Add filter write/create/delete and jail-filter assign endpoints (Task 2.2)

- PUT /api/config/filters/{name}: updates failregex/ignoreregex/datepattern/
  journalmatch in filter.d/{name}.local; validates regex via re.compile();
  supports ?reload=true
- POST /api/config/filters: creates filter.d/{name}.local from FilterCreateRequest;
  returns 409 if file already exists
- DELETE /api/config/filters/{name}: deletes .local only; returns 409 for
  conf-only (readonly) filters
- POST /api/config/jails/{name}/filter: assigns filter to jail by writing
  'filter = {name}' to jail.d/{jail}.local; supports ?reload=true
- New models: FilterUpdateRequest, FilterCreateRequest, AssignFilterRequest
- New service helpers: _safe_filter_name, _validate_regex_patterns,
  _write_filter_local_sync, _set_jail_local_key_sync
- Fixed .local-only filter discovery in _parse_filters_sync (5-tuple return)
- Fixed get_filter extension stripping (.local is 6 chars not 5)
- Renamed file_config.py raw-write routes to /raw suffix
  (PUT /filters/{name}/raw, POST /filters/raw) to avoid routing conflicts
- Full service + router tests; all 930 tests pass

Docs/Tasks.md

@@ -144,25 +144,19 @@ fail2ban ships with a large collection of filter definitions in `filter.d/` (ove
 
 ---
 
-### Task 2.2 — Backend: Activate and Edit Filters
+### Task 2.2 — Backend: Activate and Edit Filters ✅ DONE
 
-**Goal:** Allow users to assign a filter to a jail and edit filter regex patterns.
+**Implemented:**
+- `PUT /api/config/filters/{name}` — writes `failregex`, `ignoreregex`, `datepattern`, `journalmatch` changes to `filter.d/{name}.local`. Validates regex before writing. Supports `?reload=true`.
+- `POST /api/config/filters` — creates `filter.d/{name}.local` from `FilterCreateRequest`. Returns 409 if file already exists.
+- `DELETE /api/config/filters/{name}` — deletes `.local` only; refuses with 409 if filter is conf-only (readonly).
+- `POST /api/config/jails/{name}/filter` — assigns a filter to a jail by writing `filter = {name}` to `jail.d/{jail}.local`. Supports `?reload=true`.
+- All regex patterns validated via `re.compile()` before writing; invalid patterns return 422.
+- New models: `FilterUpdateRequest`, `FilterCreateRequest`, `AssignFilterRequest`.
+- Resolved routing conflict: `file_config.py` raw-write routes renamed to `PUT /filters/{name}/raw` and `POST /filters/raw` (consistent with existing `GET /filters/{name}/raw`).
+- Full service + router tests added; all 930 tests pass.
 
-**Details:**
-
-- Add a `PUT /api/config/filters/{name}` endpoint that writes changes to a filter's `.local` override file. Accepts updated `failregex`, `ignoreregex`, `datepattern`, and `journalmatch` values. Never write to the `.conf` file directly.
-- Add a `POST /api/config/jails/{jail_name}/filter` endpoint that changes which filter a jail uses. This writes `filter = {filter_name}` to the jail's `.local` config. Requires a reload for the change to take effect.
-- Add a `POST /api/config/filters` endpoint to create a brand-new filter. Accepts a name and the filter definition fields. Creates a new file at `filter.d/{name}.local`.
-- Add a `DELETE /api/config/filters/{name}` endpoint that deletes a custom filter's `.local` file. Refuse to delete files that are `.conf` (shipped defaults) — only user-created `.local` files without a corresponding `.conf` can be fully removed.
-- Validate all regex patterns using Python's `re` module before writing them to disk. Return 422 with specific error details if any pattern is invalid.
-- After any write operation, optionally trigger a fail2ban reload if the user requests it (query param `?reload=true`).
-
-**Files to create/modify:**
-- `app/services/config_file_service.py` (add filter write/create/delete methods)
-- `app/routers/config.py` (add endpoints)
-- `app/models/config.py` (add `FilterUpdateRequest`, `FilterCreateRequest`)
-
-**References:** [Features.md §6](Features.md), [Backend-Development.md](Backend-Development.md)
+**Files modified:** `app/models/config.py`, `app/services/config_file_service.py`, `app/routers/config.py`, `app/routers/file_config.py`, `tests/test_services/test_config_file_service.py`, `tests/test_routers/test_config.py`, `tests/test_routers/test_file_config.py`
 
 ---
 

backend/app/models/config.py

@@ -370,6 +370,79 @@ class FilterConfigUpdate(BaseModel):
     journalmatch: str | None = Field(default=None)
 
 
+class FilterUpdateRequest(BaseModel):
+    """Payload for ``PUT /api/config/filters/{name}``.
+
+    Accepts only the user-editable ``[Definition]`` fields.  Fields left as
+    ``None`` are not changed; the existing value from the merged conf/local is
+    preserved.
+    """
+
+    model_config = ConfigDict(strict=True)
+
+    failregex: list[str] | None = Field(
+        default=None,
+        description="Updated failure-detection regex patterns. ``None`` = keep existing.",
+    )
+    ignoreregex: list[str] | None = Field(
+        default=None,
+        description="Updated bypass-ban regex patterns. ``None`` = keep existing.",
+    )
+    datepattern: str | None = Field(
+        default=None,
+        description="Custom date-parsing pattern. ``None`` = keep existing.",
+    )
+    journalmatch: str | None = Field(
+        default=None,
+        description="Systemd journal match expression. ``None`` = keep existing.",
+    )
+
+
+class FilterCreateRequest(BaseModel):
+    """Payload for ``POST /api/config/filters``.
+
+    Creates a new user-defined filter at ``filter.d/{name}.local``.
+    """
+
+    model_config = ConfigDict(strict=True)
+
+    name: str = Field(
+        ...,
+        description="Filter base name (e.g. ``my-custom-filter``). Must not already exist in ``filter.d/``.",
+    )
+    failregex: list[str] = Field(
+        default_factory=list,
+        description="Failure-detection regex patterns.",
+    )
+    ignoreregex: list[str] = Field(
+        default_factory=list,
+        description="Regex patterns that bypass ban logic.",
+    )
+    prefregex: str | None = Field(
+        default=None,
+        description="Prefix regex prepended to every failregex.",
+    )
+    datepattern: str | None = Field(
+        default=None,
+        description="Custom date-parsing pattern.",
+    )
+    journalmatch: str | None = Field(
+        default=None,
+        description="Systemd journal match expression.",
+    )
+
+
+class AssignFilterRequest(BaseModel):
+    """Payload for ``POST /api/config/jails/{jail_name}/filter``."""
+
+    model_config = ConfigDict(strict=True)
+
+    filter_name: str = Field(
+        ...,
+        description="Filter base name to assign to the jail (e.g. ``sshd``).",
+    )
+
+
 class FilterListResponse(BaseModel):
     """Response for ``GET /api/config/filters``."""
 

backend/app/routers/config.py

@@ -9,6 +9,7 @@ global settings, test regex patterns, add log paths, and preview log files.
 * ``GET  /api/config/jails/inactive``               — list all inactive jails
 * ``POST /api/config/jails/{name}/activate``        — activate an inactive jail
 * ``POST /api/config/jails/{name}/deactivate``      — deactivate an active jail
+* ``POST /api/config/jails/{name}/filter``          — assign a filter to a jail
 * ``GET  /api/config/global``                       — global fail2ban settings
 * ``PUT  /api/config/global``                       — update global settings
 * ``POST /api/config/reload``                       — reload fail2ban
@@ -17,6 +18,9 @@ global settings, test regex patterns, add log paths, and preview log files.
 * ``POST /api/config/preview-log``                  — preview log matches
 * ``GET  /api/config/filters``                      — list all filters with active/inactive status
 * ``GET  /api/config/filters/{name}``               — full parsed detail for one filter
+* ``PUT  /api/config/filters/{name}``               — update a filter's .local override
+* ``POST /api/config/filters``                      — create a new user-defined filter
+* ``DELETE /api/config/filters/{name}``             — delete a filter's .local file
 """
 
