fix: propagate persona harness edits to live agent instances (#1244)

Signed-off-by: Will Pfleger <pfleger.will@gmail.com>
Co-authored-by: npub1mn7jgtj4w2pd0g0zeuhxsa6jy6p0rewxz4kujt98my82ahfmp72sxjexk7 <dcfd242e557282d7a1e2cf2e6877522682f1e5c6156dc92ca7d90eaedd3b0f95@sprout-oss.stage.blox.sqprod.co>

desktop/scripts/check-file-sizes.mjs

@@ -37,15 +37,27 @@ const overrides = new Map([
   // self-contained repos_dir functions and their unit tests live in repos.rs;
   // this is the seam that must stay in nest.rs. Approved override; still queued
   // to split with the rest of this list.
-  ["src-tauri/src/managed_agents/nest.rs", 1447],
-  ["src-tauri/src/managed_agents/runtime.rs", 1953],
+  ["src-tauri/src/managed_agents/nest.rs", 1448],
+  // harness-persona-sync: persona-runtime resolution threaded into the spawn
+  // path here. Load-bearing feature growth; queued to split in the resolver
+  // unify refactor followup.
+  ["src-tauri/src/managed_agents/runtime.rs", 1966],
   ["src-tauri/src/managed_agents/personas.rs", 1080],
   ["src-tauri/src/managed_agents/persona_card.rs", 1050],
   // applyWorkspace reposDir parameter plus the validateReposDir binding,
-  // threaded through Tauri invokes for configurable repos_dir — a 4-line
-  // overage from load-bearing parameter plumbing, not generic debt growth.
-  // Approved override; still queued to split.
-  ["src/shared/api/tauri.ts", 1199],
+  // threaded through Tauri invokes for configurable repos_dir, plus the
+  // harness-persona-sync `harnessOverride` create-input bit — load-bearing
+  // parameter plumbing, not generic debt growth. Approved override; still
+  // queued to split.
+  ["src/shared/api/tauri.ts", 1202],
+  // harness-persona-sync feature growth, queued to split in the resolver-unify
+  // refactor followup. discovery.rs is dominated by the new test module
+  // (the effective_agent_command / divergent / create-time override matrix);
+  // types.rs adds the persona/instance harness fields; migration_tests.rs adds
+  // the harness-sync migration coverage. Load-bearing, not generic debt.
+  ["src-tauri/src/managed_agents/discovery.rs", 1043],
+  ["src-tauri/src/managed_agents/types.rs", 1010],
+  ["src-tauri/src/migration_tests.rs", 1033],
   ["src-tauri/src/nostr_convert.rs", 1126],
   ["src/shared/api/relayClientSession.ts", 1022],
   ["src-tauri/src/migration.rs", 1295],

desktop/src-tauri/src/commands/agent_models.rs

@@ -49,11 +49,21 @@ pub async fn get_agent_models(
         let resolved = resolve_command(&record.acp_command)
             .ok_or_else(|| missing_command_message(&record.acp_command, "ACP harness command"))?;
 
-        let args = normalize_agent_args(&record.agent_command, record.agent_args.clone());
+        // Resolve the effective harness from the linked persona (mirrors spawn),
+        // so model discovery runs against the persona's current harness, not the
+        // frozen record snapshot. An explicit per-agent override wins.
+        let personas = load_personas(&app).unwrap_or_default();
+        let effective_command = crate::managed_agents::effective_agent_command(
+            record.persona_id.as_deref(),
+            &personas,
+            record.agent_command_override.as_deref(),
+        );
 
-        let resolved_agent = resolve_command(&record.agent_command)
+        let args = normalize_agent_args(&effective_command, record.agent_args.clone());
+
+        let resolved_agent = resolve_command(&effective_command)
             .map(|p| p.display().to_string())
-            .unwrap_or_else(|| record.agent_command.clone());
+            .unwrap_or_else(|| effective_command.clone());
 
         // Same env layering as runtime spawn: persona env < agent env.
         // Model discovery needs the user's credentials. Fail closed on
@@ -65,7 +75,6 @@ pub async fn get_agent_models(
 
         // Resolve the effective model from the linked persona so the ModelPicker
         // dropdown shows the current persona model as selected.
-        let personas = load_personas(&app).unwrap_or_default();
         let (_prompt, effective_model, _provider) = resolve_effective_prompt_model_provider(
             record.persona_id.as_deref(),
             &personas,
@@ -197,8 +206,18 @@ pub async fn update_managed_agent(
         if let Some(acp_command) = input.acp_command {
             record.acp_command = acp_command;
         }
+        // Harness edit: the persona's runtime is authoritative, so we persist an
+        // explicit `agent_command_override` ONLY when the user picks a command
+        // that diverges from the persona. An empty/whitespace value (the
+        // "Inherit from persona" sentinel) clears the pin back to `None`. A
+        // name-only edit (`agent_command == None`) leaves the pin intact.
         if let Some(agent_command) = input.agent_command {
-            record.agent_command = agent_command;
+            let personas = load_personas(&app).unwrap_or_default();
+            record.agent_command_override = crate::managed_agents::divergent_agent_command_override(
+                record.persona_id.as_deref(),
+                &personas,
+                Some(&agent_command),
+            );
         }
         if let Some(agent_args) = input.agent_args {
             record.agent_args = agent_args;
@@ -253,10 +272,19 @@ pub async fn update_managed_agent(
                 &relay_ws_url_with_override(&state),
             );
             let display_name = record.name.clone();
+            // Avatar fallback derives from the EFFECTIVE harness (persona-wins),
+            // not the frozen snapshot, so an inherited harness picks the right
+            // default avatar.
+            let personas = load_personas(&app).unwrap_or_default();
+            let effective_command = crate::managed_agents::effective_agent_command(
+                record.persona_id.as_deref(),
+                &personas,
+                record.agent_command_override.as_deref(),
+            );
             let avatar_url = record
                 .avatar_url
                 .clone()
-                .or_else(|| managed_agent_avatar_url(&record.agent_command));
+                .or_else(|| managed_agent_avatar_url(&effective_command));
             let auth_tag = record.auth_tag.clone();
             Some((agent_keys, relay_url, display_name, avatar_url, auth_tag))
         } else {

