feat(asgi): Migrate away from event processor in span first

[sentrivana]

Description

In span first, there are no event processors. Therefore, we need to be able to set the data we were setting in event processors in some other way.

As we migrate our integrations one by one, this will be an exercise in whether it's possible to achieve this without some sort of callback/lifecycle hooks. So far, in ASGI, it seems we can get by by simply using scope.set_attribute() for setting request related data, and updating the segment name/source just before the span ends.

Adding this enables us to actually test the new functionality.

Issues

• Closes Event processor replacement for streamed spans #5722
• Closes https://linear.app/getsentry/issue/PY-2152/event-processor-replacement-for-streamed-spans

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[linear-code]

PY-2152 Event processor replacement for streamed spans

[github-actions]

Semver Impact of This PR

🟡 Minor (new features)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

---

This PR will not appear in the changelog.

---

_{🤖 This preview updates automatically when you update the PR.}

[github-actions]

Semver Impact of This PR

🟡 Minor (new features)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

---

This PR will not appear in the changelog.

---

_{🤖 This preview updates automatically when you update the PR.}

[github-actions]

Codecov Results 📊

✅ 13 passed | Total: 13 | Pass Rate: 100% | Execution Time: 9.24s

All tests are passing successfully.

❌ Patch coverage is 6.52%. Project has 14812 uncovered lines.

Files with missing lines (2)

File	Patch %	Lines
asgi.py	15.76%	⚠️ 171 Missing
_asgi_common.py	14.49%	⚠️ 59 Missing

---

Generated by Codecov Action

[sentry-warden]

envelopes_to_spans raises KeyError when span has no attributes

The function directly accesses span_json["attributes"] which will raise a KeyError if the span has no attributes. Looking at _span_batcher.py:116-119, the attributes field is only serialized when item._attributes is truthy - spans without attributes won't have this key in the JSON. This will cause test failures if any span being parsed lacks attributes.

Verification

Read _span_batcher.py and confirmed _to_transport_format conditionally adds attributes (if item._attributes:). Read conftest.py and confirmed envelopes_to_spans uses direct dictionary access span_json["attributes"] without .get(). This would raise KeyError for spans serialized without attributes.

Suggested fix: Use .get() with an empty dict default to safely handle spans without attributes

Suggested change

	"attributes": {
	k: v["value"] for (k, v) in span_json["attributes"].items()
	},
	k: v["value"] for (k, v) in span_json.get("attributes", {}).items()

Identified by Warden code-review · 23K-KC9

[sentry-warden]

Fix attempt detected (commit e93fd1b)

The envelopes_to_spans function was added to fix the issue, but line 1231 still uses direct dictionary access span_json["attributes"].items() instead of the suggested .get("attributes", {}) pattern, leaving the KeyError vulnerability unresolved for spans without attributes.

The original issue appears unresolved. Please review and try again.

_{Evaluated by Warden}