diff --git a/.sisyphus/evidence/team-mode/task-2-category-prompt-required.txt b/.sisyphus/evidence/team-mode/task-2-category-prompt-required.txt
new file mode 100644
index 000000000..d3f55481c
--- /dev/null
+++ b/.sisyphus/evidence/team-mode/task-2-category-prompt-required.txt
@@ -0,0 +1,7 @@
+bun test v1.3.12 (700fc117)
+
+ 1 pass
+ 3 filtered out
+ 0 fail
+ 1 expect() calls
+Ran 1 test across 1 file. [64.00ms]
diff --git a/.sisyphus/evidence/team-mode/task-2-disc-both.txt b/.sisyphus/evidence/team-mode/task-2-disc-both.txt
new file mode 100644
index 000000000..1174095e7
--- /dev/null
+++ b/.sisyphus/evidence/team-mode/task-2-disc-both.txt
@@ -0,0 +1,7 @@
+bun test v1.3.12 (700fc117)
+
+ 1 pass
+ 3 filtered out
+ 0 fail
+ 1 expect() calls
+Ran 1 test across 1 file. [65.00ms]
diff --git a/.sisyphus/evidence/team-mode/task-2-disc-category.txt b/.sisyphus/evidence/team-mode/task-2-disc-category.txt
new file mode 100644
index 000000000..7aed175f2
--- /dev/null
+++ b/.sisyphus/evidence/team-mode/task-2-disc-category.txt
@@ -0,0 +1,7 @@
+bun test v1.3.12 (700fc117)
+
+ 1 pass
+ 3 filtered out
+ 0 fail
+ 3 expect() calls
+Ran 1 test across 1 file. [69.00ms]
diff --git a/.sisyphus/evidence/team-mode/task-2-eligibility-registry.txt b/.sisyphus/evidence/team-mode/task-2-eligibility-registry.txt
new file mode 100644
index 000000000..749f3d548
--- /dev/null
+++ b/.sisyphus/evidence/team-mode/task-2-eligibility-registry.txt
@@ -0,0 +1,7 @@
+bun test v1.3.12 (700fc117)
+
+ 1 pass
+ 3 filtered out
+ 0 fail
+ 12 expect() calls
+Ran 1 test across 1 file. [61.00ms]
diff --git a/.sisyphus/notepads/team-mode/learnings.md b/.sisyphus/notepads/team-mode/learnings.md
new file mode 100644
index 000000000..5349aca4e
--- /dev/null
+++ b/.sisyphus/notepads/team-mode/learnings.md
@@ -0,0 +1,5 @@
+## 2026-04-18 Task 2: types module
+
+- `MemberSchema` needs `.strict()` on the base shape so the discriminatedUnion rejects members that mix `category` and `subagent_type`.
+- `backendType` and `isActive` defaults are part of the schema contract, so tests should use `toMatchObject` instead of exact object equality.
+- The eligibility registry must preserve the plan strings verbatim, especially the hard-reject messages for Momus verification.
