diff --git a/src/features/team-mode/tools/messaging-missing-session.test.ts b/src/features/team-mode/tools/messaging-missing-session.test.ts
new file mode 100644
index 000000000..3dceab444
--- /dev/null
+++ b/src/features/team-mode/tools/messaging-missing-session.test.ts
@@ -0,0 +1,92 @@
+/// <reference types="bun-types" />
+
+import { describe, expect, mock, test } from "bun:test"
+import { mkdtemp, readdir } from "node:fs/promises"
+import { randomUUID } from "node:crypto"
+import { tmpdir } from "node:os"
+import path from "node:path"
+
+import type { ToolContext } from "@opencode-ai/plugin/tool"
+
+import { TeamModeConfigSchema } from "../../../config/schema/team-mode"
+import { getInboxDir, resolveBaseDir } from "../team-registry/paths"
+
+function createToolContext(sessionID: string, directory: string): ToolContext {
+  return {
+    sessionID,
+    messageID: randomUUID(),
+    agent: "test-agent",
+    directory,
+    worktree: directory,
+    abort: new AbortController().signal,
+    metadata: () => {},
+    ask: async () => undefined,
+  }
+}
+
+describe("createTeamSendMessageTool missing recipient session fallback", () => {
+  test("releases the .delivering reservation when the recipient session disappears before live delivery", async () => {
+    // given
+    const baseDir = await mkdtemp(path.join(tmpdir(), "team-send-message-missing-session-"))
+    const config = TeamModeConfigSchema.parse({ base_dir: baseDir })
+    const teamRunId = randomUUID()
+    const leadSessionId = randomUUID()
+    const memberOneSessionId = randomUUID()
+    const memberTwoSessionId = randomUUID()
+
+    const runtimeStateWithRecipientSession = {
+      teamRunId,
+      leadSessionId,
+      status: "active",
+      members: [
+        { name: "team-lead", agentType: "leader", sessionId: leadSessionId },
+        { name: "m1", agentType: "member", sessionId: memberOneSessionId },
+        { name: "m2", agentType: "member", sessionId: memberTwoSessionId },
+      ],
+    }
+    const runtimeStateWithoutRecipientSession = {
+      ...runtimeStateWithRecipientSession,
+      members: runtimeStateWithRecipientSession.members.map((member) => (
+        member.name === "m2"
+          ? { ...member, sessionId: undefined }
+          : member
+      )),
+    }
+
+    let loadRuntimeStateCalls = 0
+    mock.module("../team-state-store/store", () => ({
+      listActiveTeams: async () => [{ teamRunId }],
+      loadRuntimeState: async () => {
+        loadRuntimeStateCalls += 1
+        return loadRuntimeStateCalls >= 3
+          ? runtimeStateWithoutRecipientSession
+          : runtimeStateWithRecipientSession
+      },
+    }))
+
+    const { createTeamSendMessageTool } = await import("./messaging")
+    type LiveDeliveryClient = Parameters<typeof createTeamSendMessageTool>[1]
+    const client = {
+      session: {
+        promptAsync: async () => {
+          throw new Error("promptAsync should not run when the recipient session is missing")
+        },
+      },
+    } satisfies LiveDeliveryClient
+    const tool = createTeamSendMessageTool(config, client)
+
+    // when
+    const result = await tool.execute({
+      teamRunId,
+      to: "m2",
+      body: "ping",
+    }, createToolContext(memberOneSessionId, baseDir))
+    const parsedResult = JSON.parse(result) as { deliveredTo: string[]; messageId: string }
+    const inboxDir = getInboxDir(resolveBaseDir(config), teamRunId, "m2")
+    const inboxEntries = (await readdir(inboxDir)).filter((entry) => entry.endsWith(".json"))
+
+    // then
+    expect(parsedResult.deliveredTo).toEqual(["m2"])
+    expect(inboxEntries).toEqual([`${parsedResult.messageId}.json`])
+  })
+})
diff --git a/src/features/team-mode/tools/messaging.test.ts b/src/features/team-mode/tools/messaging.test.ts
new file mode 100644
index 000000000..0faf67771
--- /dev/null
+++ b/src/features/team-mode/tools/messaging.test.ts
@@ -0,0 +1,623 @@
+/// <reference types="bun-types" />
+
+import { afterEach, describe, expect, test } from "bun:test"
+import { mkdtemp, readdir, readFile } from "node:fs/promises"
+import { randomUUID } from "node:crypto"
+import { tmpdir } from "node:os"
+import path from "node:path"
+
+import { type ToolContext } from "@opencode-ai/plugin/tool"
