feat(security): add data flow security with agent hook integration (Spec 027)

[Dumbris]

Summary

• Add data flow security system that detects and prevents data exfiltration by tracking how data moves between internal tools (Read, databases) and external tools (WebFetch, Slack)
• Support two operating modes: proxy-only (universal, works with any MCP agent) and full mode (with agent hook integration for intercepting agent-internal tool calls like Read, Write, Bash)
• Implement complete hook CLI (mcpproxy hook install/uninstall/status/evaluate) for Claude Code integration

Key Components

• Classifier (internal/security/flow/classifier.go): Categorizes tools/servers as internal, external, hybrid, or unknown using name heuristics and config overrides
• Content Hasher (internal/security/flow/hasher.go): SHA256 per-field extraction from JSON for content flow matching without storing raw data
• Flow Tracker (internal/security/flow/tracker.go): Session-scoped origin recording and flow edge detection with configurable policies
• Policy Evaluator (internal/security/flow/policy.go): Configurable actions (allow/warn/ask/deny) with graceful degradation in proxy-only mode (ask→warn)
• Session Correlator (internal/security/flow/correlator.go): Links agent hook sessions to MCP proxy sessions via argument hash matching
• Hook CLI (cmd/mcpproxy/hook_cmd.go): Install/uninstall/status/evaluate commands for Claude Code agent hooks
• REST API (internal/httpapi/hooks.go): POST /api/v1/hooks/evaluate endpoint for hook event processing
• Activity Logging: New hook_evaluation and flow_summary activity types with full metadata
• Web UI Nudge: Dashboard hint encouraging hook installation when running in proxy-only mode
• Diagnostics: Security coverage recommendation in mcpproxy doctor output
• OpenAPI: Updated swagger.yaml with new endpoint, activity filters, and schemas

Architecture

Agent (Claude Code)
  ├── Internal tools (Read, Write, Bash) ──→ Hook CLI ──→ POST /api/v1/hooks/evaluate
  └── MCP tools (call_tool_read/write) ──→ MCP Proxy ──→ Upstream servers
                                              ↕
                                    Flow Tracker (session-scoped)
                                    Content hash matching
                                    Policy evaluation

Test plan

• 68/70 TDD tasks complete (2 benchmarks deferred to pre-merge)
• Unit tests: all pass including internal/security/flow/... (25 tests), internal/httpapi/..., internal/runtime/...
• Race detection: go test -race ./internal/security/flow/... passes cleanly
• E2E test: proxy-only flow detection pipeline (TestE2E_FlowSecurity_ProxyOnlyDetection)
• E2E test: hook-enhanced flow detection via HTTP API (TestE2E_FlowSecurity_HookEnhancedDetection) — verifies deny decision with flow_type=internal_to_external, risk_level=high
• API E2E: test-api-e2e.sh — no regressions (61/71 pass, 10 failures pre-existing)
• OpenAPI: verify-oas-coverage.sh — new endpoint documented
• Frontend: vue-tsc --noEmit passes cleanly

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[tjsingleton]

Code review

Found 3 issues:

1. Data race in CheckFlow method — Writing to session fields (LastActivity, ToolsUsed, Flows) while holding only a read lock. Will fail go test -race which is required per CLAUDE.md. Lock type should be upgraded to Lock() before mutations at lines 113-120.

mcpproxy-go/internal/security/flow/tracker.go

Lines 80 to 123 in ec787a4

	session.mu.RLock()
	defer session.mu.RUnlock()
	var edges []*FlowEdge
	matched := make(map[string]bool) // Avoid duplicate edges for same content hash
	for hash := range argHashes {
	if matched[hash] {
	continue
	}
	origin, found := session.Origins[hash]
	if !found {
	continue
	}
	matched[hash] = true
	flowType := determineFlowType(origin.Classification, destClassification)
	riskLevel := assessRisk(flowType, origin.HasSensitiveData)
	edge := &FlowEdge{
	FromOrigin: origin,
	ToToolName: toolName,
	ToServerName: serverName,
	ToClassification: destClassification,
	FlowType: flowType,
	RiskLevel: riskLevel,
	ContentHash: hash,
	Timestamp: time.Now(),
	}
	edges = append(edges, edge)
	}
	// Update session activity
	session.LastActivity = time.Now()
	if toolName != "" {
	session.ToolsUsed[toolName] = true
	}
	// Append detected flows
	if len(edges) > 0 {
	session.Flows = append(session.Flows, edges...)
	}
	return edges, nil

