apps/api/src/bridge/discord/discord.service.spec.ts

@@ -7,6 +7,7 @@ import type { ChatMessage, ChatCommand } from "../interfaces";
 
 // Mock discord.js Client
 const mockReadyCallbacks: Array<() => void> = [];
+const mockErrorCallbacks: Array<(error: Error) => void> = [];
 const mockClient = {
   login: vi.fn().mockImplementation(async () => {
     // Trigger ready callback when login is called
@@ -14,7 +15,11 @@ const mockClient = {
     return Promise.resolve();
   }),
   destroy: vi.fn().mockResolvedValue(undefined),
-  on: vi.fn(),
+  on: vi.fn().mockImplementation((event: string, callback: (error: Error) => void) => {
+    if (event === "error") {
+      mockErrorCallbacks.push(callback);
+    }
+  }),
   once: vi.fn().mockImplementation((event: string, callback: () => void) => {
     if (event === "ready") {
       mockReadyCallbacks.push(callback);
@@ -73,8 +78,9 @@ describe("DiscordService", () => {
     process.env.DISCORD_CONTROL_CHANNEL_ID = "test-channel-id";
     process.env.DISCORD_WORKSPACE_ID = "test-workspace-id";
 
-    // Clear ready callbacks
+    // Clear callbacks
     mockReadyCallbacks.length = 0;
+    mockErrorCallbacks.length = 0;
 
     const module: TestingModule = await Test.createTestingModule({
       providers: [
@@ -533,4 +539,117 @@ describe("DiscordService", () => {
       process.env.DISCORD_WORKSPACE_ID = "test-workspace-id";
     });
   });
+
+  describe("Error Logging Security", () => {
+    it("should sanitize sensitive data in error logs", () => {
+      const loggerErrorSpy = vi.spyOn((service as any).logger, "error");
+
+      // Simulate an error with sensitive data
+      const errorWithSecrets = new Error("Connection failed");
+      (errorWithSecrets as any).config = {
+        headers: {
+          Authorization: "Bearer secret_token_12345",
+        },
+      };
+      (errorWithSecrets as any).token = "MTk4NjIyNDgzNDcxOTI1MjQ4.Cl2FMQ.ZnCjm1XVW7vRze4b7Cq4se7kKWs";
+
+      // Trigger error event handler
+      expect(mockErrorCallbacks.length).toBeGreaterThan(0);
+      mockErrorCallbacks[0]?.(errorWithSecrets);
+
+      // Verify error was logged
+      expect(loggerErrorSpy).toHaveBeenCalled();
+
+      // Get the logged error
+      const loggedArgs = loggerErrorSpy.mock.calls[0];
+      const loggedError = loggedArgs[1];
+
+      // Verify sensitive data was redacted
+      expect(loggedError.config.headers.Authorization).toBe("[REDACTED]");
+      expect(loggedError.token).toBe("[REDACTED]");
+      expect(loggedError.message).toBe("Connection failed");
+      expect(loggedError.name).toBe("Error");
+    });
+
+    it("should not leak bot token in error logs", () => {
+      const loggerErrorSpy = vi.spyOn((service as any).logger, "error");
+
+      // Simulate an error with bot token in message
+      const errorWithToken = new Error(
+        "Discord authentication failed with token MTk4NjIyNDgzNDcxOTI1MjQ4.Cl2FMQ.ZnCjm1XVW7vRze4b7Cq4se7kKWs"
+      );
+
+      // Trigger error event handler
+      expect(mockErrorCallbacks.length).toBeGreaterThan(0);
+      mockErrorCallbacks[0]?.(errorWithToken);
+
+      // Verify error was logged
+      expect(loggerErrorSpy).toHaveBeenCalled();
+
+      // Get the logged error
+      const loggedArgs = loggerErrorSpy.mock.calls[0];
+      const loggedError = loggedArgs[1];
+
+      // Verify token was redacted from message
+      expect(loggedError.message).not.toContain(
+        "MTk4NjIyNDgzNDcxOTI1MjQ4.Cl2FMQ.ZnCjm1XVW7vRze4b7Cq4se7kKWs"
+      );
+      expect(loggedError.message).toContain("[REDACTED]");
+    });
+
+    it("should sanitize API keys in error logs", () => {
+      const loggerErrorSpy = vi.spyOn((service as any).logger, "error");
+
+      // Simulate an error with API key
+      const errorWithApiKey = new Error("Request failed");
+      (errorWithApiKey as any).apiKey = "sk_live_1234567890abcdef";
+      (errorWithApiKey as any).response = {
+        data: {
+          error: "Invalid API key: sk_live_1234567890abcdef",
+        },
+      };
+
+      // Trigger error event handler
+      expect(mockErrorCallbacks.length).toBeGreaterThan(0);
+      mockErrorCallbacks[0]?.(errorWithApiKey);
+
+      // Verify error was logged
+      expect(loggerErrorSpy).toHaveBeenCalled();
+
+      // Get the logged error
+      const loggedArgs = loggerErrorSpy.mock.calls[0];
+      const loggedError = loggedArgs[1];
+
+      // Verify API key was redacted
+      expect(loggedError.apiKey).toBe("[REDACTED]");
+      expect(loggedError.response.data.error).not.toContain("sk_live_1234567890abcdef");
+      expect(loggedError.response.data.error).toContain("[REDACTED]");
+    });
+
+    it("should preserve non-sensitive error information", () => {
+      const loggerErrorSpy = vi.spyOn((service as any).logger, "error");
+
+      // Simulate a normal error without secrets
+      const normalError = new Error("Connection timeout");
+      (normalError as any).code = "ETIMEDOUT";
+      (normalError as any).statusCode = 408;
+
+      // Trigger error event handler
+      expect(mockErrorCallbacks.length).toBeGreaterThan(0);
+      mockErrorCallbacks[0]?.(normalError);
+
+      // Verify error was logged
+      expect(loggerErrorSpy).toHaveBeenCalled();
+
+      // Get the logged error
+      const loggedArgs = loggerErrorSpy.mock.calls[0];
+      const loggedError = loggedArgs[1];
+
+      // Verify non-sensitive data was preserved
+      expect(loggedError.message).toBe("Connection timeout");
+      expect(loggedError.name).toBe("Error");
+      expect(loggedError.code).toBe("ETIMEDOUT");
+      expect(loggedError.statusCode).toBe(408);
+    });
+  });
 });

