diff --git a/desktop/src-tauri/src/managed_agents/discovery.rs b/desktop/src-tauri/src/managed_agents/discovery.rs
index 09c464675..ab9baa719 100644
--- a/desktop/src-tauri/src/managed_agents/discovery.rs
+++ b/desktop/src-tauri/src/managed_agents/discovery.rs
@@ -11,7 +11,9 @@ pub(crate) struct KnownAcpRuntime {
     pub commands: &'static [&'static str],
     pub aliases: &'static [&'static str],
     pub avatar_url: &'static str,
-    /// MCP server binary for this runtime, or `None` for no MCP server.
+    /// MCP server binary to use instead of the default `sprout-mcp-server`.
+    /// `None` means this runtime does not need a Sprout MCP server —
+    /// no MCP tools will be registered for the agent session.
     pub mcp_command: Option<&'static str>,
     /// Whether to enable MCP hook tools (`_Stop`, `_PostCompact`) for this agent.
     pub mcp_hooks: bool,
@@ -32,12 +34,16 @@ pub(crate) struct KnownAcpRuntime {
     /// pointing to the canonical `.agents/skills/sprout-cli`. `None` → this
     /// runtime reads the canonical path directly or has no skill support.
     pub skill_dir: Option<&'static str>,
+    // Phase 3: these fields are consumed by runtime.rs spawn logic to replace ad-hoc env var injection.
+    /// Whether this runtime supports ACP model switching mid-session.
     pub supports_acp_model_switching: bool,
+    /// Environment variable name used to set the model for this runtime, if any.
     pub model_env_var: Option<&'static str>,
-    #[allow(dead_code)]
+    /// Environment variable name used to set the LLM provider for this runtime, if any.
     pub provider_env_var: Option<&'static str>,
-    #[allow(dead_code)]
+    /// Whether the LLM provider is locked (not user-selectable) for this runtime.
     pub provider_locked: bool,
+    /// Default environment variables injected when spawning agents using this runtime.
     pub default_env: &'static [(&'static str, &'static str)],
 }
 
diff --git a/desktop/src-tauri/src/migration.rs b/desktop/src-tauri/src/migration.rs
index 8b1436eb2..975c27d00 100644
--- a/desktop/src-tauri/src/migration.rs
+++ b/desktop/src-tauri/src/migration.rs
@@ -6,6 +6,11 @@
 //! `SPROUT_SHARE_IDENTITY=1` and `SPROUT_PRIVATE_KEY` is set. All dev
 //! instances share the same physical files — edits in any worktree are
 //! immediately visible to all others.
+//!
+//! **Provider reconciliation** (`reconcile_provider_mcp_commands`): Per-launch
+//! fix-up of `mcp_command` values in `managed-agents.json` against the
+//! discovery table. Ensures known providers always have their canonical
+//! `mcp_command`; unknown/custom agents are left untouched.
 
 use std::path::{Path, PathBuf};
 use tauri::Manager;
@@ -259,6 +264,53 @@ pub fn sync_shared_agent_data(app: &tauri::AppHandle) {
     }
 }
 
