feat(controlplane): always sample batch subgraph publish traces

[gausie]

Problem

Batch subgraph publishes go through the PublishFederatedSubgraphs RPC, which is rare, slow, and frequently hits the ~90s request timeout. In prod, SENTRY_TRACES_SAMPLE_RATE is below 1.0, so the flat tracesSampleRate drops most successful batch publishes — only the timed-out ones reliably show up in Sentry. That makes it hard to track the end-to-end composition cost of a publish over time.

Change

Replace the flat tracesSampleRate with a tracesSampler that:

• returns 1.0 for the batch publish RPC (/wg.cosmo.platform.v1.PlatformService/PublishFederatedSubgraphs), matched against the span name / http.route / http.target / url.path / url.full;
• falls back to SENTRY_TRACES_SAMPLE_RATE for everything else (no change for other transactions);
• honors an upstream sampling decision (parentSampled) so distributed traces stay intact.

Child composition spans (e.g. ComposeGraphsWorker.composeGraphsInWorker) inherit the parent's sampling decision, so the full trace — including per-federated-graph compose timings — is captured.

The forced-sample list is a single constant (ALWAYS_SAMPLE_PATHS), easy to extend to other operations later.

Notes

• tracesSampler takes precedence over tracesSampleRate; the sampler returns the configured rate as its default, so overall sampling behaviour is unchanged except for the batch publish path.
• Takes effect after a control plane deploy.

Summary by CodeRabbit

• Chores
  • Improved distributed tracing: selected RPC paths are now always fully sampled, existing upstream parent/child sampling decisions are preserved when present, and all other traces follow the configured sample rate—resulting in more accurate end-to-end trace coverage and clearer diagnostics for publish-related operations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

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Run ID: 9c7d851f-9b0d-4468-89f8-84cbf21aaa67

📥 Commits

Reviewing files that changed from the base of the PR and between 070e28a and abf4bab.

📒 Files selected for processing (1)

• controlplane/src/core/sentry.config.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• controlplane/src/core/sentry.config.ts

---

Walkthrough

Sentry distributed-tracing sampling is now customized via a new tracesSampler. The configuration introduces path-based sampling rules and preserves upstream sampling decisions from distributed traces, replacing the previous static tracesSampleRate approach.

Changes

Sentry tracing sampling customization

Layer / File(s)

Summary

Distributed-tracing sampling logic and configuration controlplane/src/core/sentry.config.ts

ALWAYS_SAMPLE_PATHS lists RPC endpoints that require 100% trace sampling. publishAwareTracesSampler checks ctx.name and span attributes (http.route, http.target, url.path, url.full) for substring matches to always-sampled paths, returns 1/0 when ctx.parentSampled is a boolean to preserve upstream sampling, and otherwise falls back to SENTRY_TRACES_SAMPLE_RATE. Sentry.init is updated to use tracesSampler: publishAwareTracesSampler (removing tracesSampleRate).

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• wundergraph/cosmo#2905: Updates Sentry configuration to parse sentryEnvVariables, both PRs touch Sentry init and tracing configuration.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: introducing selective tracing for batch subgraph publish operations to ensure these critical traces are always sampled.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@controlplane/src/core/sentry.config.ts`:
- Around line 28-30: The current check using ctx.parentSampled wrongly returns
SENTRY_TRACES_SAMPLE_RATE when ctx.parentSampled is false; update the sampling
decision so that if typeof ctx.parentSampled === 'boolean' you return 1 when
ctx.parentSampled is true and 0 when false (do not fall back to
SENTRY_TRACES_SAMPLE_RATE), i.e. honor ctx.parentSampled exactly; update the
branch that references ctx.parentSampled and SENTRY_TRACES_SAMPLE_RATE
accordingly so child spans are not sampled when parentSampled === false.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 117d1f6e-006b-4eee-8e49-b21addcf17ec

📥 Commits

Reviewing files that changed from the base of the PR and between ce8f3c5 and 936d085.

📒 Files selected for processing (1)

• controlplane/src/core/sentry.config.ts

[codecov]

Codecov Report

❌ Patch coverage is 0% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.63%. Comparing base (9aef4ca) to head (1da4058).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
controlplane/src/core/sentry.config.ts	0.00%	29 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2957       +/-   ##
===========================================
+ Coverage   41.64%   65.63%   +23.99%     
===========================================
  Files        1053      329      -724     
  Lines      133865    47321    -86544     
  Branches     6472     5300     -1172     
===========================================
- Hits        55742    31059    -24683     
+ Misses      76332    16238    -60094     
+ Partials     1791       24     -1767     

Files with missing lines	Coverage Δ
controlplane/src/core/sentry.config.ts	0.00% <0.00%> (ø)

... and 725 files with indirect coverage changes

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[comatory]

I am worried that this code is in the hot path and I'd try to optimize here. Maybe I'm paranoid? I know we can't be sure if we don't benchmark but still... wDYT?