+import { TeamModeConfigSchema } from "../../../config/schema/team-mode"
+import { _resetForTesting, registerAgentName } from "../../claude-code-session-state"
+import { SessionCategoryRegistry } from "../../../shared/session-category-registry"
+import {
+  clearAllSessionPromptParams,
+  getSessionPromptParams,
+} from "../../../shared/session-prompt-params-state"
+import { listUnreadMessages } from "../team-mailbox/inbox"
+import { BroadcastNotPermittedError } from "../team-mailbox/send"
+import { getInboxDir, resolveBaseDir } from "../team-registry/paths"
+import { createRuntimeState, saveRuntimeState } from "../team-state-store/store"
+import { clearTeamSessionRegistry, registerTeamSession } from "../team-session-registry"
+import type { Message } from "../types"
+import { MessageSchema } from "../types"
+import { createTeamSendMessageTool } from "./messaging"
+
+type PromptAsyncCall = {
+  sessionId: string
+  parts: Array<{ type: string; text?: string }>
+  agent?: string
+  model?: { providerID: string; modelID: string }
+  variant?: string
+  directory?: string
+}
+
+type LiveDeliveryClient = {
+  session: {
+    promptAsync(input: {
+      path: { id: string }
+      body: {
+        parts: Array<{ type: "text"; text: string }>
+        agent?: string
+        model?: { providerID: string; modelID: string }
+        variant?: string
+      }
+      query?: { directory: string }
+    }): Promise<unknown>
+  }
+}
+
+function createRecordingClient(): { client: LiveDeliveryClient; calls: PromptAsyncCall[] } {
+  const calls: PromptAsyncCall[] = []
+  const client = {
+    session: {
+      promptAsync: async (input: {
+        path: { id: string }
+        body: {
+          parts: Array<{ type: "text"; text: string }>
+          agent?: string
+          model?: { providerID: string; modelID: string }
+          variant?: string
+        }
+        query?: { directory: string }
+      }) => {
+        calls.push({
+          sessionId: input.path.id,
+          parts: input.body.parts,
+          agent: input.body.agent,
+          model: input.body.model,
+          variant: input.body.variant,
+          directory: input.query?.directory,
+        })
+        return undefined
+      },
+    },
+  }
+  return { client, calls }
+}
+
+const mockClient: LiveDeliveryClient = {
+  session: {
+    promptAsync: async () => { throw new Error("live delivery disabled in fixture") },
+  },
+}
+
+afterEach(() => {
+  clearTeamSessionRegistry()
+  SessionCategoryRegistry.clear()
+  clearAllSessionPromptParams()
+  _resetForTesting()
+})
+
+async function createFixtureBaseDir(): Promise<string> {
+  return await mkdtemp(path.join(tmpdir(), "team-send-message-"))
+}
+
+function createConfig(baseDir: string) {
+  return TeamModeConfigSchema.parse({ base_dir: baseDir })
+}
+
+function createToolContext(sessionID: string, directory: string): ToolContext {
+  return {
+    sessionID,
+    messageID: randomUUID(),
+    agent: "test-agent",
+    directory,
+    worktree: directory,
+    abort: new AbortController().signal,
+    metadata: () => {},
+    ask: async () => undefined,
+  }
+}
+
+async function createTeamFixture() {
+  const baseDir = await createFixtureBaseDir()
+  const config = createConfig(baseDir)
+  const leadSessionId = randomUUID()
+  const memberOneSessionId = randomUUID()
+  const memberTwoSessionId = randomUUID()
+
+  const runtimeState = await createRuntimeState(
+    {
+      version: 1,
+      name: "team-alpha",
+        createdAt: Date.now(),
+        leadAgentId: "team-lead",
+        members: [
+          { kind: "subagent_type", name: "team-lead", subagent_type: "sisyphus-junior", backendType: "in-process", isActive: true },
+          { kind: "subagent_type", name: "m1", subagent_type: "sisyphus-junior", backendType: "in-process", isActive: true },
+          { kind: "subagent_type", name: "m2", subagent_type: "sisyphus-junior", backendType: "in-process", isActive: true },
+        ],
+      },
+    leadSessionId,
+    "project",
+    config,
+  )
+
+  runtimeState.leadSessionId = leadSessionId
+  runtimeState.members[0].sessionId = leadSessionId
+  runtimeState.members[1].sessionId = memberOneSessionId
+  runtimeState.members[2].sessionId = memberTwoSessionId
