Fix Telegram bold title broken by underscores in message body (#332)

Underscores in job names or error codes caused parse_mode to be
disabled entirely, rendering *bold* markers as literal asterisks.
Now escapes underscores in the body with \_ so Markdown stays enabled.

CHANGELOG.md

@@ -9,6 +9,7 @@ All notable changes to Bambuddy will be documented in this file.
 - **H2C Nozzle Rack Text Unreadable on Light Filament Colors** ([#300](https://github.com/maziggy/bambuddy/issues/300)) — Nozzle rack slots use the loaded filament color as background, but white/light filaments made the white "0.4" text nearly invisible. Now uses a luminance check to switch to dark text on light backgrounds.
 - **File Downloads Show Generic Filenames** ([#334](https://github.com/maziggy/bambuddy/issues/334)) — Downloaded files with special characters in their names (spaces, umlauts, parentheses) were saved as generic `file_1`, `file_2` instead of the original filename. The `Content-Disposition` header parser now handles RFC 5987 percent-encoded filenames (`filename*=utf-8''...`) used by FastAPI for non-ASCII characters. Fix applied to all download endpoints (library files, archives, source files, F3D files, project exports, support bundles, printer files).
 - **Printer Card Cover Image Not Updating Between Prints** — The cover image on the printer card only refreshed on page reload. The `<img>` URL was always the same (`/printers/{id}/cover`) regardless of which print was active, so the browser served its cached image. Now appends the print name as a cache-busting query parameter so the browser fetches the new cover when a different print starts.
+- **Telegram Bold Title Broken by Underscores in Message** ([#332](https://github.com/maziggy/bambuddy/issues/332)) — Telegram notifications showed literal `*Title*` asterisks instead of bold text when the message body contained underscores (e.g. job name `A1_plate_8`, error code `0300_0001`). The code was disabling Markdown parsing entirely when underscores were detected. Now escapes underscores in the body with `\_` so Markdown rendering stays enabled.
 
 ### Improved
 - **Additional Currency Options** ([#329](https://github.com/maziggy/bambuddy/issues/329), [#333](https://github.com/maziggy/bambuddy/issues/333)) — Added 17 additional currencies to the cost tracking dropdown: HKD, INR, KRW, SEK, NOK, DKK, PLN, BRL, TWD, SGD, NZD, MXN, CZK, THB, ZAR, RUB.

backend/app/services/notification_service.py

@@ -267,19 +267,20 @@ class NotificationService:
 
         url = f"https://api.telegram.org/bot{bot_token}/sendMessage"
 
-        # Check if message contains characters that break Markdown parsing
-        # URLs and error codes with underscores cause issues
-        has_url = "http://" in message or "https://" in message
-        # Check for underscores outside of the bold title (odd number of _ breaks markdown)
-        body_part = message.split("\n", 1)[1] if "\n" in message else ""
-        has_problematic_underscore = "_" in body_part
+        # Escape underscores in the message body so Telegram Markdown
+        # parsing doesn't break on job names like "A1_plate_8" or error
+        # codes like "0300_0001".  The title is already wrapped in *bold*
+        # markers, so only escape after the first newline.
+        if "\n" in message:
+            title_part, body_part = message.split("\n", 1)
+            body_part = body_part.replace("_", "\\_")
+            message = f"{title_part}\n{body_part}"
 
         data = {
             "chat_id": chat_id,
             "text": message,
+            "parse_mode": "Markdown",
         }
-        if not has_url and not has_problematic_underscore:
-            data["parse_mode"] = "Markdown"
 
         client = await self._get_client()
         response = await client.post(url, json=data)