fix: Potential fix for code scanning alert no. 12: Uncontrolled data used in path expression

[skyoo2003]

Potential fix for https://github.com/skyoo2003/devcloud/security/code-scanning/12

Use strict input validation for uploadID before any filesystem path construction/use in uploadPart.
Best fix without changing behavior: enforce that uploadID matches the expected server-generated format (hex string). This codebase already uses hex utilities/imports, so validating as lowercase/uppercase hex with a reasonable non-empty length is appropriate and minimally invasive.

Concretely in internal/services/s3/provider.go:

• Add a package-level regex for upload ID validation (allowlist).
• In uploadPart, reject invalid uploadID early with an S3-style InvalidArgument response.
• Keep existing filepath.Base and metadata checks; this adds defense-in-depth and satisfies path taint concerns.

No new imports are required because regexp is already imported.

Suggested fixes powered by Copilot Autofix. Review carefully before merging.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adds strict validation for S3 multipart upload IDs in uploadPart to mitigate an uncontrolled data in path expression code scanning alert, rejecting malformed upload IDs before any filesystem or metadata operations.

File-Level Changes

Change	Details	Files
Introduce allowlist-based validation for multipart upload IDs and enforce it early in uploadPart.	Define a package-level regular expression that only allows upload IDs consisting of 16–128 hexadecimal characters. Add an early check in uploadPart that validates the uploadID against the regex and returns an S3 InvalidArgument error if it fails. Leave existing partNumber validation, filepath.Base usage, and metadata lookups unchanged to preserve behavior while adding defense-in-depth.	internal/services/s3/provider.go

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[sourcery-ai]

Hey - I've left some high level feedback:

• The uploadIDPattern length bounds (16–128 chars) implicitly encode assumptions about server-generated IDs; consider deriving these limits from the actual upload ID generator or documenting the rationale nearby to avoid future divergence.
• If uploadID is validated in other paths (e.g., multipart init/complete handlers), you may want to reuse uploadIDPattern there as well to keep validation centralized and consistent.
• The new error message "invalid upload id" differs slightly from existing wording patterns; consider aligning it with other S3-style messages in this file for consistency (e.g., capitalization or phrasing).

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The `uploadIDPattern` length bounds (16–128 chars) implicitly encode assumptions about server-generated IDs; consider deriving these limits from the actual upload ID generator or documenting the rationale nearby to avoid future divergence.
- If `uploadID` is validated in other paths (e.g., multipart init/complete handlers), you may want to reuse `uploadIDPattern` there as well to keep validation centralized and consistent.
- The new error message `"invalid upload id"` differs slightly from existing wording patterns; consider aligning it with other S3-style messages in this file for consistency (e.g., capitalization or phrasing).

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