diff --git a/docs/cordis-catalog/events.md b/docs/cordis-catalog/events.md
index f522790fd0..5bd4d7b6f8 100644
--- a/docs/cordis-catalog/events.md
+++ b/docs/cordis-catalog/events.md
@@ -542,7 +542,7 @@ A ready child settled. Scope-filtered dispatch uses the same delegating parent c
 
 Types: [Scoped](../core-data-structures/scope.md) · [SubagentService](../core-data-structures/subagent.md)
 
-Source: [`packages/subagent/subagent/src/index.ts:112`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:138`](../../packages/subagent/subagent/src/index.ts)
 
 ### `subagent/provider-added` — emit
 
@@ -559,7 +559,7 @@ A provider became resolvable in the registry.
 
 Types: [SubagentProvider](../core-data-structures/subagent.md)
 
-Source: [`packages/subagent/subagent/src/index.ts:86`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:112`](../../packages/subagent/subagent/src/index.ts)
 
 ### `subagent/provider-removed` — emit
 
@@ -574,7 +574,7 @@ A provider left the registry. Accepted runs remain holder-owned.
 'subagent/provider-removed'(name: string): void
 ```
 
-Source: [`packages/subagent/subagent/src/index.ts:92`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:118`](../../packages/subagent/subagent/src/index.ts)
 
 ### `subagent/start` — emit
 
@@ -596,7 +596,7 @@ A provider established a ready child. For in-process providers, `ctx.agents.get(
 
 Types: [Scoped](../core-data-structures/scope.md) · [SubagentService](../core-data-structures/subagent.md)
 
-Source: [`packages/subagent/subagent/src/index.ts:103`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:129`](../../packages/subagent/subagent/src/index.ts)
 
 ## `system-prompt/*`
 
diff --git a/docs/cordis-catalog/services.md b/docs/cordis-catalog/services.md
index 267c2f0caa..378bb03ae8 100644
--- a/docs/cordis-catalog/services.md
+++ b/docs/cordis-catalog/services.md
@@ -216,7 +216,7 @@ roots(): Agent[]
 
 Types: [Agent](../core-data-structures/core.md) · [SessionId](../core-data-structures/core.md)
 
-Source: [`packages/core/agent/src/index.ts:217`](../../packages/core/agent/src/index.ts)
+Source: [`packages/core/agent/src/index.ts:223`](../../packages/core/agent/src/index.ts)
 
 ## `ctx.approval` — `ApprovalService`
 
@@ -820,7 +820,7 @@ fork(source: SessionForkSource, boundary?: number, childSessionId?: SessionId):
 
 Types: [CreateSessionOptions](../core-data-structures/persistence.md) · [Session](../core-data-structures/session.md) · [SessionId](../core-data-structures/core.md)
 
-Source: [`packages/core/session/src/index.ts:577`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:581`](../../packages/core/session/src/index.ts)
 
 ## `ctx.skills` — `SkillService`
 
@@ -934,7 +934,7 @@ async start(name: string, request: SubagentStartRequest): Promise<SubagentRun>
 
 Types: [SubagentProvider](../core-data-structures/subagent.md) · [SubagentRun](../core-data-structures/subagent.md) · [SubagentStartRequest](../core-data-structures/subagent.md)
 
-Source: [`packages/subagent/subagent/src/index.ts:153`](../../packages/subagent/subagent/src/index.ts)
+Source: [`packages/subagent/subagent/src/index.ts:179`](../../packages/subagent/subagent/src/index.ts)
 
 ## `ctx.systemPrompt` — `SystemPrompt`
 
diff --git a/docs/core-data-structures/persistence.md b/docs/core-data-structures/persistence.md
index 72ebcc5852..c4cbf97cdf 100644
--- a/docs/core-data-structures/persistence.md
+++ b/docs/core-data-structures/persistence.md
@@ -60,6 +60,12 @@ 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
 }
 ```
 
@@ -85,6 +91,7 @@ interface CreateSessionOptions {
     readonly parentSession?: SessionId
     readonly createdAt?: number
     readonly seedLength?: number
+    readonly delegationDepth?: number
   }
 }
 ```
diff --git a/docs/event-producer-consumer.md b/docs/event-producer-consumer.md
index 78f878106c..8f70dd00b6 100644
--- a/docs/event-producer-consumer.md
+++ b/docs/event-producer-consumer.md
@@ -30,10 +30,10 @@ This matrix shows which packages dispatch each harness-owned event and which pac
 | `session/disposed` | `emit` | [`packages/core/session/src/index.ts:57`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`agent-loop`](../packages/core/agent-loop), [`session-persistence`](../packages/session-persistence/session-persistence) |
 | `session/event` | `emit` | [`packages/core/session/src/index.ts:69`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`acp`](../packages/ui/acp), [`cli-demo`](../packages/examples/cli-demo), [`invariants`](../packages/support/invariants), [`jsonrpc`](../packages/ui/jsonrpc), [`session-persistence`](../packages/session-persistence/session-persistence), [`stdio`](../packages/ui/stdio), [`token-meter`](../packages/llm/token-meter), [`tui`](../packages/ui/tui), [`workspace-context`](../packages/context/workspace-context) |
 | `session/flush` | `parallel` | [`packages/core/session/src/index.ts:79`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`session-persistence`](../packages/session-persistence/session-persistence) |
-| `subagent/end` | `emit` | [`packages/subagent/subagent/src/index.ts:112`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`jsonrpc`](../packages/ui/jsonrpc) |
-| `subagent/provider-added` | `emit` | [`packages/subagent/subagent/src/index.ts:86`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`emit`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
-| `subagent/provider-removed` | `emit` | [`packages/subagent/subagent/src/index.ts:92`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
-| `subagent/start` | `emit` | [`packages/subagent/subagent/src/index.ts:103`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude) |
+| `subagent/end` | `emit` | [`packages/subagent/subagent/src/index.ts:138`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`jsonrpc`](../packages/ui/jsonrpc) |
+| `subagent/provider-added` | `emit` | [`packages/subagent/subagent/src/index.ts:112`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`emit`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
+| `subagent/provider-removed` | `emit` | [`packages/subagent/subagent/src/index.ts:118`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`tool-subagent`](../packages/subagent/tool-subagent) |
+| `subagent/start` | `emit` | [`packages/subagent/subagent/src/index.ts:129`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude) |
 | `system-prompt/assemble` | `waterfall` | [`packages/core/system-prompt/src/index.ts:27`](../packages/core/system-prompt/src/index.ts) | [`system-prompt`](../packages/core/system-prompt) (`waterfall`) | [`acp`](../packages/ui/acp) |
 | `system-prompt/change` | `emit` | [`packages/core/system-prompt/src/index.ts:33`](../packages/core/system-prompt/src/index.ts) | [`system-prompt`](../packages/core/system-prompt) (`emit`) | - |
 | `tools/change` | `emit` | [`packages/core/tools/src/index.ts:116`](../packages/core/tools/src/index.ts) | [`tools`](../packages/core/tools) (`emit`) | - |
diff --git a/docs/persistence-catalog.md b/docs/persistence-catalog.md
index 3bc15253a5..2a0500d79b 100644
--- a/docs/persistence-catalog.md
+++ b/docs/persistence-catalog.md
@@ -79,7 +79,7 @@ export type SessionEvent<T extends SessionEventType = SessionEventType> = {
 }[T]
 ```
 
