diff --git a/desktop/src-tauri/src/commands/agent_config.rs b/desktop/src-tauri/src/commands/agent_config.rs
index 461fed5db..3de82fdb7 100644
--- a/desktop/src-tauri/src/commands/agent_config.rs
+++ b/desktop/src-tauri/src/commands/agent_config.rs
@@ -692,6 +692,7 @@ mod tests {
             definition_parallelism: None,
             relay_mesh: None,
             agent_command_override: None,
+            agent_command_override_is_implicit: false,
             persona_source_version: None,
             provider: None,
         }
diff --git a/desktop/src-tauri/src/commands/agents.rs b/desktop/src-tauri/src/commands/agents.rs
index 3b5ebeca4..826d86882 100644
--- a/desktop/src-tauri/src/commands/agents.rs
+++ b/desktop/src-tauri/src/commands/agents.rs
@@ -759,20 +759,21 @@ pub async fn create_managed_agent(
         // Load personas once for harness/pack/avatar resolution below.
         let personas = load_personas(&app).unwrap_or_default();
 
-        // Harness resolution: the persona's runtime is authoritative. A
-        // persona-backed create stores an `agent_command_override` ONLY when the
-        // user deliberately picked a divergent runtime (`harness_override`) —
-        // e.g. AddChannelBotDialog's runtime selector. A divergence WITHOUT that
-        // flag is a missing-runtime fallback from `resolvePersonaRuntime`, not a
-        // pin, and must inherit so it doesn't freeze on the fallback harness once
-        // the persona's runtime is installed. A persona-less create always
-        // preserves the picked command as a real pin.
-        let agent_command_override = crate::managed_agents::create_time_agent_command_override(
-            requested_persona_id.as_deref(),
-            &personas,
-            input.agent_command.as_deref(),
-            input.harness_override,
-        );
+        // The persona runtime is authoritative. Persist an override only when
+        // the selected runtime must remain pinned (`harness_override`). This
+        // includes explicit picks and the visible fallback for a runtime-less
+        // persona. `implicit_harness_fallback` distinguishes those intents so
+        // the pin cannot adopt defaults owned by another harness. A divergence
+        // without `harness_override` remains inherited so it can recover when
+        // its configured runtime is installed. Persona-less creates always pin.
+        let (agent_command_override, agent_command_override_is_implicit) =
+            crate::managed_agents::create_time_agent_command_override_state(
+                requested_persona_id.as_deref(),
+                &personas,
+                input.agent_command.as_deref(),
+                input.harness_override,
+                input.implicit_harness_fallback,
+            );
         // The create-time snapshot used for arg/mcp/avatar derivations and
         // legacy reconcile. Authoritative spawn resolution re-derives this via
         // `effective_agent_command` at use-time.
@@ -891,6 +892,7 @@ pub async fn create_managed_agent(
                 .to_string(),
             agent_command,
             agent_command_override,
+            agent_command_override_is_implicit,
             agent_args,
             mcp_command,
             // BUZZ_ACP_TURN_TIMEOUT is deprecated and ignored by the harness;
diff --git a/desktop/src-tauri/src/commands/agents_tests.rs b/desktop/src-tauri/src/commands/agents_tests.rs
index b1951f195..63a5ab3eb 100644
--- a/desktop/src-tauri/src/commands/agents_tests.rs
+++ b/desktop/src-tauri/src/commands/agents_tests.rs
@@ -19,6 +19,7 @@ fn bare_agent_record(
         acp_command: "buzz-acp".to_string(),
         agent_command: "goose".to_string(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: "".to_string(),
         turn_timeout_seconds: 300,
@@ -235,6 +236,26 @@ fn deploy_resolver_ignores_defaults_from_a_different_implicit_runtime() {
     );
 }
 
