docs: add resolve-forward-references skill; fix OR REPLACE bug in overview-pages

- New skill: `.claude/skills/mendix/resolve-forward-references.md` — documents
  the placeholder pattern (why forward refs fail, three common patterns, ordering
  rules, CREATE OR MODIFY vs ALTER SNIPPET, full CRUD scaffold template)
- Fix: `overview-pages.md` used `CREATE OR REPLACE SNIPPET` for the fill-in step,
  which destroys the placeholder UUID and breaks all page bindings; corrected to
  `CREATE OR MODIFY SNIPPET` with an explanation and cross-reference
- Update: `check-syntax.md` — adds "snippet not found / page not found" error
  section with fix options and the declaration ordering rule; links to new skill

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ako

.claude/skills/mendix/check-syntax.md

@@ -219,6 +219,36 @@ widgets (
 
 ## Troubleshooting Parse Errors
 
+### Error: "snippet not found" / "page not found"
+
+A reference to a document that hasn't been created yet in the script:
+
+```
+Error: snippet not found: MyModule.NavMenu
+Error: page not found: MyModule.Customer_NewEdit
+```
+
+Script execution is sequential — each `CREATE` commits immediately. Forward references
+fail because the target doesn't exist in the database at the moment the referencing
+document is created.
+
+**Fix options:**
+1. **Reorder** — move the target document's `CREATE` earlier in the script (simplest fix)
+2. **Placeholder pattern** — for circular dependencies (e.g. a snippet that shows pages
+   that embed the snippet), create a minimal placeholder first, then create the referencing
+   documents, then fill in the placeholder with `CREATE OR MODIFY` — which preserves the
+   original UUID so all existing bindings remain valid
+   (see [Resolve Forward References](./resolve-forward-references.md))
+
+Declaration order that avoids most forward references:
+```
+enumerations → entities → snippets (placeholder) → pages → snippets (fill-in) → microflows → navigation
+```
+
+> **Never use `CREATE OR REPLACE` for the placeholder fill-in step.** OR REPLACE deletes
+> the placeholder and creates a new document with a different UUID, silently breaking
+> every page or snippet that references it.
+
 ### Error: "mismatched input 'X'"
 
 The word `X` is either:
@@ -244,4 +274,5 @@ Extra tokens found:
 
 - [/write-microflows](./write-microflows.md) - Detailed microflow syntax
 - [/overview-pages](./overview-pages.md) - Page building syntax
+- [/resolve-forward-references](./resolve-forward-references.md) - Placeholder pattern and declaration ordering
 - [/migrate-oracle-forms](./migrate-oracle-forms.md) - Migration-specific guidance

.claude/skills/mendix/overview-pages.md

@@ -527,8 +527,10 @@ create page Module.Customer_Overview
 }
 /
 
--- Step 3: Replace snippet with full navigation (pages now exist)
-create or replace snippet Module.NavigationMenu
+-- Step 3: Fill in the snippet with real content (pages now exist)
+-- Use CREATE OR MODIFY (preserves the snippet's ID → page bindings stay valid)
+-- Do NOT use CREATE OR REPLACE — that would assign a new ID and break existing page references
+create or modify snippet Module.NavigationMenu
 {
   layoutgrid navGrid {
     row row1 {
@@ -543,15 +545,19 @@ create or replace snippet Module.NavigationMenu
 
 ### Key Points
 
-- The placeholder snippet must exist before pages are created (for SNIPPETCALL to resolve)
-- Use `create or replace snippet` to update the placeholder after pages exist
-- Page references in the final snippet will resolve correctly because pages already exist
+- The placeholder snippet must exist before pages are created (for `snippetcall` to resolve)
+- Use `create or modify snippet` for the fill-in step — it preserves the snippet's UUID so pages that already reference it remain valid
+- **Do not use `create or replace snippet`** — that deletes the placeholder and creates a fresh UUID, silently breaking every page that references the old one
+- Page references in the final snippet resolve correctly because pages already exist
+
+See [Resolve Forward References](./resolve-forward-references.md) for the full pattern including page→page and microflow→page cases, declaration ordering rules, and the choice between `CREATE OR MODIFY` and `ALTER SNIPPET`.
 
 ## Related Skills
 
 - [Create Page](./create-page.md) - Basic page creation syntax
 - [ALTER PAGE/SNIPPET](./alter-page.md) - Modify existing pages/snippets in-place (SET, INSERT, DROP, REPLACE)
 - [Master-Detail Pages](./master-detail-pages.md) - Selection binding pattern
+- [Resolve Forward References](./resolve-forward-references.md) - Placeholder pattern, declaration ordering
 
 ## Snippet Commands Reference