fix(mcp): ListDomainModels must reconstruct dirty existing modules

CREATE ASSOCIATION failed over --mcp when its from/to entities were created
earlier in the same script, inside an existing module:

  Created entity: MyFirstModule.Address
  Error: parent entity not found: MyFirstModule.Address

The executor resolves an association's entities via findEntity → ListDomainModels.
GetDomainModel already reconstructs a written-this-session module from Studio Pro's
live model (dirty routing), but ListDomainModels only reconstructed *session-
created* modules — for a *dirty existing* module it returned the stale on-disk
snapshot, so entities created earlier in the run were invisible. The two read paths
were inconsistent; this is why new-module scripts worked but an existing module
(e.g. MyFirstModule in a fresh app) failed.

Apply the same dirty routing in ListDomainModels: reconstruct any local domain
model whose module is dirty, then append session-created modules as before.

Repro (MCP-only, existing module): mdl-examples/bug-tests/mcp-association-existing-module.mdl.
Live verification pending Studio Pro restart; the fix mirrors GetDomainModel's
proven routing and is build/test-clean. Not unit-tested in isolation because the
backend's *mpr.Reader has no mock seam (consistent with the package's tests).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ako

mdl-examples/bug-tests/mcp-association-existing-module.mdl

@@ -0,0 +1,48 @@
+-- ============================================================================
+-- Bug — CREATE ASSOCIATION fails over --mcp when the from/to entities were
+-- created earlier in the SAME run, inside an EXISTING module.
+--
+--   Created entity: MyFirstModule.Contact
+--   Created entity: MyFirstModule.Address
+--   Error: parent entity not found: MyFirstModule.Address
+--
+-- Root cause: the executor resolves an association's from/to entities via
+-- findEntity, which lists modules through Backend.ListDomainModels. In the MCP
+-- backend that method reconstructed only *session-created* modules from Studio
+-- Pro's live model — for a *dirty existing* module it returned the stale on-disk
+-- snapshot, hiding entities created earlier in the run. (Backend.GetDomainModel
+-- already had the correct dirty routing; ListDomainModels did not — the two were
+-- inconsistent.) Fix: ListDomainModels applies the same dirty routing.
+--
+-- IMPORTANT — how to reproduce: run this OVER --mcp against a project where
+-- MyFirstModule ALREADY EXISTS on disk (e.g. a fresh Mendix app). The bug is
+-- specific to dirty *existing* modules: if the module is created in-script it
+-- becomes a "session module", which always reconstructed correctly and does NOT
+-- reproduce. On the file (MPR) backend this also passes — the bug is MCP-only.
+--
+--   mxcli exec mcp-association-existing-module.mdl -p app.mpr \
+--     --mcp http://localhost:7782/mcp
+--
+-- Expected after the fix: both entities and the association are created; no
+-- "parent entity not found".
+-- ============================================================================
+
+create persistent entity MyFirstModule.BugContact (
+  Name: string(100) not null error 'Name is required'
+);
+/
+
+create persistent entity MyFirstModule.BugAddress (
+  Street: string(200),
+  City: string(100)
+);
+/
+
+-- This statement failed before the fix because BugAddress (just created over MCP)
+-- was not visible to the association's entity resolution.
+create association MyFirstModule.BugContact_BugAddress
+from MyFirstModule.BugContact to MyFirstModule.BugAddress
+type reference
+owner default
+delete_behavior DELETE_BUT_KEEP_REFERENCES;
+/

mdl/backend/mcp/backend.go

@@ -321,13 +321,25 @@ func (b *Backend) ListDomainModels() ([]*domainmodel.DomainModel, error) {
 	if err != nil {
 		return nil, err
 	}
-	if len(b.sessionModules) == 0 {
-		return local, nil
+	out := make([]*domainmodel.DomainModel, 0, len(local)+len(b.sessionModules))
+	// A module written this session must be reconstructed from Studio Pro's live
+	// model here too, with the SAME dirty routing GetDomainModel applies — otherwise
+	// the stale on-disk snapshot hides entities/associations created earlier in the
+	// same run. This is what made CREATE ASSOCIATION fail when its from/to entities
+	// were just created in an existing module: findEntity lists via this method, and
+	// it previously reconstructed only session-created modules, not dirty existing
+	// ones. Best-effort: keep the local copy if reconstruction fails.
+	for _, dm := range local {
+		if mod, merr := b.reader.GetModule(dm.ContainerID); merr == nil && b.dirty[mod.Name] {
+			if recon, rerr := b.reconstructDomainModel(mod.Name, dm.ContainerID); rerr == nil {
+				out = append(out, recon)
+				continue
+			}
+		}
+		out = append(out, dm)
 	}
-	// Append a live-reconstructed domain model for each session-created module, so
-	// entity references into a freshly created module (e.g. a microflow parameter
-	// or workflow context typed X.Foo) resolve in the same run. Best-effort.
-	out := append([]*domainmodel.DomainModel(nil), local...)
+	// Session-created modules have no on-disk domain model; reconstruct each so
+	// references into a freshly created module resolve in the same run.
 	for _, m := range b.sessionModules {
 		if dm, derr := b.reconstructDomainModelFromPED(m.Name, model.ID(sessionDMPrefix+m.Name), m.ID); derr == nil {
 			out = append(out, dm)