diff --git a/.architecture-rules/auth.yaml b/.architecture-rules/auth.yaml
index f9ac6358..3fa76ab6 100644
--- a/.architecture-rules/auth.yaml
+++ b/.architecture-rules/auth.yaml
@@ -61,6 +61,82 @@ auth_rules:
       required_patterns:
         - "require_vendor_context\\(\\)|# public"
 
+  - id: "AUTH-005"
+    name: "Routes must use UserContext, not User model attributes"
+    severity: "error"
+    description: |
+      When using current_user from dependency injection, it is a UserContext
+      (Pydantic schema), NOT a User (SQLAlchemy model). Do not access:
+
+      FORBIDDEN (SQLAlchemy relationships/columns not in UserContext):
+        - current_user.admin_platforms    → Use accessible_platform_ids
+        - current_user.vendors            → Use token_vendor_id
+        - current_user.owned_companies    → Query via service
+        - current_user.hashed_password    → Never needed in routes
+        - current_user.created_at         → Query User if needed
+        - current_user.updated_at         → Query User if needed
+
+      CORRECT ALTERNATIVES:
+        - current_user.accessible_platform_ids  # list[int] | None
+        - current_user.token_platform_id        # Selected platform from JWT
+        - current_user.token_vendor_id          # Vendor from JWT
+        - current_user.is_super_admin           # Boolean
+        - current_user.can_access_platform(id)  # Helper method
+
+      See: docs/architecture/user-context-pattern.md
+    pattern:
+      file_pattern: "app/modules/*/routes/**/*.py"
+      anti_patterns:
+        - "current_user\\.admin_platforms"
+        - "current_user\\.vendors"
+        - "current_user\\.owned_companies"
+        - "current_user\\.hashed_password"
+
+  - id: "AUTH-006"
+    name: "JWT token context fields must be defined in UserContext"
+    severity: "error"
+    description: |
+      When adding new context to JWT tokens, ensure the field is:
+
+      1. Added to UserContext schema (models/schema/auth.py)
+      2. Extracted in verify_token() (middleware/auth.py)
+      3. Attached to User in get_current_user() (middleware/auth.py)
+      4. Copied in UserContext.from_user() method
+
+      Pattern: token_* prefix for JWT-derived fields
+        - token_platform_id, token_platform_code (admin platform context)
+        - token_vendor_id, token_vendor_code, token_vendor_role (vendor context)
+
+      If getattr(current_user, "token_X", None) is needed, the field is missing
+      from UserContext and should be added.
+
+      See: docs/architecture/user-context-pattern.md
+    pattern:
+      file_pattern: "app/modules/*/routes/**/*.py"
+      anti_patterns:
+        - "getattr\\(current_user,\\s*['\"]token_"
+
+  - id: "AUTH-007"
+    name: "Response models must match available UserContext data"
+    severity: "error"
+    description: |
+      When returning user data from endpoints that use UserContext:
+
+      1. Do NOT return LoginResponse(user=current_user) if LoginResponse.user
+         expects UserResponse with created_at/updated_at
+
+      2. Create dedicated response models for different contexts:
+         - LoginResponse: Full user data (from login, has timestamps)
+         - PlatformSelectResponse: Token + platform info (no user data)
+         - TokenRefreshResponse: Just new token data
+
+      3. If user timestamps are needed, query the User model explicitly
+
+      See: docs/architecture/user-context-pattern.md
+    pattern:
+      file_pattern: "app/modules/*/routes/**/*.py"
+      enforcement: "review"
+
 # ============================================================================
 # MULTI-TENANCY RULES
 # ============================================================================
diff --git a/.architecture-rules/module.yaml b/.architecture-rules/module.yaml
index e617330b..5bbb6340 100644
--- a/.architecture-rules/module.yaml
+++ b/.architecture-rules/module.yaml
@@ -723,3 +723,41 @@ module_rules:
       file_pattern: "app/modules/*/definition.py"
       validates:
         - "router imports -> get_*_with_routers function"
+
+  # =========================================================================
+  # Static File Mounting Rules
+  # =========================================================================
+
+  - id: "MOD-024"
+    name: "Module static file mount order - specific paths first"
+    severity: "error"
+    description: |
+      When mounting module static files in main.py, more specific paths must
+      be mounted BEFORE less specific paths. FastAPI processes mounts in
+      registration order.
+
+      WRONG ORDER (locales 404):
+        # Less specific first - intercepts /static/modules/X/locales/*
+        app.mount("/static/modules/X", StaticFiles(...))
