test(host-packages): capture intermittent drift diagnostics

[ramboz]

Summary

• register bug 008 as a gnarly, medium-severity diagnosis linked to Flaky: run_tests.py intermittently fails host-package drift guard on hosts/claude/.claude-plugin/plugin.json #95
• add opt-in host-drift metadata for source, scratch, and committed manifests
• trace whether the Claude manifest was enumerated and which builder modules were active
• preserve scratch output only for the unexpected in-sync failure, not intentional negative tests

This is diagnostic instrumentation, not a claimed root-cause fix. Bug 008 remains DIAGNOSING.

Verification

• 34 focused host-package/Claude-builder tests pass on CPython 3.14.0
• 34 focused tests pass on CPython 3.13.13
• full unit suites pass on 3.14.0 (3,456 tests) and 3.13.13 (3,457 tests), six skips each
• repository-pinned Ruff 0.15.16 passes on the changed Python files
• host-package drift check remains clean

The wrapper's post-suite pyright invocation cannot access the sandboxed uv cache in the local environment; the unit suites themselves pass.

Refs #95