fix(protos): honor PROTOC for protobuf codegen

[embeaken]

Summary

Use the conventional PROTOC environment variable for the protobuf-codegen invocations in datadog-protos when it is set. Continue searching PATH when it is unset so existing Cargo builds keep working.

Also declare PROTOC as a build-script input so Cargo reruns code generation when it changes.

This allows hermetic build systems such as Bazel to provide an explicitly declared compiler instead of requiring protoc on the host PATH.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

How did you test this PR?

Ran the datadog-protos check both with an explicit compiler and with the existing PATH fallback:

PROTOC=/opt/homebrew/bin/protoc cargo check -p datadog-protos
env -u PROTOC cargo check -p datadog-protos

[chatgpt-codex-connector]

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[pr-commenter]

Binary Size Analysis (Agent Data Plane)

Baseline: bfbd168 · Comparison: b1bc60b · diff
Analysis Configuration: stripped binaries · Pass/Fail Threshold: +5%
Sizes: 41.55 MiB (baseline) vs 41.55 MiB (comparison)
Size Change: -264 B (-0.00%)

✅ Binary size difference within threshold

Changes by Module

Module	File Size	Symbols
anon.9b66f8c6094f89350371ac7937de7c72.830.llvm.14734938299648409202	-17.00 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.830.llvm.7519367550485861600	+17.00 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.200.llvm.7519367550485861600	+10.18 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.200.llvm.14734938299648409202	-10.18 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.816.llvm.7519367550485861600	+9.61 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.816.llvm.14734938299648409202	-9.61 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.811.llvm.14734938299648409202	-4.58 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.811.llvm.7519367550485861600	+4.57 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.28.llvm.14734938299648409202	-3.65 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.28.llvm.7519367550485861600	+3.65 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.637.llvm.7519367550485861600	+3.28 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.637.llvm.14734938299648409202	-3.28 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.826.llvm.7519367550485861600	+2.83 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.826.llvm.14734938299648409202	-2.83 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.1055.llvm.14734938299648409202	-2.60 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.1055.llvm.7519367550485861600	+2.59 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.828.llvm.14734938299648409202	-2.47 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.828.llvm.7519367550485861600	+2.47 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.185.llvm.14734938299648409202	-1.77 KiB	1
anon.9b66f8c6094f89350371ac7937de7c72.185.llvm.7519367550485861600	+1.77 KiB	1

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [NEW] +17.0Ki  [NEW]     +76    anon.9b66f8c6094f89350371ac7937de7c72.830.llvm.7519367550485861600
  [NEW] +10.2Ki  [NEW]     +79    anon.9b66f8c6094f89350371ac7937de7c72.200.llvm.7519367550485861600
  [NEW] +9.61Ki  [NEW]     +91    anon.9b66f8c6094f89350371ac7937de7c72.816.llvm.7519367550485861600
  [NEW] +4.57Ki  [NEW]     +74    anon.9b66f8c6094f89350371ac7937de7c72.811.llvm.7519367550485861600
  [NEW] +3.65Ki  [NEW]     +16    anon.9b66f8c6094f89350371ac7937de7c72.28.llvm.7519367550485861600
  [NEW] +3.28Ki  [NEW]      +2    anon.9b66f8c6094f89350371ac7937de7c72.637.llvm.7519367550485861600
  [NEW] +2.83Ki  [NEW]     +76    anon.9b66f8c6094f89350371ac7937de7c72.826.llvm.7519367550485861600
  [NEW] +2.59Ki  [NEW]    +101    anon.9b66f8c6094f89350371ac7937de7c72.1055.llvm.7519367550485861600
  [NEW] +2.47Ki  [NEW]     +80    anon.9b66f8c6094f89350371ac7937de7c72.828.llvm.7519367550485861600
  [NEW] +1.77Ki  [NEW]     +95    anon.9b66f8c6094f89350371ac7937de7c72.185.llvm.7519367550485861600
  -0.1%    -258  [ = ]       0    [1151 Others]
  [DEL] -1.77Ki  [DEL]     -95    anon.9b66f8c6094f89350371ac7937de7c72.185.llvm.14734938299648409202
  [DEL] -2.47Ki  [DEL]     -80    anon.9b66f8c6094f89350371ac7937de7c72.828.llvm.14734938299648409202
  [DEL] -2.60Ki  [DEL]    -101    anon.9b66f8c6094f89350371ac7937de7c72.1055.llvm.14734938299648409202
  [DEL] -2.83Ki  [DEL]     -76    anon.9b66f8c6094f89350371ac7937de7c72.826.llvm.14734938299648409202
  [DEL] -3.28Ki  [DEL]      -2    anon.9b66f8c6094f89350371ac7937de7c72.637.llvm.14734938299648409202
  [DEL] -3.65Ki  [DEL]     -16    anon.9b66f8c6094f89350371ac7937de7c72.28.llvm.14734938299648409202
  [DEL] -4.58Ki  [DEL]     -74    anon.9b66f8c6094f89350371ac7937de7c72.811.llvm.14734938299648409202
  [DEL] -9.61Ki  [DEL]     -91    anon.9b66f8c6094f89350371ac7937de7c72.816.llvm.14734938299648409202
  [DEL] -10.2Ki  [DEL]     -79    anon.9b66f8c6094f89350371ac7937de7c72.200.llvm.14734938299648409202
  [DEL] -17.0Ki  [DEL]     -76    anon.9b66f8c6094f89350371ac7937de7c72.830.llvm.14734938299648409202
  -0.0%    -264  [ = ]       0    TOTAL

