Preserve tool annotations and output schema through vmcp#4090
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MCP tool annotations (readOnlyHint, destructiveHint, idempotentHint, openWorldHint) were silently dropped during vmcp aggregation, and OutputSchema was never populated from backends. This blocks downstream authorization profiles that need annotation data. Add ToolAnnotations type to vmcp domain model and propagate both Annotations and OutputSchema through the full pipeline: backend query → tool adapter → conflict resolvers → merge → SDK adapter. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
yrobla
approved these changes
Mar 11, 2026
Codecov Report❌ Patch coverage is
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## main #4090 +/- ##
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+ Coverage 68.50% 68.52% +0.02%
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Files 447 447
Lines 45663 45746 +83
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+ Hits 31281 31349 +68
- Misses 11964 11973 +9
- Partials 2418 2424 +6 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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Summary
readOnlyHint,destructiveHint,idempotentHint,openWorldHint,Title) were silently dropped during vmcp aggregation, blocking downstream authorization profiles. This adds theToolAnnotationsvmcp domain type and propagates it through the full pipeline.OutputSchemaexisted onvmcp.Toolbut was never populated from backend MCP servers. This populates it using the same JSON round-trip pattern asInputSchema.Type of change
Test plan
task test)task lint-fix)22 new test cases across 4 test files:
pkg/vmcp/conversion/content_test.go— conversion functions (15 cases including round-trip)pkg/vmcp/aggregator/tool_adapter_annotations_test.go— preservation through overrides (3 cases)pkg/vmcp/server/adapter/capability_adapter_annotations_test.go— SDK output (4 cases)Changes
pkg/vmcp/types.goToolAnnotationsstruct andAnnotationsfield toToolpkg/vmcp/conversion/content.goConvertToolAnnotations,ConvertToolOutputSchema,ToMCPToolAnnotationspkg/vmcp/client/client.goAnnotations+OutputSchemafrom backendpkg/vmcp/session/internal/backend/mcp_session.gopkg/vmcp/aggregator/aggregator.goResolvedToolpkg/vmcp/aggregator/prefix_resolver.gopkg/vmcp/aggregator/priority_resolver.gopkg/vmcp/aggregator/manual_resolver.gopkg/vmcp/aggregator/default_aggregator.gopkg/vmcp/aggregator/tool_adapter.gopkg/vmcp/server/adapter/capability_adapter.goAnnotationsandRawOutputSchemato SDK typesDoes this introduce a user-facing change?
No direct user-facing change. Backend MCP tool annotations and output schemas are now preserved through vmcp aggregation instead of being silently dropped. This enables downstream consumers (like authorization profiles) to use these fields.
Special notes for reviewers
vmcp.ToolAnnotationsis a vmcp-owned type (notmcp.ToolAnnotationdirectly) to maintain the Anti-Corruption Layer — mcp-go is only used at ingestion and SDK adapter boundaries.Icons,Execution, ResourceAnnotations, and PromptIconsare deferred to a follow-up PR per the split strategy.ConvertToolOutputSchemanil check: Usesschema.Type == ""rather than byte-length check because a zero-valuedToolOutputSchemamarshals to{"type":"","properties":{},"required":[]}(non-empty JSON but semantically empty).Generated with Claude Code