apps/api/src/bridge/discord/discord.service.ts

@@ -1,6 +1,7 @@
 import { Injectable, Logger } from "@nestjs/common";
 import { Client, Events, GatewayIntentBits, TextChannel, ThreadChannel } from "discord.js";
 import { StitcherService } from "../../stitcher/stitcher.service";
+import { sanitizeForLogging } from "../../common/utils";
 import type {
   IChatProvider,
   ChatMessage,
@@ -80,8 +81,10 @@ export class DiscordService implements IChatProvider {
       }
     });
 
-    this.client.on(Events.Error, (error) => {
-      this.logger.error("Discord client error:", error);
+    this.client.on(Events.Error, (error: Error) => {
+      // Sanitize error before logging to prevent secret exposure
+      const sanitizedError = sanitizeForLogging(error);
+      this.logger.error("Discord client error:", sanitizedError);
     });
   }
 

apps/api/src/common/utils/index.ts

@@ -1 +1,2 @@
 export * from "./query-builder";
+export * from "./log-sanitizer";

apps/api/src/common/utils/log-sanitizer.spec.ts

@@ -0,0 +1,311 @@
+import { describe, it, expect } from "vitest";
+import { sanitizeForLogging } from "./log-sanitizer";
+
+describe("sanitizeForLogging", () => {
+  describe("String sanitization", () => {
+    it("should redact API keys", () => {
+      const input = "Error with API key: sk_live_1234567890abcdef";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("Error with API key: [REDACTED]");
+    });
+
+    it("should redact bearer tokens", () => {
+      const input = "Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("Authorization: Bearer [REDACTED]");
+    });
+
+    it("should redact Discord bot tokens", () => {
+      const input = "Bot token: MTk4NjIyNDgzNDcxOTI1MjQ4.Cl2FMQ.ZnCjm1XVW7vRze4b7Cq4se7kKWs";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("Bot token: [REDACTED]");
+    });
+
+    it("should redact passwords in strings", () => {
+      const input = 'Connection failed with password="secret123"';
+      const result = sanitizeForLogging(input);
+      expect(result).toBe('Connection failed with password="[REDACTED]"');
+    });
+
+    it("should redact email addresses", () => {
+      const input = "User email: user@example.com failed to authenticate";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("User email: [REDACTED] failed to authenticate");
+    });
+
+    it("should redact database connection strings", () => {
+      const input = "postgresql://user:password123@localhost:5432/mydb";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("postgresql://user:[REDACTED]@localhost:5432/mydb");
+    });
+
+    it("should redact authorization headers", () => {
+      const input = "Authorization: Basic dXNlcjpwYXNzd29yZA==";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("Authorization: Basic [REDACTED]");
+    });
+
+    it("should preserve non-sensitive strings", () => {
+      const input = "This is a regular log message without secrets";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("This is a regular log message without secrets");
+    });
+
+    it("should redact environment variable style secrets", () => {
+      const input = "API_KEY=abc123def456 failed";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("API_KEY=[REDACTED] failed");
+    });
+
+    it("should redact multiple secrets in one string", () => {
+      const input = "token=xyz123 and password=secret456";
+      const result = sanitizeForLogging(input);
+      expect(result).toBe("token=[REDACTED] and password=[REDACTED]");
+    });
+  });
+
+  describe("Object sanitization", () => {
+    it("should redact secrets in flat objects", () => {
+      const input = {
+        message: "Error occurred",
+        apiKey: "sk_live_1234567890",
+        token: "Bearer abc123",
+      };
+      const result = sanitizeForLogging(input);
+      expect(result).toEqual({
+        message: "Error occurred",
+        apiKey: "[REDACTED]",
+        token: "[REDACTED]",
+      });
+    });
+
+    it("should redact secrets in nested objects", () => {
+      const input = {
+        error: {
+          message: "Auth failed",
+          credentials: {
+            username: "admin",
+            password: "secret123",
+          },
+        },
+      };
+      const result = sanitizeForLogging(input);
+      expect(result).toEqual({
+        error: {
+          message: "Auth failed",
+          credentials: {
+            username: "admin",
+            password: "[REDACTED]",
+          },
+        },
+      });
+    });
+
+    it("should redact secrets based on key names", () => {
+      const input = {
+        apiKey: "secret",
+        api_key: "secret",
+        API_KEY: "secret",
+        bearerToken: "token",
+        accessToken: "token",
+        password: "pass",
+        secret: "secret",
+        client_secret: "secret",
+      };
+      const result = sanitizeForLogging(input);
+      expect(result).toEqual({
+        apiKey: "[REDACTED]",
+        api_key: "[REDACTED]",
+        API_KEY: "[REDACTED]",
+        bearerToken: "[REDACTED]",
+        accessToken: "[REDACTED]",
+        password: "[REDACTED]",
+        secret: "[REDACTED]",
+        client_secret: "[REDACTED]",
+      });
+    });
+
+    it("should preserve non-sensitive object properties", () => {
+      const input = {
+        message: "Test message",
+        statusCode: 500,
+        timestamp: new Date("2024-01-01"),
+        count: 42,
+      };
+      const result = sanitizeForLogging(input);
+      expect(result).toEqual({
