feat(snapshots): Follow the server-selected objectstore usecase

[NicoHinderling]

Snapshot uploads now request usecase=auto from the upload-options endpoint and use the server's returned usecase for both HEAD deduplication checks and PUT uploads, rather than hardcoding preprod. This keeps Objectstore paths aligned with the minted token and lets the backend move new snapshot content into preprod_snapshots without another CLI change.

When older servers omit usecase, response parsing defaults it to preprod, preserving the existing upload behavior. Object keys remain unchanged; because deduplication is scoped by usecase, the first upload after a server-side switch re-uploads images once.

Pairs with getsentry/sentry#124194 (cross-usecase reads and the upload-options contract) and getsentry/sentry#124210 (server-controlled write selection). getsentry/sentry-cli#3408 implements the same contract in the legacy CLI; both clients are being updated. The backend option remains off by default: register preprod_snapshots in Objectstore before deploying the backend prerequisite, then enable the option only after the backend rollout. Older CLI releases keep writing to preprod and remain readable through fallback reads.

[vercel]

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Project	Deployment	Actions	Updated
cli	Ready	Preview	Sep 14, 2026 6:28pm UTC

1 Skipped Deployment

Project	Deployment	Actions	Updated
sentry-local	Skipped		Sep 14, 2026 6:28pm UTC

[sentry]

Bug: The schema for fetchSnapshotsUploadOptions uses optional() for the usecase field, which will throw an error if the API returns null instead of defaulting as intended.
_{Severity: MEDIUM}

Suggested Fix

Change the schema validation for the usecase field from optional(string(), "preprod") to nullish(string(), "preprod"). This will correctly handle both null and undefined values by applying the default value, making the code more defensive and consistent with codebase patterns.

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: packages/cli/src/lib/api/preprod-artifacts.ts#L26

Potential issue: The schema validation for the response in `fetchSnapshotsUploadOptions`
uses `valibot`'s `optional(string(), "preprod")` for the `usecase` field. This correctly
handles cases where the field is `undefined` (omitted), but it will throw a validation
error if the API explicitly returns `null` for this field. This is inconsistent with
other fields in the same schema and the codebase's documented best practice to use
`.nullish()` for optional fields. If the server returns `"usecase": null`, the
validation will fail, and the unhandled error will crash the entire snapshot upload
command.

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