diff --git a/packages/core/src/plugin/host.ts b/packages/core/src/plugin/host.ts
index 007a53ed70e..9b175a80b4f 100644
--- a/packages/core/src/plugin/host.ts
+++ b/packages/core/src/plugin/host.ts
@@ -333,8 +333,8 @@ export const make = Effect.fn("PluginHost.make")(function* (plugin: PluginV2.Int
               tool: event.tool,
               sessionID: event.sessionID,
               agent: event.agent,
-              assistantMessageID: event.assistantMessageID,
-              toolCallID: event.toolCallID,
+              messageID: event.messageID,
+              callID: event.callID,
               input: event.input,
             }
             return Reflect.apply(callback, undefined, [output]).pipe(
@@ -347,8 +347,8 @@ export const make = Effect.fn("PluginHost.make")(function* (plugin: PluginV2.Int
             tool: event.tool,
             sessionID: event.sessionID,
             agent: event.agent,
-            assistantMessageID: event.assistantMessageID,
-            toolCallID: event.toolCallID,
+            messageID: event.messageID,
+            callID: event.callID,
             input: event.input,
             result: event.result,
             output: event.output,
diff --git a/packages/core/src/plugin/promise.ts b/packages/core/src/plugin/promise.ts
index 75c8b300afd..53caee351c1 100644
--- a/packages/core/src/plugin/promise.ts
+++ b/packages/core/src/plugin/promise.ts
@@ -256,10 +256,22 @@ function fromPromiseTool(tool: AnyTool) {
   if ("jsonSchema" in tool)
     return Tool.make({
       ...tool,
-      execute: (input, context) => Effect.promise(() => tool.execute(input, context)),
+      execute: (input, context) =>
+        Effect.promise(() =>
+          tool.execute(input, {
+            ...context,
+            progress: (update) => Effect.runPromise(context.progress(update)),
+          }),
+        ),
     })
   return Tool.make({
     ...tool,
-    execute: (input, context) => Effect.promise(() => tool.execute(input, context)),
+    execute: (input, context) =>
+      Effect.promise(() =>
+        tool.execute(input, {
+          ...context,
+          progress: (update) => Effect.runPromise(context.progress(update)),
+        }),
+      ),
   })
 }
diff --git a/packages/core/src/session/runner/llm.ts b/packages/core/src/session/runner/llm.ts
index 6a15137c077..48fcc4d8d60 100644
--- a/packages/core/src/session/runner/llm.ts
+++ b/packages/core/src/session/runner/llm.ts
@@ -265,8 +265,18 @@ const layer = Layer.effect(
                   toolMaterialization.settle({
                     sessionID: session.id,
                     agent: agent.id,
-                    assistantMessageID,
+                    messageID: assistantMessageID,
                     call: event,
+                    progress: (update) =>
+                      serialized(
+                        events.publish(SessionEvent.Tool.Progress, {
+                          sessionID: session.id,
+                          assistantMessageID,
+                          callID: event.id,
+                          structured: { ...update.structured },
+                          content: [...update.content],
+                        }),
+                      ),
                   }),
                 ).pipe(
                   Effect.flatMap((settlement) =>
diff --git a/packages/core/src/tool-output-store.ts b/packages/core/src/tool-output-store.ts
index 1030ff22ffc..690f2cc85ba 100644
--- a/packages/core/src/tool-output-store.ts
+++ b/packages/core/src/tool-output-store.ts
@@ -18,7 +18,7 @@ export const MANAGED_DIRECTORY = "tool-output"
 
 export interface BoundInput {
   readonly sessionID: SessionSchema.ID
-  readonly toolCallID: string
+  readonly callID: string
   readonly output: ToolOutput
 }
 
diff --git a/packages/core/src/tool/edit.ts b/packages/core/src/tool/edit.ts
index 436a60e7cea..1d79459550d 100644
--- a/packages/core/src/tool/edit.ts
+++ b/packages/core/src/tool/edit.ts
@@ -122,8 +122,8 @@ export const Plugin = {
                 return Effect.gen(function* () {
                   const permissionSource = {
                     type: "tool" as const,
-                    messageID: context.assistantMessageID,
-                    callID: context.toolCallID,
+                    messageID: context.messageID,
+                    callID: context.callID,
                   }
                   if (input.oldString === input.newString) {
                     return yield* new ToolFailure({
diff --git a/packages/core/src/tool/execute.ts b/packages/core/src/tool/execute.ts
index 89672dbfc6c..701b5ff2bb0 100644
--- a/packages/core/src/tool/execute.ts
+++ b/packages/core/src/tool/execute.ts
@@ -113,12 +113,13 @@ export const create = (registrations: ReadonlyMap<string, Registration>) => {
               const index = yield* Ref.getAndUpdate(callIndex, (index) => index + 1)
               const output = yield* settle(
                 registration.tool,
-                { type: "tool-call", id: context.toolCallID, name, input },
+                { type: "tool-call", id: context.callID, name, input },
                 {
                   sessionID: context.sessionID,
                   agent: context.agent,
-                  assistantMessageID: context.assistantMessageID,
-                  toolCallID: context.toolCallID,
+                  messageID: context.messageID,
+                  callID: context.callID,
+                  progress: context.progress,
                 },
               ).pipe(Effect.mapError((failure) => toolError(failure.message, failure)))
               const outputFileParts = outputFiles(output)
diff --git a/packages/core/src/tool/glob.ts b/packages/core/src/tool/glob.ts
index 3cde812aaa9..f71102c3627 100644
--- a/packages/core/src/tool/glob.ts
+++ b/packages/core/src/tool/glob.ts
@@ -72,7 +72,7 @@ export const Plugin = {
                   },
                   sessionID: context.sessionID,
                   agent: context.agent,
-                  source: { type: "tool", messageID: context.assistantMessageID, callID: context.toolCallID },
+                  source: { type: "tool", messageID: context.messageID, callID: context.callID },
                 })
                 const cwd = path.resolve(location.directory, input.path ?? ".")
                 yield* fs
diff --git a/packages/core/src/tool/grep.ts b/packages/core/src/tool/grep.ts
index cdf61866c6d..99e64af50aa 100644
--- a/packages/core/src/tool/grep.ts
+++ b/packages/core/src/tool/grep.ts
@@ -90,7 +90,7 @@ export const Plugin = {
                   },
                   sessionID: context.sessionID,
                   agent: context.agent,
-                  source: { type: "tool", messageID: context.assistantMessageID, callID: context.toolCallID },
+                  source: { type: "tool", messageID: context.messageID, callID: context.callID },
                 })
                 const target = path.resolve(location.directory, input.path ?? ".")
                 const info = yield* fs
diff --git a/packages/core/src/tool/hooks.ts b/packages/core/src/tool/hooks.ts
index 4b491c57cdb..abe829aa1b4 100644
--- a/packages/core/src/tool/hooks.ts
+++ b/packages/core/src/tool/hooks.ts
@@ -12,8 +12,8 @@ export interface BeforeEvent {
   readonly tool: string
   readonly sessionID: Session.ID
   readonly agent: Agent.ID
-  readonly assistantMessageID: SessionMessage.ID
-  readonly toolCallID: string
+  readonly messageID: SessionMessage.ID
+  readonly callID: string
   input: unknown
 }
 
