Genkit Flows as senro Steps: Extremely Powerful AI Pipelines in Go

Introduction

A Genkit flow is an excellent unit of AI work. It is typed, traced, testable, and genkit.DefineFlow gives you something you can call from anywhere.

What a flow is not is a unit of orchestration. The moment you have twelve documents to summarise, a flow whose output feeds two other flows, or a model call that fails on the third of forty items, you end up writing the same scaffolding again: a worker pool, a retry loop, a way to avoid re-running the eleven items that already succeeded, logs you can actually read, and some way to find out what happened at three in the morning.

senro is a pipeline engine where a step already has all of that: retries that distinguish infrastructure from workload, an action cache that skips work it has already done, an append-only event stream, and a live attach protocol. I covered it in the introduction and the monorepo article.

This article shows how to combine them. Put a Genkit flow inside a senro step and every model call becomes a graph node with its own log, state, retry policy and cache entry.

Every example below ran against the real Gemini API with googleai/gemini-2.5-flash, on Genkit Go v1.13.1 and senro v1.4.0. The summaries are what the model actually returned.

What you need

go get github.com/firebase/genkit/go
go get github.com/xavidop/senro

The example is a small corpus of release notes in docs/*.md that gets summarised one document at a time, then merged into a digest.

Step 1: the flow

Nothing senro-specific here. This is an ordinary Genkit flow:

// SummarizeInput is what the summarize flow takes.
type SummarizeInput struct {
    Path string `json:"path"`
    Text string `json:"text"`
}

// Summary is what it returns.
type Summary struct {
    Path    string `json:"path"`
    Summary string `json:"summary"`
}

func defineFlows(g *genkit.Genkit) *core.Flow[SummarizeInput, Summary, struct{}] {
    return genkit.DefineFlow(g, "summarize",
        func(ctx context.Context, in SummarizeInput) (Summary, error) {
            text, err := genkit.GenerateText(ctx, g,
                ai.WithSystem("You summarize release notes for an operator. "+
                    "Answer in one sentence, no preamble."),
                ai.WithPrompt(fmt.Sprintf("Summarize these release notes:\n\n%s", in.Text)))
            if err != nil {
                return Summary{}, err
            }
            return Summary{Path: in.Path, Summary: text}, nil
        })
}

Called on its own it does what you expect:

The billing reconciliation job was moved to a queue worker, accelerating invoice
settlement from up to 24 hours to within two minutes.

Step 2: wrap the flow in a step

senro has two kinds of step: a command, and a registered Go function. A Genkit flow is a Go function, so it is the second kind:

// summarize is the registered flow. A func step runs in the pipeline's own
// process, so a package-level handle is all the wiring the two need.
var summarize *core.Flow[SummarizeInput, Summary, struct{}]

type SummarizeParams struct {
    Path string `json:"path"`
    Name string `json:"name"`
}

func init() { senro.RegisterFunc("ai/summarize", RunSummarize) }

// RunSummarize runs the flow and writes the summary into the one workspace
// this step mounts.
func RunSummarize(ctx senro.Ctx, p SummarizeParams) error {
    dir, ok := ctx.Workspace("doc-" + p.Name)
    if !ok {
        return fmt.Errorf("step %s mounts no doc-%s workspace", ctx.StepID(), p.Name)
    }

    text, err := os.ReadFile(filepath.Join(string(dir), "doc.md"))
    if err != nil {
        return err
    }

    res, err := summarize.Run(ctx, SummarizeInput{Path: p.Path, Text: string(text)})
    if err != nil {
        return err
    }

    fmt.Fprintf(ctx.Stdout(), "%s\n", res.Summary)
    return os.WriteFile(filepath.Join(string(dir), "summary.txt"), []byte(res.Summary+"\n"), 0o644)
}

Three details make this work smoothly:

senro.Ctx embeds context.Context, so it passes straight into summarize.Run with no adapter. Genkit's tracing and cancellation behave exactly as they always did.
ctx.Stdout() is the step's real log stream, recorded and redacted like a command's output. Writing to os.Stdout instead reaches your terminal and no log file.
ctx.Workspace(name) hands the function the same path a mount gives a command, on every executor. The function body does not change when the step later runs in a container or a pod.

RegisterFunc registers the function once, from an init. The name is the function's identity: it is what the plan records and what feeds the step's cache key, so renaming it invalidates the cache exactly as renaming a command would. Parameters must be JSON-serializable, and decoding is strict, so a renamed field fails loudly instead of running with a zero value.

