Add Python task conditional authoring (v0.1.8)

[Volv-G]

Summary

• add first-class Python task metadata is_enabled=, serialized as canonical TaskSpec.isEnabled
• support string constants, GraphInputPlaceholder, and TaskOutputProxy; normalize Python booleans to lowercase "true" / "false"
• track task-output conditions as dependencies for validation, cycle detection, and layout
• align runnable/dehydrated schemas with backend-supported condition forms and keep schema refreshes from reintroducing unsupported dynamicData
• reject unsupported authoring values (including DynamicData, Raw, structured values, and None) before writing output
• scope conditional execution to container-component tasks and document the component-input collision escape
• add a runnable examples/python_pipeline/is_enabled_pipeline.py sample covering constant false, graph-input, and task-output conditions
• bump tangle-cli from 0.1.7 to 0.1.8 across project metadata, runtime fallback, packaging expectations, and the lockfile

Python authoring contract

Pipeline/component inputs are not specially marked as conditions. Declare an ordinary runtime graph input and pass its placeholder through the reserved task-call metadata keyword:

@pipeline("Conditional greeting")
def conditional_greeting(enabled: In[str]) -> Out[str]:
    greeting = write_greeting(who="world", is_enabled=enabled)
    return greeting.out

This emits task metadata, not a component argument:

isEnabled:
  graphInput:
    inputName: enabled

Supported is_enabled= values are:

• Python bool, normalized to the lowercase string "true" or "false"
• string constants
• ordinary In[...] graph-input placeholders
• task outputs, for example is_enabled=gate.Output

If a component itself declares an input named is_enabled, bind that component argument separately with .bind(is_enabled=...); the bound value remains under arguments.is_enabled, while call-site is_enabled= remains task metadata. Conditional execution is container-task-only: subpipeline(...)(is_enabled=...) is rejected with guidance, while subpipeline(...).bind(is_enabled=...) remains available for a child graph input collision.

This intentionally does not add a condition alias.

Validation

• uv run pytest -q — 830 passed, 4 existing NamedTuple deprecation warnings
• focused changed tests — 24 passed
• reviewer regression selection — 11 passed
• git diff --check
• uv lock --check
• uv run pytest -q tests/test_packaging.py — 10 passed
• editable CLI version checks — tangle version and tangle-cli version both reported 0.1.8
• uv build and uv build --package tangle-api
• release-workflow smoke coverage passed for the tangle-cli wheel/sdist entry points, tangle-api wheel/sdist integration, and the native compatibility extra
• sample compile:

  uv run tangle sdk pipelines compile \
    examples/python_pipeline/is_enabled_pipeline.py \
    --pipeline conditional_pipeline \
    --output /tmp/tangle-is-enabled-demo/pipeline.yaml

  Result: compiled 4 tasks and wrote the pipeline plus component sidecar.
• sample validation:

  uv run tangle sdk pipelines validate /tmp/tangle-is-enabled-demo/pipeline.yaml

  Result: Valid pipeline.