-Sources: [`packages/core/session/src/types.ts:255`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:262`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:292`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:324`](../packages/core/session/src/types.ts)
+Sources: [`packages/core/session/src/types.ts:262`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:269`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:299`](../packages/core/session/src/types.ts) · [`packages/core/session/src/types.ts:331`](../packages/core/session/src/types.ts)
 
 ## Events
 
@@ -151,7 +151,7 @@ Source: [`packages/ui/user-approval/src/index.ts:68`](../packages/ui/user-approv
 
 Types: [StreamChunk](core-data-structures/llm-streaming.md)
 
-Source: [`packages/core/session/src/types.ts:219`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:226`](../packages/core/session/src/types.ts)
 
 #### `assistant/message` — surface
 
@@ -167,7 +167,7 @@ Source: [`packages/core/session/src/types.ts:219`](../packages/core/session/src/
 
 Types: [ContentBlock](core-data-structures/core.md) · [TokenUsage](core-data-structures/llm-streaming.md)
 
-Source: [`packages/core/session/src/types.ts:226`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:233`](../packages/core/session/src/types.ts)
 
 ### `bash/*`
 
@@ -258,7 +258,7 @@ Source: [`packages/compact/compact/src/types.ts:22`](../packages/compact/compact
 
 Types: [ContentBlock](core-data-structures/core.md) · [MessageSource](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:212`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:219`](../packages/core/session/src/types.ts)
 
 ### `hook/*`
 
@@ -336,7 +336,7 @@ Source: [`packages/ui/permission/src/index.ts:33`](../packages/ui/permission/src
 
 Types: [ContentBlock](core-data-structures/core.md) · [MessageSource](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:204`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:211`](../packages/core/session/src/types.ts)
 
 ### `request/*`
 
@@ -350,7 +350,7 @@ Source: [`packages/core/session/src/types.ts:204`](../packages/core/session/src/
 'request/header': { header: EpochHeader; reason: RequestHeaderReason }
 ```
 
-Source: [`packages/core/session/src/types.ts:251`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:258`](../packages/core/session/src/types.ts)
 
 ### `steering/*`
 
@@ -363,7 +363,7 @@ Source: [`packages/core/session/src/types.ts:251`](../packages/core/session/src/
 
 Types: [ContentBlock](core-data-structures/core.md) · [MessageSource](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:244`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:251`](../packages/core/session/src/types.ts)
 
 ### `step/*`
 
@@ -374,7 +374,7 @@ Source: [`packages/core/session/src/types.ts:244`](../packages/core/session/src/
 'step/end': { turn: number; step: number }
 ```
 
-Source: [`packages/core/session/src/types.ts:197`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:204`](../packages/core/session/src/types.ts)
 