 from __future__ import annotations
@@ -29,8 +33,11 @@ from app.dependencies import AuthDep
 from app.models.config import (
     ActivateJailRequest,
     AddLogPathRequest,
+    AssignFilterRequest,
     FilterConfig,
+    FilterCreateRequest,
     FilterListResponse,
+    FilterUpdateRequest,
     GlobalConfigResponse,
     GlobalConfigUpdate,
     InactiveJailListResponse,
@@ -48,7 +55,11 @@ from app.models.config import (
 from app.services import config_file_service, config_service, jail_service
 from app.services.config_file_service import (
     ConfigWriteError,
+    FilterAlreadyExistsError,
+    FilterInvalidRegexError,
+    FilterNameError,
     FilterNotFoundError,
+    FilterReadonlyError,
     JailAlreadyActiveError,
     JailAlreadyInactiveError,
     JailNameError,
@@ -731,3 +742,229 @@ async def get_filter(
             status_code=status.HTTP_404_NOT_FOUND,
             detail=f"Filter not found: {name!r}",
         ) from None
+
+
+# ---------------------------------------------------------------------------
+# Filter write endpoints (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+_FilterNamePath = Annotated[
+    str,
+    Path(description="Filter base name, e.g. ``sshd`` or ``sshd.conf``."),
+]
+
+
+def _filter_not_found(name: str) -> HTTPException:
+    return HTTPException(
+        status_code=status.HTTP_404_NOT_FOUND,
+        detail=f"Filter not found: {name!r}",
+    )
+
+
+@router.put(
+    "/filters/{name}",
+    response_model=FilterConfig,
+    summary="Update a filter's .local override with new regex/pattern values",
+)
+async def update_filter(
+    request: Request,
+    _auth: AuthDep,
+    name: _FilterNamePath,
+    body: FilterUpdateRequest,
+    reload: bool = Query(default=False, description="Reload fail2ban after writing."),
+) -> FilterConfig:
+    """Update a filter's ``[Definition]`` fields by writing a ``.local`` override.
+
+    All regex patterns are validated before writing.  The original ``.conf``
+    file is never modified.  Fields left as ``null`` in the request body are
+    kept at their current values.
+
+    Args:
+        request: FastAPI request object.
+        _auth: Validated session.
+        name: Filter base name (with or without ``.conf`` extension).
+        body: Partial update — ``failregex``, ``ignoreregex``, ``datepattern``,
+              ``journalmatch``.
+        reload: When ``true``, trigger a fail2ban reload after writing.
+
+    Returns:
+        Updated :class:`~app.models.config.FilterConfig`.
+
+    Raises:
+        HTTPException: 400 if *name* contains invalid characters.
+        HTTPException: 404 if the filter does not exist.
+        HTTPException: 422 if any regex pattern fails to compile.
+        HTTPException: 500 if writing the ``.local`` file fails.
+    """
+    config_dir: str = request.app.state.settings.fail2ban_config_dir
+    socket_path: str = request.app.state.settings.fail2ban_socket
+    try:
+        return await config_file_service.update_filter(
+            config_dir, socket_path, name, body, do_reload=reload
+        )
+    except FilterNameError as exc:
+        raise _bad_request(str(exc)) from exc
+    except FilterNotFoundError:
+        raise _filter_not_found(name) from None
+    except FilterInvalidRegexError as exc:
+        raise _unprocessable(str(exc)) from exc
+    except ConfigWriteError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"Failed to write filter override: {exc}",
+        ) from exc
+
+
+@router.post(
+    "/filters",
+    response_model=FilterConfig,
+    status_code=status.HTTP_201_CREATED,
+    summary="Create a new user-defined filter",
+)
+async def create_filter(
+    request: Request,
+    _auth: AuthDep,
+    body: FilterCreateRequest,
+    reload: bool = Query(default=False, description="Reload fail2ban after creating."),
+) -> FilterConfig:
+    """Create a new user-defined filter at ``filter.d/{name}.local``.
+
+    The filter is created as a ``.local`` file so it can coexist safely with
+    shipped ``.conf`` files.  Returns 409 if a ``.conf`` or ``.local`` for
+    the requested name already exists.
+
+    Args:
+        request: FastAPI request object.
+        _auth: Validated session.
+        body: Filter name and ``[Definition]`` fields.
+        reload: When ``true``, trigger a fail2ban reload after creating.
+
+    Returns:
+        :class:`~app.models.config.FilterConfig` for the new filter.
+
+    Raises:
+        HTTPException: 400 if the name contains invalid characters.
+        HTTPException: 409 if the filter already exists.
+        HTTPException: 422 if any regex pattern is invalid.
+        HTTPException: 500 if writing fails.
+    """
+    config_dir: str = request.app.state.settings.fail2ban_config_dir
+    socket_path: str = request.app.state.settings.fail2ban_socket
+    try:
+        return await config_file_service.create_filter(
+            config_dir, socket_path, body, do_reload=reload
+        )
+    except FilterNameError as exc:
+        raise _bad_request(str(exc)) from exc
+    except FilterAlreadyExistsError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_409_CONFLICT,
+            detail=f"Filter {exc.name!r} already exists.",
+        ) from exc
+    except FilterInvalidRegexError as exc:
+        raise _unprocessable(str(exc)) from exc
+    except ConfigWriteError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"Failed to write filter: {exc}",
+        ) from exc
+
+
+@router.delete(
+    "/filters/{name}",
+    status_code=status.HTTP_204_NO_CONTENT,
+    summary="Delete a user-created filter's .local file",
+)
+async def delete_filter(
+    request: Request,
+    _auth: AuthDep,
+    name: _FilterNamePath,
+) -> None:
+    """Delete a user-created filter's ``.local`` override file.
+
+    Shipped ``.conf``-only filters cannot be deleted (returns 409).  When
+    both a ``.conf`` and a ``.local`` exist, only the ``.local`` is removed.
+    When only a ``.local`` exists (user-created filter), the file is deleted
+    entirely.
+
+    Args:
+        request: FastAPI request object.
+        _auth: Validated session.
+        name: Filter base name.
+
+    Raises:
+        HTTPException: 400 if *name* contains invalid characters.
+        HTTPException: 404 if the filter does not exist.
+        HTTPException: 409 if the filter is a shipped default (conf-only).
+        HTTPException: 500 if deletion fails.
+    """
+    config_dir: str = request.app.state.settings.fail2ban_config_dir
+    try:
+        await config_file_service.delete_filter(config_dir, name)
+    except FilterNameError as exc:
+        raise _bad_request(str(exc)) from exc
+    except FilterNotFoundError:
+        raise _filter_not_found(name) from None
+    except FilterReadonlyError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_409_CONFLICT,
+            detail=str(exc),
+        ) from exc
+    except ConfigWriteError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"Failed to delete filter: {exc}",
+        ) from exc
+
+
+@router.post(
+    "/jails/{name}/filter",
+    status_code=status.HTTP_204_NO_CONTENT,
+    summary="Assign a filter to a jail",
+)
+async def assign_filter_to_jail(
+    request: Request,
+    _auth: AuthDep,
+    name: _NamePath,
+    body: AssignFilterRequest,
+    reload: bool = Query(default=False, description="Reload fail2ban after assigning."),
+) -> None:
+    """Write ``filter = {filter_name}`` to the jail's ``.local`` config.
+
+    Existing keys in the jail's ``.local`` file are preserved.  If the file
+    does not exist it is created.
+
+    Args:
+        request: FastAPI request object.
+        _auth: Validated session.
+        name: Jail name.
+        body: Filter to assign.
+        reload: When ``true``, trigger a fail2ban reload after writing.
+
+    Raises:
+        HTTPException: 400 if *name* or *filter_name* contain invalid characters.
+        HTTPException: 404 if the jail or filter does not exist.
+        HTTPException: 500 if writing fails.
+    """
+    config_dir: str = request.app.state.settings.fail2ban_config_dir
+    socket_path: str = request.app.state.settings.fail2ban_socket
+    try:
+        await config_file_service.assign_filter_to_jail(
+            config_dir, socket_path, name, body, do_reload=reload
+        )
+    except (JailNameError, FilterNameError) as exc:
+        raise _bad_request(str(exc)) from exc
+    except JailNotFoundInConfigError:
+        raise _not_found(name) from None
+    except FilterNotFoundError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Filter not found: {exc.name!r}",
+        ) from exc
+    except ConfigWriteError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"Failed to write jail override: {exc}",
+        ) from exc
+

backend/app/routers/file_config.py

@@ -9,8 +9,8 @@ Endpoints:
 * ``PUT  /api/config/jail-files/{filename}``        — overwrite a jail config file
 * ``PUT  /api/config/jail-files/{filename}/enabled`` — enable/disable a jail config
 * ``GET  /api/config/filters/{name}/raw``          — get one filter file raw content
-* ``PUT  /api/config/filters/{name}``              — update a filter file
-* ``POST /api/config/filters``                     — create a new filter file
+* ``PUT  /api/config/filters/{name}/raw``           — update a filter file (raw content)
+* ``POST /api/config/filters/raw``                 — create a new filter file (raw content)
 * ``GET  /api/config/filters/{name}/parsed``        — parse a filter file into a structured model
 * ``PUT  /api/config/filters/{name}/parsed``        — update a filter file from a structured model
 * ``GET  /api/config/actions``                     — list all action files
@@ -23,7 +23,8 @@ Endpoints:
 Note: ``GET /api/config/filters`` (enriched list) and
 ``GET /api/config/filters/{name}`` (full parsed detail) are handled by the
 config router (``config.py``), which is registered first and therefore takes
-precedence.  The raw-content variant is at ``/filters/{name}/raw``.
+precedence.  Raw-content read/write variants are at ``/filters/{name}/raw``
+and ``POST /filters/raw``.
 """
 
 from __future__ import annotations
@@ -347,9 +348,9 @@ async def get_filter_file_raw(
 
 
 @router.put(
-    "/filters/{name}",
+    "/filters/{name}/raw",
     status_code=status.HTTP_204_NO_CONTENT,
-    summary="Update a filter definition file",
+    summary="Update a filter definition file (raw content)",
 )
 async def write_filter_file(
     request: Request,
@@ -384,10 +385,10 @@ async def write_filter_file(
 
 
 @router.post(
-    "/filters",
+    "/filters/raw",
     status_code=status.HTTP_201_CREATED,
     response_model=ConfFileContent,
-    summary="Create a new filter definition file",
+    summary="Create a new filter definition file (raw content)",
 )
 async def create_filter_file(
     request: Request,

backend/app/services/config_file_service.py

@@ -23,6 +23,7 @@ from __future__ import annotations
 import asyncio
 import configparser
 import contextlib
+import io
 import os
 import re
 import tempfile
@@ -33,8 +34,12 @@ import structlog
 
 from app.models.config import (
     ActivateJailRequest,
+    AssignFilterRequest,
     FilterConfig,
+    FilterConfigUpdate,
+    FilterCreateRequest,
     FilterListResponse,
+    FilterUpdateRequest,
     InactiveJail,
     InactiveJailListResponse,
     JailActivationResponse,
@@ -117,6 +122,54 @@ class ConfigWriteError(Exception):
     """Raised when writing a ``.local`` override file fails."""
 
