diff --git a/packages/subagent/subagent-inprocess/src/structured.ts b/packages/subagent/subagent-inprocess/src/structured.ts
index 370f7a538d..a557e44785 100644
--- a/packages/subagent/subagent-inprocess/src/structured.ts
+++ b/packages/subagent/subagent-inprocess/src/structured.ts
@@ -36,14 +36,20 @@
  * closes the within-step window the continuation veto cannot: a
  * `tools/pre-execute` deny for any call arriving after the agent's capture, so
  * a response that lists `structured_output` before further tool calls cannot
- * run side effects after the final answer was accepted.
+ * run side effects after the final answer was accepted. A fourth,
+ * `tools/post-execute`, is the capture COMMIT: the tool body only stages the
+ * validated value, and it becomes the run's captured result only when the
+ * final post-execute decision accepts the call — a blocking hook downstream
+ * yields `isError` in the log, and the run must not report success for it.
  *
- * Lifetime is refcounted with two kinds of holder: each backend acquires for
- * its plugin lifetime (so the tool exists before any run), and each structured
- * RUN acquires from start to settle (so a backend hot-reload mid-run cannot
- * unregister the capture tool out from under a live child). Registrations are
- * effects on the ROOT context — their natural upper bound is app teardown — and
- * the refcount disposes them when the last holder releases.
+ * Lifetime is refcounted by structured RUNS: each acquires from start to
+ * settle, so the registrations exist exactly while at least one structured
+ * child is live — a plain deployment that never passes `outputSchema` carries
+ * no always-on global state, and a backend hot-reload mid-run cannot
+ * unregister the capture tool out from under a live child (the run holds its
+ * own acquisition). Registrations land on the ROOT context and the refcount
+ * disposes them when the last run settles; the next structured run
+ * re-registers them.
  *
  * @module @deepseek-ai/dsh-subagent-inprocess/structured
  */
@@ -53,7 +59,7 @@ import type { Agent } from '@deepseek-ai/dsh-agent'
 import type { ContentBlock, ToolSchema } from '@deepseek-ai/dsh-llm'
 import type { ContinuationDecision } from '@deepseek-ai/dsh-agent'
 import type { AssembleContext, PromptAssembly } from '@deepseek-ai/dsh-system-prompt'
-import type { PreToolDecision, ToolExecution } from '@deepseek-ai/dsh-tools'
+import type { PostToolDecision, PreToolDecision, ToolExecution, ToolExecutionResult } from '@deepseek-ai/dsh-tools'
 import { ToolArgsError, validateStructuredValue, type StructuredOutputSchema } from '@deepseek-ai/dsh-tools'
 
 /** The model-facing tool name a structured child must call to finish. */
@@ -75,6 +81,15 @@ export const STRUCTURED_OUTPUT_INSTRUCTION
 /** One structured run's state: the schema to enforce and the captured value, once recorded. */
 interface RunState {
   readonly schema: StructuredOutputSchema
+  /**
+   * A validated value awaiting the post-execute verdict on ITS OWN call. Set
+   * by the capture tool's body, promoted to {@link RunState.captured} only
+   * when the final `tools/post-execute` decision accepts the call — a
+   * downstream block turns the logged result into `isError`, and a value
+   * committed at body time would let the run report success for a call the
+   * model saw fail.
+   */
+  pending?: { value: unknown }
   captured?: { value: unknown }
 }
 
@@ -106,7 +121,7 @@ export interface StructuredAcquisition {
 
 /**
  * Acquire the per-root-context structured runtime, registering the capture tool
- * and the two waterfall listeners on the FIRST acquisition. See the module doc
+ * and the runtime's listeners on the FIRST acquisition. See the module doc
  * for the enforcement and lifetime design.
  * @param ctx - any context of the app; the runtime keys off `ctx.root`.
  * @returns this holder's handle (attach/captured/detach + idempotent release).
@@ -179,7 +194,9 @@ function registerRuntime(root: Context, runtime: StructuredRuntime): void {
         // ToolArgsError → isError result with INVALID_ARGS: the model retries
         // within the same turn, exactly like a schema-validated defineTool call.
         if (violations.length > 0) throw new ToolArgsError(violations)
-        state.captured = { value: args }
+        // Two-phase commit: the body only STAGES the value; the post-execute
+        // listener below promotes it once the final decision accepts the call.
+        state.pending = { value: args }
         return Promise.resolve([{ type: 'text', text: 'Structured output recorded.' }])
       },
     })
@@ -243,6 +260,33 @@ function registerRuntime(root: Context, runtime: StructuredRuntime): void {
     return next()
   }, { prepend: true }))
 
