diff --git a/apps/cli/src/commands/setup.ts b/apps/cli/src/commands/setup.ts
index 8716a25..213cb89 100644
--- a/apps/cli/src/commands/setup.ts
+++ b/apps/cli/src/commands/setup.ts
@@ -219,9 +219,9 @@ async function setupRouter(): Promise<ShannonConfig> {
 
   const router: ShannonConfig['router'] = { default: defaultModel };
   if (routerProvider === 'openai') {
-    router!.openai_key = apiKey;
+    router.openai_key = apiKey;
   } else {
-    router!.openrouter_key = apiKey;
+    router.openrouter_key = apiKey;
   }
 
   return { router };
diff --git a/apps/cli/src/commands/start.ts b/apps/cli/src/commands/start.ts
index cd8aa4e..c049522 100644
--- a/apps/cli/src/commands/start.ts
+++ b/apps/cli/src/commands/start.ts
@@ -65,11 +65,8 @@ export function start(args: StartArgs): void {
   const containerName = `shannon-worker-${suffix}`;
 
   // 8. Generate workspace name if not provided
-  let workspace = args.workspace;
-  if (!workspace) {
-    const hostname = new URL(args.url).hostname.replace(/[^a-zA-Z0-9-]/g, '-');
-    workspace = `${hostname}_shannon-${Date.now()}`;
-  }
+  const workspace =
+    args.workspace ?? `${new URL(args.url).hostname.replace(/[^a-zA-Z0-9-]/g, '-')}_shannon-${Date.now()}`;
 
   // 9. Resolve credentials
   const credentialsDir = getCredentialsDir();
@@ -142,7 +139,7 @@ export function start(args: StartArgs): void {
 
         // Clear waiting line and show info
         process.stdout.write('\r\x1b[K');
-        printInfo(args, useRouter, workspace!, workflowId, repo.hostPath, workspacesDir);
+        printInfo(args, useRouter, workspace, workflowId, repo.hostPath, workspacesDir);
         return;
       }
     } catch {
diff --git a/apps/worker/src/ai/claude-executor.ts b/apps/worker/src/ai/claude-executor.ts
index 1612589..3c159c5 100644
--- a/apps/worker/src/ai/claude-executor.ts
+++ b/apps/worker/src/ai/claude-executor.ts
@@ -88,7 +88,10 @@ function buildMcpServers(
       // NOTE: Explicit allowlist — the Playwright MCP subprocess must not inherit
       // secrets (API keys, AWS tokens) from the parent process.
       const MCP_ENV_ALLOWLIST = [
-        'PATH', 'HOME', 'NODE_PATH', 'DISPLAY',
+        'PATH',
+        'HOME',
+        'NODE_PATH',
+        'DISPLAY',
         'PLAYWRIGHT_CHROMIUM_EXECUTABLE_PATH',
       ] as const;
 
@@ -98,8 +101,9 @@ function buildMcpServers(
       };
 
       for (const key of MCP_ENV_ALLOWLIST) {
-        if (process.env[key]) {
-          envVars[key] = process.env[key]!;
+        const val = process.env[key];
+        if (val) {
+          envVars[key] = val;
         }
       }
 
@@ -252,8 +256,9 @@ export async function runClaudePrompt(
     'ANTHROPIC_LARGE_MODEL',
   ];
   for (const name of passthroughVars) {
-    if (process.env[name]) {
-      sdkEnv[name] = process.env[name]!;
+    const val = process.env[name];
+    if (val) {
+      sdkEnv[name] = val;
     }
   }
 
diff --git a/apps/worker/src/ai/output-formatters.ts b/apps/worker/src/ai/output-formatters.ts
index 1e44280..8a0b2ed 100644
--- a/apps/worker/src/ai/output-formatters.ts
+++ b/apps/worker/src/ai/output-formatters.ts
@@ -89,14 +89,14 @@ function summarizeTodoUpdate(input: ToolCallInput | undefined): string | null {
   const inProgress = todos.filter((t) => t.status === 'in_progress');
 
   // Show recently completed tasks
-  if (completed.length > 0) {
-    const recent = completed[completed.length - 1]!;
+  const recent = completed.at(-1);
+  if (recent) {
     return `✅ ${recent.content}`;
   }
 
   // Show current in-progress task
-  if (inProgress.length > 0) {
-    const current = inProgress[0]!;
+  const current = inProgress.at(0);
+  if (current) {
     return `🔄 ${current.content}`;
   }
 
diff --git a/apps/worker/src/audit/metrics-tracker.ts b/apps/worker/src/audit/metrics-tracker.ts
index f88a6c1..1ce9ea4 100644
--- a/apps/worker/src/audit/metrics-tracker.ts
+++ b/apps/worker/src/audit/metrics-tracker.ts
@@ -336,6 +336,7 @@ export class MetricsTracker {
 
