diff --git a/apps/mana/apps/web/src/lib/data/ai/missions/server-iteration-staging.ts b/apps/mana/apps/web/src/lib/data/ai/missions/server-iteration-staging.ts
index fdfa89ec5..1ccc09ef0 100644
--- a/apps/mana/apps/web/src/lib/data/ai/missions/server-iteration-staging.ts
+++ b/apps/mana/apps/web/src/lib/data/ai/missions/server-iteration-staging.ts
@@ -21,7 +21,7 @@ import { db } from '../../database';
 import { MISSIONS_TABLE } from './types';
 import { createProposal } from '../proposals/store';
 import { getMission } from './store';
-import { runAsAsync } from '../../events/actor';
+import { runAsAsync, makeAgentActor, LEGACY_AI_PRINCIPAL } from '../../events/actor';
 import type { Mission, MissionIteration, PlanStep } from './types';
 
 const processedIterations = new Set<string>();
@@ -96,12 +96,16 @@ async function stageIteration(mission: Mission, iteration: MissionIteration): Pr
 		if (intent.kind !== 'toolCall') continue;
 		if (step.proposalId) continue; // already staged
 
-		const actor = {
-			kind: 'ai' as const,
+		// Phase 1: server-iteration writes under the legacy AI principal.
+		// Phase 2 will swap this for the mission's owning-agent identity
+		// once agents are wired into the data layer.
+		const actor = makeAgentActor({
+			agentId: LEGACY_AI_PRINCIPAL,
+			displayName: 'Mana',
 			missionId: mission.id,
 			iterationId: iteration.id,
 			rationale: step.summary || iteration.summary || mission.objective,
-		};
+		});
 
 		// createProposal runs through Dexie hooks under the AI actor — the
 		// row lands in `pendingProposals` and the AiProposalInbox renders
diff --git a/apps/mana/apps/web/src/lib/data/ai/policy.test.ts b/apps/mana/apps/web/src/lib/data/ai/policy.test.ts
index 129837e85..618d73034 100644
--- a/apps/mana/apps/web/src/lib/data/ai/policy.test.ts
+++ b/apps/mana/apps/web/src/lib/data/ai/policy.test.ts
@@ -2,11 +2,24 @@ import { describe, it, expect } from 'vitest';
 import { resolvePolicy, setAiPolicy, DEFAULT_AI_POLICY } from './policy';
 import { registerTools } from '../tools/registry';
 import { AI_PROPOSABLE_TOOL_NAMES } from '@mana/shared-ai';
-import type { Actor } from '../events/actor';
+import {
+	makeUserActor,
+	makeAgentActor,
+	makeSystemActor,
+	LEGACY_AI_PRINCIPAL,
+	SYSTEM_PROJECTION,
+	type Actor,
+} from '../events/actor';
 
-const AI: Actor = { kind: 'ai', missionId: 'm', iterationId: 'i', rationale: 'r' };
-const USER: Actor = { kind: 'user' };
-const SYSTEM: Actor = { kind: 'system', source: 'projection' };
+const AI: Actor = makeAgentActor({
+	agentId: LEGACY_AI_PRINCIPAL,
+	displayName: 'Mana',
+	missionId: 'm',
+	iterationId: 'i',
+	rationale: 'r',
+});
+const USER: Actor = makeUserActor('u-1', 'Till');
+const SYSTEM: Actor = makeSystemActor(SYSTEM_PROJECTION);
 
 describe('resolvePolicy', () => {
 	it('always returns auto for user actors', () => {
diff --git a/apps/mana/apps/web/src/lib/data/ai/proposals/queries.test.ts b/apps/mana/apps/web/src/lib/data/ai/proposals/queries.test.ts
index 88a367eb8..715bed886 100644
--- a/apps/mana/apps/web/src/lib/data/ai/proposals/queries.test.ts
+++ b/apps/mana/apps/web/src/lib/data/ai/proposals/queries.test.ts
@@ -11,7 +11,7 @@ import { db } from '../../database';
 import { registerTools } from '../../tools/registry';
 import { createProposal } from './store';
 import { PROPOSALS_TABLE } from './types';
-import type { Actor } from '../../events/actor';
+import { makeAgentActor, LEGACY_AI_PRINCIPAL, type AiActor } from '../../events/actor';
 
 // Register two tools in distinct modules so the `module` filter has
 // something to discriminate against.
@@ -36,12 +36,13 @@ registerTools([
 	},
 ]);
 
-const AI: Extract<Actor, { kind: 'ai' }> = {
-	kind: 'ai',
+const AI: AiActor = makeAgentActor({
+	agentId: LEGACY_AI_PRINCIPAL,
+	displayName: 'Mana',
 	missionId: 'm-a',
 	iterationId: 'i-a',
 	rationale: 'r',
-};
+});
 
 beforeEach(async () => {
 	await db.table(PROPOSALS_TABLE).clear();
diff --git a/apps/mana/apps/web/src/lib/data/ai/proposals/store.test.ts b/apps/mana/apps/web/src/lib/data/ai/proposals/store.test.ts
index 575964c28..ef77f1b5e 100644
--- a/apps/mana/apps/web/src/lib/data/ai/proposals/store.test.ts
+++ b/apps/mana/apps/web/src/lib/data/ai/proposals/store.test.ts
@@ -18,14 +18,15 @@ import {
 	getProposal,
 } from './store';
 import { PROPOSALS_TABLE } from './types';
-import type { Actor } from '../../events/actor';
+import { makeAgentActor, LEGACY_AI_PRINCIPAL, type AiActor } from '../../events/actor';
 
