Gadoes is wiring Mike up to outside legal sources

- Fixed StdioClientTransport mock to use class constructor (arrow fn can't be used with `new`)
- Fixed callTool() to catch spawn errors and return structured source_unavailable error
- Fixed afterEach to use resetAllMocks() instead of clearAllMocks() to prevent mockImplementationOnce queue leakage between tests
- Fixed dispose() test to clear mockClose call count before the assertion

All 10 Chunk 1 tests pass.

Acceptance criteria:
[x] listTools() returns at least one tool from a running MCP server
[x] No spawn occurs on second warm call within idle TTL
[x] Child process exit triggers reconnect within 1s (fake timers)
[x] 3 consecutive spawn failures → permanently_failed state
[x] dispose() kills all spawned processes (spy verification)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

- Added spike-mcp-host.ts POC: validates StdioClientTransport + server-filesystem stdio server (14 tools, listTools + callTool both pass)
- Implemented McpClientManager singleton with lazy-spawn, 15-min idle TTL, per-server request queue (max 10), auto-reconnect with exponential backoff, permanently_failed state after 3 failures, and dispose() for SIGTERM/SIGINT cleanup
- Added types.ts with McpServerConfig, McpToolDefinition, McpServerState, McpCallResult, McpHealthResult
- Installed @modelcontextprotocol/server-filesystem, vitest, @vitest/coverage-v8
- All 10 Vitest tests pass (cold-start, warm reuse, idle disposal, reconnect, permanently_failed, queue throttle, dispose, health check)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

- Created backend/src/__mocks__/mockMcpServer.ts - in-process MCP server
  using @modelcontextprotocol/sdk's InMemoryTransport + Server
- Pre-defined tool set: search_cases, retrieve_case
- respondWith(toolName, response) for scripted responses
- createMockMcpServer() returns started server + connected McpClientManager
- 5 unit tests: scripted responses, listTools, respondWith overrides,
  default responses, unknown tool error

Acceptance criteria:
[x] createMockMcpServer() usable in any Vitest test file without spawning child processes
[x] Returns deterministic responses per respondWith() config

Tests: 15 pass (10 Chunk 1 + 5 Chunk 2)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

- Added isMcpTool(), parseMcpToolName(), mcpToolToOpenAI() helpers in chatTools.ts
- Extended runToolCalls() with optional mcpManager param; detects mcp__ prefix
  and dispatches to McpClientManager.callTool()
- Emits mcp_tool_call_start SSE event per MCP tool call
- Extended runLLMStream() with mcpServerTools, openCircuitSources, mcpManager params
- MCP tools appended to activeTools after existing TOOLS and WORKFLOW_TOOLS
- Open-circuit sources excluded from activeTools; unavailability note appended
  to system prompt (spec Section 2.7)
- Active MCP source names and tools listed in system prompt

Acceptance criteria:
[x] LLM emits MCP tool call by prefixed name (mcp__{server}__{tool})
[x] runToolCalls() dispatches to McpClientManager
[x] Tool result returned in { role: "tool", tool_call_id, content } format
[x] mcp_tool_call_start SSE event emitted with correct fields
[x] Open-circuit source tools absent from activeTools

Tests: 24 pass (10+5+9)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>