feat(use-cases): add inline use-case definitions

Adds RequestIX.use_case_inline so callers can define ad-hoc extraction
schemas in the request itself, bypassing the backend registry. The
pipeline builds a fresh (Request, Response) Pydantic class pair per
call via ix.use_cases.inline.build_use_case_classes; structural errors
(dup field, bad identifier, choices-on-non-str, empty fields) raise
IX_001_001 to match the registry-miss path. Inline wins when both
use_case and use_case_inline are set. Existing REST callers see no
behavioural change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -6,6 +6,8 @@ Designed to be used by other on-prem services (e.g. mammon) as a reliable fallba
 
 Status: MVP deployed (2026-04-18) at `http://192.168.68.42:8994` — LAN only. Full reference spec at `docs/spec-core-pipeline.md`; MVP spec at `docs/superpowers/specs/2026-04-18-ix-mvp-design.md`; deploy runbook at `docs/deployment.md`.
 
+Use cases: the built-in registry lives in `src/ix/use_cases/__init__.py` (`bank_statement_header` for MVP). Callers without a registered entry can ship an ad-hoc schema inline via `RequestIX.use_case_inline` (see README "Ad-hoc use cases"); the pipeline builds the Pydantic classes on the fly per request.
+
 ## Guiding Principles
 
 - **On-prem always.** All LLM inference, OCR, and user-data processing run on the home server (192.168.68.42). No cloud APIs — OpenAI, Anthropic, Azure, AWS Bedrock/Textract, Google Document AI, Mistral, etc. are not to be used for user data or inference. LLM backend is Ollama (:11434); OCR runs locally (pluggable `OCRClient` interface, first engine: Surya on the RTX 3090); job state lives in local Postgres on the postgis container. The spec's references to Azure / AWS / OpenAI are examples to *replace*, not inherit.

README.md

@@ -40,6 +40,28 @@ curl -X POST http://192.168.68.42:8994/jobs \
 
 Poll `GET /jobs/{job_id}` until `status` is `done` or `error`. Optionally pass `callback_url` to receive a webhook on completion (one-shot, no retry; polling stays authoritative).
 
+### Ad-hoc use cases
+
+For one-offs where a registered use case doesn't exist yet, ship the schema inline:
+
+```jsonc
+{
+  "use_case": "adhoc-invoice",        // free-form label (logs/metrics only)
+  "use_case_inline": {
+    "use_case_name": "Invoice totals",
+    "system_prompt": "Extract vendor and total amount.",
+    "fields": [
+      {"name": "vendor", "type": "str", "required": true},
+      {"name": "total",  "type": "decimal"},
+      {"name": "currency", "type": "str", "choices": ["USD", "EUR", "CHF"]}
+    ]
+  },
+  // ...ix_client_id, request_id, context...
+}
+```
+
+When `use_case_inline` is set, the pipeline builds the response schema on the fly and skips the registry. Supported types: `str`, `int`, `float`, `decimal`, `date`, `datetime`, `bool`. `choices` is only allowed on `str` fields. Precedence: inline wins over `use_case` when both are present.
+
 Full REST surface + provenance response shape documented in the MVP design spec.
 
 ## Running locally

docs/superpowers/specs/2026-04-18-ix-mvp-design.md

@@ -108,6 +108,25 @@ class ProvenanceOptions(BaseModel):
 
 **Dropped from spec (no-ops under MVP):** `OCROptions.computer_vision_scaling_factor`, `include_page_tags` (always on), `GenAIOptions.use_vision`/`vision_scaling_factor`/`vision_detail`/`reasoning_effort`, `ProvenanceOptions.granularity`/`include_bounding_boxes`/`source_type`/`min_confidence`, `RequestIX.version`.
 
