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deepseek-harness/docs/architecture.md
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Hypatia May 8a8c1965d7 feat(web): show durable token usage and context occupancy in the stats line 
The chat stats line took its token totals from the loaded conversation nodes,
so paging changed them and compaction erased the billing behind replaced
content. It also had no way to show context occupancy: the numerator and
capacity never reached the browser.

Both now come from token-meter session projections read through the standard
useProjection seat. Window nodes keep supplying turn and step counts plus LLM
and tool wall times, which are correctly window-scoped facts about what is on
screen; accounting no longer comes from there.

`tokenUsage` supplies billing and cache hit. `contextPressure` supplies
occupancy, pairing the newest provider-reported prompt size with the newest
capacity recorded by `request/context`. Deployments without token-meter drop
the token groups; a route whose adapter advertises no capacity drops the
occupancy group rather than rendering a placeholder.

Occupancy is deliberately approximate: the numerator and capacity are
independent last-wins fields, not one atomic request observation, so switching
models pairs a fresh capacity with the prior route's pressure until the next
request reports usage. It is a user-facing reference figure that nothing in the
harness makes decisions from, and it matches how the TUI status line has always
computed occupancy. The Agent Note and token-meter README state this as a
decision, including why the atomic alternative was implemented and rejected, so
it is not re-litigated as a defect.

Snapshot delta is one added `Context N% of 128K` segment across eight web
goldens; the preceding commit absorbed master's pre-existing golden drift.
2026-07-30 14:48:19 +08:00

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# DeepSeek Harness Architecture
English | [中文](architecture.zh.md)
**DeepSeek Harness SDK** uses Cordis: **everything is a plugin**, including the loop.
## Overview
Harnesses are [Cordis](cordis-primer.md) contexts; packages contribute services, typed events, and disposable registrations.
`packages/core/` groups the default agent flow; capabilities remain plugins.
### Default Services
| ctx key | Package | Role |
|---|---|---|
| — | [`dsh-scope`](../packages/core/scope/README.md) | scoped-context registrations and shared layer storage (library) |
| `ctx.sessions` | `dsh-session` | in-memory event-sourced sessions |
| `ctx.systemPrompt` | `dsh-system-prompt` | ordered prompt sections, tool schemas, and variables |
| `ctx.tools` | `dsh-tools` | tool registry and [execution pipeline](tool-execution-pipeline.md) |
| `ctx.agents` | `dsh-agent` | live agents, delegated creation, `agent/*` events, process-local initiator scope |
| `ctx.agentLoop` | `dsh-agent-loop` | concrete `Agent` driver |
### Capability Services
| ctx key | Package family | Role |
|---|---|---|
| `ctx.llm` | [`llm/`](../packages/llm/README.md) | adapter registry, streaming model calls |
| `ctx.tokenMeter` | [`llm/token-meter`](../packages/llm/token-meter/README.md) | replay-aware request and surface pressure |
| `ctx.bash` | [`bash/`](../packages/bash/README.md) | foreground/background command execution |
| `ctx.subprocess` | [`subprocess/`](../packages/subprocess/README.md) | managed child-process trees for bash, LSP, and ACP subagent backends |
| `ctx.pty` | [`pty/`](../packages/pty/README.md) | owner-scoped persistent terminal sessions |
| `ctx.sandbox` | [`sandbox/`](../packages/sandbox/README.md) | same-world process confinement through argv wrapping and per-call policy |
| `ctx.sandboxPolicy` | [`sandbox/`](../packages/sandbox/README.md) | shared sandbox policy home |
| `ctx.codeRuntime` | [`code-runtime/`](../packages/code-runtime/README.md) | model-written program execution |
| `ctx.fs` | [`fs/`](../packages/fs/README.md) | filesystem provider primitives and policy events |
| `ctx.lsp` | [`lsp/`](../packages/lsp/README.md) | semantic navigation registry |
| `ctx.skills` | [`skill/`](../packages/skill/README.md) | skill provider registry, progressive disclosure |
| `ctx.web` | [`web/`](../packages/web/README.md) | search/fetch provider registries |
| `ctx.compact`, `ctx.toolResultPrune` | [`compact/`](../packages/compact/README.md)/[`compact-tool-result-prune`](../packages/compact/compact-tool-result-prune/README.md) | summary compaction, optional model-free result pruning |
| `ctx.subagents` | [`subagent/`](../packages/subagent/README.md) | named delegation providers |
| `ctx.planMode` | [`plan/`](../packages/plan/README.md) | logged plan collaboration state |
