Recover transient Syncthing and SQLite job failures

deploy/production/README.md

@@ -13,10 +13,37 @@ initial x1/x2/lithium topology.
   `archive_control_token`, `qb_password`, and `syncthing_api_key`, each a
   regular non-empty file with mode `0600`.
 
-The Syncthing mounts intentionally reproduce each instance's `/var/syncthing`
-layout, including nested data binds. This lets route discovery and route
-provisioning use one safe API-to-local path mapping without altering an
-existing Syncthing configuration.
+## Hardlink-safe bind-mount topology
+
+For an archive source, the qB content path and every Syncthing route used for
+staging must resolve through the **same container mount**. Matching host
+filesystem device IDs alone is insufficient: two separate Docker bind mounts
+have different mount IDs and `link(2)` may return `EXDEV` across them. The
+client deliberately treats that case as copy-only and performs a full payload
+free-space check.
+
+When a Syncthing route is physically nested below the qB root, mount the qB
+root once and map the exact Syncthing API folder through it:
+
+```yaml
+volumes:
+  - /srv/downloads:/data/qb
+  - /srv/syncthing-config:/data/sync
+```
+
+```toml
+[syncthing]
+api_root = "/var/syncthing"
+local_root = "/data/sync"
+local_path_overrides = { "/var/syncthing/Downloads/Sync" = "/data/qb/Sync" }
+```
+
+Do **not** additionally mount `/srv/downloads/Sync` at a path beneath
+`/data/sync`. The override is the authoritative mapping for that folder and
+keeps qB source files and staging destinations in one mount namespace. Use
+the folder's normalized API-visible **path** as the override key (for example,
+Syncthing `~/Downloads/Sync` becomes `/var/syncthing/Downloads/Sync`); do not
+use the folder ID.
 
 Before starting a stack, validate it with:
 

deploy/production/lithium/client.toml

@@ -19,7 +19,7 @@ reconnect_jitter = true
 stall_after = "30m" # Status warning only; it does not fail the job.
 verification_timeout = "30m"
 poll_interval = "1s"
-free_space_reserve_bytes = 1073741824 # Rechecked immediately before work.
+free_space_reserve_bytes = 33554432 # 32 MiB; payload bytes are added for copy paths.
 
 [backup]
 interval = "6h"

deploy/production/lithium/compose.yaml

@@ -2,7 +2,7 @@ name: archive-control-archive
 
 services:
   archive-client:
-    image: sodium/archive-clients:v0.1.2
+    image: sodium/archive-clients:v0.1.14
     user: "1000:1000"
     restart: unless-stopped
     command: ["--config", "/etc/archive-control/client.toml"]

deploy/production/x1/client.toml

@@ -19,7 +19,7 @@ reconnect_jitter = true
 stall_after = "30m" # Status warning only; it does not fail the job.
 verification_timeout = "30m"
 poll_interval = "1s"
-free_space_reserve_bytes = 1073741824 # Rechecked immediately before work.
+free_space_reserve_bytes = 33554432 # 32 MiB; payload bytes are added for copy paths.
 
 [backup]
 interval = "6h"
@@ -39,4 +39,7 @@ endpoint = "http://127.0.0.1:8384"
 api_key_file = "/run/secrets/syncthing_api_key"
 api_root = "/var/syncthing"
 local_root = "/data/sync"
+# This existing folder is physically inside the qB data tree. Map it through
+# that same client bind mount so source staging can use hardlinks.
+local_path_overrides = { "/var/syncthing/DownloadsSync" = "/data/qb/Sync" }
 advertised_addresses = ["dynamic"]

deploy/production/x1/compose.yaml

@@ -2,7 +2,7 @@ name: archive-control-cache
 
 services:
   archive-client:
-    image: sodium/archive-clients:v0.1.2
+    image: sodium/archive-clients:v0.1.14
     user: "1001:1001"
     restart: unless-stopped
     network_mode: host
@@ -16,4 +16,3 @@ services:
       - ./backups:/var/backups/archive-control
       - /home/ubuntu/Downloads:/data/qb
       - /home/ubuntu/compose/syncthing/st_home:/data/sync
-      - /home/ubuntu/Downloads/Sync:/data/sync/DownloadsSync

deploy/production/x2/client.toml

@@ -19,7 +19,7 @@ reconnect_jitter = true
 stall_after = "30m" # Status warning only; it does not fail the job.
 verification_timeout = "30m"
 poll_interval = "1s"
-free_space_reserve_bytes = 1073741824 # Rechecked immediately before work.
+free_space_reserve_bytes = 33554432 # 32 MiB; payload bytes are added for copy paths.
 
 [backup]
 interval = "6h"
@@ -39,4 +39,8 @@ endpoint = "http://127.0.0.1:8384"
 api_key_file = "/run/secrets/syncthing_api_key"
 api_root = "/var/syncthing"
 local_root = "/data/sync"
+# `DownloadsSync-X2` is ~/Downloads/Sync on the host, nested below the qB
+# root. Resolve it through /data/qb rather than a second nested bind mount so
+# source staging can hardlink it.
+local_path_overrides = { "/var/syncthing/Downloads/Sync" = "/data/qb/Sync" }
 advertised_addresses = ["dynamic"]

deploy/production/x2/compose.yaml

@@ -2,7 +2,7 @@ name: archive-control-cache
 
 services:
   archive-client:
-    image: sodium/archive-clients:v0.1.2
+    image: sodium/archive-clients:v0.1.14
     user: "1001:1001"
     restart: unless-stopped
     network_mode: host
@@ -16,4 +16,3 @@ services:
       - ./backups:/var/backups/archive-control
       - /home/ubuntu/Downloads:/data/qb
       - /home/ubuntu/compose/syncthing/st_home:/data/sync
-      - /home/ubuntu/Downloads/Sync:/data/sync/Downloads/Sync

docs/decisions.md

@@ -35,8 +35,11 @@ expand these rules but must not contradict them.
   manifests, and observed external state.
 - SQLite backups use the online backup API. Defaults are every six hours, 12
   recent, 14 daily, and eight weekly copies, plus pre/post-migration backups.
-- Default concurrency is one active data-moving job per client and per route.
-  Disjoint node pairs may run concurrently. Queueing is durable FIFO.
+- Default concurrency is unrestricted: every eligible queued job is admitted
+  in one scheduler pass and independent jobs execute concurrently on a client.
+  Physical qBittorrent, Syncthing, disk, and network capacity are therefore
+  the natural limit. `enforce_concurrency_limits=true` restores the optional
+  legacy per-client/per-route gates. Commands for one job remain serialized.
 - A queued job owns a per-resource reservation. Cancelling it removes only the
   queued record/reservation and never sends cleanup commands.
 - Connectivity or transfer stalls wait indefinitely. A configurable 30-minute

docs/deployment-and-usage.md

@@ -44,6 +44,9 @@ command_max_attempts = 3 # Total sends, including the initial attempt.
 stall_after = "30m" # Warning state only; jobs continue waiting.
 route_policy = "on_demand" # Alternative: eager_mesh.
 route_setup_timeout = "30m"
+# Default: allow all eligible jobs; disk/network/service capacity is the limit.
+enforce_concurrency_limits = false
+# Used only when enforce_concurrency_limits is true.
 max_active_per_client = 1
 max_active_per_route = 1
 max_envelope_bytes = 1048576
@@ -102,7 +105,7 @@ stall_after = "30m" # Warning only; no automatic job failure.
 verification_timeout = "30m" # Stopped qB full-recheck deadline.
 poll_interval = "1s" # Active qB/Syncthing observation interval.
 # Worst-case copy fallback must leave this many bytes free.
-free_space_reserve_bytes = 1073741824
+free_space_reserve_bytes = 33554432 # 32 MiB; payload bytes are added for copy paths.
 
 [backup]
 interval = "6h"
@@ -125,6 +128,16 @@ local_root = "/data/sync"
 advertised_addresses = ["dynamic"]
 ```
 
+When an existing Syncthing folder is physically nested in the qB data root,
+use a `local_path_overrides` entry to map that exact Syncthing API path through
+the same client bind mount. This enables hardlinks without creating two Docker
+mount boundaries for the same host files. Do not add a second bind mount for
+the nested folder: Linux treats it as a distinct mount even when it has the
+same `st_dev`, and the client correctly falls back to copy-only capacity
+accounting. The override key is the normalized Syncthing folder path beneath
+`api_root`, not its folder ID. See the production deployment README for the
+required compose and override pattern.
+
 The remaining node examples omit optional `[connection]`, `[jobs]`, and
 `[backup]` tables and therefore use these same defaults; deployments may
 override them per node.
@@ -213,7 +226,7 @@ cache/archive routes according to policy.
 ```yaml
 services:
   archive-client:
-    image: sodium/archive-clients:v0.1.2
+    image: sodium/archive-clients:v0.1.14
     user: "1001:1001"
     restart: unless-stopped
     command: ["archive-client", "--config", "/etc/archive-control/client.toml"]

docs/service-apis.md

@@ -29,6 +29,10 @@ The adapter accounts for terminology/behavior changes such as paused versus
 stopped states. It does not mutate qBittorrent preferences, categories, tags,
 limits, queueing defaults, or global save-path behavior.
 