+        message: "Test message",
+        statusCode: 500,
+        timestamp: new Date("2024-01-01"),
+        count: 42,
+      });
+    });
+
+    it("should handle objects with null and undefined values", () => {
+      const input = {
+        message: "Error",
+        token: null,
+        apiKey: undefined,
+        data: "value",
+      };
+      const result = sanitizeForLogging(input);
+      expect(result).toEqual({
+        message: "Error",
+        token: null,
+        apiKey: undefined,
+        data: "value",
+      });
+    });
+  });
+
+  describe("Array sanitization", () => {
+    it("should sanitize strings in arrays", () => {
+      const input = ["normal message", "token=abc123", "another message"];
+      const result = sanitizeForLogging(input);
+      expect(result).toEqual(["normal message", "token=[REDACTED]", "another message"]);
+    });
+
+    it("should sanitize objects in arrays", () => {
+      const input = [
+        { message: "ok" },
+        { message: "error", apiKey: "secret123" },
+        { message: "info" },
+      ];
+      const result = sanitizeForLogging(input);
+      expect(result).toEqual([
+        { message: "ok" },
+        { message: "error", apiKey: "[REDACTED]" },
+        { message: "info" },
+      ]);
+    });
+
+    it("should handle nested arrays", () => {
+      const input = [["token=abc"], ["password=xyz"]];
+      const result = sanitizeForLogging(input);
+      expect(result).toEqual([["token=[REDACTED]"], ["password=[REDACTED]"]]);
+    });
+  });
+
+  describe("Error object sanitization", () => {
+    it("should sanitize Error objects", () => {
+      const error = new Error("Auth failed with token abc123");
+      const result = sanitizeForLogging(error);
+      expect(result.message).toBe("Auth failed with token [REDACTED]");
+      expect(result.name).toBe("Error");
+    });
+
+    it("should sanitize custom error properties", () => {
+      const error = new Error("Request failed");
+      (error as any).config = {
+        headers: {
+          Authorization: "Bearer secret123",
+        },
+      };
+      const result = sanitizeForLogging(error);
+      expect(result.config.headers.Authorization).toBe("[REDACTED]");
+    });
+
+    it("should handle errors with nested objects", () => {
+      const error = new Error("Discord error");
+      (error as any).response = {
+        status: 401,
+        data: {
+          message: "Invalid token",
+          token: "abc123",
+        },
+      };
+      const result = sanitizeForLogging(error);
+      expect(result.response.data.token).toBe("[REDACTED]");
+    });
+  });
+
+  describe("Edge cases", () => {
+    it("should handle null input", () => {
+      const result = sanitizeForLogging(null);
+      expect(result).toBeNull();
+    });
+
+    it("should handle undefined input", () => {
+      const result = sanitizeForLogging(undefined);
+      expect(result).toBeUndefined();
+    });
+
+    it("should handle numbers", () => {
+      const result = sanitizeForLogging(42);
+      expect(result).toBe(42);
+    });
+
+    it("should handle booleans", () => {
+      const result = sanitizeForLogging(true);
+      expect(result).toBe(true);
+    });
+
+    it("should handle empty objects", () => {
+      const result = sanitizeForLogging({});
+      expect(result).toEqual({});
+    });
+
+    it("should handle empty arrays", () => {
+      const result = sanitizeForLogging([]);
+      expect(result).toEqual([]);
+    });
+
+    it("should handle circular references", () => {
+      const obj: any = { name: "test" };
+      obj.self = obj;
+      const result = sanitizeForLogging(obj);
+      expect(result.name).toBe("test");
+      expect(result.self).toBe("[Circular Reference]");
+    });
+
+    it("should handle large objects without performance issues", () => {
+      const largeObj: any = {};
+      for (let i = 0; i < 1000; i++) {
+        largeObj[`key${i}`] = `value${i}`;
+      }
+      largeObj.password = "secret123";
+
+      const start = Date.now();
+      const result = sanitizeForLogging(largeObj);
+      const duration = Date.now() - start;
+
+      expect(result.password).toBe("[REDACTED]");
+      expect(duration).toBeLessThan(100); // Should complete in under 100ms
+    });
+  });
+
+  describe("Discord-specific cases", () => {
+    it("should sanitize Discord bot token format", () => {
+      const input = {
+        error: "Failed to connect",
+        token: "MTk4NjIyNDgzNDcxOTI1MjQ4.Cl2FMQ.ZnCjm1XVW7vRze4b7Cq4se7kKWs",
+      };
+      const result = sanitizeForLogging(input);
+      expect(result.token).toBe("[REDACTED]");
+    });
+
+    it("should sanitize Discord error with config", () => {
+      const error = {
+        message: "Request failed",
+        config: {
+          headers: {
+            Authorization: "Bot MTk4NjIyNDgzNDcxOTI1MjQ4.Cl2FMQ.ZnCjm1XVW7vRze4b7Cq4se7kKWs",
+          },
+        },
+      };
+      const result = sanitizeForLogging(error);
+      expect(result.config.headers.Authorization).toBe("[REDACTED]");
+    });
+
+    it("should sanitize workspace IDs if configured", () => {
+      const input = {
+        message: "Job dispatched",
+        workspaceId: "ws_123456789",
+      };
+      const result = sanitizeForLogging(input);
+      // Workspace IDs are preserved by default (not considered sensitive)
+      // Can be redacted if needed in future
+      expect(result.workspaceId).toBe("ws_123456789");
+    });
+  });
+});

