feat: add flag SkipNullVariablesError

[alepane21]

Summary by CodeRabbit

• New Features
  • Added a compatibility option to skip errors for null variables during request validation.
  • Exposed the setting via configuration, schema, defaults, and full config examples.
• Bug Fixes
  • Updated router variable validation to honor the new compatibility flag.
• Chores
  • Bumped the router dependency to a newer patch build.

Checklist

• I have discussed my proposed changes in an issue and have received approval to proceed.
• I have followed the coding standards of the project.
• Tests or benchmarks have been added or updated.
• If applicable, I have provided instructions for reviewers for manually validating my changes.
• Documentation has been updated on https://github.com/wundergraph/docs-website.
• I have read the Contributors Guide.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 53fd30d9-d625-4cb3-9b14-2c2ceea6765f

📥 Commits

Reviewing files that changed from the base of the PR and between e682b66 and 5752a94.

📒 Files selected for processing (2)

• router/pkg/config/testdata/config_defaults.json
• router/pkg/config/testdata/config_full.json

✅ Files skipped from review due to trivial changes (1)

• router/pkg/config/testdata/config_defaults.json

🚧 Files skipped from review as they are similar to previous changes (1)

• router/pkg/config/testdata/config_full.json

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Walkthrough

Adds an Apollo Router compatibility flag for skipping null-variable validation errors, exposes it in config schema/defaults/full config, wires it into variable validation and usage tracking, and updates graphql-go-tools dependencies in router modules.

Changes

Apollo Router skip-null-variables flag

Layer / File(s)	Summary
Config flag contract router/pkg/config/config.go, router/pkg/config/config.schema.json, router/pkg/config/testdata/config_*.json	ApolloRouterCompatibilityFlags gains SkipNullVariablesError, the schema adds skip_null_variables_error.enabled, and the config fixtures include the new default value.
Validator wiring and usage tracking router/go.mod, router-tests/go.mod, router/core/operation_processor.go, router/core/router_config.go	github.com/wundergraph/graphql-go-tools/v2 is bumped in both modules, createParseKit passes SkipNullVariablesError into VariablesValidatorOptions, and Config.Usage() records the flag.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• wundergraph/cosmo#2913: Shares the github.com/wundergraph/graphql-go-tools/v2 dependency bump in router/go.mod and router-tests/go.mod.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding the SkipNullVariablesError feature flag.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[github-actions]

❌ Internal Query Planner CI checks failed

The Internal Query Planner CI checks failed in the celestial repository, and this is going to stop the merge of this PR.
If you are part of the WunderGraph organization, you can see the PR with more details.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.42%. Comparing base (f144989) to head (5752a94).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3024       +/-   ##
===========================================
+ Coverage   46.53%   61.42%   +14.89%     
===========================================
  Files        1120      259      -861     
  Lines      154966    30047   -124919     
  Branches    10060        0    -10060     
===========================================
- Hits        72107    18456    -53651     
+ Misses      81025    10103    -70922     
+ Partials     1834     1488      -346     

Files with missing lines	Coverage Δ
router/core/operation_processor.go	85.12% <100.00%> (+0.01%)	⬆️
router/core/router_config.go	93.82% <100.00%> (ø)
router/pkg/config/config.go	82.29% <ø> (ø)

... and 865 files with indirect coverage changes

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