refactor(release): make tech_string a derived property

ParsedRelease.tech_string was a stored str field re-computed in two
places (assemble() at parse time, enrich_from_probe() after the probe).
The second site was a reactive fix (e79ca46) for filename builders that
saw a stale value. Turn it into an @property so it stays in sync with
quality/source/codec by construction.

- Drop the field from the dataclass + the key from assemble()'s dict.
- Drop tech_string="" from parse_release's malformed-name fallback.
- Drop the manual recomputation at the end of enrich_from_probe.
- Inject the property into asdict() result in the fixtures runner
  (same treatment as is_season_pack).
- Update tests that passed tech_string= to the constructor; rewrite the
  TestTechString case that mutated p.tech_string manually.

tests/application/test_enrich_from_probe.py

@@ -46,7 +46,6 @@ def _bare(**overrides) -> ParsedRelease:
         source=None,
         codec=None,
         group="UNKNOWN",
-        tech_string="",
     )
     defaults.update(overrides)
     return ParsedRelease(**defaults)
@@ -218,8 +217,9 @@ class TestLanguages:
 
 
 class TestTechString:
-    """tech_string drives the filename builders; it must be re-derived
-    whenever quality / source / codec change."""
+    """tech_string is a derived property on ParsedRelease: it always
+    reflects the current quality/source/codec. Enrichment never writes
+    it directly — it stays in sync by construction."""
 
     def test_rebuilt_from_filled_quality_and_codec(self):
         p = _bare()
@@ -239,9 +239,9 @@ class TestTechString:
         assert p.tech_string == "1080p.BluRay.x265"
 
     def test_unchanged_when_no_enrichable_video_info(self):
-        # No video info → nothing to fill → tech_string stays as it was.
+        # No video info → nothing to fill → derived tech_string stays as it was.
         p = _bare(quality="2160p", source="WEB-DL", codec="x265")
-        p.tech_string = "2160p.WEB-DL.x265"
+        assert p.tech_string == "2160p.WEB-DL.x265"
         enrich_from_probe(p, MediaInfo())
         assert p.tech_string == "2160p.WEB-DL.x265"
 

tests/domain/release/test_parser_v2_easy.py

@@ -123,7 +123,6 @@ class TestAssemble:
         assert fields["source"] == "WEBRip"
         assert fields["codec"] == "x265"
         assert fields["group"] == "KONTRAST"
-        assert fields["tech_string"] == "1080p.WEBRip.x265"
         assert fields["media_type"] == "movie"
         assert fields["site_tag"] is None
 
@@ -150,7 +149,8 @@ class TestAssemble:
         assert fields["season"] == 2
         assert fields["episode"] is None  # season pack
         assert fields["source"] is None  # ELiTE omits it
-        assert fields["tech_string"] == "1080p.x265"
+        assert fields["quality"] == "1080p"
+        assert fields["codec"] == "x265"
         assert fields["group"] == "ELiTE"
 
 

tests/domain/release/test_parser_v2_scoring.py

@@ -78,7 +78,6 @@ def _movie(year: int = 2020, **overrides) -> ParsedRelease:
         source="BluRay",
         codec="x264",
         group="GROUP",
-        tech_string="1080p.BluRay.x264",
         media_type=MediaTypeToken.MOVIE,
         parse_path=ParsePath.DIRECT,
     )
@@ -120,7 +119,6 @@ class TestComputeScore:
             source="WEBRip",
             codec="x265",
             group="KONTRAST",
-            tech_string="1080p.WEBRip.x265",
             media_type=MediaTypeToken.TV_SHOW,
             parse_path=ParsePath.DIRECT,
         )
@@ -231,7 +229,6 @@ class TestCollectors:
             source=None,
             codec=None,
             group="UNKNOWN",
-            tech_string="",
             media_type=MediaTypeToken.UNKNOWN,
             parse_path=ParsePath.DIRECT,
         )

tests/domain/test_release_fixtures.py

@@ -44,8 +44,10 @@ def test_parse_matches_fixture(fixture: ReleaseFixture, tmp_path) -> None:
 
     parsed, _report = parse_release(fixture.release_name, _KB)
     result = asdict(parsed)
-    # ``is_season_pack`` is a @property — asdict() does not include it.
+    # ``is_season_pack`` and ``tech_string`` are @property values —
+    # ``asdict()`` does not include them.
     result["is_season_pack"] = parsed.is_season_pack
+    result["tech_string"] = parsed.tech_string
 
     for field, expected in fixture.expected_parsed.items():
         assert field in result, (