diff --git a/modules/module-postgres/src/replication/WalStream.ts b/modules/module-postgres/src/replication/WalStream.ts
index 6d2a54b54..ba1aeead6 100644
--- a/modules/module-postgres/src/replication/WalStream.ts
+++ b/modules/module-postgres/src/replication/WalStream.ts
@@ -353,7 +353,7 @@ export class WalStream {
         const fixGuidance =
           slot.invalidation_reason === 'idle_timeout'
             ? `Increase idle_replication_slot_timeout on the source database.`
-            : `Increase max_slot_wal_keep_size on the source database.`;
+            : `Increase max_slot_wal_keep_size on the source database and delete the existing slot to recover.`;
         throw new MissingReplicationSlotError(
           `[PSYNC_S1146] Replication slot ${slotName} was invalidated ` +
             `(reason: ${slot.invalidation_reason ?? 'unknown'}). ` +
diff --git a/modules/module-postgres/test/src/wal_stream.test.ts b/modules/module-postgres/test/src/wal_stream.test.ts
index 7679b2330..7373ad45a 100644
--- a/modules/module-postgres/test/src/wal_stream.test.ts
+++ b/modules/module-postgres/test/src/wal_stream.test.ts
@@ -573,8 +573,8 @@ bucket_definitions:
       // When a snapshot is interrupted and the slot is subsequently invalidated,
       // a retry calls initSlot() which finds the lost slot. Since snapshot_done
       // is still false, the error should carry phase: 'snapshot' so that
-      // shouldRetryReplication() can block futile retries. Currently initSlot()
-      // always reports phase: 'streaming' — this test should FAIL until fixed.
+      // shouldRetryReplication() can block retries for snapshot failures
+      // requiring operator intervention to recover.
       await using baseContext = await openContext({ doNotClear: true });
 
       const serverVersion = await baseContext.connectionManager.getServerVersion();
@@ -639,8 +639,7 @@ bucket_definitions:
 
         expect(caughtError).toBeInstanceOf(MissingReplicationSlotError);
         expect(caughtError.walStatus).toBe('lost');
-        // This assertion should FAIL: initSlot() currently reports 'streaming'
-        // but the correct phase is 'snapshot' because snapshot_done is false.
+        // initSlot() derives phase from snapshotDone: snapshot not done → phase is 'snapshot'
         expect(caughtError.phase).toBe('snapshot');
       }
     }
diff --git a/packages/service-core/src/api/diagnostics.ts b/packages/service-core/src/api/diagnostics.ts
index 10c515cb0..03bb93738 100644
--- a/packages/service-core/src/api/diagnostics.ts
+++ b/packages/service-core/src/api/diagnostics.ts
@@ -145,32 +145,26 @@ export async function getSyncRulesStatus(
   }
   errors.push(...syncRuleErrors.map((error) => syncConfigYamlErrorToReplicationError(error, now)));
 
-  if (slot_wal_budget) {
-    if (slot_wal_budget.wal_status === 'lost') {
+  if (
+    slot_wal_budget &&
+    slot_wal_budget.wal_status !== 'lost' &&
+    slot_wal_budget.safe_wal_size != null &&
+    slot_wal_budget.max_slot_wal_keep_size != null &&
+    slot_wal_budget.max_slot_wal_keep_size > 0
+  ) {
+    const budgetPct = Math.max(
+      0,
+      Math.round((slot_wal_budget.safe_wal_size / slot_wal_budget.max_slot_wal_keep_size) * 100)
+    );
+    if (budgetPct <= 50) {
       errors.push({
-        level: 'fatal',
+        level: 'warning',
         message:
-          `[PSYNC_S1146] Replication slot WAL status is 'lost'. ` +
-          `The slot has been invalidated. Increase max_slot_wal_keep_size ` +
-          `on the source database and delete the existing slot to recover.`,
+          `WAL budget is low: ${budgetPct}% remaining. ` +
+          `The replication slot may be invalidated if WAL consumption ` +
+          `continues at this rate. Consider increasing max_slot_wal_keep_size.`,
         ts: now
       });
-    } else if (
-      slot_wal_budget.safe_wal_size != null &&
-      slot_wal_budget.max_slot_wal_keep_size != null &&
-      slot_wal_budget.max_slot_wal_keep_size > 0
-    ) {
-      const budgetPct = Math.round((slot_wal_budget.safe_wal_size / slot_wal_budget.max_slot_wal_keep_size) * 100);
-      if (budgetPct <= 50) {
-        errors.push({
-          level: 'warning',
-          message:
-            `WAL budget is low: ${budgetPct}% remaining. ` +
-            `The replication slot may be invalidated if WAL consumption ` +
-            `continues at this rate. Consider increasing max_slot_wal_keep_size.`,
-          ts: now
-        });
-      }
     }
   }
 
diff --git a/packages/service-core/test/src/diagnostics.test.ts b/packages/service-core/test/src/diagnostics.test.ts
index 79ef5369b..cd4882a32 100644
--- a/packages/service-core/test/src/diagnostics.test.ts
+++ b/packages/service-core/test/src/diagnostics.test.ts
@@ -116,14 +116,28 @@ describe('getSyncRulesStatus WAL budget warnings', () => {
     expect(walWarnings).toHaveLength(0);
   });
 
-  test('fatal error when slot status is lost', async () => {
+  test('clamps negative safe_wal_size to 0%', async () => {
+    const api = makeRouteAPI({
+      wal_status: 'unreserved',
+      safe_wal_size: -2.4 * GB,
+      max_slot_wal_keep_size: 1 * 1024 * 1024 // 1MB
+    });
+    const result = await getSyncRulesStatus(makeBucketStorage(), api, makeSyncRulesContent(), OPTIONS);
+    const walWarnings = result!.errors.filter((e) => e.message.includes('WAL budget'));
+    expect(walWarnings).toHaveLength(1);
+    expect(walWarnings[0].message).toContain('0%');
+    expect(walWarnings[0].message).not.toMatch(/-\d+%/);
+  });
+
+  test('no WAL budget error when slot status is lost', async () => {
     const api = makeRouteAPI({
       wal_status: 'lost'
     });
     const result = await getSyncRulesStatus(makeBucketStorage(), api, makeSyncRulesContent(), OPTIONS);
-    const slotErrors = result!.errors.filter((e) => e.message.includes('PSYNC_S1146'));
-    expect(slotErrors).toHaveLength(1);
-    expect(slotErrors[0].level).toBe('fatal');
+    const walErrors = result!.errors.filter(
+      (e) => e.message.includes('WAL budget') || e.message.includes('PSYNC_S1146')
+    );
+    expect(walErrors).toHaveLength(0);
   });
 
   test('no WAL error when getSlotWalBudget is not defined', async () => {