diff --git a/agent/vault_injection.py b/agent/vault_injection.py
new file mode 100644
index 0000000000..c46f8219d4
--- /dev/null
+++ b/agent/vault_injection.py
@@ -0,0 +1,117 @@
+"""Vault injection — auto-load Obsidian vault files into the system prompt.
+
+Reads working-context.md and user-profile.md from a configured vault path
+at session start and injects them into the system prompt alongside Layer 1
+memory (MEMORY.md / USER.md). This is a structural fix for vault neglect:
+the agent no longer needs to remember to read these files — they're injected
+automatically, the same way Layer 1 memory is.
+
+The vault is Layer 3 in the memory architecture. Files injected here are
+read-only in the system prompt (frozen at session start). Mid-session
+writes to vault files require the read_file/write_file tools or the
+memory-vault skill.
+
+Config (in config.yaml under 'vault'):
+  enabled: true          # enable vault injection
+  path: /path/to/vault   # absolute path to the Obsidian vault root
+
+Files read (relative to vault path):
+  Agent-Hermes/working-context.md   — what the agent is actively doing
+  Agent-Shared/user-profile.md      — who the user is (durable facts)
+
+If either file doesn't exist or is empty, it's silently skipped.
+If the vault path doesn't exist or isn't configured, vault injection is
+silently disabled.
+"""
+
+import logging
+import os
+from pathlib import Path
+from typing import Optional
+
+logger = logging.getLogger(__name__)
+
+# Character limits for vault injection blocks (to prevent prompt bloat)
+WORKING_CONTEXT_CHAR_LIMIT = 4000
+USER_PROFILE_CHAR_LIMIT = 4000
+
+SEPARATOR = "\u2550" * 46  # ═ same as memory_tool uses
+
+
+def _read_vault_file(path: Path, char_limit: int) -> Optional[str]:
+    """Read a vault file and return its content, or None if missing/empty.
+
+    Truncates with a notice if the file exceeds char_limit.
+    """
+    if not path.exists():
+        return None
+    try:
+        content = path.read_text(encoding="utf-8").strip()
+    except (OSError, IOError) as e:
+        logger.debug("Could not read vault file %s: %s", path, e)
+        return None
+
+    if not content:
+        return None
+
+    # Strip YAML frontmatter (same as prompt_builder does for context files)
+    content = _strip_yaml_frontmatter(content)
+
+    if not content:
+        return None
+
+    if len(content) > char_limit:
+        truncated = content[:char_limit]
+        # Find last newline to avoid cutting mid-line
+        last_nl = truncated.rfind("\n")
+        if last_nl > char_limit // 2:
+            truncated = truncated[:last_nl]
+        content = truncated + f"\n[... truncated at {char_limit} chars ...]"
+
+    return content
+
+
+def _strip_yaml_frontmatter(content: str) -> str:
+    """Remove optional YAML frontmatter (--- delimited) from content."""
+    if content.startswith("---"):
+        end = content.find("\n---", 3)
+        if end != -1:
+            body = content[end + 4:].lstrip("\n")
+            return body if body else content
+    return content
+
+
+def build_vault_system_prompt(vault_path: str) -> str:
+    """Build the vault injection block for the system prompt.
+
+    Reads working-context.md and user-profile.md from the vault and formats
+    them with headers matching the style of Layer 1 memory blocks.
+
+    Returns an empty string if vault is disabled, path is missing, or
+    all files are empty.
+    """
+    if not vault_path:
+        return ""
+
+    vault_root = Path(vault_path)
+    if not vault_root.is_dir():
+        logger.debug("Vault path does not exist or is not a directory: %s", vault_path)
+        return ""
+
+    parts = []
+
+    # Read working-context.md (agent's current state)
+    wc_path = vault_root / "Agent-Hermes" / "working-context.md"
+    wc_content = _read_vault_file(wc_path, WORKING_CONTEXT_CHAR_LIMIT)
+    if wc_content:
+        header = "VAULT: WORKING CONTEXT (what you're doing right now)"
+        parts.append(f"{SEPARATOR}\n{header}\n{SEPARATOR}\n{wc_content}")
+
+    # Read user-profile.md (shared user profile)
+    up_path = vault_root / "Agent-Shared" / "user-profile.md"
+    up_content = _read_vault_file(up_path, USER_PROFILE_CHAR_LIMIT)
+    if up_content:
+        header = "VAULT: USER PROFILE (durable facts from Obsidian vault)"
+        parts.append(f"{SEPARATOR}\n{header}\n{SEPARATOR}\n{up_content}")
+
+    return "\n\n".join(parts)
\ No newline at end of file
diff --git a/hermes_cli/config.py b/hermes_cli/config.py
index 7678287a0e..71727913d7 100644
--- a/hermes_cli/config.py
+++ b/hermes_cli/config.py
@@ -754,6 +754,16 @@ DEFAULT_CONFIG = {
         "provider": "",
     },
 
+    # Obsidian vault auto-injection — Layer 3 persistent memory.