+fn reconcile_mcp_commands_in_file(path: &Path) {
+    patch_json_records(path, |obj| {
+        let agent_command = match obj.get("agent_command").and_then(|v| v.as_str()) {
+            Some(cmd) => cmd.to_string(),
+            None => return false,
+        };
+        let Some(runtime) = crate::managed_agents::known_acp_runtime(&agent_command) else {
+            return false;
+        };
+        let expected = runtime.mcp_command.unwrap_or("");
+        let current = obj
+            .get("mcp_command")
+            .and_then(|v| v.as_str())
+            .unwrap_or("");
+        if current != expected {
+            eprintln!(
+                "sprout-desktop: runtime-reconcile: {:?} ({:?}): mcp_command {:?} → {:?}",
+                obj.get("name").and_then(|v| v.as_str()).unwrap_or("?"),
+                agent_command,
+                current,
+                expected,
+            );
+            obj.insert(
+                "mcp_command".to_string(),
+                serde_json::Value::String(expected.to_string()),
+            );
+            true
+        } else {
+            false
+        }
+    });
+}
+
+/// Reconcile `mcp_command` values in managed-agents.json against the
+/// discovery table. Known runtimes get their canonical mcp_command;
+/// unknown/custom agents are left untouched.
+pub fn reconcile_provider_mcp_commands(app: &tauri::AppHandle) {
+    let Ok(dir) = app.path().app_data_dir() else {
+        return;
+    };
+    let path = dir.join("agents/managed-agents.json");
+    if !path.exists() {
+        return;
+    }
+    reconcile_mcp_commands_in_file(&path);
+}
+
 fn reconcile_pack_paths_in_file(path: &Path, canonical_dir: &Path) {
     let canonical_packs = canonical_dir.join("agents/packs");
     patch_json_records(path, |obj| {
@@ -638,6 +690,169 @@ mod tests {
         serde_json::from_str(&content).unwrap()
     }
 
