fix(matrix): Add file size to file upload, otherwise Synapse refuses media uploads (voice messages, etc.)

[pjay-io]

What does this PR do?

Fixes media uploads to Synapse homeservers by passing filesize to nio.upload().

Matrix Synapse requires a Content-Length header on media uploads. The nio library only sets this header when filesize is explicitly passed to upload(). Without it, nio uses chunked transfer encoding which Synapse rejects, causing all media uploads (images, audio, video, files) to fail with "Request must specify a Content-Length". This also prevents voice message replies from working, since TTS audio files cannot be uploaded to Matrix.

Related Issue

Fixes #4339

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Security fix
• Documentation update
• Tests (adding or improving test coverage)
• Refactor (no behavior change)
• New skill (bundled or hub)

Changes Made

• gateway/platforms/matrix.py: Added filesize=len(data) to the nio.upload() call in _upload_and_send(). This ensures the Content-Length header is set on uploads, which Synapse requires.

How to Test

1. Configure Hermes with a Synapse homeserver
2. Send an image or file via the Matrix channel — verify it uploads and sends without error
3. Send a voice message — verify Hermes can reply with a TTS audio file uploaded as a native voice bubble (MSC3245)

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: Linux (Synapse homeserver)

Documentation & Housekeeping

• N/A — no documentation changes required
• N/A — no config key changes
• N/A — no architecture changes

Screenshots / Logs

# Before (errors.log):
2026-03-30 22:34:51,939 WARNING nio.responses: Error validating response: 'content_uri' is a required property
2026-03-30 22:34:51,939 ERROR gateway.platforms.matrix: Matrix: upload failed: Request must specify a Content-Length

# After: uploads succeed with correct Content-Length header

[teknium1]

Merged via PR #5271. Your commit was cherry-picked with authorship preserved. Thanks for the Synapse fix!