From 53836cc62ee2c31db6461f923fef275c8c93fc4c Mon Sep 17 00:00:00 2001
From: danielhanchen <michaelhan2050@gmail.com>
Date: Fri, 17 Jul 2026 23:18:52 +0000
Subject: [PATCH] Never let legacy migration evict existing per-model configs

Protecting the just-migrated keys during budget enforcement meant legacy
entries could evict the user's existing current-schema configs to make room,
and could still deadlock when unevictable future-schema records were present.
Protect the existing entries instead and let only the just-migrated legacy
entries be evicted when over budget: importing old settings never discards a
newer config, and since existing entries already fit the budget it cannot
deadlock.
---
 .../model-config/per-model-config.ts          | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/studio/frontend/src/features/model-picker/model-config/per-model-config.ts b/studio/frontend/src/features/model-picker/model-config/per-model-config.ts
index 5c0cb97bad..f1b4140718 100644
--- a/studio/frontend/src/features/model-picker/model-config/per-model-config.ts
+++ b/studio/frontend/src/features/model-picker/model-config/per-model-config.ts
@@ -262,6 +262,10 @@ function migrateLegacyLoadSettingsOnce(): void {
       return;
     }
     const map = readMapRaw();
+    // Snapshot the user's existing entries before merging: legacy settings are
+    // imported only into spare budget and must never evict a config the user
+    // already saved in the current schema.
+    const existingKeys = new Set(Object.keys(map));
     const migratedKeys = mergeLegacyEntries(
       map,
       legacy as Record<string, unknown>,
@@ -270,16 +274,11 @@ function migrateLegacyLoadSettingsOnce(): void {
       localStorage.setItem(LEGACY_MIGRATION_FLAG, "1");
       return;
     }
-    // Protect the just-migrated entries from eviction, but cap the protected set
-    // to MAX_ENTRIES: an oversized legacy store would otherwise deadlock the
-    // budget loop and never finish migrating. On failure the flag stays unset so
-    // migration retries once space frees.
-    const protectedKeys = new Set(
-      migratedKeys.length > MAX_ENTRIES
-        ? migratedKeys.slice(0, MAX_ENTRIES)
-        : migratedKeys,
-    );
-    if (!enforceStorageBudget(map, protectedKeys)) {
+    // Protect existing entries so only the just-migrated legacy entries are
+    // evicted when over budget: importing old settings never discards a newer
+    // config, and since existing entries already fit the budget this cannot
+    // deadlock. On failure the flag stays unset so migration retries.
+    if (!enforceStorageBudget(map, existingKeys)) {
       return;
     }
     if (writeMap(map)) {