+Syncthing route validation normalizes both absolute and `~/` folder-path
+spellings under the configured sync root before comparing an existing folder;
+an equivalent pre-existing pair is adopted without rewriting it.
+
 ### Inventory normalization
 
 For each torrent the client derives canonical v1/v2 identity from reliable API
@@ -85,9 +89,11 @@ left unchanged.
 
 Syncthing may serialize a folder path relative to its home as `~/...`. The
 client normalizes that notation beneath the configured API-visible sync root
-before applying the API-to-local root mapping. Deployments must mirror
-Syncthing's nested bind mounts into the client so the normalized API path and
-the client filesystem path refer to the same bytes.
+before applying the API-to-local root mapping. When that folder is nested
+below qB's content root, an exact `local_path_overrides` entry must map it
+through the qB bind mount. Do not mirror it as a second nested client bind
+mount: it denotes the same host bytes but a distinct mount namespace boundary,
+which prevents hardlink staging.
 
 Provisioning uses idempotent device and folder configuration updates. Each
 client receives its peer device ID and optional advertised addresses

docs/system-design.md

@@ -133,10 +133,13 @@ a resource may be active or queued at a time. This prevents incompatible
 baselines even when jobs would use different nodes or observe different sides
 of a hybrid identity.
 
-Defaults allow one active data-moving job per client and one per route. A job
-must acquire its source client, target client, route, and resource reservation
-atomically. Disjoint node pairs may run concurrently. Route setup is a
-preflight activity and does not permit a data step to bypass these leases.
+By default every eligible queued job is claimed in the same scheduler pass and
+independent jobs run concurrently on each client; physical service and storage
+capacity are the limit. Set `enforce_concurrency_limits=true` on control to
+enable the optional one-per-client/one-per-route gates. A job always retains
+its resource reservation, and commands for the same job remain serialized.
+Route setup is a preflight activity and does not permit a data step to bypass
+the resource reservation.
 
 Offline nodes do not prevent unrelated jobs from being listed or run. A job
 requiring an offline node remains waiting indefinitely; it does not consume an
@@ -154,6 +157,12 @@ advances to the next step. On reconnect:
 4. Control observes relevant qBittorrent, Syncthing, staging, and manifest
    state before selecting retry, resume, compensation, cleanup, or manual
    intervention.
+
+If a connection disappears while a synchronous job operation is in progress,
+the client journals events locally, reconnects indefinitely, and serializes a
+replayed command behind the in-flight operation for that job. The replay reads
+the journal rather than repeating the data operation. This applies to every
+transfer step, including post-commit staging cleanup.
 5. A command is reissued with its original ID when the acceptance result is
    uncertain.
 

