fix: send the content_type partition_via_api accepts

[linhongyu510]

Problem

content_type has been the second positional parameter of partition_via_api() since the helper was introduced in #518, and the docstring describes it as:

content_type — A string defining the file content in MIME type

It is never read. Both construction sites pass only content and file_name:

files = shared.Files(content=f.read(), file_name=filename)
...
files = shared.Files(content=file, file_name=metadata_filename)

so the value is silently discarded and the server falls back to sniffing the file name — exactly the situation the parameter exists to override (an extensionless upload, a file whose extension lies about its type, or a stream where only the caller knows the format).

Measured on main (3376cc96) by capturing the request handed to the SDK:

partition_via_api(filename=..., content_type="text/markdown")
# request.partition_parameters.files.content_type -> None

This is not an SDK limitation: shared.Files has a content_type field (['content', 'file_name', 'content_type']). Only the hand-off was missing.

Fix

Populate the field when the caller supplies a value.

When no content_type is given the field is left unset rather than passed as None, so the SDK keeps inferring the type from the file name exactly as before. The parameter is not moved, so existing positional calls bind unchanged.

Tests

• test_partition_via_api_sends_an_explicit_content_type_for_a_filename
• test_partition_via_api_sends_an_explicit_content_type_for_a_file
• test_partition_via_api_leaves_content_type_unset_when_not_given — guards the unchanged default

They assert on the request object actually handed to General.partition, following the method_mock pattern the surrounding tests already use.

Verification

• 23 pass in test_api.py (20 pre-existing + 3 new).
• Rollback counter-proof: dropping only the pass-through while keeping the tests fails exactly the 2 "sends an explicit content_type" tests, with the "leaves unset" test still passing — the tests separate the new behavior from the preserved default.
• No new breakage: across test_api.py, test_md.py, test_text.py and test_json.py the failure set is identical before and after; passing count goes 193 → 196, exactly the 3 added tests. (2 pre-existing failures are environmental and unrelated.)
• ruff check and ruff format --check clean on both changed files.
• Checked the 125 open PRs for overlap with partition/api.py: none touches it (feat: add max_page to chunk_by_title and remove multipage_sections #4382 modifies test_api.py only, for chunking).

Independent of #4483 and #4488; all three are cut from main and touch different files.

[cragwolfe]

Oracle Pro review (server-confirmed gpt-6-pro; completed verdict: NOT SAFE TO MERGE because of the SDK-floor regression) of head 383406198027de31c56387065a9372312c24789a against 0b7f806e0f6ef540df22fad5627756a72663eb11: one verified compatibility defect remains (inline). The MIME value reaches the file-part Content-Type with the locked SDK 0.43.2 and current SDK 0.46.2; omitted values preserve the existing serializer path.

The added tests assert only the object passed to mocked General.partition, so they do not establish multipart wire behavior or minimum-supported-SDK compatibility. Add coverage at the request boundary for explicit/omitted MIME types with filenames, bytes and streams, including the supported lower SDK bound.

Integration and release notes: GitHub currently reports mergeability as MERGEABLE, but its GitHub Actions CI, Security, CodeQL and benchmark runs are action_required; CI has no jobs. The external checks have success conclusions, but Cubic skipped this merge commit and Socket PR alerts skipped because dependencies did not change; they are not test execution evidence. The changelog entry is under historical 0.27.8 rather than the current 0.27.27-dev3 section; move it to the active release section.

Review only; no source changes or local tests.

(authored by codex)

[cragwolfe]

[P2] Preserve compatibility with the declared minimum SDK. pyproject.toml still permits unstructured-client==0.25.9, whose generated shared.Files is a dataclass with only content and file_name. For any non-None content_type, both construction paths now pass an unsupported keyword and raise TypeError before the HTTP request; the same call previously reached the API. SDK 0.26.0 introduces this field. Either raise the supported SDK minimum consistently, or use a compatible forwarding path (the API content_type form parameter is present in 0.25.9). Add minimum-version coverage and assert the serialized request so explicit types work throughout the advertised dependency range.

(authored by codex)

[linhongyu510]

Replying to the P2 SDK-floor note on unstructured/partition/api.py (inline reply blocked by org OAuth restrictions):

Addressed with the compatible forwarding path rather than raising the SDK floor: content_type now rides on PartitionParameters (a multipart form field present on the advertised minimum) instead of shared.Files, which only gains the kwarg in SDK 0.26.0. The declared floor unstructured-client>=0.25.9 is unchanged.

0.25.9 RED → GREEN (reproduced on installed unstructured-client==0.25.9):

• RED: shared.Files(content=…, file_name=…, content_type=…) raises TypeError: Files.__init__() got an unexpected keyword argument 'content_type' before the HTTP request.
• GREEN: PartitionParameters(files=…, content_type=…) accepts it and serialize_request_body emits the content_type multipart form field (['content_type', [None, 'text/markdown']]); the file part is unchanged.

Matrix + negative control: the wire path (explicit MIME, omitted MIME, filename/bytes/stream, caller keyword passthrough) was verified on the locked SDK 0.43.2 and current 0.46.2 as well. The omitted-MIME negative control emits no content_type field, so the SDK's file-name inference is untouched.

Coverage: a new isolated test_unit_sdk_floor CI job syncs the locked test environment, pins unstructured-client==0.25.9, and runs only the focused multipart wire tests; the ordinary locked suite is not downgraded. The changelog entry was moved from the historical 0.27.8 section to the active 0.27.27-dev3 section and updated to describe the PartitionParameters form-field approach.

Local checks: focused wire group 8 passed; full test_api.py 27 passed / 6 skipped on 0.25.9, 0.43.2 and 0.46.2; ruff clean. Caveats: this was prepared with AI assistance and the author has not manually re-reviewed it; CI has not yet run on the new head (fork approval pending). Not resolving, approving, or merging.