[datadog-prod-us1-4]

When PROTOC points to a compiler outside PATH, the helper sets its path but does not select the protoc parser. The build script fails before it invokes the compiler, so the hermetic-build case remains broken.

_{Open Bits AI session}

_{🤖 Datadog Autotest · Commit 79e62c3 · What is Autotest? · @DataDog review to ask questions · Any feedback? Reach out in #autotest}

[pr-commenter]

Regression Detector (Agent Data Plane)

Run ID: d6705047-6c48-4e46-82f8-6b8346d42c1d
Baseline: bfbd1687 · Comparison: b1bc60ba · diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment (5)

Experiments configured erratic: true are tagged (ignored) and skipped when determining which experiments regressed or improved. Experiments which are detected as erratic at runtime are tagged (erratic) to flag that the run's sample dispersion was high, but their regression / improvement signal still counts.

experiment	goal	Δ mean %	links
quality_gates_rss_dsd_low	memory	⚪ +0.42	metrics profiles logs
quality_gates_rss_dsd_medium	memory	⚪ +0.26	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory	⚪ -0.13	metrics profiles logs
quality_gates_rss_idle	memory	⚪ -0.50	metrics profiles logs
quality_gates_rss_dsd_heavy	memory	⚪ -0.83	metrics profiles logs

Bounds Checks: ✅ Passed (5)

experiment	check	replicates	observed	links
quality_gates_rss_dsd_heavy	memory_usage	10/10	✅ 227 MiB ≤ 250 MiB	metrics profiles logs
quality_gates_rss_dsd_low	memory_usage	10/10	✅ 51.4 MiB ≤ 60 MiB	metrics profiles logs
quality_gates_rss_dsd_medium	memory_usage	10/10	✅ 90.4 MiB ≤ 100 MiB	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory_usage	10/10	✅ 392 MiB ≤ 420 MiB	metrics profiles logs
quality_gates_rss_idle	memory_usage	10/10	✅ 31.7 MiB ≤ 40 MiB	metrics profiles logs

Explanation

A change is flagged as a regression when |Δ mean %| > 5.00% in the regressing direction for its optimization goal AND SMP marks the experiment as a regression (is_regression: true). Improvements use the matching criteria for the improving direction. Experiments configured erratic: true (tagged (ignored)) are skipped outright; experiments detected as erratic at runtime (tagged (erratic)) still count, since that flag describes sample dispersion rather than directional certainty. The Δ mean % cell is colored accordingly: 🟢 = improvement, 🔴 = regression, ⚪ = neutral. Reduction in CPU or memory is an improvement; reduction in ingress throughput is a regression. Experiments tagged (no analysis) show ⚠️ n/a: SMP ran them but produced no analysis, usually because a replicate failed and exhausted its retries. Check the SMP report for that experiment's replicate failures.