feat(events): interception seams — the typed-Decision surface for hooks

Reshape the agent's interception surface so every seam returns a small, typed
Decision union, and the set covers the hook points a CC/Codex bridge (and a
native plugin) needs. "Native hooks" are not a package — a native hook is just a
cordis plugin on these canonical events; the bridges (a later PR) only translate
an external protocol onto the same surface.

dsh-agent:
- NEW agent/session-start(agent, source) emit (once before turn 1; SessionStartSource
  startup|resume|clear|compact) — a pure notification, seeds context via inject().
- NEW agent/prompt-submit waterfall → PromptDecision (allow, optionally rewriting the
  prompt or attaching additionalContext, or block).
- RESHAPE agent/turn-continuation boolean → ContinuationDecision ({action:'stop'} |
  {action:'continue', reason?}; a continue reason is recorded as next-step steering).
- New HookContext envelope (required source — inject() would mislabel a missing one).

dsh-tools: split the single tools/execute waterfall into tools/pre-execute
(PreToolDecision allow/deny/ask gate) and tools/post-execute (PostToolDecision
accept/block, optionally replacing content or attaching additionalContext). Core
dispatch sits between as plain code; the tool body keeps its inner try/catch so a
thrown tool still reaches post-execute as an isError. ToolExecutionResult gains
additionalContext (ferried to the loop's per-step buffer). Input rewrite is
deliberately NOT offered (a proposed RFC designs it consistently).

dsh-session: new `rejected` TurnEndReason — a turn whose whole prompt batch was
blocked by prompt-submit.

agent-loop firing points: session-start emitted at create (source threaded —
startup for create/fork, resume for resume()); prompt-submit per drained message
with the always-open-turn rule (a fully-blocked batch is a zero-step rejected
turn); the continuation reshape; post-tool additionalContext buffered and appended
after all tool/results (adjacency). ACP codec maps rejected→cancelled.

A worked native-plugin example (interception.spec.ts) proves all four seams compose
end-to-end through the real loop with NO hook/* events (those belong to the bridge
lib). All existing tools/execute + turn-continuation tests migrated. The
tool-subagent abort test now aborts after a microtask so it still exercises the
live onAbort bridge (execute() awaits pre-execute before the body runs).

RFCs: implemented/feature/2026-06-30-interception-seams.md (the reshape) +
proposed/feature/2026-06-30-pre-tool-input-rewrite.md (the deferred rewrite design).
This commit is contained in:
Tianyi Cui
2026-06-30 17:11:18 +08:00
parent 13c6e847a2
commit dc95a7881d
28 changed files with 1255 additions and 146 deletions

