[drevendev]

Editable source-tree tests can pass when a built distribution is incomplete or its metadata drifts. This change adds a separate ten-minute Ubuntu/Python 3.12 job that builds the exact PR head and exercises only the installed wheel from a fresh venv outside the checkout, using copied offline fixtures.

The stdlib-only gate checks source/wheel/imported/CLI versions, required wheel members, the console entry point, and the empty runtime dependency contract. It runs CLI help/version, core/work/code example verification and replay, and a fixture build/verify. Four damaged copies of the actual built wheel must be rejected: missing CLI, wrong version, a runtime dependency, and an extra-marker OR bypass. Complex dependency markers fail closed. Every subprocess is bounded. Scratch is removed on exit; no wheel/fixture artifacts are uploaded, and ordinary workflow logs use the repository's existing retention. Existing source-test jobs are unchanged.

Fixes #84 upon verified integration into release/0.6.0. Base: 22a2894057d9b1bc003efe4ef932ed4de601e26b; exact reviewed/tested head: 0f7c65a230b0411571ef36decb4343f991cbb8f8. No runtime source/dependency or publication/release-acceptance change.

Validation, 2026-10-24:

• Native Windows build 26200 / Python 3.14.7 / pytest 9.1.1: 2385 passed in 56.20s; focused packaging regressions 12 passed.
• Real built wheel installed with --no-index --no-deps in a fresh venv; isolated import, all seven offline commands and four damaged-wheel refusals passed.
• Exact-head CI run 40102292043: all four jobs success, including installed-wheel consumption on Ubuntu 24.04.5 / Python 3.12.15 and existing source tests on Python 3.12/3.13/3.14.
• Separate read-only agent reviewed the five-file diff and independently repeated all 12 focused tests and the complete wheel gate from an exact git archive export. No actionable findings. This is same-host agent/process independence, not separate credentials or formal forge approval; the reviewer did not independently run Ubuntu CI.
• git diff --check passed; worktree clean.

macOS, other installed-wheel combinations and privileged path behavior remain unqualified. This gate neither publishes 0.6.0 nor accepts the unrelated pending #81–#90 release chain.