Remove legacy optimizer decorator path

[kocaemre]

Summary

• The optimizer-without-AdvertiseFromCore path is now rejected by sessionmanager.New, so the old factory-level optimizer decorator branch can no longer run.
• Remove the unreachable legacy optimizer decorator path and its private tool-adaptation helper.
• Wire the session manager directly to the undecorated base factory; the resolved optimizer factory continues to be surfaced to the Serve layer via Manager.OptimizerFactory().

Fixes #6103

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)

Manual testing:

• PATH=/usr/local/go/bin:/root/go/bin:$PATH go test ./pkg/vmcp/server/sessionmanager
• PATH=/usr/local/go/bin:/root/go/bin:$PATH go test ./pkg/vmcp/server/sessionmanager ./pkg/vmcp/server
• PATH=/usr/local/go/bin:/root/go/bin:$PATH go test -race ./pkg/vmcp/server/sessionmanager
• PATH=/usr/local/go/bin:/root/go/bin:$PATH task lint
• git diff --check

API Compatibility

• This PR does not break the v1beta1 API, OR the api-break-allowed label is applied and the migration guidance is described above.

Does this introduce a user-facing change?

No.

Special notes for reviewers

This is intentionally a deletion-only follow-up to the constructor guard merged in #6033. The optimizer is still resolved, cleaned up by the manager, and consumed by the Serve layer when enabled; the removed path was unreachable because New rejects an optimizer unless AdvertiseFromCore is set.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.75%. Comparing base (8343851) to head (b908e1e).
⚠️ Report is 40 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6119      +/-   ##
==========================================
+ Coverage   72.96%   77.75%   +4.78%     
==========================================
  Files         742      756      +14     
  Lines       78236    72727    -5509     
==========================================
- Hits        57085    56546     -539     
+ Misses      17172    16176     -996     
+ Partials     3979        5    -3974     

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[ChrisJBurns]

Two stale doc comments elsewhere in this file describe the removed decorator path — not required for this PR, but worth a quick follow-up.

[ChrisJBurns]

New()'s doc comment at lines 95-96 still says: "It builds the decorating session factory from cfg, wiring the optimizer and composite tool layers internally." That's no longer accurate — the factory is now just cfg.Base with no decorators, and the optimizer is surfaced solely via sm.optimizerFactory/OptimizerFactory() for the Serve layer to consume. Worth rewording.

[ChrisJBurns]

The comment at lines 132-133 above sm := &Manager{...} says "Build the Manager first so we can reference sm.Terminate and sm.sessions directly in closures..." — with buildDecoratingFactory (and its sm.Terminate param) gone, nothing built in New() references sm.Terminate anymore, only sm.loadSession/sm.checkSession/sm.sessions. The comment should drop the sm.Terminate mention.

[kocaemre]

Rebased this PR onto current main and resolved the stale conflict in pkg/vmcp/server/sessionmanager/factory.go.

Follow-up included:

• preserved the current BackendHealth wiring from main;
• kept the legacy optimizer decorator removal;
• refreshed the stale FactoryConfig comments mentioned in review so they no longer describe the removed decorator path.

Local verification:

• go test -ldflags=-extldflags=-Wl,-w -race ./pkg/vmcp/server/sessionmanager → passed
• task lint → passed (golangci-lint + go vet, 0 issues)
• git diff --check → passed

[kocaemre]

Updated the two stale comments called out in review:

• New() now describes wrapping cfg.Base and surfacing the optimizer factory to the Serve layer instead of saying the optimizer/composite layers are wired internally.
• The constructor-local comment now refers to sm.loadSession, sm.checkSession, and sm.sessions, and no longer mentions sm.Terminate.

Verification after the comment-only follow-up:

• go test -ldflags=-extldflags=-Wl,-w ./pkg/vmcp/server/sessionmanager — passed
• git diff --check — clean

I also tried the repository-preferred broad lint command with Go 1.26.7:

• task lint started golangci-lint run --allow-parallel-runners ./... but the local process was killed with exit status 137 in this container. The last full CI run on the previous commit was green, and this follow-up only changes comments.