chore(deps): bump python base digest to a7fb1e6; drop pip from the runtime image

[richardmhope]

The python:3.14-slim digest bump (Dependabot #301) failed the Trivy image
gate: the new digest is CPython 3.14.7, which bundles pip 26.2.1, and pip
26.2 started shipping a CycloneDX SBOM declaring its vendored libraries.
Trivy now sees vendored msgpack 1.1.2 (GHSA-6v7p-g79w-8964, fixed 1.2.1)
and setuptools/pkg_resources 70.3.0 (CVE-2025-47273, fixed 78.1.1) — both
HIGH with an upstream fix, so the fixable-HIGH gate trips. The previous
image's pip 26.1.2 vendors the exact same versions, just without the SBOM,
so the bump introduces no actual regression; the copies live inside pip's
_vendor tree and are only reachable by running pip itself.

The runtime image never runs pip — the venv is resolved by uv in the
builder stage and copied across — so remove pip, its console scripts and
the ensurepip bootstrap wheel from the runtime stage. That resolves the
findings at the source, keeps future pip-vendored CVEs out of the gate,
and extends the existing "build-only tooling stays out of the runtime"
rule to the base image's own bootstrap tooling.

Supersedes #301.

Co-Authored-By: Claude Fable 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01RfHDhw6vo9ZeEfEcB1rvS2

[icebergai-review-bot]

Verdict

Approved

No concrete defects found in the complete base-to-head change. The runtime-only removal of pip and ensurepip is consistent with the builder-created virtual environment and does not affect the application’s packaged dependencies.

Findings

No actionable findings.

Validation

• Reviewed the full supplied Dockerfile patch from db7db35 to 46e0859.
• Confirmed builder and runtime stages use the same pinned Python base digest.
• Confirmed removal targets only base-image pip/ensurepip paths after OS package installation; application dependencies remain in the copied builder-created virtual environment.
• CI is reported as passing for the exact head SHA.

Residual risks

• The container image was not independently rebuilt in this read-only review environment.