@@ -21,8 +21,8 @@ export interface AfterEvent {
   readonly tool: string
   readonly sessionID: Session.ID
   readonly agent: Agent.ID
-  readonly assistantMessageID: SessionMessage.ID
-  readonly toolCallID: string
+  readonly messageID: SessionMessage.ID
+  readonly callID: string
   readonly input: unknown
   result: ToolResultValue
   output?: ToolOutput
diff --git a/packages/core/src/tool/mcp.ts b/packages/core/src/tool/mcp.ts
index 8aad746ed62..0a15ba23509 100644
--- a/packages/core/src/tool/mcp.ts
+++ b/packages/core/src/tool/mcp.ts
@@ -57,8 +57,8 @@ export const layer = Layer.effectDiscard(
                     agent: context.agent,
                     source: {
                       type: "tool",
-                      messageID: context.assistantMessageID,
-                      callID: context.toolCallID,
+                      messageID: context.messageID,
+                      callID: context.callID,
                     },
                   })
                   const result = yield* mcp
diff --git a/packages/core/src/tool/patch.ts b/packages/core/src/tool/patch.ts
index 4d7c3030b98..8d986790ce6 100644
--- a/packages/core/src/tool/patch.ts
+++ b/packages/core/src/tool/patch.ts
@@ -85,8 +85,8 @@ export const Plugin = {
                 return Effect.gen(function* () {
                   const source = {
                     type: "tool" as const,
-                    messageID: context.assistantMessageID,
-                    callID: context.toolCallID,
+                    messageID: context.messageID,
+                    callID: context.callID,
                   }
                   if (!input.patchText.trim()) return yield* new ToolFailure({ message: "patchText is required" })
                   const hunks = yield* Effect.try({
diff --git a/packages/core/src/tool/question.ts b/packages/core/src/tool/question.ts
index 41c9d2dd50e..6b179fe9b8b 100644
--- a/packages/core/src/tool/question.ts
+++ b/packages/core/src/tool/question.ts
@@ -73,7 +73,7 @@ export const Plugin = {
                   resources: ["*"],
                   sessionID: context.sessionID,
                   agent: context.agent,
-                  source: { type: "tool", messageID: context.assistantMessageID, callID: context.toolCallID },
+                  source: { type: "tool", messageID: context.messageID, callID: context.callID },
                 })
                 .pipe(
                   Effect.mapError((error) => new ToolFailure({ message: "Permission denied: question", error })),
@@ -84,7 +84,7 @@ export const Plugin = {
                         title: "Questions",
                         metadata: {
                           kind: "question",
-                          tool: { messageID: context.assistantMessageID, callID: context.toolCallID },
+                          tool: { messageID: context.messageID, callID: context.callID },
                         },
                         fields: [
                           toField(input.questions[0], 0),
diff --git a/packages/core/src/tool/read.ts b/packages/core/src/tool/read.ts
index aa2e81b5645..646e09daf6b 100644
--- a/packages/core/src/tool/read.ts
+++ b/packages/core/src/tool/read.ts
@@ -62,8 +62,8 @@ export const Plugin = {
               return Effect.gen(function* () {
                 const source = {
                   type: "tool" as const,
-                  messageID: context.assistantMessageID,
-                  callID: context.toolCallID,
+                  messageID: context.messageID,
+                  callID: context.callID,
                 }
                 const target = yield* mutation.resolve({ path: input.path, kind: "directory" })
                 const external = target.externalDirectory
diff --git a/packages/core/src/tool/registry.ts b/packages/core/src/tool/registry.ts
index b1087c78228..6e1910ae565 100644
--- a/packages/core/src/tool/registry.ts
+++ b/packages/core/src/tool/registry.ts
@@ -19,8 +19,14 @@ import { toSessionError } from "../session/to-session-error"
 export type ExecuteInput = {
   readonly sessionID: SessionSchema.ID
   readonly agent: AgentV2.ID
-  readonly assistantMessageID: SessionMessage.ID
+  readonly messageID: SessionMessage.ID
   readonly call: ToolCall
+  readonly progress?: (update: Progress) => Effect.Effect<void>
+}
+
+export interface Progress {
+  readonly structured: Readonly<Record<string, unknown>>
+  readonly content: ToolOutput["content"]
 }
 
