Trust only uploaded blobs for deduplication (closes #148)

An interrupted blob upload left the blob's chunks, blob_chunks, and blobs rows committed before the upload was attempted, so a later run deduplicated against data that never reached storage and produced a snapshot that reported success but could not be restored.

Fix (issue option b): a chunk counts as known only when a blob holding it has uploaded_ts set, and each run drops un-uploaded blob rows and the chunks they orphan at startup, so the affected data is re-chunked and re-uploaded. A blob recorded with no remote backend is marked uploaded so the invariant holds uniformly.

The reproduction is the interrupted-upload test from #72: its t.Skip is removed and it passes against this fix, and this branch's earlier duplicate copy is dropped. The interrupted metadata-export case is split to #177.

Model: opus-4-8

TODO.md

@@ -25,6 +25,19 @@ release" is exactly the contradiction
 
 # Completed Steps
 
+- 2026-09-21: Stopped an interrupted blob upload from making a later
+  backup deduplicate against data that was never stored
+  ([issue #148](https://git.eeqj.de/sneak/vaultik/issues/148)). The
+  packer commits a blob's `chunks`, `blob_chunks`, and `blobs` rows
+  before the upload is attempted, so a failed upload left chunk rows
+  behind and the next run skipped re-uploading them, producing a
+  snapshot that reported success but could not be restored. A run now
+  deduplicates only against chunks held by a blob whose `uploaded_ts` is
+  set, and at startup drops any un-uploaded blob rows (and the chunks
+  they orphan) so the affected data is re-chunked and re-uploaded. Blobs
+  recorded with no remote backend are marked uploaded so this invariant
+  holds uniformly.
+
 - 2026-09-21: Stopped `--json` from silencing stderr diagnostics
   ([issue #112](https://git.eeqj.de/sneak/vaultik/issues/112)). `--json`
   used to be folded into `Quiet`, which pinned the log level to `WARN`,