Implementation Plan: T5-P4-A5-WP1 Replace three-way gpt-5.5 collision in CODEX_MODEL_ALIASES

src/autoskillit/core/__init__.pyi

@@ -359,6 +359,7 @@ from .types import extract_positional_args as extract_positional_args
 from .types import extract_skill_name as extract_skill_name
 from .types import fleet_error as fleet_error
 from .types import is_path_like_token as is_path_like_token
+from .types import model_class as model_class
 from .types import resolve_payload_field as resolve_payload_field
 from .types import resolve_skill_name as resolve_skill_name
 from .types import resolve_target_skill as resolve_target_skill

src/autoskillit/core/types/_type_backend.py

@@ -29,6 +29,7 @@
     "CodexEventData",
     "SessionEvent",
     "AgentSessionResult",
+    "model_class",
     "strip_context_window_suffix",
 ]
 
@@ -169,9 +170,9 @@ class BackendCapabilities:
 }
 
 CODEX_MODEL_ALIASES: dict[str, str] = {
-    "sonnet": "gpt-5.5",
+    "sonnet": "gpt-5.4",
     "opus": "gpt-5.5",
-    "haiku": "gpt-5.5",
+    "haiku": "gpt-5.4-mini",
 }
 
 CODEX_EFFORT_MAPPING: dict[str, str] = {
@@ -180,6 +181,14 @@ class BackendCapabilities:
     "haiku": "medium",
 }
 
+_CODEX_MODEL_REVERSE: dict[str, str] = {v: k for k, v in CODEX_MODEL_ALIASES.items()}
+_codex_alias_values = list(CODEX_MODEL_ALIASES.values())
+assert len(_CODEX_MODEL_REVERSE) == len(CODEX_MODEL_ALIASES), (
+    "CODEX_MODEL_ALIASES values must be unique — duplicate makes an alias unreachable "
+    f"via model_class(). Duplicates: "
+    f"{[v for v in _codex_alias_values if _codex_alias_values.count(v) > 1]}"
+)
+
 
 @dataclass(frozen=True, slots=True)
 class ModelTranslation:
@@ -198,6 +207,13 @@ def strip_context_window_suffix(model: str) -> str:
     return _CONTEXT_WINDOW_SUFFIX_RE.sub("", model)
 
 
+def model_class(model: str) -> str:
+    base = strip_context_window_suffix(model)
+    if base in CLAUDE_MODEL_ALIASES:
+        return base
+    return _CODEX_MODEL_REVERSE.get(base, base)
+
+
 CLAUDE_CODE_CAPABILITIES: BackendCapabilities = BackendCapabilities(
     channel_b_capable=True,
     pty_required=True,

tests/arch/test_backend_translate_model.py

@@ -66,3 +66,19 @@ def test_translate_model_called_at_terminal_model_sites() -> None:
                 f"{backend_name}.{method_name} appends --model but does not call "
                 f"self.translate_model"
             )
+
+
+def test_translate_model_distinct_per_alias_class() -> None:
+    from autoskillit.core.types._type_backend import CLAUDE_MODEL_ALIASES
+
+    alias_keys = list(CLAUDE_MODEL_ALIASES.keys())
+    for backend_name, cls in BACKEND_REGISTRY.items():
+        try:
+            backend = cls()
+        except TypeError:
+            pytest.skip(f"{backend_name}: requires constructor args — cannot validate")
+        translated = [backend.translate_model(k) for k in alias_keys]
+        assert len(translated) == len(set(translated)), (
+            f"{backend_name}: translate_model produced duplicate outputs for alias keys "
+            f"{alias_keys}: {translated}"
+        )

tests/core/test_backend_dataclasses.py

@@ -204,6 +204,7 @@ def test_backend_module_all_exhaustive():
         "CodexEventData",
         "SessionEvent",
         "AgentSessionResult",
+        "model_class",
         "strip_context_window_suffix",
     }
 

tests/execution/backends/test_model_translation.py

@@ -183,3 +183,31 @@ def test_interactive_cmd_has_effort(self) -> None:
     def test_no_effort_for_native_model_in_headless_cmd(self) -> None:
         spec = CodexBackend().build_headless_cmd("test prompt", model="gpt-5.5")
         assert "model_reasoning_effort" not in " ".join(spec.cmd)
+
+
+class TestModelClass:
+    def test_canonical_keys(self) -> None:
+        from autoskillit.core import model_class
+
+        assert model_class("opus") == "opus"
+        assert model_class("sonnet") == "sonnet"
+        assert model_class("haiku") == "haiku"
+
+    def test_suffix_stripping(self) -> None:
+        from autoskillit.core import model_class
+
+        assert model_class("opus[1m]") == "opus"
+        assert model_class("sonnet[1m]") == "sonnet"
+        assert model_class("haiku[1m]") == "haiku"
+
+    def test_codex_reverse_map(self) -> None:
+        from autoskillit.core import model_class
+
+        assert model_class(CODEX_MODEL_ALIASES["opus"]) == "opus"
+        assert model_class(CODEX_MODEL_ALIASES["sonnet"]) == "sonnet"
+        assert model_class(CODEX_MODEL_ALIASES["haiku"]) == "haiku"
+
+    def test_unknown_passthrough(self) -> None:
+        from autoskillit.core import model_class
+
+        assert model_class("custom-model-xyz") == "custom-model-xyz"

tests/execution/test_model_alias_registry.py

@@ -6,7 +6,7 @@
 
 pytestmark = [pytest.mark.layer("execution"), pytest.mark.small]
 
-VALID_CODEX_MODEL_IDS: frozenset[str] = frozenset({"gpt-5.5"})
+VALID_CODEX_MODEL_IDS: frozenset[str] = frozenset({"gpt-5.4", "gpt-5.4-mini", "gpt-5.5"})
 
 VALID_CLAUDE_MODEL_IDS: frozenset[str] = frozenset({"sonnet", "opus", "haiku"})