 export interface Interface {
@@ -65,8 +71,8 @@ const registryLayer = Layer.effect(
         tool: input.call.name,
         sessionID: input.sessionID,
         agent: input.agent,
-        assistantMessageID: input.assistantMessageID,
-        toolCallID: input.call.id,
+        messageID: input.messageID,
+        callID: input.call.id,
         input: input.call.input,
       }
       yield* toolHooks.runBefore(beforeEvent)
@@ -76,8 +82,22 @@ const registryLayer = Layer.effect(
         {
           sessionID: input.sessionID,
           agent: input.agent,
-          assistantMessageID: input.assistantMessageID,
-          toolCallID: input.call.id,
+          messageID: input.messageID,
+          callID: input.call.id,
+          progress: (update) =>
+            input.progress?.({
+              structured: update.structured,
+              content: (update.content ?? []).map((part) =>
+                part.type === "text"
+                  ? { type: "text" as const, text: part.text }
+                  : {
+                      type: "file" as const,
+                      uri: `data:${part.mime};base64,${part.data}`,
+                      mime: part.mime,
+                      name: part.name,
+                    },
+              ),
+            }) ?? Effect.void,
         },
       ).pipe(
         Effect.map((output) => ({ output })),
@@ -94,7 +114,7 @@ const registryLayer = Layer.effect(
       } else {
         const bounded = yield* resources.bound({
           sessionID: input.sessionID,
-          toolCallID: input.call.id,
+          callID: input.call.id,
           output: pending.output,
         })
         const result = ToolOutput.toResultValue(bounded.output)
@@ -111,8 +131,8 @@ const registryLayer = Layer.effect(
         tool: input.call.name,
         sessionID: input.sessionID,
         agent: input.agent,
-        assistantMessageID: input.assistantMessageID,
-        toolCallID: input.call.id,
+        messageID: input.messageID,
+        callID: input.call.id,
         input: beforeEvent.input,
         result: settlement.result,
         output: settlement.output,
diff --git a/packages/core/src/tool/shell.ts b/packages/core/src/tool/shell.ts
index 34583387d78..5109e2a5355 100644
--- a/packages/core/src/tool/shell.ts
+++ b/packages/core/src/tool/shell.ts
@@ -165,8 +165,8 @@ export const Plugin = {
               Effect.gen(function* () {
                 const source = {
                   type: "tool" as const,
-                  messageID: context.assistantMessageID,
-                  callID: context.toolCallID,
+                  messageID: context.messageID,
+                  callID: context.callID,
                 }
                 const target = yield* mutation.resolve({ path: input.workdir ?? ".", kind: "directory" })
                 const external = target.externalDirectory
@@ -231,7 +231,7 @@ export const Plugin = {
                   Effect.onInterrupt(() => shell.remove(info.id).pipe(Effect.ignore)),
                 )
                 const job = yield* runtime.job.start({
-                  id: context.toolCallID,
+                  id: context.callID,
                   type: name,
                   title: input.command,
                   metadata: { sessionID: context.sessionID, shellID: info.id },
@@ -240,7 +240,7 @@ export const Plugin = {
 
                 if (input.background === true) {
                   yield* runtime.job.background(job.id)
-                  yield* notifyWhenDone(context.sessionID, context.toolCallID, input.command)
+                  yield* notifyWhenDone(context.sessionID, context.callID, input.command)
                   return {
                     output: BACKGROUND_STARTED,
                     shellID: info.id,
@@ -255,7 +255,7 @@ export const Plugin = {
                   .pipe(Effect.onInterrupt(() => runtime.job.cancel(job.id).pipe(Effect.ignore)))
                 if (result?.type === "backgrounded") {
                   yield* shell.timeout(info.id, 0)
-                  yield* notifyWhenDone(context.sessionID, context.toolCallID, input.command)
+                  yield* notifyWhenDone(context.sessionID, context.callID, input.command)
                   return {
                     output: BACKGROUND_STARTED,
                     shellID: info.id,
diff --git a/packages/core/src/tool/skill.ts b/packages/core/src/tool/skill.ts
index 2589fd08ad9..07d935a1273 100644
--- a/packages/core/src/tool/skill.ts
+++ b/packages/core/src/tool/skill.ts
@@ -79,7 +79,7 @@ export const Plugin = {
                     save: [skill.id],
                     sessionID: context.sessionID,
                     agent: context.agent,
-                    source: { type: "tool", messageID: context.assistantMessageID, callID: context.toolCallID },
+                    source: { type: "tool", messageID: context.messageID, callID: context.callID },
                   })
                   const directory = path.dirname(skill.location)
                   const files =
diff --git a/packages/core/src/tool/subagent.ts b/packages/core/src/tool/subagent.ts
index 6fcda996dce..ea4dc87d5ee 100644
--- a/packages/core/src/tool/subagent.ts
+++ b/packages/core/src/tool/subagent.ts
@@ -136,8 +136,8 @@ export const Plugin = {
                     agent: context.agent,
                     source: {
                       type: "tool",
-                      messageID: context.assistantMessageID,
-                      callID: context.toolCallID,
+                      messageID: context.messageID,
+                      callID: context.callID,
                     },
                   })
                   .pipe(Effect.mapError((error) => new ToolFailure({ message: `Subagent denied: ${agent.id}`, error })))
@@ -160,6 +160,9 @@ export const Plugin = {
                   )
 