 #### `step/start` — log-only
 
@@ -383,7 +383,7 @@ Source: [`packages/core/session/src/types.ts:197`](../packages/core/session/src/
 'step/start': { turn: number; step: number }
 ```
 
-Source: [`packages/core/session/src/types.ts:195`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:202`](../packages/core/session/src/types.ts)
 
 ### `todo/*`
 
@@ -396,7 +396,7 @@ Source: [`packages/core/session/src/types.ts:195`](../packages/core/session/src/
 
 Types: [TodoItem](core-data-structures/session.md)
 
-Source: [`packages/core/session/src/types.ts:246`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:253`](../packages/core/session/src/types.ts)
 
 ### `tool/*`
 
@@ -413,7 +413,7 @@ Source: [`packages/core/session/src/types.ts:246`](../packages/core/session/src/
 
 Types: [CallId](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:232`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:239`](../packages/core/session/src/types.ts)
 
 #### `tool/code-dispatch` — log-only
 
@@ -457,7 +457,7 @@ Source: [`packages/core/tools/src/code-mode.ts:34`](../packages/core/tools/src/c
 
 Types: [CallId](core-data-structures/core.md) · [ContentBlock](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:242`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:249`](../packages/core/session/src/types.ts)
 
 ### `turn/*`
 
@@ -474,7 +474,7 @@ Source: [`packages/core/session/src/types.ts:242`](../packages/core/session/src/
 
 Types: [TurnEndReason](core-data-structures/session.md)
 
-Source: [`packages/core/session/src/types.ts:193`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:200`](../packages/core/session/src/types.ts)
 
 #### `turn/start` — log-only
 
@@ -490,7 +490,7 @@ Source: [`packages/core/session/src/types.ts:193`](../packages/core/session/src/
 
 Types: [TurnTrigger](core-data-structures/session.md)
 
-Source: [`packages/core/session/src/types.ts:187`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:194`](../packages/core/session/src/types.ts)
 
 ### `user/*`
 
@@ -503,4 +503,4 @@ Source: [`packages/core/session/src/types.ts:187`](../packages/core/session/src/
 
 Types: [ContentBlock](core-data-structures/core.md) · [MessageSource](core-data-structures/core.md)
 
-Source: [`packages/core/session/src/types.ts:199`](../packages/core/session/src/types.ts)
+Source: [`packages/core/session/src/types.ts:206`](../packages/core/session/src/types.ts)
diff --git a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
index b4e8cd6340..d8affeaab8 100644
--- a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
+++ b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783950001000,"cwd":"/tmp/advanced-headless","parentSession":"11111111-1111-4111-8111-111111111111"}
+{"type":"session","version":0,"id":"22222222-2222-4222-8222-222222222222","createdAt":1783950001000,"cwd":"/tmp/advanced-headless","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783957884563,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884563,"data":{"content":[{"type":"text","text":"Reply with exactly DIRECT_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884564,"data":{"turn":1,"step":1}}
diff --git a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
index d8d2e59e6e..f0b6154472 100644
--- a/examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
+++ b/examples/headless-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
@@ -1,4 +1,4 @@
-{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1783950002000,"cwd":"/tmp/advanced-headless","parentSession":"11111111-1111-4111-8111-111111111111"}
+{"type":"session","version":0,"id":"33333333-3333-4333-8333-333333333333","createdAt":1783950002000,"cwd":"/tmp/advanced-headless","parentSession":"11111111-1111-4111-8111-111111111111","delegationDepth":1}
 {"type":"turn/start","seq":0,"time":1783957884700,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
 {"type":"user/message","seq":1,"time":1783957884700,"data":{"content":[{"type":"text","text":"Reply with exactly WORKFLOW_CHILD_OK and nothing else."}],"source":{"kind":"user"}},"surfaceOp":"append"}
 {"type":"step/start","seq":2,"time":1783957884700,"data":{"turn":1,"step":1}}
diff --git a/packages/cordis/tool-cordis/src/api-catalog.ts b/packages/cordis/tool-cordis/src/api-catalog.ts
index 5d99506c8a..65f828c383 100644
--- a/packages/cordis/tool-cordis/src/api-catalog.ts
+++ b/packages/cordis/tool-cordis/src/api-catalog.ts
@@ -709,11 +709,11 @@ export const TYPE_API: readonly TypeApiEntry[] = [
   },
   {
     name: 'CreateAgentOptions',
-    declaration: 'export interface CreateAgentOptions {\n    readonly sessionId: SessionId;\n    readonly meta?: {\n        readonly cwd?: string;\n        readonly parentSession?: SessionId;\n        readonly seedLength?: number;\n    };\n    readonly seed?: readonly SessionEvent[];\n    readonly agentOptions?: AgentOptions;\n    readonly signal?: AbortSignal;\n    readonly setup?: (agentCtx: Context) => Promise<void> | void;\n}',
+    declaration: 'export interface CreateAgentOptions {\n    readonly sessionId: SessionId;\n    readonly meta?: {\n        readonly cwd?: string;\n        readonly parentSession?: SessionId;\n        readonly seedLength?: number;\n        readonly delegationDepth?: number;\n    };\n    readonly seed?: readonly SessionEvent[];\n    readonly agentOptions?: AgentOptions;\n    readonly signal?: AbortSignal;\n    readonly setup?: (agentCtx: Context) => Promise<void> | void;\n}',
   },
   {
     name: 'CreateSessionOptions',
-    declaration: 'export interface CreateSessionOptions {\n    readonly seed?: readonly SessionEvent[];\n    readonly meta?: {\n        readonly cwd?: string;\n        readonly parentSession?: SessionId;\n        readonly createdAt?: number;\n        readonly seedLength?: number;\n    };\n}',
+    declaration: 'export interface CreateSessionOptions {\n    readonly seed?: readonly SessionEvent[];\n    readonly meta?: {\n        readonly cwd?: string;\n        readonly parentSession?: SessionId;\n        readonly createdAt?: number;\n        readonly seedLength?: number;\n        readonly delegationDepth?: number;\n    };\n}',
   },
   {
     name: 'DiffCallView',
@@ -929,7 +929,7 @@ export const TYPE_API: readonly TypeApiEntry[] = [
   },
   {
     name: 'SessionHeader',
-    declaration: 'export interface SessionHeader {\n    readonly version: number;\n    readonly id: SessionId;\n    readonly createdAt: number;\n    readonly cwd?: string;\n    readonly parentSession?: SessionId;\n    readonly seedLength?: number;\n}',
+    declaration: 'export interface SessionHeader {\n    readonly version: number;\n    readonly id: SessionId;\n    readonly createdAt: number;\n    readonly cwd?: string;\n    readonly parentSession?: SessionId;\n    readonly seedLength?: number;\n    readonly delegationDepth?: number;\n}',
   },
   {
     name: 'SessionId',
diff --git a/packages/core/agent-loop/src/index.ts b/packages/core/agent-loop/src/index.ts
index 2a77afc983..519edfdb7e 100644
--- a/packages/core/agent-loop/src/index.ts
+++ b/packages/core/agent-loop/src/index.ts
@@ -625,6 +625,7 @@ export class AgentLoop extends Service implements AgentFactory {
           ...loaded.meta.cwd === undefined ? {} : { cwd: loaded.meta.cwd },
           ...loaded.meta.parentSession === undefined ? {} : { parentSession: loaded.meta.parentSession },
           ...loaded.meta.seedLength === undefined ? {} : { seedLength: loaded.meta.seedLength },
+          ...loaded.meta.delegationDepth === undefined ? {} : { delegationDepth: loaded.meta.delegationDepth },
         },
       })
       const agent = transaction.prepare(agentOptions, session, this.maxParallelToolCalls)
