diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Program/InstallModeMergeTests.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Program/InstallModeMergeTests.cs
new file mode 100644
index 00000000..d4ef44f1
--- /dev/null
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Program/InstallModeMergeTests.cs
@@ -0,0 +1,158 @@
+using AutopilotMonitor.Agent.V2;
+using AutopilotMonitor.Agent.V2.Core.Configuration;
+using Xunit;
+
+namespace AutopilotMonitor.Agent.V2.Core.Tests.Program
+{
+    /// <summary>
+    /// Pinpoints the <c>--install</c> bootstrap-config merge semantics. The earlier
+    /// implementation overwrote the file from CLI args alone, so a redeploy with only
+    /// <c>--tenant-id-wait</c> wiped a previously-persisted BootstrapToken / TenantId
+    /// and pushed devices to cert-auth before their cert was usable. The merge now
+    /// preserves prior fields when their corresponding CLI flag is absent on this
+    /// invocation, and honours an explicit value (including empty / 0) when present.
+    /// </summary>
+    public sealed class InstallModeMergeTests
+    {
+        [Fact]
+        public void Wait_only_redeploy_preserves_existing_token_and_tenantid()
+        {
+            var existing = new BootstrapConfigFile
+            {
+                BootstrapToken = "tok-abc",
+                TenantId = "tenant-xyz",
+                TenantIdWaitSeconds = 0,
+            };
+
+            var merged = AutopilotMonitor.Agent.V2.Program.MergeBootstrapConfig(
+                existing,
+                bootstrapTokenArg: null!, bootstrapTokenGiven: false,
+                tenantIdArg: null!, tenantIdGiven: false,
+                tenantIdWaitSeconds: 600, tenantIdWaitGiven: true);
+
+            Assert.Equal("tok-abc", merged.BootstrapToken);
+            Assert.Equal("tenant-xyz", merged.TenantId);
+            Assert.Equal(600, merged.TenantIdWaitSeconds);
+        }
+
+        [Fact]
+        public void Explicit_zero_wait_overrides_existing_nonzero()
+        {
+            var existing = new BootstrapConfigFile
+            {
+                BootstrapToken = "tok-abc",
+                TenantId = "tenant-xyz",
+                TenantIdWaitSeconds = 600,
+            };
+
+            var merged = AutopilotMonitor.Agent.V2.Program.MergeBootstrapConfig(
+                existing,
+                bootstrapTokenArg: null!, bootstrapTokenGiven: false,
+                tenantIdArg: null!, tenantIdGiven: false,
+                tenantIdWaitSeconds: 0, tenantIdWaitGiven: true);
+
+            // Token + tenantId untouched, wait explicitly disabled.
+            Assert.Equal("tok-abc", merged.BootstrapToken);
+            Assert.Equal("tenant-xyz", merged.TenantId);
+            Assert.Equal(0, merged.TenantIdWaitSeconds);
+        }
+
+        [Fact]
+        public void Tenant_only_redeploy_preserves_existing_wait()
+        {
+            var existing = new BootstrapConfigFile
+            {
+                BootstrapToken = "tok-abc",
+                TenantId = "tenant-old",
+                TenantIdWaitSeconds = 1500,
+            };
+
+            var merged = AutopilotMonitor.Agent.V2.Program.MergeBootstrapConfig(
+                existing,
+                bootstrapTokenArg: null!, bootstrapTokenGiven: false,
+                tenantIdArg: "tenant-new", tenantIdGiven: true,
+                tenantIdWaitSeconds: 0, tenantIdWaitGiven: false);
+
+            Assert.Equal("tok-abc", merged.BootstrapToken);
+            Assert.Equal("tenant-new", merged.TenantId);
+            Assert.Equal(1500, merged.TenantIdWaitSeconds);
+        }
+
+        [Fact]
+        public void Token_only_redeploy_preserves_existing_wait_and_tenant()
+        {
+            var existing = new BootstrapConfigFile
+            {
+                BootstrapToken = "tok-old",
+                TenantId = "tenant-xyz",
