fix(apiproxy,client): the list projection column becomes a seedable watermarked block

Review finding (PR #791): the column carried bare values (no seq), so the
client could not seed its value store without risking a stale list block
outranking newer push frames — and nothing consumed the column at all,
leaving cold titles absent after a restart. SessionSummary.projections is
now the same SessionProjectionsBlock as the history tail (values +
asOfSeq; attached rows cut the live registry, cold rows serve the cache's
identity-checked cachedSnapshot whose asOfSeq is the lowest served-row
watermark). SessionManager.refreshList seeds each row's block into the
per-session projection store via per-key apply — partial-baseline
semantics: an absent key never clears, and higher-seq-wins keeps stale
list blocks beneath push frames and tail baselines — so cold titles
surface in the sidebar without opening a session.

packages/host/apiproxy/src/api/sessions.ts

@@ -144,16 +144,17 @@ export interface SessionSummary {
   /** Session working directory (header.cwd passthrough); absent when unrecorded. */
   cwd?: string
   /**
-   * Whole current value per projection key, with zero log loads: attached
-   * sessions read the registry's live watermark cut; cold sessions read the
-   * persisted projection cache's stored rows — as stale as that session's
-   * last durable checkpoint, never wrong, superseded by the history tail
-   * baseline the moment the session is opened. Absent when no value is
-   * available (no registry, no cache row for a cold session, or a fail-soft
-   * cache read miss); a listing client treats absence as "no title yet",
-   * exactly like a blank session.
+   * Projection baseline for this row, with zero log loads: attached sessions
+   * read the registry's live watermark cut; cold sessions read the persisted
+   * projection cache's stored rows — as stale as that session's last durable
+   * checkpoint (`asOfSeq` says exactly how stale), never wrong, and directly
+   * seedable into the client's per-session value store under its
+   * higher-seq-wins rule (a list baseline can never overwrite a newer push
+   * frame). Absent when no value is available (no registry, no cache row for
+   * a cold session, or a fail-soft cache read miss); a listing client treats
+   * absence as "no title yet", exactly like a blank session.
    */
-  projections?: Partial<SessionProjectionMap>
+  projections?: SessionProjectionsBlock
 }
 
 /** Session-domain unary methods (the map keys session.* of RpcMethodMap). */