+  runtimeState.members[0].status = "idle"
+  runtimeState.members[1].status = "idle"
+  runtimeState.members[2].status = "idle"
+  await saveRuntimeState(runtimeState, config)
+
+  return {
+    config,
+      teamRunId: runtimeState.teamRunId,
+      leadSessionId,
+      memberOneSessionId,
+      memberTwoSessionId,
+      tool: createTeamSendMessageTool(config, mockClient),
+      toolContext: (sessionID: string) => createToolContext(sessionID, baseDir),
+    }
+}
+
+describe("createTeamSendMessageTool", () => {
+  test("routes a member message to one recipient", async () => {
+    // given
+    const fixture = await createTeamFixture()
+
+    // when
+    const result = await fixture.tool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "hello",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+    const parsedResult = JSON.parse(result)
+
+    // then
+    expect(parsedResult.deliveredTo).toEqual(["m2"])
+    const inboxDir = getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m2")
+    const [messageFile] = (await readdir(inboxDir)).filter((entry) => entry.endsWith(".json"))
+    const message = MessageSchema.parse(JSON.parse(await readFile(path.join(inboxDir, messageFile), "utf8")))
+    expect(message.from).toBe("m1")
+  })
+
+  test("gates broadcast to the lead and fans out to active members", async () => {
+    // given
+    const fixture = await createTeamFixture()
+
+    // when
+    const nonLeadResult = fixture.tool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "*",
+      body: "hello everyone",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    expect(nonLeadResult).rejects.toBeInstanceOf(BroadcastNotPermittedError)
+
+    // when
+    const leadResult = await fixture.tool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "*",
+      body: "team announcement",
+      kind: "announcement",
+    }, fixture.toolContext(fixture.leadSessionId))
+    const parsedLeadResult = JSON.parse(leadResult)
+
+    // then
+    expect(parsedLeadResult.deliveredTo).toEqual(["m1", "m2"])
+    const memberOneInbox = await readdir(getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m1"))
+    const memberTwoInbox = await readdir(getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m2"))
+    expect(memberOneInbox.filter((entry) => entry.endsWith(".json") && !entry.startsWith("."))).toHaveLength(1)
+    expect(memberTwoInbox.filter((entry) => entry.endsWith(".json") && !entry.startsWith("."))).toHaveLength(1)
+  })
+
+  test("live-delivers the envelope via promptAsync to the recipient session", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    expect(calls).toHaveLength(1)
+    expect(calls[0].sessionId).toBe(fixture.memberTwoSessionId)
+    expect(calls[0].directory).toBe(resolveBaseDir(fixture.config))
+    const envelopeText = calls[0].parts[0]?.text ?? ""
+    expect(envelopeText).toContain("<peer_message")
+    expect(envelopeText).toContain('from="m1"')
+    expect(envelopeText).toContain("ping")
+  })
+
+  test("live delivery targets the recipient worktree when available", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { loadRuntimeState: loadState, saveRuntimeState: saveState } = await import("../team-state-store/store")
+    const state = await loadState(fixture.teamRunId, fixture.config)
+    const memberTwo = state.members.find((member) => member.name === "m2")
+    if (!memberTwo) throw new Error("m2 runtime member missing")
+    memberTwo.worktreePath = "/tmp/team-worker-m2"
+    await saveState(state, fixture.config)
+
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    expect(calls).toHaveLength(1)
+    expect(calls[0]?.directory).toBe("/tmp/team-worker-m2")
+  })
+
+  test("live-delivers to running recipients so active teammates receive messages immediately", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { loadRuntimeState: loadState, saveRuntimeState: saveState } = await import("../team-state-store/store")
+    const state = await loadState(fixture.teamRunId, fixture.config)
+    const memberTwo = state.members.find((member) => member.name === "m2")
+    if (!memberTwo) throw new Error("m2 runtime member missing")
+    memberTwo.status = "running"
+    await saveState(state, fixture.config)
+
