feat(source): bound a file scan's window at zero

[kz930]

What changes were proposed in this PR?

Every file-scan source takes a Limit and an Offset from ScanSourceOpDesc, and neither field said it cannot be negative. Both now declare minimum: 0.

Neither value means anything below zero, and a negative one is not read the same way twice. The executors take the window with Scala's drop and take, where a negative drop keeps every row and a negative take keeps none. The scripts the export writes take the same window with iloc, which counts from the end instead. So offset = -1 is every row on one side and the last row on the other, and limit = -1 is no rows on one side and all but the last on the other.

Declaring the bound states what the operators already assume, and the property editor then refuses the value rather than passing it on. It reaches CSV, CSVOld, JSONL, Arrow and the file scans at once, all of which inherit the two fields.

No executor changes. This is a bound on the form: a plan submitted straight through the API can still carry a negative, and nothing about how one is processed is touched here.

Any related issues, documentation, discussions?

Closes #8513, the task this change is the whole of.

How was this PR tested?

A case in ScanSourceOpDescSpec validates -1, 0 and 5 against the generated schema for both fields, through the same validator the property editor uses rather than restating the bound the schema declares. The 163 tests across the scan-source specs pass unchanged.

The four numbers quoted above were read off the two runtimes rather than from memory: Iterator(1,2,3,4,5).drop(-1) keeps all five and .take(-1) keeps none, while pandas' iloc[-1:] is the last row and iloc[:-1] is the first four.

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

Generated-by: Claude Code (Claude Opus 5)

🤖 Generated with Claude Code

[github-actions]

Automated Reviewer Suggestions

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

• Contributors with relevant context: @xuang7, @eugenegujing
  You can notify them by mentioning @xuang7, @eugenegujing in a comment.

[kz930]

@carloea2 a small one, independent of the export series: a file scan's Limit and Offset accepted a negative value, and a negative one is not read the same way twice, drop(-1) keeps every row where iloc[-1:] keeps the last. Would you take a look when you have a moment?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.62%. Comparing base (75c85aa) to head (76c98b3).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8514   +/-   ##
=========================================
  Coverage     93.62%   93.62%           
  Complexity     4857     4857           
=========================================
  Files          1212     1212           
  Lines         50037    50037           
  Branches       6132     6132           
=========================================
+ Hits          46847    46848    +1     
+ Misses         1676     1675    -1     
  Partials       1514     1514           

Flag	Coverage Δ		*Carryforward flag
access-control-service	80.18% <ø> (ø)
agent-service	99.32% <ø> (ø)		Carriedforward from 75c85aa
amber	89.86% <ø> (+<0.01%)	⬆️
computing-unit-managing-service	77.14% <ø> (ø)
config-service	87.12% <ø> (ø)
file-service	83.65% <ø> (ø)
frontend	96.16% <ø> (ø)		Carriedforward from 75c85aa
notebook-migration-service	83.73% <ø> (ø)
pyamber	98.47% <ø> (ø)		Carriedforward from 75c85aa
workflow-compiling-service	74.09% <ø> (ø)

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

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

⚠️ Benchmark changes need a look

🟢 4 better · 🔴 3 worse · ⚪ 8 noise (<±5%) · 0 without baseline

Compared against main 75c85aa 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	402	0.245	23,376/32,548/32,548 us	🟢 -9.1% / 🔴 +101.7%
🟢	bs=100 sw=10 sl=64	812	0.496	120,120/140,297/140,297 us	🟢 -14.2% / 🔴 +29.0%
⚪	bs=1000 sw=10 sl=64	908	0.554	1,106,007/1,133,334/1,133,334 us	⚪ within ±5% / 🔴 +11.0%

Baseline details

Latest main 75c85aa from same runner

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	402 tuples/sec	426 tuples/sec	755.28 tuples/sec	-5.6%	-46.8%
bs=10 sw=10 sl=64	MB/s	0.245 MB/s	0.26 MB/s	0.461 MB/s	-5.8%	-46.9%
bs=10 sw=10 sl=64	p50	23,376 us	21,503 us	12,957 us	+8.7%	+80.4%
bs=10 sw=10 sl=64	p95	32,548 us	35,807 us	16,134 us	-9.1%	+101.7%
bs=10 sw=10 sl=64	p99	32,548 us	35,807 us	20,333 us	-9.1%	+60.1%
bs=100 sw=10 sl=64	throughput	812 tuples/sec	809 tuples/sec	980.1 tuples/sec	+0.4%	-17.2%
bs=100 sw=10 sl=64	MB/s	0.496 MB/s	0.494 MB/s	0.598 MB/s	+0.4%	-17.1%
bs=100 sw=10 sl=64	p50	120,120 us	120,537 us	101,894 us	-0.3%	+17.9%
bs=100 sw=10 sl=64	p95	140,297 us	163,499 us	108,718 us	-14.2%	+29.0%
bs=100 sw=10 sl=64	p99	140,297 us	163,499 us	122,482 us	-14.2%	+14.5%
bs=1000 sw=10 sl=64	throughput	908 tuples/sec	924 tuples/sec	1,011 tuples/sec	-1.7%	-10.2%
bs=1000 sw=10 sl=64	MB/s	0.554 MB/s	0.564 MB/s	0.617 MB/s	-1.8%	-10.2%
bs=1000 sw=10 sl=64	p50	1,106,007 us	1,085,513 us	996,422 us	+1.9%	+11.0%
bs=1000 sw=10 sl=64	p95	1,133,334 us	1,117,886 us	1,037,670 us	+1.4%	+9.2%
bs=1000 sw=10 sl=64	p99	1,133,334 us	1,117,886 us	1,072,152 us	+1.4%	+5.7%

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
0,10,10,64,20,497.29,200,128000,402,0.245,23376.14,32548.45,32548.45
1,100,10,64,20,2461.69,2000,1280000,812,0.496,120120.31,140296.76,140296.76
2,1000,10,64,20,22025.47,20000,12800000,908,0.554,1106006.72,1133334.30,1133334.30