diff --git a/docs/nano.md b/docs/nano.md
index 5ed2f6f4..bc05a7ad 100644
--- a/docs/nano.md
+++ b/docs/nano.md
@@ -75,6 +75,12 @@ The Harbor adapter forwards nano with `--ak nano=1`; see
   reviewer model — its schema + instructions would break the fixed-payload
   and byte-stability contracts, and a two-model loop is not what a nano
   benchmark measures.
+- **One conditional seventh tool**: when a vision model is explicitly
+  configured (global config `vision.enabled`, e.g. seeded by the harbor
+  adapter's `--ak vision=provider:model`), nano registers
+  `vision_analyze` — ask the vision model about a local image. This
+  mirrors pi's own terminal-bench extension, which adds the identical
+  tool for text-only main models; unconfigured nano stays exactly six.
 - `--allowed-tools`/`--disallowed-tools` still filter the six.
 - Nano is process-global (the /eco contract): on the TUI's `--stdio`
   transport that is exactly one session; on a multi-session
diff --git a/eval/harbor/RUN_NANO_TB21.md b/eval/harbor/RUN_NANO_TB21.md
index ad39b64d..9907134b 100644
--- a/eval/harbor/RUN_NANO_TB21.md
+++ b/eval/harbor/RUN_NANO_TB21.md
@@ -75,6 +75,16 @@ what the A/B measures. Don't describe the runs as "same tools".
 
 ## Fair nano-vs-pi setup
 
+**Matching a pi run that used the TB extension** (vision_analyze +
+websearch — e.g. `jobs/tb21-pi-flash-max-2`, which ran
+`vision_model: gpt-5.6-luna`): add `--ak vision=openai:gpt-5.6-luna` to
+the nano arm so nano registers its identically-named `vision_analyze`
+tool. The 2026-08 run analysis found 4–5 of pi's exclusive wins used
+vision/websearch (chess-best-move, video-processing, path-tracing…);
+without the kwarg those tasks measure a capability gap, not the harness.
+Nano has no websearch analog wired yet — note it when comparing.
+
+
 For a clean head-to-head against pi, pair **nano** with **stock pi**
 (`--ak tools=off`, its native 4-tool surface): both are then text-only
 with no web access — capability parity of absence on TB's image/web
diff --git a/src/nano/prompt.py b/src/nano/prompt.py
index 11dc5d10..ec13bfb6 100644
--- a/src/nano/prompt.py
+++ b/src/nano/prompt.py
@@ -46,6 +46,12 @@
     "Write": "create new files or fully overwrite existing ones",
     "Grep": "search file contents with regex (respects .gitignore)",
     "Glob": "find files by glob pattern",
+    # Conditional seventh tool — listed only when a vision model is
+    # configured and the registry registered it (see nano/registry.py).
+    "vision_analyze": (
+        "ask a configured vision model a question about a local image "
+        "(screenshots, plots, photos, rendered output)"
+    ),
 }
 
 # The three non-tool guidelines at the end are distilled from clawcodex's
diff --git a/src/nano/registry.py b/src/nano/registry.py
index 38fb4f32..22b5b734 100644
--- a/src/nano/registry.py
+++ b/src/nano/registry.py
@@ -40,7 +40,7 @@
 
 
 def build_nano_registry() -> ToolRegistry:
-    """Registry holding exactly the six nano tools, none deferred.
+    """Registry holding the six nano tools, none deferred.
 
     Each tool is a registry-local copy carrying its pi-length doc
     (``NANO_TOOL_DOCS``) as ``prompt`` — ``query()`` sends ``tool.prompt()``
@@ -48,6 +48,17 @@ def build_nano_registry() -> ToolRegistry:
     payload from ~2K to ~250 tokens without touching the default registry's
     instances. Schemas are kept in full: parameter shapes are behavioral,
     docs are advisory.
+
+    Plus one conditional seventh: ``vision_analyze``, registered only when
+    a vision model is explicitly configured (the tool's own is_enabled
+    gate — global config ``vision.enabled``, seeded by the harbor
+    adapter's ``--ak vision=provider:model``). This mirrors pi's own TB
+    extension, which adds the same tool for text-only main models; an
+    unconfigured nano stays exactly six. Conditional REGISTRATION rather
+    than registering-disabled is load-bearing: a registered-but-disabled
+    tool would resurrect the ``<available-deferred-tools>`` message-0
+    block (query.py's deferred list includes disabled tools) and bust
+    nano's byte-stability.
     """
     registry = ToolRegistry()
     for tool in NANO_TOOLS:
@@ -55,4 +66,11 @@ def build_nano_registry() -> ToolRegistry:
         if doc is not None:
             tool = replace(tool, prompt=lambda _doc=doc: _doc)
         registry.register(tool)
+    try:
+        from src.tool_system.tools import VisionAnalyzeTool
+
+        if VisionAnalyzeTool.is_enabled():
+            registry.register(VisionAnalyzeTool)
+    except Exception:  # noqa: BLE001 — a broken vision config never blocks nano
+        pass
     return registry
diff --git a/tests/nano/conftest.py b/tests/nano/conftest.py
index c06551b2..8ee858db 100644
--- a/tests/nano/conftest.py
+++ b/tests/nano/conftest.py
@@ -21,6 +21,22 @@ def _reset_nano_state():
     reset_eco()
 
 
+@pytest.fixture(autouse=True)
+def _vision_unconfigured(monkeypatch):
+    """Hermetic default: the dev machine's real vision config must not flip
+    the conditional seventh tool on. Vision-specific tests override."""
+    import src.providers.vision_config as vision_config
+
+    monkeypatch.setattr(vision_config, "vision_is_configured", lambda: False)
+
+
+@pytest.fixture
+def vision_configured(monkeypatch):
+    import src.providers.vision_config as vision_config
+
+    monkeypatch.setattr(vision_config, "vision_is_configured", lambda: True)
+
+
 @pytest.fixture
 def no_skills(monkeypatch):
     """Hermetic prompt tests: no developer-machine skills leak in."""
diff --git a/tests/nano/test_nano_registry.py b/tests/nano/test_nano_registry.py
index 8a8a90be..6a65f67d 100644
--- a/tests/nano/test_nano_registry.py
+++ b/tests/nano/test_nano_registry.py
@@ -56,6 +56,26 @@ def test_pi_length_docs_but_full_schemas():
         assert json.dumps(dict(t.input_schema))
 
 
+def test_vision_analyze_joins_only_when_configured(vision_configured):
+    reg = build_nano_registry()
+    names = [t.name for t in reg.list_tools()]
+    assert names == [
+        "Read", "Bash", "Edit", "Write", "Grep", "Glob", "vision_analyze",
+    ]
+    vision = next(t for t in reg.list_tools() if t.name == "vision_analyze")
+    # Registered live, never deferred/disabled — a registered-but-disabled
+    # tool would resurrect the <available-deferred-tools> message-0 block.
+    assert not vision.should_defer
+
+
+def test_vision_snippet_renders_in_prompt(vision_configured, tmp_path):
+    from src.nano.prompt import build_nano_prompt_text
+
+    names = tuple(t.name for t in build_nano_registry().list_tools())
+    text = build_nano_prompt_text(cwd=str(tmp_path), tool_names=names)
+    assert "- vision_analyze: " in text
+
+
 def test_default_registry_instances_untouched():
     # The nano registry carries copies; the shared static instances (and
     # therefore the default registry) must keep their full docs.