apps/api/src/common/utils/log-sanitizer.ts

@@ -0,0 +1,185 @@
+/**
+ * Log Sanitizer Utility
+ *
+ * Sanitizes sensitive information from logs to prevent secret exposure.
+ * This is critical for security when logging errors, especially to external
+ * services like Discord.
+ *
+ * @module log-sanitizer
+ */
+
+/**
+ * Patterns for detecting sensitive data in strings
+ * Order matters - more specific patterns should come first
+ */
+const SENSITIVE_PATTERNS = [
+  // Quoted passwords and secrets (must come before general key-value patterns)
+  { pattern: /(password|secret|token|key)\s*=\s*"([^"]+)"/gi, replacement: '$1="[REDACTED]"' },
+  { pattern: /(password|secret|token|key)\s*=\s*'([^']+)'/gi, replacement: "$1='[REDACTED]'" },
+  // Discord bot tokens (specific format, must come before generic token patterns)
+  {
+    pattern: /\b[MN][A-Za-z\d]{23,25}\.[A-Za-z\d]{6}\.[A-Za-z\d_-]{27,}\b/g,
+    replacement: "[REDACTED]",
+  },
+  // API Keys and tokens (Stripe-style)
+  { pattern: /\b(?:sk|pk)_(?:live|test)_[a-zA-Z0-9]{16,}/gi, replacement: "[REDACTED]" },
+  // Bearer tokens
+  { pattern: /Bearer\s+[A-Za-z0-9\-._~+/]+=*/gi, replacement: "Bearer [REDACTED]" },
+  // JWT tokens
+  { pattern: /eyJ[a-zA-Z0-9_-]*\.eyJ[a-zA-Z0-9_-]*\.[a-zA-Z0-9_-]*/g, replacement: "[REDACTED]" },
+  // Authorization Basic
+  { pattern: /Basic\s+[A-Za-z0-9+/]+=*/gi, replacement: "Basic [REDACTED]" },
+  // Email addresses
+  { pattern: /\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b/g, replacement: "[REDACTED]" },
+  // Connection string passwords
+  { pattern: /(:\/\/[^:]+:)([^@]+)(@)/g, replacement: "$1[REDACTED]$3" },
+  // Generic tokens in text with colon (e.g., "token: abc123")
+  {
+    pattern: /\b(token|password|secret|key)\s*:\s+([a-zA-Z0-9._-]{6,})/gi,
+    replacement: "$1: [REDACTED]",
+  },
+  // Generic tokens in text without colon (e.g., "token abc123")
+  {
+    pattern: /\b(token|password|secret|key)\s+([a-zA-Z0-9._-]{6,})/gi,
+    replacement: "$1 [REDACTED]",
+  },
+  // Key-value pairs with = sign (should be last as it's most general)
+  {
+    pattern:
+      /\b(token|password|secret|api[_-]?key|apikey|client[_-]?secret|bearer)\s*=\s*[^\s,;)}\]"']+/gi,
+    replacement: "$1=[REDACTED]",
+  },
+];
+
+/**
+ * Sensitive key names that should have their values redacted
+ */
+const SENSITIVE_KEYS = [
+  "password",
+  "secret",
+  "token",
+  "apikey",
+  "api_key",
+  "apiKey",
+  "API_KEY",
+  "bearertoken",
+  "bearerToken",
+  "bearer_token",
+  "accesstoken",
+  "accessToken",
+  "access_token",
+  "refreshtoken",
+  "refreshToken",
+  "refresh_token",
+  "clientsecret",
+  "clientSecret",
+  "client_secret",
+  "authorization",
+  "Authorization",
+];
+
+/**
+ * Checks if a key name is sensitive
+ */
+function isSensitiveKey(key: string): boolean {
+  const lowerKey = key.toLowerCase();
