diff --git a/coworker/engine.py b/coworker/engine.py
index 561eee11..1e393199 100644
--- a/coworker/engine.py
+++ b/coworker/engine.py
@@ -20,6 +20,7 @@ from enum import Enum
 from typing import Any, AsyncIterator, Awaitable, Callable, Optional
 
 from . import compaction as _compaction
+from . import toolchain as _toolchain
 from .events import Event, EventType
 from .permissions import Mode, PermissionEngine
 from .providers import AssistantTurn, ProviderClient, ToolCall
@@ -963,7 +964,20 @@ class TurnEngine:
                 ),
             }
         else:
-            yield Event(EventType.TOOL_REQUESTED, {"name": name, "reason": reason})
+            # The prompt must say up front whether WE can install this (pinned build for
+            # this platform) — a card that offers Install for a tool we can't fetch turns
+            # the user's approval into a guaranteed error. Absence of metadata means NO.
+            info = _toolchain.describe(name)
+            yield Event(
+                EventType.TOOL_REQUESTED,
+                {
+                    "name": name,
+                    "reason": reason,
+                    "installable": info is not None,
+                    "version": (info or {}).get("version", ""),
+                    "summary": (info or {}).get("summary", ""),
+                },
+            )
             self._audit(tool_call, stage="tool_requested", reason=reason)
             result = await self._interruptible(
                 self.tool_requester(dict(args), tool_call.id),
diff --git a/surfaces/gui/e2e/fixtures.ts b/surfaces/gui/e2e/fixtures.ts
index 9e7527f1..f1da713e 100644
--- a/surfaces/gui/e2e/fixtures.ts
+++ b/surfaces/gui/e2e/fixtures.ts
@@ -610,6 +610,16 @@ export async function mockApi(page: import("@playwright/test").Page) {
           });
           return; // suspended on the approval
         }
+        // The pre-fix payload shape (owner-hit 2026-08-14): no installable/version/summary
+        // — an older sidecar, or any surface that forgets the field. Must render NOT
+        // installable, never a guessed Install offer.
+        if (/request an unpinned tool/i.test(msg.text)) {
+          send("tool_requested", {
+            name: "somescanner",
+            reason: "scan the Terraform for misconfigurations",
+          });
+          return; // suspended on the tool request
+        }
         // OPE-85: the agent hits a missing scanner and asks instead of skipping the check.
         if (/scan for secrets/i.test(msg.text)) {
           send("tool_requested", {
diff --git a/surfaces/gui/e2e/toolreq.spec.ts b/surfaces/gui/e2e/toolreq.spec.ts
index 67f47def..b3a879cf 100644
--- a/surfaces/gui/e2e/toolreq.spec.ts
+++ b/surfaces/gui/e2e/toolreq.spec.ts
@@ -23,6 +23,21 @@ test("request_tool surfaces a card naming the tool, the reason and the pinned ve
   await expect(card.getByTestId("toolreq-skip")).toBeVisible();
 });
 
+test("an event without install metadata fails CLOSED — Install disabled, skip offered", async ({
+  page,
+}) => {
+  // Owner-hit 2026-08-14: the card offered "pinned build, checksum-verified" for a tool
+  // with no pinned build; approval could only produce an error. Absence of metadata is NO.
+  await page.goto("/");
+  await page.getByPlaceholder(/Ask the coworker/).fill("request an unpinned tool");
+  await page.getByRole("button", { name: "Send" }).click();
+  const card = page.locator(".dirreq-card");
+  await expect(card).toContainText("somescanner");
+  await expect(card).toContainText(/no verified build/i);
+  await expect(card.getByTestId("toolreq-install")).toBeDisabled();
+  await expect(card.getByTestId("toolreq-skip")).toBeEnabled();
+});
+
 test("installing runs the check; skipping still reports coverage", async ({ page }) => {
   await ask(page);
   await page.getByTestId("toolreq-install").click();
diff --git a/surfaces/gui/src/App.tsx b/surfaces/gui/src/App.tsx
index aa7d7cf4..e9ae5662 100644
--- a/surfaces/gui/src/App.tsx
+++ b/surfaces/gui/src/App.tsx
@@ -737,7 +737,8 @@ export function App() {
               kind: "toolreq",
               tool: d.name || "",
               reason: d.reason || "",
-              installable: d.installable !== false,
+              // Fail CLOSED: only offer Install when the event says a pinned build exists.
+              installable: d.installable === true,
               version: d.version || "",
               summary: d.summary || "",
             },
diff --git a/tests/test_tool_request.py b/tests/test_tool_request.py
index 309d6a10..8da512c5 100644
--- a/tests/test_tool_request.py
+++ b/tests/test_tool_request.py
@@ -17,8 +17,9 @@ from coworker.tools import ToolRegistry
 class ScriptedProvider(ProviderClient):
     """One turn that calls request_tool, then a plain reply."""
 
-    def __init__(self):
+    def __init__(self, tool: str = "gitleaks"):
         self.calls = 0
+        self.tool = tool
 
     def complete(self, *, model, messages, tools=None, **settings):
         self.calls += 1
@@ -29,7 +30,7 @@ class ScriptedProvider(ProviderClient):
                     ToolCall(
                         id="t1",
                         name="request_tool",
-                        arguments={"name": "gitleaks", "reason": "scan history for secrets"},
+                        arguments={"name": self.tool, "reason": "scan history for secrets"},
                     )
                 ],
             )
@@ -39,9 +40,9 @@ class ScriptedProvider(ProviderClient):
         return ModelCapabilities(tools=True)
 
 
-def _engine(tmp_path, requester):
+def _engine(tmp_path, requester, tool: str = "gitleaks"):
     return TurnEngine(
-        provider=ScriptedProvider(),
+        provider=ScriptedProvider(tool),
         registry=ToolRegistry(),
         permissions=PermissionEngine(workspace_root=tmp_path, mode=Mode.INTERACTIVE),
         model="m",
@@ -85,6 +86,30 @@ async def test_declining_tells_the_agent_to_fall_back_openly(tmp_path):
     assert "degraded" in body or "fallback" in body
 
 
+@pytest.mark.asyncio
+async def test_event_tells_the_truth_about_installability(tmp_path, monkeypatch):
+    """Owner-hit 2026-08-14: the card offered Install for a tool with no pinned build —
+    the surface guessed because the event said nothing. The event must carry the
+    registry's verdict, and no metadata means NO."""
+    from coworker import toolchain
+
+    monkeypatch.setattr(toolchain, "_platform_key", lambda: "darwin_arm64")
+
+    async def requester(args, tool_call_id=None):
+        return {"installed": False, "reason": "declined"}
+
+    events = await _run(_engine(tmp_path, requester, tool="gitleaks"))
+    data = [e for e in events if e.type is EventType.TOOL_REQUESTED][0].data
+    assert data["installable"] is True
+    assert data["version"] == toolchain.MANAGED["gitleaks"].version
+    assert data["summary"]
+
+    events = await _run(_engine(tmp_path, requester, tool="not-a-managed-tool"))
+    data = [e for e in events if e.type is EventType.TOOL_REQUESTED][0].data
+    assert data["installable"] is False
+    assert data["version"] == "" and data["summary"] == ""
+
+
 @pytest.mark.asyncio
 async def test_no_requester_still_returns_guidance(tmp_path):
     """Headless surfaces have nobody to ask — the agent must still be told to disclose