fix: prevent LoopStart state variable collision

[VuMartin]

What changes were proposed in this PR?

Fixes LoopStart state variables being silently overwritten by upstream state. LoopStart now detects collisions between existing loop variables and incoming state variables and raises an error instead of overwriting the loop variable.

Before:

After:

Any related issues, documentation, discussions?

Fixes #7248

How was this PR tested?

Added a unit test verifying that LoopStart rejects incoming state that attempts to overwrite an existing loop state variable.

Ran the targeted pytest test successfully: 1 passed.

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

Generated-by: ChatGPT (5.5 mini)

[github-actions]

Automated Reviewer Suggestions

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

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

[github-actions]

Backport auto-label report

This fix: PR was checked against each actively-supported release branch. release/* labels drive the post-merge backport, so add or remove one to change where this fix lands.

Release branch	Analysis
⚠️ release/v1.3	Not labeled automatically — none of the files this PR modifies exist on this branch (amber/src/main/python/core/models/operator.py, amber/src/test/python/core/models/test_operator.py). The fix may target code that isn't on this release, or the files were moved/renamed after the branch was cut. Please check and add release/v1.3 by hand if this fix should be backported here.
✅ release/v1.2	Change detected on this branch — label added; this fix is queued to backport here. Requested review from @xuang7.

Auto-label run.

[github-actions]

⚠️ Benchmark changes need a look

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

Compared against main 98588bf 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	569	0.347	17,567/34,252/34,252 us	🔴 +32.5% / 🔴 +132.0%
🟢	bs=100 sw=10 sl=64	1,317	0.804	73,779/102,903/102,903 us	🟢 -7.7% / 🟢 -22.0%
⚪	bs=1000 sw=10 sl=64	1,554	0.948	640,764/689,027/689,027 us	⚪ within ±5% / 🟢 +39.8%

Baseline details

Latest main 98588bf from same runner

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	569 tuples/sec	672 tuples/sec	842.25 tuples/sec	-15.3%	-32.4%
bs=10 sw=10 sl=64	MB/s	0.347 MB/s	0.41 MB/s	0.514 MB/s	-15.4%	-32.5%
bs=10 sw=10 sl=64	p50	17,567 us	14,530 us	11,860 us	+20.9%	+48.1%
bs=10 sw=10 sl=64	p95	34,252 us	25,841 us	14,764 us	+32.5%	+132.0%
bs=10 sw=10 sl=64	p99	34,252 us	25,841 us	17,870 us	+32.5%	+91.7%
bs=100 sw=10 sl=64	throughput	1,317 tuples/sec	1,311 tuples/sec	1,084 tuples/sec	+0.5%	+21.5%
bs=100 sw=10 sl=64	MB/s	0.804 MB/s	0.8 MB/s	0.662 MB/s	+0.5%	+21.5%
bs=100 sw=10 sl=64	p50	73,779 us	73,840 us	94,616 us	-0.1%	-22.0%
bs=100 sw=10 sl=64	p95	102,903 us	111,541 us	100,981 us	-7.7%	+1.9%
bs=100 sw=10 sl=64	p99	102,903 us	111,541 us	108,141 us	-7.7%	-4.8%
bs=1000 sw=10 sl=64	throughput	1,554 tuples/sec	1,554 tuples/sec	1,112 tuples/sec	0.0%	+39.8%
bs=1000 sw=10 sl=64	MB/s	0.948 MB/s	0.949 MB/s	0.679 MB/s	-0.1%	+39.7%
bs=1000 sw=10 sl=64	p50	640,764 us	641,575 us	930,623 us	-0.1%	-31.1%
bs=1000 sw=10 sl=64	p95	689,027 us	709,762 us	974,308 us	-2.9%	-29.3%
bs=1000 sw=10 sl=64	p99	689,027 us	709,762 us	1,002,806 us	-2.9%	-31.3%

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
0,10,10,64,20,351.57,200,128000,569,0.347,17566.85,34251.50,34251.50
1,100,10,64,20,1519.17,2000,1280000,1317,0.804,73779.38,102902.89,102902.89
2,1000,10,64,20,12872.32,20000,12800000,1554,0.948,640764.21,689027.20,689027.20

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.03%. Comparing base (98588bf) to head (dc5faff).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8126   +/-   ##
=========================================
  Coverage     94.03%   94.03%           
  Complexity     4762     4762           
=========================================
  Files          1181     1181           
  Lines         47877    47880    +3     
  Branches       5324     5324           
=========================================
+ Hits          45020    45023    +3     
  Misses         1433     1433           
  Partials       1424     1424           

Flag	Coverage Δ		*Carryforward flag
access-control-service	81.00% <ø> (ø)		Carriedforward from 98588bf
agent-service	99.32% <ø> (ø)		Carriedforward from 98588bf
amber	90.03% <ø> (ø)		Carriedforward from 98588bf
computing-unit-managing-service	73.67% <ø> (ø)		Carriedforward from 98588bf
config-service	86.86% <ø> (ø)		Carriedforward from 98588bf
file-service	87.91% <ø> (ø)		Carriedforward from 98588bf
frontend	96.68% <ø> (ø)		Carriedforward from 98588bf
notebook-migration-service	79.31% <ø> (ø)		Carriedforward from 98588bf
pyamber	98.87% <100.00%> (+<0.01%)	⬆️
workflow-compiling-service	77.19% <ø> (ø)		Carriedforward from 98588bf

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

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