fix(telemetry): nest product errors in app-started payload

[e-n-0]

What does this PR do?

Serializes telemetry product details directly under products.<product> and keeps optional startup errors inside that product object.

The existing object-level emplace throws when an integration registers a product, preventing app-started telemetry from being sent. This unblocks integrations such as nginx-datadog from reporting their authoritative AppSec startup state.

Validation

• cmake --build build -j4
• ./build/test/tests (199852 assertions in 134 test cases)
• exercised from a local NGINX worker with AppSec enabled and disabled

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-09-03 16:16:59

Comparing candidate commit 9c61349 in PR branch flavien.darche/fix-telemetry-product-payload with baseline commit 83cbde0 in branch main.

Found 4 performance improvements and 1 performance regressions! Performance is the same for 3 metrics, 0 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:BM_HexPadded_uint64/NoPadding

• 🟩 execution_time [-1.872ns; -1.818ns] or [-3.388%; -3.289%]

scenario:BM_HexPadded_uint64/WorstCasePadding

• 🟩 execution_time [-1.440ns; -1.381ns] or [-2.894%; -2.775%]

scenario:BM_Hex_uint64

• 🟥 execution_time [+0.460ns; +0.501ns] or [+2.031%; +2.212%]

scenario:BM_TraceID_ParseHex/128bit

• 🟩 execution_time [-33.854ns; -33.780ns] or [-19.876%; -19.832%]

scenario:BM_TraceID_ParseHex/64bit

• 🟩 execution_time [-18.715ns; -18.587ns] or [-20.068%; -19.932%]

[xlamorlette-datadog]

Neat!