-const AI: Extract<Actor, { kind: 'ai' }> = {
-	kind: 'ai',
+const AI: AiActor = makeAgentActor({
+	agentId: LEGACY_AI_PRINCIPAL,
+	displayName: 'Mana',
 	missionId: 'mission-1',
 	iterationId: 'iter-1',
 	rationale: 'test run',
-};
+});
 
 let executed: { name: string; params: Record<string, unknown> }[] = [];
 
diff --git a/apps/mana/apps/web/src/lib/data/ai/timeline/queries.test.ts b/apps/mana/apps/web/src/lib/data/ai/timeline/queries.test.ts
index 9e0607035..5f20e6c27 100644
--- a/apps/mana/apps/web/src/lib/data/ai/timeline/queries.test.ts
+++ b/apps/mana/apps/web/src/lib/data/ai/timeline/queries.test.ts
@@ -1,7 +1,7 @@
 import { describe, it, expect } from 'vitest';
 import { bucketByIteration } from './queries';
 import type { DomainEvent } from '../../events/types';
-import { USER_ACTOR } from '../../events/actor';
+import { USER_ACTOR, makeAgentActor, LEGACY_AI_PRINCIPAL } from '../../events/actor';
 
 function aiEvent(
 	missionId: string,
@@ -20,7 +20,13 @@ function aiEvent(
 			collection: 'tasks',
 			recordId: crypto.randomUUID(),
 			userId: 'u1',
-			actor: { kind: 'ai', missionId, iterationId, rationale },
+			actor: makeAgentActor({
+				agentId: LEGACY_AI_PRINCIPAL,
+				displayName: 'Mana',
+				missionId,
+				iterationId,
+				rationale,
+			}),
 		},
 	};
 }
diff --git a/apps/mana/apps/web/src/lib/data/events/actor.test.ts b/apps/mana/apps/web/src/lib/data/events/actor.test.ts
index 73866b77b..2488bc89e 100644
--- a/apps/mana/apps/web/src/lib/data/events/actor.test.ts
+++ b/apps/mana/apps/web/src/lib/data/events/actor.test.ts
@@ -1,17 +1,29 @@
 import { describe, it, expect, beforeEach } from 'vitest';
-import { runAs, runAsAsync, getCurrentActor, USER_ACTOR, isAiActor, isSystemActor } from './actor';
+import {
+	runAs,
+	runAsAsync,
+	getCurrentActor,
+	USER_ACTOR,
+	isAiActor,
+	isSystemActor,
+	makeAgentActor,
+	makeSystemActor,
+	SYSTEM_PROJECTION,
+	LEGACY_AI_PRINCIPAL,
+} from './actor';
 import { emitDomainEvent } from './emit';
 import { eventBus } from './event-bus';
 import type { DomainEvent } from './types';
 
-const AI_ACTOR = {
-	kind: 'ai',
+const AI_ACTOR = makeAgentActor({
+	agentId: LEGACY_AI_PRINCIPAL,
+	displayName: 'Mana',
 	missionId: 'm-1',
 	iterationId: 'i-1',
 	rationale: 'test',
-} as const;
+});
 
-const SYSTEM_ACTOR = { kind: 'system', source: 'projection' } as const;
+const SYSTEM_ACTOR = makeSystemActor(SYSTEM_PROJECTION);
 
 describe('actor context', () => {
 	it('defaults to the user actor', () => {
@@ -42,20 +54,29 @@ describe('actor context', () => {
 	});
 
 	it('supports nesting', () => {
-		runAs({ ...AI_ACTOR, missionId: 'outer' }, () => {
-			expect((getCurrentActor() as { missionId: string }).missionId).toBe('outer');
-			runAs({ ...AI_ACTOR, missionId: 'inner' }, () => {
-				expect((getCurrentActor() as { missionId: string }).missionId).toBe('inner');
-			});
-			expect((getCurrentActor() as { missionId: string }).missionId).toBe('outer');
-		});
+		runAs(
+			makeAgentActor({ ...AI_ACTOR, agentId: AI_ACTOR.principalId, missionId: 'outer' }),
+			() => {
+				expect((getCurrentActor() as { missionId: string }).missionId).toBe('outer');
+				runAs(
+					makeAgentActor({ ...AI_ACTOR, agentId: AI_ACTOR.principalId, missionId: 'inner' }),
+					() => {
+						expect((getCurrentActor() as { missionId: string }).missionId).toBe('inner');
+					}
+				);
+				expect((getCurrentActor() as { missionId: string }).missionId).toBe('outer');
+			}
+		);
 	});
 
