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

---

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]

Router image scan passed

✅ No security vulnerabilities found in image:

ghcr.io/wundergraph/cosmo/router:sha-afae35e70a639c24e933bf79e30f3affb5098995

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.80%. Comparing base (5570bf9) to head (ba59309).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3024      +/-   ##
==========================================
+ Coverage   61.77%   61.80%   +0.02%     
==========================================
  Files         261      261              
  Lines       30612    30613       +1     
==========================================
+ Hits        18912    18920       +8     
+ Misses      10184    10180       -4     
+ Partials     1516     1513       -3     

Files with missing lines	Coverage Δ
router/core/operation_processor.go	85.85% <100.00%> (+0.01%)	⬆️
router/core/router_config.go	93.97% <100.00%> (ø)
router/pkg/config/config.go	82.29% <ø> (ø)

... and 3 files with indirect coverage changes

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