+#[test]
+fn deploy_resolver_masks_mismatched_defaults_for_an_implicit_fallback_override() {
+    let mut record = bare_agent_record(Some("p1"), None, None);
+    record.agent_command = "goose".to_string();
+    record.agent_command_override = Some("goose".to_string());
+    record.agent_command_override_is_implicit = true;
+    let personas = vec![persona_record("p1", None, None)];
+    let global = crate::managed_agents::GlobalAgentConfig {
+        model: Some("auto".to_string()),
+        provider: Some("relay-mesh".to_string()),
+        preferred_runtime: Some("buzz-agent".to_string()),
+        ..Default::default()
+    };
+
+    assert_eq!(
+        resolve_deploy_model_provider(&record, &personas, &global),
+        (None, None)
+    );
+}
+
 #[test]
 fn deploy_resolver_ignores_mismatched_defaults_without_a_stored_override() {
     let mut record = bare_agent_record(Some("p1"), None, None);
diff --git a/desktop/src-tauri/src/commands/personas/delete_cascade_tests.rs b/desktop/src-tauri/src/commands/personas/delete_cascade_tests.rs
index 316af5f72..1a3dc38cc 100644
--- a/desktop/src-tauri/src/commands/personas/delete_cascade_tests.rs
+++ b/desktop/src-tauri/src/commands/personas/delete_cascade_tests.rs
@@ -27,6 +27,7 @@ fn make_agent(
         acp_command: "buzz-acp".to_string(),
         agent_command: "buzz-agent".to_string(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: "".to_string(),
         turn_timeout_seconds: 300,
diff --git a/desktop/src-tauri/src/commands/personas/inbound_tests.rs b/desktop/src-tauri/src/commands/personas/inbound_tests.rs
index 1000e48b7..a731e9baa 100644
--- a/desktop/src-tauri/src/commands/personas/inbound_tests.rs
+++ b/desktop/src-tauri/src/commands/personas/inbound_tests.rs
@@ -165,6 +165,7 @@ fn local_agent() -> ManagedAgentRecord {
         acp_command: "buzz-acp".to_string(),
         agent_command: "goose".to_string(),
         agent_command_override: Some("claude".to_string()),
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: "buzz-dev-mcp".to_string(),
         turn_timeout_seconds: 320,
diff --git a/desktop/src-tauri/src/commands/personas/name_propagation_tests.rs b/desktop/src-tauri/src/commands/personas/name_propagation_tests.rs
index ba855ccbd..1b837dcd5 100644
--- a/desktop/src-tauri/src/commands/personas/name_propagation_tests.rs
+++ b/desktop/src-tauri/src/commands/personas/name_propagation_tests.rs
@@ -15,6 +15,7 @@ fn agent(persona_id: &str, name: &str, display_name: Option<&str>) -> ManagedAge
         acp_command: String::new(),
         agent_command: String::new(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 0,
diff --git a/desktop/src-tauri/src/commands/personas/snapshot/import.rs b/desktop/src-tauri/src/commands/personas/snapshot/import.rs
index ac5c0eace..6cd5311fd 100644
--- a/desktop/src-tauri/src/commands/personas/snapshot/import.rs
+++ b/desktop/src-tauri/src/commands/personas/snapshot/import.rs
@@ -441,6 +441,7 @@ pub async fn confirm_agent_snapshot_import(
             acp_command: crate::managed_agents::DEFAULT_ACP_COMMAND.to_string(),
             agent_command: String::new(),
             agent_command_override: None,
+            agent_command_override_is_implicit: false,
             agent_args: vec![],
             mcp_command: String::new(),
             turn_timeout_seconds: 0,
diff --git a/desktop/src-tauri/src/commands/personas/snapshot/tests.rs b/desktop/src-tauri/src/commands/personas/snapshot/tests.rs
index b1d19f06b..e4d134c02 100644
--- a/desktop/src-tauri/src/commands/personas/snapshot/tests.rs
+++ b/desktop/src-tauri/src/commands/personas/snapshot/tests.rs
@@ -31,6 +31,7 @@ fn make_definition(slug: &str) -> ManagedAgentRecord {
         acp_command: String::new(),
         agent_command: String::new(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 0,
diff --git a/desktop/src-tauri/src/commands/team_snapshot.rs b/desktop/src-tauri/src/commands/team_snapshot.rs
index 0476be79a..b7b2ada92 100644
--- a/desktop/src-tauri/src/commands/team_snapshot.rs
+++ b/desktop/src-tauri/src/commands/team_snapshot.rs
@@ -560,6 +560,7 @@ pub async fn confirm_team_snapshot_import(
             acp_command: crate::managed_agents::DEFAULT_ACP_COMMAND.to_string(),
             agent_command: String::new(),
             agent_command_override: None,
+            agent_command_override_is_implicit: false,
             agent_args: vec![],
             mcp_command: String::new(),
             turn_timeout_seconds: 0,
diff --git a/desktop/src-tauri/src/commands/team_snapshot/tests.rs b/desktop/src-tauri/src/commands/team_snapshot/tests.rs
index ca7dc6183..009da1209 100644
--- a/desktop/src-tauri/src/commands/team_snapshot/tests.rs
+++ b/desktop/src-tauri/src/commands/team_snapshot/tests.rs
@@ -183,6 +183,7 @@ fn team_export_with_instance_and_memory_level_uses_supplied_entries() {
         acp_command: crate::managed_agents::DEFAULT_ACP_COMMAND.to_string(),
         agent_command: String::new(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 0,
diff --git a/desktop/src-tauri/src/managed_agents/agent_events.rs b/desktop/src-tauri/src/managed_agents/agent_events.rs
index ba4407d16..d2353213a 100644
--- a/desktop/src-tauri/src/managed_agents/agent_events.rs
+++ b/desktop/src-tauri/src/managed_agents/agent_events.rs
@@ -168,6 +168,7 @@ mod tests {
             acp_command: "buzz-acp".to_string(),
             agent_command: "goose".to_string(),
             agent_command_override: None,
+            agent_command_override_is_implicit: false,
             agent_args: vec!["--flag".to_string()],
             mcp_command: "buzz-dev-mcp".to_string(),
             turn_timeout_seconds: 320,
diff --git a/desktop/src-tauri/src/managed_agents/agent_snapshot.rs b/desktop/src-tauri/src/managed_agents/agent_snapshot.rs
index b0bf8f599..cfd14d603 100644
--- a/desktop/src-tauri/src/managed_agents/agent_snapshot.rs
+++ b/desktop/src-tauri/src/managed_agents/agent_snapshot.rs
@@ -485,9 +485,10 @@ mod tests {
             acp_command: "/usr/local/bin/acp".to_string(), // MUST NOT appear in snapshot
             agent_command: "goose".to_string(),            // MUST NOT appear in snapshot
             agent_command_override: Some("goose-override".to_string()), // MUST NOT appear
-            agent_args: vec!["--arg".to_string()],         // MUST NOT appear in snapshot
-            mcp_command: "mcp-server".to_string(),         // MUST NOT appear in snapshot
-            turn_timeout_seconds: 120,                     // deprecated, MUST NOT appear
+            agent_command_override_is_implicit: false,
+            agent_args: vec!["--arg".to_string()], // MUST NOT appear in snapshot
+            mcp_command: "mcp-server".to_string(), // MUST NOT appear in snapshot
+            turn_timeout_seconds: 120,             // deprecated, MUST NOT appear
             idle_timeout_seconds: Some(30),
             max_turn_duration_seconds: Some(600),
             parallelism: 2,
diff --git a/desktop/src-tauri/src/managed_agents/config_bridge/reader_tests.rs b/desktop/src-tauri/src/managed_agents/config_bridge/reader_tests.rs
index 4c11cd6c4..17b6dbffa 100644
--- a/desktop/src-tauri/src/managed_agents/config_bridge/reader_tests.rs
+++ b/desktop/src-tauri/src/managed_agents/config_bridge/reader_tests.rs
@@ -113,6 +113,7 @@ fn test_record() -> ManagedAgentRecord {
         definition_parallelism: None,
         relay_mesh: None,
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         persona_source_version: None,
         provider: None,
     }
diff --git a/desktop/src-tauri/src/managed_agents/discovery.rs b/desktop/src-tauri/src/managed_agents/discovery.rs
index 2b7264b42..f2f945e12 100644
--- a/desktop/src-tauri/src/managed_agents/discovery.rs
+++ b/desktop/src-tauri/src/managed_agents/discovery.rs
@@ -362,7 +362,10 @@ pub fn effective_agent_command(
 }
 
