refactor(store)!: remove ObjectStore.signed_post

[earakely-scale]

Summary

Breaking: removes ObjectStore.signed_post from the base class and from S3ObjectStore, GCSObjectStore and the routing store.

issue_upload_policy is the upload-policy API. It returns a typed UploadPolicy whose HttpPostPolicyGrant names the uploader's path and file fields. Its lifetime is one the store either honours or refuses. signed_post returned boto3's raw {url, fields} dict and behaved differently per store:

• S3 kept the prefix as given until fix(store): S3 upload policies are scoped to a directory and signed through a private _post_policy #93;
• GCS returned None without a signer and silently clamped the expiry;
• every other store returned None.

Nothing in this repo calls it any more, and neither do the downstream stores we know of.

Migrating:

# before
post = store.signed_post(prefix, expires_in=3600, max_bytes=n)          # {"url", "fields"} or None
# after
policy = store.issue_upload_policy(prefix, max_object_bytes=n, expires_in=3600)
policy.write.url, policy.write.fields, policy.write.path_field, policy.write.file_field

issue_upload_policy raises GrantUnavailableError where signed_post returned None, and NotImplementedError on stores without grants. A caller that only needs one object at a known URL can use issue_write_grant (an HTTPS PUT signed for the object's content type).

S3ObjectStore._post_policy and GCSObjectStore._post_policy now take a required max_bytes, since issue_upload_policy always passes one.

Testing

• Removed tests: tst/unit/store/s3_signed_post_test.py is deleted. Its upload-policy cases are covered by test_object_transfer_grants.py, which checks the exact generate_presigned_post call for prefixes with and without a trailing slash. Its signed_post-only cases (no size bound, None from stores that can't sign) have no successor.
• GCS: the signed_post test's bucket-root case is now an issue_upload_policy test.
• Write fence: the local-run write fence no longer lists signed_post.
• Suite: tst/unit 6066 passed (13 skipped); protocol 330 passed.
• Plugin API check: passes.

Labelled bump-version.

🤖 Generated with Claude Code

Confidence Score: 5/5

The PR appears safe to merge as the intended breaking API change.

Summary

The PR removes signed_post from object stores and routes prefix uploads through the typed issue_upload_policy API. S3 and GCS policies now require a per-object size limit.

• Prefix uploads use a typed policy with a required size limit.

_{Reviews (1) · Last reviewed commit: "refactor(store)!: remove ObjectStore.sig..." · Reviewed by Greptile}