+        # More specific second - never reached!
+        app.mount("/static/modules/X/locales", StaticFiles(...))
+
+      RIGHT ORDER (locales work):
+        # More specific first
+        app.mount("/static/modules/X/locales", StaticFiles(...))
+        # Less specific second - catches everything else
+        app.mount("/static/modules/X", StaticFiles(...))
+
+      This applies to all nested static file mounts:
+        - locales/ must be mounted before static/
+        - img/ or css/ subdirectories must be mounted before parent
+
+      SYMPTOMS OF WRONG ORDER:
+        - 404 errors for nested paths like /static/modules/tenancy/locales/en.json
+        - Requests to subdirectories served as 404 instead of finding files
+
+      See: docs/architecture/user-context-pattern.md (Static File Mount Order section)
+    pattern:
+      file_pattern: "main.py"
+      validates:
+        - "module_locales mount BEFORE module_static mount"
diff --git a/docs/architecture/user-context-pattern.md b/docs/architecture/user-context-pattern.md
new file mode 100644
index 00000000..259201f0
--- /dev/null
+++ b/docs/architecture/user-context-pattern.md
@@ -0,0 +1,231 @@
+# UserContext Pattern
+
+This document describes the `UserContext` pattern used for dependency injection in API routes, and the important distinction between `UserContext` (Pydantic schema) and `User` (SQLAlchemy model).
+
+## Overview
+
+The platform uses two different representations of users:
+
+| Type | Purpose | Location | Contains |
+|------|---------|----------|----------|
+| `User` | Database model | `app/modules/tenancy/models/user.py` | All DB columns + relationships |
+| `UserContext` | API dependency injection | `models/schema/auth.py` | Subset of fields + JWT token context |
+
+## Why UserContext?
+
+Routes should not import database models directly (architecture rule API-007). Instead, they receive user context through dependency injection:
+
+```python
+# CORRECT: Use UserContext from dependencies
+from models.schema.auth import UserContext
+
+@router.get("/endpoint")
+def my_endpoint(current_user: UserContext = Depends(get_current_admin_api)):
+    # current_user is a Pydantic schema, not a SQLAlchemy model
+    pass
+
+# WRONG: Don't import User model in routes
+from app.modules.tenancy.models import User  # noqa: API-007 violation
+```
+
+## UserContext Fields
+
+### Core User Fields
+```python
+id: int                 # User ID
+email: str              # Email address
+username: str           # Username
+role: str               # "admin" or "vendor"
+is_active: bool         # Account status
+```
+
+### Admin-Specific Fields
+```python
+is_super_admin: bool                      # True for super admins
+accessible_platform_ids: list[int] | None # Platform IDs (None = all for super admin)
+token_platform_id: int | None             # Selected platform from JWT
+token_platform_code: str | None           # Selected platform code from JWT
+```
+
+### Vendor-Specific Fields
+```python
+token_vendor_id: int | None    # Vendor ID from JWT
+token_vendor_code: str | None  # Vendor code from JWT
+token_vendor_role: str | None  # Role in vendor (owner, manager, etc.)
+```
+
+### Profile Fields
+```python
+first_name: str | None
+last_name: str | None
+preferred_language: str | None
+```
+
+## What UserContext Does NOT Have
+
+`UserContext` is intentionally limited. It does NOT have:
+
+| Missing | Why | Alternative |
+|---------|-----|-------------|
+| `admin_platforms` | SQLAlchemy relationship | Use `accessible_platform_ids` |
+| `vendors` | SQLAlchemy relationship | Use `token_vendor_id` |
+| `owned_companies` | SQLAlchemy relationship | Query via service |
+| `hashed_password` | Security - never expose | N/A |
+| `created_at` / `updated_at` | Not needed in most routes | Query User if needed |
+
+## Authentication Flow
+
+### Platform Admin Login Flow
+
+```
+1. POST /api/v1/admin/auth/login
+   - Returns LoginResponse with user data and token
+   - Token includes: user_id, role, is_super_admin, accessible_platforms
+
+2. GET /api/v1/admin/auth/accessible-platforms
+   - Returns list of platforms admin can access
+
+3. POST /api/v1/admin/auth/select-platform
+   - Platform admin selects a platform
+   - Returns PlatformSelectResponse with NEW token
+   - New token includes: platform_id, platform_code
+
+4. Subsequent API calls
+   - Token decoded → UserContext populated
+   - current_user.token_platform_id available
+```
+
+### JWT Token → UserContext Mapping
+
+When a JWT token is decoded, these fields are mapped:
+
+| JWT Claim | UserContext Field |
+|-----------|-------------------|
+| `sub` | `id` |
+| `username` | `username` |
+| `email` | `email` |
+| `role` | `role` |
+| `is_super_admin` | `is_super_admin` |
+| `accessible_platforms` | `accessible_platform_ids` |
+| `platform_id` | `token_platform_id` |
+| `platform_code` | `token_platform_code` |
+| `vendor_id` | `token_vendor_id` |
+| `vendor_code` | `token_vendor_code` |
+| `vendor_role` | `token_vendor_role` |
+
+## Helper Methods
+
+`UserContext` provides helper methods:
+
+```python
+# Check platform access
+if current_user.can_access_platform(platform_id):
+    ...
