""Path\.home\(\)\s*/\s*['"]\.hermes['"]\s*/"""
+)
+
+# Pattern 3: ~/.hermes in strings (but not in comments or docs)
+_RE_TILDE_HERMES = re.compile(
+    r"""['"]~/?\.hermes(/|['"])"""
+)
+
+# Pattern 4: os.path.expanduser("~/.hermes")
+_RE_EXPANDUSER_HERMES = re.compile(
+    r"""os\.path\.expanduser\(\s*['"]~/?\.hermes"""
+)
+
+# Pattern 5: os.path.join(os.path.expanduser("~"), ".hermes")
+_RE_JOIN_EXPANDUSER = re.compile(
+    r"""os\.path\.join\(\s*os\.path\.expanduser\(\s*['"]~['"]\s*\)\s*,\s*['"]\.hermes['"]"""
+)
+
+# All patterns combined
+_ALL_PATTERNS = [
+    (_RE_PATH_HOME_HERMES, "Path.home() / '.hermes' — use get_hermes_home() instead"),
+    (_RE_PATH_HOME_HERMES_SUB, "Path.home() / '.hermes' / ... — use get_hermes_home() / '...' instead"),
+    (_RE_TILDE_HERMES, "'~/.hermes' — use get_hermes_home() for paths, display_hermes_home() for display"),
+    (_RE_EXPANDUSER_HERMES, "os.path.expanduser('~/.hermes') — use get_hermes_home() instead"),
+    (_RE_JOIN_EXPANDUSER, "os.path.join(expanduser('~'), '.hermes') — use get_hermes_home() instead"),
+]
+
+# Safe contexts (don't flag these)
+_SAFE_CONTEXTS = [
+    # hermes_constants.py is allowed (it's the source of truth)
+    "hermes_constants.py",
+    # Test files can mock/test the behavior
+    "test_",
+    "_test.py",
+    "/tests/",
+    # Documentation files
+    ".md",
+    "README",
+    "CHANGELOG",
+    "AGENTS.md",
+    # Example/template files
+    ".example",
+    "template",
+]
+
+
+def _is_safe_context(filename: str) -> bool:
+    """Check if the file is in a safe context where hardcoded paths are OK."""
+    for safe in _SAFE_CONTEXTS:
+        if safe in filename:
+            return True
+    return False
+
+
+def _is_comment_or_doc(line: str) -> bool:
+    """Check if the line is a comment or documentation."""
+    stripped = line.strip()
+    if stripped.startswith("#"):
+        return True
+    if stripped.startswith('"""') or stripped.startswith("'''"):
+        return True
+    if '"""' in stripped or "'''" in stripped:
+        return True
+    return False
+
+
+def scan_line_for_hardcoded_paths(line: str, filename: str, line_no: int) -> Iterable[Finding]:
+    """Scan a single line for hardcoded ~/.hermes paths."""
+    if _is_safe_context(filename):
+        return
+    
+    stripped = line.rstrip("\n")
+    if not stripped:
+        return
+    
+    # Skip comments and docstrings
+    if _is_comment_or_doc(stripped):
+        return
+    
+    for pattern, message in _ALL_PATTERNS:
+        if pattern.search(stripped):
+            yield Finding(
+                filename,
+                line_no,
+                message,
+                "Use get_hermes_home() from hermes_constants for paths, display_hermes_home() for display",
+            )
+            return  # One finding per line is enough
+
+
+def get_staged_files() -> List[str]:
+    """Get list of staged files in the git index."""
+    try:
+        result = subprocess.run(
+            ["git", "diff", "--cached", "--name-only", "--diff-filter=ACM"],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+        return [f.strip() for f in result.stdout.splitlines() if f.strip()]
+    except subprocess.CalledProcessError:
+        return []
+
+
+def get_staged_content(filename: str) -> str:
+    """Get the staged content of a file."""
+    try:
+        result = subprocess.run(
+            ["git", "show", f":{filename}"],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+        return result.stdout
+    except subprocess.CalledProcessError:
+        return ""
+
+
+def scan_file(filename: str) -> List[Finding]:
+    """Scan a file for hardcoded ~/.hermes paths."""
+    if _is_safe_context(filename):
+        return []
+    
+    # Only scan Python files
+    if not filename.endswith(".py"):
+        return []
+    
+    content = get_staged_content(filename)
+    if not content:
+        return []
+    
+    findings = []
+    for line_no, line in enumerate(content.splitlines(), start=1):
+        for finding in scan_line_for_hardcoded_paths(line, filename, line_no):
+            findings.append(finding)
+    
+    return findings
+
+
+def main() -> int:
+    """Main entry point for the pre-commit hook."""