diff --git a/packages/core/agent-loop/tests/resume.spec.ts b/packages/core/agent-loop/tests/resume.spec.ts
index 74192dde90..452f1d66b5 100644
--- a/packages/core/agent-loop/tests/resume.spec.ts
+++ b/packages/core/agent-loop/tests/resume.spec.ts
@@ -411,7 +411,7 @@ describe('the session-persistence RFC: AgentLoop factory create/resume', () => {
     await ctx.fiber.dispose()
   })
 
-  it('resume of a forked session preserves the parentSession lineage and seed boundary in the header', async () => {
+  it('resume of a forked session preserves the lineage, seed boundary, and delegation depth in the header', async () => {
     // Lifecycle 1: persist a FORKED session (carries parentSession + seedLength
     // in its header) by creating it with a complete-turn seed — the write path
     // materializes the fork (header + seed) on disk.
@@ -423,7 +423,7 @@ describe('the session-persistence RFC: AgentLoop factory create/resume', () => {
     const { ctx: ctx1, root } = await persistentHarness(adapter1)
     const forked = ctx1.sessions.create(SessionId('forked-sess'), {
       seed,
-      meta: { cwd: '/w', parentSession: SessionId('parent-sess'), seedLength: seed.length },
+      meta: { cwd: '/w', parentSession: SessionId('parent-sess'), seedLength: seed.length, delegationDepth: 1 },
     })
     await ctx1.parallel('session/flush', forked)
     await ctx1.fiber.dispose()
@@ -447,6 +447,9 @@ describe('the session-persistence RFC: AgentLoop factory create/resume', () => {
     expect(a2.session.header.parentSession).toBe('parent-sess')
     expect(a2.session.header.cwd).toBe('/w')
     expect(a2.session.header.seedLength).toBe(seed.length)
+    // The recursion budget survives resume — a dropped depth would let a
+    // resumed child delegate as if it were top-level.
+    expect(a2.session.header.delegationDepth).toBe(1)
     await ctx2.fiber.dispose()
   })
 
diff --git a/packages/core/agent/src/index.ts b/packages/core/agent/src/index.ts
index 75f00daebb..061ddae53f 100644
--- a/packages/core/agent/src/index.ts
+++ b/packages/core/agent/src/index.ts
@@ -46,15 +46,21 @@ export interface CreateAgentOptions {
   readonly sessionId: SessionId
   /**
    * Session creation metadata: validated absolute `cwd`, `parentSession`
-   * fork lineage, and the `seedLength` seed boundary. Mirrors the
-   * `cwd`/`parentSession`/`seedLength` fields of
+   * fork lineage, the `seedLength` seed boundary, and the `delegationDepth`
+   * recursion budget. Mirrors the
+   * `cwd`/`parentSession`/`seedLength`/`delegationDepth` fields of
    * {@link CreateSessionOptions.meta} in dsh-session (the internal-only
    * `createdAt`, used when reconstructing a persisted session, is deliberately
    * excluded — a factory caller never sets it). This is durable session data,
    * so the session boundary validates and snapshots it before asynchronous
    * setup begins.
    */
-  readonly meta?: { readonly cwd?: string; readonly parentSession?: SessionId; readonly seedLength?: number }
+  readonly meta?: {
+    readonly cwd?: string
+    readonly parentSession?: SessionId
+    readonly seedLength?: number
+    readonly delegationDepth?: number
+  }
   /**
    * Seed events to reconstruct the child session's log from (the fork lineage
    * primitive). When present, the factory creates the session with this event
diff --git a/packages/core/session/README.md b/packages/core/session/README.md
index ba4e8ea94a..ec7daf9408 100644
--- a/packages/core/session/README.md
+++ b/packages/core/session/README.md
@@ -38,7 +38,7 @@ Plain class (not a Cordis Service). Create via `ctx.sessions.create()`.
 - `session.surface` exposes the readonly `SessionSurface` view owned by the session's single incremental surface manager; `replaceGeneration` changes on every committed rewrite.
 - `session.events` is a cached frozen snapshot invalidated by append; accepted events remain deeply frozen.
 - `session.seq`, `session.id` — current sequence and readonly typed identity.
-- `session.header: SessionHeader` — detached, deep-frozen creation metadata (`version`, `id`, `createdAt`, optional `cwd`/`parentSession`/`seedLength`). Construction validates the durable record and requires its id to match `session.id`.
+- `session.header: SessionHeader` — detached, deep-frozen creation metadata (`version`, `id`, `createdAt`, optional `cwd`/`parentSession`/`seedLength`/`delegationDepth`). Construction validates the durable record and requires its id to match `session.id`.
 
 ### Lossless JSON utilities
 
@@ -73,7 +73,7 @@ Every `SessionEvent` carries two optional top-level fields (structural metadata)
 
 ### Metadata types (`types.ts`)
 
-- `SessionHeader` — session metadata written once when published as `Session.header`, where detachment and deep-freezing enforce immutability at runtime: `{ version, id, createdAt, cwd?, parentSession?, seedLength? }`. Persistence loaders may return mutable detached copies of the same data type. Owned here (beside `SessionId`) because `Session.header` is typed by it; persistence backends re-export it rather than own it (which would force a package cycle).
+- `SessionHeader` — session metadata written once when published as `Session.header`, where detachment and deep-freezing enforce immutability at runtime: `{ version, id, createdAt, cwd?, parentSession?, seedLength?, delegationDepth? }`. Persistence loaders may return mutable detached copies of the same data type. Owned here (beside `SessionId`) because `Session.header` is typed by it; persistence backends re-export it rather than own it (which would force a package cycle).
 
 ### Extension points
 
diff --git a/packages/core/session/src/index.ts b/packages/core/session/src/index.ts
index b8b76ec2ed..37025ed1c7 100644
--- a/packages/core/session/src/index.ts
+++ b/packages/core/session/src/index.ts
@@ -128,6 +128,10 @@ 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)
 }
 
@@ -650,6 +654,7 @@ 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)
   }
diff --git a/packages/core/session/src/types.ts b/packages/core/session/src/types.ts
index dc34760e9c..31903d97db 100644
--- a/packages/core/session/src/types.ts
+++ b/packages/core/session/src/types.ts
@@ -50,6 +50,12 @@ 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
 }
 
 /**
@@ -69,6 +75,7 @@ export interface CreateSessionOptions {
     readonly parentSession?: SessionId
     readonly createdAt?: number
     readonly seedLength?: number
+    readonly delegationDepth?: number
   }
 }
 
diff --git a/packages/core/session/tests/session.spec.ts b/packages/core/session/tests/session.spec.ts
index 3b15157bde..243908d27f 100644
--- a/packages/core/session/tests/session.spec.ts
+++ b/packages/core/session/tests/session.spec.ts
@@ -882,6 +882,19 @@ describe('SessionStore', () => {
     })
   })
 
+  it('attaches delegationDepth from meta to the header', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const session = ctx.sessions.create(SessionId('delegated-child'), {
+      meta: { parentSession: SessionId('parent'), delegationDepth: 2 },
+    })
+    expect(session.header).toMatchObject({
+      id: 'delegated-child',
+      parentSession: 'parent',
+      delegationDepth: 2,
+    })
+  })
+
   it('rejects non-JSON and invalid scalar session metadata', async () => {
     const ctx = new Context()
     await ctx.plugin(SessionStore)
@@ -893,6 +906,9 @@ describe('SessionStore', () => {
       { meta: { seedLength: '1' }, error: /seedLength must be a non-negative safe integer/ },
       { meta: { seedLength: 0.5 }, error: /seedLength must be a non-negative safe integer/ },
       { meta: { seedLength: -1 }, error: /seedLength must be a non-negative safe integer/ },
