fix: preserve covered prefixes and reject ambiguous compaction ownership

[100yenadmin]

Problem and behavior

Compaction can reject a contiguous new leaf when a retained summary already covers the leading part of the logical conversation but the lifecycle frontier is stale. Source mapping and publication must use the same ownership domain; widening only publication is insufficient.

This change credits only a proven retained leading prefix, leaves original leaf lineage unchanged, and publishes new source occurrences once. Explicit conversation ownership remains authoritative. Ambiguous legacy ownership, duplicate claims, missing coverage, or inadmissible potentially emitted summary lineage reject publication without advancing the frontier.

The ownership check conservatively validates all current uncondensed roots that could be emitted, independently of token-budget prediction. This can refuse compaction for an invalid legacy root even when one particular cap would omit it. It does not delete, reassign, or silently repair that history.

Refs #247. This is a bounded replacement implementation; contributor PR #397 remains preserved. This PR does not close #247 or claim retained-session recovery, release acceptance, or a deployed repair.

Validation

• The retained-leading-prefix product regression fails on unmodified main 7fb19f8d3518080c8d07408a2a28c3c66c15c51b.
• At f063c8f3be4b3f0037e930d539c58ba33d73a918, PYTHONPATH=<pinned-Hermes-checkout> python -m pytest -q tests/test_issue_247_multisession_publication.py: 9 passed. The file exercises atomic refusal, exact leading-prefix credit, rollover, mixed below/above-frontier duplicate claims, conflicting blank legacy bindings, and capped emitted-root ownership.
• Independent semantic review of the original surface plus targeted corrections passed. This is source review, not the protected exact-head release/merge receipt.
• The canonical Hermes tool-result shape completes five ordinary compaction publications on both baseline and candidate, reducing the synthetic context from 51 to 26 messages. A prior fixture using name instead of Hermes's tool_name was corrected; it is not counted as a product defect.
• Exact-head CI passes on Python 3.11–3.14, lint and workflow-lint. The existing contiguous-frontier focused file also passes all 11 tests.
• A complete retained-session copy still refuses normal host compaction without changing its active context or losing original data. The isolated ledger-prefix proof does not establish retained-session recovery. Release qualification remains incomplete.

No schema migration, provider-routing change, host protocol, native fallback, or historical re-summarization is introduced. Existing original messages and summary nodes remain stored.

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[100yenadmin]

Thanks for this bounded attempt at #247. That issue is now closed, and the underlying publication_invariant_conflict mechanism across compaction boundaries was fixed on main in v0.24.0 (#484, together with #462), with further occurrence-projection work in v0.24.1 (#510/#515). Closing as superseded. If ambiguous legacy ownership still blocks publication on current main, please open a fresh issue with a v0.24.1 reproduction and a PR against main.