fix(desktop): preserve agent model/provider when persona snapshot fields are blank

desktop/scripts/check-file-sizes.mjs

@@ -60,14 +60,17 @@ const overrides = new Map([
   // config-bridge: get_agent_config_surface/write_agent_config_field/put_agent_session_config
   // commands add ~40 lines. Queued to split.
   // branch cut; override bumped to cover the merged total. Queued to split.
+  // persona-blank-fallback: persona_snapshot_with_agent_config_fallback call
+  // sites add ~4 lines (extra fallback params + inline comments). build_deploy_payload
+  // fix (blank-persona provider/model fallback) adds ~6 lines. Bug fix.
   // archive/mod_tests.rs carries the full test module for archive/mod.rs:
   // unit tests + 4 real-relay integration tests (ignored, live-relay only).
   // Production logic in mod.rs is now ~527 lines (under 1000). mod_tests.rs
   // is test-only content; the override covers the test growth accumulated
   // across the local-archive + agent-metric-archive PR series. store_tests.rs
   // (~731 lines) is under 1000 so needs no override.
   ["src-tauri/src/archive/mod_tests.rs", 1208],
-  ["src-tauri/src/commands/agents.rs", 1437],
+  ["src-tauri/src/commands/agents.rs", 1443],
   // #1418 read-path fix: get_thread_replies' blocker fix (shared TIMELINE_KINDS
   // const + build_thread_replies_filter helper, mirroring the channel sibling so
   // the two p-gate filters can't drift) plus two guard unit tests. The file was
@@ -91,7 +94,9 @@ const overrides = new Map([
   // activity-feed threads avatar_url into build_managed_agent_summary for the
   // assistant-bubble pinned snapshot.
   // +1 for agent_pubkey field in setup payload (config-nudge card wire).
-  ["src-tauri/src/managed_agents/runtime.rs", 2208],
+  // persona-blank-fallback: resolve_effective_prompt_model_provider gains a
+  // record_provider param + applies persona_field_with_record_fallback. +5 lines.
+  ["src-tauri/src/managed_agents/runtime.rs", 2213],
   // config-bridge setup-payload env-boundary fix adds readiness wiring in
   // spawn_agent_child; load-bearing security fix, queued to split.
   ["src-tauri/src/managed_agents/config_bridge/reader.rs", 1016],

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

@@ -65,6 +65,7 @@ fn resolve_config_surface(
         personas,
         record.system_prompt.clone(),
         record.model.clone(),
+        record.provider.clone(),
     );
 
     // Build the baseline the reader overrides a live model against, paired with

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

@@ -258,12 +258,19 @@ async fn start_local_agent_with_preflight(
     // starts with the current persona config (system_prompt, model, provider,
     // env_vars). This clears the "out of date" drift badge without requiring a
     // delete+recreate. Agent-level env_vars overrides still win (persona_snapshot
-    // layers persona env under agent overrides).
+    // layers persona env under agent overrides). When the persona leaves model or
+    // provider blank, the agent record's own configured values are preserved so a
+    // user-set model/provider is never clobbered by an unconfigured persona.
     if let Some(persona_id) = record.persona_id.clone() {
         let personas = load_personas(app).unwrap_or_default();
         if let Some(persona) = personas.iter().find(|p| p.id == persona_id) {
             let snapshot =
-                crate::managed_agents::persona_events::persona_snapshot(persona, &record.env_vars);
+                crate::managed_agents::persona_events::persona_snapshot_with_agent_config_fallback(
+                    persona,
+                    &record.env_vars,
+                    record.model.as_deref(),    // fallback: record.model
+                    record.provider.as_deref(), // fallback: record.provider
+                );
             if let Some(prompt) = snapshot.system_prompt {
                 record.system_prompt = Some(prompt);
             }
@@ -330,9 +337,10 @@ fn build_deploy_payload(
     // stale derived env copies in `env_vars` (or have no provider at all for
     // imported personas whose derived keys were filtered at import time).
     //
-    // Precedence mirrors local spawn: persona structured model is authoritative
-    // when present; the agent record's `model` is a fallback for personas that
-    // don't specify one (or when no persona is linked).
+    // Precedence: persona field wins when non-blank; otherwise falls back to the
+    // record's own field (same blank-normalization as the snapshot path). This
+    // matches `persona_snapshot_with_agent_config_fallback` exactly — a blank
+    // persona field must not wipe a record value that the user configured.
     let (effective_model, effective_provider) = if let Some(pid) = record.persona_id.as_deref() {
         let personas = load_personas(app).map_err(|e| {
             format!(
@@ -343,11 +351,12 @@ fn build_deploy_payload(
             .into_iter()
             .find(|p| p.id == pid)
             .ok_or_else(|| format!("persona `{pid}` not found while building deploy payload"))?;
-        let model = persona.model.clone().or(record.model.clone());
-        let provider = persona.provider;
+        let fallback = crate::managed_agents::persona_events::persona_field_with_record_fallback;
+        let model = fallback(persona.model.as_deref(), record.model.as_deref()); // fallback: record.model
+        let provider = fallback(persona.provider.as_deref(), record.provider.as_deref()); // fallback: record.provider
         (model, provider)
     } else {
-        (record.model.clone(), None)
+        (record.model.clone(), record.provider.clone())
     };
 
     Ok(serde_json::json!({