Function analyze_duplicate_loop_endpoint 

pub fn analyze_duplicate_loop_endpoint(
    clip: &Clip,
) -> Result<Option<DuplicateLoopEndpointOutcome>, DuplicateLoopEndpointError>

Analyze whether a clip has a safe, duplicated loop endpoint.

The authored timeline must be finite, strictly increasing, and exactly shared by every track; each track must have exact key/value cardinality, at least three keys, and a final time exactly equal to clip duration. Closing vectors compare component-wise within 1e-5; quaternions compare with sign-invariant shortest-path angular distance within 1e-4 radians. The predicate is the mechanically removable subset of #22’s future duplicate_endpoint mode, not a parallel endpoint-mode classifier. Ok(None) is a valid non-candidate, including two-key clips and stationary holds.