+    #[test]
+    fn reconcile_clears_mcp_command_for_goose() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([{
+                "name": "Scout",
+                "agent_command": "goose",
+                "mcp_command": "sprout-mcp-server"
+            }]),
+        );
+        reconcile_mcp_commands_in_file(&dir.path().join("agents/managed-agents.json"));
+        let records = read_agents_json(dir.path());
+        assert_eq!(records[0]["mcp_command"], "");
+    }
+
+    #[test]
+    fn reconcile_clears_mcp_command_for_claude() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([{
+                "name": "Claude Agent",
+                "agent_command": "claude-agent-acp",
+                "mcp_command": "sprout-mcp-server"
+            }]),
+        );
+        reconcile_mcp_commands_in_file(&dir.path().join("agents/managed-agents.json"));
+        let records = read_agents_json(dir.path());
+        assert_eq!(records[0]["mcp_command"], "");
+    }
+
+    #[test]
+    fn reconcile_preserves_sprout_dev_mcp() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([{
+                "name": "Solo",
+                "agent_command": "sprout-agent",
+                "mcp_command": "sprout-dev-mcp"
+            }]),
+        );
+        let before =
+            std::fs::read_to_string(dir.path().join("agents/managed-agents.json")).unwrap();
+        reconcile_mcp_commands_in_file(&dir.path().join("agents/managed-agents.json"));
+        let after = std::fs::read_to_string(dir.path().join("agents/managed-agents.json")).unwrap();
+        assert_eq!(
+            before, after,
+            "file should not be rewritten when already correct"
+        );
+    }
+
+    #[test]
+    fn reconcile_fixes_sprout_agent_if_stale() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([{
+                "name": "Solo",
+                "agent_command": "sprout-agent",
+                "mcp_command": "sprout-mcp-server"
+            }]),
+        );
+        reconcile_mcp_commands_in_file(&dir.path().join("agents/managed-agents.json"));
+        let records = read_agents_json(dir.path());
+        assert_eq!(records[0]["mcp_command"], "sprout-dev-mcp");
+    }
+
+    #[test]
+    fn reconcile_leaves_unknown_agent_untouched() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([{
+                "name": "Custom Bot",
+                "agent_command": "my-custom-agent",
+                "mcp_command": "my-custom-mcp"
+            }]),
+        );
+        reconcile_mcp_commands_in_file(&dir.path().join("agents/managed-agents.json"));
+        let records = read_agents_json(dir.path());
+        assert_eq!(records[0]["mcp_command"], "my-custom-mcp");
+    }
+
+    #[test]
+    fn reconcile_is_idempotent() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([{
+                "name": "Scout",
+                "agent_command": "goose",
+                "mcp_command": "sprout-mcp-server"
+            }]),
+        );
+        let path = dir.path().join("agents/managed-agents.json");
+        reconcile_mcp_commands_in_file(&path);
+        let after_first = std::fs::read_to_string(&path).unwrap();
+        reconcile_mcp_commands_in_file(&path);
+        let after_second = std::fs::read_to_string(&path).unwrap();
+        assert_eq!(after_first, after_second);
+    }
+
+    #[test]
+    fn reconcile_handles_mixed_records() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([
+                {"name": "Scout", "agent_command": "goose", "mcp_command": "sprout-mcp-server"},
+                {"name": "Claude", "agent_command": "claude-agent-acp", "mcp_command": "sprout-mcp-server"},
+                {"name": "Solo", "agent_command": "sprout-agent", "mcp_command": "sprout-dev-mcp"},
+                {"name": "Custom", "agent_command": "my-bot", "mcp_command": "my-mcp"},
+                {"name": "Codex", "agent_command": "codex-acp", "mcp_command": "sprout-mcp-server"}
+            ]),
+        );
+        reconcile_mcp_commands_in_file(&dir.path().join("agents/managed-agents.json"));
+        let records = read_agents_json(dir.path());
+        assert_eq!(records[0]["mcp_command"], "", "goose should be cleared");
+        assert_eq!(records[1]["mcp_command"], "", "claude should be cleared");
+        assert_eq!(
+            records[2]["mcp_command"], "sprout-dev-mcp",
+            "sprout-agent preserved"
+        );
+        assert_eq!(
+            records[3]["mcp_command"], "my-mcp",
+            "custom agent untouched"
+        );
+        assert_eq!(records[4]["mcp_command"], "", "codex should be cleared");
+    }
+
+    #[test]
+    fn reconcile_adds_mcp_command_when_key_absent() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([{
+                "name": "Solo",
+                "agent_command": "sprout-agent"
+            }]),
+        );
+        reconcile_mcp_commands_in_file(&dir.path().join("agents/managed-agents.json"));
+        let records = read_agents_json(dir.path());
+        assert_eq!(records[0]["mcp_command"], "sprout-dev-mcp");
+    }
+
+    #[test]
+    fn reconcile_treats_null_mcp_command_as_empty() {
+        let dir = tempfile::tempdir().unwrap();
+        write_agents_json(
+            dir.path(),
+            &serde_json::json!([{
+                "name": "Solo",
+                "agent_command": "sprout-agent",
+                "mcp_command": null
+            }]),
+        );
+        reconcile_mcp_commands_in_file(&dir.path().join("agents/managed-agents.json"));
+        let records = read_agents_json(dir.path());
+        assert_eq!(records[0]["mcp_command"], "sprout-dev-mcp");
+    }
+
     #[test]
     fn sync_creates_packs_directory_symlink() {
         let (_parent, canonical, worktree) = setup_sync_layout();
diff --git a/desktop/src/features/channels/ui/AddChannelBotDialog.tsx b/desktop/src/features/channels/ui/AddChannelBotDialog.tsx
index 139931e63..f58945a25 100644
--- a/desktop/src/features/channels/ui/AddChannelBotDialog.tsx
+++ b/desktop/src/features/channels/ui/AddChannelBotDialog.tsx
@@ -29,15 +29,16 @@ import {
   DropdownMenuContent,
   DropdownMenuRadioGroup,
   DropdownMenuRadioItem,
-  DropdownMenuSeparator,
   DropdownMenuTrigger,
 } from "@/shared/ui/dropdown-menu";
 import {
   coerceConfigValues,
   ProviderConfigFields,
 } from "@/features/agents/ui/ProviderConfigFields";
-import { resolvePersonaRuntime } from "@/features/agents/lib/resolvePersonaRuntime";
-import { useEffectiveRuntimes } from "@/features/channels/ui/useEffectiveRuntimes";
+import {
+  collectRuntimeWarnings,
+  resolvePersonaRuntime,
+} from "@/features/agents/lib/resolvePersonaRuntime";
 import { getActivePersonas } from "@/features/agents/lib/catalog";
 import { getUsableTeams } from "@/features/agents/lib/teamPersonas";
 import { useLastRuntime } from "@/features/agents/lib/useLastRuntime";
@@ -55,8 +56,6 @@ type AddChannelBotDialogProps = {
   onOpenChange: (open: boolean) => void;
 };
 