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    const result = await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+    const parsedResult = JSON.parse(result)
+
+    // then
+    expect(parsedResult.deliveredTo).toEqual(["m2"])
+    expect(calls).toHaveLength(1)
+    expect(calls[0]?.sessionId).toBe(fixture.memberTwoSessionId)
+    expect(calls[0]?.directory).toBe(resolveBaseDir(fixture.config))
+  })
+
+  test("live delivery pins the recipient's resolved subagent_type and model on promptAsync", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { loadRuntimeState: loadState, saveRuntimeState: saveState } = await import("../team-state-store/store")
+    const state = await loadState(fixture.teamRunId, fixture.config)
+    const memberTwo = state.members.find((member) => member.name === "m2")
+    if (!memberTwo) throw new Error("m2 runtime member missing")
+    memberTwo.subagent_type = "atlas"
+    memberTwo.model = { providerID: "anthropic", modelID: "claude-opus-4-7", variant: "high" }
+    await saveState(state, fixture.config)
+
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    expect(calls).toHaveLength(1)
+    expect(calls[0].sessionId).toBe(fixture.memberTwoSessionId)
+    expect(calls[0].agent).toBe("atlas")
+    expect(calls[0].model).toEqual({ providerID: "anthropic", modelID: "claude-opus-4-7" })
+    expect(calls[0].variant).toBe("high")
+  })
+
+  test("live delivery uses the registered agent alias when the runtime stores a config-key agent name", async () => {
+    // given
+    registerAgentName("\u200B\u200B\u200B\u200BAtlas - Plan Executor")
+    const fixture = await createTeamFixture()
+    const { loadRuntimeState: loadState, saveRuntimeState: saveState } = await import("../team-state-store/store")
+    const state = await loadState(fixture.teamRunId, fixture.config)
+    const memberTwo = state.members.find((member) => member.name === "m2")
+    if (!memberTwo) throw new Error("m2 runtime member missing")
+    memberTwo.subagent_type = "atlas"
+    await saveState(state, fixture.config)
+
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    expect(calls).toHaveLength(1)
+    expect(calls[0]?.agent).toBe("\u200B\u200B\u200B\u200BAtlas - Plan Executor")
+  })
+
+  test("live delivery reapplies category routing and advanced model params for category members", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { loadRuntimeState: loadState, saveRuntimeState: saveState } = await import("../team-state-store/store")
+    const state = await loadState(fixture.teamRunId, fixture.config)
+    const memberTwo = state.members.find((member) => member.name === "m2")
+    if (!memberTwo) throw new Error("m2 runtime member missing")
+    memberTwo.subagent_type = "Sisyphus-Junior"
+    memberTwo.category = "quick"
+    memberTwo.model = {
+      providerID: "openai",
+      modelID: "gpt-5.4",
+      variant: "medium",
+      reasoningEffort: "high",
+      temperature: 0.2,
+      top_p: 0.8,
+      maxTokens: 4096,
+      thinking: { type: "enabled", budgetTokens: 2048 },
+    }
+    await saveState(state, fixture.config)
+
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    expect(calls).toHaveLength(1)
+    expect(calls[0].agent).toBe("Sisyphus-Junior")
+    expect(calls[0].model).toEqual({ providerID: "openai", modelID: "gpt-5.4" })
+    expect(calls[0].variant).toBe("medium")
+    expect(SessionCategoryRegistry.get(fixture.memberTwoSessionId)).toBe("quick")
+    expect(getSessionPromptParams(fixture.memberTwoSessionId)).toEqual({
+      temperature: 0.2,
+      topP: 0.8,
+      maxOutputTokens: 4096,
+      options: {
+        reasoningEffort: "high",
+        thinking: { type: "enabled", budgetTokens: 2048 },
+      },
+    })
+  })
+
+  test("live delivery omits agent and model on promptAsync when the runtime member has none recorded", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    expect(calls).toHaveLength(1)
+    expect(calls[0].agent).toBeUndefined()
+    expect(calls[0].model).toBeUndefined()
+    expect(calls[0].variant).toBeUndefined()
+  })
+
+  test("prefers the team session registry when the runtime member session has not been persisted yet", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    registerTeamSession(fixture.memberOneSessionId, {
