refactor: stabilize Go tests and adapters

[morluto]

Summary

This refactor stabilizes the Go test and adapter boundaries while preserving existing behavior.

• Cache reflected MCP schemas with type-keyed single-flight initialization, including cached errors.
• Deep-clone schema trees before tool-specific customization so nested definitions, array items, defaults, enums, and ranges remain independent.
• Isolate npm environment variables in upgrade tests and correct the MCP portfolio fixture contract.
• Reuse a current-schema SQLite template for ordinary corpus fixtures without sharing WAL/SHM sidecars.
• Replace the CLI's large dispatch switch with a focused routing table.
• Re-enable test linting, address context/resource findings, and add behavior coverage for previously untested packages.

Review order

1. internal/mcpserver/schemas.go and internal/mcpserver/schemas_test.go
2. internal/corpus/corpus_test.go and internal/corpus/corpus_fixture_test.go
3. internal/cli/cli.go and internal/cli/dispatch.go
4. Environment, lint, and targeted coverage changes

Testing

• npm_command=exec npm_lifecycle_event=npx go test ./... -count=1 — passed
• make verify — passed
• make test-race — passed
• make lint-full — 0 issues
• gofmt and git diff --check — passed

Compatibility and scope

• No public product API or persisted schema changes.
• Offline corpus-read, network-write, authorization, snapshot, and recovery boundaries are preserved.
• The larger internal/app/mcp package extraction and exhaustive sleep replacement are intentionally deferred; the existing MCP implementation remains split across its capability-specific internal/app/mcp_*.go files.

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