diff --git a/Backend/ERPCore.Tests/GlAccountCodeValidatorTests.cs b/Backend/ERPCore.Tests/GlAccountCodeValidatorTests.cs
index 739d843..73196d9 100644
--- a/Backend/ERPCore.Tests/GlAccountCodeValidatorTests.cs
+++ b/Backend/ERPCore.Tests/GlAccountCodeValidatorTests.cs
@@ -26,8 +26,12 @@ public class GlAccountCodeValidatorTests
         await validator.StartAsync(CancellationToken.None);
     }
 
+    /// <summary>
+    /// The default must not block startup. Throwing here cost an outage on 2026-10-07 — a config
+    /// mismatch that had existed all along became a core-dump the moment the check shipped.
+    /// </summary>
     [Fact]
-    public async Task StartAsync_Throws_AndNamesEveryMissingCode()
+    public async Task StartAsync_DoesNotThrow_WhenCodesAreMissing_ByDefault()
     {
         var validator = CreateValidator(
             new()
@@ -36,6 +40,22 @@ public class GlAccountCodeValidatorTests
                 ["SalesDayEnd:GlCashAccountCode"] = "1000-01",
                 ["Adjustment:GlLossAccountCode"] = "5100"
             },
+            new StubGl(["1000-01"]));
+
+        await validator.StartAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task StartAsync_Throws_AndNamesEveryMissingCode_WhenConfiguredToFail()
+    {
+        var validator = CreateValidator(
+            new()
+            {
+                ["GeneralLedgerService:FailOnMissingAccountCodes"] = "true",
+                ["Grn:GlInventoryAccountCode"] = "1100",
+                ["SalesDayEnd:GlCashAccountCode"] = "1000-01",
+                ["Adjustment:GlLossAccountCode"] = "5100"
+            },
             new StubGl(["1100"]));
 
         var ex = await Assert.ThrowsAsync<InvalidOperationException>(
@@ -43,6 +63,7 @@ public class GlAccountCodeValidatorTests
 
         Assert.Contains("1000-01", ex.Message);
         Assert.Contains("5100", ex.Message);
+        Assert.Contains("2 of 3", ex.Message);
         Assert.DoesNotContain("1100,", ex.Message);
     }
 
diff --git a/Backend/ERPCore/Infra/Gl/GlAccountCodeValidator.cs b/Backend/ERPCore/Infra/Gl/GlAccountCodeValidator.cs
index 74340bf..ece1c0a 100644
--- a/Backend/ERPCore/Infra/Gl/GlAccountCodeValidator.cs
+++ b/Backend/ERPCore/Infra/Gl/GlAccountCodeValidator.cs
@@ -9,10 +9,17 @@ namespace ERPCore.Infra.Gl;
 /// as a 404 when some user happened to trigger that one flow, mid-transaction — one flow, one
 /// discovery, repeat. This asserts the whole set once, at boot.
 /// <para>
-/// Deliberately asymmetric about failure: a <em>confirmed missing</em> code is fatal (the config is
-/// wrong and no amount of waiting fixes it), but an <em>unreachable</em> GL only logs a warning.
-/// GL runs on the same host as ERPCore, so on a host reboot it may simply not be listening yet —
-/// hard-failing there would turn a transient ordering issue into a deploy crash-loop.
+/// <b>Reports, does not block.</b> An earlier revision threw on a missing code, on the reasoning
+/// that the config is wrong and waiting won't fix it. In practice that took erpcore.service down
+/// with a core-dump on 2026-10-07: 11 of the 12 configured codes turned out never to have existed
+/// in GL, so a long-standing data mismatch became an immediate outage. Detection was the point;
+/// refusing to serve the other 90% of the app was not. GL already rejects a posting to an unknown
+/// account, so the per-flow error remains the real enforcement — this just surfaces the whole set
+/// at boot instead of one flow at a time.
+/// </para>
+/// <para>
+/// Set <c>GeneralLedgerService:FailOnMissingAccountCodes</c> to <c>true</c> to restore hard-fail
+/// once the chart of accounts is known-good and you want drift to stop a deploy.
 /// </para>
 /// </summary>
 public sealed class GlAccountCodeValidator(
@@ -78,9 +85,19 @@ public sealed class GlAccountCodeValidator(
 
         var missing = expected.Where(c => !present.Contains(c)).ToArray();
         if (missing.Length > 0)
-            throw new InvalidOperationException(
-                $"General Ledger is missing {missing.Length} configured account code(s): {string.Join(", ", missing)}. " +
-                "Seed them in GL's chart of accounts, or correct the Gl*Code settings in configuration.");
+        {
+            var message =
+                $"General Ledger is missing {missing.Length} of {expected.Length} configured account code(s): " +
+                $"{string.Join(", ", missing.Order(StringComparer.Ordinal))}. Every flow that posts to one of these " +
+                "will fail against GL until they are seeded in GL's chart of accounts, or the Gl*Code settings are " +
+                "corrected to match the codes GL actually uses.";
+
+            if (configuration.GetValue("GeneralLedgerService:FailOnMissingAccountCodes", false))
+                throw new InvalidOperationException(message);
+
+            logger.LogError("{Message}", message);
+            return;
+        }
 
         logger.LogInformation("GL account codes verified: {Count} present.", expected.Length);
     }