deepseek-harness/packages/compaction/command-compact

description, kind

description	kind
The on-demand /compact command for interactive compositions: what it does, what you see, and how to mount it.	package-reference

@deepseek-ai/dsh-command-compact

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Summary

dsh-command-compact adds a /compact command to chat UIs: type it and the conversation condenses on demand — the older history is replaced by one summary even before automatic pressure triggers. The command works with any condensation backend and does not consume a model turn; after it finishes you see how many history items were condensed and the estimated tokens saved. While the agent is mid-turn or condensation is already running, it tells you condensation is unavailable. Prompts you send while it runs stay queued and start after it finishes.

Table of Contents

• Use this package
• Understand the implementation
• Further Exploration
• Model Experience
• Known Limitations and Deferred Work
• Dev Note

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Use this package

Type /compact in a chat UI when the conversation has grown long and you want to condense it immediately. The shipped dsh base mounts the command next to the default backend, so it is usually already available.

Using the command

Input	Result
/compact	Condense one useful balanced older span even below automatic pressure, then report the replaced history-item count and estimated tokens.
/compact with no compactable history	No compactable history yet. — nothing changes.
/compact <anything>	Usage: /compact (no arguments) — the command takes no arguments.

What you see

The command turns each expected failure into a stable message you can show directly; the situation on the left is what produced the message on the right.

Situation	Message you see
Compaction already running, or the agent is mid-turn	Compaction is unavailable because this process has an active compaction, or the agent is not idle.
The history changed while condensing	The history selected for compaction changed before it could be replaced. The attempt is recorded in the session log.
No useful summary could be produced	Compaction could not produce a useful summary. The attempt is recorded in the session log.
Condensation did not finish cleanly	Compaction did not finish cleanly; some session history may have changed. Inspect the current session state before retrying.
The conversation could not be saved	Compaction finished, but the session could not be saved.

Cancelling the command stops the wait: the backend finishes its required cleanup, and the command settles as Compaction cancelled. while the UI stops waiting. Failures other than these expected cases surface as errors rather than being silently converted.

Composing the command

Mount the command registry, one condensation backend, and this plugin:

- id: commands
  name: '@deepseek-ai/dsh-commands'
- id: compaction-basic
  name: '@deepseek-ai/dsh-compaction-basic'
- id: command-compact
  name: '@deepseek-ai/dsh-command-compact'

The shipped dsh base mounts it beside the default backend, and the Web client provides the command adapter. Automation surfaces that compose no command adapter keep automatic condensation only.

What happens to the conversation

When the command succeeds, the selected older span is replaced by one summary and the recent history is untouched; the command reports the number of condensed items and estimated tokens. Prompts you submit while condensation runs are accepted and start only after it finishes — they are not lost or reordered. The command lifecycle is recorded in the session log but never enters model history.

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Understand the implementation

Implementation internals — click to expand

This section explains the design decisions behind the command; the observable behavior is fully covered in Use this package.

Design philosophy

The command is built on three commitments:

• Backend-independent control. The handler depends only on compactNow(agent, signal), so it works with any CompactionEngine implementation. The invoking agent is the exact target, and the dispatching UI's cancellation signal is forwarded through the seam.
• The command lifecycle stays out of model history. command/run and command/done are log-only events; sourceEventSeq correlates the successful result with the compaction/summary event without relying on text or row adjacency.
• Quiescent teardown. The lifecycle effect unregisters /compact before draining already-started handlers, so an aborted command's close and flush work settles before root disposal completes.

Lifecycle and correlation

Every resolved invocation records the executor-owned log-only pair command/run / command/done; neither event joins model history. On success, command/done.sourceEventSeq names the transaction's compaction/summary event so a presentation can fold the command lifecycle into its checkpoint without parsing result text or assuming adjacent rows. The busy outcome is intentionally process-scoped: a live unmatched marker blocks, while a marker older than the newest session/end-seed is stale and does not. The plugin tracks each real handler promise and unregisters /compact before draining handlers that already started, so root teardown cannot pass an aborted command's close or flush boundary. Prompts submitted while compaction runs remain accepted in the agent's ordinary FIFO and start only after the compaction's explicit durability checkpoint and admission release; idle injected context may sit between compaction/start and compaction/end and stays visible after the checkpoint.

Source map

File	Role
src/index.ts	Plugin entry: /compact registration, argument rejection, error-code mapping, lifecycle drain

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Further Exploration

Read these pages when the package-level contract is not enough; they move from the command to the seam, the shipped backend, and the design decisions.

• Compaction seam — the condensation contract this command triggers.
• Compaction basic backend — the shipped backend that condenses automatically and on demand.
• Commands package — the registry and dispatch contract behind chat commands.
• Compaction subsystem reference — the condensation vocabulary, results, and service behavior.
• Queued manual compaction reference — how on-demand condensation serializes against running turns.

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Model Experience

Human /compact control

What the model sees

The slash input and direct result never enter a model request. An accepted compaction separately replaces an older span with the backend's user-role checkpoint inside a standalone compaction/* { turn: null } bracket.

Token effect

The command lifecycle adds no model tokens. A successful compaction reduces later requests by replacing the selected span with one framed summary; summarization itself is one auxiliary request.

KV Cache effect

Discovery and command bookkeeping do not affect the cache. The accepted surface replacement invalidates reuse from the first shadowed history token.

Known Limitations and Deferred Work

These limits define when the command is a poor fit; they are the current package constraints.

• Idle-only — /compact reports that condensation is unavailable when a turn or already accepted waking prompt has right of way; the command itself is not queued.
• No range or policy arguments — the argument-free form keeps behavior stable across command adapters. Explicit ranges remain the programmatic compactRegion() path.
• Command adapters only — surfaces without ctx.commands cannot invoke it and rely on automatic pressure compaction.

Dev Note

Working context for maintainers — click to expand

This Dev Note is working context for maintainers and is explicitly non-authoritative; shipped behavior lives in the sections above, the package code, and the linked Agent Notes.

• Queued commands, undecided — a /compact submitted while a turn has right of way reports busy; queuing the request instead of rejecting it remains an open direction.
• Range and policy arguments, undecided — argument-free stability is deliberate; adding arguments would need a shared grammar across every command adapter.