 	it('preserves the actor across awaits inside runAsAsync', async () => {
-		await runAsAsync({ ...AI_ACTOR, missionId: 'async' }, async () => {
-			await Promise.resolve();
-			expect((getCurrentActor() as { missionId: string }).missionId).toBe('async');
-		});
+		await runAsAsync(
+			makeAgentActor({ ...AI_ACTOR, agentId: AI_ACTOR.principalId, missionId: 'async' }),
+			async () => {
+				await Promise.resolve();
+				expect((getCurrentActor() as { missionId: string }).missionId).toBe('async');
+			}
+		);
 		expect(getCurrentActor()).toEqual(USER_ACTOR);
 	});
 });
diff --git a/apps/mana/apps/web/src/lib/data/events/actor.ts b/apps/mana/apps/web/src/lib/data/events/actor.ts
index 41c1688b8..f82d3c610 100644
--- a/apps/mana/apps/web/src/lib/data/events/actor.ts
+++ b/apps/mana/apps/web/src/lib/data/events/actor.ts
@@ -1,46 +1,92 @@
 /**
- * Actor attribution — who triggered a write.
+ * Actor attribution — runtime side (ambient context + configurable user
+ * default). The TYPE + factories + predicates live in `@mana/shared-ai`
+ * so the server-side mana-ai runner parses identical shapes.
  *
- * Every DomainEvent, pending-change row, and synced record carries an Actor so
- * the UI can distinguish user-initiated work from AI-initiated work, render
- * ghost state for proposals, attribute field-level edits, and let the user
- * revert a whole mission.
+ * Threading model: a module-level "current actor" acts like an
+ * AsyncLocalStorage fiber. The browser is single-threaded and the
+ * Dexie write path is synchronous, so a mutable slot wrapped by
+ * `runAs(actor, fn)` is enough at the boundaries (UI handlers,
+ * executor, runners). At the primitive sites (Dexie hooks,
+ * `emitDomainEvent`) the actor is **captured synchronously** and
+ * frozen onto the data — ambient context is never the source of truth
+ * past that point.
  *
- * Three actor kinds:
- *  - `user`   — the human at the keyboard
- *  - `ai`     — autonomous AI work, carrying mission/iteration metadata so the
- *               Workbench can group, review, and revert per-mission
- *  - `system` — derived writes (projections, rule engines, data migrations)
- *               that are neither user nor AI
- *
- * Threading model: a module-level "current actor" acts like an AsyncLocalStorage
- * fiber. The browser is single-threaded and the Dexie write path is synchronous,
- * so a mutable slot wrapped by `runAs(actor, fn)` is enough at the boundaries
- * (UI handlers, executor, runners). At the primitive sites (Dexie hooks,
- * `emitDomainEvent`) the actor is **captured synchronously** and frozen onto
- * the data — ambient context is never the source of truth past that point.
+ * Default user identity: `USER_ACTOR` (re-exported from shared-ai)
+ * starts with a `legacy:user` placeholder. The layout's login effect
+ * must call `bindDefaultUser(userId, displayName)` so the real
+ * identity gets stamped onto subsequent writes.
  */
 
-export type Actor =
-	| { readonly kind: 'user' }
-	| {
-			readonly kind: 'ai';
-			/** Mission this write belongs to. */
-			readonly missionId: string;
-			/** Iteration within the mission (nth autonomous run). */
-			readonly iterationId: string;
-			/** Human-readable reason the AI took this action. */
-			readonly rationale: string;
-	  }
-	| {
-			readonly kind: 'system';
-			/** Subsystem responsible for this derived write. */
-			readonly source: 'projection' | 'rule' | 'migration' | 'mission-runner';
-	  };
+import { type Actor, makeUserActor, USER_ACTOR as LEGACY_USER_ACTOR } from '@mana/shared-ai';
 
-export const USER_ACTOR: Actor = Object.freeze({ kind: 'user' });
+export type {
+	Actor,
+	ActorKind,
+	BaseActor,
+	UserActor,
+	AiActor,
+	SystemActor,
+	SystemSource,
+} from '@mana/shared-ai';
+export {
+	SYSTEM_PROJECTION,
+	SYSTEM_RULE,
+	SYSTEM_MIGRATION,
+	SYSTEM_STREAM,
+	SYSTEM_MISSION_RUNNER,
+	LEGACY_USER_PRINCIPAL,
+	LEGACY_AI_PRINCIPAL,
+	LEGACY_SYSTEM_PRINCIPAL,
+	LEGACY_DISPLAY_NAME,
+	makeUserActor,
+	makeAgentActor,
+	makeSystemActor,
+	normalizeActor,
+	isUserActor,
+	isAiActor,
+	isSystemActor,
+	isFromMissionRunner,
+} from '@mana/shared-ai';
 
