fix(mattermost): avoid aiohttp timeout context in sends

[yinkev]

Summary

• remove aiohttp.ClientTimeout from Mattermost send, upload, and download paths
• keep bounded request behavior by wrapping Mattermost HTTP operations in asyncio.wait_for()
• cover gateway MattermostAdapter.send() and standalone cron delivery so scheduled Mattermost sends do not hit aiohttp's timeout task-context error

Fixes #39836.

Tests

• .venv/bin/python -m pytest tests/gateway/test_mattermost.py::TestMattermostSend tests/tools/test_send_message_missing_platforms.py::TestSendMattermost -q -o addopts= --tb=short
• .venv/bin/python -m pytest tests/gateway/test_mattermost.py tests/tools/test_send_message_missing_platforms.py tests/gateway/test_send_multiple_images.py::TestMattermostMultiImage tests/gateway/test_media_download_retry.py::TestMattermostSendUrlAsFile -q -o addopts= --tb=short
• .venv/bin/python -m py_compile plugins/platforms/mattermost/adapter.py tests/gateway/test_mattermost.py tests/tools/test_send_message_missing_platforms.py
• /opt/homebrew/bin/ruff check plugins/platforms/mattermost/adapter.py tests/gateway/test_mattermost.py tests/tools/test_send_message_missing_platforms.py
• git diff --check

Duplicate check

• gh search prs --repo NousResearch/hermes-agent --state open '39836 Mattermost ClientTimeout timeout context cron'
• gh search prs --repo NousResearch/hermes-agent --state open 'Mattermost "Timeout context manager should be used inside a task"'

[teknium1]

Thanks for tracing the standalone Mattermost delivery path.

Problems

• The reported no-task mechanism is not demonstrated on current main. Cron executes the standalone sender through asyncio.run() in cron/scheduler.py:1902-1905; the submitted standalone test likewise calls it through asyncio.run() in tests/tools/test_send_message_missing_platforms.py:108.
• The new tests assert that ClientTimeout is not called, but do not reproduce the reported error or exercise the cron dispatch path.
• The issue identifies _standalone_send, while this diff also changes live gateway helpers, downloads, uploads, and the adapter session timeout in plugins/platforms/mattermost/adapter.py.

Suggested changes

• Add a regression that reproduces the failure through the real cron standalone-delivery path.
• If confirmed, scope the fix to _standalone_send and preserve the existing bounded timeout there; keep live gateway timeout behavior unchanged unless independently reproduced.

Automated hermes-sweeper review.

[teknium1]

This only asserts that ClientTimeout is absent. Please add a regression that reproduces the reported cron standalone-delivery failure; the existing standalone test already uses asyncio.run(), so it does not establish the claimed missing-task context.

[yinkev]

Closing this broad implementation because the reported mechanism is not reproducible on the current cron path: scheduler delivery enters through asyncio.run(), which creates a task, and a fresh aiohttp ClientSession with ClientTimeout works in that context. The patch also changes gateway upload/download/session timeouts beyond the reported standalone sender. A future fix needs a current-main cron-path regression that reproduces the actual failure first.