                 const background = input.background === true
+                yield* context.progress({
+                  structured: { sessionID: child.id, status: "running" },
+                })
 
                 const run = Effect.gen(function* () {
                   // The child session owns its agent/model (set at create); prompt only admits input.
diff --git a/packages/core/src/tool/webfetch.ts b/packages/core/src/tool/webfetch.ts
index 3b900e17842..6a5910c057e 100644
--- a/packages/core/src/tool/webfetch.ts
+++ b/packages/core/src/tool/webfetch.ts
@@ -141,7 +141,7 @@ export const Plugin = {
                   metadata: input,
                   sessionID: context.sessionID,
                   agent: context.agent,
-                  source: { type: "tool", messageID: context.assistantMessageID, callID: context.toolCallID },
+                  source: { type: "tool", messageID: context.messageID, callID: context.callID },
                 })
 
                 const { body, contentType } = yield* Effect.gen(function* () {
diff --git a/packages/core/src/tool/websearch.ts b/packages/core/src/tool/websearch.ts
index ab65c33a4cf..0e23fc8a32a 100644
--- a/packages/core/src/tool/websearch.ts
+++ b/packages/core/src/tool/websearch.ts
@@ -213,7 +213,7 @@ export const Plugin = {
                   metadata: { ...input, provider },
                   sessionID: context.sessionID,
                   agent: context.agent,
-                  source: { type: "tool", messageID: context.assistantMessageID, callID: context.toolCallID },
+                  source: { type: "tool", messageID: context.messageID, callID: context.callID },
                 })
 
                 const text =
diff --git a/packages/core/src/tool/write.ts b/packages/core/src/tool/write.ts
index d7cd8c54f4c..e634411e011 100644
--- a/packages/core/src/tool/write.ts
+++ b/packages/core/src/tool/write.ts
@@ -64,8 +64,8 @@ export const Plugin = {
                 Effect.gen(function* () {
                   const source = {
                     type: "tool" as const,
-                    messageID: context.assistantMessageID,
-                    callID: context.toolCallID,
+                    messageID: context.messageID,
+                    callID: context.callID,
                   }
                   const target = yield* mutation.resolve({ path: input.path, kind: "file" })
                   const external = target.externalDirectory
diff --git a/packages/core/test/lib/tool.ts b/packages/core/test/lib/tool.ts
index 10d68c7fa38..468f9e3d9ce 100644
--- a/packages/core/test/lib/tool.ts
+++ b/packages/core/test/lib/tool.ts
@@ -10,7 +10,7 @@ import { host } from "../plugin/host"
 
 export const toolIdentity = {
   agent: AgentV2.ID.make("build"),
-  assistantMessageID: SessionMessage.ID.make("msg_tool_test"),
+  messageID: SessionMessage.ID.make("msg_tool_test"),
 }
 
 export const toolDefinitions = (registry: ToolRegistry.Interface, permissions?: PermissionV2.Ruleset) =>
diff --git a/packages/core/test/mcp.test.ts b/packages/core/test/mcp.test.ts
index 2fca0e0b955..f6b39e86aa8 100644
--- a/packages/core/test/mcp.test.ts
+++ b/packages/core/test/mcp.test.ts
@@ -663,7 +663,7 @@ it.effect("waits for permission before calling an MCP tool", () =>
       agent: toolIdentity.agent,
       source: {
         type: "tool",
-        messageID: toolIdentity.assistantMessageID,
+        messageID: toolIdentity.messageID,
         callID: "call_mcp_permission",
       },
     })
diff --git a/packages/core/test/plugin.test.ts b/packages/core/test/plugin.test.ts
index 6d9e0aac3dc..9ff717d6657 100644
--- a/packages/core/test/plugin.test.ts
+++ b/packages/core/test/plugin.test.ts
@@ -363,7 +363,7 @@ describe("PluginV2", () => {
       const settlement = yield* materialized.settle({
         sessionID: SessionV2.ID.make("ses_hooks"),
         agent: AgentV2.ID.make("build"),
-        assistantMessageID: SessionMessage.ID.make("msg_hooks"),
+        messageID: SessionMessage.ID.make("msg_hooks"),
         call: { type: "tool-call", id: "call-hooks", name: "echo", input: { text: "original" } },
       })
 