-let currentActor: Actor = USER_ACTOR;
+/**
+ * The "logged-in user" actor, used as the default ambient context.
+ * Starts as the shared-ai legacy placeholder so early module-init
+ * writes (before login has finished) still produce a valid actor.
+ * Replaced by `bindDefaultUser` once the auth store has resolved.
+ */
+let defaultUserActor: Actor = LEGACY_USER_ACTOR;
+
+/**
+ * Bind the real user identity to the default ambient actor. Called
+ * once from the app-shell `onMount` after the auth store resolves.
+ * Safe to call multiple times (e.g. on user switch); the most recent
+ * call wins.
+ */
+export function bindDefaultUser(userId: string, displayName: string): void {
+	const next = makeUserActor(userId, displayName);
+	if (currentActor === defaultUserActor) {
+		currentActor = next;
+	}
+	defaultUserActor = next;
+	if (typeof window !== 'undefined') {
+		console.info(`[actor] bindDefaultUser: ${displayName} (${userId.slice(0, 8)}…)`);
+	}
+}
+
+/** Re-export the legacy constant for call sites that haven't been
+ *  migrated yet. Prefer `getCurrentActor()` or `defaultUser()` for new
+ *  code; this stays around because a grep-rewrite of every test fixture
+ *  would add no value. */
+export const USER_ACTOR = LEGACY_USER_ACTOR;
+
+/** The currently bound default user actor. Use when you want to attribute
+ *  a write to "the logged-in user" without reading ambient context. */
+export function defaultUser(): Actor {
+	return defaultUserActor;
+}
+
+let currentActor: Actor = defaultUserActor;
 
 /** Returns the actor attributed to the currently executing write. */
 export function getCurrentActor(): Actor {
@@ -48,15 +94,16 @@ export function getCurrentActor(): Actor {
 }
 
 /**
- * Run `fn` with the given actor pinned to the current context. Restores the
- * previous actor on exit, even if `fn` throws. Supports nesting.
+ * Run `fn` with the given actor pinned to the current context. Restores
+ * the previous actor on exit, even if `fn` throws. Supports nesting.
  *
  * Use this at the three defined boundaries only:
  *   1. Tool executor (AI-initiated tool calls)
  *   2. Mission runner (background AI loop)
  *   3. Projection / rule dispatcher (system-initiated cascades)
- * Past those boundaries every write primitive freezes the actor onto data —
- * do not rely on ambient context across `setTimeout` / `queueMicrotask` hops.
+ * Past those boundaries every write primitive freezes the actor onto
+ * data — do not rely on ambient context across `setTimeout` /
+ * `queueMicrotask` hops.
  */
 export function runAs<T>(actor: Actor, fn: () => T): T {
 	const previous = currentActor;
@@ -69,10 +116,11 @@ export function runAs<T>(actor: Actor, fn: () => T): T {
 }
 
 /**
- * Async variant of {@link runAs}. The actor stays pinned across awaits within
- * the same Promise chain, but NOT across `setTimeout` or un-awaited work.
- * That is fine only because every primitive (emitDomainEvent, Dexie hooks)
- * captures the actor synchronously at the write moment.
+ * Async variant of {@link runAs}. The actor stays pinned across awaits
+ * within the same Promise chain, but NOT across `setTimeout` or
+ * un-awaited work. That is fine only because every primitive
+ * (emitDomainEvent, Dexie hooks) captures the actor synchronously at
+ * the write moment.
  */
 export async function runAsAsync<T>(actor: Actor, fn: () => Promise<T>): Promise<T> {
 	const previous = currentActor;
@@ -83,13 +131,3 @@ export async function runAsAsync<T>(actor: Actor, fn: () => Promise<T>): Promise
 		currentActor = previous;
 	}
 }
-
-/** True when an AI agent wrote this record/event/field. */
-export function isAiActor(actor: Actor | undefined): boolean {
-	return actor?.kind === 'ai';
-}
-
-/** True when a derived subsystem (projection / rule / migration) wrote it. */
-export function isSystemActor(actor: Actor | undefined): boolean {
-	return actor?.kind === 'system';
-}
diff --git a/apps/mana/apps/web/src/lib/data/projections/streaks.ts b/apps/mana/apps/web/src/lib/data/projections/streaks.ts
index 4bd719919..3e28304e8 100644
--- a/apps/mana/apps/web/src/lib/data/projections/streaks.ts
+++ b/apps/mana/apps/web/src/lib/data/projections/streaks.ts
@@ -17,11 +17,11 @@
 import { db } from '../database';
 import { useLiveQueryWithDefault } from '@mana/local-store/svelte';
 import { eventBus } from '../events/event-bus';
-import { runAsAsync } from '../events/actor';
+import { runAsAsync, makeSystemActor, SYSTEM_PROJECTION } from '../events/actor';
 import type { DomainEvent } from '../events/types';
 import type { StreakInfo } from './types';
 
-const PROJECTION_ACTOR = { kind: 'system', source: 'projection' } as const;
+const PROJECTION_ACTOR = makeSystemActor(SYSTEM_PROJECTION, 'Streak-Tracker');
 