+  return SENSITIVE_KEYS.some((sensitiveKey) => lowerKey.includes(sensitiveKey.toLowerCase()));
+}
+
+/**
+ * Sanitizes a string by redacting sensitive patterns
+ */
+function sanitizeString(value: string): string {
+  let sanitized = value;
+  for (const { pattern, replacement } of SENSITIVE_PATTERNS) {
+    sanitized = sanitized.replace(pattern, replacement);
+  }
+  return sanitized;
+}
+
+/**
+ * Type guard to check if value is an object
+ */
+function isObject(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null && !Array.isArray(value);
+}
+
+/**
+ * Sanitizes data for logging by redacting sensitive information
+ *
+ * @param data - The data to sanitize (can be string, object, array, etc.)
+ * @param seen - Internal set to track circular references
+ * @returns Sanitized version of the data with secrets redacted
+ *
+ * @example
+ * ```typescript
+ * const error = new Error("Auth failed");
+ * error.config = { headers: { Authorization: "Bearer secret123" } };
+ * const sanitized = sanitizeForLogging(error);
+ * // sanitized.config.headers.Authorization === "[REDACTED]"
+ * ```
+ */
+export function sanitizeForLogging(data: unknown, seen = new WeakSet()): unknown {
+  // Handle primitives
+  if (data === null || data === undefined) {
+    return data;
+  }
+
+  if (typeof data === "boolean" || typeof data === "number") {
+    return data;
+  }
+
+  if (typeof data === "string") {
+    return sanitizeString(data);
+  }
+
+  // Handle arrays
+  if (Array.isArray(data)) {
+    return data.map((item) => sanitizeForLogging(item, seen));
+  }
+
+  // Handle Date objects (preserve them as-is)
+  if (data instanceof Date) {
+    return data;
+  }
+
+  // Handle objects (including Error objects)
+  if (isObject(data)) {
+    // Check for circular references
+    if (seen.has(data)) {
+      return "[Circular Reference]";
+    }
+    seen.add(data);
+
+    const sanitized: Record<string, unknown> = {};
+
+    // Handle Error objects specially to preserve their properties
+    if (data instanceof Error) {
+      sanitized.name = data.name;
+      sanitized.message = sanitizeString(data.message);
+      if (data.stack) {
+        sanitized.stack = sanitizeString(data.stack);
+      }
+    }
+
+    // Process all enumerable properties
+    for (const key in data) {
+      if (Object.prototype.hasOwnProperty.call(data, key)) {
+        const value = data[key];
+
+        // If the key is sensitive, redact the value
+        if (isSensitiveKey(key)) {
+          sanitized[key] = value === null || value === undefined ? value : "[REDACTED]";
+        } else {
+          // Recursively sanitize nested values
+          sanitized[key] = sanitizeForLogging(value, seen);
+        }
+      }
+    }
+
+    return sanitized;
+  }
+
+  // Return other types as-is (functions, symbols, etc.)
+  return data as unknown;
+}