+                TenantIdWaitSeconds = 300,
+            };
+
+            var merged = AutopilotMonitor.Agent.V2.Program.MergeBootstrapConfig(
+                existing,
+                bootstrapTokenArg: "tok-new", bootstrapTokenGiven: true,
+                tenantIdArg: null!, tenantIdGiven: false,
+                tenantIdWaitSeconds: 0, tenantIdWaitGiven: false);
+
+            Assert.Equal("tok-new", merged.BootstrapToken);
+            Assert.Equal("tenant-xyz", merged.TenantId);
+            Assert.Equal(300, merged.TenantIdWaitSeconds);
+        }
+
+        [Fact]
+        public void First_install_with_no_existing_config_uses_args_only()
+        {
+            var merged = AutopilotMonitor.Agent.V2.Program.MergeBootstrapConfig(
+                existing: null,
+                bootstrapTokenArg: "tok-fresh", bootstrapTokenGiven: true,
+                tenantIdArg: "tenant-fresh", tenantIdGiven: true,
+                tenantIdWaitSeconds: 600, tenantIdWaitGiven: true);
+
+            Assert.Equal("tok-fresh", merged.BootstrapToken);
+            Assert.Equal("tenant-fresh", merged.TenantId);
+            Assert.Equal(600, merged.TenantIdWaitSeconds);
+        }
+
+        [Fact]
+        public void First_install_with_only_wait_arg_writes_null_token_and_tenant()
+        {
+            // PS1's default invocation: agent --install --tenant-id-wait 600
+            // No existing config, no token, no tenantId. Result: nullable fields stay null,
+            // wait gets the new value. Subsequent runtime config-load falls back to the
+            // registry resolver for TenantId — that's the OOBE happy path.
+            var merged = AutopilotMonitor.Agent.V2.Program.MergeBootstrapConfig(
+                existing: null,
+                bootstrapTokenArg: null!, bootstrapTokenGiven: false,
+                tenantIdArg: null!, tenantIdGiven: false,
+                tenantIdWaitSeconds: 600, tenantIdWaitGiven: true);
+
+            Assert.Null(merged.BootstrapToken);
+            Assert.Null(merged.TenantId);
+            Assert.Equal(600, merged.TenantIdWaitSeconds);
+        }
+
+        [Fact]
+        public void Existing_config_without_wait_field_treated_as_zero()
+        {
+            // BackCompat: pre-fix bootstrap-config.json has no TenantIdWaitSeconds field;
+            // Newtonsoft deserialises that to 0. New install with --tenant-id-wait 600
+            // overrides cleanly; no extra migration logic required.
+            var existing = new BootstrapConfigFile
+            {
+                BootstrapToken = "tok-legacy",
+                TenantId = "tenant-legacy",
+                TenantIdWaitSeconds = 0,
+            };
+
+            var merged = AutopilotMonitor.Agent.V2.Program.MergeBootstrapConfig(
+                existing,
+                bootstrapTokenArg: null!, bootstrapTokenGiven: false,
+                tenantIdArg: null!, tenantIdGiven: false,
+                tenantIdWaitSeconds: 600, tenantIdWaitGiven: true);
+
+            Assert.Equal("tok-legacy", merged.BootstrapToken);
+            Assert.Equal("tenant-legacy", merged.TenantId);
+            Assert.Equal(600, merged.TenantIdWaitSeconds);
+        }
+    }
+}
diff --git a/src/Agent/AutopilotMonitor.Agent.V2/Program.InstallMode.cs b/src/Agent/AutopilotMonitor.Agent.V2/Program.InstallMode.cs
index 7ed20878..9885386b 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2/Program.InstallMode.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2/Program.InstallMode.cs
@@ -65,35 +65,66 @@ namespace AutopilotMonitor.Agent.V2
                 // Persist bootstrap config if any of --bootstrap-token / --tenant-id /
                 // --tenant-id-wait was provided. The Scheduled Task command line has no args —
                 // the agent picks the persisted values up on the first post-install run.
