oss_17_jaeger_debug_and_parentbased_trace_state

[ocelotl]

Closes #28

Jaeger inject now propagates only the SAMPLED bit (no forced DEBUG); ParentBased forwards trace_state to its delegate and the SDK passes the parent trace_state into should_sample (Linear OSS-17, findings P4/T4).

Validation: scope contained to propagator-jaeger + opentelemetry-sdk + changelog; jaeger suite 18 passed, sdk sampling+trace 124 passed. Note: one pre-existing test that asserted the old forced-DEBUG behavior was replaced.

Linear issue: https://linear.app/dash0/issue/OSS-17/p4-t4-jaeger-forces-debug-bit-on-all-sampled-spans-parentbased-drops

[ocelotl]

🔒 Internal (dash0) — not for upstream.

• Linear: https://linear.app/dash0/issue/OSS-17/p4-t4-jaeger-forces-debug-bit-on-all-sampled-spans-parentbased-drops (findings P4/T4)
• Closes: oss_17_jaeger_debug_and_parentbased_trace_state #28 · Branch: oss_17_jaeger_debug_and_parentbased_trace_state · Commit: 16648be08
• Validation: jaeger 18 passed, sdk sampling+trace 124 passed; scope jaeger + sdk + changelog.

[ocelotl]

📣 Public-facing draft — to be used for the upstream PR in open-telemetry/opentelemetry-python. No internal references; copy verbatim.

Title: Fix Jaeger inject debug flag and ParentBased trace_state forwarding

What

• Jaeger propagator: on inject, propagate only the SAMPLED trace flag instead of OR-ing in the Jaeger DEBUG flag (0x02) for every sampled span.
• ParentBased.should_sample: forward the incoming trace_state to the selected delegate sampler.
• SDK Tracer.start_span: pass the parent span context's trace_state into self.sampler.should_sample(...).

Why

• The Jaeger DEBUG flag is a forced-keep signal; setting it on every normally-sampled span overrides downstream sampling, and inject was asymmetric with extract (which masks to SAMPLED only). After this change a normally-sampled span injects flags 0x01 with the DEBUG bit clear.
• Sampler.should_sample documents a trace_state parameter, but ParentBased dropped it and the SDK never supplied it, so custom delegates always saw None. Both now deliver trace_state, per the trace/sdk.md sampler contract.

Spec

specification/trace/sdk.md lists trace_state among ShouldSample inputs; a composite sampler must pass inputs to its delegate.

Tests

• propagator-jaeger: replaced the test asserting DEBUG-on-inject with one asserting SAMPLED set / DEBUG clear for a sampled span. Suite: 18 passed.
• opentelemetry-sdk: added a test that a delegate under ParentBased receives the forwarded trace_state. test_sampling.py + test_trace.py: 124 passed.