+      { meta: { delegationDepth: '1' }, error: /delegationDepth must be a non-negative safe integer/ },
+      { meta: { delegationDepth: 0.5 }, error: /delegationDepth must be a non-negative safe integer/ },
+      { meta: { delegationDepth: -1 }, error: /delegationDepth must be a non-negative safe integer/ },
     ]
 
     for (const [index, { meta, error }] of cases.entries()) {
diff --git a/packages/session-persistence/session-persistence-jsonl/src/format.ts b/packages/session-persistence/session-persistence-jsonl/src/format.ts
index 39bdecf751..3fe3b2485c 100644
--- a/packages/session-persistence/session-persistence-jsonl/src/format.ts
+++ b/packages/session-persistence/session-persistence-jsonl/src/format.ts
@@ -25,6 +25,7 @@ export interface HeaderLine {
   cwd?: string
   parentSession?: SessionId
   seedLength?: number
+  delegationDepth?: number
 }
 
 /**
@@ -41,6 +42,7 @@ export function toHeaderLine(header: SessionHeader): HeaderLine {
     ...header.cwd !== undefined ? { cwd: header.cwd } : {},
     ...header.parentSession !== undefined ? { parentSession: header.parentSession } : {},
     ...header.seedLength !== undefined ? { seedLength: header.seedLength } : {},
+    ...header.delegationDepth !== undefined ? { delegationDepth: header.delegationDepth } : {},
   }
 }
 
@@ -57,6 +59,7 @@ export function fromHeaderLine(line: HeaderLine): SessionHeader {
     ...line.cwd !== undefined ? { cwd: line.cwd } : {},
     ...line.parentSession !== undefined ? { parentSession: line.parentSession } : {},
     ...line.seedLength !== undefined ? { seedLength: line.seedLength } : {},
+    ...line.delegationDepth !== undefined ? { delegationDepth: line.delegationDepth } : {},
   }
 }
 
diff --git a/packages/session-persistence/session-persistence-sqlite/src/index.ts b/packages/session-persistence/session-persistence-sqlite/src/index.ts
index 4661b41309..edba26d9ae 100644
--- a/packages/session-persistence/session-persistence-sqlite/src/index.ts
+++ b/packages/session-persistence/session-persistence-sqlite/src/index.ts
@@ -253,14 +253,15 @@ export class SessionPersistenceSqlite extends SessionPersistence implements Pers
    */
   private writeRow(meta: SessionHeader): void {
     this.db.prepare(`
-      INSERT INTO sessions (id, version, created_at, cwd, parent_session, seed_length)
-      VALUES (?, ?, ?, ?, ?, ?)
+      INSERT INTO sessions (id, version, created_at, cwd, parent_session, seed_length, delegation_depth)
+      VALUES (?, ?, ?, ?, ?, ?, ?)
       ON CONFLICT(id) DO UPDATE SET
         version = excluded.version,
         created_at = excluded.created_at,
         cwd = excluded.cwd,
         parent_session = excluded.parent_session,
-        seed_length = excluded.seed_length
+        seed_length = excluded.seed_length,
+        delegation_depth = excluded.delegation_depth
     `).run(
       meta.id,
       meta.version,
@@ -268,6 +269,7 @@ export class SessionPersistenceSqlite extends SessionPersistence implements Pers
       meta.cwd ?? null,
       meta.parentSession ?? null,
       meta.seedLength ?? null,
+      meta.delegationDepth ?? null,
     )
   }
 }
diff --git a/packages/session-persistence/session-persistence-sqlite/src/schema.ts b/packages/session-persistence/session-persistence-sqlite/src/schema.ts
index adb23cbb43..4a7f12e759 100644
--- a/packages/session-persistence/session-persistence-sqlite/src/schema.ts
+++ b/packages/session-persistence/session-persistence-sqlite/src/schema.ts
@@ -15,7 +15,7 @@ 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 = 4
+export const SCHEMA_VERSION = 5
 
 /**
  * A row of the `sessions` table — the out-of-log metadata ({@link SessionHeader}).
@@ -31,6 +31,7 @@ export interface SessionRow {
   cwd: string | null
   parent_session: string | null
   seed_length: number | null
+  delegation_depth: number | null
 }
 
 /** An `events` table row: one `SessionEvent` mapped 1:1 (`data` is JSON text). */
@@ -83,9 +84,10 @@ export function openDatabase(path: string, journalMode: JournalMode): DatabaseSy
       id             TEXT PRIMARY KEY,
       version        INTEGER NOT NULL,
       created_at     INTEGER NOT NULL,
-      cwd            TEXT,
-      parent_session TEXT,
-      seed_length    INTEGER
+      cwd              TEXT,
+      parent_session   TEXT,
+      seed_length      INTEGER,
+      delegation_depth INTEGER
     ) STRICT
   `)
   db.exec(`
@@ -116,6 +118,7 @@ export function rowToMeta(row: SessionRow): SessionHeader {
     ...row.cwd !== null ? { cwd: row.cwd } : {},
     ...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 } : {},
   }
 }
 
diff --git a/packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts b/packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts
index f26edfa54d..83d16b3315 100644
--- a/packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts
+++ b/packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts
@@ -385,7 +385,7 @@ describe('SessionPersistenceSqlite: durability and crash semantics', () => {
   })
 
   it('exposes the schema version constant', () => {
-    expect(SCHEMA_VERSION).toBe(4)
+    expect(SCHEMA_VERSION).toBe(5)
   })
 })
 
diff --git a/packages/session-persistence/session-persistence/tests/coordinator-contract.ts b/packages/session-persistence/session-persistence/tests/coordinator-contract.ts
index defcaefb6d..5ef2ce2fad 100644
--- a/packages/session-persistence/session-persistence/tests/coordinator-contract.ts
+++ b/packages/session-persistence/session-persistence/tests/coordinator-contract.ts
@@ -106,6 +106,27 @@ export function runCoordinatorContract(name: string, makeFixture: () => Promise<
       }
     })
 
+    it('round-trips the delegation depth through persistence', async () => {
+      // A subagent child's recursion budget lives in its header; a reload that
+      // dropped it would reset the child to top-level and un-bound maxDepth
+      // (JSONL stores it in the header line; SQLite uses `delegation_depth`).
+      const fix = await makeFixture()
+      const { ctx, fiber } = await freshCtx(fix)
+      try {
+        const session = ctx.sessions.create(SessionId('delegated-child'), {
+          meta: { cwd: WORK, parentSession: SessionId('root'), delegationDepth: 2 },
+        })
+        send(session, oneTurnLog())
+        await ctx.parallel('session/flush', session)
+
+        const loaded = await ctx.sessionPersistence.load(SessionId('delegated-child'))
+        expect(loaded.meta.delegationDepth).toBe(2)
+      } finally {
+        await fiber.dispose()
+        await fix.cleanup()
+      }
+    })
+
     it('source-frozen events cannot be mutated after buffering and persist unchanged', async () => {
       const fix = await makeFixture()
       const { ctx, fiber } = await freshCtx(fix)
diff --git a/packages/subagent/subagent-inprocess/README.md b/packages/subagent/subagent-inprocess/README.md
index ca54dab7c0..46d4457764 100644
--- a/packages/subagent/subagent-inprocess/README.md
+++ b/packages/subagent/subagent-inprocess/README.md
@@ -8,7 +8,7 @@ This package is the shared run driver for the two in-process providers. Spawn pa
 
 The driver follows this sequence:
 
-1. Validate the parent depth and optional absolute `maxDepth`, then derive child depth as parent depth plus one.
+1. Validate the parent depth and optional absolute `maxDepth`, then derive child depth as parent depth plus one and persist it in the child session header.
 2. Call `parent.ctx.agents.create` directly, passing the required request signal into the factory's creation transaction.
 3. During that transaction's unpublished setup window, install the requested persona, tool restriction, and structured-output runtime.