+**Ad-hoc use cases (post-MVP add-on).** `RequestIX` carries an optional `use_case_inline: InlineUseCase | None = None`. When set, the pipeline builds the `(Request, Response)` Pydantic class pair on the fly from that inline definition and **skips the registry lookup entirely** — the `use_case` field becomes a free-form label (still required for metrics / logging). Inline definitions look like:
+
+```python
+class UseCaseFieldDef(BaseModel):
+    name: str                               # valid Python identifier
+    type: Literal["str", "int", "float", "decimal", "date", "datetime", "bool"]
+    required: bool = False
+    description: str | None = None
+    choices: list[str] | None = None        # str-typed fields only; builds Literal[*choices]
+
+class InlineUseCase(BaseModel):
+    use_case_name: str
+    system_prompt: str
+    default_model: str | None = None
+    fields: list[UseCaseFieldDef]
+```
+
+Precedence: `use_case_inline` wins when both are set. Structural errors (dup field name, invalid identifier, `choices` on a non-str type, empty fields list) raise `IX_001_001` (same code as registry miss). The builder lives in `ix.use_cases.inline.build_use_case_classes` and returns fresh classes per call — the pipeline never caches them.
+
 ### ResponseIX
 
 Identical to spec §2.2 except `FieldProvenance` gains two fields:

src/ix/contracts/request.py

@@ -83,6 +83,44 @@ class Options(BaseModel):
     provenance: ProvenanceOptions = Field(default_factory=ProvenanceOptions)
 
 
+class UseCaseFieldDef(BaseModel):
+    """One field in an ad-hoc, caller-defined extraction schema.
+
+    The UI (and any other caller that doesn't want to wait on a backend
+    registry entry) ships one of these per desired output field. The pipeline
+    builds a fresh Pydantic response class from the list on each request.
+
+    ``choices`` only applies to ``type == "str"`` — it turns the field into a
+    ``Literal[*choices]``. For any other type the builder raises
+    ``IX_001_001``.
+    """
+
+    model_config = ConfigDict(extra="forbid")
+
+    name: str  # must be a valid Python identifier
+    type: Literal["str", "int", "float", "decimal", "date", "datetime", "bool"]
+    required: bool = False
+    description: str | None = None
+    choices: list[str] | None = None
+
+
+class InlineUseCase(BaseModel):
+    """Caller-defined use case bundled into the :class:`RequestIX`.
+
+    When present on a request, the pipeline builds the ``(Request, Response)``
+    Pydantic class pair on the fly from :attr:`fields` and skips the
+    registered use-case lookup. The registry-based ``use_case`` field is still
+    required on the request for metrics/logging but becomes a free-form label.
+    """
+
+    model_config = ConfigDict(extra="forbid")
+
+    use_case_name: str
+    system_prompt: str
+    default_model: str | None = None
+    fields: list[UseCaseFieldDef]
+
+
 class RequestIX(BaseModel):
     """Top-level job request.
 
@@ -90,6 +128,12 @@ class RequestIX(BaseModel):
     it; the REST adapter / pg-queue adapter populates it on insert. The field
     is kept here so the contract is closed-over-construction round-trips
     (e.g. when the worker re-hydrates a job out of the store).
+
+    When ``use_case_inline`` is present, the pipeline uses it verbatim to
+    build an ad-hoc ``(Request, Response)`` class pair and skips the registry
+    lookup; ``use_case`` becomes a free-form label (still required for
+    metrics/logging). When ``use_case_inline`` is absent, ``use_case`` is
+    looked up in :data:`ix.use_cases.REGISTRY` as before.
     """
 
     model_config = ConfigDict(extra="forbid")
@@ -101,3 +145,4 @@ class RequestIX(BaseModel):
     context: Context
     options: Options = Field(default_factory=Options)
     callback_url: str | None = None
+    use_case_inline: InlineUseCase | None = None

src/ix/pipeline/setup_step.py

@@ -34,6 +34,7 @@ from ix.ingestion import (
 )
 from ix.pipeline.step import Step
 from ix.use_cases import get_use_case
+from ix.use_cases.inline import build_use_case_classes
 
