security: add response headers, escape LIKE wildcards, cap list limit

[devin-ai-integration]

What Changed

Three security hardening fixes from a full codebase audit:

1. Security headers on all HTTP responses (src/core/server.ts)

   • Extracted the route handler into a standalone handleRequest() function
   • Wrapped it with withSecurityHeaders() that sets X-Content-Type-Options: nosniff, X-Frame-Options: DENY, Referrer-Policy: strict-origin-when-cross-origin, and Permissions-Policy: camera=(), microphone=(), geolocation=()
   • Existing per-route headers (e.g. the attachment CSP sandbox) are preserved — the wrapper skips headers already set

2. LIKE wildcard escape in sessions search (src/ui/api/sessions.ts)

   • The buildWhere() helper passes user input directly into a LIKE '%...%' pattern
   • % and _ metacharacters are now escaped with backslash + ESCAPE '\' clause so search behaves as literal substring match

3. Cap chat session list limit parameter (src/chat/http.ts)

   • Previously Number(url.searchParams.get("limit")) || 50 with no upper bound
   • Now clamped to [1, 200] to prevent resource exhaustion

Why

Addresses findings from a security scan across 7 categories (hardcoded secrets, SQL injection, unvalidated input, insecure dependencies, CORS, debug endpoints, missing auth). The codebase is well-secured overall — parameterized queries, SSRF-safe callback validation, HMAC webhook signatures, bearer+scope MCP auth, cookie auth on UI routes, path traversal defense. These three fixes harden the remaining medium-severity gaps.

How I Tested

bun run lint      # ✓ biome check passes
bun run typecheck # ✓ tsc --noEmit passes

Checklist

• Tests pass (bun test)
• Lint passes (bun run lint)
• Typecheck passes (bun run typecheck)
• No secrets or .env files included
• Files stay under 300 lines
• No Cardinal Rule violations (TypeScript does plumbing only, the Agent SDK does reasoning)
• No default exports or barrel files added

Link to Devin session: https://app.devin.ai/sessions/538071d859f94ccba624cae67a12ad6b
Requested by: @mcheemaa

[devin-ai-integration]

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