Remove DIFC documentation from user-facing docs

[Copilot]

DIFC (Decentralized Information Flow Control) is implemented but not production-ready. Removing documentation to avoid confusion until the feature is officially supported.

Changes

README.md:

• Removed --enable-difc flag from CLI usage
• Removed "DIFC Integration" section (~47 lines covering architecture, components, and usage)

AGENTS.md:

• Removed internal/difc/ from project structure
• Removed DIFC references from security notes and resources

CONTRIBUTING.md:

• Removed internal/difc/ from project structure diagram and directory descriptions
• Removed "DIFC Integration" section

Note

The internal/difc/ implementation and --enable-difc flag remain in the codebase. Only documentation is removed.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• this-host-does-not-exist-12345.com
  • Triggering command: /tmp/go-build3387392684/b281/mcp.test /tmp/go-build3387392684/b281/mcp.test -test.testlogfile=/tmp/go-build3387392684/b281/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true 64/src/runtime/c-p 64/src/math/exp_github.com/stretchr/testify/assert/yaml 64/bin/as user.email (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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