ponder-lab / Hybridize-Functions-Refactoring / #3196

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Narrow a broader supplied input signature, and report a disagreeing one (#985)

* Narrow a broader supplied input signature, and report a disagreeing one

When inference is on and a hybrid function already has an
`input_signature`, the supplied signature is compared with the inferred
one. Until now every relation was only reported. Under the closed-world
assumption the reachable call sites are all the callers, and the
inferred signature is their join, which changes the reasoning:

- A supplied signature strictly BROADER than the inferred one is now
  narrowed to it (P5). Every reachable caller already conforms to the
  inferred signature, so the narrowing preserves behavior. It is
  declined when the signature is given by name, since the binding may
  be shared with other decorators, and when it would change a shape the
  function reads statically at trace time, since that changes the
  traced program. A supplied dtype the tool did not read never reaches
  this path, because the parser declines to model such a signature; a
  defensive check keeps that so.
- A supplied signature strictly TIGHTER than the inferred one, or
  INCOMPARABLE with it, means some reachable call already violates it,
  so rewriting it would repair the program rather than refactor it. It
  is now a failing precondition, with a warning per parameter saying
  what the violating call does: a shape mismatch raises, and a dtype
  mismatch raises for a tensor argument and is silently cast for a
  non-tensor one. The argument kind comes from the origins of the values
  the reachable call sites pass.

Three failure codes are new: 26 for a disagreeing signature, 27 for a
narrowing that would change a statically read shape, and 28 for a
signature shared by name.

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

* Decline narrowing a signature the program exports

A SavedModel written by `tf.saved_model.save`, o... (continued)

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