diff --git a/src/features/team-mode/index.ts b/src/features/team-mode/index.ts
new file mode 100644
index 000000000..51f739d01
--- /dev/null
+++ b/src/features/team-mode/index.ts
@@ -0,0 +1 @@
+export * from "./types"
diff --git a/src/features/team-mode/types.test.ts b/src/features/team-mode/types.test.ts
new file mode 100644
index 000000000..042f220e5
--- /dev/null
+++ b/src/features/team-mode/types.test.ts
@@ -0,0 +1,96 @@
+import { describe, expect, test } from "bun:test"
+import {
+  AGENT_ELIGIBILITY_REGISTRY,
+  CategoryMemberSchema,
+  MemberSchema,
+  SubagentMemberSchema,
+} from "./types"
+
+describe("team-mode types", () => {
+  test("member category branch parses and narrows", () => {
+    // given
+    const member = { kind: "category", name: "m1", category: "deep", prompt: "impl X" }
+
+    // when
+    const result = MemberSchema.safeParse(member)
+
+    // then
+    expect(result.success).toBe(true)
+    if (result.success) {
+      expect(result.data).toMatchObject(member)
+      expect(result.data).toMatchObject({ kind: "category", category: "deep" })
+    }
+  })
+
+  test("both kinds rejected", () => {
+    // given
+    const member = {
+      kind: "category",
+      name: "m1",
+      category: "deep",
+      subagent_type: "sisyphus",
+      prompt: "impl X",
+    }
+
+    // when
+    const result = MemberSchema.safeParse(member)
+
+    // then
+    expect(result.success).toBe(false)
+  })
+
+  test("category requires prompt", () => {
+    // given
+    const member = { kind: "category", name: "m1", category: "deep" }
+
+    // when
+    const result = CategoryMemberSchema.safeParse(member)
+
+    // then
+    expect(result.success).toBe(false)
+  })
+
+  test("eligibility registry shape", () => {
+    // given
+    const entries = Object.entries(AGENT_ELIGIBILITY_REGISTRY)
+
+    // when
+    const verdictCounts = entries.reduce(
+      (counts, [, value]) => {
+        counts[value.verdict] += 1
+        return counts
+      },
+      { eligible: 0, conditional: 0, "hard-reject": 0 },
+    )
+
+    // then
+    expect(entries).toHaveLength(11)
+    expect(verdictCounts).toEqual({ eligible: 3, conditional: 1, "hard-reject": 7 })
+    expect(AGENT_ELIGIBILITY_REGISTRY.hephaestus.rejectionMessage).toBe(
+      "Agent 'hephaestus' lacks teammate permission. Either apply D-36 (add teammate: \"allow\" in tool-config-handler.ts) or use subagent_type: \"sisyphus\" instead.",
+    )
+    expect(AGENT_ELIGIBILITY_REGISTRY.oracle.rejectionMessage).toBe(
+      "Agent 'oracle' is read-only (cannot write files). Team members must write to mailbox inbox files. Use delegate-task with subagent_type: 'oracle' for read-only analysis instead.",
+    )
+    expect(AGENT_ELIGIBILITY_REGISTRY.librarian.rejectionMessage).toBe(
+      "Agent 'librarian' is read-only (write/edit denied). Cannot write to mailbox as team member. Use delegate-task for research queries instead.",
+    )
+    expect(AGENT_ELIGIBILITY_REGISTRY.explore.rejectionMessage).toBe(
+      "Agent 'explore' is read-only (write/edit denied). Cannot write to mailbox as team member. Use delegate-task for codebase exploration instead.",
+    )
+    expect(AGENT_ELIGIBILITY_REGISTRY["multimodal-looker"].rejectionMessage).toBe(
+      "Agent 'multimodal-looker' has read-only tool access (only 'read' allowed). Cannot write to mailbox as team member.",
+    )
+    expect(AGENT_ELIGIBILITY_REGISTRY.metis.rejectionMessage).toBe(
+      "Agent 'metis' is read-only (pre-planning consultant). Cannot write to mailbox as team member. Use delegate-task for pre-planning analysis instead.",
+    )
+    expect(AGENT_ELIGIBILITY_REGISTRY.momus.rejectionMessage).toBe(