docs/telegram-ux.md

@@ -25,8 +25,10 @@ What do you want to do?
 [ Evict Cache ] [ Job Status ]
 ```
 
-All subsequent pages edit this message. `Cancel` closes the active selection
-flow. `Back` returns one level while retaining validated filters/selections.
+All subsequent pages edit this message. Leaving a resource/tree selection
+returns to the Archive Control operation menu without closing the shared
+conversation. Confirmation `Cancel` returns to its immediate prior selection;
+the main menu alone can close Archive Control.
 Callback payloads contain opaque session/action IDs, not resource names or
 paths, and are validated against persisted session revision and expiry.
 

docs/testing.md

@@ -225,7 +225,7 @@ Fixtures include small deterministic v1, v2, and hybrid torrents with:
 | Recovery | restart every step on source/target/control, lost DB with proof, ambiguous loss fails closed |
 | Messaging | duplicate command/event, lost ack, sequence gap, stale revision, duplicate client ID |
 | Safety | attempted download, corrupt same-size file, symlink/path escape, special file, partfile mismatch |
-| Operations | stall retains percent, offline wait, cancellation each phase, postcommit cleanup retry |
+| Operations | stall retains percent, offline wait, cancellation each phase, postcommit cleanup retry, disconnect/reconnect during every transfer step with exactly-once replay |
 | Database | online backup under load, pre/post migration, retention, corrupt backup rejection, offline restore |
 | UI | pagination/filter chain, stale/double callback, persisted session, clear vs evict separation |
 

docs/workflows.md

@@ -102,6 +102,10 @@ and placement policy differ.
   external state rather than being downloaded or silently deselected.
 - Confirm free space/reserve, permissions, sparse capability, supported
   partfile format, route health, and negotiated protocol features.
+- Charge payload bytes against free space only when the specific source and
+  destination files cannot be hardlinked. Same-filesystem hardlink stages and
+  merges retain the configured reserve plus small metadata artifacts, rather
+  than reserving a duplicate logical payload.
 - Export the source `.torrent` metainfo.
 - Persist the exact source, target baseline, requested selection, and delta.
 

examples/client.toml

@@ -21,7 +21,7 @@ verification_timeout = "30m"
 # Poll qBittorrent and Syncthing at this interval while a step is active.
 poll_interval = "1s"
 # Space that must remain free after a worst-case copy fallback.
-free_space_reserve_bytes = 1073741824
+free_space_reserve_bytes = 33554432
 
 [backup]
 interval = "6h"

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "archive-clients"
-version = "0.1.2"
+version = "0.1.15"
 requires-python = ">=3.11"
 dependencies = ["protobuf==7.35.1", "websockets==16.0"]
 

src/archive_clients/config.py

@@ -27,17 +27,28 @@ _ENV = re.compile(r"\$\{([A-Za-z_][A-Za-z0-9_]*)\}")
 class RootMapping:
     api_root: PurePosixPath
     local_root: Path
+    local_path_overrides: tuple[tuple[PurePosixPath, Path], ...] = ()
 
     def api_to_local(self, api_path: str) -> Path:
         candidate = PurePosixPath(api_path)
-        try:
-            relative = candidate.relative_to(self.api_root)
-        except ValueError as exc:
-            raise ConfigError("API path is outside its configured root") from exc
-        if any(part in {"", ".", ".."} for part in relative.parts):
-            raise ConfigError("API path contains an unsafe component")
+        for api_root, local_root in self.local_path_overrides:
+            relative = _safe_relative(candidate, api_root)
+            if relative is not None:
+                return local_root.joinpath(*relative.parts)
+        relative = _safe_relative(candidate, self.api_root)
+        if relative is None:
+            raise ConfigError("API path is outside its configured root")
         return self.local_root.joinpath(*relative.parts)
 
+    def local_root_for_api(self, api_path: str) -> Path:
+        candidate = PurePosixPath(api_path)
+        for api_root, local_root in self.local_path_overrides:
+            if _safe_relative(candidate, api_root) is not None:
+                return local_root
+        if _safe_relative(candidate, self.api_root) is None:
+            raise ConfigError("API path is outside its configured root")
+        return self.local_root
+
 
 @dataclass(frozen=True)
 class ServiceConfig:
@@ -48,10 +59,13 @@ class ServiceConfig:
     password_file: Path | None = None
     api_key_file: Path | None = None
     advertised_addresses: tuple[str, ...] = ()
+    local_path_overrides: tuple[tuple[PurePosixPath, Path], ...] = ()
 
     @property
     def roots(self) -> RootMapping:
-        return RootMapping(self.api_root, self.local_root)
+        return RootMapping(
+            self.api_root, self.local_root, self.local_path_overrides
+        )
 
     def read_password(self) -> str | None:
         return (
@@ -82,7 +96,7 @@ class JobsConfig:
     stall_after: float = 30 * 60
     verification_timeout: float = 30 * 60
     poll_interval: float = 1
-    free_space_reserve_bytes: int = 1024 * 1024 * 1024
+    free_space_reserve_bytes: int = 32 * 1024 * 1024
 
 
 @dataclass(frozen=True)
@@ -160,7 +174,7 @@ def _service(value: Any, name: str) -> ServiceConfig:
         raise ConfigError(f"{name} must be a table")
     allowed = {
         "endpoint", "api_root", "local_root", "username", "password_file",
-        "api_key_file", "advertised_addresses",
+        "api_key_file", "advertised_addresses", "local_path_overrides",
     }
     _keys(value, allowed, name)
     api_root = PurePosixPath(_string(value, "api_root"))
@@ -182,6 +196,7 @@ def _service(value: Any, name: str) -> ServiceConfig:
         raise ConfigError("qbittorrent username and password_file are required")
     if name == "syncthing" and "api_key_file" not in value:
         raise ConfigError("syncthing api_key_file is required")
+    overrides = _local_path_overrides(value, api_root, name)
     return ServiceConfig(
         _endpoint(value, "endpoint", {"http", "https"}), api_root,
         _absolute_path(value, "local_root"), username,
@@ -189,10 +204,46 @@ def _service(value: Any, name: str) -> ServiceConfig:
         if "password_file" in value else None,
         _absolute_path(value, "api_key_file")
         if "api_key_file" in value else None,
-        tuple(addresses),
+        tuple(addresses), overrides,
     )
 
 
+def _local_path_overrides(
+    value: dict[str, Any], api_root: PurePosixPath, name: str
+) -> tuple[tuple[PurePosixPath, Path], ...]:
+    raw = value.get("local_path_overrides", {})
+    if name != "syncthing" and raw:
+        raise ConfigError(f"{name}.local_path_overrides is unsupported")
+    if not isinstance(raw, dict):
+        raise ConfigError(f"{name}.local_path_overrides must be a table")
+    parsed: list[tuple[PurePosixPath, Path]] = []
+    for raw_api_path, raw_local_path in raw.items():
+        if not isinstance(raw_api_path, str) or not isinstance(raw_local_path, str):
+            raise ConfigError(f"{name}.local_path_overrides entries must be strings")
+        candidate = PurePosixPath(raw_api_path)
+        if not candidate.is_absolute() or ".." in candidate.parts:
+            raise ConfigError(f"{name}.local_path_overrides API path is invalid")
+        if _safe_relative(candidate, api_root) is None:
+            raise ConfigError(f"{name}.local_path_overrides API path is outside root")
+        local = Path(raw_local_path)
+        if not local.is_absolute():
+            raise ConfigError(f"{name}.local_path_overrides local path is invalid")
+        parsed.append((candidate, local))
+    return tuple(sorted(parsed, key=lambda item: len(item[0].parts), reverse=True))
+
+
+def _safe_relative(
+    candidate: PurePosixPath, root: PurePosixPath
+) -> PurePosixPath | None:
+    try:
+        relative = candidate.relative_to(root)
+    except ValueError:
+        return None
+    if any(part in {"", ".", ".."} for part in relative.parts):
+        raise ConfigError("API path contains an unsafe component")
+    return relative
+
+
 def _connection(value: Any) -> ConnectionConfig:
     if not isinstance(value, dict):
         raise ConfigError("connection must be a table")
@@ -239,7 +290,7 @@ def _jobs(value: Any) -> JobsConfig:
         ),
         poll_interval=_duration(value.get("poll_interval", "1s")),
         free_space_reserve_bytes=_positive_int(
-            value.get("free_space_reserve_bytes", 1024 * 1024 * 1024),
+            value.get("free_space_reserve_bytes", 32 * 1024 * 1024),
             "jobs.free_space_reserve_bytes",
         ),
     )

src/archive_clients/daemon.py

@@ -11,6 +11,7 @@ from pathlib import Path, PurePosixPath
 from typing import Any
 
 from websockets.asyncio.client import connect
+from websockets.exceptions import ConnectionClosedOK
 
 from archive_clients.backup import SQLiteBackupManager
 from archive_clients.config import ClientConfig
@@ -42,6 +43,19 @@ from archive_control.v1 import (
 logger = logging.getLogger(__name__)
 
 
+def _job_id_for_command(command: control_pb2.Command) -> str:
+    """Return the durable job key for commands whose execution is serialized."""
+
+    payload = command.WhichOneof("payload")
+    if payload == "assign_job":
+        return command.assign_job.job.job_id
+    if payload == "execute_step":
+        return command.execute_step.job_id
+    if payload == "cancel_job":
+        return command.cancel_job.job_id
+    raise ValueError(f"command {command.command_id} does not execute a job")
+
+
 class ArchiveClientDaemon:
     def __init__(
         self,
@@ -94,7 +108,10 @@ class ArchiveClientDaemon:
         self._lease = DatabaseLease(config.state_db)
         self._active_route_commands: set[str] = set()
         self._active_job_commands: set[str] = set()
-        self._job_execution_lock = asyncio.Lock()
+        # Commands for one job remain ordered locally, while unrelated jobs
+        # may use the node's available qB/Syncthing/filesystem capacity in
+        # parallel. The control daemon owns admission policy.
+        self._job_execution_locks: dict[str, asyncio.Lock] = {}
         self.jobs = (
             ClientJobExecutor(
                 client_id=config.client_id,
@@ -205,7 +222,23 @@ class ArchiveClientDaemon:
             command_tasks: set[asyncio.Task[None]] = set()
             try:
                 await self._resume_commands(outbound, command_tasks)
-                async for frame in websocket:
+                # A proxy can leave the TCP/WebSocket socket apparently open
+                # after the control server has discarded its session.  The
+                # server then cannot deliver durable commands and its pending
+                # outbox remains stranded unless the client independently
