fix(mcp): invalidate cached sessions when DynamicHeaders change

.golangci.yml

@@ -47,10 +47,12 @@ linters:
       # Exclude G301 (directory permissions) - workspace needs readable directories
       # Exclude G304 (file inclusion) - paths are validated via safePath()
       # Exclude G306 (file permissions) - workspace files need to be readable
+      # Exclude G706 (log injection) - we use slog structured logging which is inherently safe
       excludes:
         - G301
         - G304
         - G306
+        - G706
 
 formatters:
   enable:

mcp/client.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"fmt"
 	"log/slog"
+	"sort"
 	"strings"
 	"sync"
 	"time"
@@ -31,54 +32,69 @@ type ClientManager struct {
 	mu       sync.Mutex
 	clients  map[string]*sdk_mcp.Client
 	sessions map[string]*sdk_mcp.ClientSession
+	// headerHashes tracks the hash of headers used when creating each session,
+	// so we can detect when DynamicHeaders change and invalidate stale sessions.
+	headerHashes map[string]string
 }
 
 // NewClientManager creates a new ClientManager.
 func NewClientManager() *ClientManager {
 	return &ClientManager{
-		clients:  make(map[string]*sdk_mcp.Client),
-		sessions: make(map[string]*sdk_mcp.ClientSession),
+		clients:      make(map[string]*sdk_mcp.Client),
+		sessions:     make(map[string]*sdk_mcp.ClientSession),
+		headerHashes: make(map[string]string),
 	}
 }
 
 // GetSession returns or creates an MCP session for the given server.
+// Sessions are cached by server name. If DynamicHeaders change (e.g. a different
+// user or rotated credentials), the stale session is invalidated and recreated.
 func (m *ClientManager) GetSession(ctx context.Context, server *protocol.MCPServerConfig, logger *slog.Logger) (*sdk_mcp.ClientSession, error) {
 	if logger == nil {
 		logger = slog.With("server", server.Name)
 	}
 
+	serverName := server.Name
+	currentHash := headersCacheKey(server.Headers, server.DynamicHeaders)
+
 	m.mu.Lock()
 	defer m.mu.Unlock()
 
-	serverName := server.Name
-
 	logger.Debug("mcp resolving session",
 		"transport", server.Transport,
 		"url", server.URL,
 		"command", server.Command,
+		"auth_key", maskKey(server.DynamicHeaders["Authorization"]),
 	)
 
-	// Check if session exists and is still valid
+	// Check if session exists and headers haven't changed
 	if session, ok := m.sessions[serverName]; ok {
-		logger.Debug("mcp reusing session")
-		return session, nil
+		if m.headerHashes[serverName] == currentHash {
+			logger.Debug("mcp reusing session")
+			return session, nil
+		}
+		logger.Info("mcp headers changed, invalidating cached session",
+			"server", serverName,
+		)
+		_ = session.Close()
+		delete(m.sessions, serverName)
+		delete(m.clients, serverName)
+		delete(m.headerHashes, serverName)
 	}
 
-	// Create client if not exists
-	client, ok := m.clients[serverName]
-	if !ok {
-		client = sdk_mcp.NewClient(&sdk_mcp.Implementation{
-			Name:    "flashduty-runner",
-			Version: "1.0.0",
-		}, nil)
-		m.clients[serverName] = client
-	}
+	// Create client
+	client := sdk_mcp.NewClient(&sdk_mcp.Implementation{
+		Name:    "flashduty-runner",
+		Version: "1.0.0",
+	}, nil)
+	m.clients[serverName] = client
 
 	// Create transport
 	logger.Info("mcp creating transport",
 		"transport", server.Transport,
 		"url", server.URL,
 		"command", server.Command,
+		"auth_key", maskKey(server.DynamicHeaders["Authorization"]),
 	)
 
 	transport, err := createTransport(server)
@@ -103,8 +119,11 @@ func (m *ClientManager) GetSession(ctx context.Context, server *protocol.MCPServ
 		return nil, fmt.Errorf("failed to connect to MCP server '%s': %w", serverName, err)
 	}
 