+      "Agent 'momus' is read-only (plan reviewer). Cannot write to mailbox as team member. Use delegate-task for plan review instead.",
+    )
+    expect(AGENT_ELIGIBILITY_REGISTRY.prometheus.rejectionMessage).toBe(
+      "Agent 'prometheus' is plan-mode-only; can only write to .sisyphus/*.md (enforced by prometheusMdOnly hook). Cannot write to team mailbox. Use category: 'plan' instead.",
+    )
+    expect(CategoryMemberSchema).toBeDefined()
+    expect(SubagentMemberSchema).toBeDefined()
+  })
+})
diff --git a/src/features/team-mode/types.ts b/src/features/team-mode/types.ts
new file mode 100644
index 000000000..2b2da3f2a
--- /dev/null
+++ b/src/features/team-mode/types.ts
@@ -0,0 +1,190 @@
+import { z } from "zod"
+
+export const MESSAGE_KINDS = [
+  "message",
+  "shutdown_request",
+  "shutdown_approved",
+  "shutdown_rejected",
+  "announcement",
+] as const
+
+export const MEMBER_KINDS = ["category", "subagent_type"] as const
+
+export const TASK_STATUSES = ["pending", "claimed", "in_progress", "completed", "deleted"] as const
+
+export const RUNTIME_STATUSES = [
+  "creating",
+  "active",
+  "shutdown_requested",
+  "deleting",
+  "deleted",
+  "failed",
+  "orphaned",
+] as const
+
+const MemberBaseSchema = z.object({
+  name: z.string().min(1).regex(/^[a-z0-9-]+$/),
+  cwd: z.string().optional(),
+  worktreePath: z.string().optional(),
+  subscriptions: z.array(z.string()).optional(),
+  backendType: z.enum(["in-process", "tmux"]).default("in-process"),
+  color: z.string().optional(),
+  isActive: z.boolean().default(true),
+}).strict()
+
+export const CategoryMemberSchema = MemberBaseSchema.extend({
+  kind: z.literal("category"),
+  category: z.string().min(1),
+  prompt: z.string().min(1),
+})
+
+export const SubagentMemberSchema = MemberBaseSchema.extend({
+  kind: z.literal("subagent_type"),
+  subagent_type: z.string().min(1),
+  prompt: z.string().optional(),
+})
+
+export const MemberSchema = z.discriminatedUnion("kind", [CategoryMemberSchema, SubagentMemberSchema])
+
+const TeamReferenceSchema = z.object({
+  path: z.string(),
+  description: z.string().optional(),
+}).strict()
+
+export const TeamSpecSchema = z.object({
+  version: z.literal(1),
+  name: z.string().min(1).regex(/^[a-z0-9-]+$/),
+  description: z.string().optional(),
+  createdAt: z.number().int().positive(),
+  leadAgentId: z.string(),
+  teamAllowedPaths: z.array(z.string()).optional(),
+  sessionPermission: z.string().optional(),
+  members: z.array(MemberSchema).min(1).max(8),
+})
+
+export const MessageSchema = z.object({
+  version: z.literal(1),
+  messageId: z.string().uuid(),
+  from: z.string(),
+  to: z.string(),
+  kind: z.enum(MESSAGE_KINDS),
+  body: z.string().max(32 * 1024),
+  summary: z.string().optional(),
+  references: z.array(TeamReferenceSchema).optional(),
+  timestamp: z.number().int().positive(),
+  correlationId: z.string().uuid().optional(),
+  color: z.string().optional(),
+})
+
+export const TaskSchema = z.object({
+  version: z.literal(1),
+  id: z.string(),
+  subject: z.string(),
+  description: z.string(),
+  activeForm: z.string().optional(),
+  status: z.enum(TASK_STATUSES),
+  owner: z.string().optional(),
+  blocks: z.array(z.string()).default([]),
+  blockedBy: z.array(z.string()).default([]),
+  metadata: z.record(z.string(), z.unknown()).optional(),
+  createdAt: z.number().int().positive(),
+  updatedAt: z.number().int().positive(),
+  claimedAt: z.number().int().positive().optional(),
+})
+
+const RuntimeStateMemberSchema = z.object({
+  name: z.string(),
+  sessionId: z.string().optional(),
+  tmuxPaneId: z.string().optional(),
+  agentType: z.enum(["leader", "general-purpose"]),
+  status: z.enum(["pending", "running", "idle", "errored", "completed", "shutdown_approved"]),