 
 class _Fetcher(Protocol):
@@ -88,9 +89,18 @@ class SetupStep(Step):
     async def process(
         self, request_ix: RequestIX, response_ix: ResponseIX
     ) -> ResponseIX:
-        # 1. Load the use-case pair — early so an unknown name fails before
-        # we waste time downloading files.
-        use_case_request_cls, use_case_response_cls = get_use_case(request_ix.use_case)
+        # 1. Load the use-case pair — either from the caller's inline
+        # definition (wins over registry) or from the registry by name.
+        # Done early so an unknown name / bad inline definition fails
+        # before we waste time downloading files.
+        if request_ix.use_case_inline is not None:
+            use_case_request_cls, use_case_response_cls = build_use_case_classes(
+                request_ix.use_case_inline
+            )
+        else:
+            use_case_request_cls, use_case_response_cls = get_use_case(
+                request_ix.use_case
+            )
         use_case_request = use_case_request_cls()
 
         # 2. Resolve the per-request scratch directory. ix_id is assigned

src/ix/use_cases/inline.py

@@ -0,0 +1,132 @@
+"""Dynamic Pydantic class builder for caller-supplied use cases.
+
+Input: an :class:`ix.contracts.request.InlineUseCase` carried on the
+:class:`~ix.contracts.request.RequestIX`.
+
+Output: a fresh ``(RequestClass, ResponseClass)`` pair with the same shape
+as a registered use case. The :class:`~ix.pipeline.setup_step.SetupStep`
+calls this when ``request_ix.use_case_inline`` is set, bypassing the
+registry lookup entirely.
+
+The builder returns brand-new classes on every call — safe to call per
+request, so two concurrent jobs can't step on each other's schemas even if
+they happen to share a ``use_case_name``. Validation errors map to
+``IX_001_001`` (same code the registry-miss path uses); the error is
+recoverable from the caller's perspective (fix the JSON and retry), not an
+infra problem.
+"""
+
+from __future__ import annotations
+
+import keyword
+import re
+from datetime import date, datetime
+from decimal import Decimal
+from typing import Any, Literal, cast
+
+from pydantic import BaseModel, ConfigDict, Field, create_model
+
+from ix.contracts.request import InlineUseCase, UseCaseFieldDef
+from ix.errors import IXErrorCode, IXException
+
+# Map the ``UseCaseFieldDef.type`` literal to concrete Python types.
+_TYPE_MAP: dict[str, type] = {
+    "str": str,
+    "int": int,
+    "float": float,
+    "decimal": Decimal,
+    "date": date,
+    "datetime": datetime,
+    "bool": bool,
+}
+
+
+def _fail(detail: str) -> IXException:
+    return IXException(IXErrorCode.IX_001_001, detail=detail)
+
+
+def _valid_field_name(name: str) -> bool:
+    """Require a valid Python identifier that isn't a reserved keyword."""
+
+    return name.isidentifier() and not keyword.iskeyword(name)
+
+
+def _resolve_field_type(field: UseCaseFieldDef) -> Any:
+    """Return the annotation for a single field, with ``choices`` honoured."""
+
+    base = _TYPE_MAP[field.type]
+    if field.choices:
+        if field.type != "str":
+            raise _fail(
+                f"field {field.name!r}: 'choices' is only allowed for "
+                f"type='str' (got {field.type!r})"
+            )
+        return Literal[tuple(field.choices)]  # type: ignore[valid-type]
+    return base
+
+
+def _sanitise_class_name(raw: str) -> str:
+    """``re.sub(r"\\W", "_", name)`` + ``Inline_`` prefix.
+
+    Keeps the generated class name debuggable (shows up in repr / tracebacks)
+    while ensuring it's always a valid Python identifier.
+    """
+
+    return "Inline_" + re.sub(r"\W", "_", raw)
+
+
+def build_use_case_classes(
+    inline: InlineUseCase,
+) -> tuple[type[BaseModel], type[BaseModel]]:
+    """Build a fresh ``(RequestClass, ResponseClass)`` from ``inline``.
+
+    * Every call returns new classes. The caller may cache if desired; the
+      pipeline intentionally does not.
+    * Raises :class:`~ix.errors.IXException` with code
+      :attr:`~ix.errors.IXErrorCode.IX_001_001` on any structural problem
+      (empty fields, bad name, dup name, bad ``choices``).
+    """
+
+    if not inline.fields:
+        raise _fail("inline use case must define at least one field")
+
+    seen: set[str] = set()
+    for fd in inline.fields:
+        if not _valid_field_name(fd.name):
+            raise _fail(f"field name {fd.name!r} is not a valid Python identifier")
+        if fd.name in seen:
+            raise _fail(f"duplicate field name {fd.name!r}")
+        seen.add(fd.name)
+
+    response_fields: dict[str, Any] = {}
+    for fd in inline.fields:
+        annotation = _resolve_field_type(fd)
+        field_info = Field(
+            ...,
+            description=fd.description,
+        ) if fd.required else Field(
+            default=None,
+            description=fd.description,
+        )
+        if not fd.required:
+            annotation = annotation | None
+        response_fields[fd.name] = (annotation, field_info)
+
+    response_cls = create_model(  # type: ignore[call-overload]
+        _sanitise_class_name(inline.use_case_name),
+        __config__=ConfigDict(extra="forbid"),
+        **response_fields,
+    )
+
+    request_cls = create_model(  # type: ignore[call-overload]
+        "Inline_Request_" + re.sub(r"\W", "_", inline.use_case_name),
+        __config__=ConfigDict(extra="forbid"),
+        use_case_name=(str, inline.use_case_name),
+        system_prompt=(str, inline.system_prompt),
+        default_model=(str | None, inline.default_model),
+    )
+
+    return cast(type[BaseModel], request_cls), cast(type[BaseModel], response_cls)
+
+
+__all__ = ["build_use_case_classes"]

