fix: add .compaction-plan to handle in-mid compaction crash

[dkharms]

Description

Compaction's substitute-and-delete of stale fractions isn't atomic, so a crash mid-compaction could leave source fractions behind and produce duplicates on restart.

This adds a .compaction-plan file recording the participating fractions, which is written before merging and used on startup to clean up any leftover sources from an interrupted compaction.

Closes #336

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[dkharms]

@seqbenchbot up main bulk

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Identificator for your ongoing benchmark - 8eedacf8.

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[dkharms]

@seqbenchbot down 8eedacf8

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The benchmark with identificator 8eedacf8 was finished.
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Query	Type	mean (ms)			stddev (ms)			p(50) (ms)			p(95) (ms)			p(99) (ms)			iterations
		base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff
bulk	warm	68.14	66.54	-2.34%	39.10	28.75	-26.46%	55.00	59.00	+7.27%	163.00	119.00	-26.99%	223.00	194.00	-13.00%	92689.00	92790.00	+0.11%

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[dkharms]

@seqbenchbot up main bulk

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Nice, @dkharms <(-^,^-)=b!

Your request was successfully served.
Identificator for your ongoing benchmark - 1c283919.

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[dkharms]

@seqbenchbot down 1c283919

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Nice, @dkharms <(-^,^-)=b!

The benchmark with identificator 1c283919 was finished.
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Query	Type	mean (ms)			stddev (ms)			p(50) (ms)			p(95) (ms)			p(99) (ms)			iterations
		base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff
bulk	warm	89.78	83.67	-6.80%	58.54	42.06	-28.15%	67.00	70.00	+4.48%	225.00	167.00	-25.78%	298.00	252.00	-15.44%	1540251.00	1540362.00	+0.01%

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[dkharms]

@seqbenchbot up main bulk

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Nice, @dkharms <(-^,^-)=b!

Your request was successfully served.
Identificator for your ongoing benchmark - 36d0de9f.

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[dkharms]

@seqbenchbot down 36d0de9f

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Nice, @dkharms <(-^,^-)=b!

The benchmark with identificator 36d0de9f was finished.
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Query	Type	mean (ms)			stddev (ms)			p(50) (ms)			p(95) (ms)			p(99) (ms)			iterations
		base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff
bulk	warm	67.39	62.57	-7.16%	43.57	29.77	-31.69%	51.00	53.00	+3.92%	173.00	118.00	-31.79%	234.00	193.00	-17.52%	716648.00	716757.00	+0.02%

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[dkharms]

@seqbenchbot up main mixed

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Nice, @dkharms <(-^,^-)=b!

Your request was successfully served.
Identificator for your ongoing benchmark - 29d571ac.

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[dkharms]

@seqbenchbot down 29d571ac

[seqbenchbot]

Nice, @dkharms <(-^,^-)=b!

The benchmark with identificator 29d571ac was finished.
I've prepared a summary for you. Click on Show summary button to see it:

Show summary

Query	Type	mean (ms)			stddev (ms)			p(50) (ms)			p(95) (ms)			p(99) (ms)			iterations
		base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff
bulk	warm	48.99	50.87	+3.84%	11.90	13.74	+15.47%	47.00	48.00	+2.13%	70.00	76.00	+8.57%	93.00	102.00	+9.68%	45658.00	45585.00	-0.16%
service:payment-backend-eu AND k8s_namespace:prod AND level:[0 to 3] AND ( message:'failed' OR message:'timeout' )	warm	53.72	58.03	+8.02%	20.62	24.77	+20.15%	45.00	48.00	+6.67%	97.00	113.00	+16.49%	117.00	139.50	+19.23%	9615.00	9596.00	-0.20%

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 46.91358% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.37%. Comparing base (59fdb2b) to head (4d59887).

Files with missing lines	Patch %	Lines
fracmanager/frac_manifest.go	32.20%	37 Missing and 3 partials ⚠️
compaction/merge.go	87.50%	1 Missing and 1 partial ⚠️
compaction/planner.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #453      +/-   ##
==========================================
- Coverage   70.48%   70.37%   -0.11%     
==========================================
  Files         232      232              
  Lines       18269    18348      +79     
==========================================
+ Hits        12876    12912      +36     
- Misses       4432     4471      +39     
- Partials      961      965       +4     

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