+  color: z.string().optional(),
+  worktreePath: z.string().optional(),
+  lastInjectedTurnMarker: z.string().optional(),
+  pendingInjectedMessageIds: z.array(z.string()).default([]),
+}).strict()
+
+const RuntimeBoundsSchema = z.object({
+  maxMembers: z.number().int().default(8),
+  maxParallelMembers: z.number().int().default(4),
+  maxMessagesPerRun: z.number().int().default(10000),
+  maxWallClockMinutes: z.number().int().default(120),
+  maxMemberTurns: z.number().int().default(500),
+}).strict()
+
+const ShutdownRequestSchema = z.object({
+  memberId: z.string(),
+  requestedAt: z.number().int().positive(),
+  approvedAt: z.number().int().positive().optional(),
+  rejectedReason: z.string().optional(),
+}).strict()
+
+export const RuntimeStateSchema = z.object({
+  version: z.literal(1),
+  teamRunId: z.string().uuid(),
+  teamName: z.string(),
+  specSource: z.enum(["project", "user"]),
+  createdAt: z.number().int().positive(),
+  status: z.enum(RUNTIME_STATUSES),
+  leadSessionId: z.string().optional(),
+  members: z.array(RuntimeStateMemberSchema),
+  shutdownRequests: z.array(ShutdownRequestSchema).default([]),
+  bounds: RuntimeBoundsSchema,
+})
+
+export const AGENT_ELIGIBILITY_REGISTRY: Readonly<Record<string, {
+  verdict: "eligible" | "conditional" | "hard-reject"
+  rejectionMessage?: string
+}>> = {
+  sisyphus: { verdict: "eligible" },
+  hephaestus: {
+    verdict: "conditional",
+    rejectionMessage:
+      "Agent 'hephaestus' lacks teammate permission. Either apply D-36 (add teammate: \"allow\" in tool-config-handler.ts) or use subagent_type: \"sisyphus\" instead.",
+  },
+  oracle: {
+    verdict: "hard-reject",
+    rejectionMessage:
+      "Agent 'oracle' is read-only (cannot write files). Team members must write to mailbox inbox files. Use delegate-task with subagent_type: 'oracle' for read-only analysis instead.",
+  },
+  librarian: {
+    verdict: "hard-reject",
+    rejectionMessage:
+      "Agent 'librarian' is read-only (write/edit denied). Cannot write to mailbox as team member. Use delegate-task for research queries instead.",
+  },
+  explore: {
+    verdict: "hard-reject",
+    rejectionMessage:
+      "Agent 'explore' is read-only (write/edit denied). Cannot write to mailbox as team member. Use delegate-task for codebase exploration instead.",
+  },
+  "multimodal-looker": {
+    verdict: "hard-reject",
+    rejectionMessage:
+      "Agent 'multimodal-looker' has read-only tool access (only 'read' allowed). Cannot write to mailbox as team member.",
+  },
+  metis: {
+    verdict: "hard-reject",
+    rejectionMessage:
+      "Agent 'metis' is read-only (pre-planning consultant). Cannot write to mailbox as team member. Use delegate-task for pre-planning analysis instead.",
+  },
+  momus: {
+    verdict: "hard-reject",
+    rejectionMessage:
+      "Agent 'momus' is read-only (plan reviewer). Cannot write to mailbox as team member. Use delegate-task for plan review instead.",
+  },
+  atlas: { verdict: "eligible" },
+  prometheus: {
+    verdict: "hard-reject",
+    rejectionMessage:
+      "Agent 'prometheus' is plan-mode-only; can only write to .sisyphus/*.md (enforced by prometheusMdOnly hook). Cannot write to team mailbox. Use category: 'plan' instead.",
+  },
+  "sisyphus-junior": { verdict: "eligible" },
+} as const
+
+export type TeamSpec = z.infer<typeof TeamSpecSchema>
+export type Member = z.infer<typeof MemberSchema>
+export type CategoryMember = z.infer<typeof CategoryMemberSchema>
+export type SubagentMember = z.infer<typeof SubagentMemberSchema>
+export type Message = z.infer<typeof MessageSchema>
+export type Task = z.infer<typeof TaskSchema>
+export type RuntimeState = z.infer<typeof RuntimeStateSchema>