fix(engines): keep the license reason so Supertonic-3 and PocketTTS can be enabled

The Model Catalogue shows an engine's license Accept button only when its
reason matches /license not accepted/i. public_backends() replaces probe
text with owned sentences, and no category covered a license gate, so the
reason arrived as the generic "Engine unavailable" line and the only way
to enable Supertonic-3 or PocketTTS never rendered (#2017).

A license category, matched first, keeps those words. The test reads the
regex out of EngineCompatibilityMatrix.jsx, so a wording change on either
side fails CI instead of silently hiding the button.

CHANGELOG.md

@@ -9,6 +9,7 @@ the frozen-backend fallback mirror it for their toolchains.
 ## [Unreleased]
 
 **Highlights**
+- Supertonic-3 and PocketTTS show their license Accept button again, so they can be enabled (#2017)
 - A pronunciation entry that is stored but not applied yet says so, instead of looking like it did not match (#1949)
 - A bare 500 report now names the backend error class, so two unrelated faults stop filing the same issue (#1773)
 - A rejected dubbing source language now names the code it rejected (#1960)

backend/api/public_engine_metadata.py

@@ -43,6 +43,15 @@ _UNAVAILABLE_NOT_INSTALLED = (
     "This engine's package isn't installed yet. Install it from "
     "Model Catalogue → Engines."
 )
+# An engine gated behind an in-app license review (Supertonic-3, PocketTTS).
+# The Model Catalogue shows its Accept button only when the reason matches
+# /license not accepted/i (EngineCompatibilityMatrix.reasonMentionsLicense), so
+# this sentence must keep those words: collapsing it into the generic line hid
+# the only way to enable those engines.
+_UNAVAILABLE_LICENSE = (
+    "License not accepted yet. Review and accept it in "
+    "Model Catalogue → Engines to enable this engine."
+)
 _UNAVAILABLE_NEEDS_CONFIG = (
     "This engine needs to be configured before it can run. Open "
     "Model Catalogue → Engines to finish setting it up."
@@ -56,6 +65,9 @@ _UNAVAILABLE_FILE_MISSING = (
 # missing file often also says "not installed", and the file case has the more
 # useful remedy of the two.
 _UNAVAILABLE_SIGNATURES = (
+    # First: its probe text also says "Open Model Catalogue", and the
+    # license is the one gap only the user can close.
+    (_UNAVAILABLE_LICENSE, ("license not accepted",)),
     (_UNAVAILABLE_FILE_MISSING, (
         "file is missing", "file is empty", "file is unreadable",
         "script missing", "binary", "not found at",

tests/test_engine_unavailable_reason_1866.py

@@ -106,3 +106,38 @@ def test_the_input_row_is_not_mutated():
     original = {"id": "e", "reason": "voxcpm package not installed."}
     public_backends([original])
     assert original["reason"] == "voxcpm package not installed."
+
+
+@pytest.mark.parametrize(
+    "diagnostic",
+    [
+        # The engines' own wording (Supertonic3Backend / PocketTTSBackend).
+        "Supertonic-3 license not accepted. Open Model Catalogue → Engines → "
+        "Supertonic-3 and click Accept to enable. (MIT code license + OpenRAIL-M "
+        "model license.)",
+        "PocketTTS license not accepted. Open Model Catalogue → Engines → "
+        "PocketTTS and review the MIT code license, CC-BY-4.0 model license, "
+        "and gated-access conditions before enabling it.",
+    ],
+)
+@pytest.mark.parametrize("one_click", [None, True, False])
+def test_a_license_gate_keeps_the_words_the_accept_button_needs(diagnostic, one_click):
+    """The Accept button renders only when the reason matches the matrix's
+    /license not accepted/i. Collapsing the reason into the generic line left
+    Supertonic-3 and PocketTTS with no way to be enabled."""
+    import re
+    from pathlib import Path
+
+    row = {"id": "e", "reason": diagnostic}
+    if one_click is not None:
+        row["one_click_install"] = one_click
+    reason = public_backends([row])[0]["reason"]
+
+    matrix = (
+        Path(__file__).resolve().parents[1]
+        / "frontend/src/components/EngineCompatibilityMatrix.jsx"
+    ).read_text(encoding="utf-8")
+    m = re.search(r"function reasonMentionsLicense\(reason\)[^}]*?return /([^/]+)/(\w*)\.test", matrix, re.S)
+    assert m, "EngineCompatibilityMatrix.reasonMentionsLicense changed shape"
+    flags = re.I if "i" in m.group(2) else 0
+    assert re.search(m.group(1), reason, flags), reason