+                # detects the missing application heartbeats and reconnects.
+                while True:
+                    try:
+                        frame = await asyncio.wait_for(
+                            websocket.recv(),
+                            self.config.connection.offline_timeout,
+                        )
+                    except ConnectionClosedOK:
+                        return
+                    except asyncio.TimeoutError as exc:
+                        raise RuntimeError(
+                            "control heartbeat timed out"
+                        ) from exc
                     await self._handle(decode(frame), outbound, command_tasks)
             finally:
                 writer.cancel()
@@ -543,7 +576,9 @@ class ArchiveClientDaemon:
         correlation_id: str,
         outbound: asyncio.Queue[str],
     ) -> None:
-        async with self._job_execution_lock:
+        job_id = _job_id_for_command(command)
+        lock = self._job_execution_locks.setdefault(job_id, asyncio.Lock())
+        async with lock:
             await self._execute_job_command_locked(
                 command, correlation_id, outbound
             )

src/archive_clients/jobs.py

@@ -4,12 +4,15 @@ from __future__ import annotations
 
 import hashlib
 import json
+import logging
+import os
 import shutil
+import stat
 import threading
 import time
 import uuid
 from pathlib import Path, PurePosixPath
-from typing import Callable
+from typing import Callable, Iterable
 
 from archive_clients.protocol import decode_message, encode_message
 from archive_clients.eviction import (
@@ -25,10 +28,11 @@ from archive_clients.qbittorrent import (
 )
 from archive_clients.resources import NormalizedResource
 from archive_clients.state import ClientStore
-from archive_clients.syncthing import SyncthingTransferObserver
+from archive_clients.syncthing import RouteSetupError, SyncthingTransferObserver
 from archive_clients.transfer import (
     TransferError,
     TransferIntegrityError,
+    cleanup_partial_transfer,
     cleanup_transfer,
     load_published_transfer,
     materialize_transfer,
@@ -51,6 +55,9 @@ class JobCancelled(JobExecutionError):
     pass
 
 
+logger = logging.getLogger(__name__)
+
+
 class ClientJobExecutor:
     def __init__(
         self,
@@ -65,7 +72,7 @@ class ClientJobExecutor:
         sparse_supported: bool,
         poll_interval: float = 1,
         verification_timeout: float = 30 * 60,
-        free_space_reserve_bytes: int = 1024 * 1024 * 1024,
+        free_space_reserve_bytes: int = 32 * 1024 * 1024,
     ):
         self.client_id = client_id
         self.qbittorrent = qbittorrent
@@ -79,6 +86,8 @@ class ClientJobExecutor:
         self.verification_timeout = verification_timeout
         self.free_space_reserve_bytes = free_space_reserve_bytes
         self._cancel_events: dict[str, threading.Event] = {}
+        self._execution_locks: dict[str, threading.Lock] = {}
+        self._execution_locks_guard = threading.Lock()
 
     def request_cancel(self, job_id: str) -> None:
         self._cancel_events.setdefault(job_id, threading.Event()).set()
@@ -108,12 +117,32 @@ class ClientJobExecutor:
         self,
         command: control_pb2.ExecuteStepCommand,
         event_callback: Callable[[control_pb2.JobEvent], None] | None = None,
+    ) -> list[control_pb2.JobEvent]:
+        # asyncio cancellation of a connection-bound task cannot stop the
+        # synchronous filesystem/qB operation already running in its worker
+        # thread. A replay after reconnect therefore waits for that operation
+        # and then reads its durable event journal instead of executing twice.
+        with self._execution_lock(command.job_id):
+            return self._execute_locked(command, event_callback)
+
+    def _execution_lock(self, job_id: str) -> threading.Lock:
+        with self._execution_locks_guard:
+            return self._execution_locks.setdefault(job_id, threading.Lock())
+
+    def _execute_locked(
+        self,
+        command: control_pb2.ExecuteStepCommand,
+        event_callback: Callable[[control_pb2.JobEvent], None] | None = None,
     ) -> list[control_pb2.JobEvent]:
         definition = self._definition(command.job_id)
         replay = self._replay(
             command.job_id, command.expected_last_event_sequence
         )
-        if replay and replay[-1].type in {
+        step_replay = [
+            event for event in replay
+            if event.progress.step == command.step
+        ]
+        if step_replay and step_replay[-1].type in {
             control_pb2.JOB_EVENT_TYPE_STEP_SUCCEEDED,
             control_pb2.JOB_EVENT_TYPE_COMMITTED,
             control_pb2.JOB_EVENT_TYPE_SUCCEEDED,
@@ -125,32 +154,51 @@ class ClientJobExecutor:
                 for event in replay:
                     event_callback(event)
             return replay
-        started = replay[0] if replay else self._event(
-            definition,
-            sequence=command.expected_last_event_sequence + 1,
-            revision=command.expected_job_revision + 1,
-            event_type=control_pb2.JOB_EVENT_TYPE_STEP_STARTED,
-            state=job_pb2.JOB_STATE_RUNNING,
-            committed=(
-                self._committed(command.job_id)
-                or command.step == job_pb2.JOB_STEP_KIND_STAGING_CLEANUP
-                or (
-                    command.step == job_pb2.JOB_STEP_KIND_SAFE_FILE_UNLINK
-                    and self.store.get_job_artifact(
-                        command.job_id, "qb-entry-removed"
-                    ) is not None
-                )
-            ),
-            step=command.step,
-            step_state=job_pb2.STEP_STATE_RUNNING,
-        )
-        if not replay:
+        if step_replay:
+            started = step_replay[0]
+            cursor = step_replay[-1]
+            emitted = list(step_replay)
+        else:
+            previous = replay[-1] if replay else None
+            started = self._event(
+                definition,
+                sequence=(
+                    previous.sequence + 1
+                    if previous is not None
+                    else command.expected_last_event_sequence + 1
+                ),
+                revision=(
+                    previous.job_revision + 1
+                    if previous is not None
+                    else command.expected_job_revision + 1
+                ),
+                event_type=control_pb2.JOB_EVENT_TYPE_STEP_STARTED,
+                state=job_pb2.JOB_STATE_RUNNING,
+                committed=(
+                    self._committed(command.job_id)
+                    or command.step == job_pb2.JOB_STEP_KIND_STAGING_CLEANUP
+                    or (
+                        command.step == job_pb2.JOB_STEP_KIND_SAFE_FILE_UNLINK
+                        and self.store.get_job_artifact(
+                            command.job_id, "qb-entry-removed"
+                        ) is not None
+                    )
+                ),
+                step=command.step,
+                step_state=job_pb2.STEP_STATE_RUNNING,
+            )
             self._record(definition, started)
+            cursor = started
+            emitted = [started]
         if event_callback is not None:
-            event_callback(started)
-        emitted = [started]
-        cursor = started
-        speed_sample = [time.monotonic(), 0]
+            for event in emitted:
+                event_callback(event)
+        # A newly-started step must publish its first observation.  In
+        # particular, a sparse Syncthing temporary file may retain the same
+        # allocated-block count for a long time while data is still needed;
+        # suppressing that first observation made a healthy transfer look
+        # permanently stalled to the control daemon.
+        speed_sample: list[float | int | None] = [None, 0]
 
         def progress(
             fraction: float,
@@ -160,8 +208,12 @@ class ClientJobExecutor:
         ) -> None:
             nonlocal cursor
             now = time.monotonic()
-            elapsed = now - float(speed_sample[0])
-            if fraction < 1 and elapsed < 1:
+            previous_time = speed_sample[0]
+            elapsed = (
+                now - float(previous_time)
+                if previous_time is not None else 0.0
+            )
+            if previous_time is not None and fraction < 1 and elapsed < 1:
                 return
             speed = (
                 max(0, bytes_complete - int(speed_sample[1])) / elapsed
@@ -541,15 +593,29 @@ class ClientJobExecutor:
             sha256_hex=hashlib.sha256(resource.metainfo_bytes).hexdigest(),
         )
         del artifact
+        route_root = self.route_path(definition.transfer.route_id)
+        # Staging is normally zero-copy when qB's data root and the paired
+        # Syncthing route share a filesystem.  Do not reserve the complete
+        # logical payload in that case: FileMaterializer will use link(2),
+        # which consumes only directory/inode metadata.  Retain the metainfo
+        # allowance and reserve, and account for any source files that really
+        # must fall back to a data-copy path.
         self._require_space(
-            self.route_path(definition.transfer.route_id),
-            definition.transfer.transfer_delta_logical_bytes
+            route_root,
+            self._copy_required_bytes(
+                self.qb_root,
+                route_root,
+                (
+                    (entry.target_canonical_path, entry.logical_bytes)
+                    for entry in manifest.files
+                ),
+            )
             + len(resource.metainfo_bytes),
         )
         stage_transfer(
             manifest,
             source_root=self.qb_root,
-            sync_root=self.route_path(definition.transfer.route_id),
+            sync_root=route_root,
             store=self.store,
             artifact_sources={"metainfo/source.torrent": metainfo_path},
             sparse_supported=self.sparse_supported,
@@ -563,7 +629,17 @@ class ClientJobExecutor:
                 f"staged {completed} of {total} bytes",
             ),
         )
-        self._observer(definition).rescan()
+        try:
+            self._observer(definition).rescan()
+        except RouteSetupError as exc:
+            # A manual Syncthing scan may take longer than the bounded REST
+            # request timeout for a large newly linked file. The folder watch
+            # and the following transfer observation still converge, so do
+            # not roll back an otherwise durable staged transfer.
+            logger.warning("syncthing_rescan_deferred", extra={
+                "job_id": definition.job_id,
+                "error_type": type(exc).__name__,
+            })
 