-	logger.Info("mcp connected")
+	logger.Info("mcp connected",
+		"auth_key", maskKey(server.DynamicHeaders["Authorization"]),
+	)
 	m.sessions[serverName] = session
+	m.headerHashes[serverName] = currentHash
 	return session, nil
 }
 
@@ -174,9 +193,34 @@ func (m *ClientManager) ListTools(ctx context.Context, server *protocol.MCPServe
 func (m *ClientManager) invalidateSession(serverName string) {
 	m.mu.Lock()
 	delete(m.sessions, serverName)
+	delete(m.headerHashes, serverName)
 	m.mu.Unlock()
 }
 
+func headersCacheKey(headers, dynamicHeaders map[string]string) string {
+	encode := func(m map[string]string) string {
+		keys := make([]string, 0, len(m))
+		for k := range m {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+		parts := make([]string, len(keys))
+		for i, k := range keys {
+			parts[i] = k + "=" + m[k]
+		}
+		return strings.Join(parts, "\x00")
+	}
+	return "s:" + encode(headers) + "\x01d:" + encode(dynamicHeaders)
+}
+
+func maskKey(key string) string {
+	key = strings.TrimPrefix(key, "Bearer ")
+	if len(key) <= 6 {
+		return key
+	}
+	return key[:6] + "***"
+}
+
 // Close closes all active sessions and clients.
 func (m *ClientManager) Close() {
 	m.mu.Lock()

mcp/transport.go

@@ -1,6 +1,7 @@
 package mcp
 
 import (
+	"context"
 	"log/slog"
 	"net/http"
 	"os"
@@ -12,7 +13,7 @@ import (
 
 // NewStdioTransport creates a new stdio transport for MCP.
 func NewStdioTransport(command string, args []string, env map[string]string) sdk_mcp.Transport {
-	cmd := exec.Command(command, args...)
+	cmd := exec.CommandContext(context.Background(), command, args...) //nolint:gosec // G204: command comes from cloud-controlled MCP server config
 	cmd.Env = buildEnv(env)
 	return &sdk_mcp.CommandTransport{
 		Command: cmd,
@@ -41,6 +42,7 @@ func NewSSETransport(endpoint string, headers map[string]string, dynamicHeaders
 		"endpoint", endpoint,
 		"headers_count", len(headers),
 		"dynamic_headers_count", len(dynamicHeaders),
+		"auth_key", maskKey(dynamicHeaders["Authorization"]),
 	)
 
 	return &sdk_mcp.StreamableClientTransport{

workspace/large_output.go

@@ -134,18 +134,18 @@ func (p *LargeOutputProcessor) truncateContent(content string, filePath string)
 	// Build truncation message
 	var sb strings.Builder
 	sb.WriteString("<output_truncated>\n")
-	sb.WriteString(fmt.Sprintf("Output too large (%d chars, %d lines).", len(content), totalLines))
+	fmt.Fprintf(&sb, "Output too large (%d chars, %d lines).", len(content), totalLines)
 
 	if filePath != "" {
-		sb.WriteString(fmt.Sprintf(" Full content saved to: %s\n\n", filePath))
+		fmt.Fprintf(&sb, " Full content saved to: %s\n\n", filePath)
 	} else {
 		sb.WriteString(" Could not save full content.\n\n")
 	}
 
