[Eduard van Valkenburg (eavanvalkenburg)]

Motivation and Context

Prompt template argument encoding supports text and a set of scalar values. bytes values do not have an implicit text encoding and currently render using their Python representation. This change uses the existing unsupported-value path so callers must decode or otherwise handle byte content explicitly.

Description

• Remove bytes from the primitive types accepted by automatic prompt argument encoding.
• Add parameterized regression coverage for Semantic Kernel, Jinja2, and Handlebars templates.
• Verify strings remain encoded as a single message and integer rendering is unchanged.

Callers that currently pass bytes with default content handling will now receive the existing NotImplementedError. Textual byte content should be decoded with the intended encoding before rendering.

Validation:

• cd python && uv run --python 3.12 --frozen pre-commit run -a — passed.
• cd python && uv run --python 3.12 --frozen pytest tests/unit/prompt_template -q — passed.
• cd python && uv run --python 3.12 --frozen pytest tests/unit --ignore=tests/unit/processes/dapr_runtime -q — passed.
• cd python && uv run --python 3.12 --frozen pytest tests/unit/processes/dapr_runtime -q — passed after installing the Dapr FastAPI and Flask test extras in the local uv environment.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[Copilot]

🟢 Approval recommended

The narrow change matches the intended behavior and includes targeted regression coverage with no unresolved issues.

No open issues 🎉

What changed in this PR

This PR makes Python prompt argument encoding reject bytes, requiring callers to decode byte content explicitly before rendering.

Changes:

• Remove bytes from the primitive types accepted by automatic encoding.
• Add regression coverage across Semantic Kernel, Jinja2, and Handlebars templates.
• Verify decoded strings remain a single user message and integer rendering is unchanged.

File	Description
python/​tests/​unit/​prompt_template/​test_prompt_template_e2e.py	Test byte rejection and preserved string and integer behavior across three engines.
python/​semantic_kernel/​prompt_template/​prompt_template_base.py	Route byte arguments through existing unsupported-value handling.

_{Review effort: Balanced}