ponder-lab / Hybridize-Functions-Refactoring / #3456

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Refuse Python over a parameter's value that tracing cannot carry (#1079)

* Refuse Python over a parameter's value that tracing cannot carry

A function was converted when its body applied Python to a value flowing
from its parameters in a way tracing cannot carry, so the converted
function raised where the eager one ran. Measured on TensorFlow 2.9.3:

- float() of the value raises TypeError, and bool() raises
  OperatorNotAllowedInGraphError.
- A branch on the value whose paths disagree about None raises
  ValueError from AutoGraph's conversion of the branch to tf.cond. That
  covers a return None beside a returned tensor, and a variable left
  None on one path.

The numpy-on-parameters walk now also decides these, from the same
taint, across callees and closures. It records float and bool calls on
a tainted value, and branches on a tainted value whose two successor
regions return None and a value, or whose merge block joins None with a
value. A failing function gets a new precondition failure,
HAS_UNTRACEABLE_PYTHON_ON_PARAMETERS (35). A branch whose paths agree,
and int(), which AutoGraph converts to a cast, are left alone.

Fixes #1074.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NTnpjPjJj2aZy1ZkUD1eAn

* Leave float() alone, and pin unbound-local and primitive controls

Measured on TensorFlow 2.9.3, float() of a tensor traces under
AutoGraph as int() does, converted to a cast; the earlier case failed
only because it wrapped the result in tf.constant, which rejects any
symbolic tensor. Only bool() stays a sink. Two controls are added: a
local bound only inside a branch on a tensor value, which is unbound
rather than None on the other path, still hybridizes, and a branch on a
primitive parameter is refused for the primitive (code 12), not by
this check.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NTnpjPjJj2aZy1ZkUD1eAn

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