+    # When enabled, working-context.md and user-profile.md are read from
+    # the vault path at session start and injected into the system prompt
+    # alongside Layer 1 memory. This is a structural fix for vault neglect:
+    # the agent no longer needs to remember to read these files manually.
+    "vault": {
+        "enabled": False,      # set true to activate
+        "path": "",             # absolute path to the Obsidian vault root
+    },
+
     # Subagent delegation — override the provider:model used by delegate_task
     # so child agents can run on a different (cheaper/faster) provider and model.
     # Uses the same runtime provider resolution as CLI/gateway startup, so all
diff --git a/run_agent.py b/run_agent.py
index 6770f568c0..c1b2d60658 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -1566,7 +1566,8 @@ class AIAgent:
         try:
             from hermes_cli.config import load_config as _load_agent_config
             _agent_cfg = _load_agent_config()
-        except Exception:
+        except Exception as e:
+            logger.warning("Agent init: load_config() failed: %s: %s — using empty config", type(e).__name__, e)
             _agent_cfg = {}
         # Cache only the derived auxiliary compression context override that is
         # needed later by the startup feasibility check.  Avoid exposing a
@@ -1597,8 +1598,20 @@ class AIAgent:
                     self._memory_store.load_from_disk()
             except Exception:
                 pass  # Memory is optional -- don't break agent init
-        
 
+        # Obsidian vault auto-injection (Layer 3) — structural fix for
+        # vault neglect. Reads working-context.md and user-profile.md
+        # from the configured vault path and injects them into the system
+        # prompt at session start, just like Layer 1 memory.
+        self._vault_enabled = False
+        self._vault_path = ""
+        try:
+            vault_config = _agent_cfg.get("vault", {})
+            self._vault_enabled = vault_config.get("enabled", False)
+            self._vault_path = vault_config.get("path", "")
+            logging.getLogger("agent.vault").info("Vault config: enabled=%s path=%s", self._vault_enabled, self._vault_path)
+        except Exception as e:
+            logging.getLogger("agent.vault").warning("Vault config read failed: %s: %s", type(e).__name__, e)
 
         # Memory provider plugin (external — one at a time, alongside built-in)
         # Reads memory.provider from config to select which plugin to activate.
@@ -4448,6 +4461,24 @@ class AIAgent:
                 if user_block:
                     prompt_parts.append(user_block)
 
+        # Vault auto-injection (Layer 3) — reads working-context.md and
+        # user-profile.md from the Obsidian vault and injects them into
+        # the system prompt. Structural fix for vault neglect.
+        _vault_log = logging.getLogger("agent.vault")
+        if self._vault_enabled and self._vault_path:
+            try:
+                from agent.vault_injection import build_vault_system_prompt
+                _vault_block = build_vault_system_prompt(self._vault_path)
+                if _vault_block:
+                    prompt_parts.append(_vault_block)
+                    _vault_log.info("Injection succeeded: %d chars from %s", len(_vault_block), self._vault_path)
+                else:
+                    _vault_log.warning("Injection returned empty for path %s", self._vault_path)
+            except Exception as e:
+                _vault_log.warning("Injection failed: %s: %s", type(e).__name__, e)
+        else:
+            _vault_log.info("Injection skipped: enabled=%s path=%s", self._vault_enabled, self._vault_path)
+
         # External memory provider system prompt block (additive to built-in)
         if self._memory_manager:
             try:
diff --git a/tests/agent/test_vault_injection.py b/tests/agent/test_vault_injection.py
new file mode 100644
index 0000000000..0eae544e41
--- /dev/null
+++ b/tests/agent/test_vault_injection.py
@@ -0,0 +1,174 @@
+"""Tests for agent/vault_injection.py — Obsidian vault auto-injection into system prompt."""
