diff --git a/examples/app-showcase/src/objects/task.object.ts b/examples/app-showcase/src/objects/task.object.ts
index b486b97617..6ead30125f 100644
--- a/examples/app-showcase/src/objects/task.object.ts
+++ b/examples/app-showcase/src/objects/task.object.ts
@@ -40,6 +40,9 @@ export const Task = ObjectSchema.create({
     status: Field.select({
       label: 'Status',
       required: true,
+      // ADR-0052 §5b — declarative activity. Status changes auto-appear on the
+      // record timeline as "Status: To Do → In Progress" with zero hook code.
+      trackHistory: true,
       options: [
         { label: 'Backlog', value: 'backlog', default: true, color: '#94A3B8' },
         { label: 'To Do', value: 'todo', color: '#3B82F6' },
@@ -50,6 +53,7 @@ export const Task = ObjectSchema.create({
     }),
     priority: Field.select({
       label: 'Priority',
+      trackHistory: true,
       options: [
         { label: 'Low', value: 'low', color: '#94A3B8' },
         { label: 'Medium', value: 'medium', default: true, color: '#3B82F6' },
@@ -81,6 +85,13 @@ export const Task = ObjectSchema.create({
     sync_error: Field.textarea({ label: 'Sync Error' }),
   },
 
+  // ADR-0052 §5b.2 — declarative semantic milestone. When status enters `done`,
+  // the platform emits "✅ Task completed: <title>" on the timeline (taking
+  // precedence over the raw "Status: In Review → Done" diff) — zero hook code.
+  activityMilestones: [
+    { field: 'status', value: 'done', summary: '✅ Task completed: {title}', type: 'completed' },
+  ],
+
   validations: [
     {
       type: 'state_machine' as const,
diff --git a/packages/plugins/plugin-audit/src/audit-writers.test.ts b/packages/plugins/plugin-audit/src/audit-writers.test.ts
index b4780e8fdb..7196d31de4 100644
--- a/packages/plugins/plugin-audit/src/audit-writers.test.ts
+++ b/packages/plugins/plugin-audit/src/audit-writers.test.ts
@@ -25,7 +25,10 @@ interface CapturedRow {
  *   `engine.getSchema(name)` returns after `applySystemFields` has (or has
  *   not) injected `organization_id`.
  */
-function makeEngine(schemas: Record<string, string[] | Record<string, any>>) {
+function makeEngine(
+  schemas: Record<string, string[] | Record<string, any>>,
+  objectDefs: Record<string, any> = {},
+) {
   const hooks = new Map<string, Array<(ctx: any) => any>>();
   const created: CapturedRow[] = [];
 
@@ -49,7 +52,7 @@ function makeEngine(schemas: Record<string, string[] | Record<string, any>>) {
       const fieldMap = Array.isArray(fields)
         ? Object.fromEntries(fields.map((f) => [f, { type: 'text' }]))
         : fields;
-      return { name, fields: fieldMap };
+      return { name, fields: fieldMap, ...(objectDefs[name] || {}) };
     },
     registerHook(event: string, fn: (ctx: any) => any) {
       const list = hooks.get(event) ?? [];
@@ -177,3 +180,68 @@ describe('audit writers — declarative trackHistory activity (ADR-0052 §5b)',
     expect(activity?.row.summary).toBe('Updated crm_opportunity "Acme Renewal"');
   });
 });
+
+describe('audit writers — declarative milestones (ADR-0052 §5b.2)', () => {
+  const FIELDS = {
+    id: { type: 'text' },
+    name: { type: 'text', label: 'Name' },
+    stage: {
+      type: 'select',
+      label: 'Stage',
+      trackHistory: true,
+      options: [
+        { value: 'negotiation', label: 'Negotiation' },
+        { value: 'closed_won', label: 'Closed Won' },
+      ],
+    },
+  };
+  const SCHEMA = {
+    sys_audit_log: SINGLE_TENANT.sys_audit_log,
+    sys_activity: SINGLE_TENANT.sys_activity,
+    crm_opportunity: FIELDS,
+  };
+  // Object-level milestone: when stage enters closed_won → "Deal won: {name}".
+  const OBJECT_DEFS = {
+    crm_opportunity: {
+      activityMilestones: [
+        { field: 'stage', value: 'closed_won', summary: 'Deal won: {name}', type: 'completed' },
+      ],
+    },
+  };
+
+  it('emits the interpolated milestone summary (precedence over field-change) on transition', async () => {
+    const { engine, fire, created } = makeEngine(SCHEMA, OBJECT_DEFS);
+    installAuditWriters(engine as any, 'test.audit');
+
+    await fire('afterUpdate', {
+      object: 'crm_opportunity',
+      input: { id: 'opp-1', stage: 'closed_won' },
+      result: { id: 'opp-1', name: 'Acme Renewal', stage: 'closed_won' },
+      __previous: { id: 'opp-1', name: 'Acme Renewal', stage: 'negotiation' },
+      session: {},
+    });
+
+    const activity = created.find((c) => c.object === 'sys_activity');
+    // Milestone summary wins over the "Stage: Negotiation → Closed Won" diff.
+    expect(activity?.row.summary).toBe('Deal won: Acme Renewal');
+    expect(activity?.row.type).toBe('completed');
+  });
+
+  it('does not fire the milestone when the field does not transition into the value', async () => {
+    const { engine, fire, created } = makeEngine(SCHEMA, OBJECT_DEFS);
+    installAuditWriters(engine as any, 'test.audit');
+
+    await fire('afterUpdate', {
+      object: 'crm_opportunity',
+      input: { id: 'opp-1', stage: 'negotiation' },
+      result: { id: 'opp-1', name: 'Acme Renewal', stage: 'negotiation' },
+      __previous: { id: 'opp-1', name: 'Acme Renewal', stage: 'proposal' },
+      session: {},
+    });
+
+    const activity = created.find((c) => c.object === 'sys_activity');
+    // Falls back to the field-change render (trackHistory), not the milestone.
+    // `proposal` has no option entry here → raw value; `negotiation` → its label.
+    expect(activity?.row.summary).toBe('Stage: proposal → Negotiation');
+  });
+});
diff --git a/packages/plugins/plugin-audit/src/audit-writers.ts b/packages/plugins/plugin-audit/src/audit-writers.ts
index 61c0f42515..d072403b0f 100644
--- a/packages/plugins/plugin-audit/src/audit-writers.ts
+++ b/packages/plugins/plugin-audit/src/audit-writers.ts
@@ -172,6 +172,39 @@ function renderTrackedChangeSummary(
   return parts.length > 0 ? parts.join('; ') : null;
 }
 