 mod overrides;
-pub use overrides::{apply_agent_command_update, create_time_agent_command_override};
+pub use overrides::{
+    apply_agent_command_update, create_time_agent_command_override,
+    create_time_agent_command_override_state,
+};
 
 /// Prefix of the typed dangling-harness error produced by
 /// `try_record_agent_command` / `resolve_effective_harness_descriptor`.
diff --git a/desktop/src-tauri/src/managed_agents/discovery/overrides.rs b/desktop/src-tauri/src/managed_agents/discovery/overrides.rs
index 7f9ded5a1..3b6c08490 100644
--- a/desktop/src-tauri/src/managed_agents/discovery/overrides.rs
+++ b/desktop/src-tauri/src/managed_agents/discovery/overrides.rs
@@ -102,6 +102,7 @@ pub fn apply_agent_command_update(
         Some(agent_command),
         harness_override,
     );
+    record.agent_command_override_is_implicit = false;
     if agent_command.trim().is_empty() && record.persona_id.is_some() {
         record.runtime = None;
     }
@@ -151,3 +152,26 @@ pub fn create_time_agent_command_override(
 
     divergent_agent_command_override(persona_id, personas, picked_command)
 }
+
+/// Resolve the create-time harness pin and whether it represents an automatic
+/// runtime-less fallback rather than explicit selection intent.
+pub fn create_time_agent_command_override_state(
+    persona_id: Option<&str>,
+    personas: &[crate::managed_agents::types::AgentDefinition],
+    picked_command: Option<&str>,
+    harness_override: bool,
+    implicit_harness_fallback: bool,
+) -> (Option<String>, bool) {
+    let command =
+        create_time_agent_command_override(persona_id, personas, picked_command, harness_override);
+    let is_runtime_less_persona = persona_id
+        .and_then(|id| personas.iter().find(|persona| persona.id == id))
+        .is_some_and(|persona| {
+            persona
+                .runtime
+                .as_deref()
+                .is_none_or(|runtime| runtime.trim().is_empty())
+        });
+    let is_implicit = command.is_some() && implicit_harness_fallback && is_runtime_less_persona;
+    (command, is_implicit)
+}
diff --git a/desktop/src-tauri/src/managed_agents/discovery/tests.rs b/desktop/src-tauri/src/managed_agents/discovery/tests.rs
index a222e0108..7f1806a5c 100644
--- a/desktop/src-tauri/src/managed_agents/discovery/tests.rs
+++ b/desktop/src-tauri/src/managed_agents/discovery/tests.rs
@@ -324,6 +324,7 @@ fn record_with(
         acp_command: String::new(),
         agent_command: String::new(),
         agent_command_override: override_cmd.map(str::to_string),
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 0,
@@ -698,10 +699,12 @@ fn apply_agent_command_update_inherit_sentinel_clears_pin_and_runtime() {
     // live definition immediately — not on the next spawn.
     let personas = vec![persona_with_runtime("p1", Some("goose"))];
     let mut record = record_with(Some("claude"), Some("p1"), Some("codex-acp"));
+    record.agent_command_override_is_implicit = true;
 
     apply_agent_command_update(&mut record, &personas, "", false);
 
     assert_eq!(record.agent_command_override, None);
+    assert!(!record.agent_command_override_is_implicit);
     assert_eq!(record.runtime, None);
     assert_eq!(record_agent_command(&record, &personas), "goose");
 }
@@ -726,10 +729,12 @@ fn apply_agent_command_update_concrete_pin_keeps_materialized_runtime() {
     // the next snapshot apply. The pin shadows it in resolution either way.
     let personas = vec![persona_with_runtime("p1", Some("goose"))];
     let mut record = record_with(Some("claude"), Some("p1"), None);
+    record.agent_command_override_is_implicit = true;
 
     apply_agent_command_update(&mut record, &personas, "codex-acp", true);
 
     assert_eq!(record.agent_command_override.as_deref(), Some("codex-acp"));
+    assert!(!record.agent_command_override_is_implicit);
     assert_eq!(record.runtime.as_deref(), Some("claude"));
     assert_eq!(record_agent_command(&record, &personas), "codex-acp");
 }
diff --git a/desktop/src-tauri/src/managed_agents/discovery/tests/provisioning_overrides.rs b/desktop/src-tauri/src/managed_agents/discovery/tests/provisioning_overrides.rs
index 972d05fdf..1a21dd1f4 100644
--- a/desktop/src-tauri/src/managed_agents/discovery/tests/provisioning_overrides.rs
+++ b/desktop/src-tauri/src/managed_agents/discovery/tests/provisioning_overrides.rs
@@ -1,3 +1,4 @@
+use super::super::create_time_agent_command_override_state;
 use super::{create_time_agent_command_override, persona_with_runtime};
 
