subagent: seed inherited policy events at creation

The parent implementation introduced sandboxMode and approvalPolicy as generic SessionHeader fields, then propagated those fields through both persistence backends, session-query indexes, collision checks, policy-specific seed-boundary folds, catalogs, and a broad test matrix. That storage plane is unnecessary: Session already accepts a validated constructor seed, and persistence captures that seed when the session is announced before committing its first batch.

Capture each parent override synchronously at delegation, append source-tagged sandbox/mode and approval/policy records after the optional fork prefix, and create the child with that combined seed. Keeping header.seedLength at the original fork-prefix length preserves lineage while ordinary last-event-wins folds make the inherited records outrank stale parent history and remain subordinate to later child switches. Unswitched parents still stamp nothing, so children continue to follow deployment defaults.

Remove the generic header fields and every persistence/query/schema branch built around them. Collapse the inheritance suite from ten leaking scenarios to four owned-context cases covering real filesystem confinement, stale fork precedence, delegation-time capture, and the no-override path. The assembled headless snapshot now asserts the persisted inheritance event directly.

This keeps the security behavior while restoring policy ownership to the existing event log and deleting the speculative durability machinery that the original tests did not exercise.

packages/session-persistence/session-persistence-sqlite/src/schema.ts

@@ -17,7 +17,7 @@ import type { SessionEvent, SessionId, SessionHeader, SurfaceOp } from '@deepsee
  * layout; orthogonal to a session's own `version` (which versions the EVENT
  * vocabulary, stored per session in the `sessions` row).
  */
-export const SCHEMA_VERSION = 11
+export const SCHEMA_VERSION = 10
 
 /** SQLite application id protecting unrelated databases from persistence writes. */
 export const SESSION_PERSISTENCE_SQLITE_APPLICATION_ID = 0x44534850
@@ -41,10 +41,6 @@ export interface SessionRow {
   /** Monotonic log-change token incremented in each mutating transaction. */
   revision: number
   delegation_depth: number | null
-  /** The inherited sandbox-mode delegation baseline, or NULL. */
-  sandbox_mode: string | null
-  /** The inherited approval-policy delegation baseline, or NULL. */
-  approval_policy: string | null
 }
 
 /** An `events` table row: one `SessionEvent` mapped 1:1 (`data` is JSON text). */
@@ -128,9 +124,7 @@ function configureDatabase(db: DatabaseSync, path: string, journalMode: JournalM
         seed_length      INTEGER,
         delegation_depth INTEGER,
         incarnation      TEXT NOT NULL,
-        revision         INTEGER NOT NULL,
-        sandbox_mode     TEXT,
-        approval_policy  TEXT
+        revision         INTEGER NOT NULL
       ) STRICT;
 
       CREATE TABLE IF NOT EXISTS events (
@@ -187,8 +181,6 @@ export function rowToMeta(row: SessionRow): SessionHeader {
     ...row.parent_session !== null ? { parentSession: row.parent_session as SessionId } : {},
     ...row.seed_length !== null ? { seedLength: row.seed_length } : {},
     ...row.delegation_depth !== null ? { delegationDepth: row.delegation_depth } : {},
-    ...row.sandbox_mode !== null ? { sandboxMode: row.sandbox_mode } : {},
-    ...row.approval_policy !== null ? { approvalPolicy: row.approval_policy } : {},
   }
 }