diff --git a/desktop/src-tauri/src/managed_agents/discovery.rs b/desktop/src-tauri/src/managed_agents/discovery.rs
index 8d1b8a5013..473fecaf38 100644
--- a/desktop/src-tauri/src/managed_agents/discovery.rs
+++ b/desktop/src-tauri/src/managed_agents/discovery.rs
@@ -468,6 +468,7 @@ fn default_agent_args(command: &str) -> Option<Vec<String>> {
         "goose" => Some(vec!["acp".to_string()]),
         "codex" | "codex-acp" | "claude-agent-acp" | "claude-code-acp" | "claude-code"
         | "claudecode" | "buzz-agent" => Some(Vec::new()),
+        "kimi" => Some(vec!["acp".to_string()]),
         _ => None,
     }
 }
@@ -477,6 +478,20 @@ pub fn normalize_agent_args(command: &str, agent_args: Vec<String>) -> Vec<Strin
         .into_iter()
         .map(|arg| arg.trim().to_string())
         .filter(|arg| !arg.is_empty())
+        .map(|arg| {
+            // Canonicalize a stray `--acp`/`-acp` flag form to the bare `acp`
+            // subcommand. Subcommand-style harnesses (kimi, omp, opencode,
+            // devin, cursor-agent, goose…) reject the flag form outright
+            // ("unknown option '--acp'"), and earlier releases persisted
+            // `--acp` into harness definitions and instance args. The flag
+            // form is never meaningful input for a flag-style CLI, so this is
+            // a pure repair with no behaviour change for flag-style agents.
+            if arg.eq_ignore_ascii_case("--acp") || arg.eq_ignore_ascii_case("-acp") {
+                "acp".to_string()
+            } else {
+                arg
+            }
+        })
         .collect::<Vec<_>>();
 
     let Some(default_args) = default_agent_args(command) else {
diff --git a/desktop/src-tauri/src/managed_agents/discovery/tests.rs b/desktop/src-tauri/src/managed_agents/discovery/tests.rs
index 6fe6a77521..88074b5888 100644
--- a/desktop/src-tauri/src/managed_agents/discovery/tests.rs
+++ b/desktop/src-tauri/src/managed_agents/discovery/tests.rs
@@ -94,6 +94,70 @@ fn normalizes_buzz_agent_args_to_empty() {
     );
 }
 
+#[test]
+fn canonicalizes_stray_acp_flag_to_subcommand() {
+    // Regression for #4106: subcommand-style harnesses (kimi, omp, opencode,
+    // devin, cursor-agent…) reject the `--acp` flag form with
+    // "unknown option '--acp'". Earlier releases persisted `--acp` into
+    // harness definitions and instance args; normalize it to the subcommand.
+    assert_eq!(
+        normalize_agent_args("kimi", vec!["--acp".into()]),
+        vec!["acp".to_string()]
+    );
+    assert_eq!(
+        normalize_agent_args("kimi", vec!["-acp".into()]),
+        vec!["acp".to_string()]
+    );
+    assert_eq!(
+        normalize_agent_args("/Users/dev/.kimi-code/bin/kimi", vec!["--acp".into()]),
+        vec!["acp".to_string()]
+    );
+    assert_eq!(
+        normalize_agent_args("opencode", vec!["--acp".into()]),
+        vec!["acp".to_string()]
+    );
+    // Case-insensitive, and extra args are preserved.
+    assert_eq!(
+        normalize_agent_args("kimi", vec!["--ACP".into(), "--verbose".into()]),
+        vec!["acp".to_string(), "--verbose".to_string()]
+    );
+    // The correct subcommand form passes through unchanged.
+    assert_eq!(
+        normalize_agent_args("kimi", vec!["acp".into()]),
+        vec!["acp".to_string()]
+    );
+    // Flag-style agents (codex/claude/buzz-agent) still strip the ACP arg.
+    assert_eq!(
+        normalize_agent_args("codex-acp", vec!["--acp".into()]),
+        Vec::<String>::new()
+    );
+    // Unrelated flags are left alone for subcommand-style CLIs.
+    assert_eq!(
+        normalize_agent_args("kimi", vec!["--model".into(), "kimi-k3".into()]),
+        vec!["--model".to_string(), "kimi-k3".to_string()]
+    );
+}
+
+#[test]
+fn kimi_default_args_fallback_covers_empty_args() {
+    // When no args are persisted at all (empty instance args + empty harness
+    // definition args), kimi still launches as `kimi acp` via the same
+    // known-harness fallback that covers goose.
+    assert_eq!(
+        normalize_agent_args("kimi", Vec::new()),
+        vec!["acp".to_string()]
+    );
+    assert_eq!(
+        normalize_agent_args("kimi", vec!["  ".into(), "".into()]),
+        vec!["acp".to_string()]
+    );
+    // Explicit instance args still win over the fallback.
+    assert_eq!(
+        normalize_agent_args("kimi", vec!["--verbose".into()]),
+        vec!["--verbose".to_string()]
+    );
+}
+
 #[test]
 fn login_shell_lookup_treats_command_as_data() {
     let marker =