feat: Implement Mattermost sync functionality and enhance workspace context management

.opencode/commands/mattermost-sync.md

@@ -0,0 +1,28 @@
+---
+description: Force a Mattermost sync using the configured local script
+---
+
+Use the configured Mattermost sync command to fetch fresh communication context.
+
+Preferred command sources:
+
+- `FIDELITY_MATTERMOST_SYNC_CMD`
+- fallback: `bash scripts/mattermost/sync.sh`
+
+Run the command and use its output as fresh communication context:
+
+!`if [ -n "$FIDELITY_MATTERMOST_SYNC_CMD" ]; then bash -lc "$FIDELITY_MATTERMOST_SYNC_CMD"; elif [ -f scripts/mattermost/sync.sh ]; then bash scripts/mattermost/sync.sh; else echo "No Mattermost sync command is configured."; fi`
+
+Then:
+
+- if the command fails, stop there and do not edit any workspace files
+- if no `ai/inbox/mattermost-latest.md` exists after the sync attempt, do not update logs or stable context
+- inspect `ai/inbox/mattermost-latest.md` if it exists
+- decide whether the new information belongs in today's log, current state, or stable project context
+- update the workspace only if the sync succeeded and durable facts were learned
+
+Return:
+
+1. What was synchronized
+2. Which files were updated
+3. What still needs human confirmation