 
+class FilterNameError(Exception):
+    """Raised when a filter name contains invalid characters."""
+
+
+class FilterAlreadyExistsError(Exception):
+    """Raised when trying to create a filter whose ``.conf`` or ``.local`` already exists."""
+
+    def __init__(self, name: str) -> None:
+        """Initialise with the filter name that already exists.
+
+        Args:
+            name: The filter name that already exists.
+        """
+        self.name: str = name
+        super().__init__(f"Filter already exists: {name!r}")
+
+
+class FilterReadonlyError(Exception):
+    """Raised when trying to delete a shipped ``.conf`` filter with no ``.local`` override."""
+
+    def __init__(self, name: str) -> None:
+        """Initialise with the filter name that cannot be deleted.
+
+        Args:
+            name: The filter name that is read-only (shipped ``.conf`` only).
+        """
+        self.name: str = name
+        super().__init__(
+            f"Filter {name!r} is a shipped default (.conf only); "
+            "only user-created .local files can be deleted."
+        )
+
+
+class FilterInvalidRegexError(Exception):
+    """Raised when a regex pattern fails to compile."""
+
+    def __init__(self, pattern: str, error: str) -> None:
+        """Initialise with the invalid pattern and the compile error.
+
+        Args:
+            pattern: The regex string that failed to compile.
+            error: The ``re.error`` message.
+        """
+        self.pattern: str = pattern
+        self.error: str = error
+        super().__init__(f"Invalid regex {pattern!r}: {error}")
+
+
 # ---------------------------------------------------------------------------
 # Internal helpers
 # ---------------------------------------------------------------------------
@@ -143,6 +196,27 @@ def _safe_jail_name(name: str) -> str:
     return name
 
 
+def _safe_filter_name(name: str) -> str:
+    """Validate *name* and return it unchanged or raise :class:`FilterNameError`.
+
+    Args:
+        name: Proposed filter name (without extension).
+
+    Returns:
+        The name unchanged if valid.
+
+    Raises:
+        FilterNameError: If *name* contains unsafe characters.
+    """
+    if not _SAFE_FILTER_NAME_RE.match(name):
+        raise FilterNameError(
+            f"Filter name {name!r} contains invalid characters. "
+            "Only alphanumeric characters, hyphens, underscores, and dots are "
+            "allowed; must start with an alphanumeric character."
+        )
+    return name
+
+
 def _ordered_config_files(config_dir: Path) -> list[Path]:
     """Return all jail config files in fail2ban merge order.
 
@@ -479,6 +553,144 @@ def _write_local_override_sync(
     )
 
 
+def _validate_regex_patterns(patterns: list[str]) -> None:
+    """Validate each pattern in *patterns* using Python's ``re`` module.
+
+    Args:
+        patterns: List of regex strings to validate.
+
+    Raises:
+        FilterInvalidRegexError: If any pattern fails to compile.
+    """
+    for pattern in patterns:
+        try:
+            re.compile(pattern)
+        except re.error as exc:
+            raise FilterInvalidRegexError(pattern, str(exc)) from exc
+
+
+def _write_filter_local_sync(filter_d: Path, name: str, content: str) -> None:
+    """Write *content* to ``filter.d/{name}.local`` atomically.
+
+    The write is atomic: content is written to a temp file first, then
+    renamed into place.  The ``filter.d/`` directory is created if absent.
+
+    Args:
+        filter_d: Path to the ``filter.d`` directory.
+        name: Validated filter base name (used as filename stem).
+        content: Full serialized filter content to write.
+
+    Raises:
+        ConfigWriteError: If writing fails.
+    """
+    try:
+        filter_d.mkdir(parents=True, exist_ok=True)
+    except OSError as exc:
+        raise ConfigWriteError(
+            f"Cannot create filter.d directory: {exc}"
+        ) from exc
+
+    local_path = filter_d / f"{name}.local"
+    try:
+        with tempfile.NamedTemporaryFile(
+            mode="w",
+            encoding="utf-8",
+            dir=filter_d,
+            delete=False,
+            suffix=".tmp",
+        ) as tmp:
+            tmp.write(content)
+            tmp_name = tmp.name
+        os.replace(tmp_name, local_path)
+    except OSError as exc:
+        with contextlib.suppress(OSError):
+            os.unlink(tmp_name)  # noqa: F821
+        raise ConfigWriteError(
+            f"Failed to write {local_path}: {exc}"
+        ) from exc
+
+    log.info("filter_local_written", filter=name, path=str(local_path))
+
+
+def _set_jail_local_key_sync(
+    config_dir: Path,
+    jail_name: str,
+    key: str,
+    value: str,
+) -> None:
+    """Update ``jail.d/{jail_name}.local`` to set a single key in the jail section.
+
+    If the ``.local`` file already exists it is read, the key is updated (or
+    added), and the file is written back atomically without disturbing other
+    settings.  If the file does not exist a new one is created containing
+    only the BanGUI header comment, the jail section, and the requested key.
+
+    Args:
+        config_dir: The fail2ban configuration root directory.
+        jail_name: Validated jail name (used as section name and filename stem).
+        key: Config key to set inside the jail section.
+        value: Config value to assign.
+
+    Raises:
+        ConfigWriteError: If writing fails.
+    """
+    jail_d = config_dir / "jail.d"
+    try:
+        jail_d.mkdir(parents=True, exist_ok=True)
+    except OSError as exc:
+        raise ConfigWriteError(
+            f"Cannot create jail.d directory: {exc}"
+        ) from exc
+
+    local_path = jail_d / f"{jail_name}.local"
+
+    parser = _build_parser()
+    if local_path.is_file():
+        try:
+            parser.read(str(local_path), encoding="utf-8")
+        except (configparser.Error, OSError) as exc:
+            log.warning(
+                "jail_local_read_for_update_error",
+                jail=jail_name,
+                error=str(exc),
+            )
+
+    if not parser.has_section(jail_name):
+        parser.add_section(jail_name)
+    parser.set(jail_name, key, value)
+
+    # Serialize: write a BanGUI header then the parser output.
+    buf = io.StringIO()
+    buf.write("# Managed by BanGUI — do not edit manually\n\n")
+    parser.write(buf)
+    content = buf.getvalue()
+
+    try:
+        with tempfile.NamedTemporaryFile(
+            mode="w",
+            encoding="utf-8",
+            dir=jail_d,
+            delete=False,
+            suffix=".tmp",
+        ) as tmp:
+            tmp.write(content)
+            tmp_name = tmp.name
+        os.replace(tmp_name, local_path)
+    except OSError as exc:
+        with contextlib.suppress(OSError):
+            os.unlink(tmp_name)  # noqa: F821
+        raise ConfigWriteError(
+            f"Failed to write {local_path}: {exc}"
+        ) from exc
+
+    log.info(
+        "jail_local_key_set",
+        jail=jail_name,
+        key=key,
+        path=str(local_path),
+    )
+
+
 # ---------------------------------------------------------------------------
 # Public API
 # ---------------------------------------------------------------------------
@@ -743,32 +955,43 @@ def _build_filter_to_jails_map(
 
 def _parse_filters_sync(
     filter_d: Path,
-) -> list[tuple[str, str, str, bool]]:
+) -> list[tuple[str, str, str, bool, str]]:
     """Synchronously scan ``filter.d/`` and return per-filter tuples.
 
     Each tuple contains:
 
     - ``name``          — filter base name (``"sshd"``).
-    - ``filename``      — actual filename (``"sshd.conf"``).
+    - ``filename``      — actual filename (``"sshd.conf"`` or ``"sshd.local"``).
     - ``content``       — merged file content (``conf`` overridden by ``local``).
-    - ``has_local``     — whether a ``.local`` override exists.
+    - ``has_local``     — whether a ``.local`` override exists alongside a ``.conf``.
+    - ``source_path``   — absolute path to the primary (``conf``) source file, or
+                          to the ``.local`` file for user-created (local-only) filters.
+
+    Also discovers ``.local``-only files (user-created filters with no
+    corresponding ``.conf``).  These are returned with ``has_local = False``
+    and ``source_path`` pointing to the ``.local`` file itself.
 
     Args:
         filter_d: Path to the ``filter.d`` directory.
 
     Returns:
-        List of ``(name, filename, content, has_local)`` tuples, sorted by name.
+        List of ``(name, filename, content, has_local, source_path)`` tuples,
+        sorted by name.
     """
     if not filter_d.is_dir():
         log.warning("filter_d_not_found", path=str(filter_d))
         return []
 
-    results: list[tuple[str, str, str, bool]] = []
+    conf_names: set[str] = set()
+    results: list[tuple[str, str, str, bool, str]] = []
+
+    # ---- .conf-based filters (with optional .local override) ----------------
     for conf_path in sorted(filter_d.glob("*.conf")):
         if not conf_path.is_file():
             continue
         name = conf_path.stem
         filename = conf_path.name
+        conf_names.add(name)
         local_path = conf_path.with_suffix(".local")
         has_local = local_path.is_file()
 
@@ -794,8 +1017,29 @@ def _parse_filters_sync(
                     error=str(exc),
                 )
 
-        results.append((name, filename, content, has_local))
+        results.append((name, filename, content, has_local, str(conf_path)))
 
+    # ---- .local-only filters (user-created, no corresponding .conf) ----------
+    for local_path in sorted(filter_d.glob("*.local")):
+        if not local_path.is_file():
+            continue
+        name = local_path.stem
+        if name in conf_names:
+            # Already covered above as a .conf filter with a .local override.
+            continue
+        try:
+            content = local_path.read_text(encoding="utf-8")
+        except OSError as exc:
+            log.warning(
+                "filter_local_read_error",
+                name=name,
+                path=str(local_path),
+                error=str(exc),
+            )
+            continue
+        results.append((name, local_path.name, content, False, str(local_path)))
+
+    results.sort(key=lambda t: t[0])
     log.debug("filters_scanned", count=len(results), filter_d=str(filter_d))
     return results
 
@@ -832,7 +1076,7 @@ async def list_filters(
     loop = asyncio.get_event_loop()
 
     # Run the synchronous scan in a thread-pool executor.
-    raw_filters: list[tuple[str, str, str, bool]] = await loop.run_in_executor(
+    raw_filters: list[tuple[str, str, str, bool, str]] = await loop.run_in_executor(
         None, _parse_filters_sync, filter_d
     )
 
@@ -846,8 +1090,7 @@ async def list_filters(
     filter_to_jails = _build_filter_to_jails_map(all_jails, active_names)
 
     filters: list[FilterConfig] = []
-    for name, filename, content, has_local in raw_filters:
-        conf_path = filter_d / filename
+    for name, filename, content, has_local, source_path in raw_filters:
         cfg = conffile_parser.parse_filter_file(
             content, name=name, filename=filename
         )
@@ -867,7 +1110,7 @@ async def list_filters(
                 journalmatch=cfg.journalmatch,
                 active=len(used_by) > 0,
                 used_by_jails=used_by,
-                source_file=str(conf_path),
+                source_file=source_path,
                 has_local_override=has_local,
             )
         )
@@ -897,35 +1140,46 @@ async def get_filter(
         :class:`~app.models.config.FilterConfig` with status fields populated.
 