+    staged_files = get_staged_files()
+    if not staged_files:
+        return 0
+    
+    all_findings = []
+    for filename in staged_files:
+        findings = scan_file(filename)
+        all_findings.extend(findings)
+    
+    if not all_findings:
+        return 0
+    
+    # Print findings
+    print(f"\n{RED}✗ Hardcoded ~/.hermes paths detected:{NC}\n")
+    for finding in all_findings:
+        print(f"  {YELLOW}{finding.filename}:{finding.line}{NC}")
+        print(f"    {finding.message}")
+        if finding.suggestion:
+            print(f"    {GREEN}Fix: {finding.suggestion}{NC}")
+        print()
+    
+    print(f"{RED}Found {len(all_findings)} hardcoded path(s).{NC}")
+    print(f"{YELLOW}Use get_hermes_home() from hermes_constants for paths.{NC}")
+    print(f"{YELLOW}Use display_hermes_home() for user-facing display.{NC}")
+    print(f"\n{YELLOW}To bypass: git commit --no-verify{NC}\n")
+    
+    return 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/.githooks/pre-commit.py b/.githooks/pre-commit.py
index a48ade0af..da4156bac 100755
--- a/.githooks/pre-commit.py
+++ b/.githooks/pre-commit.py
@@ -295,6 +295,22 @@ def main() -> int:
             if line.startswith("+") and not line.startswith("+++"):
                 findings.extend(scan_line(line[1:], "<diff>", line_no))
 
+    # Also check for hardcoded ~/.hermes paths
+    print(f"{GREEN}🔍 Scanning for hardcoded ~/.hermes paths...{NC}")
+    try:
+        import subprocess as sp
+        result = sp.run(
+            [sys.executable, str(Path(__file__).parent / "check_hardcoded_paths.py")],
+            capture_output=True,
+            text=True,
+        )
+        if result.returncode != 0:
+            # Print the output from the hardcoded path check
+            print(result.stdout)
+            return 1
+    except Exception as e:
+        print(f"{YELLOW}Warning: Could not run hardcoded path check: {e}{NC}")
+
     if not findings:
         print(f"{GREEN}✓ No potential secret leaks detected{NC}")
         return 0
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 120cf01bf..054373f3a 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -12,6 +12,23 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  check-hardcoded-paths:
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Python 3.11
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
+      - name: Check for hardcoded ~/.hermes paths
+        run: |
+          python .githooks/check_hardcoded_paths.py
+        # This will fail if any hardcoded paths are found
+
   test:
     runs-on: ubuntu-latest
     container: catthehacker/ubuntu:act-22.04
diff --git a/tests/test_hardcoded_paths.py b/tests/test_hardcoded_paths.py
new file mode 100644
index 000000000..789f33868
--- /dev/null
+++ b/tests/test_hardcoded_paths.py
@@ -0,0 +1,175 @@
+"""
+Tests for hardcoded ~/.hermes path detection (poka-yoke).
+
+These tests verify that the pre-commit hook correctly detects hardcoded
+paths and that the codebase uses get_hermes_home() correctly.
+"""
+
+import os
+import tempfile
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+# Import the scanner
+import sys
+sys.path.insert(0, str(Path(__file__).parent.parent / ".githooks"))
+from check_hardcoded_paths import scan_line_for_hardcoded_paths, Finding
+
+
+class TestHardcodedPathDetection:
+    """Test the hardcoded path detection logic."""
+
+    def test_detects_path_home_hermes(self):
+        """Detect Path.home() / '.hermes' pattern."""
+        line = '    home = Path.home() / ".hermes"'
+        findings = list(scan_line_for_hardcoded_paths(line, "test.py", 1))
+        assert len(findings) == 1
+        assert "Path.home()" in findings[0].message
+
+    def test_detects_path_home_hermes_subpath(self):
+        """Detect Path.home() / '.hermes' / 'subdir' pattern."""
+        line = '    config_dir = Path.home() / ".hermes" / "config"'
+        findings = list(scan_line_for_hardcoded_paths(line, "test.py", 1))
+        assert len(findings) == 1
+
+    def test_detects_tilde_hermes_in_string(self):
+        """Detect '~/.hermes' in string literals."""
+        line = '    path = "~/.hermes/config.yaml"'
+        findings = list(scan_line_for_hardcoded_paths(line, "test.py", 1))
+        assert len(findings) == 1
+
+    def test_detects_expanduser_hermes(self):
+        """Detect os.path.expanduser('~/.hermes') pattern."""
+        line = '    home = os.path.expanduser("~/.hermes")'
+        findings = list(scan_line_for_hardcoded_paths(line, "test.py", 1))
+        assert len(findings) == 1
+
+    def test_detects_join_expanduser(self):
+        """Detect os.path.join(expanduser('~'), '.hermes') pattern."""
+        line = '    home = os.path.join(os.path.expanduser("~"), ".hermes")'
+        findings = list(scan_line_for_hardcoded_paths(line, "test.py", 1))
+        assert len(findings) == 1
+
+    def test_ignores_comments(self):
+        """Ignore hardcoded paths in comments."""
+        line = '    # This is ~/.hermes in a comment'
+        findings = list(scan_line_for_hardcoded_paths(line, "test.py", 1))
+        assert len(findings) == 0
+
+    def test_ignores_docstrings(self):
+        """Ignore hardcoded paths in docstrings."""