-const RUNTIME_NONE_SENTINEL = "__none__";
-
 function defaultBotName(runtime: AcpRuntime | null) {
   if (!runtime) {
     return "";
@@ -104,7 +103,7 @@ export function AddChannelBotDialog({
   onAdded,
   onOpenChange,
 }: AddChannelBotDialogProps) {
-  const { setLastRuntime } = useLastRuntime();
+  const { lastRuntimeId, setLastRuntime } = useLastRuntime();
   const personasQuery = usePersonasQuery();
   const teamsQuery = useTeamsQuery();
   const inChannelPersonaIds = useInChannelPersonaIds(
@@ -153,13 +152,11 @@ export function AddChannelBotDialog({
 
   const selectedRuntime = React.useMemo(
     () =>
-      selectedRuntimeId
-        ? (providers.find((runtime) => runtime.id === selectedRuntimeId) ??
-          null)
-        : null,
+      providers.find((runtime) => runtime.id === selectedRuntimeId) ??
+      providers[0] ??
+      null,
     [providers, selectedRuntimeId],
   );
-  const isOverrideActive = selectedRuntime !== null;
   const selectedPersonas = React.useMemo(
     () => personas.filter((persona) => selectedPersonaIds.includes(persona.id)),
     [personas, selectedPersonaIds],
@@ -169,18 +166,21 @@ export function AddChannelBotDialog({
   const reusableAgent = useReusableAgentDetection(
     channelId,
     open && channelId !== null,
-    selectedRuntime ?? providers[0] ?? null,
+    selectedRuntime,
     selectedPersonas,
     includeGeneric,
     customPrompt,
   );
 
-  const { runtimeWarnings, effectiveRuntimes } = useEffectiveRuntimes(
-    personas,
-    selectedPersonas,
-    providers,
-    selectedRuntime,
-    isOverrideActive,
+  // Surface warnings when a persona's preferred runtime differs from the
+  // user-selected runtime. In this dialog the user explicitly picks a
+  // runtime via the dropdown, so the fallback is `selectedRuntime` (their
+  // choice), NOT `providers[0]`. This differs intentionally from
+  // AddTeamToChannelDialog which has no runtime selector and falls back
+  // to the first available runtime.
+  const runtimeWarnings = React.useMemo(
+    () => collectRuntimeWarnings(selectedPersonas, providers, selectedRuntime),
+    [selectedPersonas, providers, selectedRuntime],
   );
 
   const isProviderMode = runOn !== "local";
@@ -197,6 +197,19 @@ export function AddChannelBotDialog({
     );
   }, [isProviderMode, probedProvider, providerConfig]);
 
+  React.useEffect(() => {
+    if (!open) {
+      return;
+    }
+
+    if (!selectedRuntimeId && providers.length > 0) {
+      const remembered = lastRuntimeId
+        ? providers.find((p) => p.id === lastRuntimeId)
+        : null;
+      setSelectedRuntimeId(remembered ? remembered.id : providers[0].id);
+    }
+  }, [open, providers, selectedRuntimeId, lastRuntimeId]);
+
   React.useEffect(() => {
     if (!selectedRuntime || hasEditedCustomName) {
       return;
@@ -305,7 +318,7 @@ export function AddChannelBotDialog({
   }
 
   async function handleSubmit() {
-    if (providers.length === 0 || selectedCount === 0) {
+    if (!selectedRuntime || selectedCount === 0) {
       return;
     }
 
