When assigning streamed caller transcript fragments to a delegated voice turn, retain

When assigning streamed caller transcript fragments to a delegated voice turn, retain an already-received fragment that starts at or before the handoff boundary even if its end crosses that boundary. Filtering only by end_ms <= handoff_offset can discard the last spoken digit. A valid lookup then fails caller-grounding validation, and the assistant appears to have forgotten an identifier it correctly heard. Preserve the whole overlapping fragment, keep genuinely later speech queued, and leave exact identifier grounding in the business handler.

Applicability and limits: This addresses boundary-overlap loss when input captions provide start/end intervals and delegation provides a timeline offset. Input transcript deltas are fragments, not complete-turn events. This rule does not establish that every fragment has arrived, solve semantic assignment of arbitrary later speech, or justify bypassing grounding with model-provided values or historical digits.