ci: report backport auto-label decisions on the PR

[Yicong-Huang]

What changes were proposed in this PR?

The backport auto-label workflow (.github/workflows/backport-auto-label.yml) decides, per actively-supported release branch, whether to add a release/* label to a fix: PR. Until now every skip was silent — visible only in the Actions log. Its cheap "is this feature on the branch?" check compares exact file paths, so a file moved or renamed after the branch was cut reads as absent and the label is dropped with no signal to the author. #6960 hit exactly this: its files live under coordinator/ on main but controller/ on release/v1.2, so a fix that genuinely applied to v1.2 was never labeled.

This PR makes the workflow write its reasoning back to the PR as a single report comment:

• One row per actively-supported release branch, with the decision and why:
  • ✅ labeled — change detected on the branch; label added (and who was requested for review);
  • ⚠️ skipped — none of the modified files exist on the branch (the files are listed), with a prompt to check and add the label by hand if the fix should be backported;
  • 🚫 declined — a previously removed label (opt-out), not re-added.
• The comment is upserted in place via a hidden marker, so edited re-runs update the same comment instead of stacking new ones (editing a comment sends no notification, so re-runs stay quiet).
• It links the auto-label run, and is authored by github-actions[bot] like the existing review request (no label PAT needed).
• Inactive branches and non-fix: PRs are unchanged (no comment); a no-backport-needed PR gets a one-line note instead of the table.

Labeling behavior itself is unchanged — this only surfaces the decisions that were already being made.

Any related issues, documentation, discussions?

Resolves #6961. Follow-up to the backport lifecycle automation (#6941, #6959). Motivated by #6960, which was silently not labeled for release/v1.2.

How was this PR tested?

• YAML parses and the embedded github-script passes node --check (async-wrapped).
• Walked the branch/label/timeline/file-status cases against fix(amber): advance region executions in a later coordinator round, not inside portCompleted #6960's real data to confirm the rows and skip reasons render as intended.
• Full end-to-end exercise needs a live pull_request_target event with the org PAT/secrets, which only runs once merged.

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

Generated-by: Claude Code (Claude Opus 4.8)

[github-actions]

Automated Reviewer Suggestions

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

• No candidates found from git blame history.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.97%. Comparing base (ee41d9a) to head (2ef56e0).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6962      +/-   ##
============================================
- Coverage     78.98%   78.97%   -0.02%     
+ Complexity     3786     3782       -4     
============================================
  Files          1160     1160              
  Lines         46105    46105              
  Branches       5115     5115              
============================================
- Hits          36418    36410       -8     
- Misses         8067     8072       +5     
- Partials       1620     1623       +3     

Flag	Coverage Δ
access-control-service	70.00% <ø> (ø)
agent-service	76.76% <ø> (ø)
amber	72.15% <ø> (-0.05%)	⬇️
computing-unit-managing-service	20.49% <ø> (ø)
config-service	66.66% <ø> (ø)
file-service	67.21% <ø> (ø)
frontend	82.99% <ø> (ø)
notebook-migration-service	78.94% <ø> (ø)
pyamber	95.38% <ø> (ø)
workflow-compiling-service	26.31% <ø> (ø)

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[github-actions]

⚠️ Benchmark changes need a look

🟢 2 better · 🔴 7 worse · ⚪ 6 noise (<±5%) · 0 without baseline

Compared against main ee41d9a 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	395	0.241	22,971/35,532/35,532 us	🔴 +17.0% / 🔴 +118.9%
🟢	bs=100 sw=10 sl=64	937	0.572	107,315/130,715/130,715 us	🟢 -17.8% / 🔴 +20.3%
🔴	bs=1000 sw=10 sl=64	1,081	0.66	919,953/1,040,820/1,040,820 us	🔴 +9.5% / 🟢 -8.0%

Baseline details

Latest main ee41d9a from same runner

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	395 tuples/sec	470 tuples/sec	767.9 tuples/sec	-16.0%	-48.6%
bs=10 sw=10 sl=64	MB/s	0.241 MB/s	0.287 MB/s	0.469 MB/s	-16.0%	-48.6%
bs=10 sw=10 sl=64	p50	22,971 us	19,638 us	12,502 us	+17.0%	+83.7%
bs=10 sw=10 sl=64	p95	35,532 us	33,001 us	16,234 us	+7.7%	+118.9%
bs=10 sw=10 sl=64	p99	35,532 us	33,001 us	18,919 us	+7.7%	+87.8%
bs=100 sw=10 sl=64	throughput	937 tuples/sec	900 tuples/sec	974.8 tuples/sec	+4.1%	-3.9%
bs=100 sw=10 sl=64	MB/s	0.572 MB/s	0.55 MB/s	0.595 MB/s	+4.0%	-3.9%
bs=100 sw=10 sl=64	p50	107,315 us	103,811 us	102,449 us	+3.4%	+4.7%
bs=100 sw=10 sl=64	p95	130,715 us	159,047 us	108,652 us	-17.8%	+20.3%
bs=100 sw=10 sl=64	p99	130,715 us	159,047 us	116,310 us	-17.8%	+12.4%
bs=1000 sw=10 sl=64	throughput	1,081 tuples/sec	1,114 tuples/sec	1,004 tuples/sec	-3.0%	+7.7%
bs=1000 sw=10 sl=64	MB/s	0.66 MB/s	0.68 MB/s	0.613 MB/s	-2.9%	+7.7%
bs=1000 sw=10 sl=64	p50	919,953 us	896,619 us	999,606 us	+2.6%	-8.0%
bs=1000 sw=10 sl=64	p95	1,040,820 us	950,443 us	1,046,770 us	+9.5%	-0.6%
bs=1000 sw=10 sl=64	p99	1,040,820 us	950,443 us	1,076,937 us	+9.5%	-3.4%

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
0,10,10,64,20,506.21,200,128000,395,0.241,22971.12,35531.92,35531.92
1,100,10,64,20,2133.59,2000,1280000,937,0.572,107314.77,130714.83,130714.83
2,1000,10,64,20,18497.70,20000,12800000,1081,0.660,919953.02,1040820.14,1040820.14

[xuang7]

LGTM