     def _wait_for_syncthing(
         self,
@@ -595,6 +671,15 @@ class ClientJobExecutor:
                 # Syncthing can expose the per-job directory before the
                 # ready marker and manifest have arrived atomically as a set.
                 pass
+            except RouteSetupError as exc:
+                # A network interruption can temporarily make the local
+                # Syncthing REST API unavailable.  The staged payload is
+                # durable and the job must remain recoverable; keep polling
+                # instead of turning a transient outage into a failed job.
+                logger.warning("syncthing_status_deferred", extra={
+                    "job_id": definition.job_id,
+                    "error_type": type(exc).__name__,
+                })
             time.sleep(self.poll_interval)
 
     def _target_materialize(
@@ -607,9 +692,18 @@ class ClientJobExecutor:
                 "target materialization was sent to the wrong client"
             )
         published = load_published_transfer(self._job_directory(definition))
+        # The target can likewise hardlink an arrived Syncthing payload into
+        # qB's content root when those directories share a filesystem.
         self._require_space(
             self.qb_root,
-            definition.transfer.transfer_delta_logical_bytes,
+            self._copy_required_bytes(
+                published.job_directory,
+                self.qb_root,
+                (
+                    (entry.payload_relative_path, entry.logical_bytes)
+                    for entry in published.manifest.files
+                ),
+            ),
         )
         info_hash = _info_hash(definition)
         resource = self.qbittorrent.get_resource(info_hash)
@@ -794,6 +888,11 @@ class ClientJobExecutor:
             qb_root=job_directory,
             store=self.store,
         )
+        cleanup_partial_transfer(
+            job_directory,
+            job_id=definition.job_id,
+            store=self.store,
+        )
         for name in ("ready.json", "manifest.json"):
             candidate = job_directory / name
             if candidate.is_file() and not candidate.is_symlink():
@@ -843,6 +942,37 @@ class ClientJobExecutor:
                 f"{required} bytes required including reserve"
             )
 
+    @staticmethod
+    def _copy_required_bytes(
+        source_root: Path,
+        destination_root: Path,
+        files: Iterable[tuple[str, int]],
+    ) -> int:
+        """Return logical bytes that cannot be materialized by hardlink.
+
+        A hardlink is possible only for regular files on the destination
+        filesystem.  Conservatively charge a file when it cannot be inspected;
+        the normal materializer will then provide the precise integrity error.
+        """
+
+        destination_device = destination_root.stat().st_dev
+        required = 0
+        for relative_path, logical_bytes in files:
+            relative = PurePosixPath(relative_path)
+            source = source_root.joinpath(*relative.parts)
+            try:
+                metadata = source.stat(follow_symlinks=False)
+            except OSError:
+                required += logical_bytes
+                continue
+            if (
+                not stat.S_ISREG(metadata.st_mode)
+                or metadata.st_dev != destination_device
+                or _mount_id(source) != _mount_id(destination_root)
+            ):
+                required += logical_bytes
+        return required
+
     def _observer(
         self, definition: job_pb2.JobDefinition
     ) -> SyncthingTransferObserver:
@@ -1089,6 +1219,8 @@ def _job_error_code(error: Exception) -> int:
         return common_pb2.ERROR_CODE_INTEGRITY_CHECK_FAILED
     if isinstance(error, PermissionError):
         return common_pb2.ERROR_CODE_PERMISSION_DENIED
+    if isinstance(error, RouteSetupError):
+        return common_pb2.ERROR_CODE_UNAVAILABLE
     if isinstance(error, JobExecutionError):
         return common_pb2.ERROR_CODE_PRECONDITION_FAILED
     if isinstance(error, TransferError):
@@ -1096,3 +1228,41 @@ def _job_error_code(error: Exception) -> int:
     if isinstance(error, EvictionError):
         return common_pb2.ERROR_CODE_PRECONDITION_FAILED
     return common_pb2.ERROR_CODE_INTERNAL
+
+
+def _mount_id(path: Path) -> str | None:
+    """Return Linux's effective mount ID for a path when procfs is available.
+
+    Bind mounts can share ``st_dev`` while still rejecting ``link(2)`` with
+    ``EXDEV``.  Mount IDs distinguish that case without creating probe files
+    inside a Syncthing folder.
+    """
+
+    try:
+        target = os.path.realpath(path)
+        best: tuple[int, str] | None = None
+        with open("/proc/self/mountinfo", encoding="utf-8") as source:
+            for line in source:
+                fields = line.rstrip("\n").split(" ")
+                if len(fields) < 5:
+                    continue
+                mountpoint = _unescape_mount_path(fields[4])
+                if target != mountpoint and not target.startswith(
+                    mountpoint.rstrip("/") + "/"
+                ):
+                    continue
+                candidate = (len(mountpoint), fields[0])
+                if best is None or candidate[0] > best[0]:
+                    best = candidate
+        return None if best is None else best[1]
+    except OSError:
+        return None
+
+
+def _unescape_mount_path(value: str) -> str:
+    return (
+        value.replace("\\040", " ")
+        .replace("\\011", "\t")
+        .replace("\\012", "\n")
+        .replace("\\134", "\\")
+    )

src/archive_clients/routes.py

@@ -37,7 +37,9 @@ def discover_routes(
             relative = normalized_api_path.relative_to(roots.api_root)
         except (ConfigError, ValueError):
             continue
-        if not _lexically_within(local_path, roots.local_root):
+        if not _lexically_within(
+            local_path, roots.local_root_for_api(normalized_api_path.as_posix())
+        ):
             continue
         if relative == PurePosixPath("."):
             continue

src/archive_clients/state.py

@@ -7,6 +7,8 @@ import json
 import os
 import sqlite3
 import stat
+import threading
+from contextlib import contextmanager
 from dataclasses import dataclass
 from pathlib import Path
 
@@ -14,6 +16,12 @@ from pathlib import Path
 SCHEMA_VERSION = 3
 
 
+# A client daemon executes unrelated jobs concurrently.  SQLite still permits
+# only one writer, so serialize this process's short state transactions rather
+# than allowing an otherwise healthy job to fail after its busy timeout.
+_DATABASE_LOCK = threading.RLock()
+
+
 class CommandConflict(RuntimeError):
     pass
 
@@ -557,14 +565,30 @@ class ClientStore:
             ).fetchall()
         return [dict(row) for row in rows]
 
-    def _connect(self) -> sqlite3.Connection:
-        connection = sqlite3.connect(self.database, isolation_level=None, timeout=5)
-        connection.row_factory = sqlite3.Row
-        connection.execute("PRAGMA foreign_keys = ON")
-        connection.execute("PRAGMA journal_mode = WAL")
-        connection.execute("PRAGMA synchronous = FULL")
-        connection.execute("PRAGMA busy_timeout = 5000")
-        return connection
+    @contextmanager
+    def _connect(self):
+        """Yield one connection while serializing local SQLite writers.
+
+        The longer SQLite timeout also covers a short lock held by a separate
+        maintenance process such as a backup.  The lock is deliberately held
+        for the full transaction, including ``BEGIN IMMEDIATE``.
+        """
+        with _DATABASE_LOCK:
+            connection = sqlite3.connect(
+                self.database, isolation_level=None, timeout=30
+            )
+            try:
+                connection.row_factory = sqlite3.Row
+                connection.execute("PRAGMA foreign_keys = ON")
+                connection.execute("PRAGMA journal_mode = WAL")
+                connection.execute("PRAGMA synchronous = FULL")
+                connection.execute("PRAGMA busy_timeout = 30000")
+                # Preserve the original ``with connection`` commit/rollback
+                # behavior used by every store operation.
+                with connection:
+                    yield connection
+            finally:
+                connection.close()
 
 
 def _canonical(value: object) -> str:

src/archive_clients/syncthing.py

@@ -139,19 +139,14 @@ class SyncthingTransferObserver:
 
     def status(self) -> SyncthingTransferStatus:
         published = load_published_transfer(self.local_job_directory)
-        total = 0
-        for entry in published.manifest.files:
-            total += _verified_job_file_size(
-                self.local_job_directory,
-                entry.payload_relative_path,
-                entry.logical_bytes,
-            )
-        for artifact in published.manifest.artifacts:
-            total += _verified_job_file_size(
-                self.local_job_directory,
-                artifact.payload_relative_path,
-                artifact.logical_bytes,
-            )
+        declared_files = [
+            (entry.payload_relative_path, entry.logical_bytes)
+            for entry in published.manifest.files
+        ] + [
+            (artifact.payload_relative_path, artifact.logical_bytes)
+            for artifact in published.manifest.artifacts
+        ]
+        total = sum(size for _, size in declared_files)
 
         completion = self.transport.get_json(
             "/rest/db/completion?"
@@ -178,11 +173,44 @@ class SyncthingTransferObserver:
             name for name in needed_names
             if name == self.job_relative_path or name.startswith(prefix)
         }
-        fraction = float(raw_fraction) / 100
-        complete = fraction == 1 and not relevant
+        complete = not relevant
+        if complete:
+            for relative_path, expected_bytes in declared_files:
+                _verified_job_file_size(
+                    self.local_job_directory,
+                    relative_path,
+                    expected_bytes,
+                )
+            completed_bytes = total
+        else:
+            observed_bytes = sum(
+                _received_job_file_bytes(
+                    self.local_job_directory,
+                    relative_path,
+                    expected_bytes,
+                )
+                for relative_path, expected_bytes in declared_files
+            )
+            observed_fraction = observed_bytes / total if total else 1.0
+            # ``/db/completion`` is folder-wide.  It can be near zero when a
+            # route contains a freshly-created item even though the tracked
+            # job's temporary payload has already received many blocks.  For
