Implement the `RECONFIGURE` modify path: reconfigure an existing `input_signature`

[khatchad]

Summary

#563 (#595) implemented the add-when-absent half of RECONFIGURE: a qualifying hybrid @tf.function that carries no input_signature gains the inferred one (passing precondition P4). The complementary modify path — reconfiguring a decorator that already supplies an input_signature — is deferred. This issue tracks it.

Current Behavior

When HybridizationParameters.hasInputSignatureParam() is true, check() does not select RECONFIGURE; the function falls through to HAS_NO_PRIMITIVE_PARAMETERS and is left unchanged. A user-supplied signature is never overwritten, per the presence/parse three-state contract from #557.

Goal

When a function already supplies an input_signature that disagrees with the inferred one, optionally rewrite it. The policy for when to overwrite versus preserve a user-supplied signature needs to be defined and is the substance of this work.

Design

• Same RECONFIGURE transformation, with a new passing-precondition code (e.g. P5) for the modify path, mirroring how P2 and P3 both reach CONVERT_TO_EAGER.
• Compare the parsed supplied signature (getSuppliedInputSignature(), available from Parse the input_signature argument of @tf.function decorators for inference #557 and Parse input_signature content when supplied positionally #573) against inferInputSignature(); when the policy calls for an overwrite, emit a RECONFIGURE edit that replaces the existing input_signature argument. The decorator-rewrite machinery from Implement the RECONFIGURE transformation to emit input_signature #595 extends from insertion to replacement.

Refs

• Emit input_signature=[tf.TensorSpec(...)] in the refactoring's @tf.function source rewrite #563, Implement the RECONFIGURE transformation to emit input_signature #595 — the add-when-absent half and the RECONFIGURE infrastructure.
• Parse the input_signature argument of @tf.function decorators for inference #557, Parse input_signature content when supplied positionally #573 — parsing the supplied signature.
• Graduate inferInputSignature from Optional to typed Result<InputSignature, AbsenceReason> #483 — a typed inference result, which may inform how preserve/overwrite decisions are modeled.

[khatchad]

The overwrite-vs-preserve policy has been settled by the maintainers and is tracked internally; implementation will proceed under maintainer coordination. Holding off on elaborating the policy publicly here until that work lands, to avoid divergence.