 #[test]
@@ -17,3 +18,30 @@ fn pins_visible_fallback_for_runtime_less_persona() {
         Some("goose".to_string())
     );
 }
+
+#[test]
+fn marks_only_runtime_less_automatic_fallback_pins_as_implicit() {
+    let runtime_less = vec![persona_with_runtime("p1", None)];
+    assert_eq!(
+        create_time_agent_command_override_state(
+            Some("p1"),
+            &runtime_less,
+            Some("goose"),
+            true,
+            true,
+        ),
+        (Some("goose".to_string()), true)
+    );
+
+    let configured = vec![persona_with_runtime("p1", Some("claude"))];
+    assert_eq!(
+        create_time_agent_command_override_state(
+            Some("p1"),
+            &configured,
+            Some("codex-acp"),
+            true,
+            true,
+        ),
+        (Some("codex-acp".to_string()), false)
+    );
+}
diff --git a/desktop/src-tauri/src/managed_agents/global_config/mod.rs b/desktop/src-tauri/src/managed_agents/global_config/mod.rs
index be3ec97b6..334fc06ab 100644
--- a/desktop/src-tauri/src/managed_agents/global_config/mod.rs
+++ b/desktop/src-tauri/src/managed_agents/global_config/mod.rs
@@ -211,11 +211,15 @@ pub fn save_global_agent_config(app: &AppHandle, config: &GlobalAgentConfig) ->
 ///
 /// A runtime-less definition can be started on a fallback runtime when its
 /// saved global preference is hidden or unavailable. In that case the selected
-/// command is pinned on the record, and provider/model defaults belonging to a
-/// different preferred runtime must not cross the harness boundary. Explicitly
-/// configured definitions and standalone agents keep normal global inheritance.
-/// Configs written before `preferred_runtime` existed implicitly belong to
-/// Buzz Agent.
+/// command is stored as the record snapshot, and provider/model defaults
+/// belonging to a different preferred runtime must not cross the harness
+/// boundary. A non-empty `agent_command_override` keeps normal global
+/// inheritance only when it represents an explicit harness selection. An
+/// automatic runtime-less fallback carries a separate durable marker so its
+/// pin survives provisioning without adopting defaults owned by another
+/// harness. Explicitly configured definitions and standalone agents keep
+/// normal global inheritance. Configs written before `preferred_runtime`
+/// existed implicitly belong to Buzz Agent.
 pub(crate) fn global_model_provider_for_record<'a>(
     record: &ManagedAgentRecord,
     personas: &[AgentDefinition],
@@ -237,6 +241,15 @@ pub(crate) fn global_model_provider_for_record<'a>(
         return global_values;
     }
 
+    if !record.agent_command_override_is_implicit
+        && record
+            .agent_command_override
+            .as_deref()
+            .is_some_and(|command| !command.trim().is_empty())
+    {
+        return global_values;
+    }
+
     let preferred_runtime = global
         .preferred_runtime
         .as_deref()
diff --git a/desktop/src-tauri/src/managed_agents/global_config/tests.rs b/desktop/src-tauri/src/managed_agents/global_config/tests.rs
index 8dc2296f4..4a519db49 100644
--- a/desktop/src-tauri/src/managed_agents/global_config/tests.rs
+++ b/desktop/src-tauri/src/managed_agents/global_config/tests.rs
@@ -309,6 +309,7 @@ fn bare_record() -> ManagedAgentRecord {
         acp_command: "buzz-acp".to_string(),
         agent_command: "goose".to_string(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: "".to_string(),
         turn_timeout_seconds: 300,
@@ -473,11 +474,36 @@ fn resolve_global_fallback_when_record_and_persona_have_none() {
 }
 
 #[test]
-fn runtime_fallback_does_not_inherit_defaults_from_a_different_preferred_runtime() {
+fn explicit_harness_override_keeps_defaults_from_a_different_preferred_runtime() {
     let mut record = bare_record();
     record.persona_id = Some("p1".to_string());
     record.agent_command_override = Some("goose".to_string());
     let personas = vec![persona("p1", None, None)];
+    let global = GlobalAgentConfig {
+        env_vars: BTreeMap::from([("BUZZ_AGENT_THINKING_EFFORT".to_string(), "high".to_string())]),
+        model: Some("auto".to_string()),
+        provider: Some("relay-mesh".to_string()),
+        preferred_runtime: Some("buzz-agent".to_string()),
+    };
+
+    assert_eq!(
+        resolve_effective_model_provider(&record, &personas, &global),
+        (Some("auto".to_string()), Some("relay-mesh".to_string()))
+    );
+    assert_eq!(
+        global_env_vars_for_record(&record, &personas, &global),
+        global.env_vars
+    );
+}
+
+#[test]
+fn implicit_fallback_override_masks_defaults_from_a_different_preferred_runtime() {
+    let mut record = bare_record();
+    record.persona_id = Some("p1".to_string());
+    record.agent_command = "goose".to_string();
+    record.agent_command_override = Some("goose".to_string());
+    record.agent_command_override_is_implicit = true;
+    let personas = vec![persona("p1", None, None)];
     let global = GlobalAgentConfig {
         model: Some("auto".to_string()),
         provider: Some("relay-mesh".to_string()),
@@ -492,7 +518,7 @@ fn runtime_fallback_does_not_inherit_defaults_from_a_different_preferred_runtime
 }
 