+      teamRunId: fixture.teamRunId,
+      memberName: "m1",
+      role: "member",
+    })
+
+    const { loadRuntimeState: loadState, saveRuntimeState: saveState } = await import("../team-state-store/store")
+    const runtimeState = await loadState(fixture.teamRunId, fixture.config)
+    const memberOne = runtimeState.members.find((member) => member.name === "m1")
+    if (!memberOne) throw new Error("m1 runtime member missing")
+    memberOne.sessionId = undefined
+    await saveState(runtimeState, fixture.config)
+
+    // when
+    const result = await fixture.tool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "hello",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+    const parsedResult = JSON.parse(result)
+
+    // then
+    expect(parsedResult.deliveredTo).toEqual(["m2"])
+    const inboxDir = getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m2")
+    const [messageFile] = (await readdir(inboxDir)).filter((entry) => entry.endsWith(".json"))
+    const message = MessageSchema.parse(JSON.parse(await readFile(path.join(inboxDir, messageFile), "utf8")))
+    expect(message.from).toBe("m1")
+  })
+
+  test("acks the message after live delivery so the transform hook does not redeliver", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { client } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    const inboxDir = getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m2")
+    const inboxEntries = (await readdir(inboxDir)).filter((entry) => entry.endsWith(".json"))
+    const processedEntries = (await readdir(path.join(inboxDir, "processed"))).filter((entry) => entry.endsWith(".json"))
+    expect(inboxEntries).toHaveLength(0)
+    expect(processedEntries).toHaveLength(1)
+  })
+
+  test("broadcast fans out live delivery to every member except the sender", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "*",
+      body: "broadcast ping",
+      kind: "announcement",
+    }, fixture.toolContext(fixture.leadSessionId))
+
+    // then
+    const targetedSessionIds = calls.map((entry) => entry.sessionId).sort()
+    expect(targetedSessionIds).toEqual([
+      fixture.memberOneSessionId,
+      fixture.memberTwoSessionId,
+    ].sort())
+  })
+
+  test("broadcast still queues for members whose session has not spawned yet", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { loadRuntimeState: loadState } = await import("../team-state-store/store")
+    const stateBefore = await loadState(fixture.teamRunId, fixture.config)
+    const pendingMember = stateBefore.members.find((member) => member.name === "m2")
+    if (!pendingMember) throw new Error("m2 runtime member missing")
+    pendingMember.sessionId = undefined
+    await saveRuntimeState(stateBefore, fixture.config)
+
+    const { client, calls } = createRecordingClient()
+    const liveTool = createTeamSendMessageTool(fixture.config, client)
+
+    // when
+    const result = await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "*",
+      body: "broadcast ping",
+      kind: "announcement",
+    }, fixture.toolContext(fixture.leadSessionId))
+    const parsedResult = JSON.parse(result)
+
+    // then
+    expect(parsedResult.deliveredTo).toEqual(["m1", "m2"])
+    const targetedSessionIds = calls.map((entry) => entry.sessionId)
+    expect(targetedSessionIds).toEqual([fixture.memberOneSessionId])
+    const memberTwoInbox = await readdir(getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m2"))
+    expect(memberTwoInbox.filter((entry) => entry.endsWith(".json") && !entry.startsWith("."))).toHaveLength(1)
+  })
+
+  test("inbox stays intact when live delivery fails so the fallback path still works", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const failingClient = {
+      session: {
+        promptAsync: async () => { throw new Error("network down") },
+      },
+    } satisfies LiveDeliveryClient
+    const liveTool = createTeamSendMessageTool(fixture.config, failingClient)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    const inboxDir = getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m2")
+    const inboxEntries = (await readdir(inboxDir)).filter((entry) => entry.endsWith(".json") && !entry.startsWith("."))
