fix(agent-loop): reject duplicate configured identities

packages/core/agent-loop/src/index.ts

@@ -369,6 +369,24 @@ export interface Config {
   })[]
 }
 
+/** Reject self-contained identity conflicts before any configured agent starts. */
+function validateConfiguredAgents(agents: Config['agents']): void {
+  const exactIdentities = new Map<SessionId, string>()
+  for (const { id, sessionId, resumeSessionId } of agents) {
+    const hasResumeId = resumeSessionId !== undefined && resumeSessionId !== ''
+    if (sessionId !== undefined && hasResumeId) {
+      throw new Error(`agent "${id}": sessionId and resumeSessionId are mutually exclusive`)
+    }
+    const exactIdentity = hasResumeId ? resumeSessionId : sessionId
+    if (exactIdentity === undefined) continue
+    const firstId = exactIdentities.get(exactIdentity)
+    if (firstId !== undefined) {
+      throw new Error(`agents "${firstId}" and "${id}" use duplicate exact session identity "${exactIdentity}"`)
+    }
+    exactIdentities.set(exactIdentity, id)
+  }
+}
+
 /** Concrete ReactLoopAgent factory and driver service. */
 export class AgentLoop extends Service implements AgentFactory {
   static inject = ['agents', 'sessions', 'llm', 'tools', 'systemPrompt']
@@ -390,6 +408,7 @@ export class AgentLoop extends Service implements AgentFactory {
 
   constructor(ctx: Context, public config: Config) {
     super(ctx, 'agentLoop')
+    validateConfiguredAgents(config.agents)
     this.ownership = new FactoryOwnership(ctx.fiber)
     this.runtime = { ctx }
     ctx.effect(() => () => this.ownership.dispose(), 'agentLoop.transactions()')
@@ -412,9 +431,6 @@ export class AgentLoop extends Service implements AgentFactory {
         }
         continue
       }
-      if (sessionId !== undefined) {
-        throw new Error(`agent "${id}": sessionId and resumeSessionId are mutually exclusive`)
-      }
       ctx.effect(() => {
         const fiber = ctx.inject(['sessionPersistence'], (childCtx: Context) => {
           void this.resumeWith(ctx, childCtx.sessionPersistence, {

packages/core/agent-loop/tests/config-session-id.spec.ts

@@ -64,6 +64,25 @@ describe('config-driven session id', () => {
     await conflicting.fiber.dispose()
   })
 
+  it('rejects duplicate exact ids before asynchronous configured startup', async () => {
+    const root = await mkdtemp(join(tmpdir(), 'dsh-cfg-exact-duplicate-'))
+    dirs.push(root)
+    const ctx = await makeCoreContext()
+    await ctx.plugin(SessionPersistenceJsonl, { root })
+
+    const outcome = await ctx.plugin(AgentLoop, {
+      agents: [
+        { id: 'first', sessionId: SessionId('shared'), model: 'mock' },
+        { id: 'second', sessionId: SessionId('shared'), model: 'mock' },
+      ],
+    }).then(() => undefined, (error: unknown) => error)
+    const published = ctx.agents.get(SessionId('shared'))
+    await ctx.fiber.dispose()
+
+    expect(outcome).toEqual(new Error('agents "first" and "second" use duplicate exact session identity "shared"'))
+    expect(published).toBeUndefined()
+  })
+
   it('restores a materialized exact id across an AgentLoop-only reload', async () => {
     const root = await mkdtemp(join(tmpdir(), 'dsh-cfg-exact-reload-'))
     dirs.push(root)