+            # an incomplete temporary file, its allocated blocks are the only
+            # job-specific signal, so do not cap them with that unrelated
+            # folder aggregate.  Once every declared file is atomically
+            # present, retain the completion value as a conservative guard
+            # until the need queue has caught up.
+            fraction = (
+                observed_fraction
+                if observed_fraction < 1.0
+                else min(1.0, float(raw_fraction) / 100)
+            )
+            completed_bytes = int(total * fraction)
+        if complete:
+            fraction = 1.0
         return SyncthingTransferStatus(
             fraction,
-            total if complete else int(total * fraction),
+            completed_bytes,
             total,
             complete,
             len(relevant),
@@ -356,7 +384,9 @@ class SyncthingRouteManager:
             local_path = self.config.roots.api_to_local(api_path)
         except ConfigError as exc:
             raise RoutePathConflict("route path is outside the sync root") from exc
-        resolved_root = self.config.local_root.resolve(strict=False)
+        resolved_root = self.config.roots.local_root_for_api(api_path).resolve(
+            strict=False
+        )
         try:
             local_path.resolve(strict=False).relative_to(resolved_root)
         except ValueError as exc:
@@ -369,8 +399,8 @@ class SyncthingRouteManager:
             raise RoutePathConflict("new route path contains unrelated data")
         path.mkdir(parents=True, exist_ok=True)
 
-    @staticmethod
     def _validate_folder(
+        self,
         folder: dict[str, Any],
         api_path: str,
         local_device_id: str,
@@ -382,7 +412,15 @@ class SyncthingRouteManager:
             for item in raw_devices
             if isinstance(item, dict) and isinstance(item.get("deviceID"), str)
         } if isinstance(raw_devices, list) else set()
-        if folder.get("path") != api_path:
+        try:
+            configured_api_path = self._normalized_folder_api_path(
+                folder.get("path")
+            )
+        except RoutePathConflict as exc:
+            raise RoutePathConflict(
+                "existing route ID uses a different path"
+            ) from exc
+        if configured_api_path != api_path:
             raise RoutePathConflict("existing route ID uses a different path")
         if folder.get("type") != "sendreceive":
             raise RouteSetupError("existing route folder is not sendreceive")
@@ -391,6 +429,27 @@ class SyncthingRouteManager:
         if folder.get("paused") is True:
             raise RouteSetupError("existing route folder is paused")
 
+    def _normalized_folder_api_path(self, value: Any) -> str:
+        """Normalize Syncthing's absolute and home-relative path spellings."""
+
+        if not isinstance(value, str) or not value:
+            raise RoutePathConflict("existing route folder path is invalid")
+        candidate = PurePosixPath(value)
+        if candidate.parts and candidate.parts[0] == "~":
+            candidate = self.config.api_root.joinpath(*candidate.parts[1:])
+        if not candidate.is_absolute() or any(
+            part in {"", ".", ".."} for part in candidate.parts
+        ):
+            raise RoutePathConflict("existing route folder path is unsafe")
+        normalized = candidate.as_posix()
+        try:
+            self.config.roots.api_to_local(normalized)
+        except ConfigError as exc:
+            raise RoutePathConflict(
+                "existing route folder path is outside the sync root"
+            ) from exc
+        return normalized
+
     def _wait(self, deadline: float) -> None:
         if time.monotonic() >= deadline:
             raise RouteSetupTimeout("route setup timed out")
@@ -441,6 +500,42 @@ def _verified_job_file_size(
     return metadata.st_size
 
 
+def _received_job_file_bytes(
+    job_directory: Path,
+    relative_path: str,
+    expected_bytes: int,
+) -> int:
+    """Return a conservative receive estimate for one job-owned file.
+
+    Syncthing writes incomplete files as ``.syncthing.<name>.tmp`` and may
+    pre-size that sparse temporary to its final logical length. Allocated
+    blocks, rather than ``st_size``, therefore provide the useful progress
+    signal until the final atomic rename occurs.
+    """
+
+    relative = PurePosixPath(relative_path)
+    current = job_directory
+    for component in relative.parts[:-1]:
+        current = current / component
+    final = current / relative.name
+    try:
+        metadata = final.lstat()
+    except FileNotFoundError:
+        metadata = None
+    if metadata is not None:
+        if stat.S_ISREG(metadata.st_mode) and metadata.st_size == expected_bytes:
+            return expected_bytes
+        return 0
+    temporary = current / f".syncthing.{relative.name}.tmp"
+    try:
+        temporary_metadata = temporary.lstat()
+    except FileNotFoundError:
+        return 0
+    if not stat.S_ISREG(temporary_metadata.st_mode):
+        return 0
+    return min(expected_bytes, temporary_metadata.st_blocks * 512)
+
+
 def _needed_names(value: dict[str, Any]) -> set[str]:
     result: set[str] = set()
     for key in ("progress", "queued", "rest"):

src/archive_clients/transfer.py

@@ -456,6 +456,36 @@ def cleanup_transfer(job_directory: Path) -> bool:
     return True
 
 
+def cleanup_partial_transfer(
+    job_directory: Path,
+    *,
+    job_id: str,
+    store: ClientStore,
+) -> None:
+    """Remove copy/reflink temporaries left before a transfer is published.
+
+    A source-stage failure before ``manifest.json``/``ready.json`` exists
+    cannot use :func:`cleanup_transfer`. The file-operation journal is the
+    authoritative list of owned destinations, so derive each temporary path
+    from it rather than recursively removing arbitrary content from a shared
+    Syncthing folder.
+    """
+
+    for row in store.file_operation_rows(job_id):
+        intent = json.loads(str(row["intent_json"]))
+        destination = job_directory / _relative_path(str(intent["destination"]))
+        temporary = _temporary_path(destination, str(row["operation_id"]))
+        try:
+            metadata = temporary.lstat()
+        except FileNotFoundError:
+            continue
+        if not stat.S_ISREG(metadata.st_mode):
+            raise TransferIntegrityError(
+                "job-owned temporary cleanup path is not a regular file"
+            )
+        temporary.unlink()
+
+
 def canonical_message_json(message: object) -> bytes:
     value = json_format.MessageToDict(
         message,

tests/test_config.py

@@ -1,7 +1,7 @@
 import os
 import tempfile
 import unittest
-from pathlib import Path
+from pathlib import Path, PurePosixPath
 from unittest.mock import patch
 
 from archive_clients.config import ClientConfig, ConfigError, RootMapping
@@ -34,6 +34,7 @@ class ConfigTests(unittest.TestCase):
                 root / "qb/a/b",
             )
             self.assertEqual(config.jobs.stall_after, 30 * 60)
+            self.assertEqual(config.jobs.free_space_reserve_bytes, 32 * 1024 * 1024)
             self.assertEqual(
                 config.syncthing.advertised_addresses, ("dynamic",)
             )
@@ -62,6 +63,21 @@ class ConfigTests(unittest.TestCase):
         with self.assertRaises(ConfigError):
             mapping.api_to_local("/elsewhere/file")
 
+    def test_mapping_can_override_one_syncthing_folder_locally(self):
+        mapping = RootMapping(
+            PurePosixPath("/sync"),
+            Path("/local/sync"),
+            ((PurePosixPath("/sync/DownloadsSync"), Path("/local/qb/Sync")),),
+        )
+        self.assertEqual(
+            mapping.api_to_local("/sync/DownloadsSync/job/ready.json"),
+            Path("/local/qb/Sync/job/ready.json"),
+        )
+        self.assertEqual(
+            mapping.local_root_for_api("/sync/DownloadsSync"),
+            Path("/local/qb/Sync"),
+        )
+
     def test_endpoint_scheme_and_job_keys_are_strict(self):
         with tempfile.TemporaryDirectory() as directory:
             root = Path(directory)

tests/test_daemon.py

@@ -22,6 +22,94 @@ from archive_control.v1 import (
 
 
 class DaemonTransportTests(unittest.IsolatedAsyncioTestCase):
+    async def test_unrelated_job_commands_execute_concurrently(self):
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            token = root / "token"
+            token.write_text("shared-secret", encoding="utf-8")
+            os.chmod(token, 0o600)
+            service = ServiceConfig("http://local", PurePosixPath("/api"), root)
+            config = ClientConfig(
+                "cache-1", "Cache 1", "cache", "ws://control", token,
+                root / "state.db", root / "backups", service, service,
+            )
+            probe = FilesystemProbe(root, True, True, True, True, True)
+            daemon = ArchiveClientDaemon(config, [probe, probe], [])
+            started: set[str] = set()
+            release = asyncio.Event()
+
+            async def execute(command, correlation_id, outbound):
+                started.add(command.assign_job.job.job_id)
+                await release.wait()
+
+            daemon._execute_job_command_locked = execute
+            commands = []
+            for _ in range(2):
+                command = control_pb2.Command(command_id=str(uuid4()))
+                command.assign_job.job.job_id = str(uuid4())
+                commands.append(command)
+            outbound = asyncio.Queue()
+            tasks = [
+                asyncio.create_task(
+                    daemon._execute_job_command(command, "", outbound)
+                )
+                for command in commands
+            ]
+            for _ in range(100):
+                if len(started) == 2:
+                    break
+                await asyncio.sleep(0.01)
+            self.assertEqual(len(started), 2)
+            release.set()
+            await asyncio.gather(*tasks)
+
+    async def test_silent_control_connection_ends_for_reconnect(self):
+        """A lost server heartbeat must not leave durable commands stranded."""
+
+        async def control(websocket):
+            registration = decode(await websocket.recv())
+            self.assertEqual(registration.WhichOneof("payload"), "register_request")
+            response = new_envelope()
+            response.correlation_id = registration.message_id
+            response.register_response.status = (
+                client_pb2.REGISTRATION_STATUS_ACCEPTED
+            )
+            response.register_response.negotiated_version.major = 1
+            await websocket.send(encode(response))
+            # Deliberately keep TCP/WebSocket open but send no application
+            # heartbeats. This models a stale proxy/server-side session.