Step 3: build the graph

Because the pipeline is a Go program, fanning out over a corpus is a for loop:

func main() {
    ctx := context.Background()

    g := genkit.Init(ctx,
        genkit.WithPlugins(&googlegenai.GoogleAI{}),
        genkit.WithDefaultModel("googleai/gemini-2.5-flash"))
    summarize = defineFlows(g)

    docs, err := filepath.Glob("docs/*.md")
    if err != nil {
        log.Fatal(err)
    }
    sort.Strings(docs)

    p := senro.New("ai")
    w := p.Workflow("summarize")

    var names, ids []string
    var wss []*senro.WorkspaceRef
    corpus := map[string]string{}

    for _, doc := range docs {
        text, err := os.ReadFile(doc)
        if err != nil {
            log.Fatal(err)
        }
        name := strings.TrimSuffix(filepath.Base(doc), ".md")
        names = append(names, name)
        ids = append(ids, "summarize/"+name)
        corpus[name] = string(text)

        // One workspace per document, so one document changing does not
        // invalidate the other summaries' cache keys.
        wss = append(wss, senro.Workspace("doc-"+name, senro.Scope(senro.ScopeRun)))
    }

    seed := w.Step("seed", senro.Func("ai/seed", SeedParams{Docs: corpus}))
    for i, ws := range wss {
        seed.Mount(ws.At("/doc-"+names[i], senro.RW))
    }

    for i, name := range names {
        // One AI call, one node: its own log, state, retry and cache entry.
        w.Step(ids[i], senro.Func("ai/summarize", SummarizeParams{
            Path: docs[i],
            Name: name,
        })).
            Needs("seed").
            Mount(wss[i].At("/doc", senro.RW)).
            Retry(3, retry.OnInfra()).
            Pure().
            Inputs(artifact.File("doc.md")).
            Outputs(artifact.File("summary.txt"))
    }

    digestStep := w.Step("digest", senro.Func("ai/digest", DigestParams{Names: names})).
        Needs(ids...)
    for i, ws := range wss {
        digestStep.Mount(ws.At("/doc-"+names[i], senro.RO))
    }

    if err := senro.Run(ctx, p); err != nil {
        log.Print(err)
        os.Exit(1)
    }
}

seed writes each document into a workspace of its own. Then one summarize step per document, running in parallel. Then digest, which waits for all of them and merges the results.

That loop produces this graph, rendered straight from the run's own plan.json:

pipeline: ai
  │
  ├─ wave 1                seed                  func
  │
  ├─ wave 2 (3 parallel)   summarize/alpha       func · retry 3/infra
  │                        summarize/beta        func · retry 3/infra
  │                        summarize/gamma       func · retry 3/infra
  │
  └─ wave 3                digest                needs summarize/alpha, summarize/beta,
                                                 summarize/gamma · func

Three documents give three parallel nodes. Thirty would give thirty, from the same for loop, with no change to the code.

Step 4: run it

Run the pipeline binary directly, the way any Go program runs:

go run .

Or hand the package to the senro CLI, which builds it, execs it and attaches automatically. You get a terminal UI on a TTY and plain streaming lines anywhere else:

senro run .

seed             -> succeeded
summarize/beta   -> succeeded
summarize/alpha  -> succeeded
summarize/gamma  -> succeeded
digest           -> succeeded

- alpha: The billing reconciliation job now uses a queue worker for invoice settlement
  within two minutes, replacing the nightly cron.
- beta: The search index now rebuilds incrementally in under a second without blocking
  writes, replacing the old full rebuild and requiring operators to delete the
  `rebuild-search` cron job.
- gamma: Service gamma's public API now features per-tenant rate limiting set at 100
  requests per second, which may cause HTTP 429 errors for existing bursting integrations.

Three real model calls in parallel, each with its own log file, and a merge step that ran once they were all done.

While that is running, a second terminal can watch it, or steer it:

senro attach          # terminal UI
senro ui              # browser view, prints a one-time link
senro attach --run <id>   # reopen a finished run from disk

Every run also lands in runs/<id>/, so senro runs lists what happened and each step's stdout is a file you can read afterwards.

One thing to know when you switch between go run and senro run. A func step's cache key includes the binary digest, so the first run after changing how the binary is built re-runs every func step once, then caches normally from there. That is correct behaviour rather than a bug: the function's body lives in the binary, and senro cannot tell whether it changed without hashing it.