-	sb.WriteString(fmt.Sprintf("Preview (first %d lines):\n```\n%s\n```\n\n", previewLines, preview))
+	fmt.Fprintf(&sb, "Preview (first %d lines):\n```\n%s\n```\n\n", previewLines, preview)
 
 	if filePath != "" {
-		sb.WriteString(fmt.Sprintf("To read more: read(\"%s\", offset=%d, limit=100)\n", filePath, previewLines))
+		fmt.Fprintf(&sb, "To read more: read(\"%s\", offset=%d, limit=100)\n", filePath, previewLines)
 	}
 
 	sb.WriteString("</output_truncated>")

workspace/workspace.go

@@ -252,7 +252,7 @@ func (w *Workspace) Grep(ctx context.Context, args *protocol.GrepArgs) (*protoco
 	// Build content string
 	var sb strings.Builder
 	for _, match := range res.Matches {
-		sb.WriteString(fmt.Sprintf("%s:%d:%s\n", match.Path, match.LineNumber, match.Content))
+		fmt.Fprintf(&sb, "%s:%d:%s\n", match.Path, match.LineNumber, match.Content)
 	}
 	content := sb.String()
 
@@ -274,13 +274,14 @@ func (w *Workspace) Grep(ctx context.Context, args *protocol.GrepArgs) (*protoco
 }
 
 func (w *Workspace) grepWithRipgrep(ctx context.Context, args *protocol.GrepArgs) (*protocol.GrepResult, error) {
-	cmdArgs := []string{"--column", "--line-number", "--no-heading", "--color", "never", "--smart-case"}
+	cmdArgs := make([]string, 0, 6+2*len(args.Include)+2)
+	cmdArgs = append(cmdArgs, "--column", "--line-number", "--no-heading", "--color", "never", "--smart-case")
 	for _, inc := range args.Include {
 		cmdArgs = append(cmdArgs, "--glob", inc)
 	}
 	cmdArgs = append(cmdArgs, args.Pattern, ".")
 
-	cmd := exec.CommandContext(ctx, "rg", cmdArgs...)
+	cmd := exec.CommandContext(ctx, "rg", cmdArgs...) //nolint:gosec // G204: args built from validated grep parameters
 	cmd.Dir = w.root
 
 	var stdout strings.Builder
@@ -393,7 +394,7 @@ func (w *Workspace) executeBashCommand(ctx context.Context, command, workdir str
 	ctx, cancel := context.WithTimeout(ctx, timeout)
 	defer cancel()
 
-	cmd := exec.CommandContext(ctx, "bash", "-c", command)
+	cmd := exec.CommandContext(ctx, "bash", "-c", command) //nolint:gosec // G204: command is user-initiated via workspace tool
 	cmd.Dir = workdir
 
 	// Use a limited writer to prevent OOM from very large outputs

ws/client.go

@@ -518,9 +518,10 @@ func getLinuxVersion() string {
 	return ""
 }
 
-// getCommandOutput executes a command and returns its trimmed output.
 func getCommandOutput(name string, args ...string) string {
-	out, err := exec.Command(name, args...).Output()
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	out, err := exec.CommandContext(ctx, name, args...).Output() //nolint:gosec // G204: args are hardcoded system info commands
 	if err == nil {
 		return strings.TrimSpace(string(out))
 	}
@@ -550,7 +551,7 @@ func getDefaultShell() string {
 func getTotalMemoryMB() int64 {
 	switch runtime.GOOS {
 	case "darwin":
-		out, err := exec.Command("sysctl", "-n", "hw.memsize").Output()
+		out, err := exec.CommandContext(context.Background(), "sysctl", "-n", "hw.memsize").Output() //nolint:gosec // G204: hardcoded command
 		if err == nil {
 			var bytes int64
 			if _, err := fmt.Sscanf(strings.TrimSpace(string(out)), "%d", &bytes); err == nil {

ws/handler.go

@@ -100,7 +100,7 @@ func (h *Handler) handleTaskRequest(ctx context.Context, msg *protocol.Message)
 		"operation", req.Operation,
 	)
 
-	taskCtx, cancel := context.WithCancel(ctx)
+	taskCtx, cancel := context.WithCancel(ctx) //nolint:gosec // G118: cancel is stored in h.runningTask and called on task completion/cancellation
 	h.mu.Lock()
 	h.runningTask[req.TaskID] = cancel
 	h.mu.Unlock()