     Raises:
-        FilterNotFoundError: If no ``{name}.conf`` file exists in
-            ``filter.d/``.
+        FilterNotFoundError: If no ``{name}.conf`` or ``{name}.local`` file
+            exists in ``filter.d/``.
     """
-    # Normalise — strip extension if provided.
-    base_name = name[:-5] if name.endswith(".conf") else name
+    # Normalise — strip extension if provided (.conf=5 chars, .local=6 chars).
+    if name.endswith(".conf"):
+        base_name = name[:-5]
+    elif name.endswith(".local"):
+        base_name = name[:-6]
+    else:
+        base_name = name
 
     filter_d = Path(config_dir) / "filter.d"
     conf_path = filter_d / f"{base_name}.conf"
-    local_path = conf_path.with_suffix(".local")
+    local_path = filter_d / f"{base_name}.local"
     loop = asyncio.get_event_loop()
 
-    def _read() -> tuple[str, bool]:
-        if not conf_path.is_file():
-            raise FilterNotFoundError(base_name)
-        content = conf_path.read_text(encoding="utf-8")
+    def _read() -> tuple[str, bool, str]:
+        """Read filter content and return (content, has_local_override, source_path)."""
         has_local = local_path.is_file()
-        if has_local:
-            try:
-                content += "\n" + local_path.read_text(encoding="utf-8")
-            except OSError as exc:
-                log.warning(
-                    "filter_local_read_error",
-                    name=base_name,
-                    path=str(local_path),
-                    error=str(exc),
-                )
-        return content, has_local
+        if conf_path.is_file():
+            content = conf_path.read_text(encoding="utf-8")
+            if has_local:
+                try:
+                    content += "\n" + local_path.read_text(encoding="utf-8")
+                except OSError as exc:
+                    log.warning(
+                        "filter_local_read_error",
+                        name=base_name,
+                        path=str(local_path),
+                        error=str(exc),
+                    )
+            return content, has_local, str(conf_path)
+        elif has_local:
+            # Local-only filter: created by the user, no shipped .conf base.
+            content = local_path.read_text(encoding="utf-8")
+            return content, False, str(local_path)
+        else:
+            raise FilterNotFoundError(base_name)
 
-    content, has_local = await loop.run_in_executor(None, _read)
+    content, has_local, source_path = await loop.run_in_executor(None, _read)
 
     cfg = conffile_parser.parse_filter_file(
         content, name=base_name, filename=f"{base_name}.conf"
@@ -954,6 +1208,299 @@ async def get_filter(
         journalmatch=cfg.journalmatch,
         active=len(used_by) > 0,
         used_by_jails=used_by,
-        source_file=str(conf_path),
+        source_file=source_path,
         has_local_override=has_local,
     )
+
+
+# ---------------------------------------------------------------------------
+# Public API — filter write operations (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+async def update_filter(
+    config_dir: str,
+    socket_path: str,
+    name: str,
+    req: FilterUpdateRequest,
+    do_reload: bool = False,
+) -> FilterConfig:
+    """Update a filter's ``.local`` override with new regex/pattern values.
+
+    Reads the current merged configuration for *name* (``conf`` + any existing
+    ``local``), applies the non-``None`` fields in *req* on top of it, and
+    writes the resulting definition to ``filter.d/{name}.local``.  The
+    original ``.conf`` file is never modified.
+
+    All regex patterns in *req* are validated with Python's ``re`` module
+    before any write occurs.
+
+    Args:
+        config_dir: Absolute path to the fail2ban configuration directory.
+        socket_path: Path to the fail2ban Unix domain socket.
+        name: Filter base name (e.g. ``"sshd"`` or ``"sshd.conf"``).
+        req: Partial update — only non-``None`` fields are applied.
+        do_reload: When ``True``, trigger a full fail2ban reload after writing.
+
+    Returns:
+        :class:`~app.models.config.FilterConfig` reflecting the updated state.
+
+    Raises:
+        FilterNameError: If *name* contains invalid characters.
+        FilterNotFoundError: If no ``{name}.conf`` or ``{name}.local`` exists.
+        FilterInvalidRegexError: If any supplied regex pattern is invalid.
+        ConfigWriteError: If writing the ``.local`` file fails.
+    """
+    base_name = name[:-5] if name.endswith(".conf") or name.endswith(".local") else name
+    _safe_filter_name(base_name)
+
+    # Validate regex patterns before touching the filesystem.
+    patterns: list[str] = []
+    if req.failregex is not None:
+        patterns.extend(req.failregex)
+    if req.ignoreregex is not None:
+        patterns.extend(req.ignoreregex)
+    _validate_regex_patterns(patterns)
+
+    # Fetch the current merged config (raises FilterNotFoundError if absent).
+    current = await get_filter(config_dir, socket_path, base_name)
+
+    # Build a FilterConfigUpdate from the request fields.
+    update = FilterConfigUpdate(
+        failregex=req.failregex,
+        ignoreregex=req.ignoreregex,
+        datepattern=req.datepattern,
+        journalmatch=req.journalmatch,
+    )
+
+    merged = conffile_parser.merge_filter_update(current, update)
+    content = conffile_parser.serialize_filter_config(merged)
+
+    filter_d = Path(config_dir) / "filter.d"
+    loop = asyncio.get_event_loop()
+    await loop.run_in_executor(None, _write_filter_local_sync, filter_d, base_name, content)
+
+    if do_reload:
+        try:
+            await jail_service.reload_all(socket_path)
+        except Exception as exc:  # noqa: BLE001
+            log.warning(
+                "reload_after_filter_update_failed",
+                filter=base_name,
+                error=str(exc),
+            )
+
+    log.info("filter_updated", filter=base_name, reload=do_reload)
+    return await get_filter(config_dir, socket_path, base_name)
+
+
+async def create_filter(
+    config_dir: str,
+    socket_path: str,
+    req: FilterCreateRequest,
+    do_reload: bool = False,
+) -> FilterConfig:
+    """Create a brand-new user-defined filter in ``filter.d/{name}.local``.
+
+    No ``.conf`` is written; fail2ban loads ``.local`` files directly.  If a
+    ``.conf`` or ``.local`` file already exists for the requested name, a
+    :class:`FilterAlreadyExistsError` is raised.
+
+    All regex patterns are validated with Python's ``re`` module before
+    writing.
+
+    Args:
+        config_dir: Absolute path to the fail2ban configuration directory.
+        socket_path: Path to the fail2ban Unix domain socket.
+        req: Filter name and definition fields.
+        do_reload: When ``True``, trigger a full fail2ban reload after writing.
+
+    Returns:
+        :class:`~app.models.config.FilterConfig` for the newly created filter.
+
+    Raises:
+        FilterNameError: If ``req.name`` contains invalid characters.
+        FilterAlreadyExistsError: If a ``.conf`` or ``.local`` already exists.
+        FilterInvalidRegexError: If any regex pattern is invalid.
+        ConfigWriteError: If writing fails.
+    """
+    _safe_filter_name(req.name)
+
+    filter_d = Path(config_dir) / "filter.d"
+    conf_path = filter_d / f"{req.name}.conf"
+    local_path = filter_d / f"{req.name}.local"
+
+    def _check_not_exists() -> None:
+        if conf_path.is_file() or local_path.is_file():
+            raise FilterAlreadyExistsError(req.name)
+
+    loop = asyncio.get_event_loop()
+    await loop.run_in_executor(None, _check_not_exists)
+
+    # Validate regex patterns.
+    patterns: list[str] = list(req.failregex) + list(req.ignoreregex)
+    _validate_regex_patterns(patterns)
+
+    # Build a FilterConfig and serialise it.
+    cfg = FilterConfig(
+        name=req.name,
+        filename=f"{req.name}.local",
+        failregex=req.failregex,
+        ignoreregex=req.ignoreregex,
+        prefregex=req.prefregex,
+        datepattern=req.datepattern,
+        journalmatch=req.journalmatch,
+    )
+    content = conffile_parser.serialize_filter_config(cfg)
+
+    await loop.run_in_executor(None, _write_filter_local_sync, filter_d, req.name, content)
+
+    if do_reload:
+        try:
+            await jail_service.reload_all(socket_path)
+        except Exception as exc:  # noqa: BLE001
+            log.warning(
+                "reload_after_filter_create_failed",
+                filter=req.name,
+                error=str(exc),
+            )
+
+    log.info("filter_created", filter=req.name, reload=do_reload)
+    # Re-fetch to get the canonical FilterConfig (source_file, active, etc.).
+    return await get_filter(config_dir, socket_path, req.name)
+
+
+async def delete_filter(
+    config_dir: str,
+    name: str,
+) -> None:
+    """Delete a user-created filter's ``.local`` file.
+
+    Deletion rules:
+    - If only a ``.conf`` file exists (shipped default, no user override) →
+      :class:`FilterReadonlyError`.
+    - If a ``.local`` file exists (whether or not a ``.conf`` also exists) →
+      the ``.local`` file is deleted.  The shipped ``.conf`` is never touched.
+    - If neither file exists → :class:`FilterNotFoundError`.
+
+    Args:
+        config_dir: Absolute path to the fail2ban configuration directory.
+        name: Filter base name (e.g. ``"sshd"``).
+
+    Raises:
+        FilterNameError: If *name* contains invalid characters.
+        FilterNotFoundError: If no filter file is found for *name*.
+        FilterReadonlyError: If only a shipped ``.conf`` exists (no ``.local``).
+        ConfigWriteError: If deletion of the ``.local`` file fails.
+    """
+    base_name = name[:-5] if name.endswith(".conf") or name.endswith(".local") else name
+    _safe_filter_name(base_name)
+
+    filter_d = Path(config_dir) / "filter.d"
+    conf_path = filter_d / f"{base_name}.conf"
+    local_path = filter_d / f"{base_name}.local"
+
+    loop = asyncio.get_event_loop()
+
+    def _delete() -> None:
+        has_conf = conf_path.is_file()
+        has_local = local_path.is_file()
+
+        if not has_conf and not has_local:
+            raise FilterNotFoundError(base_name)
+
+        if has_conf and not has_local:
+            # Shipped default — nothing user-writable to remove.
+            raise FilterReadonlyError(base_name)
+
+        try:
+            local_path.unlink()
+        except OSError as exc:
+            raise ConfigWriteError(
+                f"Failed to delete {local_path}: {exc}"
+            ) from exc
+
+        log.info("filter_local_deleted", filter=base_name, path=str(local_path))
+
+    await loop.run_in_executor(None, _delete)
+
+
+async def assign_filter_to_jail(
+    config_dir: str,
+    socket_path: str,
+    jail_name: str,
+    req: AssignFilterRequest,
+    do_reload: bool = False,
+) -> None:
+    """Assign a filter to a jail by updating the jail's ``.local`` file.
+
+    Writes ``filter = {req.filter_name}`` into the ``[{jail_name}]`` section
+    of ``jail.d/{jail_name}.local``.  If the ``.local`` file already contains
+    other settings for this jail they are preserved.
+
+    Args:
+        config_dir: Absolute path to the fail2ban configuration directory.
+        socket_path: Path to the fail2ban Unix domain socket.
+        jail_name: Name of the jail to update.
+        req: Request containing the filter name to assign.
+        do_reload: When ``True``, trigger a full fail2ban reload after writing.
+
+    Raises:
+        JailNameError: If *jail_name* contains invalid characters.
+        FilterNameError: If ``req.filter_name`` contains invalid characters.
+        JailNotFoundInConfigError: If *jail_name* is not defined in any config
+            file.
+        FilterNotFoundError: If ``req.filter_name`` does not exist in
+            ``filter.d/``.
+        ConfigWriteError: If writing fails.
+    """
+    _safe_jail_name(jail_name)
+    _safe_filter_name(req.filter_name)
+
+    loop = asyncio.get_event_loop()
+
+    # Verify the jail exists in config.
+    all_jails, _src = await loop.run_in_executor(
+        None, _parse_jails_sync, Path(config_dir)
+    )
+    if jail_name not in all_jails:
+        raise JailNotFoundInConfigError(jail_name)
+
+    # Verify the filter exists (conf or local).
+    filter_d = Path(config_dir) / "filter.d"
+
+    def _check_filter() -> None:
+        conf_exists = (filter_d / f"{req.filter_name}.conf").is_file()
+        local_exists = (filter_d / f"{req.filter_name}.local").is_file()
+        if not conf_exists and not local_exists:
+            raise FilterNotFoundError(req.filter_name)
+
+    await loop.run_in_executor(None, _check_filter)
+
+    await loop.run_in_executor(
+        None,
+        _set_jail_local_key_sync,
+        Path(config_dir),
+        jail_name,
+        "filter",
+        req.filter_name,
+    )
+
+    if do_reload:
+        try:
+            await jail_service.reload_all(socket_path)
+        except Exception as exc:  # noqa: BLE001
+            log.warning(
+                "reload_after_assign_filter_failed",
+                jail=jail_name,
+                filter=req.filter_name,
+                error=str(exc),
+            )
+
+    log.info(
+        "filter_assigned_to_jail",
+        jail=jail_name,
+        filter=req.filter_name,
+        reload=do_reload,
+    )
+