 4. Publish the child, retain the returned `AgentHandle`, and drive one task with `child.send(prompt)` followed by `child.whenIdle()`.
@@ -26,7 +26,7 @@ After fulfillment, the caller owns the run. Provider-plugin unload does not revo
 
 `InProcessRunOptions` is `{ seed?: SessionEvent[] }`. Spawn omits it. Fork supplies a balanced completed-turn prefix and records its length so the result reader never mistakes a seeded parent message for child output.
 
-Depth enforcement is internal to `startInProcessRun`: it reads `AgentOptions.subagentDepth`, treats absence as top-level depth zero, rejects malformed stored values, and reports an attempted child depth above `maxDepth`. An unrepresentable depth above the safe-integer domain is a `RangeError`.
+Depth enforcement is internal to `startInProcessRun`: it reads the parent depth via `delegationDepthOf` (the persisted `SessionHeader.delegationDepth` is authoritative; runtime `AgentOptions.subagentDepth` may deepen but never lower it, so a resumed child keeps its budget), treats absence as top-level depth zero, rejects malformed stored values, and reports an attempted child depth above `maxDepth`. An unrepresentable depth above the safe-integer domain is a `RangeError`. The child depth is written to the child header, so it survives persistence and resume.
 
 ## Structured output
 
diff --git a/packages/subagent/subagent-inprocess/src/index.ts b/packages/subagent/subagent-inprocess/src/index.ts
index 6e62ee5127..f0e9731c9d 100644
--- a/packages/subagent/subagent-inprocess/src/index.ts
+++ b/packages/subagent/subagent-inprocess/src/index.ts
@@ -12,7 +12,7 @@ import type { Context } from 'cordis'
 import type { Agent, AgentOptions } from '@deepseek-ai/dsh-agent'
 import { SessionId, type SessionEvent, type TurnEndReason } from '@deepseek-ai/dsh-session'
 import type { ContentBlock } from '@deepseek-ai/dsh-llm'
-import { assertSubagentMaxDepth } from '@deepseek-ai/dsh-subagent'
+import { assertSubagentMaxDepth, delegationDepthOf } from '@deepseek-ai/dsh-subagent'
 import type { SubagentResult, SubagentRun, SubagentStartRequest, SubagentStopReason } from '@deepseek-ai/dsh-subagent'
 import {
   attachStructuredRuntime,
@@ -24,27 +24,6 @@ export {
   STRUCTURED_OUTPUT_INSTRUCTION,
 } from './structured.ts'
 
-declare module '@deepseek-ai/dsh-agent' {
-  interface AgentOptions {
-    /** Delegation depth: zero for a top-level agent and parent depth + 1 for a child. */
-    subagentDepth?: number
-  }
-}
-
-/**
- * Read an agent's delegation depth, treating absence as top-level depth zero.
- * @param agent - the agent whose options carry the depth.
- * @returns its non-negative safe-integer depth.
- */
-function depthOf(agent: Agent): number {
-  const depth = agent.options.subagentDepth
-  if (depth === undefined) return 0
-  if (!Number.isSafeInteger(depth) || depth < 0 || Object.is(depth, -0)) {
-    throw new TypeError('agent subagentDepth must be a non-negative safe integer')
-  }
-  return depth
-}
-
 /** Thrown when starting a child would exceed the requested depth cap. */
 class SubagentDepthError extends Error {
   constructor(public readonly attemptedDepth: number, public readonly maxDepth: number) {
@@ -96,7 +75,7 @@ export async function startInProcessRun(
   assertSubagentMaxDepth(request.maxDepth)
   if (request.signal.aborted) throw prePublicationAbort()
   const parent = request.parent
-  const childDepth = depthOf(parent) + 1
+  const childDepth = delegationDepthOf(parent) + 1
   if (!Number.isSafeInteger(childDepth)) {
     throw new RangeError('subagent child depth exceeds the safe-integer range')
   }
@@ -133,6 +112,8 @@ export async function startInProcessRun(
     meta: {
       ...parentHeader.cwd !== undefined ? { cwd: parentHeader.cwd } : {},
       parentSession: parentHeader.id,
+      // Durable: the recursion budget must survive persistence and resume.
+      delegationDepth: childDepth,
       ...seedLength > 0 ? { seedLength } : {},
     },
     ...options.seed !== undefined ? { seed: options.seed } : {},
diff --git a/packages/subagent/subagent-inprocess/tests/subagent-inprocess.spec.ts b/packages/subagent/subagent-inprocess/tests/subagent-inprocess.spec.ts
index 13029ef3e7..9c645bc78a 100644
--- a/packages/subagent/subagent-inprocess/tests/subagent-inprocess.spec.ts
+++ b/packages/subagent/subagent-inprocess/tests/subagent-inprocess.spec.ts
@@ -58,6 +58,44 @@ describe('startInProcessRun', () => {
     await run.dispose()
   })
 
+  it('persists the child depth in its session header', async () => {
+    const { ctx, parent } = await setup([textResponse('child answer')])
+    const run = await startInProcessRun(request(parent), {})
+    await run.result
+    // The recursion budget is durable session data, not only runtime options —
+    // a depth that lived only in AgentOptions would reset to 0 on resume.
+    expect(ctx.agents.get(run.id)!.session.header.delegationDepth).toBe(1)
+    await run.dispose()
+  })
+
+  it('counts a RESUMED child by its persisted header depth, not the absent runtime depth', async () => {
+    // The review-reproduced failure chain: a depth-1 child comes back from
+    // persistence with a fresh AgentOptions (no subagentDepth). Its header must
+    // stay authoritative, or maxDepth: 1 would let it delegate as top-level.
+    const { ctx } = await setup([textResponse('unused')])
+    const resumed = (await ctx.agents.create({
+      sessionId: SessionId('resumed-child'),
+      meta: { parentSession: SessionId('root'), delegationDepth: 1 },
+      agentOptions: { provider: 'mock', model: 'mock' },
+      signal: new AbortController().signal,
+    })).agent
+    await expect(startInProcessRun({ ...request(resumed), maxDepth: 1 }, {}))
+      .rejects.toMatchObject({ name: 'SubagentDepthError', attemptedDepth: 2, maxDepth: 1 })
+  })
+
+  it('lets runtime options deepen but never lower the persisted depth', async () => {
+    const { ctx } = await setup([textResponse('unused')])
+    const parent = (await ctx.agents.create({
+      sessionId: SessionId('deep-parent'),
+      meta: { delegationDepth: 2 },
+      agentOptions: { provider: 'mock', model: 'mock', subagentDepth: 1 },
+      signal: new AbortController().signal,
+    })).agent
+    // Persisted 2 vs runtime 1: the child is depth 3, so maxDepth 2 rejects.
+    await expect(startInProcessRun({ ...request(parent), maxDepth: 2 }, {}))
+      .rejects.toMatchObject({ name: 'SubagentDepthError', attemptedDepth: 3, maxDepth: 2 })
+  })
+
   it('rejects invalid and exceeded depth before publication', async () => {
     const { parent } = await setup([])
     await expect(startInProcessRun({ ...request(parent), maxDepth: -1 }, {}))
@@ -65,11 +103,11 @@ describe('startInProcessRun', () => {
     await expect(startInProcessRun({ ...request(parent), maxDepth: 0 }, {}))
       .rejects.toMatchObject({ name: 'SubagentDepthError' })
     for (const value of [Number.NaN, 1.5, -1, -0, Number.MAX_SAFE_INTEGER + 1]) {
-      const malformed = { options: { subagentDepth: value } } as unknown as Agent
+      const malformed = { options: { subagentDepth: value }, session: { header: {} } } as unknown as Agent
       await expect(startInProcessRun(request(malformed), {}))
         .rejects.toThrow('agent subagentDepth must be a non-negative safe integer')
     }
-    const maxParent = { options: { subagentDepth: Number.MAX_SAFE_INTEGER } } as unknown as Agent
+    const maxParent = { options: { subagentDepth: Number.MAX_SAFE_INTEGER }, session: { header: {} } } as unknown as Agent
     await expect(startInProcessRun(request(maxParent), {})).rejects.toBeInstanceOf(RangeError)