+
+# Get accessible platforms
+platform_ids = current_user.get_accessible_platform_ids()
+# Returns None for super admins (all platforms)
+# Returns list[int] for platform admins
+
+# Check role
+if current_user.is_admin:
+    ...
+if current_user.is_vendor:
+    ...
+
+# Full name
+name = current_user.full_name  # First + Last, or username
+```
+
+## Common Mistakes to Avoid
+
+### 1. Accessing SQLAlchemy Relationships
+
+```python
+# WRONG - admin_platforms is a SQLAlchemy relationship
+if current_user.admin_platforms:
+    platform_id = current_user.admin_platforms[0].id
+
+# CORRECT - use accessible_platform_ids
+if current_user.accessible_platform_ids:
+    platform_id = current_user.accessible_platform_ids[0]
+```
+
+### 2. Using User Model Attributes
+
+```python
+# WRONG - created_at exists on User, not UserContext
+return {"created": current_user.created_at}
+
+# CORRECT - if you need timestamps, query the User
+user = db.query(User).filter(User.id == current_user.id).first()
+return {"created": user.created_at}
+```
+
+### 3. Using getattr for Token Fields
+
+```python
+# WRONG - use getattr only for optional fallback
+platform_id = getattr(current_user, "token_platform_id", None)
+
+# CORRECT - use the field directly (it's defined on UserContext)
+platform_id = current_user.token_platform_id
+```
+
+### 4. Response Models Requiring Unavailable Fields
+
+```python
+# WRONG - LoginResponse.user expects UserResponse with created_at
+return LoginResponse(user=current_user)  # ValidationError!
+
+# CORRECT - use a response model that matches available data
+return PlatformSelectResponse(
+    access_token=token,
+    platform_id=platform.id,
+    platform_code=platform.code,
+)
+```
+
+## Adding New Fields to UserContext
+
+When adding JWT token context that should be available in routes:
+
+1. **Add field to UserContext** (`models/schema/auth.py`):
+   ```python
+   token_new_field: str | None = None
+   ```
+
+2. **Add to JWT payload** (`middleware/auth.py` - `create_access_token`):
+   ```python
+   if new_field is not None:
+       payload["new_field"] = new_field
+   ```
+
+3. **Extract from JWT** (`middleware/auth.py` - `verify_token`):
+   ```python
+   if "new_field" in payload:
+       user_data["new_field"] = payload["new_field"]
+   ```
+
+4. **Attach to User object** (`middleware/auth.py` - `get_current_user`):
+   ```python
+   if "new_field" in user_data:
+       user.token_new_field = user_data["new_field"]
+   ```
+
+5. **Copy in from_user()** (`models/schema/auth.py`):
+   ```python
+   data["token_new_field"] = getattr(user, "token_new_field", None)
+   ```
+
+## Related Documentation
+
+- [Authentication & RBAC](auth-rbac.md) - Complete auth guide
+- [Middleware Reference](middleware.md) - Request processing
+
+## Related Architecture Rules
+
+See `.architecture-rules/auth.yaml` for:
+- AUTH-005: Routes must use UserContext, not User model attributes
+- AUTH-006: JWT token context fields must be defined in UserContext
+- AUTH-007: Response models must match available UserContext data
diff --git a/mkdocs.yml b/mkdocs.yml
index 3cd7daab..2a2546ff 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -44,6 +44,7 @@ nav:
       - Observability: architecture/observability.md
       - Request Flow: architecture/request-flow.md
       - Authentication & RBAC: architecture/auth-rbac.md
+      - UserContext Pattern: architecture/user-context-pattern.md
       - Frontend Structure: architecture/frontend-structure.md
       - Models Structure: architecture/models-structure.md
       - Background Tasks: architecture/background-tasks.md