diff --git a/agent/agent_init.py b/agent/agent_init.py
index 41f7cc11bbb..28a7e1cfad6 100644
--- a/agent/agent_init.py
+++ b/agent/agent_init.py
@@ -1325,6 +1325,12 @@ def init_agent(
     # single turn; the runtime already executes such batches concurrently.
     agent._parallel_tool_call_guidance = bool(_agent_section.get("parallel_tool_call_guidance", True))
 
+    # Universal disabled/unavailable-capability guidance toggle.  Default True.
+    # Separate flag because a user may want the other guidance blocks but not
+    # this one.  Steers the model to report a named-but-unavailable capability
+    # as disabled rather than substituting a different tool to work around it.
+    agent._disabled_tool_guidance = bool(_agent_section.get("disabled_tool_guidance", True))
+
     # Local Python toolchain probe toggle.  Default True.  When False,
     # the probe is skipped entirely (no subprocess calls, no system-prompt
     # line).  Useful for users on exotic setups where the probe heuristics
diff --git a/agent/prompt_builder.py b/agent/prompt_builder.py
index 319be7255e2..c80a525632f 100644
--- a/agent/prompt_builder.py
+++ b/agent/prompt_builder.py
@@ -366,6 +366,46 @@ PARALLEL_TOOL_CALL_GUIDANCE = (
     "in doubt and the calls are independent, batch them."
 )
 
+# Universal disabled/unavailable-capability guidance — applied to ALL models.
+#
+# Why this matters: when a user disables a tool via `hermes tools` (or runs a
+# restricted-toolset session — subagent, kanban worker, curated gateway), that
+# tool is removed from the model's tool schema. The runtime already *enforces*
+# this: a disabled tool cannot be invoked, including through the tool_search
+# bridge (model_tools.py rejects out-of-scope underlying calls). What was
+# missing is the *behavioral* steer. A model whose dedicated email tool is
+# disabled will happily shell out via `terminal` to send the mail anyway, or
+# curl an API to stand in for a disabled integration tool — silently routing
+# around the user's explicit decision to turn that capability off. The user
+# disabled it for a reason (cost, safety, privacy, scope); substituting a
+# different tool defeats that intent without telling them.
+#
+# This block tells the model: if the user names a capability that isn't in your
+# available tools, say it's unavailable/disabled — do NOT substitute another
+# tool as a workaround. It does not stop the model from using general-purpose
+# tools (terminal, etc.) for their own legitimate purposes; it stops the model
+# from using them as a stand-in for a capability the user deliberately removed.
+#
+# Short on purpose — shipped in the cached system prompt to every user, every
+# session. Token cost is paid once at install and amortised across all sessions
+# via prefix caching. Keep it tight.
+#
+# Ported from nearai/ironclaw#5307 ("discourage disabled tool workarounds"),
+# adapted from IronClaw's Rust capability-surface usage policy to hermes-agent's
+# Python prompt-assembly architecture.
+DISABLED_TOOL_GUIDANCE = (
+    "# Disabled or unavailable capabilities\n"
+    "Use only the tools available to you in this session. If the user asks you "
+    "to use a specific capability by name and no tool for it is available — "
+    "because it was disabled in this session's toolset, or never enabled — tell "
+    "the user that capability is unavailable or disabled. Do NOT route around it "
+    "by using a different tool as a substitute (e.g. shelling out via the "
+    "terminal to do what a disabled dedicated tool would have done). The user "
+    "turned it off deliberately; honor that rather than working around it. "
+    "General-purpose tools are still fine for their own legitimate tasks — just "
+    "don't use them as a stand-in for a capability the user removed."
+)
+
 # OpenAI GPT/Codex-specific execution guidance.  Addresses known failure modes
 # where GPT models abandon work on partial results, skip prerequisite lookups,
 # hallucinate instead of using tools, and declare "done" without verification.
diff --git a/agent/system_prompt.py b/agent/system_prompt.py
index b9b26e07abc..c92b0dc32c1 100644
--- a/agent/system_prompt.py
+++ b/agent/system_prompt.py
@@ -28,6 +28,7 @@ from typing import Any, Dict, List, Optional
 
 from agent.prompt_builder import (
     DEFAULT_AGENT_IDENTITY,
+    DISABLED_TOOL_GUIDANCE,
     GOOGLE_MODEL_OPERATIONAL_GUIDANCE,
     HERMES_AGENT_HELP_GUIDANCE,
     KANBAN_GUIDANCE,
@@ -184,6 +185,18 @@ def build_system_prompt_parts(agent: Any, system_message: Optional[str] = None)
     if getattr(agent, "_parallel_tool_call_guidance", True) and agent.valid_tool_names:
         stable_parts.append(PARALLEL_TOOL_CALL_GUIDANCE)
 
