diff --git a/src/container-runner.test.ts b/src/container-runner.test.ts
new file mode 100644
index 000000000..cd18a7289
--- /dev/null
+++ b/src/container-runner.test.ts
@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest';
+
+import { resolveProviderName } from './container-runner.js';
+
+describe('resolveProviderName', () => {
+  it('prefers session over group and container.json', () => {
+    expect(resolveProviderName('codex', 'opencode', 'claude')).toBe('codex');
+  });
+
+  it('falls back to group when session is null', () => {
+    expect(resolveProviderName(null, 'codex', 'claude')).toBe('codex');
+  });
+
+  it('falls back to container.json when session and group are null', () => {
+    expect(resolveProviderName(null, null, 'opencode')).toBe('opencode');
+  });
+
+  it('defaults to claude when nothing is set', () => {
+    expect(resolveProviderName(null, null, undefined)).toBe('claude');
+  });
+
+  it('lowercases the resolved name', () => {
+    expect(resolveProviderName('CODEX', null, null)).toBe('codex');
+    expect(resolveProviderName(null, 'OpenCode', null)).toBe('opencode');
+    expect(resolveProviderName(null, null, 'Claude')).toBe('claude');
+  });
+
+  it('treats empty string as unset (falls through)', () => {
+    expect(resolveProviderName('', 'codex', null)).toBe('codex');
+    expect(resolveProviderName(null, '', 'opencode')).toBe('opencode');
+  });
+});
diff --git a/src/container-runner.ts b/src/container-runner.ts
index fca88c490..029b5fe3d 100644
--- a/src/container-runner.ts
+++ b/src/container-runner.ts
@@ -191,12 +191,31 @@ export function killContainer(sessionId: string, reason: string): void {
   }
 }
 
+/**
+ * Resolve the provider name for a session using the precedence documented in
+ * the provider-install skills:
+ *
+ *   sessions.agent_provider
+ *     → agent_groups.agent_provider
+ *     → container.json `provider`
+ *     → 'claude'
+ *
+ * Pure so the precedence can be unit-tested without a DB or filesystem.
+ */
+export function resolveProviderName(
+  sessionProvider: string | null | undefined,
+  agentGroupProvider: string | null | undefined,
+  containerConfigProvider: string | null | undefined,
+): string {
+  return (sessionProvider || agentGroupProvider || containerConfigProvider || 'claude').toLowerCase();
+}
+
 function resolveProviderContribution(
   session: Session,
   agentGroup: AgentGroup,
   containerConfig: import('./container-config.js').ContainerConfig,
 ): { provider: string; contribution: ProviderContainerContribution } {
-  const provider = (containerConfig.provider || 'claude').toLowerCase();
+  const provider = resolveProviderName(session.agent_provider, agentGroup.agent_provider, containerConfig.provider);
   const fn = getProviderContainerConfig(provider);
   const contribution = fn
     ? fn({