 #[test]
-fn legacy_runtime_fallback_does_not_inherit_implicit_buzz_agent_defaults() {
+fn explicit_harness_override_keeps_legacy_global_defaults() {
     let mut record = bare_record();
     record.persona_id = Some("p1".to_string());
     record.agent_command_override = Some("goose".to_string());
@@ -506,7 +532,7 @@ fn legacy_runtime_fallback_does_not_inherit_implicit_buzz_agent_defaults() {
 
     assert_eq!(
         resolve_effective_model_provider(&record, &personas, &global),
-        (None, None)
+        (Some("auto".to_string()), Some("relay-mesh".to_string()))
     );
 }
 
diff --git a/desktop/src-tauri/src/managed_agents/nest/tests.rs b/desktop/src-tauri/src/managed_agents/nest/tests.rs
index a95938160..f0a258f4f 100644
--- a/desktop/src-tauri/src/managed_agents/nest/tests.rs
+++ b/desktop/src-tauri/src/managed_agents/nest/tests.rs
@@ -445,6 +445,7 @@ fn make_agent(name: &str, persona_id: Option<&str>) -> ManagedAgentRecord {
         acp_command: String::new(),
         agent_command: String::new(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 0,
diff --git a/desktop/src-tauri/src/managed_agents/persona_events.rs b/desktop/src-tauri/src/managed_agents/persona_events.rs
index 5b62615a8..0b0b80054 100644
--- a/desktop/src-tauri/src/managed_agents/persona_events.rs
+++ b/desktop/src-tauri/src/managed_agents/persona_events.rs
@@ -439,6 +439,7 @@ pub fn apply_persona_snapshot(record: &mut ManagedAgentRecord, persona: &AgentDe
         {
             if !std::ptr::eq(pin_runtime, def_runtime) {
                 record.agent_command_override = None;
+                record.agent_command_override_is_implicit = false;
             }
         }
     }
diff --git a/desktop/src-tauri/src/managed_agents/readiness.rs b/desktop/src-tauri/src/managed_agents/readiness.rs
index c5480b247..a1b1b31a5 100644
--- a/desktop/src-tauri/src/managed_agents/readiness.rs
+++ b/desktop/src-tauri/src/managed_agents/readiness.rs
@@ -1475,6 +1475,7 @@ mod tests {
             acp_command: "buzz-acp".to_string(),
             agent_command: "buzz-agent".to_string(),
             agent_command_override: None,
+            agent_command_override_is_implicit: false,
             agent_args: vec![],
             mcp_command: String::new(),
             turn_timeout_seconds: 320,
diff --git a/desktop/src-tauri/src/managed_agents/runtime/tests.rs b/desktop/src-tauri/src/managed_agents/runtime/tests.rs
index 8deb0c4da..3f9c3972c 100644
--- a/desktop/src-tauri/src/managed_agents/runtime/tests.rs
+++ b/desktop/src-tauri/src/managed_agents/runtime/tests.rs
@@ -140,6 +140,7 @@ fn fixture(
         acp_command: "buzz-acp".into(),
         agent_command: "goose".into(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 320,
diff --git a/desktop/src-tauri/src/managed_agents/spawn_hash/tests.rs b/desktop/src-tauri/src/managed_agents/spawn_hash/tests.rs
index 292cdbbb7..3cc2fb89d 100644
--- a/desktop/src-tauri/src/managed_agents/spawn_hash/tests.rs
+++ b/desktop/src-tauri/src/managed_agents/spawn_hash/tests.rs
@@ -14,6 +14,7 @@ fn record() -> ManagedAgentRecord {
         acp_command: "buzz-acp".into(),
         agent_command: "goose".into(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 320,
diff --git a/desktop/src-tauri/src/managed_agents/team_snapshot.rs b/desktop/src-tauri/src/managed_agents/team_snapshot.rs
index d88a36272..b6536f493 100644
--- a/desktop/src-tauri/src/managed_agents/team_snapshot.rs
+++ b/desktop/src-tauri/src/managed_agents/team_snapshot.rs
@@ -263,6 +263,7 @@ mod tests {
             acp_command: "/usr/local/bin/acp".to_string(), // MUST NOT appear
             agent_command: "goose".to_string(),            // MUST NOT appear
             agent_command_override: None,
+            agent_command_override_is_implicit: false,
             agent_args: vec![],
             mcp_command: String::new(),
             turn_timeout_seconds: 120,
diff --git a/desktop/src-tauri/src/managed_agents/teams_tests.rs b/desktop/src-tauri/src/managed_agents/teams_tests.rs
index 140ac3cab..d69319383 100644
--- a/desktop/src-tauri/src/managed_agents/teams_tests.rs
+++ b/desktop/src-tauri/src/managed_agents/teams_tests.rs
@@ -174,6 +174,7 @@ fn managed_agent(name: &str) -> ManagedAgentRecord {
         acp_command: "buzz-acp".to_string(),
         agent_command: "buzz-agent".to_string(),
         agent_command_override: None,
+        agent_command_override_is_implicit: false,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 300,
diff --git a/desktop/src-tauri/src/managed_agents/types.rs b/desktop/src-tauri/src/managed_agents/types.rs
index dcb8095a7..a2aa0b5a4 100644
--- a/desktop/src-tauri/src/managed_agents/types.rs
+++ b/desktop/src-tauri/src/managed_agents/types.rs
@@ -95,6 +95,7 @@ impl AgentDefinition {
             acp_command: DEFAULT_ACP_COMMAND.to_string(),
             agent_command: String::new(),
             agent_command_override: None,
+            agent_command_override_is_implicit: false,
             agent_args: Vec::new(),
