[grade=B] DC-081: Input validation for 20 highest-risk mutating routes

Secures 20 mutating routes across 7 files against path traversal, shell
injection, and ReDoS vectors:
- containers.js: container ID validation + resource limit bounds (6 routes)
- recipes/manage.js: recipe ID slug validation (4 routes)
- tailscale.js: subdomain regex before interpolation + shell char blocking (2)
- workflows.js: workflow ID slug validation (3 routes)
- dependencies.js: service ID + dependsOn array validation (3 routes)
- logs.js: YYYY-MM-DD date format validation (1 route)
- sites.js: additional domain validation (1 route)

Uses existing REGEX patterns from constants.js. No new dependencies.
Codex: B (no blocking issues, 4 Low follow-ups for tests + strict bools).
1552/1552 tests pass, 0 regressions.

dashcaddy-api/routes/containers.js

@@ -1,9 +1,49 @@
 const express = require('express');
 const { DOCKER } = require('../src/utilities/constants');
 const { paginate, parsePaginationParams } = require('../src/utilities/pagination');
-const { NotFoundError } = require('../src/utilities/errors');
+const { NotFoundError, ValidationError } = require('../src/utilities/errors');
 const { success } = require('../src/utils/responses');
 
+/**
+ * Validate a Docker container identifier (ID or name).
+ * Allows hex container IDs and Docker-compliant names.
+ * Blocks path traversal and shell metacharacters.
+ * @param {string} id - Container ID or name from route param
+ * @throws {ValidationError} if the ID is malformed
+ */
+function validateContainerId(id) {
+  if (!id || typeof id !== 'string') {
+    throw new ValidationError('Container ID is required');
+  }
+  // Docker names: [a-zA-Z0-9][a-zA-Z0-9_.-]*
+  // Docker IDs: 64-char hex — also matches the above pattern
+  // Max 128 chars covers IDs and names
+  if (!/^[a-zA-Z0-9][a-zA-Z0-9_.-]{0,127}$/.test(id)) {
+    throw new ValidationError('Invalid container ID format');
+  }
+}
+
+/**
+ * Validate numeric resource limits for container update.
+ * @param {*} memory - Memory in MB (optional)
+ * @param {*} cpus - CPU count (optional)
+ * @throws {ValidationError} if values are out of range
+ */
+function validateResourceLimits(memory, cpus) {
+  if (memory !== undefined) {
+    const memNum = Number(memory);
+    if (isNaN(memNum) || memNum < 0 || memNum > 1048576) {
+      throw new ValidationError('Memory must be a number between 0 and 1048576 MB');
+    }
+  }
+  if (cpus !== undefined) {
+    const cpuNum = Number(cpus);
+    if (isNaN(cpuNum) || cpuNum < 0 || cpuNum > 1024) {
+      throw new ValidationError('CPUs must be a number between 0 and 1024');
+    }
+  }
+}
+
 /**
  * Containers route factory
  * @param {Object} deps - Explicit dependencies
@@ -18,6 +58,7 @@ module.exports = function({ docker, log, asyncHandler, workflowEngine }) {
 
   // Helper: verify container exists before operating on it
   async function getVerifiedContainer(id) {
+    validateContainerId(id);
     const container = docker.client.getContainer(id);
     try {
       await container.inspect();
@@ -205,6 +246,10 @@ module.exports = function({ docker, log, asyncHandler, workflowEngine }) {
   router.put('/:id/resources', asyncHandler(async (req, res) => {
     const container = await getVerifiedContainer(req.params.id);
     const { memory, cpus } = req.body;
+
+    // Validate resource limits before applying to Docker
+    validateResourceLimits(memory, cpus);
+
     const updateConfig = {};
 
     if (memory !== undefined) {