Materialize complete accepted source before the GEAK handoff

[iraj465]

• Description: GEAK can receive sparse snapshots from the latest accepted current_best while Python still imports an installed regular package, or a supposedly deleted module. Materialize the accepted Git trees into a complete, hashed source bundle before the GEAK handoff. The producer records ordered layer coverage, import roots, file modes, affected modules and deletions; includes this identity in the baseline fingerprint; and captures source changes across accepted commits and outside-root artifacts. Unsupported or unresolved source fails explicitly. The runner requires a consumer that advertises the source protocol before launching.
• Linked issue: Verify accepted source inheritance before benchmarking orchestrator baselines GEAK#475. Paired GEAK consumer PR: Preserve accepted upstream Python source through measurement and replay GEAK#477 (frozen local L0 passed with 2,498 tests, 90 subtests and 97.05% coverage).
• Tests: 327 distinct focused/boundary cases passed, plus independent producer/identity and cross-repository import/relocation checks. Frozen full suite at 6492a806: 22,768 passed, 55 skipped, 77 deselected, 3 subtests passed, 2 failed. Both failures reproduce on unchanged base 2cc382a8: earlier tests leave the canonical Forge selector in the environment, and a supervisor fixture assumes host PID123 is dead. Whole-repository Ruff, formatting and REUSE pass; mypy has the same 1,325 normalized diagnostics as base, with no new diagnostics. Hosted checks will provide the CI result.
• CHANGELOG.md entry under [Unreleased]: yes.
• Breaking changes: source-bearing handoffs require the paired source-capable GEAK consumer. Controls-only handoffs retain their existing behavior. Version 1 supports regular pure-Python source with complete Git/layer coverage; unsupported compiled, namespace and ambiguous ownership changes fail explicitly. A ready descriptor proves bundle completeness, not serving-process engagement or a performance gain.
• PR addresses single concern: yes, accepted-source fidelity at the Hyperloom-to-GEAK boundary. This does not change the frozen online A/B, infer a cause for its baseline drift, or alter native accuracy/acceptance thresholds.
• Root cause spans the producer and consumer boundary; upstream ticket: Verify accepted source inheritance before benchmarking orchestrator baselines GEAK#475. GEAK owns serving-process measurement/replay proof; this PR owns complete accepted source production and capability negotiation.