docs/scratchpads/188-sanitize-discord-logs.md

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+# Issue #188: Sanitize Discord error logs to prevent secret exposure
+
+## Objective
+Implement log sanitization in Discord error logging to prevent exposure of sensitive information including API keys, tokens, credentials, and PII.
+
+## Security Context
+- **Priority**: P1 SECURITY
+- **Risk**: Credential leakage through logs
+- **Impact**: Could expose authentication tokens, API keys, passwords to unauthorized parties
+
+## Approach
+1. **Discovery Phase**: Locate all Discord logging points
+2. **Test Phase**: Write tests for log sanitization (TDD)
+3. **Implementation Phase**: Create sanitization utility
+4. **Integration Phase**: Apply sanitization to Discord logging
+5. **Verification Phase**: Ensure all tests pass with ≥85% coverage
+
+## Progress
+- [x] Create scratchpad
+- [x] Locate Discord error logging code
+- [x] Identify sensitive data patterns to redact
+- [x] Write tests for log sanitization (TDD RED phase)
+- [x] Implement sanitization utility (TDD GREEN phase)
+- [x] Integrate with Discord service
+- [x] Refactor for quality (TDD REFACTOR phase)
+- [x] Verify test coverage ≥85%
+- [x] Security review
+- [x] Implementation complete (commit pending due to pre-existing lint issues in @mosaic/api package)
+
+## Discovery
+
+### Sensitive Data to Redact
+1. **Authentication**: API keys, tokens, bearer tokens
+2. **Headers**: Authorization headers, API key headers
+3. **Credentials**: Passwords, secrets, client secrets
+4. **Database**: Connection strings, database passwords
+5. **PII**: Email addresses, user names, phone numbers
+6. **Identifiers**: Workspace IDs (if considered sensitive)
+
+### Logging Points Found
+- **discord.service.ts:84** - `this.logger.error("Discord client error:", error)`
+  - This logs raw error objects which may contain sensitive data
+  - Error objects from Discord.js may contain authentication tokens
+  - Error stack traces may reveal environment variables or configuration
+
+### Implementation Plan
+1. Create `apps/api/src/common/utils/log-sanitizer.ts`
+2. Create `apps/api/src/common/utils/log-sanitizer.spec.ts` (TDD - tests first)
+3. Implement sanitization patterns:
+   - Redact tokens, API keys, passwords
+   - Redact authorization headers
+   - Redact connection strings
+   - Redact email addresses
+   - Deep scan objects and arrays
+4. Apply to Discord error logging
+5. Export from common/utils/index.ts
+
+## Testing
+TDD approach:
+1. RED - Write failing tests for sanitization
+2. GREEN - Implement minimal sanitization logic
+3. REFACTOR - Improve code quality
+
+Test cases:
+- Sanitize string with API key
+- Sanitize string with bearer token
+- Sanitize string with password
+- Sanitize object with nested secrets
+- Sanitize array with secrets
+- Sanitize error objects
+- Preserve non-sensitive data
+- Handle null/undefined inputs
+- Sanitize connection strings
+- Sanitize email addresses
+
+## Implementation Summary
+
+### Files Created
+1. `/home/localadmin/src/mosaic-stack/apps/api/src/common/utils/log-sanitizer.ts` - Core sanitization utility
+2. `/home/localadmin/src/mosaic-stack/apps/api/src/common/utils/log-sanitizer.spec.ts` - Comprehensive test suite (32 tests)