2. Missing FlowService.Stop() in Close() — Runtime.Close() stops OAuth manager and supervisor but never stops the FlowService, leaking background goroutines (sessionExpiryLoop, cleanupLoop). Should follow same pattern established in PR feat(oauth): implement token refresh reliability with exponential backoff (#023) #255 with refreshManager.Stop().

mcpproxy-go/internal/runtime/runtime.go

Lines 535 to 570 in ec787a4

	func (r *Runtime) Close() error {
	r.mu.Lock()
	if r.appCancel != nil {
	r.appCancel()
	r.appCancel = nil
	r.appCtx = context.Background()
	}
	r.mu.Unlock()
	var errs []error
	// Stop OAuth refresh manager first to prevent refresh attempts during shutdown
	if r.refreshManager != nil {
	r.refreshManager.Stop()
	if r.logger != nil {
	r.logger.Info("OAuth refresh manager stopped")
	}
	}
	// Phase 6: Stop Supervisor first to stop reconciliation
	if r.supervisor != nil {
	r.supervisor.Stop()
	if r.logger != nil {
	r.logger.Info("Supervisor stopped")
	}
	}
	if r.upstreamManager != nil {
	// Use ShutdownAll instead of DisconnectAll to ensure proper container cleanup
	// ShutdownAll handles both graceful disconnection and Docker container cleanup
	// Use 45-second timeout to allow parallel container cleanup to complete
	shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 45*time.Second)
	defer shutdownCancel()
	if err := r.upstreamManager.ShutdownAll(shutdownCtx); err != nil {
	errs = append(errs, fmt.Errorf("shutdown upstream servers: %w", err))

3. Missing SetExpiryCallback registration — FlowService.SetExpiryCallback is defined but never registered during runtime initialization. This breaks flow session summary emission to the activity log, causing EventTypeActivityFlowSummary to never fire. Should register callback after flowService creation (line 210).

mcpproxy-go/internal/runtime/runtime.go

Lines 182 to 214 in ec787a4

	var flowService *flow.FlowService
	secCfg := cfg.GetSecurityConfig()
	if secCfg.IsFlowTrackingEnabled() {
	flowCfg := secCfg.GetFlowTracking()
	classCfg := secCfg.GetClassification()
	policyCfg := secCfg.GetFlowPolicy()
	classifier := flow.NewClassifier(classCfg.ServerOverrides)
	tracker := flow.NewFlowTracker(&flow.TrackerConfig{
	SessionTimeoutMin: flowCfg.SessionTimeoutMin,
	MaxOriginsPerSession: flowCfg.MaxOriginsPerSession,
	HashMinLength: flowCfg.HashMinLength,
	MaxResponseHashBytes: flowCfg.MaxResponseHashBytes,
	})
	policy := flow.NewPolicyEvaluator(&flow.PolicyConfig{
	InternalToExternal: flow.PolicyAction(policyCfg.InternalToExternal),
	SensitiveDataExternal: flow.PolicyAction(policyCfg.SensitiveDataExternal),
	RequireJustification: policyCfg.RequireJustification,
	SuspiciousEndpoints: policyCfg.SuspiciousEndpoints,
	ToolOverrides: convertToolOverrides(policyCfg.ToolOverrides),
	})
	var det flow.SensitiveDataDetector
	if sensitiveDetector != nil {
	det = flow.NewDetectorAdapter(sensitiveDetector)
	}
	correlator := flow.NewCorrelator(5 * time.Second)
	flowService = flow.NewFlowService(classifier, tracker, policy, det, correlator)
	logger.Info("Data flow security enabled (Spec 027)",
	zap.Int("session_timeout_min", flowCfg.SessionTimeoutMin),
	zap.Int("max_origins", flowCfg.MaxOriginsPerSession))
	}

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[tjsingleton]

Opened #299 as a stacked PR with fixes for the 3 issues identified in the code review:

1. Race condition in CheckFlow() — RLock → Lock (writes to session fields require write lock)
2. Goroutine leak — added FlowService.Stop() in Runtime.Close()
3. Missing callback — registered SetExpiryCallback so flow summaries emit to activity log

All 34 flow tests pass with -race. Includes 3 regression tests.

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