feat(ingest-metrics): Ensure billing metrics consumer avoids outcome double-billing

[klochek]

With relay producing billing outcomes here, introduce and check for a new tag ("billing_outcome_accepted") to avoid double-billing.

I checked for prior string existence with:

SELECT string, count(*) 
FROM sentry_{perf,}stringindexer 
WHERE 1=1
    AND string IN (
        'billing_outcome_accepted'
    ) 
GROUP BY string;

Guarded by a new temporary flag organizations:relay-generate-billing-outcome

[Dav1dde]

The feature flag also needs to be exposed to Relay, search for EXPOSABLE_FEATURES

[jjbayer]

Suggested change

@with_feature("organizations:relay-generate-billing-outcome")

Mentioning the feature here should not be necessary because the consumer-side behavior is determined by the tag, not the feature flag, right? This might also be what confused sentry[bot] in their comment above.

[jjbayer]

Not sure if you already bikeshedded on the name but billing_outcome_emitted would make slightly more sense to me (the outcome is Accepted but the thing relay does is emitting it).

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[sentry]

Bug: The variable billing_outcome_accepted_tag is misleadingly named, as it references the string "billing_outcome_emitted". If the external service sends "billing_outcome_accepted", the double-billing prevention will fail.
_{Severity: CRITICAL}

Suggested Fix

Verify the exact tag name sent by the corresponding Relay change. If Relay sends "billing_outcome_accepted", update the string registered in src/sentry/sentry_metrics/indexer/strings.py to match. If Relay sends "billing_outcome_emitted", rename the variable billing_outcome_accepted_tag to billing_outcome_emitted_tag for clarity.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: src/sentry/ingest/billing_metrics_consumer.py#L45

Potential issue: A new mechanism to prevent double-billing for span metrics relies on a
tag check. The variable `billing_outcome_accepted_tag` is used for this check, but it is
assigned the string value `"billing_outcome_emitted"`. The pull request description and
the variable's name imply that the tag sent by the external service (Relay) is
`"billing_outcome_accepted"`. If Relay sends a tag with this name, the consumer's check
for `"billing_outcome_emitted"` will not find it. This would cause the double-billing
prevention logic to silently fail for all metrics, defeating the purpose of the change.

Also affects:

• src/sentry/sentry_metrics/indexer/strings.py:206~206