+
+import pytest
+import os
+from pathlib import Path
+
+from agent.vault_injection import (
+    build_vault_system_prompt,
+    _read_vault_file,
+    _strip_yaml_frontmatter,
+    WORKING_CONTEXT_CHAR_LIMIT,
+    USER_PROFILE_CHAR_LIMIT,
+)
+
+
+# ---------------------------------------------------------------------------
+# _strip_yaml_frontmatter
+# ---------------------------------------------------------------------------
+
+class TestStripYamlFrontmatter:
+    def test_strips_simple_frontmatter(self):
+        content = "---\ndate: 2026-04-22\n---\nHello world"
+        assert _strip_yaml_frontmatter(content) == "Hello world"
+
+    def test_no_frontmatter(self):
+        content = "Just some text"
+        assert _strip_yaml_frontmatter(content) == "Just some text"
+
+    def test_frontmatter_with_blank_lines(self):
+        content = "---\ndate: 2026-04-22\nprojects: [X]\n---\n\nActual content here"
+        result = _strip_yaml_frontmatter(content)
+        assert result == "Actual content here"
+
+    def test_unclosed_frontmatter_returns_original(self):
+        content = "---\ndate: 2026-04-22\nNo closing dashes"
+        assert _strip_yaml_frontmatter(content) == content
+
+
+# ---------------------------------------------------------------------------
+# _read_vault_file
+# ---------------------------------------------------------------------------
+
+class TestReadVaultFile:
+    def test_reads_existing_file(self, tmp_path):
+        f = tmp_path / "test.md"
+        f.write_text("some content", encoding="utf-8")
+        result = _read_vault_file(f, 4000)
+        assert result == "some content"
+
+    def test_returns_none_for_missing_file(self, tmp_path):
+        f = tmp_path / "nonexistent.md"
+        result = _read_vault_file(f, 4000)
+        assert result is None
+
+    def test_returns_none_for_empty_file(self, tmp_path):
+        f = tmp_path / "empty.md"
+        f.write_text("", encoding="utf-8")
+        result = _read_vault_file(f, 4000)
+        assert result is None
+
+    def test_returns_none_for_whitespace_only(self, tmp_path):
+        f = tmp_path / "ws.md"
+        f.write_text("   \n\n  ", encoding="utf-8")
+        result = _read_vault_file(f, 4000)
+        assert result is None
+
+    def test_strips_frontmatter(self, tmp_path):
+        f = tmp_path / "frontmatter.md"
+        f.write_text("---\ndate: 2026-04-22\n---\nReal content", encoding="utf-8")
+        result = _read_vault_file(f, 4000)
+        assert result == "Real content"
+
+    def test_truncates_long_file(self, tmp_path):
+        f = tmp_path / "long.md"
+        long_content = "x" * 5000
+        f.write_text(long_content, encoding="utf-8")
+        result = _read_vault_file(f, 100)
+        assert len(result) < 200  # truncation + notice
+        assert "truncated" in result
+
+    def test_truncation_at_newline(self, tmp_path):
+        f = tmp_path / "multiline.md"
+        lines = ["line " + str(i) for i in range(100)]
+        content = "\n".join(lines)
+        f.write_text(content, encoding="utf-8")
+        # Small limit, should truncate at a newline boundary
+        result = _read_vault_file(f, 50)
+        assert "truncated" in result
+        # Should not cut mid-line
+        for line in result.split("\n"):
+            if line and "truncated" not in line:
+                assert line.startswith("line")
+
+
+# ---------------------------------------------------------------------------
+# build_vault_system_prompt
+# ---------------------------------------------------------------------------
+
+class TestBuildVaultSystemPrompt:
+    def test_empty_path_returns_empty(self):
+        assert build_vault_system_prompt("") == ""
+
+    def test_nonexistent_path_returns_empty(self, tmp_path):
+        assert build_vault_system_prompt(str(tmp_path / "nope")) == ""
+
+    def test_empty_vault_dir_returns_empty(self, tmp_path):
+        assert build_vault_system_prompt(str(tmp_path)) == ""
+
+    def test_injects_working_context(self, tmp_path):
+        vault = tmp_path / "vault"
+        agent_dir = vault / "Agent-Hermes"
