Coerce types for non-advertised backend tools in composite workflows

[yrobla]

Summary

When backend tools are excluded from advertising via excludeAll or filter, the workflow engine could not find their InputSchema for argument type coercion. This caused string arguments (e.g. "42") to be forwarded to the backend as-is instead of being coerced to the correct type (e.g. float64(42)), resulting in backend rejection.

Root cause: ProcessPreQueriedCapabilities only returned the advertised tool list. Sessions stored only those tools, and the workflow engine used sess.Tools() for schema lookup — so hidden tools were invisible to it.

Fix:

• ProcessPreQueriedCapabilities now returns both advertisedTools (filtered, for MCP clients) and allResolvedTools (every resolved tool regardless of filter, for internal schema lookup).
• MultiSession gains AllTools() []vmcp.Tool, backed by the new allTools field on defaultMultiSession.
• The per-session workflow engine is built from sess.AllTools() so it can coerce arguments for any backend tool, whether advertised or not.

Fixes #4287

Type of change

• Bug fix
• New feature
• Refactoring (no behavior change)
• Dependency update
• Documentation
• Other (describe):

Test plan

• Unit tests (task test)
• E2E tests (task test-e2e)
• Linting (task lint-fix)
• Manual testing (describe below)

Changes

File	Change

Does this introduce a user-facing change?

Special notes for reviewers

[Copilot]

Pull request overview

Fixes composite workflow argument type coercion for backend tools that are not advertised to MCP clients (excluded via excludeAll / filter) by ensuring the workflow engine can still access those tools’ InputSchema.

Changes:

• Split aggregator pre-queried capability processing into advertisedTools (client-visible) and allResolvedTools (internal schema lookup).
• Extended MultiSession with AllTools() and stored both advertised vs all-resolved tool lists on the session.
• Built the per-session composite workflow engine using sess.AllTools() so schema-based coercion works even for hidden tools.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/vmcp/session/types/session.go	Adds AllTools() to the MultiSession interface and clarifies Tools() semantics.
pkg/vmcp/session/types/mocks/mock_session.go	Updates GoMock session mock to implement AllTools().
pkg/vmcp/session/factory.go	Propagates both advertised and all-resolved tool lists into constructed sessions.
pkg/vmcp/session/default_session.go	Stores and exposes allTools via new AllTools() snapshot accessor.
pkg/vmcp/server/sessionmanager/factory.go	Builds per-session workflow composer using sess.AllTools() for schema lookup.
pkg/vmcp/server/telemetry_integration_test.go	Updates test session stub to satisfy the extended interface.
pkg/vmcp/server/session_management_integration_test.go	Updates session mocks/expectations for the new method.
pkg/vmcp/aggregator/aggregator.go	Updates the Aggregator interface to return both advertised and all-resolved tools.
pkg/vmcp/aggregator/default_aggregator.go	Returns advertisedTools + allResolvedTools while keeping routing table complete.
pkg/vmcp/aggregator/mocks/mock_interfaces.go	Updates GoMock aggregator mock for the new signature.
pkg/vmcp/aggregator/default_aggregator_test.go	Adjusts tests for the updated return signature (currently ignoring new value).

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[codecov]

Codecov Report

❌ Patch coverage is 91.17647% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.90%. Comparing base (27e21d0) to head (2df1431).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/vmcp/aggregator/default_aggregator.go	92.30%	1 Missing ⚠️
pkg/vmcp/server/sessionmanager/factory.go	50.00%	0 Missing and 1 partial ⚠️
pkg/vmcp/session/factory.go	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4671      +/-   ##
==========================================
+ Coverage   68.85%   68.90%   +0.05%     
==========================================
  Files         508      508              
  Lines       52604    52676      +72     
==========================================
+ Hits        36220    36299      +79     
+ Misses      13586    13574      -12     
- Partials     2798     2803       +5     

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