@@ -333,7 +346,7 @@ export function AddChannelBotDialog({
       ...(includeGeneric
         ? [
             {
-              runtime: selectedRuntime ?? providers[0],
+              runtime: selectedRuntime,
               name: customName,
               systemPrompt: customPrompt,
               role: "bot" as const,
@@ -344,15 +357,13 @@ export function AddChannelBotDialog({
           ]
         : []),
       ...selectedPersonas.map((persona) => {
-        const effectiveFallback = selectedRuntime ?? providers[0] ?? null;
         const resolved = resolvePersonaRuntime(
           persona.runtime,
           providers,
-          effectiveFallback,
-          isOverrideActive,
+          selectedRuntime,
         );
         return {
-          runtime: resolved.runtime ?? effectiveFallback ?? providers[0],
+          runtime: resolved.runtime ?? selectedRuntime,
           name: persona.displayName,
           personaId: persona.id,
           systemPrompt: persona.systemPrompt,
@@ -413,7 +424,7 @@ export function AddChannelBotDialog({
     respondTo !== "allowlist" || respondToAllowlist.length > 0;
 
   const canSubmit =
-    (selectedRuntime !== null || providers.length > 0) &&
+    selectedRuntime !== null &&
     selectedCount > 0 &&
     (!includeGeneric || customName.trim().length > 0) &&
     respondToValid &&
@@ -425,11 +436,9 @@ export function AddChannelBotDialog({
   const canChooseProvider =
     providers.length > 0 && !providersLoading && !createBotsMutation.isPending;
   const canToggleSelections = !createBotsMutation.isPending;
-  const runtimeTriggerLabel = providersLoading
+  const providerTriggerLabel = providersLoading
     ? "Loading runtimes..."
-    : providers.length === 0
-      ? "No runtimes found"
-      : (selectedRuntime?.label ?? "Use persona defaults");
+    : (selectedRuntime?.label ?? "No runtimes found");
   const addButtonLabel = createBotsMutation.isPending
     ? selectedCount > 1
       ? `Adding ${selectedCount}...`
@@ -529,7 +538,7 @@ export function AddChannelBotDialog({
                 type="button"
                 variant="ghost"
               >
-                <span className="truncate">{runtimeTriggerLabel}</span>
+                <span className="truncate">{providerTriggerLabel}</span>
                 <ChevronDown className="h-3.5 w-3.5 text-muted-foreground" />
               </Button>
             </DropdownMenuTrigger>
@@ -540,19 +549,11 @@ export function AddChannelBotDialog({
             >
               <DropdownMenuRadioGroup
                 onValueChange={(id) => {
-                  if (id === RUNTIME_NONE_SENTINEL) {
-                    setSelectedRuntimeId("");
-                  } else {
-                    setSelectedRuntimeId(id);
-                    setLastRuntime(id);
-                  }
+                  setSelectedRuntimeId(id);
+                  setLastRuntime(id);
                 }}
-                value={selectedRuntime?.id ?? RUNTIME_NONE_SENTINEL}
+                value={selectedRuntime?.id ?? ""}
               >
-                <DropdownMenuRadioItem value={RUNTIME_NONE_SENTINEL}>
-                  Use persona defaults
-                </DropdownMenuRadioItem>
-                <DropdownMenuSeparator />
                 {providers.map((provider) => (
                   <DropdownMenuRadioItem key={provider.id} value={provider.id}>
                     {provider.label}
@@ -562,9 +563,9 @@ export function AddChannelBotDialog({
             </DropdownMenuContent>
           </DropdownMenu>
           <p className="text-xs text-muted-foreground">
-            {isOverrideActive
-              ? "All agents will use this runtime, overriding persona preferences."
-              : "Each persona uses its preferred runtime. Choose a runtime above to override all."}
+            {selectedPersonas.some((p) => p.runtime)
+              ? "Personas with a preferred runtime will use their own instead of this selection."
+              : "Default runtime for all deployed agents."}
           </p>
         </div>
 
@@ -582,7 +583,6 @@ export function AddChannelBotDialog({
 
         <AddChannelBotPersonasSection
           canToggleSelections={canToggleSelections}
-          effectiveRuntimes={effectiveRuntimes}
           inChannelPersonaIds={inChannelPersonaIds}
           includeGeneric={includeGeneric}
           isLoading={personasQuery.isLoading}