tests/unit/test_contracts.py

@@ -31,6 +31,7 @@ from ix.contracts import (
     ResponseIX,
     SegmentCitation,
 )
+from ix.contracts.request import InlineUseCase, UseCaseFieldDef
 
 
 class TestFileRef:
@@ -182,6 +183,32 @@ class TestRequestIX:
         with pytest.raises(ValidationError):
             RequestIX.model_validate({"use_case": "x"})
 
+    def test_use_case_inline_defaults_to_none(self) -> None:
+        r = RequestIX(**self._minimal_payload())
+        assert r.use_case_inline is None
+
+    def test_use_case_inline_roundtrip(self) -> None:
+        payload = self._minimal_payload()
+        payload["use_case_inline"] = {
+            "use_case_name": "adhoc",
+            "system_prompt": "extract stuff",
+            "fields": [
+                {"name": "a", "type": "str", "required": True},
+                {"name": "b", "type": "int"},
+            ],
+        }
+        r = RequestIX.model_validate(payload)
+        assert r.use_case_inline is not None
+        assert isinstance(r.use_case_inline, InlineUseCase)
+        assert r.use_case_inline.use_case_name == "adhoc"
+        assert len(r.use_case_inline.fields) == 2
+        assert isinstance(r.use_case_inline.fields[0], UseCaseFieldDef)
+        # Round-trip through JSON
+        dumped = r.model_dump_json()
+        r2 = RequestIX.model_validate_json(dumped)
+        assert r2.use_case_inline is not None
+        assert r2.use_case_inline.fields[1].type == "int"
+
 
 class TestOCRResult:
     def test_minimal_defaults(self) -> None:

tests/unit/test_setup_step.py

@@ -15,6 +15,7 @@ from ix.contracts import (
     RequestIX,
     ResponseIX,
 )
+from ix.contracts.request import InlineUseCase, UseCaseFieldDef
 from ix.contracts.response import _InternalContext
 from ix.errors import IXErrorCode, IXException
 from ix.ingestion import FetchConfig
@@ -244,6 +245,102 @@ class TestTextOnly:
         assert ctx.texts == ["hello", "there"]
 