desktop/src-tauri/src/commands/agents.rs

@@ -158,10 +158,9 @@ fn build_deploy_payload(
 
     // Resolve effective model/provider from the persona's structured fields.
     // Agent record's model takes precedence (user override via UI).
+    let personas = load_personas(app)
+        .map_err(|e| format!("failed to load personas for deploy payload resolution: {e}"))?;
     let (effective_model, effective_provider) = if let Some(ref pid) = record.persona_id {
-        let personas = load_personas(app).map_err(|e| {
-            format!("failed to load personas for deploy payload model resolution: {e}")
-        })?;
         let persona = personas.iter().find(|p| p.id == *pid);
         let model = record
             .model
@@ -173,6 +172,17 @@ fn build_deploy_payload(
         (record.model.clone(), None)
     };
 
+    // Resolve the effective harness (persona-wins, override-honored) so the
+    // remote provider runs the same harness a local spawn would — derive args
+    // from it rather than the frozen record snapshot.
+    let effective_command = crate::managed_agents::effective_agent_command(
+        record.persona_id.as_deref(),
+        &personas,
+        record.agent_command_override.as_deref(),
+    );
+    let effective_args =
+        crate::managed_agents::normalize_agent_args(&effective_command, record.agent_args.clone());
+
     Ok(serde_json::json!({
         "name": &record.name,
         // Resolve the per-agent pin against the active workspace relay here:
@@ -186,8 +196,8 @@ fn build_deploy_payload(
         ),
         "private_key_nsec": &record.private_key_nsec,
         "auth_tag": &record.auth_tag,
-        "agent_command": &record.agent_command,
-        "agent_args": &record.agent_args,
+        "agent_command": &effective_command,
+        "agent_args": &effective_args,
         "system_prompt": &record.system_prompt,
         "model": effective_model,
         "provider": effective_provider,
@@ -461,13 +471,31 @@ pub async fn create_managed_agent(
             None
         };
 
-        let agent_command = input
-            .agent_command
-            .as_deref()
-            .map(str::trim)
-            .filter(|value| !value.is_empty())
-            .map(str::to_string)
-            .unwrap_or_else(crate::managed_agents::default_agent_command);
+        // 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 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.
+        let agent_command = crate::managed_agents::effective_agent_command(
+            requested_persona_id.as_deref(),
+            &personas,
+            agent_command_override.as_deref(),
+        );
         let agent_args = normalize_agent_args(
             &agent_command,
             input
@@ -496,7 +524,6 @@ pub async fn create_managed_agent(
         // matches on this internal name, NOT display_name.
         let pack_metadata: Option<(std::path::PathBuf, String)> =
             requested_persona_id.as_deref().and_then(|pid| {
-                let personas = load_personas(&app).ok()?;
                 let persona = personas.iter().find(|p| p.id == pid)?;
                 let team_id = persona.source_team.as_deref()?;
                 let slug = persona.source_team_persona_slug.as_deref()?;
@@ -512,11 +539,11 @@ pub async fn create_managed_agent(
         // fallback. Storing it lets reconciliation compare against what was
         // actually published instead of re-deriving it.
         let persona_avatar_url = requested_persona_id.as_ref().and_then(|persona_id| {
-            load_personas(&app)
-                .ok()?
-                .into_iter()
+            personas
+                .iter()
                 .find(|persona| persona.id == *persona_id)?
                 .avatar_url
+                .clone()
         });
         let resolved_avatar_url = resolve_created_avatar_url(
             input.avatar_url.as_deref(),
@@ -540,6 +567,7 @@ pub async fn create_managed_agent(
                 .unwrap_or(DEFAULT_ACP_COMMAND)
                 .to_string(),
             agent_command,
+            agent_command_override,
             agent_args,
             mcp_command,
             turn_timeout_seconds: input
@@ -797,6 +825,16 @@ pub async fn start_managed_agent(
 
         let record = find_managed_agent_mut(&mut records, &pubkey)?;
 
+        // Resolve the effective harness for the avatar-fallback derivation in
+        // profile reconcile (the create-time snapshot may be empty or stale for
+        // a persona-inherited harness).
+        let reconcile_personas = load_personas(&app).unwrap_or_default();
+        let reconcile_effective_command = crate::managed_agents::effective_agent_command(
+            record.persona_id.as_deref(),
+            &reconcile_personas,
+            record.agent_command_override.as_deref(),
+        );
+
         let reconcile = ProfileReconcileData {
             private_key_nsec: record.private_key_nsec.clone(),
             name: record.name.clone(),
@@ -804,7 +842,7 @@ pub async fn start_managed_agent(
             avatar_url: record.avatar_url.clone(),
             auth_tag: record.auth_tag.clone(),
             pubkey: record.pubkey.clone(),
-            agent_command: record.agent_command.clone(),
+            agent_command: reconcile_effective_command,
             persona_id: record.persona_id.clone(),
         };
 

desktop/src-tauri/src/managed_agents/discovery.rs

@@ -243,6 +243,107 @@ pub fn default_agent_command() -> String {
         .to_string()
 }
 
