feat(explorer): allow client to pass in metadata

[roaga]

Allows client to pass in arbitrary metadata when starting a new run and allow it to retrieve it later

[sentry]

Bug: The new metadata field might not be accepted by the external Seer backend, leading to runtime errors.
_{Severity: HIGH | Confidence: Low}

🔍 Detailed Analysis

The client-side code sends a metadata field to an external Seer service, but there's no verification or integration tests to confirm the backend accepts this new parameter. If the backend has not been updated or rejects unknown fields, it could return a 400 Bad Request, causing the client to raise requests.HTTPError() and the feature to fail at runtime.

💡 Suggested Fix

Add integration tests that call the external Seer backend with the metadata parameter to verify its acceptance and proper handling. Coordinate with the Seer backend team to ensure metadata is supported.

🤖 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/seer/explorer/client.py#L252-L254

Potential issue: The client-side code sends a `metadata` field to an external Seer
service, but there's no verification or integration tests to confirm the backend accepts
this new parameter. If the backend has not been updated or rejects unknown fields, it
could return a `400 Bad Request`, causing the client to raise `requests.HTTPError()` and
the feature to fail at runtime.

_{Did we get this right? 👍 / 👎 to inform future reviews.
Reference ID: 6582980}

[roaga]

https://github.com/getsentry/seer/pull/4218

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/sentry/seer/explorer/client.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #104606      +/-   ##
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- Coverage   80.63%    80.52%   -0.12%     
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  Files        9335      9330       -5     
  Lines      402949    400718    -2231     
  Branches    25689     25689              
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- Hits       324921    322679    -2242     
- Misses      77562     77573      +11     
  Partials      466       466