 // ── Persistent State ────────────────────────────────
 
diff --git a/apps/mana/apps/web/src/lib/data/tools/executor.test.ts b/apps/mana/apps/web/src/lib/data/tools/executor.test.ts
index 9c8b4831a..6cbb1f637 100644
--- a/apps/mana/apps/web/src/lib/data/tools/executor.test.ts
+++ b/apps/mana/apps/web/src/lib/data/tools/executor.test.ts
@@ -13,10 +13,16 @@ import { setAiPolicy } from '../ai/policy';
 import { listProposals, approveProposal } from '../ai/proposals/store';
 import { PROPOSALS_TABLE } from '../ai/proposals/types';
 import { db } from '../database';
-import type { Actor } from '../events/actor';
+import { makeAgentActor, LEGACY_AI_PRINCIPAL, type Actor } from '../events/actor';
 import type { ModuleTool } from './types';
 
-const AI: Actor = { kind: 'ai', missionId: 'm-1', iterationId: 'it-1', rationale: 'because' };
+const AI: Actor = makeAgentActor({
+	agentId: LEGACY_AI_PRINCIPAL,
+	displayName: 'Mana',
+	missionId: 'm-1',
+	iterationId: 'it-1',
+	rationale: 'because',
+});
 
 // Reset registry between tests by reloading — registry uses module-level array
 // Instead, we just register test tools and rely on dedup
diff --git a/packages/shared-ai/src/actor.test.ts b/packages/shared-ai/src/actor.test.ts
new file mode 100644
index 000000000..d732a9c40
--- /dev/null
+++ b/packages/shared-ai/src/actor.test.ts
@@ -0,0 +1,133 @@
+import { describe, it, expect } from 'vitest';
+import {
+	makeUserActor,
+	makeAgentActor,
+	makeSystemActor,
+	normalizeActor,
+	isUserActor,
+	isAiActor,
+	isSystemActor,
+	isFromMissionRunner,
+	SYSTEM_PROJECTION,
+	SYSTEM_MISSION_RUNNER,
+	LEGACY_USER_PRINCIPAL,
+	LEGACY_DISPLAY_NAME,
+	USER_ACTOR,
+} from './actor';
+
+describe('factories', () => {
+	it('makeUserActor carries userId + displayName', () => {
+		const a = makeUserActor('user-1', 'Till');
+		expect(a.kind).toBe('user');
+		expect(a.principalId).toBe('user-1');
+		expect(a.displayName).toBe('Till');
+	});
+
+	it('makeUserActor default displayName is "Du"', () => {
+		expect(makeUserActor('u').displayName).toBe('Du');
+	});
+
+	it('makeAgentActor carries mission context', () => {
+		const a = makeAgentActor({
+			agentId: 'agent-1',
+			displayName: 'Cashflow Watcher',
+			missionId: 'm1',
+			iterationId: 'it1',
+			rationale: 'weekly review',
+		});
+		expect(a.kind).toBe('ai');
+		expect(a.principalId).toBe('agent-1');
+		expect(a.displayName).toBe('Cashflow Watcher');
+		expect(a.missionId).toBe('m1');
+		expect(a.iterationId).toBe('it1');
+		expect(a.rationale).toBe('weekly review');
+	});
+
+	it('makeSystemActor picks a default displayName per source', () => {
+		expect(makeSystemActor(SYSTEM_PROJECTION).displayName).toBe('Projektion');
+		expect(makeSystemActor(SYSTEM_MISSION_RUNNER).displayName).toBe('Mission-Runner');
+	});
+
+	it('makeSystemActor accepts a displayName override', () => {
+		expect(makeSystemActor(SYSTEM_PROJECTION, 'Streak-Tracker').displayName).toBe('Streak-Tracker');
+	});
+});
+
+describe('predicates', () => {
+	const u = makeUserActor('u');
+	const a = makeAgentActor({
+		agentId: 'a1',
+		displayName: 'x',
+		missionId: 'm',
+		iterationId: 'i',
+		rationale: 'r',
+	});
+	const s = makeSystemActor(SYSTEM_PROJECTION);
+	const mr = makeSystemActor(SYSTEM_MISSION_RUNNER);
+
+	it('identifies kinds', () => {
+		expect(isUserActor(u)).toBe(true);
+		expect(isUserActor(a)).toBe(false);
+		expect(isAiActor(a)).toBe(true);
+		expect(isSystemActor(s)).toBe(true);
+	});
+
+	it('isFromMissionRunner only fires for mission-runner principalId', () => {
+		expect(isFromMissionRunner(mr)).toBe(true);
+		expect(isFromMissionRunner(s)).toBe(false);
+	});
+
