fix(sync): preserve upload checkpoint recovery evidence

[veryCrunchy]

Summary

• carry a superseded upload checkpoint's recorded stage ETag into cleanup
• use the checkpoint's durable size and content hash to reconcile an unrecorded assembled stage
• preserve publication-in-flight state so cleanup cannot mistake an already published directory replacement for an abandoned upload
• refuse to allocate a replacement upload while the previous generation remains unresolved

Advances #113.

Validation

• focused JvmResumableNextcloudUploadTest on the dedicated build host
• Android debug Kotlin compilation on the dedicated build host
• Kotlin architecture checks
• full repository hygiene checks

Limits

• this slice hardens superseded checkpoint cleanup; it does not add the remaining Android download-publication recovery work
• no live Nextcloud end-to-end run was performed

[obiente-cloud]

Obiente preview

NC Native · 3440b5ced07f · Ready

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-01T21:17:42.212966Z	3440b5c	New commits

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