Merge latest invariant service seam

packages/core/session/src/index.ts

@@ -113,6 +113,10 @@ function snapshotSessionHeader(id: SessionId, source?: SessionHeader): SessionHe
     && (typeof record.seedLength !== 'number' || !Number.isSafeInteger(record.seedLength) || record.seedLength < 0)) {
     throw new Error('session header seedLength must be a non-negative safe integer')
   }
+  if (record.delegationDepth !== undefined
+    && (typeof record.delegationDepth !== 'number' || !Number.isSafeInteger(record.delegationDepth) || record.delegationDepth < 0)) {
+    throw new Error('session header delegationDepth must be a non-negative safe integer')
+  }
   return deepFreeze(record as unknown as SessionHeader)
 }
 
@@ -558,9 +562,9 @@ export class SessionStore extends Service {
    * Create a session owned by the calling fiber: disposing that fiber stops
    * event notification and removes the session from the store. `options.seed`
    * populates the session with a copy of those events (replay/fork);
-   * `options.meta` attaches creation metadata (validated absolute `cwd`,
-   * `parentSession` lineage) as the immutable {@link SessionHeader} (the store
-   * fills `version`/`id`/`createdAt`).
+   * `options.meta` attaches creation metadata (validated absolute `cwd`, seed
+   * and parent lineage, and delegation depth) as the immutable
+   * {@link SessionHeader} (the store fills `version`/`id`/`createdAt`).
    *
    * For an agent whose session must be torn down IN ORDER with its loop (so the
    * loop's final flush is captured before the store attachment ends), do NOT use this
@@ -622,6 +626,7 @@ export class SessionStore extends Service {
       ...meta?.cwd === undefined ? {} : { cwd: meta.cwd },
       ...meta?.parentSession === undefined ? {} : { parentSession: meta.parentSession },
       ...meta?.seedLength === undefined ? {} : { seedLength: meta.seedLength },
+      ...meta?.delegationDepth === undefined ? {} : { delegationDepth: meta.delegationDepth },
     }
     return new Session(sessionId, seed, header)
   }

packages/core/session/src/types.ts

@@ -47,6 +47,12 @@ export interface SessionHeader {
    * boundary lets resume and replay distinguish parent history from child work.
    */
   readonly seedLength?: number
+  /**
+   * Delegation depth: absent (zero) for a top-level session, parent depth + 1
+   * for a subagent child. Persisted so a recursion budget survives restart and
+   * resume — a runtime-only depth would reset a resumed child to top-level.
+   */
+  readonly delegationDepth?: number
 }
 
 /**
@@ -66,6 +72,7 @@ export interface CreateSessionOptions {
     readonly parentSession?: SessionId
     readonly createdAt?: number
     readonly seedLength?: number
+    readonly delegationDepth?: number
   }
 }