+	it('predicates handle undefined', () => {
+		expect(isUserActor(undefined)).toBe(false);
+		expect(isAiActor(undefined)).toBe(false);
+		expect(isSystemActor(undefined)).toBe(false);
+	});
+});
+
+describe('normalizeActor', () => {
+	it('passes modern actors through unchanged', () => {
+		const a = makeUserActor('u', 'Till');
+		expect(normalizeActor(a)).toBe(a);
+	});
+
+	it('fills in principalId+displayName for legacy {kind:"user"} events', () => {
+		const legacy = { kind: 'user' };
+		const n = normalizeActor(legacy);
+		expect(n.kind).toBe('user');
+		expect(n.principalId).toBe(LEGACY_USER_PRINCIPAL);
+		expect(n.displayName).toBe('Du');
+	});
+
+	it('fills in AI fields for legacy {kind:"ai", missionId, ...} without identity', () => {
+		const legacy = { kind: 'ai', missionId: 'm1', iterationId: 'i1', rationale: 'r' };
+		const n = normalizeActor(legacy);
+		expect(n.kind).toBe('ai');
+		expect(n.principalId).toBe('legacy:ai-default');
+		expect(n.displayName).toBe(LEGACY_DISPLAY_NAME);
+		if (n.kind !== 'ai') throw new Error('narrowed to ai');
+		expect(n.missionId).toBe('m1');
+	});
+
+	it('maps old system.source field into new system:<source> principalId', () => {
+		const legacy = { kind: 'system', source: 'projection' };
+		const n = normalizeActor(legacy);
+		expect(n.kind).toBe('system');
+		expect(n.principalId).toBe('system:projection');
+		expect(n.displayName).toBe('Projektion');
+	});
+
+	it('handles completely garbage input', () => {
+		expect(normalizeActor(null).kind).toBe('user');
+		expect(normalizeActor('hello').kind).toBe('user');
+		expect(normalizeActor(undefined).principalId).toBe(LEGACY_USER_PRINCIPAL);
+		expect(normalizeActor({ kind: 'alien' }).kind).toBe('user');
+	});
+});
+
+describe('USER_ACTOR legacy export', () => {
+	it('uses legacy principal + "Du" display', () => {
+		expect(USER_ACTOR.kind).toBe('user');
+		expect(USER_ACTOR.principalId).toBe(LEGACY_USER_PRINCIPAL);
+		expect(USER_ACTOR.displayName).toBe('Du');
+	});
+});
diff --git a/packages/shared-ai/src/actor.ts b/packages/shared-ai/src/actor.ts
index d21119098..6f613de1c 100644
--- a/packages/shared-ai/src/actor.ts
+++ b/packages/shared-ai/src/actor.ts
@@ -1,27 +1,208 @@
 /**
- * Actor attribution type — the discriminated union stamped on every
- * event, record, and sync-change row in the Mana system.
+ * Actor attribution — the type carried on every DomainEvent, pending-
+ * change row, and sync_changes row in the Mana system.
  *
- * Runtime helpers (runAs, runAsAsync, ambient context) stay in the webapp
- * because they rely on browser single-threaded semantics and module-level
- * mutable state. The *type* is shared so server-side consumers can parse
- * incoming actors without re-declaring the union.
+ * The three kinds (user/ai/system) are discriminators for UI + revert
+ * semantics; `principalId` is the identity under the kind. For a human
+ * writing, `principalId = userId`. For an AI agent, `principalId =
+ * agentId`. For system writes, it is one of the `SystemSource` sentinel
+ * strings (see below).
+ *
+ * `displayName` is cached at write time so historical records show
+ * "Cashflow Watcher" forever — even after the agent is renamed or
+ * deleted. This keeps timelines honest: old events describe what the
+ * user actually saw when they happened.
+ *
+ * Runtime helpers (runAs, ambient context) live in the webapp —
+ * browser single-threaded semantics + module-level mutable state,
+ * neither of which is appropriate for the server-side mana-ai service.
+ * This file exposes only the types, factories, and pure predicates so
+ * both runtimes can parse/build identical actor shapes.
  */
 