   })
 
diff --git a/packages/subagent/subagent/README.md b/packages/subagent/subagent/README.md
index 17edd0e3c7..bde2b61eab 100644
--- a/packages/subagent/subagent/README.md
+++ b/packages/subagent/subagent/README.md
@@ -40,6 +40,10 @@ Start-time features are advertised in `provider.capabilities` because the servic
 - `toolFilter` — apply the requested child tool restriction.
 - `persona` — apply a per-child persona.
 
+## Delegation depth
+
+The seam owns the depth vocabulary shared by implementations and consumers: the `AgentOptions.subagentDepth` declaration, `assertSubagentMaxDepth`, and `delegationDepthOf(agent)`. The persisted `SessionHeader.delegationDepth` is authoritative and monotone — runtime options may deepen the count but never lower it, so a resumed child cannot be re-counted as top-level.
+
 Runtime features are optional methods on `SubagentRun`: `sendMessage?` steers a live child, while `resume?` asynchronously creates a continuation run. Method presence is the capability check.
 
 `inheritsParentContext` is descriptive rather than enforceable. It says only whether the child sees completed parent conversation history (`fork` does; `spawn` and ACP do not), not whether it inherits tools, services, or authority.
diff --git a/packages/subagent/subagent/src/index.ts b/packages/subagent/subagent/src/index.ts
index 19779f9137..9046ae4a94 100644
--- a/packages/subagent/subagent/src/index.ts
+++ b/packages/subagent/subagent/src/index.ts
@@ -57,6 +57,32 @@ export type {
   SubagentStopReasonMap,
 } from './types.ts'
 
+declare module '@deepseek-ai/dsh-agent' {
+  interface AgentOptions {
+    /** Delegation depth: zero for a top-level agent and parent depth + 1 for a child. */
+    subagentDepth?: number
+  }
+}
+
+/**
+ * Read an agent's delegation depth, treating absence as top-level depth zero.
+ * The persisted session header is authoritative and monotone: runtime
+ * `AgentOptions.subagentDepth` may DEEPEN the count but can never lower it —
+ * a resumed child arrives with fresh options, and counting it from zero would
+ * let it delegate as if it were top-level.
+ * @param agent - the agent whose header and options carry the depth.
+ * @returns its non-negative safe-integer depth.
+ */
+export function delegationDepthOf(agent: Agent): number {
+  const runtime = agent.options.subagentDepth
+  if (runtime !== undefined && (!Number.isSafeInteger(runtime) || runtime < 0 || Object.is(runtime, -0))) {
+    throw new TypeError('agent subagentDepth must be a non-negative safe integer')
+  }
+  // The header value was validated at the session boundary (creation and
+  // persistence load both construct through the store).
+  return Math.max(agent.session.header.delegationDepth ?? 0, runtime ?? 0)
+}
+
 /**
  * Reject a recursion cap that cannot represent an exact delegation depth.
  * @param maxDepth - the optional runtime value to validate.
diff --git a/website/zh-CN/api/harness/agents.md b/website/zh-CN/api/harness/agents.md
index bba6a7a5d4..a99e7339cb 100644
--- a/website/zh-CN/api/harness/agents.md
+++ b/website/zh-CN/api/harness/agents.md
@@ -7,7 +7,7 @@
 Agent service (`ctx.agents`): tracks live agents and carries the initiating Agent through one process-local asynchronous driver chain. Agent *creation* is provided by whichever plugin implements the AgentFactory (`@deepseek-ai/dsh-agent-loop`), registered via setFactory.
 Initiator methods provide same-process causal attribution only. Ambient presence is neither liveness proof nor authorization; subjects and owners remain explicit, as does identity at worker, process, persistence, and wire boundaries. Returned Promise boundaries drain during teardown, except a nested lineage that starts an owning-fiber unload is excluded from its own drain.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L217)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L223)
 
 ### ctx.agents.currentInitiator()
 
@@ -28,7 +28,7 @@ Read the Agent that initiated the inherited asynchronous driver chain. Use this
 
 **Returns** the inherited Agent, or `undefined` outside an initiator boundary and inside an explicit clearing boundary.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L256)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L262)
 
 ### ctx.agents.requireInitiator()
 
@@ -48,7 +48,7 @@ Read the initiating Agent and fail when no initiator boundary is active. Use thi
 
 **Returns** the inherited Agent.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L269)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L275)
 
 ### ctx.agents.withInitiator(agent, operation)
 
@@ -76,7 +76,7 @@ Run an operation with one exact Agent as its process-local initiator. The exact
 
 **Returns** the exact value returned by `operation`.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L288)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L294)
 
 ### ctx.agents.withoutInitiator(operation)
 
@@ -101,7 +101,7 @@ Run an operation inside a boundary that hides any inherited initiating Agent. Th
 
 **Returns** the exact value returned by `operation`.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L303)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L309)
 
 ### ctx.agents.setFactory(factory)
 
@@ -127,7 +127,7 @@ Register the agent-creation factory (the loop calls this on construction, effect
 
 **Returns** the disposer that clears the factory slot. The exact Cordis effect disposer (single-shot): composite (generator) effects may yield it directly — exact identity nests the teardown in order.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L319)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L325)
 
 ### ctx.agents.create(options)
 
@@ -150,7 +150,7 @@ Create and publish a new agent through the registered factory. Distinct from reg
 
 **Returns** the handle after setup, rollback-covered publication, and loop start complete.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L352)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L358)
 
 ### ctx.agents.resume(options)
 
@@ -171,7 +171,7 @@ Load a persisted session and resume an agent on it through the registered factor
 
 **Returns** the handle after setup, rollback-covered publication, and loop start complete.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L371)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L377)
 
 ### ctx.agents.register(agent)
 
@@ -203,7 +203,7 @@ Register a live agent. Throws if an agent with the same id is already registered
 
 **Returns** the EXACT Cordis effect disposer (single-shot; a repeat call returns undefined without awaiting an in-flight teardown). Exact identity is load-bearing: a composite (generator) effect that owns a teardown ORDER — the agent factory's lifecycle chain — must yield THIS function so Cordis nests the unregistration at that yield position; yielding a wrapper would leave it disposing as a concurrent sibling on owner unload, unregistering the agent (and emitting `agent/disposed`) while its final turn is still draining.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L397)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L403)
 
 ### ctx.agents.enter(agent, owner)
 
@@ -233,7 +233,7 @@ Insert an already-constructed agent without announcing it. This is the advanced
 
 **Returns** an idempotent closure that removes this exact entry and emits `agent/disposed` with listener failures contained. When called from a synchronous `agent/created` listener, removal and disposal wait until that creation dispatch unwinds.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L421)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L427)
 
 ### ctx.agents.announce(agent)
 
@@ -252,7 +252,7 @@ Announce an agent previously inserted with enter.
 
