Bug Report

Discord (and all platform) media attachments are silently dropped when outside MEDIA_DELIVERY_SAFE_ROOTS.

Symptom

When the model emits MEDIA:<path> inline directives, image/file attachments never appear in Discord (or other platforms). Text-only messages arrive fine. No error is surfaced to the user.

Root Cause

BasePlatformAdapter.filter_media_delivery_paths() validates every path against allowed roots. When a file lives outside the whitelist, the gateway logs a generic WARNING with no path name, and silently drops the attachment with zero user-visible feedback.

Current Allowed Roots

• ~/.hermes/cache/{images,audio,video,documents,screenshots}
• Legacy dirs: ~/.hermes/{image_cache,audio_cache,video_cache,document_cache,browser_screenshots}
• Any paths configured via the HERMES_MEDIA_ALLOW_DIRS environment variable

Impact

Any media stored outside these directories is silently stripped before reaching any platform.

Scope of this PR

This PR targets the send_message tool path specifically (the path where an LLM explicitly calls send_message with a MEDIA: tag).

The gateway auto-delivery path (gateway/platforms/base.py:3508/3522) is left unchanged — it still calls filter_* and only gets log-line visibility of skipped paths. Fixing that path properly would require injecting skipped-attachment warnings into the response text itself (so the user sees them), which is a distinct design decision from surfacing skips in a tool JSON result.

If desired, a follow-up PR can extend the same partition_* + user-visible warning pattern to the gateway auto-delivery path.

Changes

• gateway/platforms/base.py: Add partition_media_delivery_paths() and partition_local_delivery_paths() returning (safe, skipped) tuples. Keep filter_* as backward-compatible wrappers (they already log each skipped path by name, so no changes needed at other call sites).
• tools/send_message_tool.py: Use partition_media_delivery_paths(), surface skipped paths in JSON result under skipped_attachments and warnings, so the LLM can see why files did not arrive.
• tests/gateway/test_platform_base.py: Regression tests for partition methods plus backward-compatibility check on filter_media_delivery_paths().

Why so few files?

All other call sites (gateway/run.py, cron/scheduler.py, tools/yuanbao_tools.py, gateway/platforms/weixin.py) already get correct per-path logging via the existing filter_* wrappers. The only place where skipped attachments were truly invisible was send_message_tool.py, where the JSON result went back to the LLM without any mention of what was dropped.

Testing

pytest tests/gateway/test_platform_base.py -v -x

    100 passed in 0.79s

pytest tests/gateway/test_send_image_file.py tests/gateway/test_signal.py        tests/gateway/test_tts_media_routing.py tests/cron/test_scheduler.py::TestDeliverResultWrapping        -v -x

    149 passed in 2.22s

New regression tests:

• test_partition_media_returns_safe_and_skipped
• test_partition_local_returns_safe_and_skipped
• test_filter_backward_compatible

Fixes the silent-drop behavior on the send_message tool path.