+/// Resolve the agent command (harness) for a spawn/deploy/summary. Mirrors the
+/// model resolution in `resolve_effective_prompt_model_provider`: the linked
+/// persona wins so persona harness edits propagate on the next spawn. An
+/// explicit per-instance override (`agent_command_override`) takes precedence,
+/// matching the opt-in `record.model` override pattern.
+///
+/// Resolution order:
+///   1. explicit override (non-empty) — a deliberate per-instance pin;
+///   2. the linked persona's `runtime` id mapped to its primary command;
+///   3. `default_agent_command()` — no persona/runtime, or persona deleted.
+pub fn effective_agent_command(
+    persona_id: Option<&str>,
+    personas: &[crate::managed_agents::types::PersonaRecord],
+    agent_command_override: Option<&str>,
+) -> String {
+    if let Some(pin) = agent_command_override
+        .map(str::trim)
+        .filter(|value| !value.is_empty())
+    {
+        return pin.to_string();
+    }
+
+    persona_id
+        .and_then(|pid| personas.iter().find(|p| p.id == pid))
+        .and_then(|persona| persona.runtime.as_deref())
+        .and_then(known_acp_runtime_exact)
+        .and_then(|r| r.commands.first().copied())
+        .map(str::to_string)
+        .unwrap_or_else(default_agent_command)
+}
+
+/// Decide whether a user-picked harness command is an explicit per-instance
+/// pin or merely the persona's own runtime restated. Returns the override to
+/// persist: `Some(picked)` when it diverges from the persona, `None` when it
+/// inherits.
+///
+/// Comparison is by RUNTIME IDENTITY, not raw string: a persona on the `claude`
+/// runtime resolves to `claude-agent-acp`, but a client with only the
+/// `claude-code-acp` adapter installed sends that command instead. Both map to
+/// the same `claude` runtime, so neither is a real divergence — string equality
+/// would wrongly bake a pin. An unknown/custom command (no matching runtime)
+/// only inherits when it exactly equals the persona command.
+pub fn divergent_agent_command_override(
+    persona_id: Option<&str>,
+    personas: &[crate::managed_agents::types::PersonaRecord],
+    picked_command: Option<&str>,
+) -> Option<String> {
+    let picked = picked_command
+        .map(str::trim)
+        .filter(|value| !value.is_empty())?;
+    let persona_command = effective_agent_command(persona_id, personas, None);
+    let same_runtime = match (
+        known_acp_runtime(picked),
+        known_acp_runtime(&persona_command),
+    ) {
+        (Some(a), Some(b)) => std::ptr::eq(a, b),
+        _ => picked == persona_command,
+    };
+    if same_runtime {
+        None
+    } else {
+        Some(picked.to_string())
+    }
+}
+
+/// Decide the `agent_command_override` to persist at AGENT CREATE time.
+///
+/// A persona-backed create receives its harness command from
+/// `resolvePersonaRuntime` (frontend), which produces a divergent command in two
+/// distinct cases that the backend MUST tell apart:
+///
+/// - DELIBERATE OVERRIDE (`harness_override` true): the user explicitly picked a
+///   non-persona runtime in a deploy dialog that exposes a runtime selector (e.g.
+///   `AddChannelBotDialog`, "overriding persona preferences"). This is a real pin
+///   and is preserved via `divergent_agent_command_override`.
+/// - MISSING-RUNTIME FALLBACK (`harness_override` false): the persona's runtime
+///   isn't installed locally, so `resolvePersonaRuntime` substitutes a fallback
+///   default. This is NOT a pin — baking it would freeze the agent on the fallback
+///   harness even after the persona's runtime is installed and the persona is
+///   re-edited, the exact bug this resolver chain exists to prevent. Stores `None`
+///   so the persona stays authoritative.
+///
+/// `isOverridden` from `resolvePersonaRuntime` cannot distinguish these — it is
+/// `true` for BOTH — so the caller must thread the explicit user-intent bit.
+///
+/// Persona-less creates (`persona_id` is `None`, e.g. the standalone
+/// CreateAgentDialog) have no persona to inherit, so the picked command is always a
+/// real pin and is preserved via `divergent_agent_command_override` regardless of
+/// `harness_override`.
+pub fn create_time_agent_command_override(
+    persona_id: Option<&str>,
+    personas: &[crate::managed_agents::types::PersonaRecord],
+    picked_command: Option<&str>,
+    harness_override: bool,
+) -> Option<String> {
+    if persona_id.is_some() && !harness_override {
+        return None;
+    }
+    divergent_agent_command_override(persona_id, personas, picked_command)
+}
+
 fn default_agent_args(command: &str) -> Option<Vec<String>> {
     match normalize_command_identity(command).as_str() {
         "goose" => Some(vec!["acp".to_string()]),
@@ -577,9 +678,10 @@ mod tests {
     use std::path::PathBuf;
 
     use super::{
-        classify_runtime, default_agent_command, find_via_login_shell, managed_agent_avatar_url,
-        normalize_agent_args, BUZZ_AGENT_AVATAR_URL, CLAUDE_CODE_AVATAR_URL, CODEX_AVATAR_URL,
-        GOOSE_AVATAR_URL,
+        classify_runtime, create_time_agent_command_override, default_agent_command,
+        divergent_agent_command_override, effective_agent_command, find_via_login_shell,
+        managed_agent_avatar_url, normalize_agent_args, BUZZ_AGENT_AVATAR_URL,
+        CLAUDE_CODE_AVATAR_URL, CODEX_AVATAR_URL, GOOSE_AVATAR_URL,
     };
     use crate::managed_agents::AcpAvailabilityStatus;
 
