fix(codegen): in-memory (Dynamic) handler codegen in Production

docs/operate/backend-architecture.md

@@ -107,9 +107,12 @@ required. The Marten outbox is still active for event side-effects:
 SignalR notifications fire after `SaveChangesAsync` via
 `ProjectionSideEffects`.
 
-Codegen runs with `TypeLoadMode.Auto` — Wolverine/Marten generated
-classes are pre-generated at build time to save cold-start time and
-avoid Roslyn compilation at runtime.
+Codegen mode is environment-aware. Production runs `TypeLoadMode.Dynamic`
+— Wolverine/Marten handler classes are generated in memory on first use
+and never written to disk, so the container never tries to write into its
+read-only application directory. Local dev and tests run
+`TypeLoadMode.Auto`, which generates into `Internal/Generated/` on first
+boot and reuses it on the next.
 
 ## Marten usage
 
@@ -241,5 +244,6 @@ Integration tests (`Modgud.Api.Tests`) use:
 - **Shared PostgreSQL container** — one container instance for all
   test collections, parallelised
 - **WireMock** — fake OIDC server for external login tests
-- **Pre-generated Wolverine/Marten code** (`TypeLoadMode.Auto`) —
-  eliminates Roslyn compilation at runtime
+- **Wolverine/Marten codegen** (`TypeLoadMode.Auto`) — generated on the
+  first boot into the test working tree and reused, so repeat runs skip
+  Roslyn compilation

src/dotnet/Modgud.Api/Program.cs

@@ -885,7 +885,21 @@
         opts.Discovery.IncludeAssembly(typeof(Modgud.Authentication.Api.Admin.RecoveryCli).Assembly);
         opts.Discovery.IncludeAssembly(typeof(Modgud.Authorization.Commands.CreateGroupCommand).Assembly);
         opts.Durability.Mode = wolverineMode;
-        opts.CodeGeneration.TypeLoadMode = JasperFx.CodeGeneration.TypeLoadMode.Auto;
+        // Production generates handler code in-memory (Dynamic): each handler is
+        // compiled via Roslyn on first use and never written to disk. The previous
+        // Auto mode tried to persist the generated source under /app/Internal —
+        // which the non-root container user cannot write — logging "Access to the
+        // path '/app/Internal' is denied" on the first hit of every handler.
+        // Dev/Test keep Auto, which writes into Internal/Generated/ on a writable
+        // working tree and reuses it across restarts.
+        //
+        // (Pre-generating at build time + TypeLoadMode.Static would also avoid the
+        // runtime Roslyn pass, but it requires JasperFx's `RunJasperFxCommands`
+        // entry point, which is incompatible with this app's WebApplicationFactory
+        // integration tests — see git history for fix/wolverine-codegen-static-prod.)
+        opts.CodeGeneration.TypeLoadMode = builder.Environment.IsProduction()
+            ? JasperFx.CodeGeneration.TypeLoadMode.Dynamic
+            : JasperFx.CodeGeneration.TypeLoadMode.Auto;
 
         // Wolverine 6 made `ServiceLocationPolicy.NotAllowed` the default. We
         // keep that strict default — accidental new service-location dependencies