+            await websocket.wait_closed()
+
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            token = root / "token"
+            token.write_text("shared-secret", encoding="utf-8")
+            os.chmod(token, 0o600)
+            async with serve(control, "127.0.0.1", 0, ping_interval=None) as server:
+                port = server.sockets[0].getsockname()[1]
+                service = ServiceConfig(
+                    "http://local", PurePosixPath("/api"), root,
+                )
+                config = ClientConfig(
+                    "cache-1", "Cache 1", "cache",
+                    f"ws://127.0.0.1:{port}", token,
+                    root / "state.db", root / "backups", service, service,
+                    ConnectionConfig(
+                        registration_timeout=1,
+                        offline_timeout=0.05,
+                        reconnect_initial=0.01,
+                        reconnect_max=0.01,
+                        reconnect_jitter=False,
+                    ),
+                )
+                probe = FilesystemProbe(root, True, True, True, True, True)
+                daemon = ArchiveClientDaemon(config, [probe, probe], [])
+                await asyncio.to_thread(daemon.store.initialize)
+                with self.assertRaisesRegex(
+                    RuntimeError, "control heartbeat timed out"
+                ):
+                    await asyncio.wait_for(daemon._connection(), 1)
+
     async def test_eviction_assignment_and_steps_are_admitted(self):
         with tempfile.TemporaryDirectory() as directory:
             root = Path(directory)

tests/test_jobs.py

@@ -1,5 +1,6 @@
 import hashlib
 import tempfile
+import threading
 import unittest
 from pathlib import Path
 from unittest.mock import Mock, patch
@@ -11,6 +12,7 @@ from archive_clients.jobs import (
     JobExecutionError,
     _resource_fingerprint,
 )
+from archive_clients.syncthing import RouteSetupError, SyncthingTransferStatus
 from archive_clients.resources import normalize_resource
 from archive_clients.state import ClientStore
 from archive_control.v1 import control_pb2, job_pb2
@@ -31,7 +33,126 @@ class CompleteSyncthing:
         self.posts.append(path)
 
 
+class SlowRescanSyncthing(CompleteSyncthing):
+    def post(self, path):
+        raise RouteSetupError("Syncthing API is unavailable")
+
+
 class ClientJobHappyPathTests(unittest.TestCase):
+    def test_syncthing_api_outage_during_transfer_is_retried(self):
+        """A transient local REST outage must not terminally fail the job."""
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            store = ClientStore(root / "client.db")
+            store.initialize()
+            definition = job_pb2.JobDefinition(
+                job_id=str(uuid4()),
+                transfer={
+                    "source_client_id": "cache-1",
+                    "target_client_id": "archive-1",
+                    "route_id": "route-1",
+                },
+            )
+            observer = Mock()
+            observer.status.side_effect = [
+                RouteSetupError("Syncthing API is unavailable"),
+                SyncthingTransferStatus(1, 42, 42, True, 0),
+            ]
+            executor = ClientJobExecutor(
+                client_id="archive-1",
+                qbittorrent=Mock(),
+                store=store,
+                qb_root=root,
+                qb_api_root=Path("/downloads"),
+                route_path=lambda _: root,
+                syncthing_transport=Mock(),
+                sparse_supported=True,
+                poll_interval=0,
+            )
+            executor._observer = Mock(return_value=observer)
+            progress = Mock()
+
+            executor._wait_for_syncthing(definition, progress)
+
+            self.assertEqual(observer.status.call_count, 2)
+            progress.assert_called_once_with(1, 42, 42, "0 Syncthing items still needed")
+
+    def test_reconnect_replay_never_duplicates_any_transfer_step(self):
+        for step in (
+            job_pb2.JOB_STEP_KIND_SOURCE_STAGE,
+            job_pb2.JOB_STEP_KIND_SYNCTHING_TRANSFER,
+            job_pb2.JOB_STEP_KIND_TARGET_MATERIALIZE,
+            job_pb2.JOB_STEP_KIND_QB_VERIFY,
+            job_pb2.JOB_STEP_KIND_STAGING_CLEANUP,
+        ):
+            with self.subTest(step=step), tempfile.TemporaryDirectory() as directory:
+                root = Path(directory)
+                store = ClientStore(root / "client.db")
+                store.initialize()
+                definition = job_pb2.JobDefinition(
+                    job_id=str(uuid4()),
+                    idempotency_key=str(uuid4()),
+                    operation=job_pb2.JOB_OPERATION_ARCHIVE,
+                    resource_display_name="reconnect fixture",
+                    transfer={
+                        "source_client_id": "cache-1",
+                        "target_client_id": "archive-1",
+                        "route_id": "route-1",
+                    },
+                )
+                definition.resource_id.info_hash_v1_hex = "a" * 40
+                definition.created_at.GetCurrentTime()
+                executor = ClientJobExecutor(
+                    client_id="cache-1",
+                    qbittorrent=Mock(),
+                    store=store,
+                    qb_root=root,
+                    qb_api_root=Path("/downloads"),
+                    route_path=lambda _: root,
+                    syncthing_transport=Mock(),
+                    sparse_supported=True,
+                )
+                executor.assign(control_pb2.AssignJobCommand(
+                    job=definition,
+                    expected_job_revision=1,
+                    expected_last_event_sequence=0,
+                ))
+                entered = threading.Event()
+                release = threading.Event()
+
+                def execute_step(*_args):
+                    entered.set()
+                    release.wait(1)
+                    return None
+
+                executor._execute_step = Mock(side_effect=execute_step)
+                command = control_pb2.ExecuteStepCommand(
+                    job_id=definition.job_id,
+                    expected_job_revision=1,
+                    expected_last_event_sequence=1,
+                    step=step,
+                    attempt=1,
+                )
+                results: list[list[control_pb2.JobEvent]] = []
+                first = threading.Thread(
+                    target=lambda: results.append(executor.execute(command))
+                )
+                second = threading.Thread(
+                    target=lambda: results.append(executor.execute(command))
+                )
+                first.start()
+                self.assertTrue(entered.wait(1))
+                second.start()
+                release.set()
+                first.join(1)
+                second.join(1)
+
+                self.assertFalse(first.is_alive())
+                self.assertFalse(second.is_alive())
+                self.assertEqual(executor._execute_step.call_count, 1)
+                self.assertEqual(len(results), 2)
+                self.assertEqual(results[0][-1].event_id, results[1][-1].event_id)
+
     def test_capacity_guard_fails_before_data_movement(self):
         with tempfile.TemporaryDirectory() as directory:
             root = Path(directory)
@@ -69,14 +190,166 @@ class ClientJobHappyPathTests(unittest.TestCase):
             with self.subTest(operation=operation), tempfile.TemporaryDirectory() as directory:
                 self._run_transfer(Path(directory), operation)
 
-    def _run_transfer(self, root: Path, operation: int):
+    def test_same_filesystem_source_stage_does_not_require_payload_space(self):
+        with tempfile.TemporaryDirectory() as directory:
+            self._run_transfer(
+                Path(directory),
+                job_pb2.JOB_OPERATION_ARCHIVE,
+                source_stage_free_bytes=32 * 1024 * 1024 + 1024,
+                content=b"x" * 4096,
+            )
+
+    def test_mount_boundary_requires_copy_space_even_with_same_device(self):
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            source_root = root / "source"
+            destination_root = root / "destination"
+            source_root.mkdir()
+            destination_root.mkdir()
+            (source_root / "fixture.bin").write_bytes(b"fixture")
+            with patch(
+                "archive_clients.jobs._mount_id",
+                side_effect=("source-mount", "destination-mount"),
+            ):
+                required = ClientJobExecutor._copy_required_bytes(
+                    source_root,
+                    destination_root,
+                    (("fixture.bin", 7),),
+                )
+            self.assertEqual(required, 7)
+
+    def test_source_stage_survives_a_timed_out_syncthing_rescan(self):
+        with tempfile.TemporaryDirectory() as directory:
+            self._run_transfer(
+                Path(directory),
+                job_pb2.JOB_OPERATION_ARCHIVE,
+                syncthing=SlowRescanSyncthing(),
+            )
+
+    def test_target_step_advances_past_replayed_source_completion(self):
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            store = ClientStore(root / "client.db")
+            store.initialize()
+            definition = job_pb2.JobDefinition(
+                job_id=str(uuid4()),
+                idempotency_key=str(uuid4()),
+                operation=job_pb2.JOB_OPERATION_ARCHIVE,
+                resource_display_name="fixture",
+                transfer={
+                    "source_client_id": "cache-1",
+                    "target_client_id": "archive-1",
+                    "route_id": "route-1",
+                },
+            )
+            definition.resource_id.info_hash_v1_hex = "a" * 40
+            definition.created_at.GetCurrentTime()
+            executor = ClientJobExecutor(
+                client_id="archive-1",
+                qbittorrent=Mock(),
+                store=store,
+                qb_root=root,
+                qb_api_root=Path("/downloads"),
+                route_path=lambda _: root,
+                syncthing_transport=Mock(),
+                sparse_supported=True,
+                poll_interval=0,
+            )
+            executor.assign(control_pb2.AssignJobCommand(
+                job=definition,
+                expected_job_revision=1,
+                expected_last_event_sequence=1,
+            ))
+            source_complete = executor._event(
+                definition,
+                sequence=5,
+                revision=4,
+                event_type=control_pb2.JOB_EVENT_TYPE_STEP_SUCCEEDED,
+                state=job_pb2.JOB_STATE_RUNNING,
+                committed=False,
