AI Coding Plan Template

# [Outcome]

## Problem
[What is wrong or missing, who is affected, and why it matters.]

## Scope
- [In-scope behavior or system]
- [In-scope behavior or system]

## Not in scope
- [Explicit exclusion]

## Current evidence
- [Relevant code, issue, log, metric, or prior decision]

## Implementation
1. [Change and where it belongs]
2. [Change and how it connects]
3. [Migration, rollout, or compatibility step]

## Risks and open questions
- [Risk, uncertainty, or decision still required]

## Validation
- [Command or automated check]
- [Browser, integration, migration, or operator proof]
- [Expected result]

## Documentation
- [Maintained document that must change]

# Reject expired export links before object lookup

## Problem
Expired links still reach the storage lookup, which leaks timing and spends a request.

## Scope
- Validate expiry in the download route before calling the object store.
- Preserve the existing not-found response shape.

## Not in scope
- Changing link lifetime or token format.

## Implementation
1. Move expiry validation into the shared download gate.
2. Return the existing 404 response before storage access.
3. Add an integration test that proves the object store is not called.

## Risks and open questions
- Confirm clock-skew handling remains unchanged.

## Validation
- Run the route integration suite.
- Verify valid, expired, and malformed links return the documented responses.