Bug Description

aicr verify reports "Trust level: verified" for a bundle made with
--attest alone, but "Trust level: attested" for the same recipe
with --attest --data ./extdata (one extra registry.yaml covered
transitively via checksums.txt). Same identity, same Sigstore checks
all green (4/4), same envelope shape — yet the tier differs and no
line of output explains why.

Impact

Medium — confusing UX, undermines confidence in the attestation model.
Not destructive.

Component

Bundlers / verifier

Regression?

Unknown.

Reproduction

Requires a browser (run on laptop):

mkdir -p /tmp/attest-tier && cd /tmp/attest-tier
aicr recipe --service eks --accelerator h100 --intent training \
  --os ubuntu --platform kubeflow -o recipe.yaml

# Bundle 1: attest only
aicr bundle -r recipe.yaml -o ./b1 --deployer argocd-helm \
  --repo https://github.com/example/m --attest
aicr verify ./b1   # → Trust level: verified

# Bundle 2: attest + data
mkdir extdata
curl -sSL https://raw.githubusercontent.com/NVIDIA/aicr/v0.12.0-rc1/recipes/registry.yaml \
  -o extdata/registry.yaml
aicr bundle -r recipe.yaml -o ./b2 --deployer argocd-helm \
  --repo https://github.com/example/m --data ./extdata --attest
aicr verify ./b2   # → Trust level: attested

Where

pkg/bundler/verifier/trust.go (around line 141, "Trust level check")
— wherever the trust-tier calculation decides between verified and
attested based on what's covered by the attestation envelope.

Proposed Fix

Pick one — current state is the worst of both: behavior differs but the
user has no signal why.

A. Remove the tier delta when the attestation fully covers --data
files (it does, transitively via the checksums.txt subject). Makes
the two cases equivalent.

B. Keep the delta but emit a one-line rationale in aicr verify
output explaining which input caused the drop:

Trust level: attested
  ↳ external --data files included; verified tier requires bundle
    to use only embedded recipe data

Scope

Confirm with the bundler author whether the tier delta is intentional.
If so, fix is small: thread a reason string through the trust-level
calculation and print it. If not, fix is even smaller: equalize the tier
when transitive coverage holds.

Stable-blocking: probably not, but it is the kind of UX nit users
will keep tripping on.