fix(slack): fall back to attachment text in thread context for bot messages

[liuhao1024]

What does this PR do?

Bot messages from monitoring tools (Datadog, PagerDuty, Grafana, etc.) often use the legacy Slack "attachments" format instead of top-level text. When Hermes is @mentioned in a thread whose parent was posted by such a bot, the parent message is silently dropped from thread context because its top-level text field is empty — the actual content lives in attachments[].text or attachments[].fallback.

This fix adds a fallback: when msg_text is empty, the code now checks attachments[].text then attachments[].fallback before skipping the message.

Related Issue

Fixes #33469

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• See commit messages for detailed changes

How to Test

1. Run pytest tests/ -q — all tests should pass
2. Verify the specific scenario described above is resolved

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: macOS 26.4.1

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture and workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A

Code Intelligence

• Analyzed: gateway/platforms/slack.py _fetch_thread_context (callers: 1 — message handler)
• Blast radius: LOW — single function, additive fallback, no behavior change for existing non-empty text messages
• Related patterns: _fetch_thread_parent_text uses the same cache; no changes needed there since it has its own fallback logic

Fixes #33469

[alt-glitch]

Overlaps with open #30765 (include alert attachments in thread context) and addresses #33469 (bot messages with attachments silently skipped). Merged #16200 previously fixed bot-posted thread parent context but did not cover legacy attachment-only messages.

[SebasSotoA]

Please approve this, my team needs this change ASAP

[teknium1]

Thanks for the focused regression coverage. The reported defect is still present on current main: plugins/platforms/slack/adapter.py:3788-3790 reads only msg["text"] and drops attachment-only thread messages.

Problems

• The production diff changes gateway/platforms/slack.py, but current main relocated the active adapter to plugins/platforms/slack/adapter.py in 5600105478ffde29d7566b45421b100eaa29c4ef. The submitted source change therefore does not affect the live Slack adapter.
• The active cold parent lookup has the same gap at plugins/platforms/slack/adapter.py:3891; it reads only parent["text"]. Porting only _fetch_thread_context would still leave attachment-only parents absent from reply_to_text when the cache is cold.

Suggested changes

• Port the fallback to the active plugin adapter and reuse it in both _fetch_thread_context and _fetch_thread_parent_text.
• Add a cold parent-lookup regression case alongside the thread-context cases.

Automated hermes-sweeper review.

[alt-glitch]

This was generated by AI during triage.

Heads up: this PR edits gateway/platforms/slack.py, but the Slack adapter has since migrated to plugins/platforms/slack/adapter.py on main — it will need a rebase onto the relocated path before it can merge. Competing/superset PR #61261 already targets the relocated adapter and additionally covers Block Kit blocks + rich attachment extraction + parent-text; #52219 is a sibling on the distinct inbound-message-text code path. Maintainer to pick the canonical fix.

[teknium1]

Closing as superseded by #69316 (merged): targeted the pre-plugin-migration gateway/platforms/slack.py which no longer exists; functionality covered on the plugin path.

Thanks for digging into this — the consolidated fix stands on the cluster's collective analysis, and your work is credited in #69316's summary.