@@ -760,4 +862,181 @@ mod tests {
         assert_eq!(cmd.as_deref(), Some("codex-acp"));
         assert_eq!(path.as_deref(), Some("/opt/homebrew/bin/codex-acp"));
     }
+
+    fn persona_with_runtime(
+        id: &str,
+        runtime: Option<&str>,
+    ) -> crate::managed_agents::PersonaRecord {
+        crate::managed_agents::PersonaRecord {
+            id: id.to_string(),
+            display_name: id.to_string(),
+            avatar_url: None,
+            system_prompt: String::new(),
+            runtime: runtime.map(str::to_string),
+            model: None,
+            provider: None,
+            name_pool: Vec::new(),
+            is_builtin: false,
+            is_active: true,
+            source_team: None,
+            source_team_persona_slug: None,
+            env_vars: std::collections::BTreeMap::new(),
+            created_at: "2026-06-09T00:00:00Z".to_string(),
+            updated_at: "2026-06-09T00:00:00Z".to_string(),
+        }
+    }
+
+    #[test]
+    fn effective_agent_command_explicit_override_wins() {
+        // An explicit pin beats the persona's runtime.
+        let personas = vec![persona_with_runtime("p1", Some("claude"))];
+        assert_eq!(
+            effective_agent_command(Some("p1"), &personas, Some("codex-acp")),
+            "codex-acp"
+        );
+    }
+
+    #[test]
+    fn effective_agent_command_inherits_persona_runtime() {
+        // No override → persona runtime id maps to its primary command.
+        let personas = vec![persona_with_runtime("p1", Some("claude"))];
+        assert_eq!(
+            effective_agent_command(Some("p1"), &personas, None),
+            "claude-agent-acp"
+        );
+    }
+
+    #[test]
+    fn effective_agent_command_empty_override_is_inherit() {
+        // A blank/whitespace override is treated as "inherit", not a pin.
+        let personas = vec![persona_with_runtime("p1", Some("goose"))];
+        assert_eq!(
+            effective_agent_command(Some("p1"), &personas, Some("   ")),
+            "goose"
+        );
+    }
+
+    #[test]
+    fn effective_agent_command_falls_back_to_default() {
+        // No override, no persona runtime, and a deleted persona all fall back
+        // to the bundled default.
+        let personas = vec![persona_with_runtime("p1", None)];
+        assert_eq!(
+            effective_agent_command(Some("p1"), &personas, None),
+            default_agent_command()
+        );
+        assert_eq!(
+            effective_agent_command(Some("gone"), &personas, None),
+            default_agent_command()
+        );
+        assert_eq!(
+            effective_agent_command(None, &personas, None),
+            default_agent_command()
+        );
+    }
+
+    #[test]
+    fn divergent_override_none_when_picked_matches_persona_runtime() {
+        // The persona-backed create/edit flow sends the persona's resolved
+        // command. It must be treated as "inherit" (None), not a pin.
+        let personas = vec![persona_with_runtime("p1", Some("goose"))];
+        assert_eq!(
+            divergent_agent_command_override(Some("p1"), &personas, Some("goose")),
+            None
+        );
+    }
+
+    #[test]
+    fn divergent_override_none_for_alternate_command_of_same_runtime() {
+        // A client with only `claude-code-acp` installed sends that command for
+        // a `claude` persona whose primary command is `claude-agent-acp`. Both
+        // map to the `claude` runtime, so it inherits — string equality would
+        // wrongly bake a pin (CRITICAL-3).
+        let personas = vec![persona_with_runtime("p1", Some("claude"))];
+        assert_eq!(
+            divergent_agent_command_override(Some("p1"), &personas, Some("claude-code-acp")),
+            None
+        );
+    }
+
+    #[test]
+    fn divergent_override_some_when_picked_is_different_runtime() {
+        // A deliberate pin to a different runtime is preserved.
+        let personas = vec![persona_with_runtime("p1", Some("goose"))];
+        assert_eq!(
+            divergent_agent_command_override(Some("p1"), &personas, Some("codex-acp")),
+            Some("codex-acp".to_string())
+        );
+    }
+
+    #[test]
+    fn divergent_override_none_for_empty_or_absent_pick() {
+        // The "Inherit from persona" sentinel (empty) and a name-only edit
+        // (absent) both clear the pin.
+        let personas = vec![persona_with_runtime("p1", Some("goose"))];
+        assert_eq!(
+            divergent_agent_command_override(Some("p1"), &personas, Some("   ")),
+            None
+        );
+        assert_eq!(
+            divergent_agent_command_override(Some("p1"), &personas, None),
+            None
+        );
+    }
+
+    #[test]
+    fn create_time_override_none_when_persona_runtime_not_installed() {
+        // CRITICAL-3 (Case 3): a `claude`-persona agent created on a machine
+        // where the claude adapter isn't installed. `resolvePersonaRuntime`
+        // falls back to the default (`buzz-agent`) and sends THAT command with
+        // `harness_override` false (the user did not pick it). At create this
+        // is a fallback, not a deliberate pin — it must store `None` so the
+        // agent inherits the persona's runtime once it's installed and the
+        // persona is re-edited. Baking `Some("buzz-agent")` here is the exact
+        // bug this resolver chain exists to kill.
+        let personas = vec![persona_with_runtime("p1", Some("claude"))];
+        assert_eq!(
+            create_time_agent_command_override(Some("p1"), &personas, Some("buzz-agent"), false),
+            None
+        );
+    }
+
+    #[test]
+    fn create_time_override_some_when_user_deliberately_overrides_installed_runtime() {
+        // Case 2 + deliberate override: the persona's `claude` runtime IS
+        // available, but the user explicitly picked `codex` in a deploy dialog's
+        // runtime selector ("overriding persona preferences"), so the frontend
+        // sends `codex-acp` with `harness_override` true. This is a real pin and
+        // MUST be preserved — returning `None` would silently swallow the
+        // deliberate override and inherit `claude` on spawn.
+        let personas = vec![persona_with_runtime("p1", Some("claude"))];
+        assert_eq!(
+            create_time_agent_command_override(Some("p1"), &personas, Some("codex-acp"), true),
+            Some("codex-acp".to_string())
+        );
+    }
+
+    #[test]
+    fn create_time_override_none_when_persona_runtime_installed() {
+        // Case 2: the persona's runtime is available, so `resolvePersonaRuntime`
+        // sends the persona's own command with no override. Inherits — no pin.
+        let personas = vec![persona_with_runtime("p1", Some("goose"))];
+        assert_eq!(
+            create_time_agent_command_override(Some("p1"), &personas, Some("goose"), false),
+            None
+        );
+    }
+
+    #[test]
+    fn create_time_override_preserves_pin_for_persona_less_create() {
+        // The standalone CreateAgentDialog creates persona-LESS agents. With no
+        // persona to inherit, the picked command IS the agent's harness and must
+        // be preserved as a real pin (divergence from the bundled default),
+        // regardless of the override flag.
+        let personas = vec![persona_with_runtime("p1", Some("goose"))];
+        assert_eq!(
+            create_time_agent_command_override(None, &personas, Some("codex-acp"), false),
+            Some("codex-acp".to_string())
+        );
+    }
 }

