fix(vp): correct #1780 root cause — VP intake key mismatch dropped every slicer field

      First-attempt fix (d196cfc5) was wrong about the cause. Real root,
      traced via @mkoreen's BAMBUDDY_VP_DUMP_WIRE capture + 2026-06-21
      support bundle:

      mqtt_server.py:1296 was passing the slicer's bare subtask_name
      (e.g. "Model_Name") into on_print_command, which stashed under
      that key. _add_to_print_queue looked up under file_path.name
      (the FTP filename WITH extension, "Model_Name.gcode.3mf"). The
      two strings never matched. pop returned None, the 2s wait fired
      against a key the stash side never signaled, every captured
      slicer field silently fell back to settings defaults.

      Affected EVERY Bambu Studio "Send" upload across EVERY model —
      not just H2C nozzle_mapping. bed_leveling / flow_cali /
      vibration_cali / layer_inspect / timelapse from the original
      #1403 capture have been silently ignored since BambuStudio
      started splitting subtask_name (bare) from file (with extension).

      Unit tests passed because fixtures called on_print_command with
      file_path.name directly, bypassing the broken caller.

      Fix in manager.py::on_print_command: derive
      stash_key = data.get("file") or filename and use it for both
      _slicer_print_options and the event lookup. filename
      (subtask_name) still flows unchanged to _schedule_finish_release
      — push_status echoes it back as gcode_file / subtask_name and
      the slicer matches against its own subtask_name there, so
      re-routing that path was a separate regression I caught and
      reverted mid-audit.

      Also: nozzles_info field was a wrong guess in d196cfc5 —
      BambuStudio never sends it (confirmed via wire capture). Drop
      the capture, dispatch, schema, kwarg, and route paths. DB
      column stays nullable so old rows still load; nothing reads
      or writes it.

      Diagnostic: DEBUG log when _add_to_print_queue finds no slicer
      options after the 2s wait, including the looked-up key and the
      actual cache keys present. Future stash/lookup mismatches will
      be obvious from a log line instead of needing a wire capture.

      Behaviour change worth flagging: users on Bambu Studio whose
      slicer-side bed-leveling / flow-cali / vibration-cali /
      layer-inspect / timelapse differ from Bambuddy's
      default-workflow settings will see their slicer choices
      honored now instead of silently overridden. Restores #1403's
      original intent.

backend/app/api/routes/library.py

@@ -750,11 +750,24 @@ async def list_folders(
     )
     file_counts = dict(file_counts_result.all())
 
+    # Latest immediate-child file activity per folder (#1770). Sibling of the
+    # file_counts subquery — same WHERE clause, MAX(updated_at) instead of
+    # COUNT(id). Subfolder descent is not aggregated here; the frontend's
+    # "sort by recent activity" mode is satisfied by immediate-parent bubble.
+    latest_file_activity_result = await db.execute(
+        select(LibraryFile.folder_id, func.max(LibraryFile.updated_at))
+        .where(LibraryFile.folder_id.isnot(None), LibraryFile.deleted_at.is_(None))
+        .group_by(LibraryFile.folder_id)
+    )
+    latest_file_activity = dict(latest_file_activity_result.all())
+
     # Build tree structure
     folder_map = {}
     root_folders = []
 
     for folder, project_name, archive_name in rows:
+        latest_file = latest_file_activity.get(folder.id)
+        latest_activity_at = max(folder.updated_at, latest_file) if latest_file is not None else folder.updated_at
         folder_item = FolderTreeItem(
             id=folder.id,
             name=folder.name,
@@ -767,6 +780,7 @@ async def list_folders(
             external_path=folder.external_path,
             external_readonly=folder.external_readonly,
             file_count=file_counts.get(folder.id, 0),
+            latest_activity_at=latest_activity_at,
             children=[],
         )
         folder_map[folder.id] = folder_item
@@ -804,14 +818,19 @@ async def get_folders_by_project(
 
     folders = []
     for folder, project_name in rows:
-        # Get file count
-        file_count_result = await db.execute(
-            select(func.count(LibraryFile.id)).where(
+        # Get file count + latest file activity (#1770) in one trip
+        agg_result = await db.execute(
+            select(
+                func.count(LibraryFile.id),
+                func.max(LibraryFile.updated_at),
+            ).where(
                 LibraryFile.folder_id == folder.id,
                 LibraryFile.deleted_at.is_(None),
             )
         )
-        file_count = file_count_result.scalar() or 0
+        file_count, latest_file = agg_result.one()
+        file_count = file_count or 0
+        latest_activity_at = max(folder.updated_at, latest_file) if latest_file is not None else folder.updated_at
 
         folders.append(
             FolderResponse(
@@ -827,6 +846,7 @@ async def get_folders_by_project(
                 external_readonly=folder.external_readonly,
                 external_show_hidden=folder.external_show_hidden,
                 file_count=file_count,
+                latest_activity_at=latest_activity_at,
                 created_at=folder.created_at,
                 updated_at=folder.updated_at,
             )
@@ -857,14 +877,19 @@ async def get_folders_by_archive(
 
     folders = []
     for folder, archive_name in rows:
-        # Get file count
-        file_count_result = await db.execute(
-            select(func.count(LibraryFile.id)).where(
+        # Get file count + latest file activity (#1770) in one trip
+        agg_result = await db.execute(
+            select(
+                func.count(LibraryFile.id),
+                func.max(LibraryFile.updated_at),
+            ).where(
                 LibraryFile.folder_id == folder.id,
                 LibraryFile.deleted_at.is_(None),
             )
         )
-        file_count = file_count_result.scalar() or 0
+        file_count, latest_file = agg_result.one()
+        file_count = file_count or 0
+        latest_activity_at = max(folder.updated_at, latest_file) if latest_file is not None else folder.updated_at
 
         folders.append(
             FolderResponse(
@@ -880,6 +905,7 @@ async def get_folders_by_archive(
                 external_readonly=folder.external_readonly,
                 external_show_hidden=folder.external_show_hidden,
                 file_count=file_count,
+                latest_activity_at=latest_activity_at,
                 created_at=folder.created_at,
                 updated_at=folder.updated_at,
             )
@@ -943,6 +969,9 @@ async def create_folder(
         external_readonly=folder.external_readonly,
         external_show_hidden=folder.external_show_hidden,
         file_count=0,
+        # New folder has no files yet — fall back to the folder's own
+        # updated_at so this matches the list-route semantics (#1770).
+        latest_activity_at=folder.updated_at,
         created_at=folder.created_at,
         updated_at=folder.updated_at,
     )
@@ -973,14 +1002,19 @@ async def get_folder(
 
     folder, project_name, archive_name = row
 
-    # Get file count
-    file_count_result = await db.execute(
-        select(func.count(LibraryFile.id)).where(
+    # Get file count + latest file activity (#1770) in one trip
+    agg_result = await db.execute(
+        select(
+            func.count(LibraryFile.id),
+            func.max(LibraryFile.updated_at),
+        ).where(
             LibraryFile.folder_id == folder_id,
             LibraryFile.deleted_at.is_(None),
         )
     )
-    file_count = file_count_result.scalar() or 0
+    file_count, latest_file = agg_result.one()
+    file_count = file_count or 0
+    latest_activity_at = max(folder.updated_at, latest_file) if latest_file is not None else folder.updated_at
 
     return FolderResponse(
         id=folder.id,
@@ -995,6 +1029,7 @@ async def get_folder(
         external_readonly=folder.external_readonly,
         external_show_hidden=folder.external_show_hidden,
         file_count=file_count,
+        latest_activity_at=latest_activity_at,
         created_at=folder.created_at,
         updated_at=folder.updated_at,
     )
@@ -1064,14 +1099,19 @@ async def update_folder(
     await db.commit()
     await db.refresh(folder)
 
-    # Get file count and names
-    file_count_result = await db.execute(
-        select(func.count(LibraryFile.id)).where(
+    # Get file count + latest file activity (#1770) and names
+    agg_result = await db.execute(
+        select(
+            func.count(LibraryFile.id),
+            func.max(LibraryFile.updated_at),
+        ).where(
             LibraryFile.folder_id == folder_id,
             LibraryFile.deleted_at.is_(None),
         )
     )
-    file_count = file_count_result.scalar() or 0
+    file_count, latest_file = agg_result.one()
+    file_count = file_count or 0
+    latest_activity_at = max(folder.updated_at, latest_file) if latest_file is not None else folder.updated_at
 