-export type Actor =
-	| { readonly kind: 'user' }
-	| {
-			readonly kind: 'ai';
-			readonly missionId: string;
-			readonly iterationId: string;
-			readonly rationale: string;
-	  }
-	| {
-			readonly kind: 'system';
-			readonly source: 'projection' | 'rule' | 'migration' | 'mission-runner';
-	  };
+export type ActorKind = 'user' | 'ai' | 'system';
 
-export const USER_ACTOR: Actor = Object.freeze({ kind: 'user' });
+/**
+ * Fixed set of system-write sources. Each gets its own stable
+ * `principalId` so Workbench filters, revert logic, and forensics can
+ * distinguish projection writes from migration writes from the
+ * mission-runner's server-produced iterations.
+ */
+export const SYSTEM_PROJECTION = 'system:projection';
+export const SYSTEM_RULE = 'system:rule';
+export const SYSTEM_MIGRATION = 'system:migration';
+export const SYSTEM_STREAM = 'system:stream';
+export const SYSTEM_MISSION_RUNNER = 'system:mission-runner';
+
+export type SystemSource =
+	| typeof SYSTEM_PROJECTION
+	| typeof SYSTEM_RULE
+	| typeof SYSTEM_MIGRATION
+	| typeof SYSTEM_STREAM
+	| typeof SYSTEM_MISSION_RUNNER;
+
+/** Legacy sentinels for records that pre-date the identity-aware actor
+ *  shape. Read-path normalization maps missing fields to these. */
+export const LEGACY_USER_PRINCIPAL = 'legacy:user';
+export const LEGACY_AI_PRINCIPAL = 'legacy:ai-default';
+export const LEGACY_SYSTEM_PRINCIPAL = 'legacy:system';
+export const LEGACY_DISPLAY_NAME = 'Unbekannt';
+
+/** Fields common to every actor kind. */
+export interface BaseActor {
+	/** UUID / sentinel identifying the specific principal. For kind='user'
+	 *  this is the userId; for 'ai' it's the agentId; for 'system' it's
+	 *  one of the `SystemSource` sentinels. */
+	readonly principalId: string;
+	/** Cached display name — frozen at write time so rename doesn't
+	 *  rewrite history. */
+	readonly displayName: string;
+}
+
+export interface UserActor extends BaseActor {
+	readonly kind: 'user';
+}
+
+export interface AiActor extends BaseActor {
+	readonly kind: 'ai';
+	/** Mission this write belongs to. */
+	readonly missionId: string;
+	/** Iteration within the mission (nth autonomous run). */
+	readonly iterationId: string;
+	/** Human-readable reason the AI took this action. */
+	readonly rationale: string;
+}
+
+export interface SystemActor extends BaseActor {
+	readonly kind: 'system';
+}
+
+/** Discriminated union over the three actor kinds. `Extract<Actor,
+ *  { kind: 'ai' }>` narrows to `AiActor`. */
+export type Actor = UserActor | AiActor | SystemActor;
+
+// ─── Factories ───────────────────────────────────────────────
+
+/**
+ * Build a user actor for the given userId. `displayName` defaults to
+ * "Du" since the webapp usually doesn't know the user's canonical
+ * display name at Dexie-hook time; callers that DO know (e.g. from
+ * the auth store) should pass the real value.
+ */
+export function makeUserActor(userId: string, displayName = 'Du'): UserActor {
+	return Object.freeze({ kind: 'user' as const, principalId: userId, displayName });
+}
+
+/**
+ * Build an agent actor. This is what the mana-ai runner and the
+ * webapp's tool executor stamp when an AI agent writes. The mission
+ * context is required — a bare "this came from some AI" without
+ * mission linkage would hide the agent's work from the revert path.
+ */
+export function makeAgentActor(args: {
+	agentId: string;
+	displayName: string;
+	missionId: string;
+	iterationId: string;
+	rationale: string;
+}): AiActor {
+	return Object.freeze({
+		kind: 'ai' as const,
+		principalId: args.agentId,
+		displayName: args.displayName,
+		missionId: args.missionId,
+		iterationId: args.iterationId,
+		rationale: args.rationale,
+	});
+}
+
+/**
+ * Build a system actor for the given source. `displayName` defaults to
+ * a human-readable version of the source; callers rarely need to
+ * override this.
+ */
+export function makeSystemActor(source: SystemSource, displayName?: string): SystemActor {
+	return Object.freeze({
+		kind: 'system' as const,
+		principalId: source,
+		displayName: displayName ?? defaultSystemDisplayName(source),
+	});
+}
+
+function defaultSystemDisplayName(source: SystemSource): string {
+	switch (source) {
+		case SYSTEM_PROJECTION:
+			return 'Projektion';
+		case SYSTEM_RULE:
+			return 'Regel';
+		case SYSTEM_MIGRATION:
+			return 'Migration';
+		case SYSTEM_STREAM:
+			return 'Event-Stream';
+		case SYSTEM_MISSION_RUNNER:
+			return 'Mission-Runner';
+	}
+}
+
+// ─── Read-path compat ────────────────────────────────────────
+
+/**
+ * Normalize a raw actor blob that came off the wire (sync_changes.actor,
+ * an old DomainEvent, a pre-identity Dexie record) into the current
+ * Actor shape. Missing `principalId` / `displayName` get filled with
+ * stable `legacy:*` sentinels so downstream code never crashes on
+ * historical data.
+ *
+ * Returns the argument unchanged when it's already a valid Actor — no
+ * allocation in the hot path.
+ */
+export function normalizeActor(raw: unknown): Actor {
+	if (!raw || typeof raw !== 'object') {
+		return makeUserActor(LEGACY_USER_PRINCIPAL, LEGACY_DISPLAY_NAME);
+	}
+	const a = raw as Partial<Actor> & { source?: string };
+
+	if (a.kind === 'user') {
+		if (typeof a.principalId === 'string' && typeof a.displayName === 'string') {
+			return a as Actor;
+		}
+		return makeUserActor(a.principalId ?? LEGACY_USER_PRINCIPAL, a.displayName ?? 'Du');
+	}
+
+	if (a.kind === 'ai') {
+		if (typeof a.principalId === 'string' && typeof a.displayName === 'string') {
+			return a as Actor;
+		}
+		return {
+			kind: 'ai',
+			principalId: a.principalId ?? LEGACY_AI_PRINCIPAL,
+			displayName: a.displayName ?? LEGACY_DISPLAY_NAME,
+			missionId: a.missionId ?? '',
+			iterationId: a.iterationId ?? '',
+			rationale: a.rationale ?? '',
+		};
+	}
+
+	if (a.kind === 'system') {
+		// Old shape carried `source: 'projection'|'rule'|'migration'|'mission-runner'`.
+		// New shape carries it inside principalId as 'system:<source>'.
+		if (typeof a.principalId === 'string' && typeof a.displayName === 'string') {
+			return a as Actor;
+		}
+		const legacySource =
+			typeof a.source === 'string' ? `system:${a.source}` : LEGACY_SYSTEM_PRINCIPAL;
+		return makeSystemActor(legacySource as SystemSource);
+	}
+
+	// Unknown kind → treat as legacy user.
+	return makeUserActor(LEGACY_USER_PRINCIPAL, LEGACY_DISPLAY_NAME);
+}
+
+// ─── Predicates ──────────────────────────────────────────────
+
+export function isUserActor(actor: Actor | undefined): boolean {
+	return actor?.kind === 'user';
+}
 