+                step=job_pb2.JOB_STEP_KIND_SOURCE_STAGE,
+                step_state=job_pb2.STEP_STATE_SUCCEEDED,
+            )
+            executor._record(definition, source_complete)
+
+            with patch.object(executor, "_wait_for_syncthing"):
+                events = executor.execute(control_pb2.ExecuteStepCommand(
+                    job_id=definition.job_id,
+                    expected_job_revision=4,
+                    expected_last_event_sequence=5,
+                    step=job_pb2.JOB_STEP_KIND_SYNCTHING_TRANSFER,
+                    attempt=1,
+                ))
+
+            self.assertEqual(events[0].sequence, 6)
+            self.assertEqual(
+                events[0].progress.step,
+                job_pb2.JOB_STEP_KIND_SYNCTHING_TRANSFER,
+            )
+            self.assertEqual(events[-1].sequence, 7)
+            self.assertEqual(
+                events[-1].type,
+                control_pb2.JOB_EVENT_TYPE_STEP_SUCCEEDED,
+            )
+
+    def test_first_partial_progress_is_durable(self):
+        """A sparse transfer must not lose its only initial observation."""
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            store = ClientStore(root / "client.db")
+            store.initialize()
+            definition = job_pb2.JobDefinition(
+                job_id=str(uuid4()),
+                idempotency_key=str(uuid4()),
+                operation=job_pb2.JOB_OPERATION_ARCHIVE,
+                transfer={
+                    "source_client_id": "cache-1",
+                    "target_client_id": "archive-1",
+                    "route_id": "route-1",
+                },
+            )
+            definition.resource_id.info_hash_v1_hex = "a" * 40
+            definition.created_at.GetCurrentTime()
+            executor = ClientJobExecutor(
+                client_id="archive-1", qbittorrent=Mock(), store=store,
+                qb_root=root, qb_api_root=Path("/downloads"),
+                route_path=lambda _: root, syncthing_transport=Mock(),
+                sparse_supported=True, poll_interval=0,
+            )
+            executor.assign(control_pb2.AssignJobCommand(
+                job=definition, expected_job_revision=1,
+                expected_last_event_sequence=0,
+            ))
+
+            def partial_progress(_definition, _step, progress):
+                progress(0.001, 10, 10_000, "still receiving")
+
+            with patch.object(executor, "_execute_step", partial_progress):
+                events = executor.execute(control_pb2.ExecuteStepCommand(
+                    job_id=definition.job_id, expected_job_revision=1,
+                    expected_last_event_sequence=1,
+                    step=job_pb2.JOB_STEP_KIND_SYNCTHING_TRANSFER, attempt=1,
+                ))
+
+            self.assertEqual(len(events), 3)
+            self.assertEqual(events[1].type, control_pb2.JOB_EVENT_TYPE_PROGRESS)
+            self.assertEqual(events[1].progress.bytes_complete, 10)
+
+    def _run_transfer(
+        self,
+        root: Path,
+        operation: int,
+        *,
+        source_stage_free_bytes: int | None = None,
+        content: bytes = b"archive-control-happy-path",
+        syncthing: CompleteSyncthing | None = None,
+    ):
         source_root = root / "source"
         target_root = root / "target"
         route_root = root / "route"
         source_root.mkdir()
         target_root.mkdir()
         route_root.mkdir()
-        content = b"archive-control-happy-path"
         (source_root / "fixture.bin").write_bytes(content)
         info = {
             b"length": len(content),
@@ -137,7 +410,7 @@ class ClientJobHappyPathTests(unittest.TestCase):
         target_qb.get_resource.side_effect = [
             None, None, resource, resource,
         ]
-        syncthing = CompleteSyncthing()
+        syncthing = syncthing or CompleteSyncthing()
         source = ClientJobExecutor(
             client_id=source_id,
             qbittorrent=source_qb,
@@ -185,13 +458,21 @@ class ClientJobHappyPathTests(unittest.TestCase):
         )
         final = None
         for executor, step in pipeline:
-            events = executor.execute(control_pb2.ExecuteStepCommand(
+            command = control_pb2.ExecuteStepCommand(
                 job_id=definition.job_id,
                 expected_job_revision=cursor_revision,
                 expected_last_event_sequence=cursor_sequence,
                 step=step,
                 attempt=1,
-            ))
+            )
+            if executor is source and step == job_pb2.JOB_STEP_KIND_SOURCE_STAGE and source_stage_free_bytes is not None:
+                with patch(
+                    "archive_clients.jobs.shutil.disk_usage",
+                    return_value=Mock(free=source_stage_free_bytes),
+                ):
+                    events = executor.execute(command)
+            else:
+                events = executor.execute(command)
             self.assertEqual(
                 [event.sequence for event in events],
                 list(range(

tests/test_routes.py

@@ -62,6 +62,32 @@ class RouteDiscoveryTests(unittest.TestCase):
         self.assertEqual(routes[0].local_relative_path, "DownloadsSync")
         self.assertEqual(routes[0].state, route_pb2.ROUTE_STATE_DISCOVERED)
 
+    def test_discovery_accepts_a_safe_local_folder_override(self):
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            override = root / "qb/Sync"
+            override.mkdir(parents=True)
+            roots = RootMapping(
+                PurePosixPath("/var/syncthing"),
+                root / "sync",
+                ((PurePosixPath("/var/syncthing/DownloadsSync"), override),),
+            )
+            routes = discover_routes(
+                {"folders": [{
+                    "id": "DownloadsSync",
+                    "path": "~/DownloadsSync",
+                    "type": "sendreceive",
+                    "devices": [
+                        {"deviceID": "LOCAL"},
+                        {"deviceID": "ARCHIVE"},
+                    ],
+                }]},
+                "LOCAL",
+                roots,
+                True,
+            )
+        self.assertEqual([route.route_id for route in routes], ["DownloadsSync"])
+
 
 if __name__ == "__main__":
     unittest.main()

tests/test_state.py

@@ -1,6 +1,7 @@
 import tempfile
 import unittest
 import os
+import threading
 from pathlib import Path
 from uuid import uuid4
 
@@ -13,6 +14,40 @@ from archive_clients.state import (
 
 
 class ClientStoreTests(unittest.TestCase):
+    def test_database_connections_serialize_local_writers(self):
+        """Concurrent jobs share one daemon DB without SQLite lock failures."""
+        with tempfile.TemporaryDirectory() as directory:
+            database = Path(directory) / "state.db"
+            first = ClientStore(database)
+            second = ClientStore(database)
+            first.initialize()
+            barrier = threading.Barrier(2)
+            failures: list[Exception] = []
+
+            def write(store, command_id):
+                try:
+                    barrier.wait()
+                    store.accept_command(command_id, '{"kind":"job"}', '{"ok":true}')
+                except Exception as exc:  # pragma: no cover - assertion below
+                    failures.append(exc)
+
+            left = threading.Thread(target=write, args=(first, "command-1"))
+            right = threading.Thread(target=write, args=(second, "command-2"))
+            left.start()
+            right.start()
+            left.join(1)
+            right.join(1)
+
+            self.assertFalse(left.is_alive())
+            self.assertFalse(right.is_alive())
+            self.assertEqual(failures, [])
+            self.assertEqual(len(first.list_accepted_commands()), 2)
+            with first._connect() as connection:
+                self.assertEqual(
+                    connection.execute("PRAGMA busy_timeout").fetchone()[0],
+                    30000,
+                )
+
     def test_command_acceptance_is_durable_and_content_addressed(self):
         with tempfile.TemporaryDirectory() as directory:
             database = Path(directory) / "state.db"

tests/test_syncthing.py

@@ -125,6 +125,24 @@ class SyncthingRouteManagerTests(unittest.TestCase):
             self.manager.configure(self.spec, time.monotonic() + 1)
         self.assertEqual(self.transport.puts, [])
 
+    def test_existing_home_relative_folder_path_is_accepted(self):
+        self.transport.config["devices"].append({"deviceID": "PEER"})
+        self.transport.config["folders"].append(
+            {
+                "id": "route-1",
+                "path": "~/routes/route-1",
+                "type": "sendreceive",
+                "devices": [{"deviceID": "LOCAL"}, {"deviceID": "PEER"}],
+            }
+        )
+
+        configured = self.manager.configure(
+            self.spec, time.monotonic() + 1
+        )
+
+        self.assertEqual(self.transport.puts, [])
+        self.assertFalse(configured.local_route.archive_control_created)
+
     def test_bidirectional_nonce_and_ack_are_required(self):
         configured = self.manager.configure(self.spec, time.monotonic() + 1)
         peer_nonce = configured.local_path / (

tests/test_transfer.py

@@ -11,6 +11,7 @@ from archive_clients.transfer import (
     FileMaterializer,
     TransferIntegrityError,
     canonical_message_json,
+    cleanup_partial_transfer,
     load_published_transfer,
     materialize_transfer,
     stage_transfer,
@@ -206,6 +207,33 @@ class TransferHappyPathTests(unittest.TestCase):
             os.stat(copied).st_blocks * 512, os.stat(copied).st_size
         )
 
+    def test_partial_cleanup_removes_only_journalled_temporary(self):
+        job_id = str(uuid4())
+        job_root = self.sync / ".archive-control/jobs" / job_id
+        destination = job_root / "payload/album/one.bin"
+        destination.parent.mkdir(parents=True)
+        operation_id = "interrupted-copy"
+        self.store.begin_file_operation(
+            operation_id,
+            job_id,
+            '{"destination":"payload/album/one.bin"}',
+        )
+        temporary = destination.with_name(
+            ".one.bin.archive-control-"
+            + hashlib.sha256(operation_id.encode()).hexdigest()[:16]
+            + ".tmp"
+        )
+        temporary.write_bytes(b"partial")
+        unrelated = destination.parent / "keep-me"
+        unrelated.write_bytes(b"unrelated")
+
+        cleanup_partial_transfer(
+            job_root, job_id=job_id, store=self.store
+        )
+
+        self.assertFalse(temporary.exists())
+        self.assertTrue(unrelated.is_file())
+
     def test_canonical_manifest_json_is_stable(self):
         manifest = self._manifest()
         first = canonical_message_json(manifest)