feat: add context sharing across hook type.

[terylt]

Closes #1495

Enable Plugin Context Sharing Across Hook Types

Summary

Implements cross-hook context sharing, allowing plugins to
maintain state across different hook types (HTTP → RBAC →
MCP hooks) within a single request.

Changes

Core Implementation:

• Store plugin_context_table and plugin_global_context in
  Request.state (FastAPI pattern)
• Pass contexts from HttpAuthMiddleware → RBAC decorators →
  service layer
• Reuse existing GlobalContext across hooks for consistency
• Properly populate GlobalContext fields (server_id,
  tenant_id, user) where available

Service Layer Updates:

• tool_service.invoke_tool(): Added plugin context
  parameters, passes to hooks
• resource_service.read_resource(): Added plugin context
  parameters, passes to hooks
• prompt_service.get_prompt(): Added plugin context
  parameters, passes to hooks

Route Handler Updates:

• Extract plugin contexts from request.state in all route
  handlers
• Pass contexts to service methods
• Updated RPC endpoints for tools, resources, and prompts

Testing:

• Fixed test assertions to include new plugin context
  parameters
• Added CrossHookContextPlugin test fixture demonstrating
  context flow
• Added integration tests validating HTTP → Tool, HTTP →
  Resource, HTTP → Prompt context sharing

Benefits

• Plugins can now share state across the entire request
  lifecycle
• Enables use cases like: request tracking, risk scoring,
  audit trails, custom auth flows
• Maintains plugin isolation (each plugin only sees its own
  context)
• No threading/caching concerns - uses request-scoped state

Files Changed

• mcpgateway/middleware/rbac.py
• mcpgateway/services/{tool,resource,prompt}_service.py
• mcpgateway/main.py
• tests/unit/mcpgateway/test_main.py
• tests/integration/test_cross_hook_context_sharing.py (new)
• tests/unit/mcpgateway/plugins/fixtures/plugins/cross_hook_
  context.py (new)

[araujof]

LGTM

Nice job!

Summary
This PR adds support for sharing context data across different plugin hook types, enabling plugins to maintain state throughout the request
lifecycle.

Impact

• Enables stateful plugins: Plugins can now share data across different lifecycle stages
• Backward compatible: Falls back to creating new contexts when middleware contexts aren't available
• Consistent context handling: Global context reused throughout request lifecycle