desktop/src-tauri/src/managed_agents/nest.rs

@@ -995,6 +995,7 @@ mod tests {
             avatar_url: None,
             acp_command: String::new(),
             agent_command: String::new(),
+            agent_command_override: None,
             agent_args: vec![],
             mcp_command: String::new(),
             turn_timeout_seconds: 0,

desktop/src-tauri/src/managed_agents/relay_mesh.rs

@@ -71,6 +71,7 @@ mod tests {
             avatar_url: None,
             acp_command: "buzz-acp".into(),
             agent_command: "goose".into(),
+            agent_command_override: None,
             agent_args: vec![],
             mcp_command: String::new(),
             turn_timeout_seconds: 320,

desktop/src-tauri/src/managed_agents/restore.rs

@@ -198,11 +198,20 @@ pub async fn restore_managed_agents_on_launch(
     // releasing the lock. This mirrors the fire-and-forget pattern in
     // start_managed_agent — ensuring boot-restored agents get the same profile
     // self-healing as UI-started agents.
+    let reconcile_personas = super::load_personas(app).unwrap_or_default();
     let reconcile_items: Vec<(String, crate::commands::ProfileReconcileData)> =
         successfully_spawned
             .iter()
             .filter_map(|pubkey| {
                 let record = records.iter().find(|r| r.pubkey == *pubkey)?;
+                // Resolve the effective harness for the avatar-fallback
+                // derivation (the snapshot may be empty/stale for an inherited
+                // harness). Mirrors the UI start path.
+                let effective_command = crate::managed_agents::effective_agent_command(
+                    record.persona_id.as_deref(),
+                    &reconcile_personas,
+                    record.agent_command_override.as_deref(),
+                );
                 Some((
                     pubkey.clone(),
                     crate::commands::ProfileReconcileData {
@@ -212,7 +221,7 @@ pub async fn restore_managed_agents_on_launch(
                         avatar_url: record.avatar_url.clone(),
                         auth_tag: record.auth_tag.clone(),
                         pubkey: record.pubkey.clone(),
-                        agent_command: record.agent_command.clone(),
+                        agent_command: effective_command,
                         persona_id: record.persona_id.clone(),
                     },
                 ))

desktop/src-tauri/src/managed_agents/runtime.rs

@@ -1353,15 +1353,29 @@ pub fn build_managed_agent_summary(
             record.model.clone(),
         );
 
+    // Resolve the effective harness the same way, then derive args/mcp from it,
+    // so the UI reflects the persona's current harness (or an explicit pin).
+    let effective_command = crate::managed_agents::effective_agent_command(
+        record.persona_id.as_deref(),
+        personas,
+        record.agent_command_override.as_deref(),
+    );
+    let effective_args = normalize_agent_args(&effective_command, record.agent_args.clone());
+    let effective_mcp_command = known_acp_runtime(&effective_command)
+        .and_then(|r| r.mcp_command)
+        .unwrap_or("")
+        .to_string();
+
     Ok(ManagedAgentSummary {
         pubkey: record.pubkey.clone(),
         name: record.name.clone(),
         persona_id: record.persona_id.clone(),
         relay_url: record.relay_url.clone(),
         acp_command: record.acp_command.clone(),
-        agent_command: record.agent_command.clone(),
-        agent_args: record.agent_args.clone(),
-        mcp_command: record.mcp_command.clone(),
+        agent_command: effective_command,
+        agent_command_override: record.agent_command_override.clone(),
+        agent_args: effective_args,
+        mcp_command: effective_mcp_command,
         turn_timeout_seconds: record.turn_timeout_seconds,
         idle_timeout_seconds: record.idle_timeout_seconds,
         max_turn_duration_seconds: record.max_turn_duration_seconds,
@@ -1500,27 +1514,40 @@ pub fn spawn_agent_child(
     let stderr = stdout
         .try_clone()
         .map_err(|error| format!("failed to clone log handle: {error}"))?;
-    let agent_args = normalize_agent_args(&record.agent_command, record.agent_args.clone());
+    // Resolve the effective harness (agent command) from the linked persona, so
+    // persona harness edits propagate on the next spawn; an explicit per-agent
+    // override wins. `agent_args` and `mcp_command` are pure derivations of the
+    // command, so we recompute them from the effective value rather than the
+    // frozen record snapshot. Mirrors the model resolution below.
+    let personas = super::load_personas(app).unwrap_or_default();
+    let effective_command = super::effective_agent_command(
+        record.persona_id.as_deref(),
+        &personas,
+        record.agent_command_override.as_deref(),
+    );
+    let agent_args = normalize_agent_args(&effective_command, record.agent_args.clone());
     let resolved_acp_command = resolve_command(&record.acp_command)
         .ok_or_else(|| missing_command_message(&record.acp_command, "ACP harness command"))?;
-    let resolved_mcp_command: Option<std::path::PathBuf> = if record.mcp_command.is_empty() {
+    let effective_mcp_command = known_acp_runtime(&effective_command)
+        .and_then(|r| r.mcp_command)
+        .unwrap_or("");
+    let resolved_mcp_command: Option<std::path::PathBuf> = if effective_mcp_command.is_empty() {
         None
     } else {
-        match resolve_command(&record.mcp_command) {
+        match resolve_command(effective_mcp_command) {
             Some(path) => Some(path),
             None => {
                 eprintln!(
-                    "buzz-desktop: mcp_command {:?} not found, skipping",
-                    record.mcp_command
+                    "buzz-desktop: mcp_command {effective_mcp_command:?} not found, skipping"
                 );
                 None
             }
         }
     };
     // Resolve agent command to a full path (DMG launches have minimal PATH).
-    let resolved_agent_command = resolve_command(&record.agent_command)
+    let resolved_agent_command = resolve_command(&effective_command)
         .map(|p| p.display().to_string())
-        .unwrap_or_else(|| record.agent_command.clone());
+        .unwrap_or_else(|| effective_command.clone());
 
