feat(debugger): add Remote Enablement support

[watson]

What does this PR do?

Implements Remote Enablement (RE) for Dynamic Instrumentation/Live Debugger and Code Origin via APM_TRACING_MULTICONFIG.

Key Remote Config changes:

• Add RCClientLibConfigManager class for priority-based merging of multiple APM_TRACING configs (Service+Env > Service > Env > Cluster > Org)
• Add APM_TRACING_MULTICONFIG, APM_TRACING_ENABLE_DYNAMIC_INSTRUMENTATION, and APM_TRACING_ENABLE_CODE_ORIGIN capability flags
• Centralize client library configuration remote config logic in config/remote_config.js

Key Debugger changes:

• Add lifecycle methods (isStarted(), stop(), configure()) to debugger/index.js for dynamic control

Key Code Origin changes:

• Add runtime enable/disable support for Code Origin via Remote Config
• Update Express and Fastify code origin plugins to pre-compute entry tags at route registration time when RC is enabled (allowing runtime enabling to work immediately)
• Add integration tests for Code Origin Remote Config toggling

Motivation

The Debugger (Dynamic Instrumentation/Live Debugging) needs to support Remote Enablement, allowing operators to dynamically enable, disable, or reconfigure the debugger without requiring service restarts.

This implementation follows the APM_TRACING_MULTICONFIG RFC.

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.13%. Comparing base (cb2cd12) to head (8392030).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
packages/dd-trace/src/debugger/index.js	12.00%	22 Missing ⚠️
packages/dd-trace/src/proxy.js	53.33%	7 Missing ⚠️
packages/dd-trace/src/config/remote_config.js	96.00%	3 Missing ⚠️
packages/datadog-plugin-fastify/src/code_origin.js	85.71%	1 Missing ⚠️
packages/dd-trace/src/config.js	94.11%	1 Missing ⚠️
packages/dd-trace/src/llmobs/sdk.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7137      +/-   ##
==========================================
- Coverage   85.19%   85.13%   -0.06%     
==========================================
  Files         532      532              
  Lines       22788    22893     +105     
==========================================
+ Hits        19414    19491      +77     
- Misses       3374     3402      +28     

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[watson]

• refactor: move all config related code under config directory #7204
• feat(debugger): add Remote Enablement support #7137 👈 (View in Graphite)
• refactor(remote_config): move capability registration to feature modules #7127
• refactor(remote_config): move appsec-specific logic to appsec folder #7122
• refactor(remote-config): replace kPreUpdate with batch handler API (DEBUG-4402) #7121
• master

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[github-actions]

Overall package size

Self size: 4.41 MB
Deduped: 5.24 MB
No deduping: 5.24 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | import-in-the-middle | 2.0.0 | 68.46 kB | 797.03 kB | | dc-polyfill | 0.1.10 | 26.73 kB | 26.73 kB |

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-01-19 19:32:45

Comparing candidate commit 8392030 in PR branch watson/DEBUG-4402/remote-enablement with baseline commit cb2cd12 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 232 metrics, 28 unstable metrics.

[tylfin]

This generally looks good to me, you might want to run it against this system-test https://github.com/DataDog/system-tests/blob/da17bdc4b54f09001bfd39cf50fd63d8f377cb8d/tests/debugger/test_debugger_inproduct_enablement.py#L55, and try a few manual failure scenarios flipping and deleting the config

[watson]

@tylfin thanks for reminding me about the system tests. They uncovered a bug where this PR didn't properly enable/disable Code Origin at runtime. The last commit added to this PR now should take care of that. The system tests are now passing locally, and I will update them once this PR lands

[BridgeAR]

This is mostly LGTM, I just left a few minor things to check and some nits

[watson]

@tylfin here's the promised system test update to validate remote enablement works for the Node.js tracer: DataDog/system-tests#6063