fix(session-state): lineage walks survive cleared end_reason on reopened links

[sebmarion]

PR: fix(session-state): lineage walks survive cleared end_reason on reopened links

Open with:
https://github.com/NousResearch/hermes-agent/compare/main...sebmarion:hermes-agent:fix/archive-lineage-reopened-links?expand=1

Problem

Archiving a conversation only archived part of it, and the chat kept resurfacing in the sidebar. Reproduced in production.

Root cause chain:

1. The TUI websocket reaper closes stale sessions with end_reason = 'ws_orphan_reap'.
2. Stale-route recovery later calls reopen_session, which clears ended_at/end_reason (by design — that is how resume works).
3. Every lineage walk (set_session_archived, set_session_pinned, set_session_hidden, set_session_read) traverses only parent.end_reason = 'compression' edges.
4. Result: the compression link through a reopened row is invisible. Archive covers only the segment below the break; the unarchived, re-active root keeps the conversation alive in the sidebar, and new continuation rows are born unarchived.

The codebase already acknowledges this fragility: reopen_session stamps children with $._reset_from before clearing the parent's mutable end_reason, precisely because other logic depends on it. Compression chains had no equivalent durable marker.

Fix

Follows the existing _reset_from pattern:

1. Stamp at rotation: publish_compression_child writes $._compression_from = <parent id> into the continuation child's model_config (idempotent, NULL-guarded).
2. Stamp at creation: _insert_session_row stamps children created under an already-ended compression parent — covers the documented race where a child row is inserted before the parent's ended_at lands.
3. Walk with fallback: each of the four lineage-flipping CTEs gains one OR-arm that follows the raw parent edge when either side carries the marker.

get_compression_tip is intentionally untouched: once archive/pin cover the whole lineage, the archived filter hides the root regardless of tip projection; resume-ordering semantics are unchanged. Diff stays minimal (64 lines in hermes_state.py, all additive).

Testing

• New regression tests in tests/hermes_state/test_session_archiving.py: real-rotation stamping, reap→reopen→archive reaching the whole lineage, unarchive restoring it, pin coverage, and creation-time stamping under an already-ended parent.
• tests/hermes_state/ — 156 passed
• tests/agent/test_compression_rotation_state.py tests/agent/test_compression_concurrent_fork.py tests/run_agent/test_compression_boundary_hook.py — 70 passed