+
+### Files Modified
+1. `/home/localadmin/src/mosaic-stack/apps/api/src/common/utils/index.ts` - Export sanitization function
+2. `/home/localadmin/src/mosaic-stack/apps/api/src/bridge/discord/discord.service.ts` - Integrate sanitization
+3. `/home/localadmin/src/mosaic-stack/apps/api/src/bridge/discord/discord.service.spec.ts` - Add security tests
+
+### Test Results
+- **Log Sanitizer Tests**: 32/32 passed (100%)
+- **Discord Service Tests**: 25/25 passed (100%)
+- **Code Coverage**: 97.43% (exceeds 85% requirement)
+
+### Security Patterns Implemented
+The sanitizer detects and redacts:
+1. API keys (sk_live_*, pk_test_*)
+2. Bearer tokens
+3. Discord bot tokens (specific format)
+4. JWT tokens
+5. Basic authentication tokens
+6. Email addresses
+7. Database connection string passwords
+8. Environment variable style secrets (KEY=value)
+9. Quoted passwords and secrets
+10. Generic tokens in text
+
+### Key Features
+- Deep object traversal (handles nested objects and arrays)
+- Circular reference detection
+- Error object handling (preserves Error structure)
+- Date object preservation
+- Performance optimized (handles 1000+ key objects in <100ms)
+- Maintains non-sensitive data (status codes, error types, etc.)
+
+## Security Review
+
+### Threat Model
+**Before**: Discord error logging could expose:
+- Bot authentication tokens
+- API keys in error messages
+- User credentials from failed authentication
+- Database connection strings
+- Environment variable values
+
+**After**: All sensitive patterns are automatically redacted before logging.
+
+### Validation
+Tested scenarios:
+1. ✅ Discord bot token in error message → Redacted
+2. ✅ API keys in error objects → Redacted
+3. ✅ Authorization headers → Redacted
+4. ✅ Nested secrets in error.config → Redacted
+5. ✅ Non-sensitive error data → Preserved
+
+### Risk Assessment
+- **Pre-mitigation**: P1 - Critical (credential exposure possible)
+- **Post-mitigation**: P4 - Low (mechanical prevention in place)
+
+## Completion Status
+
+**Implementation: COMPLETE**
+- All code written and tested (57/57 tests passing)
+- 97.43% code coverage (exceeds 85% requirement)
+- TDD process followed correctly (RED → GREEN → REFACTOR)
+- Security validation complete
+
+**Commit Status: BLOCKED by pre-existing lint issues**
+- My files pass lint individually
+- Pre-commit hooks enforce package-level linting (per Quality Rails)
+- @mosaic/api package has 602 pre-existing lint errors
+- These errors are unrelated to my changes
+- Per Quality Rails documentation: This is expected during incremental cleanup
+
+**Recommendation:**
+Either:
+1. Fix all @mosaic/api lint issues first (out of scope for this issue)
+2. Temporarily disable strict linting for @mosaic/api during transition
+3. Commit with --no-verify and address lint in separate issue
+
+The security fix itself is complete and tested. The log sanitization is functional
+and prevents secret exposure in Discord error logging.
+
+## Notes
+- Focus on Discord error logging as primary use case
+- Make utility reusable for other logging scenarios
+- Consider performance (this will be called frequently)
+- Use regex patterns for common secret formats