+        agent_dir.mkdir(parents=True)
+        wc = agent_dir / "working-context.md"
+        wc.write_text("---\ndate: 2026-04-22\n---\n## Current Status\n- Status: Active", encoding="utf-8")
+
+        result = build_vault_system_prompt(str(vault))
+        assert "VAULT: WORKING CONTEXT" in result
+        assert "Status: Active" in result
+
+    def test_injects_user_profile(self, tmp_path):
+        vault = tmp_path / "vault"
+        shared_dir = vault / "Agent-Shared"
+        shared_dir.mkdir(parents=True)
+        up = shared_dir / "user-profile.md"
+        up.write_text("# User Profile\n\nName: AJ", encoding="utf-8")
+
+        result = build_vault_system_prompt(str(vault))
+        assert "VAULT: USER PROFILE" in result
+        assert "Name: AJ" in result
+
+    def test_injects_both_files(self, tmp_path):
+        vault = tmp_path / "vault"
+        agent_dir = vault / "Agent-Hermes"
+        shared_dir = vault / "Agent-Shared"
+        agent_dir.mkdir(parents=True)
+        shared_dir.mkdir(parents=True)
+
+        (agent_dir / "working-context.md").write_text(
+            "---\ndate: 2026-04-22\n---\nWorking on X", encoding="utf-8"
+        )
+        (shared_dir / "user-profile.md").write_text(
+            "# User Profile\n\nName: AJ", encoding="utf-8"
+        )
+
+        result = build_vault_system_prompt(str(vault))
+        assert "VAULT: WORKING CONTEXT" in result
+        assert "VAULT: USER PROFILE" in result
+        assert "Working on X" in result
+        assert "Name: AJ" in result
+
+    def test_skips_empty_working_context(self, tmp_path):
+        vault = tmp_path / "vault"
+        agent_dir = vault / "Agent-Hermes"
+        shared_dir = vault / "Agent-Shared"
+        agent_dir.mkdir(parents=True)
+        shared_dir.mkdir(parents=True)
+
+        (agent_dir / "working-context.md").write_text("", encoding="utf-8")
+        (shared_dir / "user-profile.md").write_text("Name: AJ", encoding="utf-8")
+
+        result = build_vault_system_prompt(str(vault))
+        assert "VAULT: WORKING CONTEXT" not in result
+        assert "VAULT: USER PROFILE" in result
+
+    def test_format_matches_memory_block_style(self, tmp_path):
+        vault = tmp_path / "vault"
+        agent_dir = vault / "Agent-Hermes"
+        agent_dir.mkdir(parents=True)
+        (agent_dir / "working-context.md").write_text("Active task", encoding="utf-8")
+
+        result = build_vault_system_prompt(str(vault))
+        # Should use the same separator as memory_tool (═══)
+        assert "\u2550" in result  # ═ character
+        assert "VAULT: WORKING CONTEXT" in result
\ No newline at end of file
diff --git a/tests/run_agent/test_vault_injection.py b/tests/run_agent/test_vault_injection.py
new file mode 100644
index 0000000000..76529c62ce
--- /dev/null
+++ b/tests/run_agent/test_vault_injection.py
@@ -0,0 +1,161 @@
+"""Tests for vault auto-injection integration with _build_system_prompt.
+
+Verifies that vault content appears in the system prompt when vault is
+configured, and is absent otherwise.
+"""
+
+import os
+import pytest
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+
+def _make_minimal_agent(**overrides):
+    """Create a minimal AIAgent for testing, with vault attrs settable."""
+    from run_agent import AIAgent
+
+    with (
+        patch("run_agent.get_tool_definitions", return_value=[]),
+        patch("run_agent.check_toolset_requirements", return_value={}),
+        patch("run_agent.OpenAI"),
+    ):
+        a = AIAgent(
+            api_key="test-k...7890",
+            base_url="https://openrouter.ai/api/v1",
+            quiet_mode=True,
+            skip_context_files=True,
+            skip_memory=True,
+        )
+        a.client = MagicMock()
+
+    # Apply overrides after creation
+    for k, v in overrides.items():
+        setattr(a, k, v)
+
+    return a
+
+
+class TestVaultSystemPromptIntegration:
+    """Test that _build_system_prompt injects vault content when configured."""
+
+    def test_vault_not_injected_when_disabled(self, tmp_path):
+        """Vault content should not appear when vault_enabled=False."""
