dsh-replay-theater
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Replay a DeepSeek Harness session at its original token cadence — an in-app playback theater with play, pause, single-step, speed and seek.
Not a static timeline: the assistant's answer grows token by token, spaced by the real millisecond gaps recorded when it was generated.
The Theater tab replaying a recorded session
More screenshots — transport controls, and side-by-side comparison
Transport bar and marker rail. Play/pause, single-step, restart, scrub, speed, and a
"max pause" ceiling. Scalar events (step/start, tool/result, …) sit on their own rail, and
the bar states how much silence was compressed — playback alters timing, so it says so.
Transport controls and the marker rail
Side-by-side comparison (v2). Load a recorded session.jsonl next to the live one and the
theater reports where the two runs stop matching, with a seek coordinate for each side.
Two runs compared, with the first divergence highlighted
Why this exists
Upstream keeps every token's real inter-arrival gap in the session log, and says why:
// packages/core/session/src/chunk-rows.ts:44
/** Epoch-ms gaps between consecutive members; length is one less than the member count. */
dt: number[]
"one entry per member, never joined — token boundaries are data" — chunk-rows.ts:48
Packed storage deliberately does not join a run's members into one string, so the cadence survives. Nothing in the harness used that data. This plugin does.
Install
dsh plugin --profile web add dsh-replay-theater
Or from a checkout:
dsh plugin --profile web add "github:ItBayMax/dsh-replay-theater#main"
The package declares dsh.bundle, so the CLI reconciles it into the profile's layer list automatically — no manual cordis.patch.yml edit. Restart dsh web and open a session: a Theater tab appears beside Chat and Trajectory.
Use
| Control | Behavior |
|---|
| ▶ / ❚❚ | Play or pause. Playing at the end restarts from the beginning. |
| ⏴ / ⏵ | Step one frame (one token) back or forward. Stepping pauses. |
| ⤾ | Restart, paused, keeping the chosen speed. |
| Scrub | Seek to an absolute position. |
| Speed | 0.5× to 8×. |
| Max pause | Compress silences longer than this (200 ms … ∞). ∞ keeps true wall-clock cadence. |
| Load earlier history | Page one older window in. Playback keeps its position. |
When any silence was compressed, the transport bar says so and by how much. Playback alters the data's timing, so it tells you.
What it replays
Everything the browser's session window holds: assistant text, reasoning, and tool-call arguments — each as its own stream — plus scalar events (step/start, tool/result, …) as markers.
Tool calls show as accumulating JSON plus the tool name, not as full tool cards. Cards are ui-tool's job; this plugin is about cadence.
Limits
- No random access. The dsh client cannot request an arbitrary sequence: history pages backwards only, one window at a time (
session.loadOlder()), and a production tail page can hold hundreds of thousands of events. So the theater replays the loaded window and gives you an explicit "load earlier" action rather than silently pulling an entire log into the browser.
- Long silences are compressed by default (2000 ms ceiling). Set
∞ for true cadence.
- Live sessions grow under you. The window is followed, and playback keeps its position when frames are appended.
- Types are mirrored, not imported.
@deepseek-ai/dsh-api-session-controller is not published to npm, so src/core/wire.ts and src/client/dsh.ts carry structural mirrors of the upstream shapes, each annotated with the file:line it was read from (pinned to dsh 0a53fb5 / 0.1.2-alpha.2). They are structurally compatible, so swapping them for real imports later needs no call-site changes.
Compatibility
Developed against dsh 0.1.2-alpha.2 (upstream commit 0a53fb5). It reads only the public client surface — session.eventSource and session.loadOlder() — because upstream removed an entire client package (client/runtime) in 0.1.2; depending on internals is not survivable.
Development
npm install
npm test # 158 tests
npm run typecheck
The replay core (src/core/) is framework-free and dsh-free, so its rules are unit-tested without a browser or a harness checkout:
npx vitest run tests/timeline.spec.ts tests/player.spec.ts
Test fixtures come in two kinds, for a documented reason:
tests/fixtures/synthetic.ts — hand-built records with exact dt arrays. Cadence assertions live here.tests/fixtures/corpus-*.json — derived from an upstream recorded session by make-corpus-fixture.mjs, to prove the wire mirror accepts real shapes. It cannot carry cadence assertions: the upstream corpus normalizes seq/time away, and the longest consecutive same-block delta run in all 118 snapshot sessions is 2 members.
See docs/ for the architecture and per-phase implementation notes.
Offline CLI
The replay core is framework-free, so the same functions the browser tab uses also work in a script:
npm run build
node scripts/replay-cli.mjs path/to/session.jsonl --frames 20
node scripts/replay-cli.mjs run-a.jsonl run-b.jsonl # compare two runs
Comparing two upstream snapshots, for example, reports where they stop matching:
comparison: diverged at frame 14 (marker-type), left seq 15 / right seq 15
License
MIT