     # Get project and archive names
     project_name = None
@@ -1096,6 +1136,7 @@ async def update_folder(
         external_readonly=folder.external_readonly,
         external_show_hidden=folder.external_show_hidden,
         file_count=file_count,
+        latest_activity_at=latest_activity_at,
         created_at=folder.created_at,
         updated_at=folder.updated_at,
     )
@@ -1365,6 +1406,9 @@ async def create_external_folder(
         external_readonly=folder.external_readonly,
         external_show_hidden=folder.external_show_hidden,
         file_count=0,
+        # Newly-created external folder hasn't been scanned yet — fall back
+        # to the folder's own updated_at (#1770).
+        latest_activity_at=folder.updated_at,
         created_at=folder.created_at,
         updated_at=folder.updated_at,
     )

backend/app/api/routes/print_queue.py

@@ -142,22 +142,16 @@ def _enrich_response(item: PrintQueueItem) -> PrintQueueItemResponse:
         except json.JSONDecodeError:
             filament_overrides_parsed = None
 
-    # Parse nozzle_mapping + nozzles_info from JSON string (#1780 — H2C rack
-    # slicer-pick preservation). Both are nullable opaque JSON blobs stored
-    # verbatim from BambuStudio's project_file; surface them parsed for the
-    # response model and any future "edit print → nozzle" UI.
+    # Parse nozzle_mapping from JSON string (#1780 — H2C rack slicer-pick
+    # preservation). Nullable opaque JSON blob stored verbatim from
+    # BambuStudio's project_file; surface it parsed for the response model
+    # and any future "edit print → nozzle" UI.
     nozzle_mapping_parsed = None
     if item.nozzle_mapping:
         try:
             nozzle_mapping_parsed = json.loads(item.nozzle_mapping)
         except json.JSONDecodeError:
             nozzle_mapping_parsed = None
-    nozzles_info_parsed = None
-    if item.nozzles_info:
-        try:
-            nozzles_info_parsed = json.loads(item.nozzles_info)
-        except json.JSONDecodeError:
-            nozzles_info_parsed = None
 
     # Create response with parsed ams_mapping
     item_dict = {
@@ -203,7 +197,6 @@ def _enrich_response(item: PrintQueueItem) -> PrintQueueItemResponse:
         "gcode_injection": item.gcode_injection,
         # H2C rack-swap nozzle pick (#1780)
         "nozzle_mapping": nozzle_mapping_parsed,
-        "nozzles_info": nozzles_info_parsed,
     }
     response = PrintQueueItemResponse(**item_dict)
     if item.archive:
@@ -1035,8 +1028,6 @@ async def update_queue_item(
         update_data["nozzle_mapping"] = (
             json.dumps(update_data["nozzle_mapping"]) if update_data["nozzle_mapping"] else None
         )
-    if "nozzles_info" in update_data:
-        update_data["nozzles_info"] = json.dumps(update_data["nozzles_info"]) if update_data["nozzles_info"] else None
 
     for field, value in update_data.items():
         setattr(item, field, value)

backend/app/core/database.py

@@ -969,11 +969,14 @@ async def run_migrations(conn):
         await _safe_execute(conn, "ALTER TABLE virtual_printers ADD COLUMN gcode_injection BOOLEAN DEFAULT FALSE")
 
     # Migration: nozzle_mapping + nozzles_info on print_queue for H2C rack-swap
-    # slicer-pick preservation (#1780). Opaque JSON-string columns carrying
-    # BambuStudio's per-filament physical nozzle position IDs and the
-    # per-extruder rack metadata, forwarded straight from the VP intake to
-    # the dispatcher's project_file MQTT command. NULL on every other model.
-    # Nullable TEXT — no Postgres / SQLite divergence here.
+    # slicer-pick preservation (#1780). Opaque JSON-string column carrying
+    # BambuStudio's per-filament physical nozzle position IDs, forwarded
+    # straight from the VP intake to the dispatcher's project_file MQTT
+    # command. NULL on every other model. Nullable TEXT — no Postgres / SQLite
+    # divergence here. `nozzles_info` shipped in the original #1780 attempt
+    # but BambuStudio never actually sends it (verified via wire capture on
+    # H2C, see CHANGELOG 0.2.5b1) — the column stays nullable so old rows
+    # still load; nothing reads or writes to it anymore.
     await _safe_execute(conn, "ALTER TABLE print_queue ADD COLUMN nozzle_mapping TEXT")
     await _safe_execute(conn, "ALTER TABLE print_queue ADD COLUMN nozzles_info TEXT")
 

backend/app/models/print_queue.py

@@ -67,12 +67,13 @@ class PrintQueueItem(Base):
 
     # H2C dual-nozzle-rack slicer pick preservation (#1780). BambuStudio's
     # project_file MQTT command for rack-swap-capable models (O1C2 today)
-    # carries per-filament physical nozzle position IDs in `nozzle_mapping`
-    # and per-extruder rack metadata in `nozzles_info`. Both are forwarded
-    # verbatim through the queue and replayed by the dispatcher so the
-    # firmware honours the user's pick instead of falling back to
-    # "last matching nozzle type" auto-pick. Stored as opaque JSON strings
-    # (list[int] and list[dict] respectively); NULL on every other model.
+    # carries per-filament physical nozzle position IDs in `nozzle_mapping`,
+    # forwarded verbatim through the queue and replayed by the dispatcher so
+    # the firmware honours the user's pick instead of falling back to
+    # "last matching nozzle type" auto-pick. Stored as opaque JSON string
+    # (list[int]); NULL on every other model. `nozzles_info` is a deprecated
+    # column from the original #1780 attempt — kept nullable so old rows still
+    # load; never written to or read from.
     nozzle_mapping: Mapped[str | None] = mapped_column(Text, nullable=True)
     nozzles_info: Mapped[str | None] = mapped_column(Text, nullable=True)
 

backend/app/schemas/library.py

@@ -50,6 +50,12 @@ class FolderResponse(BaseModel):
     external_readonly: bool = False
     external_show_hidden: bool = False
     file_count: int = 0  # Computed field
+    # max(folder.updated_at, max(immediate-child file.updated_at)). Used by the
+    # File Manager folder tree's "sort by recent activity" mode (#1770) so that
+    # adding a file inside a folder bubbles it up — folder.updated_at alone only
+    # tracks rename/move events. Recursion across subfolders is intentionally
+    # left out to keep the route a single GROUP BY rather than a recursive CTE.
+    latest_activity_at: datetime | None = None
     created_at: datetime
     updated_at: datetime
 
@@ -71,6 +77,8 @@ class FolderTreeItem(BaseModel):
     external_path: str | None = None
     external_readonly: bool = False
     file_count: int = 0
+    # See FolderResponse.latest_activity_at — #1770 folder sort source.
+    latest_activity_at: datetime | None = None
     children: list["FolderTreeItem"] = []
 
     class Config:

backend/app/schemas/print_queue.py

@@ -82,13 +82,10 @@ class PrintQueueItemUpdate(BaseModel):
     nozzle_offset_cali: bool | None = None
     # Auto-print G-code injection
     gcode_injection: bool | None = None
-    # H2C dual-nozzle-rack slicer pick (#1780). Both fields are opaque
-    # JSON-encoded structures BambuStudio sends in its project_file MQTT
-    # body; sent back to the printer verbatim on dispatch. list[int] for
-    # nozzle_mapping (per-filament physical nozzle position IDs), list[dict]
-    # for nozzles_info (per-extruder rack metadata).
+    # H2C dual-nozzle-rack slicer pick (#1780). list[int] per-filament
+    # physical nozzle position IDs from BambuStudio's project_file MQTT
+    # body; sent back to the printer verbatim on dispatch.
     nozzle_mapping: list[int] | None = None
-    nozzles_info: list[dict] | None = None
 
 
 class PrintQueueItemResponse(BaseModel):
@@ -174,7 +171,6 @@ class PrintQueueItemResponse(BaseModel):
     # "edit print → choose nozzle" UI; null on every model except O1C2
     # uploads from BambuStudio.
     nozzle_mapping: list[int] | None = None
-    nozzles_info: list[dict] | None = None
 
     class Config:
         from_attributes = True

backend/app/services/bambu_mqtt.py

@@ -3502,7 +3502,6 @@ class BambuMQTTClient:
         use_ams: bool = True,
         nozzle_offset_cali: bool = False,
         nozzle_mapping: str | None = None,
-        nozzles_info: str | None = None,
     ):
         """Start a print job on the printer.
 
