feat(discord): allow_any_attachment config to accept arbitrary file types

[teknium1]

Summary

Discord users can now upload arbitrary file types (e.g. .wav, .bin, custom extensions) instead of only the built-in SUPPORTED_DOCUMENT_TYPES allowlist (PDF / text family / zip / office). Default off — historical behavior preserved.

What was broken

Today the gateway drops any attachment whose extension isn't in the allowlist. The file gets logged as "Unsupported document type" and discarded before the agent ever sees it. A user trying to upload a .wav for the agent to inspect (e.g. ffprobe it via terminal) had no path forward.

Changes

• gateway/platforms/discord.py: two new adapter helpers (_discord_allow_any_attachment, _discord_max_attachment_bytes); document branch widened to cache unknown types as application/octet-stream when the flag is on; msg_type classifier flips to DOCUMENT for unknown types when allowed.
• hermes_cli/config.py: discord.allow_any_attachment (default false) and discord.max_attachment_bytes (default 32 MiB; 0 = unlimited) added to DEFAULT_CONFIG.
• website/docs/user-guide/messaging/discord.md: env-var table rows + a "Receiving Arbitrary File Types" prose section.
• website/docs/reference/environment-variables.md: DISCORD_ALLOW_ANY_ATTACHMENT + DISCORD_MAX_ATTACHMENT_BYTES rows.
• tests/gateway/test_discord_document_handling.py: 9 new tests (TestAllowAnyAttachment) covering default-off, flag-on cache, MIME fallback to octet-stream, size cap, unlimited mode, allowlisted-doc-still-works, env fallback, config-wins-over-env, garbage-value handling.

Behavior with the flag on

• Any uploaded file is cached under ~/.hermes/cache/documents/.
• Surfaced to the agent as a DOCUMENT-typed event with application/octet-stream MIME — gateway/run.py already handles that and emits the "[The user sent a document … saved at ]" context note with sandbox-translated paths via to_agent_visible_cache_path() (Docker / Modal safe).
• File body is not inlined — only the path — so binary uploads don't blow up the context window.
• Allowlisted text formats (.txt / .md / .log) keep their existing 100 KiB inline behavior.

Scope

Discord-only by deliberate choice. Telegram has a hard 20 MB API limit and Slack has its own caps; extending this flag to them is a separate follow-up if/when asked for.

Test plan

• scripts/run_tests.sh tests/gateway/test_discord_document_handling.py tests/gateway/test_document_cache.py — 42/42 passed.
• scripts/run_tests.sh tests/gateway/ tests/hermes_cli/test_config.py tests/hermes_cli/test_config_validation.py tests/hermes_cli/test_config_drift.py — 5592 passed, 7 skipped, 0 failed.

How to use

# ~/.hermes/config.yaml
discord:
  allow_any_attachment: true
  max_attachment_bytes: 33554432   # 32 MiB; 0 = unlimited

Or via env: DISCORD_ALLOW_ANY_ATTACHMENT=true.