---
title: internal/session/cassette/replayer
description: Go API reference for the replayer package.
---

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# replayer

```go
import "github.com/jbcom/radioactive-ralph/internal/session/cassette/replayer"
```

Package main is the cassette replayer binary.

When pointed at a cassette via RALPH\_CASSETTE\_PATH, it replays the recorded stream\-json frames to stdout and expects the same stdin sequence from the client. This lets tests use session.Session exactly as they would with a real \`claude \-p\` subprocess, without needing API credentials in CI.

Usage is identical to \`claude \-p\`:

```
session.Spawn(ctx, session.Options{
    ClaudeBin: ".../replayer",  // built from this package
})
```

The replayer:

- honors \-\-session\-id and \-\-resume by copying the value into the first "system"/init frame it emits \(so s.SessionID\(\) still observes a sensible value in replay mode\),
- waits for stdin to send each recorded "in" line before emitting the subsequent "out" frames \(ensures Send→Reply ordering matches\),
- falls back to a fast\-forward mode \(ignoring recorded timing\) when RALPH\_CASSETTE\_FAST=1 is set; otherwise it respects the recorded time offsets within a cap to avoid sleeping forever on slow cassettes.

## Index



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