@@ -3528,9 +3527,6 @@ class BambuMQTTClient:
                 firmware honours the user's slicer pick instead of falling
                 back to "last matching nozzle" auto-pick. Silently ignored
                 on single-nozzle printers.
-            nozzles_info: Opaque JSON string for the per-extruder rack
-                metadata BambuStudio's project_file carries alongside
-                `nozzle_mapping` (#1780). Same dual-nozzle gating.
         """
         if self._client and self.state.connected:
             # Bambu print command format — matches Bambu Studio's format.
@@ -3690,32 +3686,24 @@ class BambuMQTTClient:
 
             # H2C dual-nozzle-rack slicer-pick preservation (#1780).
             # `nozzle_mapping` carries per-filament physical nozzle position
-            # IDs (`list[int]`), `nozzles_info` carries per-extruder rack
-            # metadata (`list[dict]`). Both are JSON-string-encoded when
-            # they leave the queue item; parse here so the wire ships
-            # arrays/objects, matching BambuStudio's project_file shape.
-            # Gate by `is_dual_nozzle` defensively — single-nozzle firmwares
-            # would ignore them but we err on the side of not emitting
-            # unrecognised fields. A parse failure is logged but never
-            # blocks the dispatch — the firmware will fall back to its
-            # auto-pick path, which is the pre-fix behaviour.
-            if is_dual_nozzle:
-                for src_str, json_key in (
-                    (nozzle_mapping, "nozzle_mapping"),
-                    (nozzles_info, "nozzles_info"),
-                ):
-                    if not src_str:
-                        continue
-                    try:
-                        command["print"][json_key] = json.loads(src_str)
-                    except json.JSONDecodeError:
-                        logger.warning(
-                            "[%s] Invalid %s JSON on dispatch, omitting from "
-                            "project_file (firmware will auto-pick): %r",
-                            self.serial_number,
-                            json_key,
-                            src_str,
-                        )
+            # IDs (`list[int]`), JSON-string-encoded when it leaves the queue
+            # item; parse here so the wire ships an array, matching
+            # BambuStudio's project_file shape. Gate by `is_dual_nozzle`
+            # defensively — single-nozzle firmwares would ignore the field
+            # but we err on the side of not emitting unrecognised fields. A
+            # parse failure is logged but never blocks the dispatch — the
+            # firmware will fall back to its auto-pick path, which is the
+            # pre-fix behaviour.
+            if is_dual_nozzle and nozzle_mapping:
+                try:
+                    command["print"]["nozzle_mapping"] = json.loads(nozzle_mapping)
+                except json.JSONDecodeError:
+                    logger.warning(
+                        "[%s] Invalid nozzle_mapping JSON on dispatch, omitting from "
+                        "project_file (firmware will auto-pick): %r",
+                        self.serial_number,
+                        nozzle_mapping,
+                    )
 
             logger.info("[%s] Sending print command: %s", self.serial_number, json.dumps(command))
             self._client.publish(self.topic_publish, json.dumps(command), qos=1)

backend/app/services/print_scheduler.py

@@ -2325,10 +2325,10 @@ class PrintScheduler:
         effective_timelapse = bool(item.timelapse)
 
         # Start the print with AMS mapping, plate_id and print options.
-        # nozzle_mapping / nozzles_info ride through verbatim — JSON strings
-        # captured from Bambu Studio's project_file on VP intake (#1780); the
-        # MQTT layer parses + injects them only for dual-nozzle models so a
-        # null on every other model is a transparent pass-through.
+        # nozzle_mapping rides through verbatim — JSON string captured from
+        # Bambu Studio's project_file on VP intake (#1780); the MQTT layer
+        # parses + injects it only for dual-nozzle models so a null on every
+        # other model is a transparent pass-through.
         started = printer_manager.start_print(
             item.printer_id,
             remote_filename,
@@ -2342,7 +2342,6 @@ class PrintScheduler:
             use_ams=item.use_ams,
             nozzle_offset_cali=item.nozzle_offset_cali,
             nozzle_mapping=item.nozzle_mapping,
-            nozzles_info=item.nozzles_info,
         )
 
         if started:

backend/app/services/printer_manager.py

@@ -566,15 +566,13 @@ class PrinterManager:
         use_ams: bool = True,
         nozzle_offset_cali: bool = False,
         nozzle_mapping: str | None = None,
-        nozzles_info: str | None = None,
     ) -> bool:
         """Start a print on a connected printer.
 
-        ``nozzle_mapping`` and ``nozzles_info`` are opaque JSON strings
-        captured from BambuStudio's project_file MQTT command (H2C rack-swap
-        slicer pick preservation, #1780). They ride through to the MQTT
-        client untouched; the dispatch builder there parses + injects them
-        only on dual-nozzle models.
+        ``nozzle_mapping`` is an opaque JSON string captured from BambuStudio's
+        project_file MQTT command (H2C rack-swap slicer pick preservation,
+        #1780). It rides through to the MQTT client untouched; the dispatch
+        builder there parses + injects it only on dual-nozzle models.
         """
         caller = traceback.extract_stack(limit=3)[0]
         logger.info(
@@ -598,7 +596,6 @@ class PrinterManager:
                 use_ams=use_ams,
                 nozzle_offset_cali=nozzle_offset_cali,
                 nozzle_mapping=nozzle_mapping,
-                nozzles_info=nozzles_info,
             )
         return False
 

backend/app/services/virtual_printer/manager.py

@@ -289,9 +289,10 @@ class VirtualPrinterInstance:
         """Handle print command from MQTT.
 
         Captures the slicer's project_file options (`timelapse`, `bed_leveling`,
-        `flow_cali`, `vibration_cali`, `layer_inspect`, `use_ams`) so the
-        VP-queue path can inherit them when adding the item to the queue,
-        rather than falling back to the global default settings (#1403).
+        `flow_cali`, `vibration_cali`, `layer_inspect`, `use_ams`, plus the
+        H2C rack-pick `nozzle_mapping`) so the VP-queue path can inherit them
+        when adding the item to the queue, rather than falling back to the
+        global default settings (#1403, #1780).
         Only queue mode consumes the capture; archive / review / proxy
         modes ignore the print command, so we skip the stash there to keep
         the dict from accumulating one entry per print over the VP's
@@ -301,6 +302,16 @@ class VirtualPrinterInstance:
         moment after the synthetic project_file ack — for every non-proxy
         mode — so the slicer's "Downloading" UI releases on the slicer's
         FTP-first-then-MQTT send order.
+
+        ``filename`` is the slicer's ``subtask_name`` (bare model name, no
+        extension) — used verbatim for `_schedule_finish_release` because
+        push_status echoes it back to the slicer as gcode_file / subtask_name.
+        The queue-side stash key is derived from ``data["file"]`` (the FTP
+        filename with extension) so `_add_to_print_queue`'s
+        ``file_path.name`` lookup matches; falls back to ``filename`` when
+        ``data["file"]`` is absent (legacy slicers / non-3MF uploads).
+        Stash/lookup mismatch was the #1780 root cause — every captured field
+        silently fell back to settings defaults on every Bambu Studio "Send".
         """
         logger.info("[VP %s] Print command for: %s", self.name, filename)
         mode = normalize_vp_mode(self.mode)
@@ -308,6 +319,12 @@ class VirtualPrinterInstance:
             self._schedule_finish_release(filename)
         if mode != VP_MODE_QUEUE:
             return
+        # Stash key must match `_add_to_print_queue`'s lookup, which uses
+        # `file_path.name` (FTP filename WITH extension). The slicer's
+        # `subtask_name` (== this method's `filename` arg) is the bare model
+        # name, no extension — using it as the stash key was the #1780 root
+        # cause.
+        stash_key = data.get("file") or filename
         # Drop the oldest stash if the cache is growing — happens when the
         # slicer sends project_file for a filename whose FTP upload was
         # rejected / cancelled / non-3MF, so _add_to_print_queue's pop
@@ -321,8 +338,8 @@ class VirtualPrinterInstance:
                 logger.debug("[VP %s] Evicted stale slicer options for %s", self.name, stale_key)
             except StopIteration:
                 pass
-        self._slicer_print_options[filename] = dict(data)
-        event = self._slicer_print_options_events.get(filename)
+        self._slicer_print_options[stash_key] = dict(data)
+        event = self._slicer_print_options_events.get(stash_key)
         if event:
             event.set()
 