| `ctx.tasks` | [`tasks/`](../packages/tasks/README.md) | background task registry, generic `task_*` controls |
| `ctx.workflows` | [`workflow/`](../packages/workflow/README.md) | script-driven multi-agent orchestration |
| `ctx.goals` | [`goal/`](../packages/goal/README.md) | persisted same-session goals |
| `ctx.sessionPersistence` | [`session-persistence/`](../packages/session-persistence/README.md) | durable session-log storage |
| `ctx.sessionQuery` | [`session-query/`](../packages/session-query/README.md) | live-preferred exact/filter/trace queries over SQLite FTS, workspace-authorized model tools |
| `ctx.sessionTitle` | [`session-title/`](../packages/session-title/README.md) | log-backed fallbacks, one optional asynchronous provider |
| `ctx.directoryPicker` | [`host/directory-picker`](../packages/host/directory-picker/README.md) | GUI-host directory picking (`native`/`browse` interactions) |
| `ctx.typert` | [`typert/registry`](../packages/typert/registry/README.md) | runtime registry for generated package reflection and live Zod schemas |
| `ctx.invariants` | [`support/invariants`](../packages/support/invariants/README.md) | package-name-selected registry of package-owned runtime checks |
## Event
Events are the service extension API ([catalog](cordis-catalog/events.md), [producer/consumer map](event-producer-consumer.md)).
### Event Domains
- **Session events** are durable log facts emitted through `session/event`.
- **Agent events** carry live `Agent` for status, prompt admission, request shaping, validation, and continuation.
- **Capability events** let owning seams attach policy and adapters without a loop import.
### Interception Semantics
Waterfalls are around-middleware: listeners delegate with `next()`; returning without it vetoes or takes over ([semantics](cordis-primer.md#cordis-waterfall-semantics)).
## Default Loop Lifecycle
A **session** is append-only. An ordinary **turn** claims one queued `send()` item; injection claims none. A successor awaits its predecessor's checkpoint but may share its `running` interval ([decision](../.agents/notes/implemented/simplification/2026-07-17-one-send-one-turn.md)). A turn ends when model or plugins stop it; a **step** is one model request plus tools. Quotes in the [sequence below](agent-lifecycle.md) mark durable events.
Creation without an id mints `<config-id>-session-<uuid>`; `sessionId` resumes or creates, while `resumeSessionId` requires history. Resume restores lineage and delegation depth before publication. Setup failures emit `agent-loop/config-start-failed`; teardown is silent.
### Turn Flow
```text
choose declarative identity and fresh/resume path
-> prepare private session + agent.ctx -> await unpublished setup
-> enter session + agent -> session/created -> agent/created
-> enable driving -> agent/session-start(source) -> start driver
forever:
wait for queued occurrence
claim (edit/remove end) -> emit agent/status(running) if starting an interval
open the next-step acceptance window
-> agent/prompt-submit
blocked or failed prompt -> close the window without opening a turn
append a context-only caller batch immediately
keep steering and context staged beside it pending for a later admitted turn
allowed prompt:
'turn/start'
append prompt + additional contexts as separate 'user/message' events
STEP loop:
agent/step
drain injected context and steering (steering bypasses prompt-submit)
assemble system prompt and tool schemas
snapshot the derived messages (the reconstruction boundary)
'step/start'
agent/request (config only) -> prepare reasoning/default + context capacity under turn signal -> log request/header (+ request/context on route change) -> llm/stream (frozen, registration-bound)
'assistant/chunk'
'assistant/message'
schedule tool calls by ctx.tools.executionMode:
exclusive -> barrier
parallel -> rolling pool, <= maxParallelToolCalls; reclassify-at-start; scheduler failure -> stop starts, drain dispatches
start -> 'tool/call' -> ordered tools/pre-execute -> concurrent tools/execute
model-order result -> ordered tools/post-execute -> 'tool/result'
drain accepted tool context and steering
'step/end'
continue for tools or steering unless a result concluded the turn
otherwise agent/turn-stopping -> drain -> continue only for steering
close the next-step acceptance window
'turn/end' -> agent/settled
start the next waking queued message, or emit agent/status(idle)
idle inject:
append 'user/message'
do not open a turn or run the model
```
Each step assembles ordered prompt sections, tool schemas, and variables; unknown references fail the turn. `dsh-system-prompt` owns identity and persona; the loop supplies `provider`, `model`, and `cwd` ([prompt ownership](../.agents/notes/implemented/architecture/2026-07-05-prompt-variables-and-tool-guidance-ownership.md)).
