diff --git a/lib/client/index.ts b/lib/client/index.ts
index df24b6b..e3b38e4 100644
--- a/lib/client/index.ts
+++ b/lib/client/index.ts
@@ -310,6 +310,8 @@ export interface SpawnAgentRequest {
   agentType: string;
   relatedAgentId?: string;
   input?: Record<string, unknown>;
+  /** Optional custom ID for the agent. If an agent with this ID exists, it will be resumed instead of created. */
+  id?: string;
 }
 
 export interface InvokeRequest {
@@ -497,7 +499,7 @@ export class AgencyClient {
   ) {}
 
   private get path(): string {
-    return `${this.baseUrl}/agency/${this.agencyId}`;
+    return `${this.baseUrl}/agency/${encodeURIComponent(this.agencyId)}`;
   }
 
   private async request<T>(
diff --git a/lib/runtime/agency.ts b/lib/runtime/agency.ts
index 7a313ad..0faf905 100644
--- a/lib/runtime/agency.ts
+++ b/lib/runtime/agency.ts
@@ -731,9 +731,10 @@ export class Agency extends Agent<AgentEnv> {
       requestContext?: ThreadRequestContext;
       input?: Record<string, unknown>;
       relatedAgentId?: string;
+      id?: string;
     };
 
-    return this.spawnAgent(body.agentType, body.requestContext, body.input, body.relatedAgentId);
+    return this.spawnAgent(body.agentType, body.requestContext, body.input, body.relatedAgentId, body.id);
   }
 
   private async handleDeleteAgent(agentId: string): Promise<Response> {
@@ -868,10 +869,51 @@ export class Agency extends Agent<AgentEnv> {
     agentType: string,
     requestContext?: ThreadRequestContext,
     input?: Record<string, unknown>,
-    relatedAgentId?: string
+    relatedAgentId?: string,
+    providedId?: string
   ): Promise<Response> {
-    const id = crypto.randomUUID();
+    const id = providedId || crypto.randomUUID();
     const createdAt = Date.now();
+    
+    // Check if agent with this ID already exists
+    if (providedId) {
+      const existing = this.sql<{ id: string }>`
+        SELECT id FROM agents WHERE id = ${providedId}
+      `;
+      if (existing.length > 0) {
+        // Agent exists - invoke it instead of creating
+        const stub = await getAgentByName(this.exports.HubAgent, providedId);
+        
+        if (input) {
+          const userMessage =
+            typeof input.message === "string"
+              ? input.message
+              : JSON.stringify(input);
+
+          await stub.fetch(
+            new Request("http://do/invoke", {
+              method: "POST",
+              headers: { "content-type": "application/json" },
+              body: JSON.stringify({
+                messages: [{ role: "user", content: userMessage }],
+              }),
+            })
+          );
+        }
+        
+        // Return existing agent info
+        const meta = this.sql<{ metadata: string; created_at: number }>`
+          SELECT metadata, created_at FROM agents WHERE id = ${providedId}
+        `[0];
+        
+        return Response.json({
+          id: providedId,
+          createdAt: new Date(meta.created_at).toISOString(),
+          agentType,
+          resumed: true,
+        }, { status: 200 });
+      }
+    }
 
     const meta = {
       request: requestContext,
diff --git a/lib/runtime/plugins/context.ts b/lib/runtime/plugins/context.ts
index 57c1cf8..f870e12 100644
--- a/lib/runtime/plugins/context.ts
+++ b/lib/runtime/plugins/context.ts
@@ -247,8 +247,8 @@ export const context: AgentPlugin = {
         const recentMessages = store.getMessagesAfter(checkpointEndSeq);
         plan.setMessages([
           {
-            role: "assistant",
-            content: `[Conversation Summary]\n${checkpoint.summary}`,
+            role: "user",
+            content: `[Previous Conversation Summary]\n${checkpoint.summary}\n\n---\nContinue from where we left off.`,
           },
           ...recentMessages.filter((m: ChatMessage) => m.role !== "system"),
         ]);
@@ -349,10 +349,11 @@ export const context: AgentPlugin = {
     });
 