 export function isAiActor(actor: Actor | undefined): boolean {
 	return actor?.kind === 'ai';
@@ -30,3 +211,22 @@ export function isAiActor(actor: Actor | undefined): boolean {
 export function isSystemActor(actor: Actor | undefined): boolean {
 	return actor?.kind === 'system';
 }
+
+/** True when a write came from the server-side mission runner
+ *  specifically (distinct from other system subsystems). */
+export function isFromMissionRunner(actor: Actor | undefined): boolean {
+	return actor?.kind === 'system' && actor.principalId === SYSTEM_MISSION_RUNNER;
+}
+
+// ─── Legacy export ───────────────────────────────────────────
+
+/**
+ * Placeholder user actor for tests and fallback sites. Uses a
+ * `legacy:user` principalId — call sites with a real userId should use
+ * `makeUserActor(userId, displayName)` instead.
+ *
+ * The webapp overrides this at login with the real user via an ambient-
+ * context setter; see `data/events/actor.ts` in the web app for the
+ * runtime-configurable default.
+ */
+export const USER_ACTOR: Actor = makeUserActor(LEGACY_USER_PRINCIPAL, 'Du');
diff --git a/packages/shared-ai/src/index.ts b/packages/shared-ai/src/index.ts
index 5d76a3c2b..35ac92f31 100644
--- a/packages/shared-ai/src/index.ts
+++ b/packages/shared-ai/src/index.ts
@@ -7,8 +7,35 @@
  * pure functions here must work in both environments.
  */
 
-export type { Actor } from './actor';
-export { USER_ACTOR, isAiActor, isSystemActor } from './actor';
+export type {
+	Actor,
+	ActorKind,
+	BaseActor,
+	UserActor,
+	AiActor,
+	SystemActor,
+	SystemSource,
+} from './actor';
+export {
+	SYSTEM_PROJECTION,
+	SYSTEM_RULE,
+	SYSTEM_MIGRATION,
+	SYSTEM_STREAM,
+	SYSTEM_MISSION_RUNNER,
+	LEGACY_USER_PRINCIPAL,
+	LEGACY_AI_PRINCIPAL,
+	LEGACY_SYSTEM_PRINCIPAL,
+	LEGACY_DISPLAY_NAME,
+	USER_ACTOR,
+	makeUserActor,
+	makeAgentActor,
+	makeSystemActor,
+	normalizeActor,
+	isUserActor,
+	isAiActor,
+	isSystemActor,
+	isFromMissionRunner,
+} from './actor';
 
 export type {
 	IterationPhase,
diff --git a/services/mana-ai/src/db/iteration-writer.ts b/services/mana-ai/src/db/iteration-writer.ts
index 3f28956b1..3cede8764 100644
--- a/services/mana-ai/src/db/iteration-writer.ts
+++ b/services/mana-ai/src/db/iteration-writer.ts
@@ -17,6 +17,7 @@
 
 import type { Sql } from './connection';
 import { withUser } from './connection';
+import { makeSystemActor, SYSTEM_MISSION_RUNNER } from '@mana/shared-ai';
 import type { AiPlanOutput, MissionIteration, PlanStep } from '@mana/shared-ai';
 
 export interface AppendIterationInput {
@@ -36,9 +37,13 @@ export interface AppendIterationInput {
 }
 
 /** Actor blob stamped on the sync_changes row. JSON string already —
- *  we pass it as `json.RawMessage` equivalent through pgx. */
+ *  we pass it as `json.RawMessage` equivalent through pgx. Uses the
+ *  identity-aware Actor shape from @mana/shared-ai so the webapp's
+ *  timeline can group + filter server-produced iterations alongside
+ *  agent/user writes. Phase 2 will switch this to a per-agent actor
+ *  when the mission carries `agentId`. */
 function systemActorJson(): string {
-	return JSON.stringify({ kind: 'system', source: 'mission-runner' });
+	return JSON.stringify(makeSystemActor(SYSTEM_MISSION_RUNNER));
 }
 
 export async function appendServerIteration(sql: Sql, input: AppendIterationInput): Promise<void> {