fix(slack): handle leading-space text commands

[nu476]

Summary

• treat text like /stop as a gateway command after trimming leading Slack-avoidance whitespace
• avoid prepending thread context to command text in Slack thread replies
• add e2e coverage for leading-space stop commands

Test

• uv run pytest tests/e2e/test_platform_commands.py::TestSlashCommands::test_leading_space_stop_is_still_a_command tests/e2e/test_platform_commands.py::TestSlashCommands::test_stop_when_no_agent_running -q

[alt-glitch]

This was generated by AI during triage.

Related: leading-space slash-command cluster. This PR fixes it at the shared gateway/platforms/base.py MessageEvent layer (lstrip before command detection) plus the Slack adapter, whereas #21070 and #32210 fix the same class of bug scoped to Mattermost only. #25355 added !cmd as a Slack thread alternate prefix. Flagging for a maintainer to pick between the shared-base approach here vs. the per-platform patches.

[teknium1]

Thanks for the focused Slack command fix. The premise is confirmed on current main: plugins/platforms/slack/adapter.py:3410 recognizes only text beginning with /, while first thread replies fetch and prepend context at plugins/platforms/slack/adapter.py:3391-3406 before that classification.

Problems

• tests/e2e/test_platform_commands.py:60 does not exercise the changed Slack inbound path. Its helper constructs a MessageEvent directly (tests/e2e/conftest.py:273-281) and invokes adapter.handle_message(), bypassing SlackAdapter._handle_slack_message() where this PR adds the normalization and thread-context guard.

Suggested changes

• Add a raw Slack-event test in tests/gateway/test_slack.py for " /stop" through _handle_slack_message(), asserting a /stop MessageEvent with MessageType.COMMAND.
• Add a threaded case asserting _fetch_thread_context() is not called for that command.
• The Mattermost precedent is adapter-local normalization (plugins/platforms/mattermost/adapter.py:881); preserve or intentionally justify the broader shared-base behavior during salvage.

Automated hermes-sweeper review.

[teknium1]

This test creates a MessageEvent directly through send_and_capture(), so it bypasses SlackAdapter._handle_slack_message() entirely. Please add a Slack-adapter test with a raw {"text": " /stop"} event, including a thread case that verifies _fetch_thread_context() is not called.

[teknium1]

Merged via #69479 — your commit was cherry-picked/reapplied onto current main with your authorship preserved in git history: your leading-space command recognition was cherry-picked directly.

Thanks for the contribution!