+                //
+                // Read-merge-write: only fields explicitly set on this install invocation
+                // overwrite the persisted file. This protects against a redeploy that passes
+                // only --tenant-id-wait clobbering an existing BootstrapToken / TenantId, and
+                // lets an admin opt out of the wait by passing --tenant-id-wait 0 explicitly
+                // (which writes 0 over an old non-zero value).
                 var bootstrapTokenArg = GetArgValue(args, "--bootstrap-token");
                 var tenantIdArg = GetArgValue(args, "--tenant-id");
                 var tenantIdWaitArg = GetArgValue(args, "--tenant-id-wait");
+
+                bool bootstrapTokenGiven = !string.IsNullOrEmpty(bootstrapTokenArg);
+                bool tenantIdGiven = !string.IsNullOrEmpty(tenantIdArg);
+                bool tenantIdWaitGiven = !string.IsNullOrEmpty(tenantIdWaitArg);
+
                 int tenantIdWaitSeconds = 0;
-                if (!string.IsNullOrEmpty(tenantIdWaitArg) && !int.TryParse(tenantIdWaitArg, out tenantIdWaitSeconds))
+                if (tenantIdWaitGiven && !int.TryParse(tenantIdWaitArg, out tenantIdWaitSeconds))
                 {
                     logger.Warning($"Install: --tenant-id-wait '{tenantIdWaitArg}' is not a valid integer — ignoring.");
+                    tenantIdWaitGiven = false;
                     tenantIdWaitSeconds = 0;
                 }
 
-                if (!string.IsNullOrEmpty(bootstrapTokenArg) ||
-                    !string.IsNullOrEmpty(tenantIdArg) ||
-                    tenantIdWaitSeconds > 0)
+                if (bootstrapTokenGiven || tenantIdGiven || tenantIdWaitGiven)
                 {
                     var bootstrapConfigPath = Path.Combine(
                         Environment.ExpandEnvironmentVariables(Constants.AgentDataDirectory),
                         BootstrapConfigFileName);
-                    var bootstrapConfig = new BootstrapConfigFile
+
+                    BootstrapConfigFile existing = null;
+                    if (File.Exists(bootstrapConfigPath))
                     {
-                        BootstrapToken = bootstrapTokenArg,
-                        TenantId = tenantIdArg,
-                        TenantIdWaitSeconds = tenantIdWaitSeconds,
-                    };
-                    File.WriteAllText(bootstrapConfigPath, JsonConvert.SerializeObject(bootstrapConfig));
+                        try
+                        {
+                            existing = JsonConvert.DeserializeObject<BootstrapConfigFile>(
+                                File.ReadAllText(bootstrapConfigPath));
+                        }
+                        catch (Exception ex)
+                        {
+                            logger.Warning(
+                                $"Existing bootstrap-config.json could not be parsed " +
+                                $"({ex.GetType().Name}: {ex.Message}) — overwriting fresh.");
+                        }
+                    }
+
+                    var merged = MergeBootstrapConfig(
+                        existing,
+                        bootstrapTokenArg, bootstrapTokenGiven,
+                        tenantIdArg, tenantIdGiven,
+                        tenantIdWaitSeconds, tenantIdWaitGiven);
+
+                    File.WriteAllText(bootstrapConfigPath, JsonConvert.SerializeObject(merged));
                     logger.Info(
                         $"Bootstrap config persisted for Scheduled Task " +
-                        $"(token={(string.IsNullOrEmpty(bootstrapTokenArg) ? "no" : "yes")}, " +
-                        $"tenantId={(string.IsNullOrEmpty(tenantIdArg) ? "no" : "yes")}, " +
-                        $"tenantIdWait={tenantIdWaitSeconds}s).");
+                        $"(token={(string.IsNullOrEmpty(merged.BootstrapToken) ? "no" : "yes")}" +
+                        $"{(bootstrapTokenGiven ? "*" : "")}, " +
+                        $"tenantId={(string.IsNullOrEmpty(merged.TenantId) ? "no" : "yes")}" +
+                        $"{(tenantIdGiven ? "*" : "")}, " +
+                        $"tenantIdWait={merged.TenantIdWaitSeconds}s" +
+                        $"{(tenantIdWaitGiven ? "*" : "")})." +
+                        " Star = explicitly set on this --install invocation, others were preserved from prior config.");
                 }
 
                 // Persist await-enrollment config if requested.
