[BUG] Standalone Go ADK agent (no KAGENT_URL) fails with "session not found" — in-memory session never created

[braghettos]

📋 Prerequisites

• I have searched the existing issues to avoid creating a duplicate
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🐛 Bug summary

Running the Go ADK agent (go/adk) without KAGENT_URL — i.e. standalone / BYO mode with in-memory sessions — fails on every message/send with session <id> not found, before any LLM call. The agent never produces a response.

Root cause

When KAGENT_URL is unset, the runner is configured with an in-memory ADK session service:

// go/adk/pkg/runner/adapter.go
var adkSessionService adksession.Service
if sessionService != nil {
    adkSessionService = sessionService
} else {
    adkSessionService = adksession.InMemoryService() // <- nobody creates sessions in this
}

But the A2A executor only creates the session when the kagent session service is wired:

// go/adk/pkg/a2a/executor.go — Execute()
if e.sessionService != nil {
    // ... GetSession / CreateSession ...
}
// (no else branch — in standalone mode the session is never created)

So runner.Run(ctx, userID, sessionID, ...) looks up a session that was never created and returns session <id> not found. The task ends in state failed.

Reproduction

1. Build the agent and run it with a minimal config.json (any provider) and no KAGENT_URL:

   CONFIG_DIR=./cfg PORT=8080 GOOGLE_CLOUD_PROJECT=... GOOGLE_CLOUD_LOCATION=us-central1 GOOGLE_GENAI_USE_VERTEXAI=1 ./agent
   # log: "No KAGENT_URL set, using in-memory session and no task persistence"
   

2. Send an A2A message:

   curl -sX POST -H 'content-type: application/json' \
     -d '{"jsonrpc":"2.0","id":"1","method":"message/send","params":{"message":{"role":"user","parts":[{"kind":"text","text":"hi"}],"messageId":"m1"}}}' \
     http://localhost:8080/
   

3. The task returns "state":"failed" with "session <contextId> not found".

Suggested fix

In Execute, when e.sessionService == nil, create the session in the runner's session service before running, e.g.:

} else if e.runnerConfig.SessionService != nil {
    _, _ = e.runnerConfig.SessionService.Create(ctx, &adksession.CreateRequest{
        AppName: e.appName, UserID: userID, SessionID: sessionID,
    })
}

(Verified locally: with this, standalone mode completes the LLM call and returns a response.)

🎯 Affected Service(s)

App Service (go/adk agent runtime)

[EItanya]

Thanks for filing. Currently BYO is not meant to work without kagent running, but #2171 should actually help with that.

[AdityaShome]

Traced this on current main (post-#2171), still reproduces.

session.NewService() returns nil, nil when neither dbURL nor kagentURL is set. That nil becomes the runner's sessionService, which falls back to a fresh adksession.InMemoryService(). But session creation only happens in executor.go's if e.sessionService != nil block skipped when nil, so the runner's in-memory service never gets a session created before runner.Run(...) looks it up.

#2171 added a third session-service option (sqlite LocalSessionService for durableDir sandbox agents) but didn't touch this "both nil" path, so plain standalone/BYO is still broken.

Happy to open a PR leaning toward resolving the nil session service once in CreateRunnerConfig so executor.go and the runner share one instance, rather than a second Create call. LMK if that direction's right or if standalone-without-kagent isn't meant to be supported.

[0809android]

This appears to be fixed on current main by #2385.

At 74321ee6, CreateRunnerConfig supplies adksession.InMemoryService() when no external session service exists. NewKAgentExecutor now stores runnerConfig.SessionService, and Execute calls ensureSession, which creates the session before delegating to the upstream runner.

That closes the missing-session path described here even when KAGENT_URL is unset. A focused regression test for the nil external-service case may still be useful, but I do not think a second implementation fix should be opened unless the current code still reproduces the failure.