feat(slack): native MEDIA file upload via files:write scope

[dirtyren]

Summary

Adds native MEDIA:<path> file upload support for Slack in send_message_tool, matching the existing pattern for Discord, Matrix, Signal, Feishu, and Telegram.

Motivation

Slack bots with files:write scope can upload files directly to channels/threads. Previously, MEDIA: paths were silently dropped on Slack — this PR wires up the full upload path.

Changes

tools/send_message_tool.py

• _send_slack — added thread_id parameter that was previously silently dropped
• _send_slack_file — new async helper implementing the modern two-step Slack upload API:
  1. files.getUploadURLExternal — get a pre-signed upload URL + file ID
  2. PUT file bytes to the pre-signed URL
  3. files.completeUploadExternal — share the file to the channel/thread
  • Guesses MIME type via mimetypes so Slack renders PDFs, images, etc. correctly
  • Supports thread_id for posting into threads
  • 120s timeout for large file uploads
• _send_slack_file_legacy — fallback to files.upload (multipart form) when getUploadURLExternal returns ok: false
• _send_to_platform — new Slack MEDIA block added before the "non-media platforms" fallthrough:
  • Text chunks are sent first via _send_slack
  • Files are uploaded on the last chunk via _send_slack_file
  • Error propagation matches Discord/Matrix pattern
• Error strings and tool description updated to include slack in the supported platforms list

tests/tools/test_send_message_tool.py

8 new tests in two classes:

TestSendSlackFile

• test_returns_error_when_file_missing
• test_modern_upload_happy_path
• test_thread_id_passed_to_complete_payload
• test_legacy_fallback_when_modern_endpoint_fails

TestSendToPlatformSlackMedia

• test_slack_media_only_calls_send_slack_file
• test_slack_text_and_media_sends_text_then_file
• test_slack_media_thread_id_forwarded
• test_slack_media_file_error_propagates

Usage

# Upload a PDF report to a Slack channel
send_message(
    target="slack:C0ATFHY907L",
    message="Here is the RCA report MEDIA:/home/ubuntu/reports/2026-05-11-rca.pdf"
)

# Upload into a thread
send_message(
    target="slack:C0ATFHY907L:1234567890.000100",
    message="Attached MEDIA:/tmp/report.pdf"
)

Requirements

The Slack bot token must have the files:write OAuth scope.

Test Results

8 passed in 11.65s

[teknium1]

Thanks for tackling the Slack MEDIA: gap. The underlying bug is still present on current main, but this branch needs a targeted port before it can be salvaged.

Problems

• Current main rejects media-only Slack delivery at tools/send_message_tool.py:1035-1040; text-plus-media is sent with an explicit omission warning at tools/send_message_tool.py:1043-1047.
• The PR modifies the removed core _send_slack path. Slack now routes through plugins/platforms/slack/adapter.py::_standalone_send (tools/send_message_tool.py:1428-1429), so this cannot cherry-pick cleanly.
• The live adapter already owns Slack upload behavior through files_upload_v2 (plugins/platforms/slack/adapter.py:1668-1695, 2293-2324). The PR commit also carries unrelated Signal, Telegram, Yuanbao, QQBot, email, and Kanban changes beyond the stated Slack feature.

Suggested changes

• Re-scope the salvage to the Slack plugin standalone sender and the Slack MEDIA routing branch in _send_to_platform.
• Reuse the adapter's files_upload_v2 conventions and add focused standalone-routing tests for media-only, caption/text, threads, and failures.

Automated hermes-sweeper review.

[teknium1]

Closing as superseded by #69482 (merged): native files:write upload landed via #67219's files_upload_v2 path; your scope groundwork is credited.

Thanks for the work — it's credited in #69482's summary.