feat(router): reuse unchanged feature flag muxes on graph server

[dkorittki]

Makes use of the new split config poller, which has the ability to tell what feature flag configs have changed. We pass this information down to newGraphServer where we use it to reuse unchanged feature flag as well as base graph muxes. The change is backwards compatible: The old poller indicates it can' tell what changed and the callers then go the old path: rebuild everything.

Summary by CodeRabbit

• New Features
  • Added support for split configuration loading based on feature flags, enabling routers to load configuration from multiple sources conditionally.
  • Enhanced JWT token payloads to include feature flag information for improved router-level feature detection and configuration selection.

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.
• Documentation has been updated on https://github.com/wundergraph/docs-website.
• I have read the Contributors Guide.

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Walkthrough

This PR implements a feature-flag-based split-configuration loading mechanism for the router. It adds a new ActiveGraphs protobuf message, introduces a split-config-loading feature flag, enables JWT claims to carry feature information, and builds a polling system that assembles router configs from a base graph plus per-feature configuration files fetched via CDN.

Changes

Split-Config Loading Feature

Layer / File(s)	Summary
Proto & Type Definitions proto/wg/cosmo/node/v1/node.proto, connect/src/wg/cosmo/node/v1/node_pb.ts, controlplane/src/types/index.ts	ActiveGraphs message added (protobuf and TypeScript binding) with graphConfigs map field; FeatureIds extends to include 'split-config-loading'; GraphApiKeyJwtPayload adds optional features?: string[] claim.
Organization Feature Defaults controlplane/src/core/repositories/OrganizationRepository.ts	getOrganizationFeatures initializes 'split-config-loading': false in the baseline feature map.
JWT Claim Generation controlplane/src/core/bufservices/federated-graph/createFederatedGraphToken.ts	Token creation loads the split-config-loading feature flag and conditionally includes a features claim in the signed JWT when enabled.
JWT Claim Parsing router/internal/jwt/claims.go	FederatedGraphTokenClaims gains a Features []string field with a HasFeature(feature string) bool helper; ExtractFederatedGraphTokenClaims validates and parses the features claim array.
Conditional Router Initialization router/core/init_config_poller.go	InitializeConfigPoller detects the split-config-loading feature flag and returns a split-config poller immediately when enabled and no custom primary storage is configured; helper functions extract feature flags and construct the split poller.
Graph Mux Lifecycle & Reuse router/core/graph_server.go, router/core/router.go	Feature-flag mux instances are tracked in activeFeatureFlagMuxes; muxes are reused across rebuilds when their engine config unchanged; mux contexts are scoped to graph-server lifetime and canceled during shutdown.
Split-Config HTTP Fetching router/pkg/routerconfig/cdn/split_fetcher.go	SplitFetcher fetches mapper and per-feature configs from CDN via authenticated HTTP POST; supports gzip decompression, HMAC-SHA256 signature validation, and error code mapping.
Split-Config Polling & Assembly router/pkg/controlplane/configpoller/split_config_poller.go	SplitConfigPoller polls the mapper at regular intervals, detects changes via composite-version hash, fetches only modified configs, assembles a full router config by merging base + per-feature entries, and invokes a handler with the patched config; internal state updates only after handler success.
Tests & Validation router/pkg/controlplane/configpoller/split_config_poller_test.go, router/pkg/routerconfig/cdn/split_fetcher_test.go	Comprehensive unit tests for split-config poller (base-only, feature-flag addition/removal/change, error paths, state consistency) and fetcher (constructor validation, HTTP error mapping, request/response formatting, HMAC signature validation, proto-json parsing).

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

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Possibly related PRs

• wundergraph/cosmo#2814: Introduces identical split-config loading architecture with ActiveGraphs protobuf, split-config-loading feature flag, JWT features claim support, and split-config poller/fetcher implementations.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 32.73% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Title check	❓ Inconclusive	The PR title 'feat(router) router optimize graph server swap' is vague and redundant, using the term 'router' twice without clearly communicating the main change about split-config loading, feature flags, or mux optimization.	Consider a more descriptive title that clearly indicates the primary objective, such as 'feat(router): support split-config loading with feature flags and mux reuse' or 'feat: enable router split-config loading for feature-flag isolation'.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
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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[codecov]

Codecov Report

❌ Patch coverage is 61.05263% with 37 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (feat/split-configs@787d2d0). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
router/core/graph_server.go	54.54%	21 Missing and 4 partials ⚠️
router/core/router.go	63.63%	1 Missing and 3 partials ⚠️
...ter/pkg/controlplane/configpoller/config_poller.go	20.00%	4 Missing ⚠️
router/pkg/routerconfig/client.go	0.00%	3 Missing ⚠️
router/core/init_config_poller.go	0.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (61.05%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@                  Coverage Diff                  @@
##             feat/split-configs    #2823   +/-   ##
=====================================================
  Coverage                      ?   65.98%           
=====================================================
  Files                         ?      256           
  Lines                         ?    26845           
  Branches                      ?        0           
=====================================================
  Hits                          ?    17714           
  Misses                        ?     7728           
  Partials                      ?     1403           

Files with missing lines	Coverage Δ
...g/controlplane/configpoller/split_config_poller.go	81.63% <100.00%> (ø)
router/core/init_config_poller.go	2.29% <0.00%> (ø)
router/pkg/routerconfig/client.go	0.00% <0.00%> (ø)
router/core/router.go	70.07% <63.63%> (ø)
...ter/pkg/controlplane/configpoller/config_poller.go	28.72% <20.00%> (ø)
router/core/graph_server.go	83.75% <54.54%> (ø)

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[github-actions]

Router image scan passed

✅ No security vulnerabilities found in image:

ghcr.io/wundergraph/cosmo/router:sha-717ceb25160bdb9033e3d1f1a41764f26659f40d