@@ -260,6 +291,30 @@ namespace AutopilotMonitor.Agent.V2
             logger.Info($"Payload deployment completed: '{sourceDir}' -> '{targetDir}'");
         }
 
+        /// <summary>
+        /// Pure-function merge for <c>bootstrap-config.json</c>. Each <c>...Given</c> flag tells
+        /// us whether the corresponding CLI arg was explicitly set on this <c>--install</c>
+        /// invocation. When given, the new value wins (including explicit zero / empty) — this
+        /// is what makes <c>--tenant-id-wait 0</c> a real opt-out. When not given, the prior
+        /// persisted value is preserved — this is what stops a redeploy that only carries
+        /// <c>--tenant-id-wait</c> from clobbering a previously-set BootstrapToken / TenantId.
+        /// </summary>
+        internal static BootstrapConfigFile MergeBootstrapConfig(
+            BootstrapConfigFile existing,
+            string bootstrapTokenArg, bool bootstrapTokenGiven,
+            string tenantIdArg, bool tenantIdGiven,
+            int tenantIdWaitSeconds, bool tenantIdWaitGiven)
+        {
+            return new BootstrapConfigFile
+            {
+                BootstrapToken = bootstrapTokenGiven ? bootstrapTokenArg : existing?.BootstrapToken,
+                TenantId = tenantIdGiven ? tenantIdArg : existing?.TenantId,
+                TenantIdWaitSeconds = tenantIdWaitGiven
+                    ? tenantIdWaitSeconds
+                    : (existing?.TenantIdWaitSeconds ?? 0),
+            };
+        }
+
         private static void TryWriteDeploymentMarker(AgentLogger logger)
         {
             try
diff --git a/src/Agent/AutopilotMonitor.Agent.V2/Program.cs b/src/Agent/AutopilotMonitor.Agent.V2/Program.cs
index 0e81067d..ee64a9af 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2/Program.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2/Program.cs
@@ -415,6 +415,13 @@ namespace AutopilotMonitor.Agent.V2
             Console.Out.WriteLine("  --await-enrollment                Wait for MDM certificate before starting monitoring");
             Console.Out.WriteLine("  --await-enrollment-timeout <MIN>  Timeout in minutes (default: 480)");
             Console.Out.WriteLine();
+            Console.Out.WriteLine("TenantId resolution:");
+            Console.Out.WriteLine("  --tenant-id-wait <SEC>            On miss, wait up to N seconds for the registry to");
+            Console.Out.WriteLine("                                    populate (RegistryWatcher on Enrollments + CloudDomainJoin).");
+            Console.Out.WriteLine("                                    0 = disabled (legacy fast-fail). At --install time the value");
+            Console.Out.WriteLine("                                    is persisted to bootstrap-config.json so the Scheduled Task");
+            Console.Out.WriteLine("                                    picks it up on each run.");
+            Console.Out.WriteLine();
             Console.Out.WriteLine("Overrides:");
             Console.Out.WriteLine("  --api-url <URL>                   Override backend API base URL (alias: --backend-api)");
             Console.Out.WriteLine("  --ime-log-path <PATH>             Override IME logs directory");
diff --git a/src/Agent/AutopilotMonitor.Agent.V2/buildcounter.txt b/src/Agent/AutopilotMonitor.Agent.V2/buildcounter.txt
index 1c599d4f..9a26b94d 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2/buildcounter.txt
+++ b/src/Agent/AutopilotMonitor.Agent.V2/buildcounter.txt
@@ -1 +1 @@
-516
+518
diff --git a/src/Agent/AutopilotMonitor.Agent/buildcounter.txt b/src/Agent/AutopilotMonitor.Agent/buildcounter.txt
index 939b0cbc..81c545ef 100644
--- a/src/Agent/AutopilotMonitor.Agent/buildcounter.txt
+++ b/src/Agent/AutopilotMonitor.Agent/buildcounter.txt
@@ -1 +1 @@
-1233
+1234