+    expect(inboxEntries).toHaveLength(1)
+  })
+
+  test("reserves the message during live delivery so concurrent listings cannot surface it", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    let unreadDuringDelivery: Message[] = []
+    const reservingClient = {
+      session: {
+        promptAsync: async () => {
+          unreadDuringDelivery = await listUnreadMessages(fixture.teamRunId, "m2", fixture.config)
+          return undefined
+        },
+      },
+    } satisfies LiveDeliveryClient
+    const liveTool = createTeamSendMessageTool(fixture.config, reservingClient)
+
+    // when
+    await liveTool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "ping",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    expect(unreadDuringDelivery).toHaveLength(0)
+  })
+
+  test("hides the message from the inbox from the moment it is written for a live recipient", async () => {
+    // given
+    const fixture = await createTeamFixture()
+    const { sendMessage } = await import("../team-mailbox/send")
+    const messageId = randomUUID()
+
+    // when
+    await sendMessage({
+      version: 1,
+      messageId,
+      from: "m1",
+      to: "m2",
+      kind: "message",
+      body: "ping",
+      timestamp: Date.now(),
+    }, fixture.teamRunId, fixture.config, {
+      isLead: false,
+      activeMembers: ["m2"],
+      reservedRecipients: new Set(["m2"]),
+    })
+    const unreadImmediately = await listUnreadMessages(fixture.teamRunId, "m2", fixture.config)
+    const inboxDir = getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m2")
+    const rawEntries = (await readdir(inboxDir))
+      .filter((entry) => entry.endsWith(".json"))
+
+    // then
+    expect(unreadImmediately).toHaveLength(0)
+    expect(rawEntries).toEqual([`.delivering-${messageId}.json`])
+  })
+
+  test("rejects shutdown_request kind", async () => {
+    // given
+    const fixture = await createTeamFixture()
+
+    // when
+    const result = fixture.tool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m1",
+      body: "stop",
+      kind: "shutdown_request",
+    }, fixture.toolContext(fixture.leadSessionId))
+
+    // then
+    expect(result).rejects.toBeInstanceOf(Error)
+  })
+
+  test("rejects a non-UUID correlationId before writing the message", async () => {
+    // given
+    const fixture = await createTeamFixture()
+
+    // when
+    const result = fixture.tool.execute({
+      teamRunId: fixture.teamRunId,
+      to: "m2",
+      body: "hello",
+      correlationId: "task-1",
+    }, fixture.toolContext(fixture.memberOneSessionId))
+
+    // then
+    await expect(result).rejects.toThrow("correlationId")
+    await expect(readdir(getInboxDir(resolveBaseDir(fixture.config), fixture.teamRunId, "m2"))).rejects.toThrow()
+  })
+})
diff --git a/src/features/team-mode/tools/messaging.ts b/src/features/team-mode/tools/messaging.ts
new file mode 100644
index 000000000..bee322ed1
--- /dev/null
+++ b/src/features/team-mode/tools/messaging.ts
@@ -0,0 +1,271 @@
+import { randomUUID } from "node:crypto"
+
+import { tool, type ToolDefinition } from "@opencode-ai/plugin/tool"
+import { z } from "zod"
+
+import type { TeamModeConfig } from "../../../config/schema/team-mode"
+import { log } from "../../../shared/logger"
+import { applyMemberSessionRouting, buildMemberPromptBody } from "../member-session-routing"
+import { lookupTeamSession } from "../team-session-registry"
+import { loadRuntimeState } from "../team-state-store/store"
+import { buildEnvelope } from "../team-mailbox/poll"
+import {
+  commitDeliveryReservation,
+  releaseDeliveryReservation,
+  reserveMessageForDelivery,
+} from "../team-mailbox/reservation"