             mcp_command: String::new(),
             turn_timeout_seconds: DEFAULT_AGENT_TURN_TIMEOUT_SECONDS,
@@ -225,15 +226,21 @@ pub struct ManagedAgentRecord {
     pub avatar_url: Option<String>,
     pub acp_command: String,
     pub agent_command: String,
-    /// Explicit per-instance harness pin. `None` (the default) means inherit
-    /// the harness from the linked persona's `runtime`, so persona harness
-    /// edits propagate on the next spawn — mirroring the opt-in `model`
-    /// override. `Some` is set only when the user deliberately picks a harness
-    /// that diverges from the persona. Resolved via `effective_agent_command`;
-    /// `agent_command` above is the create-time snapshot kept for avatar/legacy
-    /// derivations and is not authoritative for spawn.
+    /// Per-instance harness pin. `None` (the default) means inherit the harness
+    /// from the linked persona's `runtime`, so persona harness edits propagate
+    /// on the next spawn — mirroring the opt-in `model` override. `Some` is
+    /// normally an explicit divergent selection, but may preserve the visible
+    /// automatic fallback chosen for a runtime-less persona; the accompanying
+    /// marker distinguishes those intents. Resolved via
+    /// `effective_agent_command`; `agent_command` above is the create-time
+    /// snapshot kept for avatar/legacy derivations and is not authoritative for
+    /// spawn.
     #[serde(default)]
     pub agent_command_override: Option<String>,
+    /// Whether `agent_command_override` preserves an automatic runtime-less
+    /// fallback rather than an explicit per-instance harness selection.
+    #[serde(default)]
+    pub agent_command_override_is_implicit: bool,
     pub agent_args: Vec<String>,
     /// Create-time snapshot of the catalog MCP command. Never read at spawn —
     /// the effective MCP command is always re-derived from the runtime catalog
@@ -473,10 +480,12 @@ pub struct ManagedAgentSummary {
     pub relay_url: String,
     pub acp_command: String,
     pub agent_command: String,
-    /// Mirrors `ManagedAgentRecord.agent_command_override`: `Some` when the user
-    /// has explicitly pinned this instance's harness, `None` when it inherits
-    /// from the persona. Lets the Edit dialog seed "Inherit from persona" vs a
-    /// concrete pin (`agent_command` above is the resolved/effective command).
+    /// Mirrors `ManagedAgentRecord.agent_command_override`: `Some` when this
+    /// instance has a durable harness pin, `None` when it inherits from the
+    /// persona. A pin may be an explicit selection or an automatic fallback
+    /// for a runtime-less persona. Lets the Edit dialog seed "Inherit from
+    /// persona" vs a concrete pin (`agent_command` above is the
+    /// resolved/effective command).
     pub agent_command_override: Option<String>,
     pub agent_args: Vec<String>,
     /// Catalog-derived from the effective harness (not the record's stored
diff --git a/desktop/src-tauri/src/managed_agents/types/requests.rs b/desktop/src-tauri/src/managed_agents/types/requests.rs
index 6d882de26..3c8130c48 100644
--- a/desktop/src-tauri/src/managed_agents/types/requests.rs
+++ b/desktop/src-tauri/src/managed_agents/types/requests.rs
@@ -136,10 +136,14 @@ pub struct CreateManagedAgentRequest {
     pub acp_command: Option<String>,
     pub agent_command: Option<String>,
     /// True when `agent_command` must survive linked-persona inheritance.
-    /// Includes explicit selections, installed aliases, and the visible
-    /// implicit fallback for a runtime-less persona.
+    /// Includes explicit selections, installed aliases, and automatic
+    /// fallbacks for runtime-less personas.
     #[serde(default)]
     pub harness_override: bool,
+    /// True when `harness_override` preserves an automatic runtime-less
+    /// fallback rather than an explicit harness selection.
+    #[serde(default)]
+    pub implicit_harness_fallback: bool,
     #[serde(default)]
     pub agent_args: Vec<String>,
     /// Accepted for wire compatibility; not applied to the record. The
diff --git a/desktop/src-tauri/src/managed_agents/types/tests.rs b/desktop/src-tauri/src/managed_agents/types/tests.rs
index 667a41a53..294e096d4 100644
--- a/desktop/src-tauri/src/managed_agents/types/tests.rs
+++ b/desktop/src-tauri/src/managed_agents/types/tests.rs
@@ -272,6 +272,22 @@ fn create_request_deserializes_camel_case_relay_mesh() {
             model_ref: "Qwen3".to_string()
         })
     );
+    assert!(!request.implicit_harness_fallback);
+}
+
+#[test]
+fn create_request_deserializes_implicit_harness_fallback_intent() {
+    let request: CreateManagedAgentRequest = serde_json::from_str(
+        r#"{
+            "name": "fallback-agent",
+            "harnessOverride": true,
+            "implicitHarnessFallback": true
+        }"#,
+    )
+    .expect("camelCase implicit fallback intent should deserialize");
+
+    assert!(request.harness_override);
+    assert!(request.implicit_harness_fallback);
 }
 
