fix(state): avoid double-encoding reasoning columns on fork round-trip

[nankingjing]

Summary

• Fixes forking a session double-encodes the reasoning columns — forked sessions silently lose reasoning replay #57240
• get_messages() returns reasoning columns as stored TEXT; replace_messages() (used by POST /api/sessions/{id}/fork) was calling json.dumps() on those strings, double-encoding them so forked sessions silently lost reasoning replay on resume.
• Add _encode_json_column() and use it in append_message and _insert_message_rows: live structures still serialize as before; pre-serialized TEXT from get_messages() passes through unchanged.

Test plan

• pytest tests/test_hermes_state.py::TestMessageStorage::test_get_messages_roundtrip_preserves_reasoning_columns
• Existing test_reasoning_details_persisted_and_restored still passes

[alt-glitch]

This was generated by AI during triage.

Duplicate of #57248 — same write-path-only mechanism for #57240: a helper that passes already-serialized TEXT through unchanged (else json.dumps), routed through append_message + _insert_message_rows at the same 6 dumps sites, read path untouched. #57248 (created earlier) is the canonical version; only the helper name differs. Related: #57240 (the issue) and #57454 (a sibling that additionally changes the read path — a genuine design divergence, not a dup).

[nankingjing]

Closing in favor of the earlier canonical fix path that the maintainer review identified in the comment thread.

Per the triage comment on this PR:

• fix(tools): honor plugin web providers in extract/search dispatch #57704: competing approach in the same plugin-web-provider cluster (fix(web_tools): delegate _is_backend_available to provider registry for plugin backends #31829 / fix(tools): honor available plugin extract/search backends in web selection #35327)
• fix(agent): honor custom_providers per-model max_tokens at startup #57548: duplicate of fix(agent): honor custom provider max_tokens #28154 (earliest still-open, broader superset)
• fix(kanban): terminate workers when tasks are blocked or archived #57713: duplicate of fix(kanban): terminate live workers on manual exits from running #31365 (broader superset covering done/scheduled manual exits too)
• fix(state): avoid double-encoding reasoning columns on fork round-trip #57536: duplicate of fix(state,cli,tui-gateway): keep reasoning fields intact across forks and branches #57248 (earlier canonical version with same write-path-only fix)
• fix(gateway): normalize MSYS paths in validate_media_delivery_path #57696: duplicate of fix(gateway): convert MSYS/Git Bash paths in validate_media_delivery_path (#47767) #47821 (earlier canonical MSYS path fix)

Keeping the narrower cluster open does not help the maintainer pick a canonical fix; closing these reduces the supersede noise so the maintainer can land the right one. Thanks to the alt-glitch triage for the cross-references.