Admission-time and active-turn `inject()` stage for the next step; post-tool `additionalContexts` settles after results. Steering shares that staging boundary and requests another step. Idle `inject()` appends immediately without changing turn numbers; persistence drains eagerly.
Pruning precedes summaries; overflow retries require durable progress. `agent/request-error` may authorize one retry turn between failed-step and turn close; cancellation wins. Adapter-owned `retryPolicy` makes normal mode bounded; always mode delegates specialized recovery before retrying until success or cancellation ([compaction](../.agents/notes/implemented/architecture/2026-07-10-after-call-compaction-pressure-and-overflow-recovery.md), [retry foundation](../.agents/notes/implemented/architecture/2026-06-21-bounded-llm-request-recovery.md), [provider policy](../.agents/notes/implemented/feature/2026-07-24-provider-retry-policies.md)).
### Failure Boundaries
Adapter failures close their step before `agent/request-error` receives the exact `Error`, normalized `LlmFailure`, and signal. A handled failure closes its turn and opens a retry turn from durable history without an idle notification; exhaustion leaves terminal `turn/end`. Failed chunks commit neither messages nor tool calls.
Other failures use `agent/error`. Cancellation and disposal beat recovery. Before request-header commit, the turn signal cancels asynchronous model-capability preparation; undispatched tools get synthetic `tool/call`/`ABORTED_BEFORE_DISPATCH` pairs. Effective `cancel(cause)` emits its cause before queue clearing and abort; observers cannot veto; idle calls emit nothing. Durability records user or parent cancellation as `aborted`, teardown as `disposed`; teardown awaits quiescence. The cause affects reporting, not late result-context handling ([decision](../.agents/notes/implemented/architecture/2026-07-16-explicit-turn-cancellation.md)).
Turn and step events are turn-enclosed; idle injected `user/message` events may sit between turns. Reload closes an interrupted tail with a synthetic turn end. After close, only `agent/error` reports failures. Each turn has one [TurnEndReason](core-data-structures/session.md#why-a-turn-ended-turnendreasonmap).
### Agent Handles
`ctx.agents` owns live agents and returns `AgentHandle { agent, dispose() }`. Plugins use full `send()` options or `followup()`, `steer()`, and `inject()` presets; `cancel()` and `whenIdle()` control lifecycle. One awaited disposer coordinates teardown ownership.
### Agent Scope
Each agent owns scoped `agent.ctx`; shared storage overlays its tool, prompt, and command entries on globals while preserving domain views ([decision](../.agents/notes/implemented/architecture/2026-07-12-scoped-layers-store.md)). Scoped listeners filter dispatch; contributions unwind with awaited cleanup. `CreateAgentOptions.setup(agentCtx)` composes before publication. Typed resolvers derive carrier checks from merged `Events` and `scopeTarget` ([semantic gates](../.agents/notes/implemented/process/2026-07-14-typescript-program-backed-semantic-gates.md)). Details: [agent scope](../.agents/notes/implemented/architecture/2026-07-08-agent-scope-contexts.md), [subagent composition](../.agents/notes/implemented/feature/2026-07-12-subagent-persona-tool-filter-and-depth.md). `AgentLoop` runs under `ctx.agents.withInitiator()`; private orchestration derives `agent.session`, but turn, step, signal, cwd, and authority stay explicit ([decision](../.agents/notes/implemented/architecture/2026-07-15-agent-initiator-scope.md)).
## State
### Session Log
The session log is authoritative. `deriveMessages()` projects model history; raw `assistant/chunk` events preserve replay and UI fidelity. Fork, resume, transcript rendering, telemetry, and persistence derive from this stream.
**Model-visible ⟺ logged**: messages at `step/start` plus the folded `request/header` reconstruct every request; package-owned `dsh-agent-loop/invariant` can assert this through `ctx.invariants` ([reconstructability](../.agents/notes/implemented/architecture/2026-07-05-reconstructable-requests.md)).
Durability is a plugin concern. Backends eagerly drain synchronous `session/event` notifications. `session/flush` barriers precede each request and top-level tool dispatch, then follow `turn/end` before another queued turn or idle observation. `SessionPersistence` stores `SessionEvent` directly and metadata in `SessionHeader`; JSONL defaults to checksummed Zstandard, while SQLite shares the contract ([decision](../.agents/notes/implemented/bug-fix/2026-07-21-semantic-session-checkpoints.md)).
