fix(workflow-operator): sample at least one row when Limit is 0

[VuMartin]

What changes were proposed in this PR?

Fix schema inference for CSV and JSONL file-scan operators when Limit = 0.

Previously, the scan limit was also used to determine how many rows were sampled for schema inference. When the limit was 0, no rows were sampled, causing schema inference to produce an empty schema or, for the old CSV scanner, an ArrayIndexOutOfBoundsException.

This change ensures schema inference samples at least one row when the scan limit is 0, while the actual scan output remains limited to zero rows.

Before:

After:

Any related issues, documentation, discussions?

How was this PR tested?

Added regression tests verifying that CSV, Parallel CSV, CSVOld, and JSONL file-scan operators still infer the expected columns when Limit = 0.

The CSV and JSONL test suites were run with:

sbt 'WorkflowOperator / Test / testOnly org.apache.texera.amber.operator.source.scan.csv.CSVScanSourceOpDescSpec org.apache.texera.amber.operator.source.scan.json.JSONLScanSourceOpDescSpec'

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Sonnet 5)

[github-actions]

Backport auto-label report

This fix: PR was checked against each actively-supported release branch. A release/* label nominates a backport target; the branch's release manager approving this PR is what sends the fix there. The required Backport Approvals check stays red until every label below is approved, so each manager either approves or removes their own label — which is why the labels left on a merged PR are exactly the branches it reached.

Release branch	Analysis
✅ release/v1.3	Already labeled — this fix is queued to backport here. @mengw15 decides: approving sends the fix here, removing this label declines it. The merge waits on one or the other.
✅ release/v1.2	Already labeled — this fix is queued to backport here. @xuang7 decides: approving sends the fix here, removing this label declines it. The merge waits on one or the other.

Auto-label run.

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @kz930, @roshiiiz
  You can notify them by mentioning @kz930, @roshiiiz in a comment.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.76%. Comparing base (e7d1676) to head (db104f7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8608   +/-   ##
=========================================
  Coverage     92.76%   92.76%           
- Complexity     4897     4898    +1     
=========================================
  Files          1236     1236           
  Lines         52155    52157    +2     
  Branches       6409     6410    +1     
=========================================
+ Hits          48380    48382    +2     
  Misses         2194     2194           
  Partials       1581     1581           

Flag	Coverage Δ		*Carryforward flag
access-control-service	71.78% <ø> (ø)
agent-service	99.16% <ø> (ø)		Carriedforward from e7d1676
amber	88.60% <100.00%> (+<0.01%)	⬆️
computing-unit-managing-service	55.20% <ø> (ø)
config-service	87.37% <ø> (ø)
file-service	81.53% <ø> (ø)
frontend	96.57% <ø> (ø)		Carriedforward from e7d1676
notebook-migration-service	83.73% <ø> (ø)
pyamber	98.41% <ø> (ø)		Carriedforward from e7d1676
workflow-compiling-service	74.09% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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[github-actions]

⚠️ Benchmark changes need a look

🟢 0 better · 🔴 10 worse · ⚪ 5 noise (<±5%) · 0 without baseline

Compared against main 957b6c9 benchmarked on this same runner, so the delta is largely free of cross-runner hardware noise. The "7d avg" column still reflects the gh-pages dashboard. Treat <±5% as noise unless repeated.

Dashboard · Run

	config	throughput	MB/s	latency	max Δ latest / 7d
🔴	bs=10 sw=10 sl=64	365	0.223	26,090/34,235/34,235 us	🔴 +20.5% / 🔴 +122.8%
🔴	bs=100 sw=10 sl=64	749	0.457	129,807/171,118/171,118 us	🔴 +20.5% / 🔴 +63.7%
⚪	bs=1000 sw=10 sl=64	904	0.552	1,100,943/1,153,418/1,153,418 us	⚪ within ±5% / 🔴 -15.5%

Baseline details

Latest main 957b6c9 from same runner

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	365 tuples/sec	420 tuples/sec	801.54 tuples/sec	-13.1%	-54.5%
bs=10 sw=10 sl=64	MB/s	0.223 MB/s	0.256 MB/s	0.489 MB/s	-12.9%	-54.4%
bs=10 sw=10 sl=64	p50	26,090 us	21,647 us	12,422 us	+20.5%	+110.0%
bs=10 sw=10 sl=64	p95	34,235 us	30,787 us	15,365 us	+11.2%	+122.8%
bs=10 sw=10 sl=64	p99	34,235 us	30,787 us	18,987 us	+11.2%	+80.3%
bs=100 sw=10 sl=64	throughput	749 tuples/sec	820 tuples/sec	1,039 tuples/sec	-8.7%	-27.9%
bs=100 sw=10 sl=64	MB/s	0.457 MB/s	0.5 MB/s	0.634 MB/s	-8.6%	-28.0%
bs=100 sw=10 sl=64	p50	129,807 us	122,626 us	98,524 us	+5.9%	+31.8%
bs=100 sw=10 sl=64	p95	171,118 us	142,009 us	104,534 us	+20.5%	+63.7%
bs=100 sw=10 sl=64	p99	171,118 us	142,009 us	115,146 us	+20.5%	+48.6%
bs=1000 sw=10 sl=64	throughput	904 tuples/sec	917 tuples/sec	1,070 tuples/sec	-1.4%	-15.5%
bs=1000 sw=10 sl=64	MB/s	0.552 MB/s	0.56 MB/s	0.653 MB/s	-1.4%	-15.5%
bs=1000 sw=10 sl=64	p50	1,100,943 us	1,100,059 us	963,083 us	+0.1%	+14.3%
bs=1000 sw=10 sl=64	p95	1,153,418 us	1,148,822 us	1,000,730 us	+0.4%	+15.3%
bs=1000 sw=10 sl=64	p99	1,153,418 us	1,148,822 us	1,026,043 us	+0.4%	+12.4%

Raw CSV

config_idx,batch_size,schema_width,string_len,num_batches,total_ms,total_tuples,total_bytes,tuples_per_sec,mb_per_sec,lat_p50_us,lat_p95_us,lat_p99_us
0,10,10,64,20,548.38,200,128000,365,0.223,26090.26,34234.81,34234.81
1,100,10,64,20,2671.18,2000,1280000,749,0.457,129806.87,171117.55,171117.55
2,1000,10,64,20,22129.22,20000,12800000,904,0.552,1100942.51,1153418.02,1153418.02

[VuMartin]

Closing this since #8341 already addresses #8602.