+  // The capture COMMIT: promote the staged value only when the final
+  // post-execute decision accepts the call. The capture tool's body cannot
+  // decide — `tools/post-execute` runs after it, and a blocking listener (a
+  // PostToolUse hook) turns the logged result into `isError` feedback; a value
+  // committed at body time would make readResult report `structured` success
+  // for a call whose result the model and session log saw fail. `prepend:
+  // true` = outermost at registration time, so `await next()` returns the
+  // COMPOSED downstream decision — the same final verdict the registry maps
+  // onto the result. (A later-registered outer listener that blocks without
+  // delegating skips this commit entirely: the staged value is dropped and the
+  // run errors — failure-safe in the same direction.) The staging slot clears
+  // on every path, including a rejecting downstream listener.
+  runtime.disposers.push(root.on('tools/post-execute', async function (
+    this: unknown, exec: ToolExecution, _result: ToolExecutionResult, next: () => Promise<PostToolDecision>,
+  ): Promise<PostToolDecision> {
+    const state = exec.agent ? runtime.states.get(exec.agent) : undefined
+    if (!state || exec.name !== STRUCTURED_OUTPUT_TOOL || state.pending === undefined) return next()
+    const pending = state.pending
+    try {
+      const decision = await next()
+      if (decision.kind === 'accept') state.captured = pending
+      return decision
+    } finally {
+      delete state.pending
+    }
+  }, { prepend: true }))
+
   // Terminal means terminal WITHIN the step, not only at its end: the
   // turn-continuation veto above runs after every call in the current model
   // response has executed, so a response that puts `structured_output` before
diff --git a/packages/subagent/subagent-inprocess/tests/structured.spec.ts b/packages/subagent/subagent-inprocess/tests/structured.spec.ts
index ba693cfecd..0de036a0a0 100644
--- a/packages/subagent/subagent-inprocess/tests/structured.spec.ts
+++ b/packages/subagent/subagent-inprocess/tests/structured.spec.ts
@@ -11,8 +11,7 @@ import * as Invariants from '@deepseek-ai/dsh-invariants'
 import SubagentService, { type SubagentStartRequest } from '@deepseek-ai/dsh-subagent'
 import type { StructuredOutputSchema } from '@deepseek-ai/dsh-tools'
 import { MockAdapter, textResponse, toolCallResponse } from '../../../core/agent-loop/tests/mock-adapter.ts'
-import * as spawn from '@deepseek-ai/dsh-subagent-spawn'
-import * as fork from '@deepseek-ai/dsh-subagent-fork'
+import { startInProcessRun } from '../src/index.ts'
 import {
   acquireStructuredRuntime,
   STRUCTURED_OUTPUT_INSTRUCTION,
@@ -28,11 +27,14 @@ const SCHEMA: StructuredOutputSchema = {
 }
 