     // Calculate metrics per phase
     const phaseMetrics: Record<string, PhaseMetrics> = {};
+    // biome-ignore lint/style/noNonNullAssertion: called from recalculateAggregations which guards this.data
     const totalDuration = this.data!.metrics.total_duration_ms;
 
     for (const [phaseName, agentList] of Object.entries(phases)) {
diff --git a/apps/worker/src/services/prompt-manager.ts b/apps/worker/src/services/prompt-manager.ts
index 027e918..0876431 100644
--- a/apps/worker/src/services/prompt-manager.ts
+++ b/apps/worker/src/services/prompt-manager.ts
@@ -37,7 +37,7 @@ async function buildLoginInstructions(authentication: Authentication, logger: Ac
     const getSection = (content: string, sectionName: string): string => {
       const regex = new RegExp(`<!-- BEGIN:${sectionName} -->([\\s\\S]*?)<!-- END:${sectionName} -->`, 'g');
       const match = regex.exec(content);
-      return match ? match[1]!.trim() : '';
+      return match?.[1]?.trim() ?? '';
     };
 
     // 2. Extract sections based on login type
@@ -101,14 +101,13 @@ async function processIncludes(content: string, baseDir: string): Promise<string
 
   const replacements: IncludeReplacement[] = await Promise.all(
     Array.from(content.matchAll(includeRegex)).map(async (match) => {
-      const includePath = path.resolve(baseDir, match[1]!);
+      const rawPath = match[1] ?? '';
+      const includePath = path.resolve(baseDir, rawPath);
       if (!includePath.startsWith(resolvedBase + path.sep) && includePath !== resolvedBase) {
-        throw new PentestError(
-          `Path traversal detected in @include(): ${match[1]}`,
-          'prompt',
-          false,
-          { includePath, baseDir: resolvedBase },
-        );
+        throw new PentestError(`Path traversal detected in @include(): ${rawPath}`, 'prompt', false, {
+          includePath,
+          baseDir: resolvedBase,
+        });
       }
       const sharedContent = await fs.readFile(includePath, 'utf8');
       return {
diff --git a/apps/worker/src/services/queue-validation.ts b/apps/worker/src/services/queue-validation.ts
index 86a5a04..0bb7be4 100644
--- a/apps/worker/src/services/queue-validation.ts
+++ b/apps/worker/src/services/queue-validation.ts
@@ -243,7 +243,7 @@ const validateQueueContent = async (
 
     return Object.freeze({
       ...pathsWithExistence,
-      queueData: queueValidation.data!,
+      queueData: queueValidation.data as QueueData,
     });
   } catch (readError) {
     return {
diff --git a/apps/worker/src/utils/functional.ts b/apps/worker/src/utils/functional.ts
index 3019ea5..261f2ec 100644
--- a/apps/worker/src/utils/functional.ts
+++ b/apps/worker/src/utils/functional.ts
@@ -10,7 +10,7 @@
  * Generic functional composition patterns for async operations.
  */
 
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
+// biome-ignore lint/suspicious/noExplicitAny: pipeline functions need flexible typing for composition
 type PipelineFunction = (x: any) => any | Promise<any>;
 
 /**
diff --git a/packages/mcp-server/src/tools/generate-totp.ts b/packages/mcp-server/src/tools/generate-totp.ts
index 82c9ca4..e923e7e 100644
--- a/packages/mcp-server/src/tools/generate-totp.ts
+++ b/packages/mcp-server/src/tools/generate-totp.ts
@@ -48,13 +48,14 @@ function generateHOTP(secret: string, counter: number, digits: number = 6): stri
   hmac.update(counterBuffer);
   const hash = hmac.digest();
 
-  // Dynamic truncation
-  const offset = hash[hash.length - 1]! & 0x0f;
+  // Dynamic truncation (SHA-1 always produces 20 bytes)
+  const lastByte = hash[hash.length - 1] ?? 0;
+  const offset = lastByte & 0x0f;
   const code =
-    ((hash[offset]! & 0x7f) << 24) |
-    ((hash[offset + 1]! & 0xff) << 16) |
-    ((hash[offset + 2]! & 0xff) << 8) |
-    (hash[offset + 3]! & 0xff);
+    (((hash[offset] ?? 0) & 0x7f) << 24) |
+    (((hash[offset + 1] ?? 0) & 0xff) << 16) |
+    (((hash[offset + 2] ?? 0) & 0xff) << 8) |
+    ((hash[offset + 3] ?? 0) & 0xff);
 
   // Generate digits
   const otp = (code % 10 ** digits).toString().padStart(digits, '0');