Log-only events may sit between turns. Owners append through `Session`, flushing only for durability. `session/title` relies on eager persistence and lifecycle drains. Latest title wins with provenance; fallback and provider work never delays responses. Such records are fork boundaries, so forks inherit titles ([decision](../.agents/notes/implemented/feature/2026-07-21-log-backed-session-titles.md)).
### Model Content
Messages use typed blocks from merge-extensible `ContentBlockMap`; the pattern also types `MessageSource`, `FinishReason`, `TurnTrigger`, and `TurnEndReason`. New blocks coordinate adapters, UI, compaction, token metering, and persistence; replay measurements live in [token-meter.md](core-data-structures/token-meter.md).
Streaming uses raw chunks and `BlockAssembler`. Each `LlmAdapter.stream()` is one provider attempt; adapters report normalized failure facts, and a handling `agent/request-error` plugin returns a retry action. The loop logs chunks, successful provenance, and replay state. Remote adapters use per-read idle watchdogs. Replay crosses routes only through a shared adapter instance ([contract](core-data-structures/llm-streaming.md)).
## Extension And Composition
### Capability Pattern
A swappable capability usually has **interface / implementation / consumer** layers: service/events, backend, and model-facing tools/prompts. Bash is the reference; the [capability graph](capability-seams.md) maps each family.
Exceptions combine LLM interface/consumer, filesystem policy, web registries, and named skill/subagent providers. Subagents spawn fresh, fork a completed-turn prefix, or use ACP children ([subagent.md](core-data-structures/subagent.md)).
`dsh-workspace-context` injects baseline at the first `agent/step` and appends `ctx.fs`-discovered changes through `tools/post-execute`; its [decision](../.agents/notes/implemented/feature/2026-06-24-workspace-context.md) records isolation. `dsh-paths` owns shared paths.
### Bundles And Apps
`dsh-agent-spine-demo` bundles a spine and optional goals. App packages own TUI, CLI, ACP automation, and JSON-RPC front doors ([README](../packages/examples/agent-spine-demo/README.md), [acp/](../packages/acp/README.md), [ui/](../packages/ui/README.md)). `dsh-jsonrpc-agent` boots external `cordis.yml`; the Python SDK defaults when config is absent ([Python SDK](../python/README.md)). Thin deployments use swappable backends and optional tools ([examples/](../examples/AGENTS.md), [runnable wirings](cookbook/extension-cookbook.md#runnable-wirings), [graph atlas](graph-atlas.md)).
### Where New Behavior Goes
New behavior attaches to a documented extension point; a loop change updates this map.
| Goal | Mechanism |
|---|---|
| Add a model provider | register its adapter on `ctx.llm` |
| Add a model-facing capability | register on `ctx.tools`; schemas join prompt assembly |
| Add shell execution | implement and register a `ctx.bash` backend; the local backend spawns through `ctx.subprocess` |
| Add persistent terminal execution | register a `ctx.pty` backend plus `dsh-tool-pty` |
| Add a human command | register on `ctx.commands`; adapters discover and dispatch without a model turn |
| Add background work | register on `ctx.tasks`; generic `task_*` tools collect or stop it |
| Add filesystem access or policy | implement a `ctx.fs` provider or listen to `fs/*` policy events |
| Confine spawned processes | use a `ctx.sandbox` backend; consumers wrap argv before spawning |
| Intercept a request, tool, or turn | use its `agent/*` or `tools/*` event; `agent/turn-stopping` is the stop boundary |
| Add model-facing context | call `agent.inject()` to append a sourced `user/message` without a turn |
| Add UI or editor integration | drive `ctx.agents`, render from `session/event`; terminal-only overlays use `ctx.tui` |
| Add durable session state | extend `SessionEventMap`; render and replay from the log |
| Add asynchronous session-title generation | register the sole `ctx.sessionTitle` provider |
| Manage a same-session objective | use `ctx.goals`; continue through `Agent` and `agent/*` |
| Fork a live session | call `ctx.sessions.fork(source, boundary?, childSessionId?)` |
| Scope a registration to one agent | use its `agent.ctx` (see Agent Scope) |
The [extension cookbook](cookbook/extension-cookbook.md) has plugin skeletons and the feature-to-seam map; guides cover [packages](cookbook/adding-a-package.md), [tools](cookbook/adding-a-tool.md), [LLM adapters](cookbook/adding-an-llm-adapter.md), and [vendored packages](cookbook/adding-a-vendored-package.md).
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