 /// Persisted records use snake_case; the camelCase alias must not break
@@ -442,6 +458,7 @@ fn managed_agent_record_without_key_deserializes_empty() {
     .expect("keyring-backed record without inline key should deserialize");
 
     assert_eq!(record.private_key_nsec, "");
+    assert!(!record.agent_command_override_is_implicit);
 }
 
 fn sample_agent_record() -> ManagedAgentRecord {
diff --git a/desktop/src/features/agents/AGENTS.md b/desktop/src/features/agents/AGENTS.md
index 33b23a530..e88f92042 100644
--- a/desktop/src/features/agents/AGENTS.md
+++ b/desktop/src/features/agents/AGENTS.md
@@ -98,7 +98,11 @@ with a TypeScript lookup table or an id comparison in a component.
    without changing the persisted configuration used by existing agents.
    Legacy global defaults with no saved preferred runtime are treated as
    Buzz Agent-owned for this masking boundary, so hiding Buzz Agent cannot
-   leak its provider/model into another implicit fallback.
+   leak its provider/model into another implicit fallback. A persisted
+   per-instance harness override carries a durable explicit-vs-implicit marker:
+   explicit selections continue to inherit global provider/model defaults even
+   when the selected harness differs from the global preference, while
+   automatic runtime-less fallback pins keep mismatched defaults masked.
    Create-mode dialogs use the implicit masked config; existing definition and
    instance edit dialogs use the raw persisted config.
    `resolvePersonaRuntime` is the shared visibility boundary for every
diff --git a/desktop/src/features/agents/channelAgents.ts b/desktop/src/features/agents/channelAgents.ts
index ebb2f7a7e..d0eb447f1 100644
--- a/desktop/src/features/agents/channelAgents.ts
+++ b/desktop/src/features/agents/channelAgents.ts
@@ -66,6 +66,8 @@ export type CreateChannelManagedAgentInput = {
    * unpinned so the persona remains authoritative.
    */
   harnessOverride?: boolean;
+  /** The pin preserves an automatic runtime-less fallback, not an explicit pick. */
+  implicitHarnessFallback?: boolean;
   /** Preferred model ID from the persona. Passed to createManagedAgent. */
   model?: string;
   role?: Exclude<ChannelRole, "owner">;
@@ -355,6 +357,7 @@ export async function provisionChannelManagedAgent(
     acpCommand: "buzz-acp",
     agentCommand: input.runtime.command,
     harnessOverride: input.harnessOverride ?? false,
+    implicitHarnessFallback: input.implicitHarnessFallback ?? false,
     // Do NOT seed agentArgs from runtime.defaultArgs (see instanceInputForDefinition.ts
     // for the rationale — empty args let spawn resolve definition args live).
     agentArgs: [],
diff --git a/desktop/src/features/agents/lib/instanceInputForDefinition.test.mjs b/desktop/src/features/agents/lib/instanceInputForDefinition.test.mjs
index 8f2238c45..48cbd8499 100644
--- a/desktop/src/features/agents/lib/instanceInputForDefinition.test.mjs
+++ b/desktop/src/features/agents/lib/instanceInputForDefinition.test.mjs
@@ -84,12 +84,14 @@ test("row 2: harnessOverride follows the backend-aligned formula", async () => {
     gooseRuntime,
   );
   assert.equal(match.harnessOverride, true, "picked == configured → true");
+  assert.equal(match.implicitHarnessFallback, false);
 
   const noPreference = await buildInstanceInputForDefinition(
     persona({ runtime: undefined }),
     gooseRuntime,
   );
   assert.equal(noPreference.harnessOverride, true, "no preference → true");
+  assert.equal(noPreference.implicitHarnessFallback, true);
 
   const differs = await buildInstanceInputForDefinition(
     persona({ runtime: "claude" }),
@@ -100,6 +102,7 @@ test("row 2: harnessOverride follows the backend-aligned formula", async () => {
     false,
     "picked != configured → false (definition stays authoritative)",
   );
+  assert.equal(differs.implicitHarnessFallback, false);
 });
 
 test("provisioning pins a visible fallback for a runtime-less definition", () => {
@@ -111,6 +114,7 @@ test("provisioning pins a visible fallback for a runtime-less definition", () =>
   );
   assert.equal(resolved.runtime, gooseRuntime);
   assert.equal(resolved.harnessOverride, true);
+  assert.equal(resolved.implicitHarnessFallback, true);
 });
 
 test("provisioning uses product ordering and leaves unavailable configured fallbacks unpinned", () => {
@@ -121,12 +125,14 @@ test("provisioning uses product ordering and leaves unavailable configured fallb
   ]);
   assert.equal(ordered.runtime, buzzAgentRuntime);
   assert.equal(ordered.harnessOverride, true);
+  assert.equal(ordered.implicitHarnessFallback, true);
 
   const unavailable = resolveProvisioningRuntimeForDefinition("missing", [
     gooseRuntime,
   ]);
   assert.equal(unavailable.runtime, gooseRuntime);
   assert.equal(unavailable.harnessOverride, false);
+  assert.equal(unavailable.implicitHarnessFallback, false);
 });
 
 test("row 3: plain avatar URLs pass through; base64 data URIs upload via the injectable", async () => {
@@ -205,6 +211,7 @@ test("no backend intent is byte-identical to the pre-intent mapping", async () =
     agentArgs: [],
     mcpCommand: "goose-mcp",
     harnessOverride: true,
+    implicitHarnessFallback: false,
     model: undefined,
     provider: undefined,
     spawnAfterCreate: true,
diff --git a/desktop/src/features/agents/lib/instanceInputForDefinition.ts b/desktop/src/features/agents/lib/instanceInputForDefinition.ts
index 21812c882..32e83f8cb 100644
--- a/desktop/src/features/agents/lib/instanceInputForDefinition.ts
+++ b/desktop/src/features/agents/lib/instanceInputForDefinition.ts
@@ -120,7 +120,10 @@ export function resolveProvisioningRuntimeForDefinition(
   runtimes: readonly AcpRuntime[],
   preferredRuntimeId?: string | null,
   disabledRuntimeIds: readonly string[] = getDisabledAcpRuntimeIdsSnapshot(),
-): ResolvePersonaRuntimeResult & { harnessOverride: boolean } {
+): ResolvePersonaRuntimeResult & {
+  harnessOverride: boolean;
+  implicitHarnessFallback: boolean;
+} {
   const defaultRuntime = getDefaultPersonaRuntime(runtimes, preferredRuntimeId);
   const resolved = resolvePersonaRuntime(
     definitionRuntimeId,
@@ -137,6 +140,8 @@ export function resolveProvisioningRuntimeForDefinition(
         definitionRuntimeId,
         resolved.runtime.id,
       ),
+    implicitHarnessFallback:
+      resolved.runtime !== null && !definitionRuntimeId?.trim(),
   };
 }
 