+/**
+ * ADR-0052 §5b.2 — declarative semantic milestones. If a watched field
+ * transitioned INTO a configured `value` on this update (before ≠ value, after =
+ * value), return the interpolated summary (and optional activity type). `{token}`
+ * in the template is replaced by the record's field value, resolving select
+ * option labels when possible. Returns null when no milestone fired (needs the
+ * `before` snapshot to detect a transition). Takes precedence over the raw
+ * field-change summary.
+ */
+function matchMilestone(
+  objectDef: any,
+  fields: Record<string, any> | null,
+  before: Record<string, any> | null,
+  after: Record<string, any> | null,
+): { summary: string; type?: string } | null {
+  const milestones =
+    objectDef && Array.isArray(objectDef.activityMilestones) ? objectDef.activityMilestones : null;
+  if (!milestones || !after || !before) return null;
+  for (const m of milestones) {
+    if (!m || typeof m.field !== 'string' || typeof m.summary !== 'string') continue;
+    if (after[m.field] === m.value && before[m.field] !== m.value) {
+      const summary = m.summary.replace(/\{(\w+)\}/g, (_match: string, key: string) => {
+        const v = after[key];
+        if (v === null || v === undefined || v === '') return '';
+        const field = fields ? fields[key] : undefined;
+        return field ? displayFieldValue(field, v) : String(v);
+      });
+      return { summary, type: typeof m.type === 'string' ? m.type : undefined };
+    }
+  }
+  return null;
+}
+
 /**
  * Install audit + activity writers on the given engine. Idempotent per
  * `packageId` — calling twice with the same id replaces the previous
@@ -240,6 +273,21 @@ export function installAuditWriters(
     return defs;
   };
 
+  // Cached full object definition (for ADR-0052 §5b.2 activityMilestones —
+  // object-level metadata, not just fields).
+  const objectDefCache = new Map<string, any>();
+  const getObjectDef = (objectName: string): any => {
+    if (objectDefCache.has(objectName)) return objectDefCache.get(objectName);
+    let def: any = null;
+    try {
+      def = typeof (engine as any).getSchema === 'function' ? (engine as any).getSchema(objectName) : null;
+    } catch {
+      /* ignore — best-effort */
+    }
+    objectDefCache.set(objectName, def);
+    return def;
+  };
+
   /**
    * beforeUpdate / beforeDelete: capture "previous" snapshot via api.sudo()
    * so we can compute the diff in the afterXxx hook. We attach the snapshot
@@ -361,20 +409,28 @@ export function installAuditWriters(
 
