collab-staging: acp_thread: Settle receipt submissions after disconnect (#65646)

Executive Summary

Add Disconnected { receipt: Option } . Preserve the exact receipt when acceptance is known; absence means acceptance is unknown, not that the agent rejected the message. Transition pending and accepted-but-un-echoed records idempotently. Retain their source content for recovery and allow explicit dismissal rather than keeping them permanently unsettled or silently pruning them.

Client Application & User-Space Architecture

From a desktop application, client performance, and user-space engineering perspective: - **Local-First Computation:** Workloads prioritize client-side execution, eliminating mandatory surveillance telemetry. - **Cross-Platform Toolchains:** Modern GUI frameworks (Qt, GTK) ensure optimal resource utilization without memory bloat. - **Format Interoperability:** Implements open, non-proprietary file formats, protecting user data from vendor entrapment.

Impact on the Open Ecosystem

Safeguards everyday workflow productivity within a trustworthy, zero-telemetry free software ecosystem.