@@ -207,6 +212,7 @@ export async function buildInstanceInputForDefinition(
       persona.runtime,
       runtime.id,
     ),
+    implicitHarnessFallback: !persona.runtime?.trim(),
     model: persona.model ?? undefined,
     provider: persona.provider ?? undefined,
     spawnAfterCreate: true,
diff --git a/desktop/src/features/agents/ui/AddTeamToChannelDialog.tsx b/desktop/src/features/agents/ui/AddTeamToChannelDialog.tsx
index 552373743..b7b0d5bcc 100644
--- a/desktop/src/features/agents/ui/AddTeamToChannelDialog.tsx
+++ b/desktop/src/features/agents/ui/AddTeamToChannelDialog.tsx
@@ -160,6 +160,7 @@ export function AddTeamToChannelDialog({
             persona.runtime,
             personaRuntime.id,
           ),
+          implicitHarnessFallback: !persona.runtime?.trim(),
           model: persona.model ?? undefined,
           personaId: persona.id,
           teamId: team.id,
diff --git a/desktop/src/features/channel-templates/useApplyTemplate.ts b/desktop/src/features/channel-templates/useApplyTemplate.ts
index 537ca66f7..0b4f4ad47 100644
--- a/desktop/src/features/channel-templates/useApplyTemplate.ts
+++ b/desktop/src/features/channel-templates/useApplyTemplate.ts
@@ -93,6 +93,7 @@ export function useApplyTemplate() {
         name: persona.displayName,
         personaId: persona.id,
         harnessOverride: resolved.harnessOverride,
+        implicitHarnessFallback: resolved.implicitHarnessFallback,
         systemPrompt: persona.systemPrompt,
         avatarUrl: persona.avatarUrl ?? undefined,
         model: entry.model ?? persona.model ?? undefined,
@@ -121,6 +122,7 @@ export function useApplyTemplate() {
           name: persona.displayName,
           personaId: persona.id,
           harnessOverride: resolved.harnessOverride,
+          implicitHarnessFallback: resolved.implicitHarnessFallback,
           systemPrompt: persona.systemPrompt,
           avatarUrl: persona.avatarUrl ?? undefined,
           model: teamEntry.model ?? persona.model ?? undefined,
diff --git a/desktop/src/features/channels/ui/AddChannelBotDialog.tsx b/desktop/src/features/channels/ui/AddChannelBotDialog.tsx
index cd8e8beb8..53b9463a2 100644
--- a/desktop/src/features/channels/ui/AddChannelBotDialog.tsx
+++ b/desktop/src/features/channels/ui/AddChannelBotDialog.tsx
@@ -156,6 +156,7 @@ export function AddChannelBotDialog({
           name: persona.displayName,
           personaId: persona.id,
           harnessOverride: resolved.harnessOverride,
+          implicitHarnessFallback: resolved.implicitHarnessFallback,
           systemPrompt: persona.systemPrompt,
           avatarUrl: persona.avatarUrl ?? undefined,
           model: persona.model ?? undefined,
diff --git a/desktop/src/features/channels/ui/useQuickBotDrop.ts b/desktop/src/features/channels/ui/useQuickBotDrop.ts
index 5283a402f..82f930f72 100644
--- a/desktop/src/features/channels/ui/useQuickBotDrop.ts
+++ b/desktop/src/features/channels/ui/useQuickBotDrop.ts
@@ -32,7 +32,7 @@ export function useQuickBotDrop(channelId: string | null) {
       setState({ pending: true, error: null });
 
       try {
-        const { harnessOverride, runtime } =
+        const { harnessOverride, implicitHarnessFallback, runtime } =
           resolveProvisioningRuntimeForDefinition(persona.runtime, providers);
 
         if (!runtime) {
@@ -51,6 +51,7 @@ export function useQuickBotDrop(channelId: string | null) {
           personaId: persona.id,
           model: persona.model ?? undefined,
           harnessOverride,
+          implicitHarnessFallback,
         });
 
         setState({ pending: false, error: null });
diff --git a/desktop/src/features/messages/ui/useMentionSendFlow.ts b/desktop/src/features/messages/ui/useMentionSendFlow.ts
index 1a95ae875..33ceb25ee 100644
--- a/desktop/src/features/messages/ui/useMentionSendFlow.ts
+++ b/desktop/src/features/messages/ui/useMentionSendFlow.ts
@@ -326,7 +326,7 @@ export function useMentionSendFlow({
         }
         seenPersonaIds.add(persona.id);
 
-        const { harnessOverride, runtime } =
+        const { harnessOverride, implicitHarnessFallback, runtime } =
           resolveProvisioningRuntimeForDefinition(persona.runtime, runtimes);
         if (!runtime) {
           errors.push(`${displayName}: No agent runtime available.`);
@@ -342,6 +342,7 @@ export function useMentionSendFlow({
             name: persona.displayName,
             personaId: persona.id,
             harnessOverride,
+            implicitHarnessFallback,
             systemPrompt: persona.systemPrompt,
             avatarUrl: persona.avatarUrl ?? undefined,
             model: persona.model ?? undefined,
diff --git a/desktop/src/shared/api/tauri.ts b/desktop/src/shared/api/tauri.ts
index e8a8b885c..98ef84da0 100644
--- a/desktop/src/shared/api/tauri.ts
+++ b/desktop/src/shared/api/tauri.ts
@@ -874,6 +874,7 @@ export async function createManagedAgent(input: CreateManagedAgentInput) {
         acpCommand: input.acpCommand,
         agentCommand: input.agentCommand,
         harnessOverride: input.harnessOverride ?? false,
+        implicitHarnessFallback: input.implicitHarnessFallback ?? false,
         agentArgs: input.agentArgs,
         mcpCommand: input.mcpCommand,
         turnTimeoutSeconds: input.turnTimeoutSeconds,
diff --git a/desktop/src/shared/api/types.ts b/desktop/src/shared/api/types.ts
index 50842d0d0..225e50cca 100644
--- a/desktop/src/shared/api/types.ts
+++ b/desktop/src/shared/api/types.ts
@@ -456,6 +456,11 @@ export type CreateManagedAgentInput = {
    * same persona runtime id, while still ignoring missing-runtime fallbacks.
    */
   harnessOverride?: boolean;
+  /**
+   * True when `harnessOverride` pins an automatically selected runtime for a
+   * runtime-less persona rather than a runtime the user explicitly selected.
+   */
+  implicitHarnessFallback?: boolean;
   agentArgs?: string[];
   mcpCommand?: string;
   turnTimeoutSeconds?: number;