 
+class TestInlineUseCase:
+    def _make_inline_request(
+        self,
+        inline: InlineUseCase,
+        use_case: str = "adhoc-label",
+        texts: list[str] | None = None,
+    ) -> RequestIX:
+        return RequestIX(
+            use_case=use_case,
+            use_case_inline=inline,
+            ix_client_id="test",
+            request_id="r-inline",
+            context=Context(files=[], texts=texts or ["hello"]),
+            options=Options(
+                ocr=OCROptions(use_ocr=True),
+                provenance=ProvenanceOptions(include_provenance=True),
+            ),
+        )
+
+    async def test_inline_use_case_overrides_registry(self, tmp_path: Path) -> None:
+        fetcher = FakeFetcher({})
+        ingestor = FakeIngestor([])
+        step = SetupStep(
+            fetcher=fetcher,
+            ingestor=ingestor,
+            tmp_dir=tmp_path / "work",
+            fetch_config=_make_cfg(),
+            mime_detector=_AlwaysMimePdf(),
+        )
+        inline = InlineUseCase(
+            use_case_name="adhoc",
+            system_prompt="Extract things.",
+            fields=[
+                UseCaseFieldDef(name="vendor", type="str", required=True),
+                UseCaseFieldDef(name="amount", type="decimal"),
+            ],
+        )
+        req = self._make_inline_request(inline)
+        resp = _make_response()
+        resp = await step.process(req, resp)
+
+        ctx = resp.context
+        assert ctx is not None
+        # The response class must have been built from our field list.
+        resp_cls = ctx.use_case_response  # type: ignore[union-attr]
+        assert set(resp_cls.model_fields.keys()) == {"vendor", "amount"}
+        # Public display name reflects the inline label.
+        assert resp.use_case_name == "adhoc"
+
+    async def test_inline_precedence_when_both_set(self, tmp_path: Path) -> None:
+        # ``use_case`` is a valid registered name; ``use_case_inline`` is also
+        # present. Inline MUST win (documented precedence).
+        fetcher = FakeFetcher({})
+        ingestor = FakeIngestor([])
+        step = SetupStep(
+            fetcher=fetcher,
+            ingestor=ingestor,
+            tmp_dir=tmp_path / "work",
+            fetch_config=_make_cfg(),
+            mime_detector=_AlwaysMimePdf(),
+        )
+        inline = InlineUseCase(
+            use_case_name="override",
+            system_prompt="override prompt",
+            fields=[UseCaseFieldDef(name="just_me", type="str", required=True)],
+        )
+        req = self._make_inline_request(
+            inline, use_case="bank_statement_header"
+        )
+        resp = await step.process(req, _make_response())
+        resp_cls = resp.context.use_case_response  # type: ignore[union-attr]
+        assert set(resp_cls.model_fields.keys()) == {"just_me"}
+
+    async def test_inline_with_bad_field_raises_ix_001_001(
+        self, tmp_path: Path
+    ) -> None:
+        fetcher = FakeFetcher({})
+        ingestor = FakeIngestor([])
+        step = SetupStep(
+            fetcher=fetcher,
+            ingestor=ingestor,
+            tmp_dir=tmp_path / "work",
+            fetch_config=_make_cfg(),
+            mime_detector=_AlwaysMimePdf(),
+        )
+        inline = InlineUseCase(
+            use_case_name="bad",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="123bad", type="str")],
+        )
+        req = self._make_inline_request(inline)
+        with pytest.raises(IXException) as ei:
+            await step.process(req, _make_response())
+        assert ei.value.code is IXErrorCode.IX_001_001
+
+
 class TestInternalContextShape:
     async def test_context_is_internal_context_instance(self, tmp_path: Path) -> None:
         fetcher = FakeFetcher({})