diff --git a/packages/core/test/plugin/promise.test.ts b/packages/core/test/plugin/promise.test.ts
index afe72f6b59f..2c6fccc892e 100644
--- a/packages/core/test/plugin/promise.test.ts
+++ b/packages/core/test/plugin/promise.test.ts
@@ -129,6 +129,7 @@ describe("fromPromise", () => {
       const plugins = yield* PluginV2.Service
       const registry = yield* ToolRegistry.Service
       const host = yield* PluginHost.make(plugins)
+      const progress: ToolRegistry.Progress[] = []
       const promisePlugin = Plugin.define({
         id: "promise-tool",
         setup: async (ctx) => {
@@ -139,7 +140,10 @@ describe("fromPromise", () => {
               description: "Hello",
               input: Schema.Struct({ name: Schema.String }),
               output: Schema.String,
-              execute: async ({ name }) => `Hello, ${name}!`,
+              execute: async ({ name }, context) => {
+                await context.progress({ structured: { phase: "greeting" } })
+                return `Hello, ${name}!`
+              },
             })
           })
         },
@@ -153,10 +157,12 @@ describe("fromPromise", () => {
         yield* materialized.settle({
           sessionID: SessionV2.ID.make("ses_promise_tool"),
           agent: AgentV2.ID.make("build"),
-          assistantMessageID: SessionMessage.ID.make("msg_promise_tool"),
+          messageID: SessionMessage.ID.make("msg_promise_tool"),
+          progress: (update) => Effect.sync(() => progress.push(update)),
           call: { type: "tool-call", id: "call_promise_tool", name: "hello", input: { name: "world" } },
         }),
       ).toMatchObject({ result: { type: "text", value: "Hello, world!" } })
+      expect(progress).toEqual([{ structured: { phase: "greeting" }, content: [] }])
     }),
   )
 })
diff --git a/packages/core/test/session-instructions.test.ts b/packages/core/test/session-instructions.test.ts
index a682c1450e7..1591dc4ed47 100644
--- a/packages/core/test/session-instructions.test.ts
+++ b/packages/core/test/session-instructions.test.ts
@@ -109,7 +109,7 @@ const it = testEffect(testLayer)
 
 const identity = {
   agent: AgentV2.ID.make("build"),
-  assistantMessageID: SessionMessage.ID.make("msg_nearby"),
+  messageID: SessionMessage.ID.make("msg_nearby"),
 }
 const readCall = (sessionID: SessionV2.ID, id: string, readPath: string): ToolRegistry.ExecuteInput => ({
   sessionID,
diff --git a/packages/core/test/session-runner-tool-events.test.ts b/packages/core/test/session-runner-tool-events.test.ts
index 1cdc71788a1..1bfbe205577 100644
--- a/packages/core/test/session-runner-tool-events.test.ts
+++ b/packages/core/test/session-runner-tool-events.test.ts
@@ -182,7 +182,7 @@ test("binary failure emits no success event", async () => {
 test("success event data can carry a provider-executed result", () => {
   const decoded = Schema.decodeUnknownSync(SessionEvent.Tool.Success.data)({
     sessionID,
-    assistantMessageID: SessionMessage.ID.create(),
+    messageID: SessionMessage.ID.create(),
     callID: "call-old",
     structured: { type: "media", mime: "image/png" },
     content: [{ type: "file", uri: `data:image/png;base64,${base64}`, mime: "image/png" }],
diff --git a/packages/core/test/session-runner-tool-registry.test.ts b/packages/core/test/session-runner-tool-registry.test.ts
index b7351cd9009..c488c1f7fc9 100644
--- a/packages/core/test/session-runner-tool-registry.test.ts
+++ b/packages/core/test/session-runner-tool-registry.test.ts
@@ -15,10 +15,10 @@ const bounds: ToolOutputStore.BoundInput[] = []
 const retentionFailure = new ToolOutputStore.StorageError({ operation: "write", cause: new Error("disk full") })
 const outputStore = Layer.mock(ToolOutputStore.Service, {
   bound: (input) => {
-    if (input.toolCallID === "call-retention-failure") return Effect.fail(retentionFailure)
+    if (input.callID === "call-retention-failure") return Effect.fail(retentionFailure)
     return Effect.sync(() => bounds.push(input)).pipe(
       Effect.as(
-        input.toolCallID === "call-bounded"
+        input.callID === "call-bounded"
           ? {
               output: { structured: {}, content: [{ type: "text" as const, text: "bounded reference" }] },
               outputPaths: ["/managed/generic"],
@@ -32,7 +32,7 @@ const registryLayer = AppNodeBuilder.build(ToolRegistry.node, [[ToolOutputStore.
 const it = testEffect(registryLayer)
 const identity = {
   agent: AgentV2.ID.make("build"),
-  assistantMessageID: SessionMessage.ID.make("msg_registry"),
+  messageID: SessionMessage.ID.make("msg_registry"),
 }
 const sessionID = SessionV2.ID.make("ses_registry")
 const call = (name: string, id = `call-${name}`): ToolRegistry.ExecuteInput => ({
@@ -240,7 +240,9 @@ describe("ToolRegistry", () => {
         ...identity,
         call: { type: "tool-call", id: "call-context", name: "context", input: {} },
       })
-      expect(contexts).toEqual([{ sessionID, ...identity, toolCallID: "call-context" }])
+      expect(contexts).toEqual([
+        { sessionID, ...identity, callID: "call-context", progress: expect.any(Function) },
+      ])
     }),
   )
 
diff --git a/packages/core/test/session-runner.test.ts b/packages/core/test/session-runner.test.ts
index 407d5989a46..5add9239ed4 100644
--- a/packages/core/test/session-runner.test.ts
+++ b/packages/core/test/session-runner.test.ts
@@ -783,14 +783,22 @@ describe("SessionRunnerLLM", () => {
           input: Schema.Struct({ query: Schema.String }),
           output: Schema.Struct({ answer: Schema.String }),
           execute: ({ query }, context) =>
-            Effect.sync(() => {
+            Effect.gen(function* () {
               contexts.push(context)
+              yield* context.progress({ structured: { phase: "reading" } })
               return { answer: query.toUpperCase() }
             }),
         }),
       }, { codemode: false })
       yield* admit(session, "Use application context")
       responses = [reply.tool("call-location", "location_context", { query: "hello" }), []]
+      const events = yield* EventV2.Service
+      const progressFiber = yield* events.subscribe(SessionEvent.Tool.Progress).pipe(
+        Stream.filter((event) => event.data.sessionID === sessionID && event.data.callID === "call-location"),
+        Stream.take(1),
+        Stream.runCollect,
+        Effect.forkScoped({ startImmediately: true }),
+      )
 
       yield* session.resume(sessionID)
 