 /**
- * Real loop + scripted mock model + the REAL spawn backend (which acquires the
- * structured runtime at apply, exactly as shipped). The mock model script
- * drives the child's structured_output calls.
+ * Real loop + scripted mock model + an INLINE spawn-shaped provider over the
+ * shared driver. The concrete backend plugins are deliberately NOT loaded —
+ * they would devDep-cycle this package (spawn/fork already depend on the
+ * driver), and the runtime under test is the driver's; plugin-level structured
+ * coverage lives in the spawn/fork specs. The mock model script drives the
+ * child's structured_output calls.
  */
-async function setup(script: Script, options?: { withFork?: boolean }) {
+async function setup(script: Script) {
   const ctx = new Context()
   const adapter = new MockAdapter(script)
   await ctx.plugin(LlmService)
@@ -43,13 +45,15 @@ async function setup(script: Script, options?: { withFork?: boolean }) {
   await ctx.plugin(Invariants)
   await ctx.plugin(AgentLoop, { agents: [] })
   await ctx.plugin(SubagentService)
-  const fiber = await ctx.plugin(spawn, { providerName: 'spawn' })
-  const forkFiber = options?.withFork
-    ? await ctx.plugin(fork, { providerName: 'fork' })
-    : undefined
+  const disposeProvider = ctx.subagents.registerProvider({
+    name: 'spawn',
+    capabilities: { outputSchema: true, depthLimit: true, toolFilter: false },
+    inheritsParentContext: false,
+    start: (request: SubagentStartRequest) => startInProcessRun(ctx, request, { providerName: 'spawn' }),
+  })
   ctx.llm.registerAdapter(['mock'], adapter)
   const parent = ctx.agentLoop.create(AgentId('parent'), { model: 'mock' })
-  return { ctx, parent, adapter, fiber, forkFiber }
+  return { ctx, parent, adapter, disposeProvider }
 }
 
 function structuredRequest(parent: SubagentStartRequest['parent'], extra?: Partial<SubagentStartRequest>): SubagentStartRequest {
@@ -263,6 +267,62 @@ describe('in-process structured output', () => {
     expect(ctx.agents.get(AgentId('parent'))).toBeDefined()
   })
 
+  it('a schema carrying non-JSON values fails as OutputSchemaError, never as a raw clone error', async () => {
+    const { ctx, parent } = await setup([])
+    // Assertion runs BEFORE the defensive structuredClone: a function-valued
+    // annotation must surface as the subset violation it is, not escape as
+    // structuredClone's DataCloneError.
+    expect(() => ctx.subagents.start('spawn', structuredRequest(parent, {
+      outputSchema: { type: 'object', default: () => {} } as unknown as StructuredOutputSchema,
+    }))).toThrow(/unsupported output schema.*annotation must be JSON data/)
+  })
+
+  it('a post-execute BLOCK on the capture call denies the capture: log and result agree on failure', async () => {
+    const { ctx, parent, adapter } = await setup([
+      toolCallResponse('c1', STRUCTURED_OUTPUT_TOOL, { answer: 7 }),
+      textResponse('continues after the blocked capture'),
+    ])
+    // A PostToolUse-style hook, registered AFTER the runtime (so the runtime's
+    // prepend commit listener stays outermost and composes this verdict).
+    ctx.on('tools/post-execute', (exec, _result, next) => {
+      if (exec.name === STRUCTURED_OUTPUT_TOOL) {
+        return Promise.resolve({ kind: 'block' as const, feedback: [{ type: 'text' as const, text: 'capture rejected by hook' }] })
+      }
+      return next()
+    })
+    const run = ctx.subagents.start('spawn', structuredRequest(parent))
+    const result = await run.result
+    // No capture was committed: the run reports the schema shortfall...
+    expect(result.structured).toBeUndefined()
+    expect(result.stopReason).toBe('error')
+    // ...the logged tool result is the blocked isError with the feedback...
+    const child = ctx.agents.get(run.id)!
+    const results = child.session.events.filter(e => e.type === 'tool/result')
+    expect((results[0]!.data as { isError?: boolean }).isError).toBe(true)
+    expect(JSON.stringify((results[0]!.data as { content: unknown }).content)).toContain('capture rejected by hook')
+    // ...and the turn CONTINUED past the blocked call (no captured veto):
+    // the model got to react to the failure with a second step.
+    expect(adapter.requests.length).toBe(2)
+    await run.dispose()
+  })
+
+  it('a post-execute accept-with-replacement still commits the capture', async () => {
+    const { ctx, parent } = await setup([
+      toolCallResponse('c1', STRUCTURED_OUTPUT_TOOL, { answer: 8 }),
+    ])
+    ctx.on('tools/post-execute', (exec, _result, next) => {
+      if (exec.name === STRUCTURED_OUTPUT_TOOL) {
+        return Promise.resolve({ kind: 'accept' as const, content: [{ type: 'text' as const, text: 'recorded (rewritten)' }] })
+      }
+      return next()
+    })
+    const run = ctx.subagents.start('spawn', structuredRequest(parent))
+    const result = await run.result
+    expect(result.stopReason).toBe('completed')
+    expect(result.structured).toEqual({ answer: 8 })
+    await run.dispose()
+  })
+
   it('appends the structured instruction to the child REQUEST\'s system text (base prompt preserved)', async () => {
     const { ctx, parent, adapter } = await setup([toolCallResponse('c1', STRUCTURED_OUTPUT_TOOL, { answer: 1 })])
     // A context-wide section stands in for the deployment persona: the
@@ -298,6 +358,21 @@ describe('in-process structured output', () => {
   })
 