+import { BroadcastNotPermittedError, sendMessage } from "../team-mailbox/send"
+
+import type { Message } from "../types"
+import { MessageSchema } from "../types"
+
+const MESSAGE_TOOL_KINDS = ["message", "announcement"] as const
+
+export type LiveDeliveryClient = {
+  session: {
+    promptAsync(input: {
+      path: { id: string }
+      body: {
+        parts: Array<{ type: "text"; text: string }>
+        agent?: string
+        model?: { providerID: string; modelID: string }
+        variant?: string
+      }
+      query?: { directory: string }
+    }): Promise<unknown>
+  }
+}
+
+type TeamRuntimeDetails = {
+  teamRunId: string
+  isLead: boolean
+  senderName: string
+  activeMembers: string[]
+}
+
+const TeamReferenceArgsSchema = z.object({
+  path: z.string().min(1),
+  description: z.string().optional(),
+})
+
+const TeamSendMessageArgsSchema = z.object({
+  teamRunId: z.string().min(1),
+  to: z.string().min(1),
+  body: z.string(),
+  kind: z.enum(MESSAGE_TOOL_KINDS).optional(),
+  correlationId: z.string().uuid().optional(),
+  summary: z.string().optional(),
+  references: z.array(TeamReferenceArgsSchema).optional(),
+})
+
+type DeliveryReservation = Awaited<ReturnType<typeof reserveMessageForDelivery>>
+
+async function resolveTeamRuntimeDetails(teamRunId: string, sessionID: string, config: TeamModeConfig): Promise<TeamRuntimeDetails> {
+  const registryEntry = lookupTeamSession(sessionID)
+  if (registryEntry?.teamRunId === teamRunId) {
+    const runtimeState = await loadRuntimeState(teamRunId, config)
+
+    return {
+      teamRunId: runtimeState.teamRunId,
+      isLead: registryEntry.role === "lead",
+      senderName: registryEntry.memberName,
+      activeMembers: runtimeState.members
+        .map((entry) => entry.name)
+        .filter((name) => name !== registryEntry.memberName),
+    }
+  }
+
+  try {
+    const runtimeState = await loadRuntimeState(teamRunId, config)
+    const isLead = runtimeState.leadSessionId === sessionID
+    const leadMember = isLead
+      ? runtimeState.members.find((member) => member.agentType === "leader")
+      : undefined
+    const member = runtimeState.members.find((entry) => entry.sessionId === sessionID)
+    const senderName = leadMember?.name ?? member?.name ?? "unknown"
+
+    return {
+      teamRunId: runtimeState.teamRunId,
+      isLead,
+      senderName,
+      activeMembers: runtimeState.members
+        .map((entry) => entry.name)
+        .filter((name) => name !== senderName),
+    }
+  } catch {
+    return {
+      teamRunId,
+      isLead: false,
+      senderName: "unknown",
+      activeMembers: [],
+    }
+  }
+}
+
+async function releaseReservationSafely(
+  reservation: DeliveryReservation,
+  input: { teamRunId: string; recipient: string; messageId: string },
+): Promise<void> {
+  if (reservation === null) return
+
+  try {
+    await releaseDeliveryReservation(reservation)
+  } catch (releaseError) {
+    log("[team-mailbox] failed to release delivery reservation", {
+      error: releaseError instanceof Error ? releaseError.message : String(releaseError),
+      teamRunId: input.teamRunId,
+      recipient: input.recipient,
+      messageId: input.messageId,
+    })
+  }
+}
+
+async function deliverLive(
+  client: LiveDeliveryClient,
+  message: Message,
+  teamRunId: string,
+  deliveredTo: readonly string[],
+  config: TeamModeConfig,
+  directory: string,
+): Promise<void> {
+  const runtimeState = await loadRuntimeState(teamRunId, config)
+  const envelope = buildEnvelope(message)
+
+  for (const recipientName of deliveredTo) {
+    // Reserve the inbox file before delivering so the transform-hook fallback
+    // cannot re-read the same message while promptAsync is in flight.
