feat: enhance Mattermost proxy with improved post ID deduplication and file tracking

scripts/mattermost-proxy/README.md

@@ -43,11 +43,7 @@ The helper intentionally uses `open -n /Applications/Mattermost.app --args ...`
 instead of invoking `/Applications/Mattermost.app/Contents/MacOS/Mattermost`
 directly. Direct binary launch can crash sandboxed Electron apps with Mach
 rendezvous errors because their expected app/container parent process is
-missing. If you need the old behavior for debugging, set:
-
-```bash
-MATTERMOST_MIRROR_LAUNCH_MODE=binary scripts/mattermost-proxy/launch-mattermost.sh
-```
+missing.
 
 ## Output layout
 
@@ -64,6 +60,8 @@ ai/inbox/mattermost-mirror/
 
 Use `latest.md` or `latest.jsonl` for quick AI context. Use date-rotated `messages/...` files for previous-workday or channel/date-specific analysis.
 
+The mirror writes any post payload it sees, including older messages returned when the desktop app loads channel history or a thread. It dedupes by `post_id`, so scrolling back through useful history is a safe way to backfill missing local evidence without creating repeated entries.
+
 ## Normalized message schema
 
 Each line in the normalized JSONL contains:
@@ -102,6 +100,4 @@ Each line in the normalized JSONL contains:
 - `MATTERMOST_MIRROR_LATEST_LIMIT`: number of messages in `latest.*`, default `200`.
 - `MATTERMOST_MIRROR_CHANNEL_IDS`: optional comma-separated channel ID allowlist.
 - `MATTERMOST_MIRROR_WRITE_RAW`: set to `1` to save compact raw REST/WebSocket evidence.
-- `MATTERMOST_APP_BIN`: Mattermost Desktop binary path.
 - `MATTERMOST_APP_PATH`: Mattermost Desktop `.app` bundle path.
-- `MATTERMOST_MIRROR_LAUNCH_MODE`: `open` by default; `binary` only for debugging.