@@ -799,10 +807,12 @@ describe("SessionRunnerLLM", () => {
         {
           sessionID,
           agent: AgentV2.ID.make("build"),
-          assistantMessageID: expect.stringMatching(/^msg_/),
-          toolCallID: "call-location",
+          messageID: expect.stringMatching(/^msg_/),
+          callID: "call-location",
+          progress: expect.any(Function),
         },
       ])
+      expect(Array.from(yield* Fiber.join(progressFiber))[0]?.data.structured).toEqual({ phase: "reading" })
       expect(yield* session.context(sessionID)).toMatchObject([
         { type: "user", text: "Use application context" },
         {
@@ -2252,7 +2262,7 @@ describe("SessionRunnerLLM", () => {
 
       expect(requests).toHaveLength(2)
       expect(requests[1]?.messages.map((message) => message.role)).toEqual(["user", "assistant", "tool"])
-      expect(authorizations).toMatchObject([{ sessionID, toolCallID: "call-echo" }])
+      expect(authorizations).toMatchObject([{ sessionID, callID: "call-echo" }])
       expect(executions).toEqual(["hello"])
       const context = yield* session.context(sessionID)
       expect(context).toMatchObject([
diff --git a/packages/core/test/tool-execute.test.ts b/packages/core/test/tool-execute.test.ts
index 6a1000fec4e..3eedc6fbab1 100644
--- a/packages/core/test/tool-execute.test.ts
+++ b/packages/core/test/tool-execute.test.ts
@@ -26,8 +26,9 @@ test("execute preserves successful results with visible unhandled rejections", a
       {
         sessionID: Session.ID.make("ses_execute"),
         agent: Agent.ID.make("build"),
-        assistantMessageID: SessionMessage.ID.make("msg_execute"),
-        toolCallID: "call_execute",
+        messageID: SessionMessage.ID.make("msg_execute"),
+        callID: "call_execute",
+        progress: () => Effect.void,
       },
     ),
   )
diff --git a/packages/core/test/tool-output-store.test.ts b/packages/core/test/tool-output-store.test.ts
index a2d132a74bb..4de63dfdcd0 100644
--- a/packages/core/test/tool-output-store.test.ts
+++ b/packages/core/test/tool-output-store.test.ts
@@ -52,7 +52,7 @@ describe("ToolOutputStore", () => {
         const second = "y".repeat(30_000) + "-TAIL"
         const result = yield* store.bound({
           sessionID,
-          toolCallID: "call-aggregate",
+          callID: "call-aggregate",
           output: {
             structured: { kind: "report" },
             content: [
@@ -74,7 +74,7 @@ describe("ToolOutputStore", () => {
     withStore(({ store, fs }) =>
       Effect.gen(function* () {
         const structured = { text: "x".repeat(ToolOutputStore.MAX_BYTES) }
-        const result = yield* store.bound({ sessionID, toolCallID: "call-json", output: { structured, content: [] } })
+        const result = yield* store.bound({ sessionID, callID: "call-json", output: { structured, content: [] } })
         expect(result.output.structured).toEqual(structured)
         expect(result.outputPaths).toHaveLength(1)
         expect(JSON.parse(yield* fs.readFileString(result.outputPaths[0]))).toEqual(structured)
@@ -89,7 +89,7 @@ describe("ToolOutputStore", () => {
         const data = "a".repeat(6 * 1024 * 1024)
         const result = yield* store.bound({
           sessionID,
-          toolCallID: "call-file",
+          callID: "call-file",
           output: {
             structured: { caption: "pixel" },
             content: [{ type: "file", uri: `data:image/png;base64,${data}`, mime: "image/png", name: "pixel.png" }],
@@ -120,7 +120,7 @@ describe("ToolOutputStore", () => {
         }
         const result = yield* store.bound({
           sessionID,
-          toolCallID: "call-text-and-media",
+          callID: "call-text-and-media",
           output: { structured: { caption: "pixel" }, content: [{ type: "text", text }, media] },
         })
 
