test(daemon): add F1/F2 process-lifecycle integration tests; fix clobbered start error

Links the real EmbeddedDaemon into the ObsidianDragonTests target (its deps were
already present) and adds two POSIX integration tests that exercise the actual
fork/exec/waitpid fixes headlessly:

- testExecFailureReported (F2): start() against a non-executable file must fail with a
  precise "not executable or wrong architecture" reason.
- testDaemonCrashDetected (F1): a short-lived child that exits abnormally is still
  detected (crash_count_ increments) while isRunning() is hammered from the test
  thread — a regression test for the reap race.

Writing the F2 test surfaced a real bug: start()'s failure branch called
setState(State::Error, "Failed to start dragonxd process"), and setState stores the
Error message into last_error_ — clobbering the precise message startProcess() had
just set, so getLastError()/the UI only ever saw the generic string. Fixed to pass the
preserved detail to setState, so the precise reason survives and now also reaches the
state callback (crash panel / status).

ctest 1/1, green including the two new integration tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_phase4.cpp

@@ -2634,6 +2634,59 @@ void testPlatformEnsureDirectory()
     }
 }
 
+#ifndef _WIN32
+// Integration tests that drive the REAL EmbeddedDaemon fork/exec/waitpid paths (POSIX only).
+void testExecFailureReported()
+{
+    using dragonx::daemon::EmbeddedDaemon;
+    namespace fsn = std::filesystem;
+
+    // A present-but-non-executable file: execv() must fail, and the F2 self-pipe handshake
+    // must report it as a start FAILURE with a precise reason — not a transient "Running".
+    fsn::path bin = fsn::temp_directory_path() / "od_fake_daemon_bin";
+    { std::ofstream(bin.string(), std::ios::binary) << "this is not an executable"; }
+    fsn::permissions(bin, fsn::perms::owner_read, fsn::perm_options::replace);  // 0400, no +x
+
+    EmbeddedDaemon d;
+    d.setSkipPortCheck(true);   // bypass the port + datadir-lock gates so we reach startProcess()
+    EXPECT_TRUE(!d.start(bin.string()));
+    EXPECT_TRUE(d.getLastError().find("not executable or wrong architecture") != std::string::npos);
+    EXPECT_TRUE(!d.isRunning());
+
+    std::error_code ec; fsn::remove(bin, ec);
+}
+
+void testDaemonCrashDetected()
+{
+    using dragonx::daemon::EmbeddedDaemon;
+    namespace fsn = std::filesystem;
+
+    // A tiny script that ignores the injected daemon args, lives briefly, then exits abnormally
+    // — standing in for a daemon that crashes. is_script detection runs it via /bin/bash.
+    fsn::path script = fsn::temp_directory_path() / "od_fake_daemon.sh";
+    { std::ofstream(script.string()) << "#!/bin/bash\nsleep 0.2\nexit 7\n"; }
+    fsn::permissions(script, fsn::perms::owner_all, fsn::perm_options::replace);  // +x
+
+    EmbeddedDaemon d;
+    d.setSkipPortCheck(true);
+    EXPECT_TRUE(d.start(script.string()));
+    EXPECT_TRUE(d.isRunning());              // reads the atomic state_, not a racy waitpid()
+
+    // Hammer isRunning() the way the UI thread does while the child exits and monitorProcess()
+    // reaps it. Pre-fix (F1), isRunning()'s own waitpid() could steal the reap and hide the
+    // crash; with the fix the monitor is the sole reaper and always sees it.
+    for (int i = 0; i < 400 && d.getCrashCount() == 0; ++i) {
+        (void)d.isRunning();
+        std::this_thread::sleep_for(std::chrono::milliseconds(5));
+    }
+    EXPECT_TRUE(d.getCrashCount() >= 1);     // the unexpected exit was detected and counted
+    EXPECT_TRUE(!d.isRunning());             // state_ flipped to Error
+
+    d.stop();                                // join the monitor thread cleanly
+    std::error_code ec; fsn::remove(script, ec);
+}
+#endif  // !_WIN32
+
 void testDatadirLockGate()
 {
     using dragonx::daemon::EmbeddedDaemon;
@@ -6799,6 +6852,10 @@ int main()
     testWalletSecurityWorkflowExecutor();
     testDaemonShutdownPolicy();
     testDatadirLockGate();
+#ifndef _WIN32
+    testExecFailureReported();
+    testDaemonCrashDetected();
+#endif
     testPlatformEnsureDirectory();
     testVerifySaplingParams();
     testConnectHasStalled();