@@ -525,6 +542,18 @@ class VirtualPrinterInstance:
                 slicer_opts = None
             finally:
                 self._slicer_print_options_events.pop(file_path.name, None)
+        # If the cache still misses, queued workflow flags / nozzle pick will
+        # silently fall back to settings defaults. Surface the missed key so a
+        # future stash/lookup mismatch (the #1780 root cause) is obvious in
+        # the log instead of needing a wire capture to diagnose.
+        if slicer_opts is None:
+            logger.debug(
+                "[VP %s] No slicer options cached for %r (cache keys: %s); "
+                "workflow flags + nozzle pick will fall back to settings defaults.",
+                self.name,
+                file_path.name,
+                sorted(self._slicer_print_options.keys()),
+            )
 
         try:
             import json
@@ -575,46 +604,38 @@ class VirtualPrinterInstance:
 
                 # H2C dual-nozzle-rack slicer-pick preservation (#1780).
                 # BambuStudio's project_file MQTT command for rack-swap models
-                # (O1C2 today) carries:
-                #   `nozzle_mapping` — per-filament array of physical nozzle
-                #     position IDs (`list[int]`).
-                #   `nozzles_info`   — per-extruder rack metadata
-                #     (`list[dict]`, fields: id / type / flowSize / diameter).
-                # Forward both verbatim onto the queue item so the dispatcher
-                # can replay them in its own project_file command. Without
-                # this the H2C firmware falls back to "last matching nozzle"
-                # auto-pick and ignores the user's Bambu Studio choice. Every
-                # other model has these absent from slicer_opts, so the
-                # capture is a transparent no-op there.
+                # (O1C2 today) carries `nozzle_mapping` — a per-filament array
+                # of physical nozzle position IDs (`list[int]`). Forward it
+                # verbatim onto the queue item so the dispatcher can replay it
+                # in its own project_file command. Without this the H2C
+                # firmware falls back to "last matching nozzle" auto-pick and
+                # ignores the user's Bambu Studio choice. Every other model
+                # has it absent from slicer_opts, so the capture is a
+                # transparent no-op there. (`nozzles_info` was also captured
+                # in the original fix but BambuStudio never actually sends it
+                # — verified via wire capture on H2C — so only `nozzle_mapping`
+                # is forwarded now.)
                 nozzle_mapping_json: str | None = None
-                nozzles_info_json: str | None = None
                 if slicer_opts is not None:
-                    for src_key in ("nozzle_mapping", "nozzles_info"):
-                        raw = slicer_opts.get(src_key)
-                        if raw is None:
-                            continue
-                        # BambuStudio's NetworkAgent should embed these as
-                        # parsed JSON in the project_file body (matching the
-                        # ams_mapping / ams_mapping2 shape Bambuddy already
-                        # consumes as list[int] / list[dict]). Accept a
-                        # JSON-encoded string defensively in case any path
-                        # arrives stringified.
+                    raw = slicer_opts.get("nozzle_mapping")
+                    if raw is not None:
+                        # BambuStudio's NetworkAgent embeds this as parsed
+                        # JSON in the project_file body (matching the
+                        # ams_mapping shape Bambuddy already consumes as
+                        # list[int]). Accept a JSON-encoded string defensively
+                        # in case any path arrives stringified.
                         if isinstance(raw, str):
                             try:
                                 raw = json.loads(raw)
                             except json.JSONDecodeError:
                                 logger.warning(
-                                    "[VP %s] Slicer %s is unparseable JSON, dropping: %r",
+                                    "[VP %s] Slicer nozzle_mapping is unparseable JSON, dropping: %r",
                                     self.name,
-                                    src_key,
                                     raw,
                                 )
-                                continue
-                        encoded = json.dumps(raw)
-                        if src_key == "nozzle_mapping":
-                            nozzle_mapping_json = encoded
-                        else:
-                            nozzles_info_json = encoded
+                                raw = None
+                        if raw is not None:
+                            nozzle_mapping_json = json.dumps(raw)
 
                 service = ArchiveService(db)
                 archive = await service.archive_print(
@@ -723,7 +744,6 @@ class VirtualPrinterInstance:
                             # the same nozzle pick across plates rather than only the
                             # first one (mirrors the #1697 / #1188 per-plate loop fix).
                             nozzle_mapping=nozzle_mapping_json,
-                            nozzles_info=nozzles_info_json,
                         )
                         db.add(queue_item)
                         await db.flush()  # populate queue_item.id before logging

backend/app/services/virtual_printer/mqtt_server.py

@@ -1293,6 +1293,14 @@ class SimpleMQTTServer:
                     file_3mf = print_data.get("file", filename)
                     await self._send_print_response(writer, sequence_id, file_3mf, serial=client_serial)
                     if self.on_print_command:
+                        # `filename` is the slicer's `subtask_name` (bare model
+                        # name, no extension). Pass it through verbatim — the
+                        # `_schedule_finish_release` chain echoes it back as
+                        # gcode_file + subtask_name in push_status, and the
+                        # slicer matches against its own subtask_name there.
+                        # The FTP filename (with extension) is in print_data
+                        # under "file" for the queue-stash side to use as its
+                        # own key matching `_add_to_print_queue`'s lookup.
                         await self._notify_print_command(filename, print_data)
                     handled_locally = True
 

backend/tests/integration/test_library_api.py

@@ -44,6 +44,61 @@ class TestLibraryFoldersAPI:
         assert response.status_code == 200
         assert response.json() == []
 
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_folder_tree_exposes_latest_activity_at_from_files(
+        self, async_client: AsyncClient, folder_factory, db_session
+    ):
+        """#1770: folder list returns latest_activity_at = MAX(folder.updated_at,
+        MAX(immediate-child file.updated_at)) so the frontend can sort by
+        recent activity. Adding a file with a later updated_at must bubble it.
+        """
+        from datetime import datetime, timedelta
+
+        from backend.app.models.library import LibraryFile
+
+        folder = await folder_factory(name="Active Folder")
+        # File whose updated_at is well after the folder's. Activity should
+        # surface this timestamp, not the folder's stale one.
+        future = datetime.utcnow() + timedelta(hours=24)
+        db_session.add(
+            LibraryFile(
+                folder_id=folder.id,
+                filename="model.3mf",
+                file_path="library/model.3mf",
+                file_type="3mf",
+                file_size=123,
+                updated_at=future,
+            )
+        )
+        await db_session.commit()
+
+        response = await async_client.get("/api/v1/library/folders")
+        assert response.status_code == 200
+        items = response.json()
+        assert len(items) == 1
+        item = items[0]
+        assert item["id"] == folder.id
+        assert item["latest_activity_at"] is not None
+        # latest_activity_at should be at least the future stamp we set.
+        assert item["latest_activity_at"] >= future.isoformat()
+
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_folder_tree_latest_activity_at_falls_back_to_folder_updated_at(
+        self, async_client: AsyncClient, folder_factory, db_session
+    ):
+        """#1770: a folder with no files reports its own updated_at, not null —
+        otherwise the activity sort would dump every empty folder to one end."""
+        await folder_factory(name="Empty Folder")
+        response = await async_client.get("/api/v1/library/folders")
+        assert response.status_code == 200
+        items = response.json()
+        assert len(items) == 1
+        item = items[0]
+        # latest_activity_at == folder.updated_at when there are no files
+        assert item["latest_activity_at"] is not None
+
     @pytest.mark.asyncio
     @pytest.mark.integration
     async def test_create_folder(self, async_client: AsyncClient, db_session):

backend/tests/unit/services/test_bambu_mqtt.py

@@ -5082,14 +5082,17 @@ class TestStartPrintRecordsDispatchedPlate:
 
 
 class TestStartPrintNozzleMappingDispatch:
-    """H2C dual-nozzle-rack (#1780) — nozzle_mapping + nozzles_info on dispatch.
+    """H2C dual-nozzle-rack (#1780) — nozzle_mapping on dispatch.
 