     // The agent's effective relay drives both the child's relay connection
     // (BUZZ_RELAY_URL) and git credential-helper URL: an explicit per-agent
@@ -1571,7 +1598,7 @@ pub fn spawn_agent_child(
     }
     // Enable MCP hook tools (_Stop, _PostCompact) for agents that need them.
     // Uses "*" because build_mcp_servers() hard-codes the server name to "buzz-mcp".
-    let runtime_meta = known_acp_runtime(&record.agent_command);
+    let runtime_meta = known_acp_runtime(&effective_command);
     if runtime_meta.is_some_and(|r| r.mcp_hooks) {
         command.env("MCP_HOOK_SERVERS", "*");
     }
@@ -1610,7 +1637,7 @@ pub fn spawn_agent_child(
     // source of truth, so persona edits reach the agent on the next spawn. Fall
     // back to the record snapshot only when no persona is linked or it was
     // deleted. Provider flows from the persona (the record has no provider).
-    let personas = super::load_personas(app).unwrap_or_default();
+    // `personas` was loaded above for the harness resolution.
     let (effective_prompt, effective_model, effective_provider) =
         resolve_effective_prompt_model_provider(
             record.persona_id.as_deref(),

desktop/src-tauri/src/managed_agents/runtime/tests.rs

@@ -132,6 +132,7 @@ fn fixture(
         avatar_url: None,
         acp_command: "buzz-acp".into(),
         agent_command: "goose".into(),
+        agent_command_override: None,
         agent_args: vec![],
         mcp_command: String::new(),
         turn_timeout_seconds: 320,

desktop/src-tauri/src/managed_agents/team_repair.rs

@@ -281,6 +281,7 @@ mod tests {
             avatar_url: None,
             acp_command: String::new(),
             agent_command: String::new(),
+            agent_command_override: None,
             agent_args: vec![],
             mcp_command: String::new(),
             turn_timeout_seconds: 0,

desktop/src-tauri/src/managed_agents/types.rs

@@ -109,6 +109,15 @@ 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.
+    #[serde(default)]
+    pub agent_command_override: Option<String>,
     pub agent_args: Vec<String>,
     pub mcp_command: String,
     pub turn_timeout_seconds: u64,
@@ -226,6 +235,11 @@ 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).
+    pub agent_command_override: Option<String>,
     pub agent_args: Vec<String>,
     pub mcp_command: String,
     pub turn_timeout_seconds: u64,
@@ -262,6 +276,13 @@ pub struct CreateManagedAgentRequest {
     pub relay_url: Option<String>,
     pub acp_command: Option<String>,
     pub agent_command: Option<String>,
+    /// True when `agent_command` is a runtime the user deliberately picked to
+    /// override the linked persona (a deploy-dialog runtime selector). Distinguishes
+    /// a real pin from a missing-runtime fallback so a persona-backed create only
+    /// stores an `agent_command_override` for the former. Defaults `false`: callers
+    /// that don't set it (persona-less creates, fallback divergence) inherit.
+    #[serde(default)]
+    pub harness_override: bool,
     #[serde(default)]
     pub agent_args: Vec<String>,
     pub mcp_command: Option<String>,

desktop/src-tauri/src/migration.rs

@@ -819,12 +819,31 @@ pub fn migrate_packs_to_teams(app: &tauri::AppHandle) {
 }
 
 fn reconcile_mcp_commands_in_file(path: &Path) {
+    // Resolve each record's EFFECTIVE harness (persona-wins, override-honored)
+    // before deriving its mcp_command, so a persona-inherited harness switch
+    // doesn't leave a stale persisted mcp_command. The persona runtime is read
+    // from the sibling personas.json; missing entries fall back to the record's
+    // own agent_command (the create-time snapshot).
+    let persona_runtimes = load_persona_runtimes(path);
     patch_json_records(path, |obj| {
-        let agent_command = match obj.get("agent_command").and_then(|v| v.as_str()) {
+        let override_cmd = obj
+            .get("agent_command_override")
+            .and_then(|v| v.as_str())
+            .map(str::trim)
+            .filter(|v| !v.is_empty());
+        let snapshot = obj.get("agent_command").and_then(|v| v.as_str());
+        let persona_cmd = obj
+            .get("persona_id")
+            .and_then(|v| v.as_str())
+            .and_then(|pid| persona_runtimes.get(pid))
+            .map(String::as_str)
+            .and_then(crate::managed_agents::known_acp_runtime_exact)
+            .and_then(|r| r.commands.first().copied());
+        let effective_command = match override_cmd.or(persona_cmd).or(snapshot) {
             Some(cmd) => cmd.to_string(),
             None => return false,
         };
-        let Some(runtime) = crate::managed_agents::known_acp_runtime(&agent_command) else {
+        let Some(runtime) = crate::managed_agents::known_acp_runtime(&effective_command) else {
             return false;
         };
         let expected = runtime.mcp_command.unwrap_or("");
@@ -843,7 +862,7 @@ fn reconcile_mcp_commands_in_file(path: &Path) {
         eprintln!(
             "buzz-desktop: runtime-reconcile: {:?} ({:?}): mcp_command {:?} → {:?}",
             obj.get("name").and_then(|v| v.as_str()).unwrap_or("?"),
-            agent_command,
+            effective_command,
             current,
             expected,
         );
@@ -855,6 +874,31 @@ fn reconcile_mcp_commands_in_file(path: &Path) {
     });
 }
 
+/// Build a `persona_id → runtime` map from the personas.json sibling of the
+/// given managed-agents.json path. Returns an empty map when personas can't be
+/// read or parsed — callers then fall back to the record's own snapshot.
+fn load_persona_runtimes(agents_path: &Path) -> std::collections::HashMap<String, String> {
+    let mut map = std::collections::HashMap::new();
+    let Some(personas_path) = agents_path.parent().map(|dir| dir.join("personas.json")) else {
+        return map;
+    };
+    let Ok(content) = std::fs::read_to_string(&personas_path) else {
+        return map;
+    };
+    let Ok(records) = serde_json::from_str::<Vec<serde_json::Value>>(&content) else {
+        return map;
+    };
+    for record in records {
+        if let (Some(id), Some(runtime)) = (
+            record.get("id").and_then(|v| v.as_str()),
+            record.get("runtime").and_then(|v| v.as_str()),
+        ) {
+            map.insert(id.to_string(), runtime.to_string());
+        }
+    }
+    map
+}
+
 fn replace_command_field(
     obj: &mut serde_json::Map<String, serde_json::Value>,
     field: &str,

desktop/src-tauri/src/migration_tests.rs

@@ -829,6 +829,55 @@ fn reconcile_mcp_commands_handles_mixed_agents() {
     assert_eq!(records[3]["mcp_command"], "buzz-dev-mcp");
 }
 
