fix: restore documentMode 'string' default — graphql-tag not needed

Reverting the removal of documentMode: 'string'. With 'string' mode,
the generic-sdk plugin uses plain string type for documents instead of
DocumentNode, so graphql-tag is NOT required as a dependency.

The TypedDocumentString class was never needed — that was our mistake.
The generic-sdk with documentMode: 'string' + rawRequest works correctly
with plain strings, no class injection needed.

Without this default, codegen falls back to 'graphQLTag' mode which
requires the graphql-tag package, breaking builds.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: productdevbook

src/core/codegen/client.ts

@@ -33,6 +33,7 @@ export const DEFAULT_CLIENT_CODEGEN_CONFIG: ClientCodegenConfig = {
   strictScalars: true,
   maybeValue: 'T | null | undefined',
   inputMaybeValue: 'T | undefined',
+  documentMode: 'string',
   pureMagicComment: true,
   dedupeOperationSuffix: true,
   rawRequest: true,

tests/unit/codegen/client-config.test.ts

@@ -58,6 +58,7 @@ describe('dEFAULT_CLIENT_CODEGEN_CONFIG', () => {
       strictScalars: true,
       maybeValue: 'T | null | undefined',
       inputMaybeValue: 'T | undefined',
+      documentMode: 'string',
       pureMagicComment: true,
       dedupeOperationSuffix: true,
       rawRequest: true,
@@ -83,8 +84,8 @@ describe('dEFAULT_CLIENT_CODEGEN_CONFIG', () => {
     expect(scalars.File).toEqual({ input: 'File', output: 'File' })
   })
 
-  it('should not set documentMode by default (uses graphql-codegen default)', () => {
-    expect(DEFAULT_CLIENT_CODEGEN_CONFIG.documentMode).toBeUndefined()
+  it('should use string document mode (no graphql-tag dependency needed)', () => {
+    expect(DEFAULT_CLIENT_CODEGEN_CONFIG.documentMode).toBe('string')
   })
 
   it('should have rawRequest enabled for SDK generation', () => {

tests/unit/codegen/client.test.ts

@@ -507,8 +507,8 @@ describe('dEFAULT_CLIENT_CODEGEN_CONFIG', () => {
     expect(DEFAULT_CLIENT_CODEGEN_CONFIG.inputMaybeValue).toBe('T | undefined')
   })
 
-  it('should not set documentMode by default (uses graphql-codegen default)', () => {
-    expect(DEFAULT_CLIENT_CODEGEN_CONFIG.documentMode).toBeUndefined()
+  it('should use string document mode (no graphql-tag dependency needed)', () => {
+    expect(DEFAULT_CLIENT_CODEGEN_CONFIG.documentMode).toBe('string')
   })
 
   it('should have pure magic comment enabled', () => {