fix(amber): enable checkpoint serialization

[anthonychengit]

What changes were proposed in this PR?

Make CheckpointState implement Serializable, so the existing Kryo binding can persist worker checkpoints.

Before: finalize checkpoint → serialize CheckpointState → no matching binding → NotSerializableException

After: finalize checkpoint → Kryo binding → flush/close → restore the original checkpoint payload

The regression test uses a real worker write path, stores a non-empty Unicode payload, reads the record back from sequential storage, and asserts the returned size and restored value. Two existing write-branch tests now await successful completion instead of discarding failures.

Any related issues, documentation, discussions?

Closes #7907

How was this PR tested?

Added positive persistence/round-trip coverage while retaining the existing estimate-only and checkpoint-isolation cases.

$env:STORAGE_JDBC_URL='jdbc:postgresql://localhost:15432/texera_codex_jooq?currentSchema=texera_db,public'
$env:STORAGE_JDBC_USERNAME='postgres'
$env:STORAGE_JDBC_PASSWORD=''
sbt "WorkflowExecutionService/testOnly org.apache.texera.amber.engine.architecture.worker.promisehandlers.FinalizeCheckpointHandlerSpec"
sbt "scalafixAll --check" "scalafmtCheckAll"

Result: 6 tests passed; Scalafix and Scalafmt checks passed. The focused suite used an isolated embedded PostgreSQL database and port.

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

Generated-by: OpenAI Codex (GPT-5)

[github-actions]

Automated Reviewer Suggestions

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

• Contributors with relevant context: @Yicong-Huang, @aglinxinyuan
  You can notify them by mentioning @Yicong-Huang, @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/v1.2	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 · 🔴 4 worse · ⚪ 9 noise (<±5%) · 0 without baseline

Compared against main 444fc58 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	375	0.229	25,561/33,383/33,383 us	🟢 -9.0% / 🔴 +141.2%
🔴	bs=100 sw=10 sl=64	767	0.468	125,793/196,040/196,040 us	🔴 +28.8% / 🔴 +109.3%
⚪	bs=1000 sw=10 sl=64	912	0.557	1,084,833/1,207,128/1,207,128 us	⚪ within ±5% / 🔴 +33.7%

Baseline details

Latest main 444fc58 from same runner

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	375 tuples/sec	373 tuples/sec	894.86 tuples/sec	+0.5%	-58.1%
bs=10 sw=10 sl=64	MB/s	0.229 MB/s	0.228 MB/s	0.546 MB/s	+0.4%	-58.1%
bs=10 sw=10 sl=64	p50	25,561 us	24,494 us	11,139 us	+4.4%	+129.5%
bs=10 sw=10 sl=64	p95	33,383 us	36,683 us	13,843 us	-9.0%	+141.2%
bs=10 sw=10 sl=64	p99	33,383 us	36,683 us	16,839 us	-9.0%	+98.2%
bs=100 sw=10 sl=64	throughput	767 tuples/sec	815 tuples/sec	1,166 tuples/sec	-5.9%	-34.2%
bs=100 sw=10 sl=64	MB/s	0.468 MB/s	0.498 MB/s	0.711 MB/s	-6.0%	-34.2%
bs=100 sw=10 sl=64	p50	125,793 us	121,321 us	87,509 us	+3.7%	+43.7%
bs=100 sw=10 sl=64	p95	196,040 us	152,247 us	93,675 us	+28.8%	+109.3%
bs=100 sw=10 sl=64	p99	196,040 us	152,247 us	102,153 us	+28.8%	+91.9%
bs=1000 sw=10 sl=64	throughput	912 tuples/sec	897 tuples/sec	1,198 tuples/sec	+1.7%	-23.9%
bs=1000 sw=10 sl=64	MB/s	0.557 MB/s	0.547 MB/s	0.731 MB/s	+1.8%	-23.8%
bs=1000 sw=10 sl=64	p50	1,084,833 us	1,118,932 us	859,766 us	-3.0%	+26.2%
bs=1000 sw=10 sl=64	p95	1,207,128 us	1,198,616 us	902,897 us	+0.7%	+33.7%
bs=1000 sw=10 sl=64	p99	1,207,128 us	1,198,616 us	937,957 us	+0.7%	+28.7%

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
0,10,10,64,20,533.62,200,128000,375,0.229,25560.62,33383.28,33383.28
1,100,10,64,20,2607.38,2000,1280000,767,0.468,125793.43,196040.00,196040.00
2,1000,10,64,20,21921.87,20000,12800000,912,0.557,1084833.39,1207128.03,1207128.03

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.25%. Comparing base (5de9bf9) to head (a15f1ee).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #7996      +/-   ##
============================================
+ Coverage     93.21%   93.25%   +0.04%     
- Complexity     4664     4678      +14     
============================================
  Files          1175     1177       +2     
  Lines         47646    47685      +39     
  Branches       5319     5312       -7     
============================================
+ Hits          44413    44469      +56     
+ Misses         1752     1740      -12     
+ Partials       1481     1476       -5     

Flag	Coverage Δ		*Carryforward flag
access-control-service	81.00% <ø> (ø)		Carriedforward from 5de9bf9
agent-service	99.32% <ø> (ø)		Carriedforward from 5de9bf9
amber	89.43% <100.00%> (+0.12%)	⬆️
computing-unit-managing-service	73.67% <ø> (ø)		Carriedforward from 5de9bf9
config-service	86.73% <ø> (ø)		Carriedforward from 5de9bf9
file-service	86.70% <ø> (ø)		Carriedforward from 5de9bf9
frontend	95.67% <ø> (ø)		Carriedforward from 5de9bf9
notebook-migration-service	79.31% <ø> (ø)		Carriedforward from 5de9bf9
pyamber	97.74% <ø> (ø)		Carriedforward from 5de9bf9
workflow-compiling-service	77.19% <ø> (ø)		Carriedforward from 5de9bf9

*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.