tests/unit/test_use_case_inline.py

@@ -0,0 +1,313 @@
+"""Tests for :mod:`ix.use_cases.inline` — dynamic Pydantic class builder.
+
+The builder takes an :class:`InlineUseCase` (carried on :class:`RequestIX` as
+``use_case_inline``) and produces a fresh ``(RequestClass, ResponseClass)``
+pair that the pipeline can consume in place of a registered use case.
+"""
+
+from __future__ import annotations
+
+import json
+from datetime import date, datetime
+from decimal import Decimal
+
+import pytest
+from pydantic import BaseModel, ValidationError
+
+from ix.contracts.request import InlineUseCase, UseCaseFieldDef
+from ix.errors import IXErrorCode, IXException
+from ix.use_cases.inline import build_use_case_classes
+
+
+class TestUseCaseFieldDef:
+    def test_minimal(self) -> None:
+        fd = UseCaseFieldDef(name="foo", type="str")
+        assert fd.name == "foo"
+        assert fd.type == "str"
+        assert fd.required is False
+        assert fd.description is None
+        assert fd.choices is None
+
+    def test_extra_forbidden(self) -> None:
+        with pytest.raises(ValidationError):
+            UseCaseFieldDef.model_validate(
+                {"name": "foo", "type": "str", "bogus": 1}
+            )
+
+    def test_invalid_type_rejected(self) -> None:
+        with pytest.raises(ValidationError):
+            UseCaseFieldDef.model_validate({"name": "foo", "type": "list"})
+
+
+class TestInlineUseCaseRoundtrip:
+    def test_json_roundtrip(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="Vendor Total",
+            system_prompt="Extract invoice total and vendor.",
+            default_model="qwen3:14b",
+            fields=[
+                UseCaseFieldDef(name="vendor", type="str", required=True),
+                UseCaseFieldDef(
+                    name="total",
+                    type="decimal",
+                    required=True,
+                    description="total amount due",
+                ),
+                UseCaseFieldDef(
+                    name="currency",
+                    type="str",
+                    choices=["USD", "EUR", "CHF"],
+                ),
+            ],
+        )
+        dumped = iuc.model_dump_json()
+        round = InlineUseCase.model_validate_json(dumped)
+        assert round == iuc
+        # JSON is well-formed
+        json.loads(dumped)
+
+    def test_extra_forbidden(self) -> None:
+        with pytest.raises(ValidationError):
+            InlineUseCase.model_validate(
+                {
+                    "use_case_name": "X",
+                    "system_prompt": "p",
+                    "fields": [],
+                    "bogus": 1,
+                }
+            )
+
+
+class TestBuildBasicTypes:
+    @pytest.mark.parametrize(
+        "type_name, sample_value, bad_value",
+        [
+            ("str", "hello", 123),
+            ("int", 42, "nope"),
+            ("float", 3.14, "nope"),
+            ("bool", True, "nope"),
+        ],
+    )
+    def test_simple_type(
+        self, type_name: str, sample_value: object, bad_value: object
+    ) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="field", type=type_name, required=True)],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        instance = resp_cls(field=sample_value)
+        assert instance.field == sample_value
+        with pytest.raises(ValidationError):
+            resp_cls(field=bad_value)
+
+    def test_decimal_type(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="amount", type="decimal", required=True)],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        instance = resp_cls(amount="12.34")
+        assert isinstance(instance.amount, Decimal)
+        assert instance.amount == Decimal("12.34")
+
+    def test_date_type(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="d", type="date", required=True)],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        instance = resp_cls(d="2026-04-18")
+        assert instance.d == date(2026, 4, 18)
+
+    def test_datetime_type(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="ts", type="datetime", required=True)],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        instance = resp_cls(ts="2026-04-18T10:00:00")
+        assert isinstance(instance.ts, datetime)
+
+
+class TestOptionalVsRequired:
+    def test_required_field_cannot_be_missing(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="must", type="str", required=True)],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        with pytest.raises(ValidationError):
+            resp_cls()
+
+    def test_optional_field_defaults_to_none(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="maybe", type="str", required=False)],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        instance = resp_cls()
+        assert instance.maybe is None
+
+    def test_optional_field_schema_allows_null(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="maybe", type="str", required=False)],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        schema = resp_cls.model_json_schema()