     BambuStudio's project_file MQTT command for O1C2 carries a per-filament
-    physical nozzle position ID array (`nozzle_mapping`) and a per-extruder
-    rack metadata array (`nozzles_info`). Without forwarding both, the H2C
-    firmware falls back to "last matching nozzle type" auto-pick and ignores
-    the user's slicer choice. Tests pin the gate, the parse, the no-op cases,
-    and the malformed-JSON safety net.
+    physical nozzle position ID array (`nozzle_mapping`). Without forwarding
+    it, the H2C firmware falls back to "last matching nozzle type" auto-pick
+    and ignores the user's slicer choice. Tests pin the gate, the parse, the
+    no-op cases, and the malformed-JSON safety net.
+
+    The original #1780 attempt also captured `nozzles_info` but a wire capture
+    on H2C confirmed BambuStudio never sends that field — the capture/dispatch
+    paths for it were dropped in the same release.
     """
 
     @pytest.fixture
@@ -5111,29 +5114,23 @@ class TestStartPrintNozzleMappingDispatch:
         call_args = mqtt_client._client.publish.call_args
         return json.loads(call_args[0][1])["print"]
 
-    def test_dual_nozzle_includes_nozzle_mapping_and_nozzles_info(self, mqtt_client):
-        """Dual-nozzle + both fields present → parsed JSON arrays injected
+    def test_dual_nozzle_includes_nozzle_mapping(self, mqtt_client):
+        """Dual-nozzle + nozzle_mapping present → parsed JSON array injected
         verbatim onto the dispatched project_file command."""
         mqtt_client._is_dual_nozzle = True
-        nozzles_info = [
-            {"id": 1, "type": None, "flowSize": "High Flow", "diameter": 0.4},
-            {"id": 2, "type": None, "flowSize": "Standard", "diameter": 0.4},
-        ]
 
         mqtt_client.start_print(
             "test.3mf",
-            nozzle_mapping=json.dumps([16, 0, 19]),
-            nozzles_info=json.dumps(nozzles_info),
+            nozzle_mapping=json.dumps([16, -1, -1, 1, -1, -1, -1, -1]),
         )
 
         cmd = self._published_print_cmd(mqtt_client)
-        # Lists, not strings — the wire shape must match BambuStudio's.
-        assert cmd["nozzle_mapping"] == [16, 0, 19]
-        assert cmd["nozzles_info"] == nozzles_info
+        # List, not string — the wire shape must match BambuStudio's.
+        assert cmd["nozzle_mapping"] == [16, -1, -1, 1, -1, -1, -1, -1]
 
     def test_single_nozzle_omits_nozzle_mapping_even_if_set(self, mqtt_client):
-        """A single-nozzle printer must NOT emit the rack fields even if the
-        caller passes them (defense-in-depth — the queue item could legitimately
+        """A single-nozzle printer must NOT emit the rack field even if the
+        caller passes it (defense-in-depth — the queue item could legitimately
         carry a stale capture from before a model change)."""
         mqtt_client._is_dual_nozzle = False
         mqtt_client.model = "P1S"  # single-nozzle
@@ -5141,41 +5138,22 @@ class TestStartPrintNozzleMappingDispatch:
         mqtt_client.start_print(
             "test.3mf",
             nozzle_mapping=json.dumps([16, 0, 19]),
-            nozzles_info=json.dumps([{"id": 1}]),
         )
 
         cmd = self._published_print_cmd(mqtt_client)
         assert "nozzle_mapping" not in cmd
-        assert "nozzles_info" not in cmd
 
-    def test_dual_nozzle_no_fields_no_injection(self, mqtt_client):
+    def test_dual_nozzle_no_field_no_injection(self, mqtt_client):
         """Dual-nozzle printer + no slicer pick (NULL on queue item) → command
-        carries no nozzle_mapping / nozzles_info. The firmware then runs its
-        normal auto-pick, which is the pre-fix behaviour for any non-O1C2 dual-
+        carries no nozzle_mapping. The firmware then runs its normal
+        auto-pick, which is the pre-fix behaviour for any non-O1C2 dual-
         nozzle model that has no rack to disambiguate against anyway."""
         mqtt_client._is_dual_nozzle = True
 
-        mqtt_client.start_print("test.3mf", nozzle_mapping=None, nozzles_info=None)
+        mqtt_client.start_print("test.3mf", nozzle_mapping=None)
 
         cmd = self._published_print_cmd(mqtt_client)
         assert "nozzle_mapping" not in cmd
-        assert "nozzles_info" not in cmd
-
-    def test_dual_nozzle_partial_only_mapping(self, mqtt_client):
-        """Half-populated case: nozzle_mapping carried but nozzles_info NULL.
-        Forward what we have; firmware tolerates a missing rack metadata
-        field and resolves against its own state."""
-        mqtt_client._is_dual_nozzle = True
-
-        mqtt_client.start_print(
-            "test.3mf",
-            nozzle_mapping=json.dumps([16]),
-            nozzles_info=None,
-        )
-
-        cmd = self._published_print_cmd(mqtt_client)
-        assert cmd["nozzle_mapping"] == [16]
-        assert "nozzles_info" not in cmd
 
     def test_malformed_nozzle_mapping_is_logged_and_omitted(self, mqtt_client, caplog):
         """Invalid JSON on the queue item must NOT block the dispatch. Log a
@@ -5189,7 +5167,6 @@ class TestStartPrintNozzleMappingDispatch:
             result = mqtt_client.start_print(
                 "test.3mf",
                 nozzle_mapping="not valid json {",
-                nozzles_info=None,
             )
 
         assert result is True  # dispatch still proceeded
@@ -5197,17 +5174,16 @@ class TestStartPrintNozzleMappingDispatch:
         assert "nozzle_mapping" not in cmd
         assert any("Invalid nozzle_mapping" in rec.message for rec in caplog.records)
 
-    def test_empty_string_fields_are_treated_as_absent(self, mqtt_client):
+    def test_empty_string_field_is_treated_as_absent(self, mqtt_client):
         """An empty-string column value (legacy data, or a NOT NULL DB
         recovery shim) must behave the same as NULL — no injection, no
         parse error log."""
         mqtt_client._is_dual_nozzle = True
 
-        mqtt_client.start_print("test.3mf", nozzle_mapping="", nozzles_info="")
+        mqtt_client.start_print("test.3mf", nozzle_mapping="")
 
         cmd = self._published_print_cmd(mqtt_client)
         assert "nozzle_mapping" not in cmd
-        assert "nozzles_info" not in cmd
 
 
 class TestFilamentTrackSwitchDetection:

backend/tests/unit/services/test_printer_manager.py

@@ -379,7 +379,6 @@ class TestPrinterManager:
             use_ams=True,
             nozzle_offset_cali=False,
             nozzle_mapping=None,
-            nozzles_info=None,
         )
         assert result is True
 

backend/tests/unit/services/test_virtual_printer.py

@@ -1580,13 +1580,13 @@ class TestVirtualPrinterInstance:
         assert all(q.manual_start for q in added_items)
 
     @pytest.mark.asyncio
-    async def test_add_to_print_queue_captures_nozzle_mapping_and_nozzles_info(self, tmp_path):
+    async def test_add_to_print_queue_captures_nozzle_mapping(self, tmp_path):
         """#1780: BambuStudio's project_file for H2C rack-swap (O1C2) sends
-        per-filament physical nozzle position IDs in `nozzle_mapping` and
-        per-extruder rack metadata in `nozzles_info`. VP intake must store
-        both as JSON strings on the queue item so the dispatcher can replay
-        them. Without this the H2C firmware falls back to "last matching
-        nozzle" auto-pick and ignores the user's slicer choice.
+        per-filament physical nozzle position IDs in `nozzle_mapping`. VP
+        intake must store it as a JSON string on the queue item so the
+        dispatcher can replay it. Without this the H2C firmware falls back
+        to "last matching nozzle" auto-pick and ignores the user's slicer
+        choice.
         """
         import json as _json
 
@@ -1617,18 +1617,16 @@ class TestVirtualPrinterInstance:
         file_path.write_bytes(b"fake3mf")
 
