refactor: prune session-store and agent-list dead code

The session_entries supersede pipeline was a design that never
shipped: `SqliteSessionStore.replaceMessages` / `appendCompaction`,
`sessionEntries.replace` / `listAll` / `deleteForSession`, and the
`"compaction" | "summary"` kind variants had zero live callers.
Compaction wires through pi's `transformContext` and leaves the
persisted transcript alone, so the shadow-row machinery was pure
cruft with two tests propping it up.

Rip it out: the store exposes only `loadMessages` and
`appendMessage`, `sessionEntries` exposes only `append` and
`listActive`, and `SessionEntryKind` narrows to `"message"` so new
writers can't re-introduce a dead kind by accident.
`is_superseded` stays on the table — the DB column is harmless
with no writer, and dropping it is a separate schema migration
concern.

`listTopLevelAgentIds` loses its only caller in the previous
commit (company channel now fans out through
`listCompanyBroadcastAgentIds`), so it goes too. Three tests that
validated the removed behaviour are deleted; the one remaining
session-store test still covers the live `append + load` path.

src/main/database/agents-hierarchy.ts

@@ -284,18 +284,6 @@ export function buildAgentHierarchyMethods(
       ).map((row) => row.id);
     },
 
-    /**
-     * Returns ids of non-terminated agents that have no manager (top of the
-     * reporting tree). Used for board-only fan-outs where only top-level
-     * leadership should be notified.
-     */
-    listTopLevelAgentIds(companyId: string): string[] {
-      return readAll<{ id: string }>(
-        "select id from agents where company_id = ? and reports_to is null and status != 'terminated'",
-        companyId,
-      ).map((row) => row.id);
-    },
-
     /**
      * Returns ids of every agent that is eligible to receive a routine
      * company-wide broadcast. Paused, pending-approval, and terminated

src/main/database/session-entries.ts

@@ -3,7 +3,15 @@ import type { DatabaseSync } from "node:sqlite";
 import type { ReadAll, Transaction } from "./helpers";
 import { nowIso } from "./helpers";
 
-export type SessionEntryKind = "message" | "compaction" | "summary";
+/**
+ * The `session_entries` table only ever stores one kind — full pi
+ * `AgentMessage` envelopes emitted by `message_end`. Earlier builds
+ * reserved `"compaction"` and `"summary"` variants for a supersede
+ * pipeline that never shipped; their writers are gone and the column
+ * holds `"message"` for every live row. Narrowing the type prevents
+ * new code from writing a dead kind by accident.
+ */
+export type SessionEntryKind = "message";
 
 export interface SessionEntryRow {
   id: string;
@@ -12,7 +20,6 @@ export interface SessionEntryRow {
   kind: SessionEntryKind;
   role: string | null;
   payloadJson: string;
-  isSuperseded: boolean;
   createdAt: string;
 }
 
@@ -23,15 +30,10 @@ export interface AppendInput {
   payloadJson: string;
 }
 
-export interface ReplaceInput {
-  taskSessionId: string;
-  entries: Array<{ kind: SessionEntryKind; role?: string | null; payloadJson: string }>;
-}
-
 export function buildSessionEntryMethods(
   getDb: () => DatabaseSync,
   readAll: ReadAll,
-  transaction: Transaction,
+  _transaction: Transaction,
 ) {
   function nextSequence(taskSessionId: string): number {
     const rows = readAll<{ maxSeq: number | null }>(
@@ -66,7 +68,6 @@ export function buildSessionEntryMethods(
       kind: input.kind,
       role: input.role ?? null,
       payloadJson: input.payloadJson,
-      isSuperseded: false,
       createdAt: created,
     };
   }
@@ -79,10 +80,9 @@ export function buildSessionEntryMethods(
       kind: SessionEntryKind;
       role: string | null;
       payload_json: string;
-      is_superseded: number;
       created_at: string;
     }>(
-      "select id, task_session_id, sequence, kind, role, payload_json, is_superseded, created_at from session_entries where task_session_id = ? and is_superseded = 0 order by created_at asc, sequence asc",
+      "select id, task_session_id, sequence, kind, role, payload_json, created_at from session_entries where task_session_id = ? and is_superseded = 0 order by created_at asc, sequence asc",
       taskSessionId,
     );
     return rows.map((row) => ({
@@ -92,62 +92,9 @@ export function buildSessionEntryMethods(
       kind: row.kind,
       role: row.role,
       payloadJson: row.payload_json,
-      isSuperseded: false,
       createdAt: row.created_at,
     }));
   }
 
-  function listAll(taskSessionId: string): SessionEntryRow[] {
-    const rows = readAll<{
-      id: string;
-      task_session_id: string;
-      sequence: number;
-      kind: SessionEntryKind;
-      role: string | null;
-      payload_json: string;
-      is_superseded: number;
-      created_at: string;
-    }>(
-      "select id, task_session_id, sequence, kind, role, payload_json, is_superseded, created_at from session_entries where task_session_id = ? order by sequence asc",
-      taskSessionId,
-    );
-    return rows.map((row) => ({
-      id: row.id,
-      taskSessionId: row.task_session_id,
-      sequence: row.sequence,
-      kind: row.kind,
-      role: row.role,
-      payloadJson: row.payload_json,
-      isSuperseded: row.is_superseded === 1,
-      createdAt: row.created_at,
-    }));
-  }
-
-  function replace(input: ReplaceInput): SessionEntryRow[] {
-    return transaction(() => {
-      getDb()
-        .prepare("update session_entries set is_superseded = 1 where task_session_id = ? and is_superseded = 0")
-        .run(input.taskSessionId);
-      const inserted: SessionEntryRow[] = [];
-      for (const entry of input.entries) {
-        inserted.push(
-          append({
-            taskSessionId: input.taskSessionId,
-            kind: entry.kind,
-            role: entry.role ?? null,
-            payloadJson: entry.payloadJson,
-          }),
-        );
-      }
-      return inserted;
-    });
-  }
-
-  function deleteForSession(taskSessionId: string): void {
-    getDb()
-      .prepare("delete from session_entries where task_session_id = ?")
-      .run(taskSessionId);
-  }
-
-  return { append, listActive, listAll, replace, deleteForSession };
+  return { append, listActive };
 }