+    # Universal disabled/unavailable-capability guidance.  Tells the model that
+    # when the user names a capability with no available tool (disabled in this
+    # session's toolset, or never enabled), it should say so rather than
+    # substituting a different tool (e.g. shelling out via the terminal) to work
+    # around the user's explicit decision to turn that capability off.  The
+    # runtime already *enforces* that disabled tools can't be invoked; this
+    # supplies the behavioral steer so the model doesn't silently route around
+    # the missing tool.  Gated by config.yaml ``agent.disabled_tool_guidance``
+    # (default True) and only injected when tools are actually loaded.
+    if getattr(agent, "_disabled_tool_guidance", True) and agent.valid_tool_names:
+        stable_parts.append(DISABLED_TOOL_GUIDANCE)
+
     # Tool-aware behavioral guidance: only inject when the tools are loaded
     tool_guidance = []
     if "memory" in agent.valid_tool_names:
diff --git a/hermes_cli/config.py b/hermes_cli/config.py
index cf3cce9f89e..7171b3fbf5d 100644
--- a/hermes_cli/config.py
+++ b/hermes_cli/config.py
@@ -969,6 +969,16 @@ DEFAULT_CONFIG = {
         # compounds over a long conversation.  Costs ~70 tokens in the cached
         # system prompt.  Set False to disable globally.
         "parallel_tool_call_guidance": True,
+        # Universal disabled/unavailable-capability guidance — short prompt
+        # block applied to all models that tells the model: when the user names
+        # a capability that has no available tool (disabled in this session's
+        # toolset, or never enabled), report it as unavailable/disabled instead
+        # of substituting a different tool (e.g. shelling out via the terminal)
+        # to route around the user's explicit decision to turn it off.  The
+        # runtime already enforces that disabled tools can't be invoked; this is
+        # the behavioral steer.  Costs ~80 tokens in the cached system prompt.
+        # Set False to disable globally.
+        "disabled_tool_guidance": True,
         # Local-environment toolchain probe — surfaces Python/pip/uv/PEP-668
         # state in the system prompt when something non-default is detected
         # (e.g. python3 has no pip module, pip→python version mismatch, PEP
diff --git a/tests/agent/test_prompt_builder.py b/tests/agent/test_prompt_builder.py
index a2d8ec56d7e..bdb12f2fd85 100644
--- a/tests/agent/test_prompt_builder.py
+++ b/tests/agent/test_prompt_builder.py
@@ -28,6 +28,7 @@ from agent.prompt_builder import (
     TOOL_USE_ENFORCEMENT_MODELS,
     OPENAI_MODEL_EXECUTION_GUIDANCE,
     PARALLEL_TOOL_CALL_GUIDANCE,
+    DISABLED_TOOL_GUIDANCE,
     GOOGLE_MODEL_OPERATIONAL_GUIDANCE,
     MEMORY_GUIDANCE,
     SESSION_SEARCH_GUIDANCE,
@@ -1604,6 +1605,47 @@ class TestParallelToolCallGuidance:
         assert "parallel tool call" not in GOOGLE_MODEL_OPERATIONAL_GUIDANCE.lower()
 
 
+class TestDisabledToolGuidance:
+    """Behavior contracts for the disabled/unavailable-capability guidance.
+
+    Asserts the invariants the block must satisfy (steer reporting a
+    named-but-unavailable capability instead of substituting another tool, stay
+    short for the cached prompt) rather than freezing its exact wording.
+    Ported from nearai/ironclaw#5307.
+    """
+
+    def test_is_nonempty_string(self):
+        assert isinstance(DISABLED_TOOL_GUIDANCE, str)
+        assert DISABLED_TOOL_GUIDANCE.strip()
+
+    def test_steers_reporting_unavailable(self):
+        text = DISABLED_TOOL_GUIDANCE.lower()
+        # Must tell the model to surface that a named capability is off rather
+        # than silently working around it — accept any phrasing meaning that.
+        assert "unavailable" in text or "disabled" in text
+
+    def test_forbids_substituting_another_tool(self):
+        text = DISABLED_TOOL_GUIDANCE.lower()
+        # The core steer: do NOT route around a disabled capability with a
+        # different tool. Must mention substitution/working-around and a
+        # negation.
+        assert "substitut" in text or "stand-in" in text or "work around" in text or "route around" in text
+        assert "not" in text or "don't" in text or "do not" in text
+
+    def test_preserves_general_purpose_tools(self):
+        # Must not over-rotate into telling the model to stop using terminal
+        # etc. for their own legitimate purposes — only as a stand-in.
+        text = DISABLED_TOOL_GUIDANCE.lower()
+        assert "general-purpose" in text or "legitimate" in text
+
+    def test_stays_short_for_cached_prompt(self):
+        # Shipped in every cached system prompt — keep it tight.
+        assert len(DISABLED_TOOL_GUIDANCE) < 900
+
+    def test_has_a_heading(self):
+        assert DISABLED_TOOL_GUIDANCE.lstrip().startswith("#")
+
+
 # =========================================================================
 # Budget warning history stripping
 # =========================================================================