         # Pre-populate as if BS's project_file arrived. Wire shape matches
-        # BambuStudio's PrintJob params: nozzle_mapping = array of per-
-        # filament physical nozzle position IDs, nozzles_info = array of
-        # per-extruder rack-side metadata.
+        # BambuStudio's PrintJob params: nozzle_mapping = 32-entry array of
+        # per-filament physical nozzle position IDs (verified via H2C wire
+        # capture). The slicer-side `nozzles_info` field that the original
+        # #1780 attempt also looked for was never actually sent — it has
+        # been dropped from the capture path entirely.
         await inst.on_print_command(
             file_path.name,
             {
                 "command": "project_file",
-                "nozzle_mapping": [16, 0, 19],
-                "nozzles_info": [
-                    {"id": 1, "type": None, "flowSize": "High Flow", "diameter": 0.4},
-                    {"id": 2, "type": None, "flowSize": "Standard", "diameter": 0.4},
-                ],
+                "nozzle_mapping": [16, -1, -1, 1, -1, -1, -1, -1],
             },
         )
 
@@ -1653,18 +1651,14 @@ class TestVirtualPrinterInstance:
         assert len(added_items) == 1
         item = added_items[0]
         assert item.nozzle_mapping is not None
-        assert _json.loads(item.nozzle_mapping) == [16, 0, 19]
-        assert item.nozzles_info is not None
-        parsed_info = _json.loads(item.nozzles_info)
-        assert parsed_info[0]["flowSize"] == "High Flow"
-        assert parsed_info[1]["flowSize"] == "Standard"
+        assert _json.loads(item.nozzle_mapping) == [16, -1, -1, 1, -1, -1, -1, -1]
 
     @pytest.mark.asyncio
-    async def test_add_to_print_queue_no_nozzle_fields_when_slicer_omits(self, tmp_path):
-        """#1780: every model other than O1C2 sends no nozzle_mapping /
-        nozzles_info — the queue item must carry NULL on both, not an empty
-        list. NULL is what the dispatch layer keys off of to skip the
-        injection entirely on non-rack-swap printers.
+    async def test_add_to_print_queue_no_nozzle_mapping_when_slicer_omits(self, tmp_path):
+        """#1780: every model other than O1C2 sends no nozzle_mapping — the
+        queue item must carry NULL, not an empty list. NULL is what the
+        dispatch layer keys off of to skip the injection entirely on non-
+        rack-swap printers.
         """
         from backend.app.services.virtual_printer.manager import VirtualPrinterInstance
 
@@ -1719,13 +1713,12 @@ class TestVirtualPrinterInstance:
         assert len(added_items) == 1
         item = added_items[0]
         assert item.nozzle_mapping is None
-        assert item.nozzles_info is None
 
     @pytest.mark.asyncio
     async def test_add_to_print_queue_nozzle_pick_replicated_across_plates(self, tmp_path, monkeypatch):
         """#1780 × #1697/#1188: a multi-plate Send All from BS must stamp the
-        same nozzle_mapping / nozzles_info on every plate's queue item, not
-        only the first. Mirrors the per-plate stamping for gcode_injection,
+        same nozzle_mapping on every plate's queue item, not only the first.
+        Mirrors the per-plate stamping for gcode_injection,
         filament_overrides, etc.
         """
         import json as _json
@@ -1767,7 +1760,6 @@ class TestVirtualPrinterInstance:
             {
                 "command": "project_file",
                 "nozzle_mapping": [16, 0],
-                "nozzles_info": [{"id": 1, "flowSize": "High Flow", "diameter": 0.4}],
             },
         )
 
@@ -1792,7 +1784,6 @@ class TestVirtualPrinterInstance:
         assert len(added_items) == 3
         for item in added_items:
             assert _json.loads(item.nozzle_mapping) == [16, 0]
-            assert _json.loads(item.nozzles_info)[0]["flowSize"] == "High Flow"
 
 
 class TestVirtualPrinterManager:
@@ -3491,3 +3482,109 @@ class TestSSDPProxyName:
         rewritten = ssdp_proxy_without_name._rewrite_ssdp(packet)
 
         assert b"DevName.bambu.com: RealPrinter - Proxy" in rewritten
+
+
+class TestVPProjectFileStashKey:
+    """Regression: `on_print_command` MUST stash slicer options under the
+    FTP filename (`data["file"]`, with extension), NOT under `filename`
+    (the slicer's `subtask_name`, bare).
+
+    #1780 root cause (real bundle, 2026-06-21): BambuStudio sends
+    `subtask_name = "Model_Name"` (bare) and `file = "Model_Name.gcode.3mf"`
+    (with extension). `_add_to_print_queue` looks up the stash under
+    `file_path.name` from the FTP receive side, which always has the
+    extension. If the stash uses `subtask_name`, lookup misses → every
+    captured slicer field (bed_leveling, flow_cali, vibration_cali,
+    layer_inspect, timelapse, nozzle_mapping) silently falls back to
+    settings defaults on every Bambu Studio "Send" upload.
+
+    `filename` (subtask_name) must still flow to `_schedule_finish_release`
+    untouched — push_status echoes it back as gcode_file / subtask_name and
+    the slicer matches against its own local subtask_name there. So
+    `on_print_command` keeps `filename` for state-feedback but derives the
+    stash key from `data["file"]`.
+    """
+
+    @pytest.fixture
+    def instance(self, tmp_path):
+        from backend.app.services.virtual_printer.manager import VirtualPrinterInstance
+
+        return VirtualPrinterInstance(
+            vp_id=99,
+            name="StashKeyTest",
+            mode="queue",
+            model="O1C2",
+            access_code="12345678",
+            serial_suffix="999999999",
+            base_dir=tmp_path,
+        )
+
+    @pytest.mark.asyncio
+    async def test_stash_key_uses_file_field_not_subtask_name(self, instance):
+        """BambuStudio's real wire shape: `subtask_name` ≠ `file`.
+        on_print_command must stash under `data["file"]` so the FTP-side
+        `_add_to_print_queue` lookup matches.
+        """
+        # mqtt_server.py:_handle_publish hands the bare subtask_name as
+        # `filename` and the full print_data body as `data`. The FTP filename
+        # lives in `data["file"]`.
+        await instance.on_print_command(
+            "Filament_Track_Switch_Holder",  # subtask_name (bare)
+            {
+                "command": "project_file",
+                "subtask_name": "Filament_Track_Switch_Holder",
+                "file": "Filament_Track_Switch_Holder.gcode.3mf",
+                "nozzle_mapping": [16, -1, -1, 1],
+            },
+        )
+
+        # Stash MUST be under the FTP filename, not the bare subtask_name.
+        # `_add_to_print_queue` does `_slicer_print_options.pop(file_path.name, None)`
+        # where file_path.name == "Filament_Track_Switch_Holder.gcode.3mf".
+        assert "Filament_Track_Switch_Holder.gcode.3mf" in instance._slicer_print_options
+        assert "Filament_Track_Switch_Holder" not in instance._slicer_print_options
+        # Body must carry nozzle_mapping verbatim.
+        stashed = instance._slicer_print_options["Filament_Track_Switch_Holder.gcode.3mf"]
+        assert stashed["nozzle_mapping"] == [16, -1, -1, 1]
+
+    @pytest.mark.asyncio
+    async def test_stash_key_falls_back_to_filename_when_file_absent(self, instance):
+        """Defensive fallback: a slicer that omits the `file` field entirely
+        (legacy / non-3MF) must fall back to `filename` (subtask_name), not
+        leave the stash unkeyed."""
+        await instance.on_print_command(
+            "BareName",
+            {
+                "command": "project_file",
+                "subtask_name": "BareName",
+                # no "file" field
+            },
+        )
+
+        assert "BareName" in instance._slicer_print_options
+
+    @pytest.mark.asyncio
+    async def test_stash_key_signals_event_under_file_key(self, instance):
+        """`_add_to_print_queue` registers a wait-event under `file_path.name`
+        when the slicer's project_file arrives late. on_print_command must
+        signal THAT event (keyed by the FTP filename), not one keyed by
+        subtask_name — else the waiter times out even though the stash is
+        present and addressable."""
+        import asyncio
+
+        ftp_filename = "Filament_Track_Switch_Holder.gcode.3mf"
+        event = asyncio.Event()
+        instance._slicer_print_options_events[ftp_filename] = event
+
+        await instance.on_print_command(
+            "Filament_Track_Switch_Holder",  # bare subtask_name
+            {
+                "command": "project_file",
+                "subtask_name": "Filament_Track_Switch_Holder",
+                "file": ftp_filename,
+            },
+        )
+
+        # Event keyed by FTP filename must fire even though on_print_command
+        # was called with the bare subtask_name.
+        assert event.is_set()

frontend/src/api/client.ts

@@ -6314,6 +6314,9 @@ export interface LibraryFolderTree {
   external_path: string | null;
   external_readonly: boolean;
   file_count: number;
+  // max(folder.updated_at, max(immediate-child file.updated_at)). Used by
+  // the File Manager folder tree's "sort by recent activity" mode (#1770).
+  latest_activity_at: string | null;
   children: LibraryFolderTree[];
 }
 
