Prepare Python SDK 2.6.0-rc.1 for installed Nexus qualification

[rmcdaniel]

Qualification prerelease

Prepare Python SDK 2.6.0-rc.1 (PyPI 2.6.0rc1) for actual installed Nexus caller/service qualification of #111 and #112. This includes the already merged Avro transport fix #113 and explicit target addressing #114. The new optional target API warrants the 2.6 minor version.

This is a prerelease, with the current stable artifact unchanged. Normal source, package, integration and exact metadata checks run before the immutable tag is published through this repository's protected PyPI workflow. The published fixture will execute real Python callers and PHP service workers. Server payload transport #396 is currently closed without merge, and linked terminal outcomes durable-workflow/workflow#753 are still outstanding. Those issues and the full Nexus qualification stay open. No stable promotion or full execution/recovery claim here.

[rmcdaniel]

Reviewed candidate a327617 against main 6778efb. The diff changes only the three release identity fields to SemVer 2.6.0-rc.1 and normalized PyPI version 2.6.0rc1. It contains the already qualified Avro encoding and optional target namespace changes from #113 and #114.

All 13 checks pass on this exact candidate, including Python 3.10/3.11/3.12, the codec/replay corpus, integration, package build, documentation and target-branch qualification. The protected publisher accepts this exact prerelease identity and marks the GitHub release as a prerelease. No existing immutable tag will change.

This artifact is for installed-package qualification in the actual Python caller/PHP service fixture. Stable remains 2.5.4. #111 and #112 remain open until published execution verifies their changed contracts. The full service workflow gate remains red for the separate linked-outcome defect in durable-workflow/workflow#753, and oversized service input also depends on the unmerged Server transport fix.

[rmcdaniel]

Published qualification prerelease 2.6.0-rc.1, normalized as 2.6.0rc1 on PyPI, from merged commit a3d537207938990d89893445cd3e3c34bda0d3bb. The merged tree matches qualified candidate a327617e3c35e94105ea01c170f2d4e6a1b3fd84. All 13 PR checks, main CI, docs and boundary checks pass.

Protected publication passed package build/smoke, source metadata comparison, the immutable artifact handoff, PyPI publication and exact registry verification. GitHub release is a prerelease. PyPI returns the exact wheel and sdist. Wheel SHA-256 4a132da06935218da544e5ea50ca19511e6f5ec2762310908cdc36c82ebf0eb0, sdist 85b0c977bab9b581e59ce33d266fa19885739dfdd0ae7ed26784dc47fdd53318.

Stable remains 2.5.4. The actual installed Python caller/PHP worker fixture is now running in Server #394. It records Avro arguments, target namespace and original caller/run identity independently of the required terminal workflow outcome. #111 and #112 stay open until their published customer outcomes pass. Linked completion remains tracked by durable-workflow/workflow#753, and oversized service input still depends on the held Server payload correction. No full Nexus recovery or stable promotion claim.