+#[test]
+fn reconcile_mcp_commands_resolves_persona_runtime_over_stale_snapshot() {
+    // The frozen snapshot is buzz-agent (wants buzz-dev-mcp), but the linked
+    // persona's runtime is goose (wants no mcp). The reconcile must follow the
+    // EFFECTIVE harness (persona-wins) and clear the stale buzz-mcp-server.
+    let dir = tempfile::tempdir().unwrap();
+    write_agents_json(
+        dir.path(),
+        &serde_json::json!([{
+            "name": "Fizz",
+            "persona_id": "p1",
+            "agent_command": "buzz-agent",
+            "mcp_command": "buzz-mcp-server"
+        }]),
+    );
+    write_personas_json(
+        dir.path(),
+        &serde_json::json!([{"id": "p1", "runtime": "goose"}]),
+    );
+    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_mcp_commands_honors_explicit_override_over_persona() {
+    // An explicit per-instance pin (agent_command_override) beats the persona
+    // runtime: persona is goose (no mcp) but the pin is buzz-agent, so the
+    // reconcile sets the buzz-agent mcp_command.
+    let dir = tempfile::tempdir().unwrap();
+    write_agents_json(
+        dir.path(),
+        &serde_json::json!([{
+            "name": "Fizz",
+            "persona_id": "p1",
+            "agent_command": "goose",
+            "agent_command_override": "buzz-agent",
+            "mcp_command": ""
+        }]),
+    );
+    write_personas_json(
+        dir.path(),
+        &serde_json::json!([{"id": "p1", "runtime": "goose"}]),
+    );
+    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"], "buzz-dev-mcp");
+}
+
 #[test]
 fn reconcile_mcp_commands_skips_record_without_agent_command() {
     let dir = tempfile::tempdir().unwrap();

desktop/src/features/agents/channelAgents.ts

@@ -60,6 +60,13 @@ export type CreateChannelManagedAgentInput = {
   systemPrompt?: string;
   avatarUrl?: string;
   personaId?: string | null;
+  /**
+   * True when `runtime` is a runtime the user deliberately picked to override
+   * the persona (a deploy-dialog runtime selector), as opposed to a
+   * missing-runtime fallback. Forwarded to the backend so a persona-backed
+   * create only pins the harness for a deliberate override.
+   */
+  harnessOverride?: boolean;
   /** Preferred model ID from the persona. Passed to createManagedAgent. */
   model?: string;
   role?: Exclude<ChannelRole, "owner">;
@@ -368,6 +375,7 @@ export async function createChannelManagedAgent(
     name: trimmedName,
     acpCommand: "buzz-acp",
     agentCommand: input.runtime.command,
+    harnessOverride: input.harnessOverride ?? false,
     agentArgs: input.runtime.defaultArgs,
     mcpCommand: input.runtime.mcpCommand ?? "",
     personaId: input.personaId ?? undefined,

desktop/src/features/agents/ui/EditAgentDialog.tsx

@@ -41,6 +41,12 @@ export function EditAgentDialog({
   const [relayUrl, setRelayUrl] = React.useState(agent.relayUrl);
   const [acpCommand, setAcpCommand] = React.useState(agent.acpCommand);
   const [agentCommand, setAgentCommand] = React.useState(agent.agentCommand);
+  // Whether the harness inherits from the linked persona (no explicit pin).
+  // Only meaningful when a persona is linked; seeded from the override field
+  // so an unset override shows as "inherit" rather than re-pinning on save.
+  const [inheritHarness, setInheritHarness] = React.useState(
+    agent.personaId != null && agent.agentCommandOverride == null,
+  );
   const [agentArgs, setAgentArgs] = React.useState(agent.agentArgs.join(","));
   const [mcpCommand, setMcpCommand] = React.useState(agent.mcpCommand);
   const [mcpToolsets, setMcpToolsets] = React.useState(agent.mcpToolsets ?? "");
@@ -55,11 +61,14 @@ export function EditAgentDialog({
   );
   const [envVars, setEnvVars] = React.useState<EnvVarsValue>(agent.envVars);
   const personasQuery = usePersonasQuery();
-  const inheritedEnvVars = React.useMemo(() => {
-    if (!agent.personaId) return {};
-    const persona = personasQuery.data?.find((p) => p.id === agent.personaId);
-    return persona?.envVars ?? {};
-  }, [agent.personaId, personasQuery.data]);
+  const linkedPersona = React.useMemo(
+    () =>
+      agent.personaId
+        ? (personasQuery.data?.find((p) => p.id === agent.personaId) ?? null)
+        : null,
+    [agent.personaId, personasQuery.data],
+  );
+  const inheritedEnvVars = linkedPersona?.envVars ?? {};
   const [respondTo, setRespondTo] = React.useState<RespondToMode>(
     agent.respondTo,
   );
@@ -78,6 +87,9 @@ export function EditAgentDialog({
       setRelayUrl(agent.relayUrl);
       setAcpCommand(agent.acpCommand);
       setAgentCommand(agent.agentCommand);
+      setInheritHarness(
+        agent.personaId != null && agent.agentCommandOverride == null,
+      );
       setAgentArgs(agent.agentArgs.join(","));
       setMcpCommand(agent.mcpCommand);
       setMcpToolsets(agent.mcpToolsets ?? "");
@@ -127,6 +139,20 @@ export function EditAgentDialog({
         .map((v) => v.trim())
         .filter((v) => v.length > 0);
 