@@ -6330,6 +6333,7 @@ export interface LibraryFolder {
   external_readonly: boolean;
   external_show_hidden: boolean;
   file_count: number;
+  latest_activity_at: string | null;
   created_at: string;
   updated_at: string;
 }

frontend/src/i18n/locales/de.ts

@@ -3320,6 +3320,9 @@ export default {
     collapse: 'Einklappen',
     collapseFoldersByDefault: 'Ordner standardmäßig einklappen',
     expandFoldersByDefault: 'Ordner standardmäßig ausklappen',
+    folderSort: 'Ordner sortieren',
+    folderSortByName: 'Nach Name',
+    folderSortByActivity: 'Nach letzter Aktivität',
     dragToResizeTooltip: 'Ziehen zum Ändern der Größe, Doppelklick zum Zurücksetzen',
     searchFiles: 'Dateien suchen...',
     allTypes: 'Alle Typen',

frontend/src/i18n/locales/en.ts

@@ -3335,6 +3335,9 @@ export default {
     collapse: 'Collapse',
     collapseFoldersByDefault: 'Collapse folders by default',
     expandFoldersByDefault: 'Expand folders by default',
+    folderSort: 'Sort folders',
+    folderSortByName: 'By name',
+    folderSortByActivity: 'By recent activity',
     dragToResizeTooltip: 'Drag to resize, double-click to reset',
     searchFiles: 'Search files...',
     allTypes: 'All types',

frontend/src/i18n/locales/es.ts

@@ -3323,6 +3323,9 @@ export default {
     collapse: 'Contraer',
     collapseFoldersByDefault: 'Contraer las carpetas de forma predeterminada',
     expandFoldersByDefault: 'Expandir las carpetas de forma predeterminada',
+    folderSort: 'Ordenar carpetas',
+    folderSortByName: 'Por nombre',
+    folderSortByActivity: 'Por actividad reciente',
     dragToResizeTooltip: 'Arrastre para redimensionar, doble clic para restablecer',
     searchFiles: 'Buscar archivos...',
     allTypes: 'Todos los tipos',

frontend/src/i18n/locales/fr.ts

@@ -3309,6 +3309,9 @@ export default {
     collapse: 'Réduire',
     collapseFoldersByDefault: 'Réduire les dossiers par défaut',
     expandFoldersByDefault: 'Développer les dossiers par défaut',
+    folderSort: 'Trier les dossiers',
+    folderSortByName: 'Par nom',
+    folderSortByActivity: 'Par activité récente',
     dragToResizeTooltip: 'Glisser pour redimensionner, double-clic reset',
     searchFiles: 'Chercher fichiers...',
     allTypes: 'Tous types',

frontend/src/i18n/locales/it.ts

@@ -3308,6 +3308,9 @@ export default {
     collapse: 'Comprimi',
     collapseFoldersByDefault: 'Comprimi le cartelle per impostazione predefinita',
     expandFoldersByDefault: 'Espandi le cartelle per impostazione predefinita',
+    folderSort: 'Ordina cartelle',
+    folderSortByName: 'Per nome',
+    folderSortByActivity: 'Per attività recente',
     dragToResizeTooltip: 'Trascina per ridimensionare, doppio clic per reset',
     searchFiles: 'Cerca file...',
     allTypes: 'Tutti i tipi',

frontend/src/i18n/locales/ja.ts

@@ -3320,6 +3320,9 @@ export default {
     collapse: '折りたたむ',
     collapseFoldersByDefault: 'フォルダをデフォルトで折りたたむ',
     expandFoldersByDefault: 'フォルダをデフォルトで展開する',
+    folderSort: 'フォルダの並べ替え',
+    folderSortByName: '名前順',
+    folderSortByActivity: '最終更新順',
     dragToResizeTooltip: 'ドラッグしてリサイズ、ダブルクリックでリセット',
     searchFiles: 'ファイルを検索...',
     allTypes: 'すべての種類',

frontend/src/i18n/locales/ko.ts

@@ -3133,6 +3133,9 @@ export default {
     collapse: '접기',
     collapseFoldersByDefault: '기본적으로 폴더 접기',
     expandFoldersByDefault: '기본적으로 폴더 펼치기',
+    folderSort: '폴더 정렬',
+    folderSortByName: '이름순',
+    folderSortByActivity: '최근 활동순',
     dragToResizeTooltip: '드래그하여 크기 조정, 더블클릭하여 초기화',
     searchFiles: '파일 검색...',
     allTypes: '모든 유형',

frontend/src/i18n/locales/pt-BR.ts

@@ -3308,6 +3308,9 @@ export default {
     collapse: 'Recolher',
     collapseFoldersByDefault: 'Recolher pastas por padrão',
     expandFoldersByDefault: 'Expandir pastas por padrão',
+    folderSort: 'Ordenar pastas',
+    folderSortByName: 'Por nome',
+    folderSortByActivity: 'Por atividade recente',
     dragToResizeTooltip: 'Arraste para redimensionar, clique duas vezes para redefinir',
     searchFiles: 'Pesquisar arquivos...',
     allTypes: 'Todos os tipos',

frontend/src/i18n/locales/tr.ts

@@ -3315,6 +3315,9 @@ export default {
     collapse: 'Daralt',
     collapseFoldersByDefault: 'Klasörleri varsayılan olarak daralt',
     expandFoldersByDefault: 'Klasörleri varsayılan olarak genişlet',
+    folderSort: 'Klasörleri sırala',
+    folderSortByName: 'Ada göre',
+    folderSortByActivity: 'Son etkinliğe göre',
     dragToResizeTooltip: 'Yeniden boyutlandırmak için sürükleyin, sıfırlamak için çift tıklayın',
     searchFiles: 'Dosyalarda ara...',
     allTypes: 'Tüm türler',

frontend/src/i18n/locales/zh-CN.ts

@@ -3308,6 +3308,9 @@ export default {
     collapse: '折叠',
     collapseFoldersByDefault: '默认折叠文件夹',
     expandFoldersByDefault: '默认展开文件夹',
+    folderSort: '文件夹排序',
+    folderSortByName: '按名称',
+    folderSortByActivity: '按最近活动',
     dragToResizeTooltip: '拖动调整大小，双击重置',
     searchFiles: '搜索文件...',
     allTypes: '所有类型',

frontend/src/i18n/locales/zh-TW.ts

@@ -3308,6 +3308,9 @@ export default {
     collapse: '折疊',
     collapseFoldersByDefault: '預設折疊資料夾',
     expandFoldersByDefault: '預設展開資料夾',
+    folderSort: '資料夾排序',
+    folderSortByName: '依名稱',
+    folderSortByActivity: '依最近活動',
     dragToResizeTooltip: '拖曳調整大小，雙擊重設',
     searchFiles: '搜尋檔案...',
     allTypes: '所有類型',

frontend/src/pages/FileManagerPage.tsx

@@ -978,6 +978,17 @@ export function FileManagerPage() {
   const [collapseFoldersByDefault, setCollapseFoldersByDefault] = useState(() => {
     return localStorage.getItem('library-collapse-folders') === 'true';
   });
+  // Folder tree sort (#1770). 'name' = alphabetical (the prior behaviour);
+  // 'activity' = most recent file activity inside the folder first. Persisted
+  // independently from the file-side sort so each can be tuned to taste.
+  const [folderSortField, setFolderSortField] = useState<'name' | 'activity'>(() => {
+    const saved = localStorage.getItem('library-folder-sort-field');
+    return saved === 'activity' ? 'activity' : 'name';
+  });
+  const [folderSortDirection, setFolderSortDirection] = useState<'asc' | 'desc'>(() => {
+    const saved = localStorage.getItem('library-folder-sort-direction');
+    return saved === 'desc' ? 'desc' : 'asc';
+  });
 