 - `agent` — the live inserted agent to announce.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L496)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L502)
 
 ### ctx.agents.get(id)
 
@@ -271,7 +271,7 @@ Look up a live agent.
 
 **Returns** the agent, or undefined when no live agent has that id.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L530)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L536)
 
 ### ctx.agents.isOwnedBy(id, owner)
 
@@ -294,7 +294,7 @@ Test whether a live agent was created through one exact parent agent's scoped co
 
 **Returns** true only while the exact child entry is live under that owner.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L542)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L548)
 
 ### ctx.agents.list()
 
@@ -310,7 +310,7 @@ All live agents, in registration order.
 
 **Returns** a fresh array; mutating it does not affect the registry.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L550)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L556)
 
 ### ctx.agents.roots()
 
@@ -328,4 +328,4 @@ All live top-level agents in registration order. A top-level agent was created w
 
 **Returns** a fresh array; mutating it does not affect the registry.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L560)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/agent/src/index.ts#L566)
diff --git a/website/zh-CN/api/harness/events.md b/website/zh-CN/api/harness/events.md
index fcfa426a81..ae1633ddaa 100644
--- a/website/zh-CN/api/harness/events.md
+++ b/website/zh-CN/api/harness/events.md
@@ -614,7 +614,7 @@ A ready child settled. Scope-filtered dispatch uses the same delegating parent c
 
 - `info` — the run identity and terminal outcome.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L112)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L138)
 
 ### subagent/provider-added
 
@@ -633,7 +633,7 @@ A provider became resolvable in the registry.
 
 - `provider` — the registered provider.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L86)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L112)
 
 ### subagent/provider-removed
 
@@ -652,7 +652,7 @@ A provider left the registry. Accepted runs remain holder-owned.
 
 - `name` — the provider name that no longer resolves.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L92)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L118)
 
 ### subagent/start
 
@@ -676,7 +676,7 @@ A provider established a ready child. For in-process providers, `ctx.agents.get(
 
 - `info` — the provider and ready child identity.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L103)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L129)
 
 ## system-prompt/*
 
diff --git a/website/zh-CN/api/harness/sessions.md b/website/zh-CN/api/harness/sessions.md
index f59001009d..73ae4385af 100644
--- a/website/zh-CN/api/harness/sessions.md
+++ b/website/zh-CN/api/harness/sessions.md
@@ -7,7 +7,7 @@
 In-memory session store (`ctx.sessions`).
 Persistence is intentionally not implemented here — persistence plugins subscribe to `session/event` and flush on `session/flush` / dispose.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L577)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L581)
 
 ### ctx.sessions.create(id?, options?)
 
@@ -44,7 +44,7 @@ For an agent whose session must be torn down IN ORDER with its loop (so the loop
 
 **Returns** the live session, already entered and announced.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L606)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L610)
 
 ### ctx.sessions.prepare(id?, options?)
 
@@ -75,7 +75,7 @@ Build a session WITHOUT entering it into the store — validate the id/cwd and c
 
 **Returns** the constructed session, NOT yet in the store.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L635)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L639)
 
 ### ctx.sessions.enter(session)
 
@@ -112,7 +112,7 @@ Re-checks the id for a duplicate: `prepare` and `enter` are public cross-package
 
 **Returns** the detach disposer (publication hooks + store removal). When called from a synchronous `session/created` listener, removal and disposal wait until that creation dispatch unwinds.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L679)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L684)
 
 ### ctx.sessions.announce(session)
 
@@ -131,7 +131,7 @@ Emit `session/created` exactly once for an entered session (with the carrier ent
 
 - `session` — the entered session to announce to listeners.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L734)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L739)
 
 ### ctx.sessions.flush(session)
 
@@ -156,7 +156,7 @@ Dispatch the awaited `session/flush` durability checkpoint for `session`, with t
 
 **Returns** resolves when every flush listener has settled; after all settle, rejects with the first registered listener failure if any listener failed.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L786)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L791)
 
 ### ctx.sessions.get(id)
 
@@ -175,7 +175,7 @@ Look up a live session.
 
 **Returns** the session, or undefined when no live session has that id.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L818)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L823)
 
 ### ctx.sessions.list()
 
@@ -191,7 +191,7 @@ All live sessions, in creation order.
 
 **Returns** a fresh array; mutating it does not affect the store.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L826)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L831)
 
 ### ctx.sessions.fork(source, boundary?, childSessionId?)
 
@@ -220,4 +220,4 @@ Create a live child session from a turn-enclosed prefix of a live source. `bound
 
 **Returns** The created live child session.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L843)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/core/session/src/index.ts#L848)
diff --git a/website/zh-CN/api/harness/subagents.md b/website/zh-CN/api/harness/subagents.md
index de71a5effe..2e0d295eb3 100644
--- a/website/zh-CN/api/harness/subagents.md
+++ b/website/zh-CN/api/harness/subagents.md
@@ -6,7 +6,7 @@
 
 Named provider registry and capability-checked start surface.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L153)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L179)
 
 ### ctx.subagents.registerProvider(provider)
 
@@ -27,7 +27,7 @@ Register a provider under its name. Registration is effect-scoped and HMR safe;
 
 **Returns** the exact Cordis effect disposer.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L167)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L193)
 
 ### ctx.subagents.getProvider(name)
 
@@ -46,7 +46,7 @@ Look up a provider by name.
 
 **Returns** the provider, or undefined when absent.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L190)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L216)
 
 ### ctx.subagents.list()
 
@@ -62,7 +62,7 @@ List registered provider names in insertion order.
 
 **Returns** the registered names.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L198)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L224)
 
 ### ctx.subagents.start(name, request)
 
@@ -86,4 +86,4 @@ Establish a ready child on the named provider. Capability and semantic checks ru
 
 **Returns** the ready holder-owned run.
 
-[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L211)
+[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/subagent/subagent/src/index.ts#L237)