[runtime/utils/buffer/write] use Blob::write_at_sync

[andresilva]

This PR updates buffered Write to use Blob::write_at_sync when sync only needs to persist the currently buffered tip.

Write now keeps durability state alongside the tip buffer to track whether a prior plain write_at or resize requires a full Blob::sync. If no such mutation happened, sync can persist the buffered range directly (with Blob::write_at_sync), otherwise it falls back to a full sync.

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Status	Name	Latest Commit	Updated (UTC)
✅ Deployment successful! View logs	commonware-mcp	a569edb	May 22 2026, 07:45 PM

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Benchmark results

Tip

✅ PASSED: No benchmark exceeded the regression threshold.

Benchmark comparison table

Benchmark	Baseline (main)	Current	Delta	Threshold	Status
qmdb::merkleize/variant=any::unordered::fixed::mmr keys=10000 ch=false sync=false	1.577 ms	1.565 ms	-0.74%	10.00%	✅ PASS
qmdb::merkleize/variant=current::ordered::fixed::mmb chunk=256 keys=10000 ch=true sync=false	3.085 ms	3.042 ms	-1.41%	10.00%	✅ PASS

Baseline commit(s): 527763b5f80a

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View logs

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[codecov]

Codecov Report

❌ Patch coverage is 89.37198% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.76%. Comparing base (d8589a0) to head (a569edb).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
runtime/src/utils/buffer/mod.rs	86.30%	19 Missing and 1 partial ⚠️
runtime/src/utils/buffer/write.rs	96.72%	1 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main    #3852      +/-   ##
==========================================
- Coverage   95.77%   95.76%   -0.02%     
==========================================
  Files         486      486              
  Lines      200338   200864     +526     
  Branches     4858     4861       +3     
==========================================
+ Hits       191871   192349     +478     
- Misses       6833     6882      +49     
+ Partials     1634     1633       -1     

Files with missing lines	Coverage Δ
runtime/src/utils/buffer/write.rs	98.44% <96.72%> (+0.64%)	⬆️
runtime/src/utils/buffer/mod.rs	95.34% <86.30%> (-1.66%)	⬇️

... and 47 files with indirect coverage changes

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