+        line = '    """This mentions ~/.hermes in a docstring."""'
+        findings = list(scan_line_for_hardcoded_paths(line, "test.py", 1))
+        assert len(findings) == 0
+
+    def test_ignores_hermes_constants(self):
+        """hermes_constants.py is allowed to have hardcoded paths."""
+        line = '    return Path.home() / ".hermes"'
+        findings = list(scan_line_for_hardcoded_paths(line, "hermes_constants.py", 1))
+        assert len(findings) == 0
+
+    def test_ignores_test_files(self):
+        """Test files can have hardcoded paths for testing."""
+        line = '    home = Path.home() / ".hermes"'
+        findings = list(scan_line_for_hardcoded_paths(line, "test_something.py", 1))
+        assert len(findings) == 0
+
+    def test_ignores_markdown_files(self):
+        """Markdown files can have hardcoded paths in examples."""
+        line = '    home = Path.home() / ".hermes"'
+        findings = list(scan_line_for_hardcoded_paths(line, "README.md", 1))
+        assert len(findings) == 0
+
+    def test_ignores_empty_lines(self):
+        """Empty lines should not produce findings."""
+        line = ""
+        findings = list(scan_line_for_hardcoded_paths(line, "test.py", 1))
+        assert len(findings) == 0
+
+
+class TestHermesHomeUsage:
+    """Test that the codebase uses get_hermes_home() correctly."""
+
+    def test_hermes_constants_has_get_hermes_home(self):
+        """hermes_constants.py should export get_hermes_home()."""
+        from hermes_constants import get_hermes_home
+        assert callable(get_hermes_home)
+
+    def test_hermes_constants_has_display_hermes_home(self):
+        """hermes_constants.py should export display_hermes_home()."""
+        from hermes_constants import display_hermes_home
+        assert callable(display_hermes_home)
+
+    def test_get_hermes_home_returns_path(self):
+        """get_hermes_home() should return a Path object."""
+        from hermes_constants import get_hermes_home
+        result = get_hermes_home()
+        assert isinstance(result, Path)
+
+    def test_get_hermes_home_honors_env_var(self):
+        """get_hermes_home() should honor HERMES_HOME env var."""
+        from hermes_constants import get_hermes_home
+        
+        with tempfile.TemporaryDirectory() as tmpdir:
+            with patch.dict(os.environ, {"HERMES_HOME": tmpdir}):
+                result = get_hermes_home()
+                assert result == Path(tmpdir)
+
+    def test_display_hermes_home_returns_string(self):
+        """display_hermes_home() should return a string."""
+        from hermes_constants import display_hermes_home
+        result = display_hermes_home()
+        assert isinstance(result, str)
+
+    def test_display_hermes_home_uses_tilde_shorthand(self):
+        """display_hermes_home() should use ~/ shorthand for home directory."""
+        from hermes_constants import display_hermes_home, get_hermes_home
+        
+        # If HERMES_HOME is under home directory, should use ~/
+        home = get_hermes_home()
+        if home.is_relative_to(Path.home()):
+            result = display_hermes_home()
+            assert result.startswith("~/")
+
+    def test_profile_isolation_with_env_var(self):
+        """Each profile should have its own HERMES_HOME."""
+        from hermes_constants import get_hermes_home
+        
+        with tempfile.TemporaryDirectory() as tmpdir1, tempfile.TemporaryDirectory() as tmpdir2:
+            # Profile 1
+            with patch.dict(os.environ, {"HERMES_HOME": tmpdir1}):
+                home1 = get_hermes_home()
+            
+            # Profile 2
+            with patch.dict(os.environ, {"HERMES_HOME": tmpdir2}):
+                home2 = get_hermes_home()
+            
+            assert home1 != home2
+            assert home1 == Path(tmpdir1)
+            assert home2 == Path(tmpdir2)
+
+
+class TestPreCommitHookIntegration:
+    """Integration tests for the pre-commit hook."""
+
+    def test_hook_script_exists(self):
+        """The check_hardcoded_paths.py script should exist."""
+        hook_path = Path(__file__).parent.parent / ".githooks" / "check_hardcoded_paths.py"
+        assert hook_path.exists()
+
+    def test_hook_script_is_executable(self):
+        """The check_hardcoded_paths.py script should be executable."""
+        hook_path = Path(__file__).parent.parent / ".githooks" / "check_hardcoded_paths.py"
+        assert hook_path.stat().st_mode & 0o111  # Check executable bits
+
+    def test_pre_commit_calls_hardcoded_check(self):
+        """pre-commit.py should call the hardcoded path check."""
+        pre_commit_path = Path(__file__).parent.parent / ".githooks" / "pre-commit.py"
+        content = pre_commit_path.read_text()
+        assert "check_hardcoded_paths.py" in content
+
+
+if __name__ == "__main__":
+    pytest.main([__file__, "-v"])