     // Set messages for this request: summary + recent messages
+    // Use "user" role for summary since many LLMs don't allow starting with "assistant"
     plan.setMessages([
       {
-        role: "assistant",
-        content: `[Conversation Summary]\n${summary}`,
+        role: "user",
+        content: `[Previous Conversation Summary]\n${summary}\n\n---\nContinue from where we left off.`,
       },
       ...toKeep.filter((m: ChatMessage) => m.role !== "system"),
     ]);
diff --git a/lib/runtime/worker.ts b/lib/runtime/worker.ts
index d500aa2..87e1d45 100644
--- a/lib/runtime/worker.ts
+++ b/lib/runtime/worker.ts
@@ -156,7 +156,36 @@ const createAgency = async (req: IRequest, { env }: RequestContext) => {
 
 
 async function getAgencyStub(agencyId: string, ctx: CfCtx): Promise<DurableObjectStub<Agency>> {
-  return getAgentByName(ctx.exports.Agency, agencyId);
+  // Decode in case the agency ID contains slashes (e.g., "owner/repo")
+  const decodedId = decodeURIComponent(agencyId);
+  return getAgentByName(ctx.exports.Agency, decodedId);
+}
+
+/** Check if an agency exists (has been explicitly created via POST /agencies) */
+async function agencyExists(agencyId: string, env: HandlerEnv): Promise<boolean> {
+  if (!env.FS) return true; // No R2 bucket = skip check
+  const metaObj = await env.FS.head(`${agencyId}/.agency.json`);
+  return metaObj !== null;
+}
+
+/** 
+ * Require agency to exist before proceeding. Returns 404 Response if not found.
+ * Use in route handlers: const error = await requireAgency(...); if (error) return error;
+ */
+async function requireAgency(agencyId: string, env: HandlerEnv): Promise<Response | null> {
+  const decodedId = decodeURIComponent(agencyId);
+  const exists = await agencyExists(decodedId, env);
+  if (!exists) {
+    return new Response(
+      JSON.stringify({ 
+        error: "Agency not found",
+        message: `Agency '${decodedId}' does not exist. Create it first with POST /agencies`,
+        agencyId: decodedId,
+      }),
+      { status: 404, headers: { "content-type": "application/json" } }
+    );
+  }
+  return null;
 }
 
 const deleteAgency = async (req: IRequest, { ctx }: RequestContext) => {
@@ -190,12 +219,18 @@ const deleteBlueprint = async (req: IRequest, { ctx }: RequestContext) => {
   );
 };
 
-const listAgents = async (req: IRequest, { ctx }: RequestContext) => {
+const listAgents = async (req: IRequest, { ctx, env }: RequestContext) => {
+  const notFound = await requireAgency(req.params.agencyId, env);
+  if (notFound) return notFound;
+  
   const agencyStub = await getAgencyStub(req.params.agencyId, ctx);
   return agencyStub.fetch(new Request("http://do/agents"));
 };
 
-const createAgent = async (req: IRequest, { ctx }: RequestContext) => {
+const createAgent = async (req: IRequest, { ctx, env }: RequestContext) => {
+  const notFound = await requireAgency(req.params.agencyId, env);
+  if (notFound) return notFound;
+  
   const agencyStub = await getAgencyStub(req.params.agencyId, ctx);
   const body = await req.json<Record<string, unknown>>();
   body.requestContext = buildRequestContext(req);
@@ -293,12 +328,18 @@ const getScheduleRuns = async (req: IRequest, { ctx }: RequestContext) => {
 
 // --- Vars ---
 
-const getVars = async (req: IRequest, { ctx }: RequestContext) => {
+const getVars = async (req: IRequest, { ctx, env }: RequestContext) => {
+  const notFound = await requireAgency(req.params.agencyId, env);
+  if (notFound) return notFound;
+  
   const agencyStub = await getAgencyStub(req.params.agencyId, ctx);
   return agencyStub.fetch(new Request("http://do/vars"));
 };
 
-const setVars = async (req: IRequest, { ctx }: RequestContext) => {
+const setVars = async (req: IRequest, { ctx, env }: RequestContext) => {
+  const notFound = await requireAgency(req.params.agencyId, env);
+  if (notFound) return notFound;
+  
   const agencyStub = await getAgencyStub(req.params.agencyId, ctx);
   return agencyStub.fetch(
     new Request("http://do/vars", {
@@ -309,12 +350,18 @@ const setVars = async (req: IRequest, { ctx }: RequestContext) => {
   );
 };
 
-const getVar = async (req: IRequest, { ctx }: RequestContext) => {
+const getVar = async (req: IRequest, { ctx, env }: RequestContext) => {
+  const notFound = await requireAgency(req.params.agencyId, env);
+  if (notFound) return notFound;
+  
   const agencyStub = await getAgencyStub(req.params.agencyId, ctx);
   return agencyStub.fetch(new Request(`http://do/vars/${req.params.varKey}`));
 };
 
-const setVar = async (req: IRequest, { ctx }: RequestContext) => {
+const setVar = async (req: IRequest, { ctx, env }: RequestContext) => {
+  const notFound = await requireAgency(req.params.agencyId, env);
+  if (notFound) return notFound;
+  
   const agencyStub = await getAgencyStub(req.params.agencyId, ctx);
   return agencyStub.fetch(
     new Request(`http://do/vars/${req.params.varKey}`, {