Migrate session manager to DataStorage with cross-pod restore

[yrobla]

Summary

Follow-on to #4464 (merged). That PR landed the core DataStorage migration — RestorableCache, sessionmanager.Manager rewrite, MultiSessionGetter interface, and RestoreSession. This PR adds the remaining piece: Redis session storage wiring.

Redis session storage wiring

Add SessionStorage *vmcpconfig.SessionStorageConfig to vmcpserver.Config and introduce buildSessionDataStorage:

• When SessionStorage is nil, provider is "memory", or provider is empty/unset, local in-process storage is used (default behaviour unchanged).
• When provider is "redis", a RedisSessionDataStorage is constructed (password from THV_SESSION_REDIS_PASSWORD) — enabling cross-pod session persistence.
• Any other provider value is rejected immediately with a clear error (e.g. a typo like "Redis" will not silently fall back to local storage).
• Provider matching is case-insensitive for "memory".

Pass cfg.SessionStorage from commands.go so the operator-provided Redis config reaches the server.

Fixes #4220

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)

Does this introduce a user-facing change?

No new user-facing changes beyond #4464. The Redis wiring is a configuration opt-in (operator sets sessionStorage.provider: redis); default behaviour (local in-process storage) is unchanged.

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.32%. Comparing base (47c3651) to head (c56ee00).
⚠️ Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/vmcp/server/server.go	26.08%	17 Missing ⚠️
cmd/vmcp/app/commands.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4479      +/-   ##
==========================================
+ Coverage   69.30%   69.32%   +0.01%     
==========================================
  Files         502      502              
  Lines       51632    51655      +23     
==========================================
+ Hits        35786    35808      +22     
  Misses      13077    13077              
- Partials     2769     2770       +1     

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[Copilot]

Pull request overview

This PR migrates vMCP session persistence away from a direct *transportsession.Manager dependency by wiring session metadata storage through the DataStorage interface, enabling optional Redis-backed cross-pod session restore, and updates token-refresh singleflight tests to be deterministic.

Changes:

• Add SessionStorage configuration to vMCP server config and construct DataStorage via a new buildSessionDataStorage helper (local memory or Redis).
• Add test-only synchronization hooks to MonitoredTokenSource to make singleflight-deduplication tests deterministic.
• Plumb SessionStorage from CLI config (commands.go) into the vMCP server configuration.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
pkg/vmcp/server/server.go	Adds SessionStorage config and builds DataStorage (local/Redis) during server construction.
pkg/auth/monitored_token_source.go	Adds test hooks around singleflight entry to coordinate concurrent callers deterministically.
pkg/auth/monitored_token_source_test.go	Refactors the concurrency test to use a two-phase barrier and tighter call-count assertions.
cmd/vmcp/app/commands.go	Passes SessionStorage from CLI config into the server config.

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The base branch was changed.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

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