@@ -136,7 +136,7 @@ describe("ToolOutputStore", () => {
       Effect.gen(function* () {
         const text = "x".repeat(30_000)
         const output = { structured: { output: text }, content: [{ type: "text" as const, text }] }
-        expect(yield* store.bound({ sessionID, toolCallID: "call-duplicated", output })).toEqual({
+        expect(yield* store.bound({ sessionID, callID: "call-duplicated", output })).toEqual({
           output,
           outputPaths: [],
         })
@@ -151,7 +151,7 @@ describe("ToolOutputStore", () => {
         const exit = yield* store
           .bound({
             sessionID,
-            toolCallID: "call-lossy",
+            callID: "call-lossy",
             output: { structured: {}, content: [{ type: "text", text: "x".repeat(ToolOutputStore.MAX_BYTES + 1) }] },
           })
           .pipe(Effect.exit)
@@ -166,7 +166,7 @@ describe("ToolOutputStore", () => {
     withStore(({ store }) =>
       Effect.gen(function* () {
         const output = { structured: { value: 1n }, content: [{ type: "text" as const, text: "readable text" }] }
-        expect(yield* store.bound({ sessionID, toolCallID: "call-unencodable", output })).toEqual({
+        expect(yield* store.bound({ sessionID, callID: "call-unencodable", output })).toEqual({
           output,
           outputPaths: [],
         })
@@ -197,7 +197,7 @@ describe("ToolOutputStore", () => {
         const fiber = yield* service
           .bound({
             sessionID,
-            toolCallID: "call-interrupted",
+            callID: "call-interrupted",
             output: { structured: {}, content: [{ type: "text", text: "x".repeat(ToolOutputStore.MAX_BYTES + 1) }] },
           })
           .pipe(Effect.forkChild)
@@ -216,7 +216,7 @@ describe("ToolOutputStore", () => {
           expect(yield* store.limits()).toEqual({ maxLines: 2, maxBytes: 1_000 })
           const result = yield* store.bound({
             sessionID,
-            toolCallID: "call-config",
+            callID: "call-config",
             output: { structured: {}, content: [{ type: "text", text: "one\ntwo\nthree" }] },
           })
           expect(result.outputPaths).toHaveLength(1)
diff --git a/packages/core/test/tool-question.test.ts b/packages/core/test/tool-question.test.ts
index 5d20d01622d..1c91de99660 100644
--- a/packages/core/test/tool-question.test.ts
+++ b/packages/core/test/tool-question.test.ts
@@ -166,7 +166,7 @@ describe("QuestionTool", () => {
       expect(capturedInput()).toEqual({
         sessionID,
         title: "Questions",
-        metadata: { kind: "question", tool: { messageID: toolIdentity.assistantMessageID, callID: "call-question" } },
+        metadata: { kind: "question", tool: { messageID: toolIdentity.messageID, callID: "call-question" } },
         fields: [
           {
             key: "q0",
@@ -212,7 +212,7 @@ describe("QuestionTool", () => {
       expect(capturedInput()).toEqual({
         sessionID,
         title: "Questions",
-        metadata: { kind: "question", tool: { messageID: toolIdentity.assistantMessageID, callID: "call-question" } },
+        metadata: { kind: "question", tool: { messageID: toolIdentity.messageID, callID: "call-question" } },
         fields: [
           {
             key: "q0",
diff --git a/packages/core/test/tool-subagent.test.ts b/packages/core/test/tool-subagent.test.ts
index e0250065c58..e9b4a5c56e0 100644
--- a/packages/core/test/tool-subagent.test.ts
+++ b/packages/core/test/tool-subagent.test.ts
@@ -178,10 +178,12 @@ describe("SubagentTool", () => {
           const locations = yield* LocationServiceMap.Service
           const registry = yield* ToolRegistry.Service.pipe(Effect.provide(locations.get(parent.location)))
           yield* waitForTool(registry, SubagentTool.name)
+          const progress: ToolRegistry.Progress[] = []
 
           const settled = yield* settleTool(registry, {
             sessionID: parent.id,
             ...toolIdentity,
+            progress: (update) => Effect.sync(() => progress.push(update)),
             call: {
               type: "tool-call",
               id: "call-subagent",
@@ -192,6 +194,7 @@ describe("SubagentTool", () => {
 
           expect(settled.output?.structured).toMatchObject({ status: "completed", output: childText })
           const child = yield* sessions.get(outputSessionID(settled.output?.structured))
+          expect(progress[0]?.structured).toEqual({ sessionID: child.id, status: "running" })
           expect(child).toMatchObject({
             parentID: parent.id,
             location: parent.location,
diff --git a/packages/plugin/src/v2/effect/tool.ts b/packages/plugin/src/v2/effect/tool.ts
index ce53b78bd38..8668570f8fb 100644
--- a/packages/plugin/src/v2/effect/tool.ts
+++ b/packages/plugin/src/v2/effect/tool.ts
@@ -10,8 +10,14 @@ import type { Hooks, Transform } from "./registration.js"
 export interface Context {
   readonly sessionID: Session.ID
   readonly agent: Agent.ID
-  readonly assistantMessageID: SessionMessage.ID
-  readonly toolCallID: string
+  readonly messageID: SessionMessage.ID
+  readonly callID: string
+  readonly progress: (update: Progress) => Effect.Effect<void>
+}
+
+export interface Progress {
+  readonly structured: Readonly<Record<string, unknown>>
+  readonly content?: ReadonlyArray<Content>
 }
 
 export type SchemaType<A> = Schema.Codec<A, any>
@@ -253,8 +259,8 @@ export interface ToolExecuteBeforeEvent {
   readonly tool: string
   readonly sessionID: Session.ID
   readonly agent: Agent.ID
-  readonly assistantMessageID: SessionMessage.ID
-  readonly toolCallID: string
+  readonly messageID: SessionMessage.ID
+  readonly callID: string
   input: unknown
 }
 
@@ -262,8 +268,8 @@ export interface ToolExecuteAfterEvent {
   readonly tool: string
   readonly sessionID: Session.ID
   readonly agent: Agent.ID
-  readonly assistantMessageID: SessionMessage.ID
-  readonly toolCallID: string
+  readonly messageID: SessionMessage.ID
+  readonly callID: string
   readonly input: unknown
   result: ToolResultValue
   output?: ToolOutput
diff --git a/packages/plugin/src/v2/promise/tool.ts b/packages/plugin/src/v2/promise/tool.ts
index 77d936f5800..3f85aaae54b 100644
--- a/packages/plugin/src/v2/promise/tool.ts
+++ b/packages/plugin/src/v2/promise/tool.ts
@@ -5,7 +5,9 @@ import type { SessionMessage } from "@opencode-ai/schema/session-message"
 import type { JsonSchema, Schema } from "effect"
 import type { Hooks, Transform } from "./registration.js"
 