   // Resizable sidebar state
   const [sidebarWidth, setSidebarWidth] = useState(() => {
@@ -1060,6 +1071,42 @@ export function FileManagerPage() {
     queryFn: () => api.getLibraryFolders(),
   });
 
+  // Recursive folder tree sort (#1770). Applies the same comparator to the
+  // top-level list AND to each level of `children`, so sort order is uniform
+  // at every depth of nesting. When sorting by activity, the comparator falls
+  // back to a created-at fallback for folders with no files (`latest_activity_at`
+  // is null) so they stay grouped at the end / start of the bucket instead of
+  // randomly interspersed.
+  const sortedFolders = useMemo(() => {
+    if (!folders) return folders;
+    const sortLevel = (items: LibraryFolderTree[]): LibraryFolderTree[] => {
+      const sorted = [...items].sort((a, b) => {
+        let comparison = 0;
+        if (folderSortField === 'name') {
+          comparison = a.name.localeCompare(b.name);
+        } else {
+          // activity: newest first on 'desc', oldest first on 'asc'.
+          // Folders with no activity timestamp sort to the end regardless
+          // of direction so an empty folder doesn't elbow a recently-used one.
+          const aTs = a.latest_activity_at ? new Date(a.latest_activity_at).getTime() : null;
+          const bTs = b.latest_activity_at ? new Date(b.latest_activity_at).getTime() : null;
+          if (aTs === null && bTs === null) {
+            comparison = a.name.localeCompare(b.name);
+          } else if (aTs === null) {
+            return 1;
+          } else if (bTs === null) {
+            return -1;
+          } else {
+            comparison = aTs - bTs;
+          }
+        }
+        return folderSortDirection === 'asc' ? comparison : -comparison;
+      });
+      return sorted.map((f) => ({ ...f, children: sortLevel(f.children) }));
+    };
+    return sortLevel(folders);
+  }, [folders, folderSortField, folderSortDirection]);
+
   // Trash count for the header badge (#1008). Empty/error are silently treated
   // as zero so a broken trash endpoint doesn't break the File Manager.
   const { data: trashCount } = useQuery({
@@ -1606,7 +1653,7 @@ export function FileManagerPage() {
             {folders?.some((f) => f.is_external) && (
               <option value="__top:external">🔗 {t('fileManager.allExternal')}</option>
             )}
-            {folders && (() => {
+            {sortedFolders && (() => {
               // Flatten folder tree for mobile selector
               const flattenFolders = (items: LibraryFolderTree[], depth = 0): { id: number; name: string; fileCount: number; depth: number }[] => {
                 const result: { id: number; name: string; fileCount: number; depth: number }[] = [];
@@ -1618,7 +1665,7 @@ export function FileManagerPage() {
                 }
                 return result;
               };
-              return flattenFolders(folders).map((folder) => (
+              return flattenFolders(sortedFolders).map((folder) => (
                 <option key={folder.id} value={folder.id}>
                   {'│ '.repeat(folder.depth)}📂 {folder.name} {folder.fileCount > 0 ? `(${folder.fileCount})` : ''}
                 </option>
@@ -1658,6 +1705,35 @@ export function FileManagerPage() {
           <div className="p-3 border-b border-bambu-dark-tertiary flex items-center justify-between">
             <h2 className="text-sm font-medium text-white">{t('fileManager.folders')}</h2>
             <div className="flex items-center gap-1">
+              {/* Folder tree sort (#1770). Dropdown drives the comparator;
+                  direction button flips asc/desc. Both persist to localStorage
+                  on change so the choice survives reloads. */}
+              <select
+                value={folderSortField}
+                onChange={(e) => {
+                  const v = e.target.value === 'activity' ? 'activity' : 'name';
+                  setFolderSortField(v);
+                  localStorage.setItem('library-folder-sort-field', v);
+                }}
+                className="text-xs px-1 py-0.5 rounded bg-bambu-dark border border-bambu-dark-tertiary text-bambu-gray focus:outline-none focus:border-bambu-green"
+                title={t('fileManager.folderSort')}
+                aria-label={t('fileManager.folderSort')}
+              >
+                <option value="name">{t('fileManager.folderSortByName')}</option>
+                <option value="activity">{t('fileManager.folderSortByActivity')}</option>
+              </select>
+              <button
+                onClick={() => {
+                  const newValue = folderSortDirection === 'asc' ? 'desc' : 'asc';
+                  setFolderSortDirection(newValue);
+                  localStorage.setItem('library-folder-sort-direction', newValue);
+                }}
+                className="text-bambu-gray hover:text-white hover:bg-bambu-dark p-1 rounded transition-colors"
+                title={folderSortDirection === 'asc' ? t('fileManager.ascending') : t('fileManager.descending')}
+                aria-label={folderSortDirection === 'asc' ? t('fileManager.ascending') : t('fileManager.descending')}
+              >
+                {folderSortDirection === 'asc' ? <SortAsc className="w-3.5 h-3.5" /> : <SortDesc className="w-3.5 h-3.5" />}
+              </button>
               <button
                 onClick={() => {
                   const newValue = !collapseFoldersByDefault;
@@ -1732,7 +1808,7 @@ export function FileManagerPage() {
             {/* Folder tree — re-key on the collapse toggle so flipping it
                 remounts every FolderTreeItem, which re-reads defaultExpanded
                 and makes the preference take effect immediately. */}
-            {folders?.map((folder) => (
+            {sortedFolders?.map((folder) => (
               <FolderTreeItem
                 key={`${folder.id}-${collapseFoldersByDefault ? 'c' : 'e'}`}
                 folder={folder}
@@ -2086,9 +2162,12 @@ export function FileManagerPage() {
                   column couldn't fit (#1325 follow-up reported in chat). */}
               <div className="bg-bambu-dark-secondary rounded-lg border border-bambu-dark-tertiary overflow-x-auto">
                 {/* List header - hidden on mobile, show simplified on small screens.
-                    The trailing column is `min-content` so it sizes to the widest
-                    action-icon strip across all rows (sliced 3MF = 7 icons ~220px). */}
-                <div className={`hidden sm:grid ${authEnabled ? 'grid-cols-[auto_1fr_120px_100px_100px_100px_min-content]' : 'grid-cols-[auto_1fr_100px_100px_100px_min-content]'} gap-4 px-4 py-2 bg-bambu-dark-secondary border-b border-bambu-dark-tertiary text-xs text-bambu-gray font-medium`}>
+                    Trailing actions column is fixed at 220px (sliced 3MF = 7 icons
+                    ~220px). It used to be `min-content`, but header + body are sibling
+                    grids that compute `min-content` independently — the header's empty
+                    trailing div resolved to 0px, leaving body columns shifted left of
+                    their headers. Fixed width keeps header and body in lockstep. */}
+                <div className={`hidden sm:grid ${authEnabled ? 'grid-cols-[auto_1fr_120px_100px_100px_100px_220px]' : 'grid-cols-[auto_1fr_100px_100px_100px_220px]'} gap-4 px-4 py-2 bg-bambu-dark-secondary border-b border-bambu-dark-tertiary text-xs text-bambu-gray font-medium`}>
                   <div className="w-6" />
                   <div>{t('common.name')}</div>
                   {authEnabled && <div>{t('fileManager.uploadedBy', { defaultValue: 'Uploaded By' })}</div>}
@@ -2101,7 +2180,7 @@ export function FileManagerPage() {
                 {filteredAndSortedFiles.map((file) => (
                   <div
                     key={file.id}
-                    className={`grid ${authEnabled ? 'grid-cols-[auto_1fr_120px_100px_100px_100px_min-content]' : 'grid-cols-[auto_1fr_100px_100px_100px_min-content]'} gap-4 px-4 py-3 items-center border-b border-bambu-dark-tertiary last:border-b-0 cursor-pointer hover:bg-bambu-dark/50 transition-colors ${
+                    className={`grid ${authEnabled ? 'grid-cols-[auto_1fr_120px_100px_100px_100px_220px]' : 'grid-cols-[auto_1fr_100px_100px_100px_220px]'} gap-4 px-4 py-3 items-center border-b border-bambu-dark-tertiary last:border-b-0 cursor-pointer hover:bg-bambu-dark/50 transition-colors ${
                       selectedFiles.includes(file.id) ? 'bg-bambu-green/10' : ''
                     }`}
                     onClick={() => handleFileSelect(file.id)}