backend/tests/test_routers/test_config.py

@@ -955,3 +955,337 @@ class TestGetFilter:
             base_url="http://test",
         ).get("/api/config/filters/sshd")
         assert resp.status_code == 401
+
+
+# ---------------------------------------------------------------------------
+# PUT /api/config/filters/{name}  (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+class TestUpdateFilter:
+    """Tests for ``PUT /api/config/filters/{name}``."""
+
+    async def test_200_returns_updated_filter(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/filters/sshd returns 200 with updated FilterConfig."""
+        with patch(
+            "app.routers.config.config_file_service.update_filter",
+            AsyncMock(return_value=_make_filter_config("sshd")),
+        ):
+            resp = await config_client.put(
+                "/api/config/filters/sshd",
+                json={"failregex": [r"^fail from <HOST>"]},
+            )
+
+        assert resp.status_code == 200
+        assert resp.json()["name"] == "sshd"
+
+    async def test_404_for_unknown_filter(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/filters/missing returns 404."""
+        from app.services.config_file_service import FilterNotFoundError
+
+        with patch(
+            "app.routers.config.config_file_service.update_filter",
+            AsyncMock(side_effect=FilterNotFoundError("missing")),
+        ):
+            resp = await config_client.put(
+                "/api/config/filters/missing",
+                json={},
+            )
+
+        assert resp.status_code == 404
+
+    async def test_422_for_invalid_regex(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/filters/sshd returns 422 for bad regex."""
+        from app.services.config_file_service import FilterInvalidRegexError
+
+        with patch(
+            "app.routers.config.config_file_service.update_filter",
+            AsyncMock(side_effect=FilterInvalidRegexError("[bad", "unterminated")),
+        ):
+            resp = await config_client.put(
+                "/api/config/filters/sshd",
+                json={"failregex": ["[bad"]},
+            )
+
+        assert resp.status_code == 422
+
+    async def test_400_for_invalid_name(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/filters/... with bad name returns 400."""
+        from app.services.config_file_service import FilterNameError
+
+        with patch(
+            "app.routers.config.config_file_service.update_filter",
+            AsyncMock(side_effect=FilterNameError("bad")),
+        ):
+            resp = await config_client.put(
+                "/api/config/filters/bad",
+                json={},
+            )
+
+        assert resp.status_code == 400
+
+    async def test_reload_query_param_passed(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/filters/sshd?reload=true passes do_reload=True."""
+        with patch(
+            "app.routers.config.config_file_service.update_filter",
+            AsyncMock(return_value=_make_filter_config("sshd")),
+        ) as mock_update:
+            resp = await config_client.put(
+                "/api/config/filters/sshd?reload=true",
+                json={},
+            )
+
+        assert resp.status_code == 200
+        assert mock_update.call_args.kwargs.get("do_reload") is True
+
+    async def test_401_when_unauthenticated(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/filters/sshd returns 401 without session."""
+        resp = await AsyncClient(
+            transport=ASGITransport(app=config_client._transport.app),  # type: ignore[attr-defined]
+            base_url="http://test",
+        ).put("/api/config/filters/sshd", json={})
+        assert resp.status_code == 401
+
+
+# ---------------------------------------------------------------------------
+# POST /api/config/filters  (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+class TestCreateFilter:
+    """Tests for ``POST /api/config/filters``."""
+
+    async def test_201_creates_filter(self, config_client: AsyncClient) -> None:
+        """POST /api/config/filters returns 201 with FilterConfig."""
+        with patch(
+            "app.routers.config.config_file_service.create_filter",
+            AsyncMock(return_value=_make_filter_config("my-custom")),
+        ):
+            resp = await config_client.post(
+                "/api/config/filters",
+                json={"name": "my-custom", "failregex": [r"^fail from <HOST>"]},
+            )
+
+        assert resp.status_code == 201
+        assert resp.json()["name"] == "my-custom"
+
+    async def test_409_when_already_exists(self, config_client: AsyncClient) -> None:
+        """POST /api/config/filters returns 409 if filter exists."""
+        from app.services.config_file_service import FilterAlreadyExistsError
+
+        with patch(
+            "app.routers.config.config_file_service.create_filter",
+            AsyncMock(side_effect=FilterAlreadyExistsError("sshd")),
+        ):
+            resp = await config_client.post(
+                "/api/config/filters",
+                json={"name": "sshd"},
+            )
+
+        assert resp.status_code == 409
+
+    async def test_422_for_invalid_regex(self, config_client: AsyncClient) -> None:
+        """POST /api/config/filters returns 422 for bad regex."""
+        from app.services.config_file_service import FilterInvalidRegexError
+
+        with patch(
+            "app.routers.config.config_file_service.create_filter",
+            AsyncMock(side_effect=FilterInvalidRegexError("[bad", "unterminated")),
+        ):
+            resp = await config_client.post(
+                "/api/config/filters",
+                json={"name": "test", "failregex": ["[bad"]},
+            )
+
+        assert resp.status_code == 422
+
+    async def test_400_for_invalid_name(self, config_client: AsyncClient) -> None:
+        """POST /api/config/filters returns 400 for invalid filter name."""
+        from app.services.config_file_service import FilterNameError
+
+        with patch(
+            "app.routers.config.config_file_service.create_filter",
+            AsyncMock(side_effect=FilterNameError("bad")),
+        ):
+            resp = await config_client.post(
+                "/api/config/filters",
+                json={"name": "bad"},
+            )
+
+        assert resp.status_code == 400
+
+    async def test_401_when_unauthenticated(self, config_client: AsyncClient) -> None:
+        """POST /api/config/filters returns 401 without session."""
+        resp = await AsyncClient(
+            transport=ASGITransport(app=config_client._transport.app),  # type: ignore[attr-defined]
+            base_url="http://test",
+        ).post("/api/config/filters", json={"name": "test"})
+        assert resp.status_code == 401
+
+
+# ---------------------------------------------------------------------------
+# DELETE /api/config/filters/{name}  (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+class TestDeleteFilter:
+    """Tests for ``DELETE /api/config/filters/{name}``."""
+
+    async def test_204_deletes_filter(self, config_client: AsyncClient) -> None:
+        """DELETE /api/config/filters/my-custom returns 204."""
+        with patch(
+            "app.routers.config.config_file_service.delete_filter",
+            AsyncMock(return_value=None),
+        ):
+            resp = await config_client.delete("/api/config/filters/my-custom")
+
+        assert resp.status_code == 204
+
+    async def test_404_for_unknown_filter(self, config_client: AsyncClient) -> None:
+        """DELETE /api/config/filters/missing returns 404."""
+        from app.services.config_file_service import FilterNotFoundError
+
+        with patch(
+            "app.routers.config.config_file_service.delete_filter",
+            AsyncMock(side_effect=FilterNotFoundError("missing")),
+        ):
+            resp = await config_client.delete("/api/config/filters/missing")
+
+        assert resp.status_code == 404
+
+    async def test_409_for_readonly_filter(self, config_client: AsyncClient) -> None:
+        """DELETE /api/config/filters/sshd returns 409 for shipped conf-only filter."""
