fix: handle internal graph edge case with shared root field and nested entities

[wilsonrivera]

Summary by CodeRabbit

• Bug Fixes

  • Improved resilience when linking resources so missing root paths no longer cause errors; cross-linking is performed only when the root exists.

• Tests

  • Expanded coverage with scenarios that validate errors for unresolvable fields when shared root fields coexist with unreachable nested entities across multiple subgraphs.

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/cosmo-docs.
• I have read the Contributors Guide.

[coderabbitai]

Walkthrough

Replaced a strict lookup that threw on missing root resolution data with optional safe access in the resolvability graph; cross-linking between entity and root resolution data now only happens when the root path exists. Added a new test scenario and three subgraph fixtures exercising field resolvability and unreachable/inaccessible key fields.

Changes

Cohort / File(s)	Summary
Resolution data access composition/src/resolvability-graph/graph.ts	Replaced a strict getOrThrowError access on walker.resDataByPath with a safe optional .get(fullPath) lookup; cross-linking between entityResData and rootResData is performed only if the root entry exists, preventing an exception when absent.
Test coverage for resolvability composition/tests/v1/resolvability.test.ts	Added a new test case validating unresolvable fields when a shared root query field coexists with unreachable nested entities; introduced three new subgraph fixtures haaa, haab, and haac modeling inaccessible key fields and relationships, and expecting four resolvability errors.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Reasoning: Small, focused logic change in core graph code plus new multi-subgraph test fixtures. Review requires checking conditional linking semantics and verifying test coverage and expectations.

Possibly related PRs

• fix: internal graph bugs #2240: Modifies the same composition/src/resolvability-graph/graph.ts access patterns and root/entity resolution data linking; likely directly related.

Pre-merge checks and finishing touches

❌ 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%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The pull request title "fix: handle edge case with shared root field and nested entities" is directly related to the changeset. The code modifications replace a strict error-throwing approach with safe optional access that gates cross-linking behind path existence, addressing an edge case with shared root fields. The test additions validate error handling when shared root query fields coexist with unreachable nested entities. The title is specific and concise, clearly conveying that this is a fix for an edge case involving shared root field and nested entity handling, which aligns with the main technical changes implemented.

✨ Finishing touches

• 📝 Generate docstrings

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[github-actions]

Router-nonroot image scan passed

✅ No security vulnerabilities found in image:

ghcr.io/wundergraph/cosmo/router:sha-9f7be6e62d6253a9fc7566d3cc03c627f0a3fbf0-nonroot

[coderabbitai]

Actionable comments posted: 1

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 609cf13 and 8c97021.

📒 Files selected for processing (2)

• composition/src/resolvability-graph/graph.ts (1 hunks)
• composition/tests/v1/resolvability.test.ts (2 hunks)

🧰 Additional context used

🧬 Code graph analysis (1)

composition/tests/v1/resolvability.test.ts (4)

composition/tests/utils/utils.ts (1)

• federateSubgraphsFailure (49-57)

composition/src/router-compatibility-version/router-compatibility-version.ts (1)

• ROUTER_COMPATIBILITY_VERSION_ONE (3-3)

composition/src/subgraph/types.ts (1)

• Subgraph (11-15)

composition/src/ast/utils.ts (1)

• parse (272-274)

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🔇 Additional comments (2)

composition/src/resolvability-graph/graph.ts (1)

301-306: LGTM! Defensive change appropriately handles missing root resolution data.

The change from getOrThrowError to optional .get() access with existence gating prevents crashes when root path data is unavailable due to misconfigured @key fields across subgraphs. Cross-linking now only occurs when both entity and root resolution data exist.

composition/tests/v1/resolvability.test.ts (1)

3391-3461: LGTM! Subgraph definitions correctly model the error scenario.

The three subgraphs properly test resolvability errors arising from:

• Inaccessible key fields (idB: ScalarID! @inaccessible) in haaa and haab
• Mismatched key fields between subgraphs (haaa/haab use idB, haac uses idA)
• Complex nested relationships through Connection/Edge types

This setup validates that the graph handles cases where entities cannot jump between subgraphs due to incorrect @key configurations.

[Aenimus]

LGTM!