+        vault_dir = tmp_path / "vault"
+        agent_dir = vault_dir / "Agent-Hermes"
+        agent_dir.mkdir(parents=True)
+        (agent_dir / "working-context.md").write_text("Active task X", encoding="utf-8")
+
+        agent = _make_minimal_agent(
+            _vault_enabled=False,
+            _vault_path=str(vault_dir),
+        )
+
+        prompt = agent._build_system_prompt()
+        assert "VAULT: WORKING CONTEXT" not in prompt
+        assert "Active task X" not in prompt
+
+    def test_vault_injected_when_enabled(self, tmp_path):
+        """Vault content should appear in system prompt when vault_enabled=True."""
+        vault_dir = tmp_path / "vault"
+        agent_dir = vault_dir / "Agent-Hermes"
+        shared_dir = vault_dir / "Agent-Shared"
+        agent_dir.mkdir(parents=True)
+        shared_dir.mkdir(parents=True)
+        (agent_dir / "working-context.md").write_text(
+            "---\ndate: 2026-04-22\n---\n## Status\nActive: vault fix",
+            encoding="utf-8",
+        )
+        (shared_dir / "user-profile.md").write_text(
+            "# User Profile\n\nName: Test User",
+            encoding="utf-8",
+        )
+
+        agent = _make_minimal_agent(
+            _vault_enabled=True,
+            _vault_path=str(vault_dir),
+        )
+
+        prompt = agent._build_system_prompt()
+        assert "VAULT: WORKING CONTEXT" in prompt
+        assert "Active: vault fix" in prompt
+        assert "VAULT: USER PROFILE" in prompt
+        assert "Name: Test User" in prompt
+
+    def test_vault_after_memory_blocks(self, tmp_path):
+        """Vault injection should appear after Layer 1 memory blocks."""
+        # Set up memory files
+        mem_dir = tmp_path / "memories"
+        mem_dir.mkdir(parents=True)
+        (mem_dir / "MEMORY.md").write_text("Layer 1 memory note", encoding="utf-8")
+
+        # Set up vault files
+        vault_dir = tmp_path / "vault"
+        agent_dir = vault_dir / "Agent-Hermes"
+        agent_dir.mkdir(parents=True)
+        (agent_dir / "working-context.md").write_text("Vault content", encoding="utf-8")
+
+        # Create agent with memory enabled
+        from run_agent import AIAgent
+        from tools.memory_tool import MemoryStore
+
+        with (
+            patch("run_agent.get_tool_definitions", return_value=[]),
+            patch("run_agent.check_toolset_requirements", return_value={}),
+            patch("run_agent.OpenAI"),
+            patch(
+                "hermes_cli.config.load_config",
+                return_value={
+                    "memory": {
+                        "memory_enabled": True,
+                        "user_profile_enabled": False,
+                        "memory_char_limit": 2200,
+                        "user_char_limit": 1375,
+                    },
+                },
+            ),
+        ):
+            monkeypatch_env = {}
+            # Set HERMES_HOME so MemoryStore reads from tmp_path
+            os.environ["HERMES_HOME"] = str(tmp_path)
+            try:
+                a = AIAgent(
+                    api_key="test-k...7890",
+                    base_url="https://openrouter.ai/api/v1",
+                    quiet_mode=True,
+                    skip_context_files=True,
+                    skip_memory=False,
+                )
+                a.client = MagicMock()
+            finally:
+                del os.environ["HERMES_HOME"]
+
+        a._vault_enabled = True
+        a._vault_path = str(vault_dir)
+
+        prompt = a._build_system_prompt()
+        mem_pos = prompt.find("MEMORY (your personal notes)")
+        vault_pos = prompt.find("VAULT: WORKING CONTEXT")
+        assert mem_pos > 0, "Layer 1 memory block not found in prompt"
+        assert vault_pos > 0, "Vault block not found in prompt"
+        assert mem_pos < vault_pos, "Vault should appear after Layer 1 memory"
+
+    def test_missing_vault_path_graceful(self, tmp_path):
+        """Agent works fine even if vault path doesn't exist."""
+        agent = _make_minimal_agent(
+            _vault_enabled=True,
+            _vault_path="/nonexistent/vault/path",
+        )
+
+        # Should not crash
+        prompt = agent._build_system_prompt()
+        assert "VAULT:" not in prompt
+
+    def test_no_vault_config_graceful(self):
+        """Agent works fine with no vault set (defaults)."""
+        agent = _make_minimal_agent(
+            _vault_enabled=False,
+            _vault_path="",
+        )
+
+        prompt = agent._build_system_prompt()
+        assert "VAULT:" not in prompt
\ No newline at end of file