+        from app.services.config_file_service import FilterReadonlyError
+
+        with patch(
+            "app.routers.config.config_file_service.delete_filter",
+            AsyncMock(side_effect=FilterReadonlyError("sshd")),
+        ):
+            resp = await config_client.delete("/api/config/filters/sshd")
+
+        assert resp.status_code == 409
+
+    async def test_400_for_invalid_name(self, config_client: AsyncClient) -> None:
+        """DELETE /api/config/filters/... with bad name returns 400."""
+        from app.services.config_file_service import FilterNameError
+
+        with patch(
+            "app.routers.config.config_file_service.delete_filter",
+            AsyncMock(side_effect=FilterNameError("bad")),
+        ):
+            resp = await config_client.delete("/api/config/filters/bad")
+
+        assert resp.status_code == 400
+
+    async def test_401_when_unauthenticated(self, config_client: AsyncClient) -> None:
+        """DELETE /api/config/filters/sshd returns 401 without session."""
+        resp = await AsyncClient(
+            transport=ASGITransport(app=config_client._transport.app),  # type: ignore[attr-defined]
+            base_url="http://test",
+        ).delete("/api/config/filters/sshd")
+        assert resp.status_code == 401
+
+
+# ---------------------------------------------------------------------------
+# POST /api/config/jails/{name}/filter  (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+class TestAssignFilterToJail:
+    """Tests for ``POST /api/config/jails/{name}/filter``."""
+
+    async def test_204_assigns_filter(self, config_client: AsyncClient) -> None:
+        """POST /api/config/jails/sshd/filter returns 204 on success."""
+        with patch(
+            "app.routers.config.config_file_service.assign_filter_to_jail",
+            AsyncMock(return_value=None),
+        ):
+            resp = await config_client.post(
+                "/api/config/jails/sshd/filter",
+                json={"filter_name": "myfilter"},
+            )
+
+        assert resp.status_code == 204
+
+    async def test_404_for_unknown_jail(self, config_client: AsyncClient) -> None:
+        """POST /api/config/jails/missing/filter returns 404."""
+        from app.services.config_file_service import JailNotFoundInConfigError
+
+        with patch(
+            "app.routers.config.config_file_service.assign_filter_to_jail",
+            AsyncMock(side_effect=JailNotFoundInConfigError("missing")),
+        ):
+            resp = await config_client.post(
+                "/api/config/jails/missing/filter",
+                json={"filter_name": "sshd"},
+            )
+
+        assert resp.status_code == 404
+
+    async def test_404_for_unknown_filter(self, config_client: AsyncClient) -> None:
+        """POST /api/config/jails/sshd/filter returns 404 when filter not found."""
+        from app.services.config_file_service import FilterNotFoundError
+
+        with patch(
+            "app.routers.config.config_file_service.assign_filter_to_jail",
+            AsyncMock(side_effect=FilterNotFoundError("missing-filter")),
+        ):
+            resp = await config_client.post(
+                "/api/config/jails/sshd/filter",
+                json={"filter_name": "missing-filter"},
+            )
+
+        assert resp.status_code == 404
+
+    async def test_400_for_invalid_jail_name(self, config_client: AsyncClient) -> None:
+        """POST /api/config/jails/.../filter with bad jail name returns 400."""
+        from app.services.config_file_service import JailNameError
+
+        with patch(
+            "app.routers.config.config_file_service.assign_filter_to_jail",
+            AsyncMock(side_effect=JailNameError("bad")),
+        ):
+            resp = await config_client.post(
+                "/api/config/jails/sshd/filter",
+                json={"filter_name": "valid"},
+            )
+
+        assert resp.status_code == 400
+
+    async def test_400_for_invalid_filter_name(self, config_client: AsyncClient) -> None:
+        """POST /api/config/jails/sshd/filter with bad filter name returns 400."""
+        from app.services.config_file_service import FilterNameError
+
+        with patch(
+            "app.routers.config.config_file_service.assign_filter_to_jail",
+            AsyncMock(side_effect=FilterNameError("bad")),
+        ):
+            resp = await config_client.post(
+                "/api/config/jails/sshd/filter",
+                json={"filter_name": "../evil"},
+            )
+
+        assert resp.status_code == 400
+
+    async def test_reload_query_param_passed(self, config_client: AsyncClient) -> None:
+        """POST /api/config/jails/sshd/filter?reload=true passes do_reload=True."""
+        with patch(
+            "app.routers.config.config_file_service.assign_filter_to_jail",
+            AsyncMock(return_value=None),
+        ) as mock_assign:
+            resp = await config_client.post(
+                "/api/config/jails/sshd/filter?reload=true",
+                json={"filter_name": "sshd"},
+            )
+
+        assert resp.status_code == 204
+        assert mock_assign.call_args.kwargs.get("do_reload") is True
+
+    async def test_401_when_unauthenticated(self, config_client: AsyncClient) -> None:
+        """POST /api/config/jails/sshd/filter returns 401 without session."""
+        resp = await AsyncClient(
+            transport=ASGITransport(app=config_client._transport.app),  # type: ignore[attr-defined]
+            base_url="http://test",
+        ).post("/api/config/jails/sshd/filter", json={"filter_name": "sshd"})
+        assert resp.status_code == 401
+

backend/tests/test_routers/test_file_config.py

@@ -262,7 +262,7 @@ class TestUpdateFilterFile:
             AsyncMock(return_value=None),
         ):
             resp = await file_config_client.put(
-                "/api/config/filters/nginx",
+                "/api/config/filters/nginx/raw",
                 json={"content": "[Definition]\nfailregex = test\n"},
             )
 
@@ -274,7 +274,7 @@ class TestUpdateFilterFile:
             AsyncMock(side_effect=ConfigFileWriteError("disk full")),
         ):
             resp = await file_config_client.put(
-                "/api/config/filters/nginx",
+                "/api/config/filters/nginx/raw",
                 json={"content": "x"},
             )
 
@@ -293,7 +293,7 @@ class TestCreateFilterFile:
             AsyncMock(return_value="myfilter.conf"),
         ):
             resp = await file_config_client.post(
-                "/api/config/filters",
+                "/api/config/filters/raw",
                 json={"name": "myfilter", "content": "[Definition]\n"},
             )
 
@@ -306,7 +306,7 @@ class TestCreateFilterFile:
             AsyncMock(side_effect=ConfigFileExistsError("myfilter.conf")),
         ):
             resp = await file_config_client.post(
-                "/api/config/filters",
+                "/api/config/filters/raw",
                 json={"name": "myfilter", "content": "[Definition]\n"},
             )
 
@@ -318,7 +318,7 @@ class TestCreateFilterFile:
             AsyncMock(side_effect=ConfigFileNameError("bad/../name")),
         ):
             resp = await file_config_client.post(
-                "/api/config/filters",
+                "/api/config/filters/raw",
                 json={"name": "../escape", "content": "[Definition]\n"},
             )
 

backend/tests/test_services/test_config_file_service.py

@@ -660,11 +660,12 @@ class TestParseFiltersSync:
         result = _parse_filters_sync(filter_d)
 
         assert len(result) == 1
-        name, filename, content, has_local = result[0]
+        name, filename, content, has_local, source_path = result[0]
         assert name == "nginx"
         assert filename == "nginx.conf"
         assert "failregex" in content
         assert has_local is False
+        assert source_path.endswith("nginx.conf")
 
     def test_local_override_detected(self, tmp_path: Path) -> None:
         from app.services.config_file_service import _parse_filters_sync
@@ -675,7 +676,7 @@ class TestParseFiltersSync:
 
         result = _parse_filters_sync(filter_d)
 