Step 5: stop paying for the same call twice

Each summarize step declares Pure(). Run the pipeline again with nothing changed:

seed             -> succeeded
summarize/beta   -> cached
summarize/alpha  -> cached
summarize/gamma  -> cached
digest           -> succeeded

cached is a real state, not a label. Those three steps did not execute: no model call, no tokens, no latency. Their recorded outputs were restored from the content-addressed store, so digest still read three summaries and produced the same result.

Now change one document out of three:

seed             -> succeeded
summarize/alpha  -> cached
summarize/beta   -> cached
summarize/gamma  -> succeeded
digest           -> succeeded

One document changed, one model call made. And senro will tell you which component of the key moved:

$ senro cache explain --run <id> summarize/gamma
MISS  summarize/gamma  key d3eb7450 (previous f68652ad)
  ✗ input_digests: docs/gamma.md  6750cb09 → ef0fdb64
  ✗ workspace_digests: doc-gamma  16774a4e → d43e13c8
  ✓ command, env, secrets, executor_class, platform, mount_shape, step_shape, func_identity,
    tool_versions, version unchanged

For a few dozen documents this is a convenience. For a nightly re-index over ten thousand where one file changed, it is the difference between a bill you notice and one you do not.

Note func_identity in that list. For a func step the cache key covers the binary digest, the registered name and the parameter digest. So changing your prompt, your model or the flow's code all correctly invalidate the cache. It is not keyed on the input file alone, which is the mistake a hand-rolled cache usually makes.

Give each call its own workspace

This is the one structural rule to follow when caching model calls.

Inputs feeds the input_digests component of the key, but Mount feeds workspace_digests, which is the digest of the entire mounted workspace. Narrow Inputs do not narrow it.

Mount one shared tree across a fan-out and every step's key depends on every document, so changing one document re-runs all of them and the cache buys you nothing. One workspace per unit of work, as in the loop above, keeps each key dependent on its own input.

Step 6: let a model explain a failure

senro has a second place a model belongs: explaining a failed step. contrib/genkitanalyzer is a ready-made failure analyzer built on Genkit:

go get github.com/xavidop/senro/contrib/genkitanalyzer

It is a nested module with its own go.mod, so senro itself never pulls in an AI SDK. If you never install it, your dependency graph never hears about Genkit.

g := genkit.Init(ctx, genkit.WithPlugins(&googlegenai.GoogleAI{}))

p := senro.New("analyze")
w := p.Workflow("build")
w.Step("migrate", exec.Command("sh", "-c",
    `echo "dial tcp 10.0.3.7:5432: connect: connection refused" >&2; exit 1`))

err := senro.Run(ctx, p,
    senro.WithAnalyzer(
        genkitanalyzer.New(g, genkitanalyzer.Model("googleai/gemini-2.5-flash")),
        senro.AnalyzerName("genkit"),
        senro.AnalyzeTimeout(20*time.Second)))

That is the whole integration. When the step fails, an analysis.proposed event lands in the run's ledger:

{
 "id": "migrate@1",
 "analyzer": "genkit",
 "duration_ns": 8344562458,
 "summary": "The 'migrate' step failed because its command explicitly reported a database
             connection refusal error and exited.",
 "detail": "... The error message \"dial tcp 10.0.3.7:5432: connect: connection refused\"
            typically indicates that a client attempted to establish a TCP connection to a
            server at 10.0.3.7 on port 5432, but the server actively rejected the connection.
            This could be due to the database server not running, not listening on the
            specified address/port, or being blocked by a firewall ..."
}

Because it is an event, the explanation shows up in the TUI, in events.jsonl, and in anything else folding the run.

What the combination gives you

Genkit gives you the model call: typed, traced, provider-agnostic, testable. senro gives you everything around it.

Concern	What senro already does for a step
Ordering	A dependency edge, not a place in a loop
Outcome	Ten states, so a call that passed on the second attempt is `recovered`, not silently a success
Retries	`retry.OnInfra()` retries a dropped connection, never a model answer you did not like
Logs	One log file per step per attempt, redacted
Cost	An action cache keyed on the prompt, parameters, model and binary
Observability	One append-only event stream you can attach to live or replay later
Failure analysis	An analyzer gated behind a human or an explicit policy

You can build every one of those yourself. It is never quite the same twice, and it is rarely tested well.

Conclusion

The pattern is small enough to summarise in four lines:

Define the flow with genkit.DefineFlow as you always would.
Register a func step with senro.RegisterFunc that calls flow.Run(ctx, ...).
Give each call its own workspace and declare Pure() with Inputs and Outputs.
Add senro.WithAnalyzer if you want failures explained.