refactor(subtitles): introduce SubtitleKnowledge Protocol port

Domain services (SubtitleIdentifier, PatternDetector) used to import the
concrete SubtitleKnowledgeBase class directly from infrastructure for
their type hint. With this commit they depend on a structural Protocol
in alfred/domain/subtitles/ports/knowledge.py declaring just the 7
read-only query methods the domain actually consumes.

The concrete YAML-backed SubtitleKnowledgeBase in infrastructure remains
the sole adapter — no rename, no shim. With this change
alfred/domain/subtitles/ has zero imports from alfred/infrastructure/.

Also extend the changelog entry covering the full domain-io-extraction
branch.

CHANGELOG.md

@@ -143,6 +143,17 @@ callers).
     an explicit `default_rules: SubtitleMatchingRules` parameter. The
     `ManageSubtitles` use case loads defaults from the KB once and
     passes them in.
+  - **`SubtitleKnowledge` Protocol port** at
+    `alfred/domain/subtitles/ports/knowledge.py` declares the read-only
+    query surface domain services consume (7 methods:
+    `known_extensions`, `format_for_extension`, `language_for_token`,
+    `is_known_lang_token`, `type_for_token`, `is_known_type_token`,
+    `patterns`). `SubtitleIdentifier` and `PatternDetector` depend on
+    this Protocol instead of the concrete `SubtitleKnowledgeBase` from
+    infrastructure — `domain/subtitles/` now has zero imports from
+    `infrastructure/`. The remaining domain → infra leak
+    (`domain/release/` loading separator YAML at import-time) is
+    documented in tech-debt and scheduled for its own branch.
 - **`to_dot_folder_name(title)` helper** in
   `alfred/domain/shared/value_objects.py` — extracts the
   `re.sub(r"[^\w\s\.\-]", "", title).replace(" ", ".")` pattern that was

alfred/domain/subtitles/ports/__init__.py

@@ -0,0 +1,6 @@
+"""Domain ports for the subtitles domain — Protocol-based abstractions
+that decouple domain services from concrete infrastructure adapters."""
+
+from .knowledge import SubtitleKnowledge
+
+__all__ = ["SubtitleKnowledge"]

alfred/domain/subtitles/ports/knowledge.py

@@ -0,0 +1,38 @@
+"""SubtitleKnowledge port — the query surface domain services need from the
+subtitle knowledge base, expressed as a Protocol so the domain never imports
+the infrastructure adapter that backs it.
+
+The concrete implementation lives in
+``alfred/infrastructure/knowledge/subtitles/base.py`` (the YAML-backed
+``SubtitleKnowledgeBase``). Tests can supply any object that satisfies this
+structural contract.
+"""
+
+from __future__ import annotations
+
+from typing import Protocol
+
+from ..value_objects import SubtitleFormat, SubtitleLanguage, SubtitlePattern, SubtitleType
+
+
+class SubtitleKnowledge(Protocol):
+    """Read-only query surface for subtitle knowledge consumed by the domain.
+
+    Only the methods that domain services actually call belong here — anything
+    else (defaults loading, reload, pattern groups, raw dicts) stays on the
+    concrete class and is reserved for the application layer.
+    """
+
+    def known_extensions(self) -> set[str]: ...
+
+    def format_for_extension(self, ext: str) -> SubtitleFormat | None: ...
+
+    def language_for_token(self, token: str) -> SubtitleLanguage | None: ...
+
+    def is_known_lang_token(self, token: str) -> bool: ...
+
+    def type_for_token(self, token: str) -> SubtitleType | None: ...
+
+    def is_known_type_token(self, token: str) -> bool: ...
+
+    def patterns(self) -> dict[str, SubtitlePattern]: ...

alfred/domain/subtitles/services/identifier.py

@@ -4,9 +4,8 @@ import logging
 import re
 from pathlib import Path
 
-from alfred.infrastructure.knowledge.subtitles.base import SubtitleKnowledgeBase
-
 from ...shared.ports import FilesystemScanner, MediaProber
+from ..ports import SubtitleKnowledge
 from ...shared.value_objects import ImdbId
 from ..entities import MediaSubtitleMetadata, SubtitleCandidate
 from ..value_objects import ScanStrategy, SubtitlePattern, SubtitleType
@@ -59,7 +58,7 @@ class SubtitleIdentifier:
 
     def __init__(
         self,
-        kb: SubtitleKnowledgeBase,
+        kb: SubtitleKnowledge,
         prober: MediaProber,
         scanner: FilesystemScanner,
     ):

alfred/domain/subtitles/services/pattern_detector.py

@@ -3,9 +3,8 @@
 import logging
 from pathlib import Path
 
-from alfred.infrastructure.knowledge.subtitles.base import SubtitleKnowledgeBase
-
 from ...shared.ports import FilesystemScanner, MediaProber
+from ..ports import SubtitleKnowledge
 from ..value_objects import ScanStrategy, SubtitlePattern
 
 logger = logging.getLogger(__name__)
@@ -22,7 +21,7 @@ class PatternDetector:
 
     def __init__(
         self,
-        kb: SubtitleKnowledgeBase,
+        kb: SubtitleKnowledge,
         prober: MediaProber,
         scanner: FilesystemScanner,
     ):