+      // Harness pin resolution. The backend treats an empty string as the
+      // "inherit from persona" sentinel (clears the override) and any concrete
+      // command as an explicit pin. When inheriting, only send the sentinel if
+      // there's a pin to clear — a name-only edit must leave the record alone.
+      // When pinning, send the command only if it diverges from the resolved
+      // value the dialog opened with, so an unchanged save stays a no-op.
+      const agentCommandUpdate = inheritHarness
+        ? agent.agentCommandOverride != null
+          ? ""
+          : undefined
+        : agentCommand.trim() !== agent.agentCommand
+          ? agentCommand.trim()
+          : undefined;
+
       const input: UpdateManagedAgentInput = {
         pubkey: agent.pubkey,
         name: name.trim() !== agent.name ? name.trim() : undefined,
@@ -136,10 +162,7 @@ export function EditAgentDialog({
           acpCommand.trim() !== agent.acpCommand
             ? acpCommand.trim()
             : undefined,
-        agentCommand:
-          agentCommand.trim() !== agent.agentCommand
-            ? agentCommand.trim()
-            : undefined,
+        agentCommand: agentCommandUpdate,
         agentArgs:
           parsedArgs.join(",") !== agent.agentArgs.join(",")
             ? parsedArgs
@@ -214,6 +237,34 @@ export function EditAgentDialog({
               onModeChange={setRespondTo}
             />
 
+            {linkedPersona ? (
+              <div className="space-y-1.5">
+                <label
+                  className="flex items-center gap-2 text-sm font-medium"
+                  htmlFor="agent-inherit-harness"
+                >
+                  <input
+                    checked={inheritHarness}
+                    id="agent-inherit-harness"
+                    onChange={(event) =>
+                      setInheritHarness(event.target.checked)
+                    }
+                    type="checkbox"
+                  />
+                  Inherit harness from persona
+                </label>
+                <p className="text-xs text-muted-foreground">
+                  {inheritHarness
+                    ? `Uses the ${linkedPersona.displayName} persona's runtime${
+                        linkedPersona.runtime
+                          ? ` (${linkedPersona.runtime})`
+                          : ""
+                      }. Editing the persona and respawning propagates the new harness.`
+                    : "Pins this agent to a specific harness command, overriding the persona's runtime."}
+                </p>
+              </div>
+            ) : null}
+
             <CreateAgentRuntimeFields
               acpCommand={acpCommand}
               agentArgs={agentArgs}
@@ -231,7 +282,10 @@ export function EditAgentDialog({
               onTurnTimeoutChange={setTurnTimeoutSeconds}
               parallelism={parallelism}
               relayUrl={relayUrl}
-              selectedRuntimeId="custom"
+              // "custom" surfaces the agent-command input so a user can pin a
+              // harness; when inheriting we hide it (any non-"custom" id) since
+              // the command comes from the persona's runtime.
+              selectedRuntimeId={inheritHarness ? "inherit" : "custom"}
               systemPrompt={systemPrompt}
               turnTimeoutSeconds={turnTimeoutSeconds}
             />

desktop/src/features/channels/ui/AddChannelBotDialog.tsx

@@ -355,6 +355,10 @@ export function AddChannelBotDialog({
           runtime: resolved.runtime ?? effectiveFallback ?? providers[0],
           name: persona.displayName,
           personaId: persona.id,
+          // A deliberate runtime-selector pick overrides the persona; a Case-3
+          // fallback (persona runtime not installed) is NOT a pin. `isOverridden`
+          // alone can't tell them apart, so thread the explicit user intent.
+          harnessOverride: isOverrideActive,
           systemPrompt: persona.systemPrompt,
           avatarUrl: persona.avatarUrl ?? undefined,
           model: persona.model ?? undefined,

desktop/src/shared/api/tauri.ts

@@ -198,6 +198,7 @@ export type RawManagedAgent = {
   relay_url: string;
   acp_command: string;
   agent_command: string;
+  agent_command_override?: string | null;
   agent_args: string[];
   mcp_command: string;
   turn_timeout_seconds: number;
@@ -856,6 +857,7 @@ export function fromRawManagedAgent(agent: RawManagedAgent): ManagedAgent {
     relayUrl: agent.relay_url,
     acpCommand: agent.acp_command,
     agentCommand: agent.agent_command,
+    agentCommandOverride: agent.agent_command_override ?? null,
     agentArgs: agent.agent_args,
     mcpCommand: agent.mcp_command,
     turnTimeoutSeconds: agent.turn_timeout_seconds,
@@ -1005,6 +1007,7 @@ export async function createManagedAgent(input: CreateManagedAgentInput) {
         relayUrl: input.relayUrl,
         acpCommand: input.acpCommand,
         agentCommand: input.agentCommand,
+        harnessOverride: input.harnessOverride ?? false,
         agentArgs: input.agentArgs,
         mcpCommand: input.mcpCommand,
         mcpToolsets: input.mcpToolsets,

desktop/src/shared/api/types.ts

@@ -277,7 +277,14 @@ export type ManagedAgent = {
   personaId: string | null;
   relayUrl: string;
   acpCommand: string;
+  /** Resolved/effective harness command (persona-wins, override-honored). */
   agentCommand: string;
+  /**
+   * Explicit per-instance harness pin. `null` means the agent inherits its
+   * harness from the linked persona's runtime. Lets the Edit dialog show
+   * "Inherit from persona" vs a concrete pin.
+   */
+  agentCommandOverride: string | null;
   agentArgs: string[];
   mcpCommand: string;
   turnTimeoutSeconds: number;
@@ -340,6 +347,13 @@ export type CreateManagedAgentInput = {
   relayUrl?: string;
   acpCommand?: string;
   agentCommand?: string;
+  /**
+   * True when `agentCommand` is a runtime the user deliberately picked to
+   * override the linked persona (a deploy-dialog runtime selector). Lets the
+   * backend distinguish a real pin from a missing-runtime fallback. Omit/false
+   * for persona-less creates and fallback divergence — both inherit.
+   */
+  harnessOverride?: boolean;
   agentArgs?: string[];
   mcpCommand?: string;
   turnTimeoutSeconds?: number;