[tomasr78]

Bug: convertapi.convert(..., {'Files': ['a.docx', 'b.docx']}) with local files fails with TypeError: can only concatenate str (not "NoneType") to str on macOS, and on Linux with Python 3.14+. The parallel uploads ran in a multiprocessing.Pool. Under the spawn start method (macOS default) and forkserver (Linux default since 3.14), each child process re-imports convertapi, so it loses api_credentials and anything else the caller configured. Linux on 3.13 and older forks, which is why CI never saw it. I reproduced it against staging on Python 3.14/macOS.

Fix: utils.map_in_parallel now uses a ThreadPoolExecutor. Uploads are network-bound, so threads fit, and they share the caller's configuration. max_parallel_uploads keeps its meaning.

Tests: a new mocked test uploads two local files with max_parallel_uploads 1 and 10 and checks that every upload carries the token. It fails on the old code and passes now. All 12 live tests pass against stag-v2. Python 3.14 is added to the CI matrix and the classifiers.

CHANGELOG: under 2.0.1 / Fixed.

🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The focused implementation preserves configuration, ordering, and upload limits, with regression coverage and no blocking issues identified.

No open issues 🎉

What changed in this PR

Fixes multi-file uploads losing caller configuration under multiprocessing by using threads instead.

Changes:

• Replaces process-based uploads with threads while preserving ordering and concurrency limits.
• Adds regression coverage for authenticated uploads with one and multiple workers.
• Adds Python 3.14 to CI, package classifiers, and documentation.

File	Description
tests/​test_client.py	Tests authentication on multiple local-file uploads.
RELEASING.md	Updates the documented CI Python range.
README.md	Updates requirements and tested Python versions.
pyproject.toml	Adds the Python 3.14 classifier.
convertapi/​utils.py	Uses threads and returns materialized results.
CHANGELOG.md	Documents the upload fix and Python 3.14 testing.
.github/​workflows/​build.yml	Adds Python 3.14 to the test matrix.

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Concurrent reuse of an uninitialized UploadIO can consume the same stream twice, producing an empty or incomplete upload.

No open issues 🎉

1 previously missed issue

In code that hasn't changed since last review

Concurrent uploads race when the same uninitialized UploadIO is reused

convertapi/​utils.py:10

With max_parallel_uploads >= 2, passing the same uninitialized UploadIO twice in Files lets both workers see _result is None and upload its shared stream concurrently. A synchronized upload stub reproduces one complete body and one empty body, so conversion can fail or receive incomplete input. Synchronize lazy initialization per UploadIO, or resolve repeated references once before dispatch, and add a regression test confirming both entries reuse the same uploaded file ID.

_{Review effort: Balanced}