   describe('final-request enforcement (the prepend agent/request listener)', () => {
+    it('a plain agent assembling while the runtime is LIVE gets the placeholder stripped', async () => {
+      // Run-scoped acquisition means a plain deployment never registers the
+      // tool at all; the strip branch exists for the CONCURRENT case — a plain
+      // agent taking a turn while some structured child holds the runtime open.
+      const { ctx, parent, adapter } = await setup([textResponse('parent answer')])
+      const hold = acquireStructuredRuntime(ctx)
+      parent.send([{ type: 'text', text: 'hello' }])
+      await parent.whenIdle()
+      // The placeholder IS in the registry during this turn; the assembly the
+      // loop rendered must not carry it for an agent without a structured run.
+      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeDefined()
+      expect(toolNames(adapter.requests[0]!)).not.toContain(STRUCTURED_OUTPUT_TOOL)
+      hold.release()
+    })
+
     it('a structured child sees structured_output with ITS schema; a plain agent never sees the tool', async () => {
       const { ctx, parent, adapter } = await setup([
         // Parent turn (a plain agent): must NOT see the tool.
@@ -396,10 +471,13 @@ describe('in-process structured output', () => {
       // and shape a structured agent's assembly on the same path the loop
       // renders and logs as the request header.
       const { ctx, parent } = await setup([])
+      const acquisition = acquireStructuredRuntime(ctx)
+      // Bare assemble WHILE the runtime is live: the no-agent branch must
+      // strip the registered placeholder (before the acquisition there is
+      // nothing to strip — run-scoped registration).
       const bare = await ctx.systemPrompt.assemble({})
       expect(bare.tools.map(tool => tool.name)).not.toContain(STRUCTURED_OUTPUT_TOOL)
 
-      const acquisition = acquireStructuredRuntime(ctx)
       acquisition.attach(parent, SCHEMA)
       const shaped = await ctx.systemPrompt.assemble({ agent: parent })
       expect(shaped.tools.map(tool => tool.name)).toContain(STRUCTURED_OUTPUT_TOOL)
@@ -412,57 +490,37 @@ describe('in-process structured output', () => {
     })
   })
 