+    const reservation = await reserveMessageForDelivery(teamRunId, recipientName, message.messageId, config)
+    if (reservation === null) continue
+
+    const recipientMember = runtimeState.members.find((entry) => entry.name === recipientName)
+    if (!recipientMember) {
+      await releaseReservationSafely(reservation, {
+        teamRunId,
+        recipient: recipientName,
+        messageId: message.messageId,
+      })
+      continue
+    }
+
+    const recipientSessionId = recipientMember.sessionId
+    if (!recipientSessionId) {
+      log("[team-mailbox] live delivery unavailable, falling back to inbox injection", {
+        reason: "missing-session-id",
+        teamRunId,
+        recipient: recipientName,
+        messageId: message.messageId,
+      })
+      await releaseReservationSafely(reservation, {
+        teamRunId,
+        recipient: recipientName,
+        messageId: message.messageId,
+      })
+      continue
+    }
+
+    applyMemberSessionRouting(recipientSessionId, recipientMember)
+
+    try {
+      await client.session.promptAsync({
+        path: { id: recipientSessionId },
+        body: buildMemberPromptBody(recipientMember, envelope),
+        query: { directory: recipientMember.worktreePath ?? directory },
+      })
+      await commitDeliveryReservation(reservation)
+      log("[team-mailbox] live delivery committed", {
+        teamRunId,
+        recipient: recipientName,
+        recipientSessionId,
+        messageId: message.messageId,
+      })
+    } catch (error) {
+      log("[team-mailbox] live delivery failed, falling back to inbox injection", {
+        error: error instanceof Error ? error.message : String(error),
+        teamRunId,
+        recipient: recipientName,
+        messageId: message.messageId,
+      })
+      await releaseReservationSafely(reservation, {
+        teamRunId,
+        recipient: recipientName,
+        messageId: message.messageId,
+      })
+    }
+  }
+}
+
+export function createTeamSendMessageTool(config: TeamModeConfig, client: LiveDeliveryClient): ToolDefinition {
+  return tool({
+    description: "Send a message to a team member or broadcast to the team.",
+    args: {
+      teamRunId: tool.schema.string().describe("Team run ID"),
+      to: tool.schema.string().describe("Recipient name or * for broadcast"),
+      body: tool.schema.string().describe("Message body"),
+      kind: tool.schema.enum(MESSAGE_TOOL_KINDS).optional().default("message").describe("Message kind"),
+      correlationId: tool.schema.string().optional().describe("Optional UUID correlation ID. Do not use task IDs like 'task-1'."),
+      summary: tool.schema.string().optional().describe("Optional summary"),
+      references: tool.schema.array(tool.schema.object({
+        path: tool.schema.string(),
+        description: tool.schema.string().optional(),
+      })).optional().describe("Optional references as [{ path, description? }]"),
+    },
+    execute: async (rawArgs, context) => {
+      const args = TeamSendMessageArgsSchema.parse(rawArgs)
+      const runtimeContext = context as { sessionID?: string; directory?: string }
+      const sessionID = runtimeContext.sessionID
+
+      if (!sessionID) {
+        throw new Error("session ID is required")
+      }
+
+      const targetDirectory = typeof runtimeContext.directory === "string" ? runtimeContext.directory : process.cwd()
+
+      const teamRuntime = await resolveTeamRuntimeDetails(args.teamRunId, sessionID, config)
+      const message = MessageSchema.parse({
+        version: 1,
+        messageId: randomUUID(),
+        from: teamRuntime.senderName,
+        to: args.to,
+        body: args.body,
+        kind: args.kind ?? "message",
+        timestamp: Date.now(),
+        correlationId: args.correlationId,
+        summary: args.summary,
+        references: args.references,
+      })
+
+      if (message.kind === "shutdown_request" || message.kind === "shutdown_approved" || message.kind === "shutdown_rejected") {
+        throw new Error("must use lifecycle tools for shutdown kinds")
+      }
+
+      if (message.to === "*" && !teamRuntime.isLead) {
+        throw new BroadcastNotPermittedError()
+      }
+
+      const runtimeState = await loadRuntimeState(teamRuntime.teamRunId, config)
+      const reservedRecipients = new Set<string>(
+        runtimeState.members
+          .filter((member) => member.sessionId !== undefined && member.name !== teamRuntime.senderName)
+          .map((member) => member.name),
+      )
+
+      const result = await sendMessage(message, teamRuntime.teamRunId, config, {
+        isLead: teamRuntime.isLead,
+        activeMembers: teamRuntime.activeMembers,
+        reservedRecipients,
+      })
+
+      try {
+        await deliverLive(client, message, teamRuntime.teamRunId, result.deliveredTo, config, targetDirectory)
+      } catch (liveError) {
+        log("[team-mailbox] deliverLive top-level error (message already in inbox, safe to ignore)", {
+          error: liveError instanceof Error ? liveError.message : String(liveError),
+          teamRunId: teamRuntime.teamRunId,
+          messageId: message.messageId,
+        })
+      }
+
+      return JSON.stringify(result)
+    },
+  })
+}