-        _, _, _, has_local = result[0]
+        _, _, _, has_local, _ = result[0]
         assert has_local is True
 
     def test_local_content_appended_to_content(self, tmp_path: Path) -> None:
@@ -687,7 +688,7 @@ class TestParseFiltersSync:
 
         result = _parse_filters_sync(filter_d)
 
-        _, _, content, _ = result[0]
+        _, _, content, _, _ = result[0]
         assert "local tweak" in content
 
     def test_sorted_alphabetically(self, tmp_path: Path) -> None:
@@ -852,3 +853,637 @@ class TestGetFilter:
             result = await get_filter(str(tmp_path), "/fake.sock", "sshd")
 
         assert result.has_local_override is True
+
+
+# ---------------------------------------------------------------------------
+# _parse_filters_sync — .local-only filters (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+class TestParseFiltersSyncLocalOnly:
+    """Verify that .local-only user-created filters appear in results."""
+
+    def test_local_only_included(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _parse_filters_sync
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "custom.local", "[Definition]\nfailregex = ^fail\n")
+
+        result = _parse_filters_sync(filter_d)
+
+        assert len(result) == 1
+        name, filename, content, has_local, source_path = result[0]
+        assert name == "custom"
+        assert filename == "custom.local"
+        assert has_local is False  # .local-only: no conf to override
+        assert source_path.endswith("custom.local")
+
+    def test_local_only_not_duplicated_when_conf_exists(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _parse_filters_sync
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "sshd.conf", _FILTER_CONF)
+        _write(filter_d / "sshd.local", "[Definition]\n")
+
+        result = _parse_filters_sync(filter_d)
+
+        # sshd should appear exactly once (conf + local, not as separate entry)
+        names = [r[0] for r in result]
+        assert names.count("sshd") == 1
+        _, _, _, has_local, _ = result[0]
+        assert has_local is True  # conf + local → has_local_override
+
+    def test_local_only_sorted_with_conf_filters(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _parse_filters_sync
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "zzz.conf", _FILTER_CONF)
+        _write(filter_d / "aaa.local", "[Definition]\nfailregex = x\n")
+
+        result = _parse_filters_sync(filter_d)
+
+        names = [r[0] for r in result]
+        assert names == ["aaa", "zzz"]
+
+
+# ---------------------------------------------------------------------------
+# get_filter — .local-only filter (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+class TestGetFilterLocalOnly:
+    """Verify that get_filter handles .local-only user-created filters."""
+
+    async def test_returns_local_only_filter(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import get_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(
+            filter_d / "custom.local",
+            "[Definition]\nfailregex = ^fail from <HOST>\n",
+        )
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ):
+            result = await get_filter(str(tmp_path), "/fake.sock", "custom")
+
+        assert result.name == "custom"
+        assert result.has_local_override is False
+        assert result.source_file.endswith("custom.local")
+        assert len(result.failregex) == 1
+
+    async def test_raises_when_neither_conf_nor_local(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import FilterNotFoundError, get_filter
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ), pytest.raises(FilterNotFoundError):
+            await get_filter(str(tmp_path), "/fake.sock", "nonexistent")
+
+    async def test_accepts_local_extension(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import get_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "custom.local", "[Definition]\nfailregex = x\n")
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ):
+            result = await get_filter(str(tmp_path), "/fake.sock", "custom.local")
+
+        assert result.name == "custom"
+
+
+# ---------------------------------------------------------------------------
+# _validate_regex_patterns (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+class TestValidateRegexPatterns:
+    def test_valid_patterns_pass(self) -> None:
+        from app.services.config_file_service import _validate_regex_patterns
+
+        _validate_regex_patterns([r"^fail from \S+", r"\d+\.\d+"])
+
+    def test_empty_list_passes(self) -> None:
+        from app.services.config_file_service import _validate_regex_patterns
+
+        _validate_regex_patterns([])
+
+    def test_invalid_pattern_raises(self) -> None:
+        from app.services.config_file_service import (
+            FilterInvalidRegexError,
+            _validate_regex_patterns,
+        )
+
+        with pytest.raises(FilterInvalidRegexError) as exc_info:
+            _validate_regex_patterns([r"[unclosed"])
+
+        assert "[unclosed" in exc_info.value.pattern
+
+    def test_mixed_valid_invalid_raises_on_first_invalid(self) -> None:
+        from app.services.config_file_service import (
+            FilterInvalidRegexError,
+            _validate_regex_patterns,
+        )
+
+        with pytest.raises(FilterInvalidRegexError) as exc_info:
+            _validate_regex_patterns([r"\d+", r"[bad", r"\w+"])
+
+        assert "[bad" in exc_info.value.pattern
+
+
+# ---------------------------------------------------------------------------
+# _write_filter_local_sync (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+class TestWriteFilterLocalSync:
+    def test_writes_file(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _write_filter_local_sync
+
+        filter_d = tmp_path / "filter.d"
+        filter_d.mkdir()
+        _write_filter_local_sync(filter_d, "myfilter", "[Definition]\n")
+
+        local = filter_d / "myfilter.local"
+        assert local.is_file()
+        assert "[Definition]" in local.read_text()
+
+    def test_creates_filter_d_if_missing(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _write_filter_local_sync
+
+        filter_d = tmp_path / "filter.d"
+        _write_filter_local_sync(filter_d, "test", "[Definition]\n")
+        assert (filter_d / "test.local").is_file()
+
+    def test_overwrites_existing_file(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _write_filter_local_sync
+
+        filter_d = tmp_path / "filter.d"
+        filter_d.mkdir()
+        (filter_d / "myfilter.local").write_text("old content")
+
+        _write_filter_local_sync(filter_d, "myfilter", "[Definition]\nnew=1\n")
+
+        assert "new=1" in (filter_d / "myfilter.local").read_text()
+        assert "old content" not in (filter_d / "myfilter.local").read_text()
+
+
+# ---------------------------------------------------------------------------
+# _set_jail_local_key_sync (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+class TestSetJailLocalKeySync:
+    def test_creates_new_local_file(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _set_jail_local_key_sync
+
+        _set_jail_local_key_sync(tmp_path, "sshd", "filter", "myfilter")
+
+        local = tmp_path / "jail.d" / "sshd.local"
+        assert local.is_file()
+        content = local.read_text()
+        assert "filter" in content
+        assert "myfilter" in content
+
+    def test_updates_existing_local_file(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _set_jail_local_key_sync
+
+        jail_d = tmp_path / "jail.d"
+        jail_d.mkdir()
+        (jail_d / "sshd.local").write_text(
+            "[sshd]\nenabled = true\n"
+        )
+
+        _set_jail_local_key_sync(tmp_path, "sshd", "filter", "newfilter")
+
+        content = (jail_d / "sshd.local").read_text()
+        assert "newfilter" in content
+        # Existing key is preserved
+        assert "enabled" in content
+
+    def test_overwrites_existing_key(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import _set_jail_local_key_sync
+
+        jail_d = tmp_path / "jail.d"
+        jail_d.mkdir()
+        (jail_d / "sshd.local").write_text("[sshd]\nfilter = old\n")
+
+        _set_jail_local_key_sync(tmp_path, "sshd", "filter", "newfilter")
+
+        content = (jail_d / "sshd.local").read_text()
+        assert "newfilter" in content
+
+
+# ---------------------------------------------------------------------------
+# update_filter (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+_FILTER_CONF_WITH_REGEX = """\
+[Definition]
+
+failregex = ^fail from <HOST>
+            ^error from <HOST>
+
+ignoreregex =
+"""
+
+
+@pytest.mark.asyncio
+class TestUpdateFilter:
+    async def test_writes_local_override(self, tmp_path: Path) -> None:
+        from app.models.config import FilterUpdateRequest
+        from app.services.config_file_service import update_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "sshd.conf", _FILTER_CONF_WITH_REGEX)
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ):
+            result = await update_filter(
+                str(tmp_path),
+                "/fake.sock",
+                "sshd",
+                FilterUpdateRequest(failregex=[r"^new pattern <HOST>"]),
+            )
+
+        local = filter_d / "sshd.local"
+        assert local.is_file()
+        assert result.name == "sshd"
+        assert any("new pattern" in p for p in result.failregex)
+
+    async def test_accepts_conf_extension(self, tmp_path: Path) -> None:
+        from app.models.config import FilterUpdateRequest
+        from app.services.config_file_service import update_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "sshd.conf", _FILTER_CONF_WITH_REGEX)
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ):
+            result = await update_filter(
+                str(tmp_path),
+                "/fake.sock",
+                "sshd.conf",
+                FilterUpdateRequest(datepattern="%Y-%m-%d"),
+            )
+
+        assert result.name == "sshd"
+
+    async def test_raises_filter_not_found(self, tmp_path: Path) -> None:
+        from app.models.config import FilterUpdateRequest
+        from app.services.config_file_service import FilterNotFoundError, update_filter
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ), pytest.raises(FilterNotFoundError):
+            await update_filter(
+                str(tmp_path),
+                "/fake.sock",
+                "missing",
+                FilterUpdateRequest(),
+            )
+
+    async def test_raises_on_invalid_regex(self, tmp_path: Path) -> None:
+        from app.models.config import FilterUpdateRequest
+        from app.services.config_file_service import (
+            FilterInvalidRegexError,
+            update_filter,
+        )
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "sshd.conf", _FILTER_CONF_WITH_REGEX)
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ), pytest.raises(FilterInvalidRegexError):
+            await update_filter(
+                str(tmp_path),
+                "/fake.sock",
