feat: decouple startup logs from DD_TRACE_DEBUG

[bm1549]

Description

Decouples DD_TRACE_STARTUP_LOGS from DD_TRACE_DEBUG so that setting DD_TRACE_STARTUP_LOGS=true emits startup configuration logs directly to stderr, regardless of whether debug mode is enabled or how PHP's error_log is configured.

Changes:

• When DD_TRACE_STARTUP_LOGS=true, startup logs (DATADOG TRACER CONFIGURATION JSON + diagnostics) are written directly to stderr via fprintf
• The existing LOGEV(STARTUP, ...) path through the tracing log system is preserved for when DD_TRACE_DEBUG enables it
• Removes the CLI SAPI check that previously suppressed startup logs in CLI mode
• Changes the default of DD_TRACE_STARTUP_LOGS from true to false

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

🤖 Generated with Claude Code

[datadog-datadog-prod-us1]

⚠️ Tests

✨ Fix all issues with BitsAI or with Cursor

⚠️ Warnings

🧪 14 Tests failed

testInstrumentation from custom-framework-autoloading-test.DDTrace\Tests\Integrations\Custom\Autoloaded\InstrumentationTest     (Fix with Cursor)

DDTrace\Tests\Integrations\Custom\Autoloaded\InstrumentationTest::testInstrumentation
Failed asserting that an array has the key 'logs_created'.

tests/Integrations/Custom/Autoloaded/InstrumentationTest.php:79
tests/Common/RetryTraitVersionGeneric.php:28
phpvfscomposer://tests/vendor/phpunit/phpunit/phpunit:97

testDiagnosticChecksLoggedWhenDebugModeEnabled from custom-framework-autoloading-test.DDTrace\Tests\Integrations\Custom\Autoloaded\StartupLoggingDiagnosticsTest     (Fix with Cursor)

DDTrace\Tests\Integrations\Custom\Autoloaded\StartupLoggingDiagnosticsTest::testDiagnosticChecksLoggedWhenDebugModeEnabled
Failed asserting that '' contains "DATADOG TRACER DIAGNOSTICS - agent_error:".

tests/Common/BaseTestCase.php:117
tests/Integrations/Custom/Autoloaded/StartupLoggingDiagnosticsTest.php:55
tests/Common/RetryTraitVersionGeneric.php:28
phpvfscomposer://tests/vendor/phpunit/phpunit/phpunit:97

testLogsGeneratedOnFirstRequest from custom-framework-autoloading-test.DDTrace\Tests\Integrations\Custom\Autoloaded\StartupLoggingTest     (Fix with Cursor)

DDTrace\Tests\Integrations\Custom\Autoloaded\StartupLoggingTest::testLogsGeneratedOnFirstRequest
Exception: No JSON found in startup log

tests/Integrations/Custom/Autoloaded/StartupLoggingTest.php:105
tests/Integrations/Custom/Autoloaded/StartupLoggingTest.php:59
tests/Common/RetryTraitVersionGeneric.php:28
phpvfscomposer://tests/vendor/phpunit/phpunit/phpunit:97

View all

ℹ️ Info

No other issues found (see more)

❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 60.64% (-0.04%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 493a634 | Docs | Datadog PR Page | Was this helpful? React with 👍/👎 or give us feedback!}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.77%. Comparing base (fd1ba67) to head (493a634).

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #3749       +/-   ##
===========================================
+ Coverage   68.78%   86.77%   +17.98%     
===========================================
  Files         166       24      -142     
  Lines       19015     5269    -13746     
  Branches     1792        0     -1792     
===========================================
- Hits        13079     4572     -8507     
+ Misses       5124      697     -4427     
+ Partials      812        0      -812     

Flag	Coverage Δ
helper-rust-integration	78.79% <ø> (-0.03%)	⬇️
helper-rust-unit	49.17% <ø> (-0.20%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.
see 145 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fd1ba67...493a634. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[pr-commenter]

Benchmarks [ tracer ]

Benchmark execution time: 2026-03-27 23:45:59

Comparing candidate commit 493a634 in PR branch brian.marks/startup-logs-without-debug with baseline commit fd1ba67 in branch master.

Found 1 performance improvements and 2 performance regressions! Performance is the same for 190 metrics, 1 unstable metrics.

scenario:MessagePackSerializationBench/benchMessagePackSerialization

• 🟥 execution_time [+5.398µs; +6.322µs] or [+5.458%; +6.391%]

scenario:MessagePackSerializationBench/benchMessagePackSerialization-opcache

• 🟥 execution_time [+6.846µs; +8.374µs] or [+6.661%; +8.148%]

scenario:TraceSerializationBench/benchSerializeTrace

• 🟩 execution_time [-20.563µs; -8.837µs] or [-4.730%; -2.033%]