fix(mattermost): extend session-continuity root-id fix to DM channels

[wernerhp]

What does this PR do?

Extends the session-continuity fix from #37144 to DM channels, which the original PR excluded via channel_type_raw != "D".

Root DM posts had thread_id=None; replies carried root_id=<root post id>. This produced two different session keys, so the agent lost all context on the first threaded DM reply. #37144 fixed this for channels but left DMs broken.

Removing the channel_type_raw != "D" guard gives DMs the same treatment: thread_id = post.get("root_id") or post_id when reply_mode == "thread".

-        if (
-            not thread_id
-            and self._reply_mode == "thread"
-            and channel_type_raw != "D"
-            and post_id
-        ):
-            thread_id = post_id
+        if thread_id is None and self._reply_mode == "thread":
+            thread_id = post_id

Related Issue

Fixes #18279
Relates to #37144

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

• plugins/platforms/mattermost/adapter.py: remove channel_type_raw != "D" guard from thread-id seeding logic.
• tests/gateway/test_mattermost.py: 2 new tests — DM root post seeding and DM thread reply resolves to same session.

How to Test

1. Configure Hermes with a Mattermost gateway in reply_mode: thread.
2. Send a direct message to the bot. Note the session key.
3. Reply in the DM thread. The agent should retain context from step 2.
4. Without this fix, step 3 produces a fresh session (no prior context).
5. pytest tests/gateway/test_mattermost.py -v -k "dm" — both new DM tests pass.

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: Ubuntu 24.04

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — N/A
• I've updated cli-config.yaml.example if I added/changed config keys — N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — N/A
• I've considered cross-platform impact (Windows, macOS) — N/A (gateway-only)
• I've updated tool descriptions/schemas if I changed tool behavior — N/A

[tonydwb]

Clean DM session-continuity fix (57 additions). Extends root-id seeding to DM channels so threaded DM replies land in the same session. Includes regression test and reply test. Simple, well-targeted.

Reviewed by Hermes Agent

[Copilot]

Pull request overview

This PR extends the Mattermost session-continuity fix (originally added for non-DM threads) to DM threads when reply_mode == "thread", ensuring a DM thread’s root post and its replies map to the same gateway session key and therefore keep agent context across threaded follow-ups.

Changes:

• Update the Mattermost adapter’s inbound thread_id derivation so that, in thread reply mode, a root post falls back to using its own post_id as thread_id (now applied to DMs as well).
• Replace the prior DM-specific expectation in tests with new assertions that DM root posts seed thread_id, and DM threaded replies continue to use root_id as thread_id.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
plugins/platforms/mattermost/adapter.py	Extends thread-mode root-post thread_id seeding to include DM channels, preventing DM thread session splits.
tests/gateway/test_mattermost.py	Adds/updates regression tests covering DM root seeding and DM reply thread_id behavior in thread mode.

---

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[teknium1]

Thanks for the focused regression fix. Current main still excludes DM roots from thread-id seeding at plugins/platforms/mattermost/adapter.py:869-876; those roots therefore have no thread_id, while gateway/session.py:912-915 appends the reply's root_id to the DM session key. The proposed change makes both messages use the root post ID.

The existing test at tests/gateway/test_mattermost.py:1060-1086 verifies the old behavior, and the PR adds complementary root/reply coverage. The patch applies cleanly to current main because neither changed path has changed since base 4281151ae859241351ba14d8c7682dc67ff4c126.

Automated hermes-sweeper review.