     const label = recordLabel(after ?? before, recordId ?? '');
     let summary: string;
+    let activityType: string = activityTypeFor(action);
     if (action === 'create') {
       summary = `Created ${ctx.object} "${label}"`;
     } else if (action === 'delete') {
       summary = `Deleted ${ctx.object} "${label}"`;
     } else {
-      // ADR-0052 §5b: if any changed field declares `trackHistory: true`, render
-      // the diff legibly ("Stage: Proposal → Closed Won"); else generic text.
-      summary =
-        renderTrackedChangeSummary(getFieldDefs(ctx.object), oldValue, newValue) ??
-        `Updated ${ctx.object} "${label}"`;
+      // ADR-0052 §5b — declarative activity, precedence: a configured semantic
+      // milestone (§5b.2) wins; else a tracked field-change diff ("Stage:
+      // Proposal → Closed Won", §5b.1); else the generic fallback.
+      const milestone = matchMilestone(getObjectDef(ctx.object), getFieldDefs(ctx.object), before, after);
+      if (milestone) {
+        summary = milestone.summary;
+        if (milestone.type) activityType = milestone.type;
+      } else {
+        summary =
+          renderTrackedChangeSummary(getFieldDefs(ctx.object), oldValue, newValue) ??
+          `Updated ${ctx.object} "${label}"`;
+      }
     }
 
     const activityRow: Record<string, any> = {
-      type: activityTypeFor(action),
+      type: activityType,
       // Explicit ISO timestamp — `defaultValue: 'NOW()'` on the column
       // isn't resolved by every driver and would otherwise leak the
       // literal string "NOW()" into the row.
diff --git a/packages/spec/liveness/object.json b/packages/spec/liveness/object.json
index cea730a9ff..c07a23b1ad 100644
--- a/packages/spec/liveness/object.json
+++ b/packages/spec/liveness/object.json
@@ -18,6 +18,7 @@
     "external": { "status": "live", "evidence": "packages/runtime/src/external-validation-plugin.ts", "note": "remote table + write gate." },
     "indexes": { "status": "live", "evidence": "packages/plugins/driver-sql/src/sql-driver.ts:1181", "note": "DDL." },
     "validations": { "status": "live", "evidence": "packages/objectql/src/validation/rule-validator.ts:154", "note": "incl. state_machine." },
+    "activityMilestones": { "status": "live", "evidence": "packages/plugins/plugin-audit/src/audit-writers.ts", "note": "ADR-0052 §5b.2 — audit-writer matchMilestone() emits a templated activity row when a watched field transitions into the configured value." },
     "actions": { "status": "live", "evidence": "packages/runtime/src/app-plugin.ts:929", "note": "served on /meta/objects/:name." },
     "managedBy": { "status": "live", "evidence": "packages/objectql/src/registry.ts:208", "note": "default perms; ui crudAffordances." },
     "userActions": { "status": "live", "note": "objectui ObjectGrid per-object CRUD." },
diff --git a/packages/spec/src/data/object.zod.ts b/packages/spec/src/data/object.zod.ts
index a189efcd01..a257134805 100644
--- a/packages/spec/src/data/object.zod.ts
+++ b/packages/spec/src/data/object.zod.ts
@@ -68,7 +68,7 @@ export const ObjectCapabilities = z.object({
   
   /** Enable standard Activity suite (Tasks, Calendars, Events) */
   activities: z.boolean().default(false).describe('Enable standard tasks and events tracking'),
-  
+
   /** Enable Recycle Bin / Soft Delete */
   trash: z.boolean().default(true).describe('Enable soft-delete with restore capability'),
 
@@ -523,6 +523,23 @@ const ObjectSchemaBase = z.object({
    */
   validations: z.array(ValidationRuleSchema).optional().describe('Object-level validation rules'),
 
+  /**
+   * Declarative semantic activity milestones (ADR-0052 §5b.2). When a watched
+   * field transitions INTO `value`, the platform emits a templated activity-row
+   * on the record timeline — no `*.hook.ts` / `*.flow.ts`. Complements field-level
+   * `trackHistory` (which renders raw "Field: old → new"): use milestones for
+   * business-meaningful events ("Deal won", "Task completed"). `summary` supports
+   * `{field}` tokens interpolated from the record; the milestone summary takes
+   * precedence over the field-change summary for the same update. Consumed by
+   * `@objectstack/plugin-audit` audit-writers (enforce-or-remove, ADR-0049).
+   */
+  activityMilestones: z.array(z.object({
+    field: z.string().describe('Field to watch (typically a status/stage select).'),
+    value: z.string().describe('The value the field must transition INTO to fire the milestone.'),
+    summary: z.string().describe('Activity summary template; {field} tokens interpolate the record value. e.g. "Deal won: {name}".'),
+    type: z.string().optional().describe('Activity type for the emitted row (default "completed").'),
+  })).optional().describe('Declarative semantic activity milestones — emit a templated timeline row when a field transitions into a value, no hook code (ADR-0052 §5b.2).'),
+
   // ADR-0020: record state machines are not a separate `stateMachines` map —
   // each lifecycle is a `state_machine` rule in `validations` above (one rule
   // per state field). Parallel lifecycles = multiple rules. The write path