-export type Context = Tool.Context
+export type Context = Omit<Tool.Context, "progress"> & {
+  readonly progress: (update: Tool.Progress) => Promise<void>
+}
 export type SchemaType<A> = Tool.SchemaType<A>
 export type Content = Tool.Content
 export type DynamicOutput = Tool.DynamicOutput
@@ -50,8 +52,8 @@ export interface ToolExecuteBeforeEvent {
   readonly tool: string
   readonly sessionID: Session.ID
   readonly agent: Agent.ID
-  readonly assistantMessageID: SessionMessage.ID
-  readonly toolCallID: string
+  readonly messageID: SessionMessage.ID
+  readonly callID: string
   input: unknown
 }
 
@@ -59,8 +61,8 @@ export interface ToolExecuteAfterEvent {
   readonly tool: string
   readonly sessionID: Session.ID
   readonly agent: Agent.ID
-  readonly assistantMessageID: SessionMessage.ID
-  readonly toolCallID: string
+  readonly messageID: SessionMessage.ID
+  readonly callID: string
   readonly input: unknown
   result: Tool.ToolExecuteAfterEvent["result"]
   output?: Tool.ToolExecuteAfterEvent["output"]
diff --git a/packages/tui/src/routes/session/index.tsx b/packages/tui/src/routes/session/index.tsx
index 338c3dbf805..7118df30d22 100644
--- a/packages/tui/src/routes/session/index.tsx
+++ b/packages/tui/src/routes/session/index.tsx
@@ -2499,8 +2499,12 @@ function WebSearch(props: ToolProps) {
 function Subagent(props: ToolProps) {
   const { navigate } = useRoute()
   const data = useData()
-  const sessionID = createMemo(() => stringValue(props.metadata.sessionID) ?? stringValue(props.metadata.sessionId))
-  const description = createMemo(() => stringValue(props.input.description))
+  const input = createMemo(() => (typeof props.part.state.input === "string" ? {} : props.part.state.input))
+  const metadata = createMemo(() =>
+    props.part.state.status === "streaming" ? {} : props.part.state.structured,
+  )
+  const sessionID = createMemo(() => stringValue(metadata().sessionID) ?? stringValue(metadata().sessionId))
+  const description = createMemo(() => stringValue(input().description))
   const isRunning = createMemo(() => {
     const id = sessionID()
     return props.part.state.status === "running" || Boolean(id && data.session.status(id) === "running")
@@ -2518,12 +2522,12 @@ function Subagent(props: ToolProps) {
         if (id) navigate({ type: "session", sessionID: id })
       }}
       status={
-        props.input.background === true || props.metadata.status === "running" ? (
+        input().background === true || metadata().status === "running" ? (
           <StatusBadge>Background</StatusBadge>
         ) : undefined
       }
     >
-      {`${Locale.titlecase(stringValue(props.input.agent) ?? stringValue(props.input.subagent_type) ?? "General")} Subagent — ${description() ?? "Subagent"}`}
+      {`${Locale.titlecase(stringValue(input().agent) ?? stringValue(input().subagent_type) ?? "General")} Subagent — ${description() ?? "Subagent"}`}
     </InlineTool>
   )
 }
diff --git a/packages/tui/test/cli/tui/data.test.tsx b/packages/tui/test/cli/tui/data.test.tsx
index 0a49e76b215..493c2903256 100644
--- a/packages/tui/test/cli/tui/data.test.tsx
+++ b/packages/tui/test/cli/tui/data.test.tsx
@@ -2229,11 +2229,35 @@ test("settles pending tools when a live failure arrives", async () => {
         state: { call: true },
       },
     })
+    emitEvent(events, {
+      id: "evt_progress_1",
+      created: 0,
+      type: "session.tool.progress",
+      durable: durable("session-1", 5),
+      data: {
+        sessionID: "session-1",
+        assistantMessageID: "msg_explicit_assistant_9",
+        callID: "call-1",
+        structured: { sessionID: "session-child", status: "running" },
+        content: [],
+      },
+    })
+
+    await wait(() => {
+      const assistant = sync.session.message.get("session-1", "msg_explicit_assistant_9")
+      return (
+        assistant?.type === "assistant" &&
+        assistant.content[0]?.type === "tool" &&
+        assistant.content[0].state.status === "running" &&
+        assistant.content[0].state.structured.sessionID === "session-child"
+      )
+    })
+
     emitEvent(events, {
       id: "evt_failed_1",
       created: 0,
       type: "session.tool.failed",
-      durable: durable("session-1", 5),
+      durable: durable("session-1", 6),
       data: {
         sessionID: "session-1",
         assistantMessageID: "msg_explicit_assistant_9",
@@ -2264,7 +2288,7 @@ test("settles pending tools when a live failure arrives", async () => {
     if (tool.state.status !== "error") return
     expect(tool.state.error).toEqual({ type: "unknown", message: "aborted" })
     expect(tool.state.input).toEqual({})
-    expect(tool.state.structured).toEqual({})
+    expect(tool.state.structured).toEqual({ sessionID: "session-child", status: "running" })
     expect(tool.state.content).toEqual([])
     expect(tool.executed).toBe(false)
     expect(tool.providerState).toEqual({ call: true })