fix(native): retain unknown UI executable identity

bridge/native/ReaNativeUI.swift

@@ -49,7 +49,7 @@ func observe(_ request: Request) async throws -> [String: Any] {
   guard let url = app.executableURL else {
     try fail("application-executable-unavailable", "The selected application does not expose an executable URL; select a PID with an identifiable application executable")
   }
-  guard let canonicalPointer = realpath(url.path, nil) else { try fail("target-mismatch", "Running executable path cannot be resolved") }
+  guard let canonicalPointer = realpath(url.path, nil) else { try fail("executable-path-unavailable", "Running executable path cannot be resolved") }
   defer { free(canonicalPointer) }
   let canonicalExecutable = String(cString: canonicalPointer)
   guard canonicalExecutable == request.executable else {

docs/native-investigation.md

@@ -738,8 +738,10 @@ including unsafe integers, negative zero and non-finite numbers, remain null
 with a path-specific gap and incomplete capture coverage. Null alone does not
 establish that an accessibility value was successfully read or absent.
 
-An initial PID or window selection refusal is `invalid_request` on `pid` or
-`window_id` and leaves provider availability intact. Identity or window loss
+An initial PID or window mismatch is `invalid_request` on `pid` or
+`window_id` and leaves provider availability intact. An unavailable executable
+URL or unresolved executable path leaves identity unknown and reports
+`capability_unavailable`. Identity or window loss
 after the initial capture remains an observation failure with collected facts.
 Permission and other helper failures retain their specific remediation text.
 

src/native/NativeUiObservation.ts

@@ -52,7 +52,6 @@ const responseSchema = z.discriminatedUnion("ok", [
 ]);
 const initialSelectionFields = new Map<string, "pid" | "window_id">([
   ["pid-not-application", "pid"],
-  ["application-executable-unavailable", "pid"],
   ["target-mismatch", "pid"],
   ["window-mismatch", "window_id"],
   ["ambiguous-window", "window_id"],

tests/boundary/mcp/nativeUiFactsMcp.test.ts

@@ -137,7 +137,6 @@ it("keeps native UI availability after initial selection errors and preserves la
   const { client, replies, snapshot } = await connectNativeUi();
   for (const [code, field] of [
     ["pid-not-application", "pid"],
-    ["application-executable-unavailable", "pid"],
     ["target-mismatch", "pid"],
     ["window-mismatch", "window_id"],
   ] as const)
@@ -219,3 +218,24 @@ it("keeps native UI availability after initial selection errors and preserves la
   });
   await client.ping();
 });
+
+it.each([
+  "application-executable-unavailable",
+  "executable-path-unavailable",
+])("preserves unknown executable identity from %s", async (code) => {
+  const { client, replies } = await connectNativeUi();
+  const message = `Fixture ${code} diagnostic`;
+  replies.push({ ok: false, code, message });
+  const response = await client.callTool({
+    name: "observe_native_ui",
+    arguments: scope,
+  });
+  expect(parseMcpToolError(response)).toMatchObject({
+    error: {
+      code: "capability_unavailable",
+      message,
+      details: { reason: `${code}: ${message}` },
+    },
+  });
+  await client.ping();
+});