fix: modernize sync dependencies and fail closed on S3 errors

[anandpant]

Summary

• Replace the legacy AWS HTTP/TLS feature graph with the supported client, retaining SSO, process credentials, and SigV4a. Upgrade Arrow/Parquet together and refresh the affected transport dependencies.
• Fix a reproduced S3 manifest bug: AccessDenied containing the text NoSuchKey must abort publishing, not overwrite the manifest.
• Replace duplicated CI setup with one locked workspace gate, pin Rust 1.95.0 across local/CI/releases, and remove the duplicate PR template.

Supersedes the dependency scope of draft #32; leave its closure to the coordinator. No Databricks deployment or resource removal.

Verification

• cargo audit: 8 vulnerability entries and 3 warnings before; 0 vulnerabilities and 0 warnings after (RustSec database 2026-10-09).
• Formatting, Clippy, 28 Rust tests, and both built CLIs against local Convex/S3 fixtures passed. The S3 regression failed before the fix and passes after it.
• Existing v0.0.5-rc.2 release checksum/version verified; its raw Parquet reader/writer is interoperable with the upgraded CLI in both directions.
• Depot CI passed on pinned Rust 1.95.0: formatting, Clippy, 28 tests, executable builds, and local fixture flows. Workflow actionlint passed.
• Optimized build and locally packaged archive passed checksum/version and runtime checks; checkout-linked dev CLI passed. Rust CodeQL and the other hosted checks passed.

Release

Use the existing release-please / release-rc workflows after coordinator merge; verify the new release target SHA, checksum, and CLI version. Live Convex/AWS/Databricks behavior is not claimed; Databricks profiles currently fail authentication.

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	aws-sdk-s3@​1.129.0 ⏵ 1.152.0
	arrow-array@​54.3.1 ⏵ 60.0.0
	arrow-schema@​54.3.1 ⏵ 60.0.0
	aws-config@​1.8.15 ⏵ 1.12.0
	parquet@​54.3.1 ⏵ 60.0.0

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