+                "sshd",
+                FilterUpdateRequest(failregex=[r"[unclosed"]),
+            )
+
+    async def test_raises_filter_name_error_for_invalid_name(self, tmp_path: Path) -> None:
+        from app.models.config import FilterUpdateRequest
+        from app.services.config_file_service import FilterNameError, update_filter
+
+        with pytest.raises(FilterNameError):
+            await update_filter(
+                str(tmp_path),
+                "/fake.sock",
+                "../etc/passwd",
+                FilterUpdateRequest(),
+            )
+
+    async def test_triggers_reload_when_requested(self, tmp_path: Path) -> None:
+        from app.models.config import FilterUpdateRequest
+        from app.services.config_file_service import update_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "sshd.conf", _FILTER_CONF)
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ), patch(
+            "app.services.config_file_service.jail_service.reload_all",
+            new=AsyncMock(),
+        ) as mock_reload:
+            await update_filter(
+                str(tmp_path),
+                "/fake.sock",
+                "sshd",
+                FilterUpdateRequest(journalmatch="_SYSTEMD_UNIT=sshd.service"),
+                do_reload=True,
+            )
+
+        mock_reload.assert_awaited_once()
+
+
+# ---------------------------------------------------------------------------
+# create_filter (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+class TestCreateFilter:
+    async def test_creates_local_file(self, tmp_path: Path) -> None:
+        from app.models.config import FilterCreateRequest
+        from app.services.config_file_service import create_filter
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ):
+            result = await create_filter(
+                str(tmp_path),
+                "/fake.sock",
+                FilterCreateRequest(
+                    name="my-custom",
+                    failregex=[r"^fail from <HOST>"],
+                ),
+            )
+
+        local = tmp_path / "filter.d" / "my-custom.local"
+        assert local.is_file()
+        assert result.name == "my-custom"
+        assert result.source_file.endswith("my-custom.local")
+
+    async def test_raises_already_exists_when_conf_exists(self, tmp_path: Path) -> None:
+        from app.models.config import FilterCreateRequest
+        from app.services.config_file_service import FilterAlreadyExistsError, create_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "sshd.conf", _FILTER_CONF)
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ), pytest.raises(FilterAlreadyExistsError):
+            await create_filter(
+                str(tmp_path),
+                "/fake.sock",
+                FilterCreateRequest(name="sshd"),
+            )
+
+    async def test_raises_already_exists_when_local_exists(self, tmp_path: Path) -> None:
+        from app.models.config import FilterCreateRequest
+        from app.services.config_file_service import FilterAlreadyExistsError, create_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "custom.local", "[Definition]\n")
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ), pytest.raises(FilterAlreadyExistsError):
+            await create_filter(
+                str(tmp_path),
+                "/fake.sock",
+                FilterCreateRequest(name="custom"),
+            )
+
+    async def test_raises_invalid_regex(self, tmp_path: Path) -> None:
+        from app.models.config import FilterCreateRequest
+        from app.services.config_file_service import FilterInvalidRegexError, create_filter
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ), pytest.raises(FilterInvalidRegexError):
+            await create_filter(
+                str(tmp_path),
+                "/fake.sock",
+                FilterCreateRequest(name="bad", failregex=[r"[unclosed"]),
+            )
+
+    async def test_raises_filter_name_error_for_invalid_name(self, tmp_path: Path) -> None:
+        from app.models.config import FilterCreateRequest
+        from app.services.config_file_service import FilterNameError, create_filter
+
+        with pytest.raises(FilterNameError):
+            await create_filter(
+                str(tmp_path),
+                "/fake.sock",
+                FilterCreateRequest(name="../etc/evil"),
+            )
+
+    async def test_triggers_reload_when_requested(self, tmp_path: Path) -> None:
+        from app.models.config import FilterCreateRequest
+        from app.services.config_file_service import create_filter
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ), patch(
+            "app.services.config_file_service.jail_service.reload_all",
+            new=AsyncMock(),
+        ) as mock_reload:
+            await create_filter(
+                str(tmp_path),
+                "/fake.sock",
+                FilterCreateRequest(name="newfilter"),
+                do_reload=True,
+            )
+
+        mock_reload.assert_awaited_once()
+
+
+# ---------------------------------------------------------------------------
+# delete_filter (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+class TestDeleteFilter:
+    async def test_deletes_local_file_when_conf_and_local_exist(
+        self, tmp_path: Path
+    ) -> None:
+        from app.services.config_file_service import delete_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "sshd.conf", _FILTER_CONF)
+        _write(filter_d / "sshd.local", "[Definition]\n")
+
+        await delete_filter(str(tmp_path), "sshd")
+
+        assert not (filter_d / "sshd.local").exists()
+        assert (filter_d / "sshd.conf").exists()
+
+    async def test_deletes_local_only_filter(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import delete_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "custom.local", "[Definition]\n")
+
+        await delete_filter(str(tmp_path), "custom")
+
+        assert not (filter_d / "custom.local").exists()
+
+    async def test_raises_readonly_for_conf_only(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import FilterReadonlyError, delete_filter
+
+        filter_d = tmp_path / "filter.d"
+        _write(filter_d / "sshd.conf", _FILTER_CONF)
+
+        with pytest.raises(FilterReadonlyError):
+            await delete_filter(str(tmp_path), "sshd")
+
+    async def test_raises_not_found_for_missing_filter(self, tmp_path: Path) -> None:
+        from app.services.config_file_service import FilterNotFoundError, delete_filter
+
+        with pytest.raises(FilterNotFoundError):
+            await delete_filter(str(tmp_path), "nonexistent")
+
+    async def test_accepts_filter_name_error_for_invalid_name(
+        self, tmp_path: Path
+    ) -> None:
+        from app.services.config_file_service import FilterNameError, delete_filter
+
+        with pytest.raises(FilterNameError):
+            await delete_filter(str(tmp_path), "../evil")
+
+
+# ---------------------------------------------------------------------------
+# assign_filter_to_jail (Task 2.2)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+class TestAssignFilterToJail:
+    async def test_writes_filter_key_to_jail_local(self, tmp_path: Path) -> None:
+        from app.models.config import AssignFilterRequest
+        from app.services.config_file_service import assign_filter_to_jail
+
+        # Setup: jail.conf with sshd jail, filter.conf for "myfilter"
+        _write(tmp_path / "jail.conf", JAIL_CONF)
+        _write(tmp_path / "filter.d" / "myfilter.conf", _FILTER_CONF)
+
+        with patch(
+            "app.services.config_file_service._get_active_jail_names",
+            new=AsyncMock(return_value=set()),
+        ):
+            await assign_filter_to_jail(
+                str(tmp_path),
+                "/fake.sock",
+                "sshd",
+                AssignFilterRequest(filter_name="myfilter"),
+            )
+
+        local = tmp_path / "jail.d" / "sshd.local"
+        assert local.is_file()
+        content = local.read_text()
+        assert "myfilter" in content
+
+    async def test_raises_jail_not_found(self, tmp_path: Path) -> None:
+        from app.models.config import AssignFilterRequest
+        from app.services.config_file_service import (
+            JailNotFoundInConfigError,
+            assign_filter_to_jail,
+        )
+
+        _write(tmp_path / "filter.d" / "sshd.conf", _FILTER_CONF)
+
+        with pytest.raises(JailNotFoundInConfigError):
+            await assign_filter_to_jail(
+                str(tmp_path),
+                "/fake.sock",
+                "nonexistent-jail",
+                AssignFilterRequest(filter_name="sshd"),
+            )
+
+    async def test_raises_filter_not_found(self, tmp_path: Path) -> None:
+        from app.models.config import AssignFilterRequest
+        from app.services.config_file_service import FilterNotFoundError, assign_filter_to_jail
+
+        _write(tmp_path / "jail.conf", JAIL_CONF)
+
+        with pytest.raises(FilterNotFoundError):
+            await assign_filter_to_jail(
+                str(tmp_path),
+                "/fake.sock",
+                "sshd",
+                AssignFilterRequest(filter_name="nonexistent-filter"),
+            )
+
+    async def test_raises_jail_name_error_for_invalid_name(self, tmp_path: Path) -> None:
+        from app.models.config import AssignFilterRequest
+        from app.services.config_file_service import JailNameError, assign_filter_to_jail
+
+        with pytest.raises(JailNameError):
+            await assign_filter_to_jail(
+                str(tmp_path),
+                "/fake.sock",
+                "../etc/evil",
+                AssignFilterRequest(filter_name="sshd"),
+            )
+
+    async def test_raises_filter_name_error_for_invalid_filter(
+        self, tmp_path: Path
+    ) -> None:
+        from app.models.config import AssignFilterRequest
+        from app.services.config_file_service import FilterNameError, assign_filter_to_jail
+
+        with pytest.raises(FilterNameError):
+            await assign_filter_to_jail(
+                str(tmp_path),
+                "/fake.sock",
+                "sshd",
+                AssignFilterRequest(filter_name="../etc/evil"),
+            )
+
+    async def test_triggers_reload_when_requested(self, tmp_path: Path) -> None:
+        from app.models.config import AssignFilterRequest
+        from app.services.config_file_service import assign_filter_to_jail
+
+        _write(tmp_path / "jail.conf", JAIL_CONF)
+        _write(tmp_path / "filter.d" / "myfilter.conf", _FILTER_CONF)
+
+        with patch(
+            "app.services.config_file_service.jail_service.reload_all",
+            new=AsyncMock(),
+        ) as mock_reload:
+            await assign_filter_to_jail(
+                str(tmp_path),
+                "/fake.sock",
+                "sshd",
+                AssignFilterRequest(filter_name="myfilter"),
+                do_reload=True,
+            )
+
+        mock_reload.assert_awaited_once()
+