Seeded sessions survive a gateway restart and store their seed once (tui_gateway) (#107549)

* fix(tui-gateway): a seeded session is durable at create, and its seed is written once

session.create accepts opening messages. Three defects sat in that path:

- A seeded session without a parent was never persisted at create, so a
  restart before the first prompt lost it and session.resume answered
  4007. Only branch children (#93959) were persisted up front. The
  same rationale applies to any seeded create: seeded content is
  intent, not an abandoned draft. Parentless seeds now persist their
  row, transcript and client title at create; empty drafts stay lazy.
- _coerce_seed_history dropped display_kind, so a seeded row tagged
  "hidden" (model-facing scaffolding) rendered as a user bubble. The
  coercion keeps "hidden" and only "hidden"; every other kind is
  stamped by the gateway at turn time and is not accepted from the wire.
- A branch child's seed was written twice: _seed_branch_row copied it at
  create but never marked it persisted, so the first prompt's
  _persist_branch_seed appended the copy again. The create path now
  sets _branch_seed_persisted, and the gate is a create-time `seeded`
  stamp instead of parent_session_id, so a resumed session (whose
  history comes from the DB) can never re-append its transcript.

Two invariant tests, both red on main: a parentless seed survives a
gateway restart with the hidden row kept out of the wire transcript and
not re-written by the first-submit path; a branch child's seed is stored
exactly once. The reasoning-fields fixture stamps `seeded`, the flag
session.create sets.

* fix(tui-gateway): a hidden seed row stays out of the list preview and the create count

Live-testing the seeded create on every surface showed two places where
the newly durable hidden row (display_kind="hidden") still surfaced:

- session.list built a session's preview from its first user row with no
  display_kind filter, so a hidden opening row (model-facing scaffolding
  the gateway never paints) became the sidebar preview. The preview
  predicate now skips hidden rows, in every listing query that shares it.
- session.create reported message_count as the raw seed length while its
  messages array already filtered the hidden row (2 vs 1). It now counts
  what is on the wire, the same rule session.resume applies.

Both are covered by the existing seeded-create test: the create count
equals the wire transcript, and the preview of a session whose first
user row is hidden is its first visible user row.

* fix(tui-gateway): a live unpersisted resume counts the wire transcript

session.resume on a live session that has no row yet reported message_count as
the raw history length while its messages array was already filtered, the same
mismatch the previous commit fixed on session.create. Count the wire, as the
cold, deferred and reuse-live resume paths already do.

* chore: retrigger CI (zero-job dispatch failure, auto-heal)

hermes_state_common.py

@@ -74,11 +74,13 @@ _PREVIEW_MERGED_PRIOR_UNWRAPPED_SQL = (f"CASE WHEN SUBSTR({_PREVIEW_MERGED_PRIOR
 _PREVIEW_FORCE_USER_REMAINDER_SQL = _sql_after_marker(_SUMMARY_END_MARKER)
 
 # Pure compaction rows are ineligible; force-user-leading and merged carriers only when authentic content survives.
-_PREVIEW_ELIGIBLE_SQL = (f"((NOT {_PREVIEW_STANDALONE_SUMMARY_SQL} AND NOT {_PREVIEW_MERGED_SUMMARY_SQL})"
+# A display_kind="hidden" row is model-facing scaffolding the gateway never paints; the preview must not paint it either.
+_PREVIEW_ELIGIBLE_SQL = (f"(COALESCE(m.display_kind, '') <> 'hidden'"
+    f" AND ((NOT {_PREVIEW_STANDALONE_SUMMARY_SQL} AND NOT {_PREVIEW_MERGED_SUMMARY_SQL})"
     f" OR ({_PREVIEW_STANDALONE_SUMMARY_SQL} AND INSTR(m.content, {_sql_literal(_SUMMARY_END_MARKER)}) > 0"
     f" AND LENGTH({_sql_trim_whitespace(_PREVIEW_FORCE_USER_REMAINDER_SQL)}) > 0)"
     f" OR ({_PREVIEW_MERGED_SUMMARY_SQL}"
-    f" AND LENGTH({_sql_trim_whitespace(_PREVIEW_MERGED_PRIOR_UNWRAPPED_SQL)}) > 0))")
+    f" AND LENGTH({_sql_trim_whitespace(_PREVIEW_MERGED_PRIOR_UNWRAPPED_SQL)}) > 0)))")
 
 # ``_preview_raw`` SELECT for every listing query (scaffolded rows: head + tail around SKILL_EXCERPT_JOINT).
 _PREVIEW_RAW_SELECT = (