+        # "maybe" accepts string or null
+        prop = schema["properties"]["maybe"]
+        # Pydantic may express Optional as anyOf [str, null] or a type list.
+        # Either is fine — just assert null is allowed somewhere.
+        dumped = json.dumps(prop)
+        assert "null" in dumped
+
+
+class TestChoices:
+    def test_choices_for_str_produces_literal(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[
+                UseCaseFieldDef(
+                    name="kind",
+                    type="str",
+                    required=True,
+                    choices=["a", "b", "c"],
+                )
+            ],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        inst = resp_cls(kind="a")
+        assert inst.kind == "a"
+        with pytest.raises(ValidationError):
+            resp_cls(kind="nope")
+        schema = resp_cls.model_json_schema()
+        # enum or const wind up in a referenced definition; walk the schema
+        dumped = json.dumps(schema)
+        assert '"a"' in dumped and '"b"' in dumped and '"c"' in dumped
+
+    def test_choices_for_non_str_raises_ix_001_001(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[
+                UseCaseFieldDef(
+                    name="kind",
+                    type="int",
+                    required=True,
+                    choices=["1", "2"],
+                )
+            ],
+        )
+        with pytest.raises(IXException) as exc:
+            build_use_case_classes(iuc)
+        assert exc.value.code is IXErrorCode.IX_001_001
+
+    def test_empty_choices_list_ignored(self) -> None:
+        # An explicitly empty list is as-if choices were unset; builder must
+        # not break. If the caller sent choices=[] we treat the field as
+        # plain str.
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[
+                UseCaseFieldDef(
+                    name="kind", type="str", required=True, choices=[]
+                )
+            ],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        inst = resp_cls(kind="anything")
+        assert inst.kind == "anything"
+
+
+class TestValidation:
+    def test_duplicate_field_names_raise(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[
+                UseCaseFieldDef(name="foo", type="str"),
+                UseCaseFieldDef(name="foo", type="int"),
+            ],
+        )
+        with pytest.raises(IXException) as exc:
+            build_use_case_classes(iuc)
+        assert exc.value.code is IXErrorCode.IX_001_001
+
+    def test_invalid_field_name_raises(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="123abc", type="str")],
+        )
+        with pytest.raises(IXException) as exc:
+            build_use_case_classes(iuc)
+        assert exc.value.code is IXErrorCode.IX_001_001
+
+    def test_empty_fields_list_raises(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X", system_prompt="p", fields=[]
+        )
+        with pytest.raises(IXException) as exc:
+            build_use_case_classes(iuc)
+        assert exc.value.code is IXErrorCode.IX_001_001
+
+
+class TestResponseClassNaming:
+    def test_class_name_sanitised(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="Bank / Statement — header!",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="x", type="str")],
+        )
+        _req_cls, resp_cls = build_use_case_classes(iuc)
+        assert resp_cls.__name__.startswith("Inline_")
+        # Only alphanumerics and underscores remain.
+        assert all(c.isalnum() or c == "_" for c in resp_cls.__name__)
+
+    def test_fresh_instances_per_call(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="X",
+            system_prompt="p",
+            fields=[UseCaseFieldDef(name="x", type="str")],
+        )
+        req1, resp1 = build_use_case_classes(iuc)
+        req2, resp2 = build_use_case_classes(iuc)
+        assert resp1 is not resp2
+        assert req1 is not req2
+
+
+class TestRequestClassShape:
+    def test_request_class_exposes_prompt_and_default(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="My Case",
+            system_prompt="Follow directions.",
+            default_model="qwen3:14b",
+            fields=[UseCaseFieldDef(name="x", type="str")],
+        )
+        req_cls, _resp_cls = build_use_case_classes(iuc)
+        inst = req_cls()
+        assert inst.use_case_name == "My Case"
+        assert inst.system_prompt == "Follow directions."
+        assert inst.default_model == "qwen3:14b"
+        assert issubclass(req_cls, BaseModel)
+
+    def test_default_model_none_when_unset(self) -> None:
+        iuc = InlineUseCase(
+            use_case_name="My Case",
+            system_prompt="Follow directions.",
+            fields=[UseCaseFieldDef(name="x", type="str")],
+        )
+        req_cls, _resp_cls = build_use_case_classes(iuc)
+        inst = req_cls()
+        assert inst.default_model is None