fix(files): hydrate chat attachments and reject blank download URLs

[icecrasher321]

Summary

• Resolve stored attachment ownership from canonical metadata so deployed agents can hydrate remembered chat uploads under workspace authority, while preserving explicit file/chat scope and strict workspace-file APIs.
• Reject empty and whitespace-only download URLs before previews, direct requests, or authentication fallback can fetch the chat page.

Type of Change

• Bug fix

Testing

• PostgreSQL harness exercises persisted memory, real storage, OpenAI/Anthropic request building, streaming, large-file authorization, and byte-checked OpenAI uploads with mocked provider HTTP.
• 3,102 tests passed across 204 files, including all 16 PostgreSQL harness cases and the complete internal-file operation suite. The current staging merge candidate also passed all 3,107 tests. App/auth type checks, lint, all 46 repository audits, and docs-manifest validation passed.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated
docs	Skipped		Sep 16, 2026 12:07am UTC

[cubic-dev-ai]

No issues found across 10 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}

[greptile-apps]

Confidence Score: 5/5

The pull request appears safe to merge with no actionable correctness, security, or repository-rule violations identified.

Summary

This PR hardens chat attachment hydration and download handling.

• Resolves persisted workspace and mothership attachments through canonical metadata and workspace authorization.
• Preserves delegated file and chat scope while preventing known-invalid canonical bindings from falling back to legacy authorization.
• Rejects empty or whitespace-only external URLs before preview or download requests.
• Expands coverage for provider attachment handling, sandbox mounts, provenance, and stored-file authorization.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A[Remembered chat attachment] --> B[Infer workspace storage key]
  B --> C[Load canonical file metadata]
  C --> D{Metadata and workspace valid?}
  D -- No --> E[Return concealed not-found error]
  D -- Yes --> F[Authorize principal and delegated scope]
  F --> G[Recheck canonical identity]
  G --> H[Read or presign stored bytes]
  I[Chat download click] --> J{Valid storage key?}
  J -- Yes --> K[Authenticated serve route]
  J -- No --> L{Nonblank safe HTTP URL?}
  L -- Yes --> M[External download]
  L -- No --> N[Show download error]

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[icecrasher321]

@greptile

[icecrasher321]

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[cubic-dev-ai]

No issues found across 11 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}