fix(build/prisma): support custom schema directories and Prisma 6.6+ compatibility

This change makes the Prisma build extension work with any schema directory name
(e.g. "schema", "models", "db", "prisma-schemas") and ensures compatibility with Prisma 6.6+.

Configuration:
Always point the `schema` option to your main schema file, not the folder:

  prismaExtension({
    version: "6.18.0",
    schema: "../../packages/prisma/src/models/schema.prisma",  // ← Point to the file
    migrate: false,
  })

The main schema file can have any name (schema.prisma, main.prisma, etc.) and can live
in any directory. It does NOT have to be called "schema.prisma".

How it works:
- Auto-detects a "schema folder" by checking the parent directory of the schema file
  for multiple .prisma files. If 2+ .prisma files exist in that directory, we treat
  it as a folder-based schema setup.
- For folder-based schemas (multiple files), all .prisma files in that directory are
  copied to ./prisma/schema/ in the build output. For Prisma >= 6.6, we run:
    prisma generate --schema=./prisma/schema
  For older Prisma versions, we omit the --schema flag for backwards compatibility.
- For single-file schemas (only one .prisma file in the directory), the file is copied
  to ./prisma/schema.prisma and we run:
    prisma generate --schema=./prisma/schema.prisma

Examples:
  # Folder-based (multiple .prisma files):
  packages/prisma/src/models/
    ├── schema.prisma       ← Point to this in config
    ├── user.prisma
    └── post.prisma

  # Single file:
  packages/prisma/
    └── schema.prisma       ← Point to this in config

Backwards compatibility:
- Older Prisma versions (< 6.6) continue to work without the --schema flag for folder setups
- Single-file setups are unaffected
- No breaking changes

Closes #1926

Author: cameronmema

packages/build/src/extensions/prisma.ts

@@ -112,7 +112,12 @@ export class PrismaExtension implements BuildExtension {
 
     context.logger.debug(`PrismaExtension is generating the Prisma client for version ${version}`);
 
-    const usingSchemaFolder = dirname(this._resolvedSchemaPath).endsWith("schema");
+    // Auto-detect schema folder by checking for multiple .prisma files
+    const schemaDir = dirname(this._resolvedSchemaPath);
+    const prismaFilesInDir = await readdir(schemaDir)
+      .then((files) => files.filter((file) => file.endsWith(".prisma")))
+      .catch(() => []);
+    const usingSchemaFolder = prismaFilesInDir.length > 1;
 
     const commands: string[] = [];
 
@@ -155,13 +160,11 @@ export class PrismaExtension implements BuildExtension {
     }
 
     if (usingSchemaFolder) {
-      const schemaDir = dirname(this._resolvedSchemaPath);
-
       prismaDir = dirname(schemaDir);
 
       context.logger.debug(`Using the schema folder: ${schemaDir}`);
 
-      // Find all the files in schemaDir that end with .prisma (excluding the schema.prisma file)
+      // Find all the files in schemaDir that end with .prisma
       const prismaFiles = await readdir(schemaDir).then((files) =>
         files.filter((file) => file.endsWith(".prisma"))
       );
@@ -183,10 +186,14 @@ export class PrismaExtension implements BuildExtension {
         await cp(source, destination);
       }
 
+      // Prisma 6.6+ requires --schema flag for schema folders
+      const [major, minor] = version.split(".").map(Number);
+      const requiresSchemaFlag = major > 6 || (major === 6 && minor >= 6);
+
       commands.push(
-        `${binaryForRuntime(
-          manifest.runtime
-        )} node_modules/prisma/build/index.js generate ${generatorFlags.join(" ")}` // Don't add the --schema flag or this will fail
+        `${binaryForRuntime(manifest.runtime)} node_modules/prisma/build/index.js generate${
+          requiresSchemaFlag ? " --schema=./prisma/schema" : ""
+        } ${generatorFlags.join(" ")}`
       );
     } else {
       prismaDir = dirname(this._resolvedSchemaPath);