-  describe('runtime lifetime (refcount: backends + live runs)', () => {
-    it('registers the capture tool while a backend is loaded and unregisters when the last unloads', async () => {
-      const { ctx, fiber, forkFiber } = await setup([], { withFork: true })
-      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeDefined()
-      await fiber.dispose()
-      // fork still holds a reference.
-      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeDefined()
-      await forkFiber!.dispose()
-      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeUndefined()
-    })
-
-    it('a live run-level acquisition keeps the runtime registered after EVERY backend unloads', async () => {
-      // Simulates the run-holder half of the two-level lifetime: a structured
-      // run acquires at start and releases at settle, so registration ordering
-      // is settle-then-unregister even if all backends unload first. (A real
-      // in-process child dies WITH its backend's fiber — the acquisition's
-      // observable job is this ordering, which a manual holder pins directly.)
-      const { ctx, fiber, forkFiber } = await setup([], { withFork: true })
-      const runHolder = acquireStructuredRuntime(ctx)
-      await fiber.dispose()
-      await forkFiber!.dispose()
-      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeDefined()
-      runHolder.release()
-      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeUndefined()
-    })
-
-    it('a structured run releases its acquisition when it settles (backend unload mid-run)', async () => {
-      const { ctx, parent, fiber } = await setup(['hang'])
-      const run = ctx.subagents.start('spawn', structuredRequest(parent))
-      // Let the child's step start streaming, then unload the backend. The
-      // backend owns the child agent, so the unload tears the child down and
-      // the run settles — releasing its own acquisition on the way out.
-      await new Promise(resolve => setTimeout(resolve, 30))
-      await fiber.dispose()
-      const result = await run.result
-      expect(result.stopReason).toBe('error')
-      // Both holders (backend + run) released — nothing keeps the runtime now.
-      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeUndefined()
-      await run.dispose()
-    })
-
-    it('fork children capture structured output through the same runtime', async () => {
+  describe('runtime lifetime (refcount: live structured runs)', () => {
+    it('the runtime exists exactly while structured runs are live: nothing before, nothing after', async () => {
       const { ctx, parent } = await setup([
-        toolCallResponse('c1', STRUCTURED_OUTPUT_TOOL, { answer: 9 }),
-      ], { withFork: true })
-      const run = ctx.subagents.start('fork', structuredRequest(parent))
+        toolCallResponse('c1', STRUCTURED_OUTPUT_TOOL, { answer: 4 }),
+      ])
+      // No always-on global state: a context that has run no structured child
+      // carries no capture tool.
+      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeUndefined()
+      const run = ctx.subagents.start('spawn', structuredRequest(parent))
       const result = await run.result
-      expect(result.structured).toEqual({ answer: 9 })
+      // The capture succeeded — the registrations existed while the run lived.
+      expect(result.structured).toEqual({ answer: 4 })
+      // The run's settle released the last acquisition.
+      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeUndefined()
       await run.dispose()
     })
 
+    it('concurrent structured runs share one runtime; the last settle disposes it', async () => {
+      const { ctx, parent } = await setup([
+        toolCallResponse('c1', STRUCTURED_OUTPUT_TOOL, { answer: 1 }),
+        toolCallResponse('c2', STRUCTURED_OUTPUT_TOOL, { answer: 2 }),
+      ])
+      const first = ctx.subagents.start('spawn', structuredRequest(parent))
+      const second = ctx.subagents.start('spawn', structuredRequest(parent))
+      const [a, b] = await Promise.all([first.result, second.result])
+      expect([a.structured, b.structured].sort()).toEqual([{ answer: 1 }, { answer: 2 }].sort())
+      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeUndefined()
+      await first.dispose()
+      await second.dispose()
+    })
+
     it('acquisition release is idempotent (double release cannot underflow the refcount)', async () => {
       const ctx = new Context()
       await ctx.plugin(SystemPrompt)
@@ -513,13 +571,16 @@ describe('in-process structured output', () => {
       acquisition.detach(parent)
       acquisition.detach(parent)
       acquisition.release()
-      // The backend still holds its own reference from setup().
-      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeDefined()
+      // That manual acquisition was the ONLY holder - release disposes.
+      expect(ctx.tools.get(STRUCTURED_OUTPUT_TOOL)).toBeUndefined()
     })
   })
 
   it('a direct structured_output call from an agent WITHOUT a structured run is an isError', async () => {
     const { ctx, parent } = await setup([])
+    // Hold the runtime open (run-scoped: nothing is registered otherwise) so
+    // the call reaches the capture tool's own fail-loud guard, not UNKNOWN_TOOL.
+    const hold = acquireStructuredRuntime(ctx)
     const result = await ctx.tools.execute({
       callId: 'x' as never,
       name: STRUCTURED_OUTPUT_TOOL,
@@ -527,16 +588,19 @@ describe('in-process structured output', () => {
       agent: parent,
     })
     expect(result.isError).toBe(true)
-    expect(result.content[0]).toMatchObject({ type: 'text' })
+    expect(JSON.stringify(result.content)).toContain('only available to subagents')
+    hold.release()
   })
 
   it('a structured_output call with NO calling agent at all is an isError', async () => {
     const { ctx } = await setup([])
+    const hold = acquireStructuredRuntime(ctx)
     const result = await ctx.tools.execute({
       callId: 'x' as never,
       name: STRUCTURED_OUTPUT_TOOL,
       arguments: { answer: 1 },
     })
     expect(result.isError).toBe(true)
+    hold.release()
   })
 })