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@@ -69,7 +69,7 @@ Swappable capabilities are split into **three packages** so each part evolves in
The LLM seam has the same topology folded differently: `dsh-llm` carries the interface (`LlmAdapter`) AND the consumer surface (`ctx.llm.stream()`), with adapters as implementation packages — there the consumer is the loop itself, not a swappable schema surface. Use the full three-package split when the consumer is independently replaceable; keep interface + consumer together when they are one concern. Don't split preemptively: a capability with one conceivable implementation and one consumer stays one package until proven otherwise.
> **"Capability" — two unrelated meanings.** (1) The *seam pattern* above ("one plugin provides a capability, another needs it") is realized by plain Cordis **services + `inject`**: a provider registers a service (`ctx.bash`, declared in `interface Context`); a consumer declares `inject: ['bash']` and its fiber stays pending until the service exists, tearing down via HMR if it later vanishes. No extra library is needed. (2) `@cordisjs/plugin-capability` is a different axis entirely — a **permission/capability-security** service (named permissions with inheritance/dependency, tested against a session via `ctx.capability.test`). It is a candidate for the deferred permissions/sandbox work (the `tools/execute` veto seam), NOT a mechanism for swapping implementations.
> **"Capability" — two unrelated meanings.** (1) The *seam pattern* above ("one plugin provides a capability, another needs it") is realized by plain Cordis **services + `inject`**: a provider registers a service (`ctx.bash`, declared in `interface Context`); a consumer declares `inject: ['bash']` and its fiber stays pending until the service exists, tearing down via HMR if it later vanishes. No extra library is needed. (2) `@cordisjs/plugin-capability` is a different axis entirely — a **permission/capability-security** service (named permissions with inheritance/dependency, tested against a session via `ctx.capability.test`). It is a candidate for the deferred permissions/sandbox work (the `tools/pre-execute` deny/ask gate), NOT a mechanism for swapping implementations.
## The vocabulary (dsh-llm)
@@ -102,7 +102,7 @@ Tool schemas are deliberately **part of the assembly**: "what the model is told
`ToolRegistry.register()` takes schema + `execute()`. The registry feeds its schemas into the system-prompt assembly automatically.
`execute()` runs through the **`tools/execute` waterfall** — the single seam where sandbox, permission, hooks, and plan-mode plugins wrap or veto a call. This collapses Claude Code's validate → PreToolUse → permission → execute → PostToolUse pipeline into ordered waterfall listeners.
`execute()` runs through a **two-waterfall pipeline**`tools/pre-execute` (the allow/deny/ask gate) → core dispatch → `tools/post-execute` (inspect/replace the result, attach context) — the seams where sandbox, permission, hooks, and plan-mode plugins gate or transform a call. This maps Claude Code's validate → PreToolUse → permission → execute → PostToolUse pipeline onto two ordered waterfalls: `pre-execute` returns a `PreToolDecision` (allow/deny/ask), `post-execute` a `PostToolDecision` (accept/block, optionally replacing content or attaching `additionalContext`). Core dispatch sits between them as plain code, inside `execute`'s outer try/catch, with the tool body's own try/catch preserved so a thrown tool still reaches `post-execute` as an `isError`.
**TODO**: tool shapes get revisited now that real tools exist (the bash suite landed; the `TODO(review)` in dsh-tools is still open) — e.g. a concurrency-safety hint for parallel execution; phase 1 executes tool calls sequentially.
@@ -126,11 +126,16 @@ Tool schemas are deliberately **part of the assembly**: "what the model is told
- **Step**: one model request + its tool executions.
```
create agent → emit agent/session-start(source) ⟵ once, before turn 1 (startup|resume)
forever:
wait for queued messages (idle)
emit agent/status(running)
TURN (error-contained — a throwing plugin ends the turn, never the loop):
drain queued → 'turn/start' → session('user/message'…) → emit agent/turn-start
'turn/start'
each queued msg: waterfall agent/prompt-submit ⟵ allow (rewrite/+context) | block
allow → session('user/message'…); inject additionalContext
every prompt blocked → 'turn/end'(rejected), 0 steps ⟵ zero-step turn, model never called
emit agent/turn-start
STEP loop:
drain steering (late steering from previous step's listeners)
session('step/start') ⟵ durable step boundary (no agent/* mirror)
@@ -145,15 +150,19 @@ forever:
msg = waterfall agent/step-result ⟵ runs BEFORE the log append, so the
session('assistant/message' {content, usage?}) log records what tool dispatch uses
each tool-call (sequential, abort-checked between calls):
session('tool/call'); ctx.tools.execute() ⟵ waterfall tools/execute
session('tool/call'); ctx.tools.execute() ⟵ waterfall tools/pre-execute (allow/
deny/ask gate) → dispatch → tools/post-execute (accept/block, replace, +context)
tool execution may append tool-owned session events, e.g. `todo/write`
session('tool/result')
append buffered post-execute additionalContext → session('context/message')(s)
⟵ after ALL tool/results (adjacency)
drain steering → session('steering/message'); emit agent/steering
session('step/end') ⟵ durable step boundary (no agent/* mirror)
cont = waterfall agent/turn-continuation(default = hadToolCalls || steered)
steering pending forces cont = true (from continuation listeners OR from
step/end session-event listeners — the /goal pattern; hasSteering override)
if !cont: break
cont = waterfall agent/turn-continuation(default = {action: hadToolCalls||steered
? 'continue' : 'stop'}) → ContinuationDecision
a continue's reason is recorded as next-step steering (same turn); steering pending
also forces continue (continuation OR step/end listeners — the /goal pattern)
if action==stop: break
session('turn/end'); emit agent/turn-end
await ctx.parallel('session/flush', session) ⟵ durability checkpoint (failure
reported via agent/error, not fatal)
@@ -163,7 +172,7 @@ forever:
Error containment: a throwing `agent/turn-continuation` listener or a broken step ends the **turn** with `turn/end { reason: { kind: 'error', step, message, code? } }` — the failure's step number rides on the durable turn reason (there is no separate session `error` event); live diagnostics fire via `agent/error`. Never the driver loop. An adapter that ends its stream with a `finish {kind:'error'}` or `{kind:'aborted'}` chunk (the in-band error path, for adapters that can't throw mid-stream) is likewise translated into a step error, so the turn ends `error`/`aborted` instead of logging a normal `completed` assistant message. A `cancel()` is honored mid-stream **and** between tool calls; disposal mid-turn ends the turn with reason `disposed` and emits `agent/status('disposed')`.
Turn-end reasons: a turn ends with one `TurnEndReason``completed`, `aborted`, `error`, `disposed`, or `max-tokens`. `max-tokens` mirrors the model-call `FinishReason` of the same name (DeepSeek's `length`): a step that hit the output-token ceiling makes the turn end `max-tokens` rather than `completed`, by the rule *any `max-tokens` step in the turn surfaces as `max-tokens`* (a continuation plugin may run further steps after one, but the cut-short fact wins; the `disposed`/`aborted`/`error` outcomes still take precedence). This lets a consumer distinguish a clean stop from a truncated one (the ACP bridge maps it to the `max_tokens` stop reason). `TurnEndReason` is merge-extensible; `refusal` and `max_turn_requests` are the next variants to add when an adapter/loop first emits them.
Turn-end reasons: a turn ends with one `TurnEndReason``completed`, `aborted`, `error`, `disposed`, `max-tokens`, `rejected`, or `interrupted`. `max-tokens` mirrors the model-call `FinishReason` of the same name (DeepSeek's `length`): a step that hit the output-token ceiling makes the turn end `max-tokens` rather than `completed`, by the rule *any `max-tokens` step in the turn surfaces as `max-tokens`* (a continuation plugin may run further steps after one, but the cut-short fact wins; the `disposed`/`aborted`/`error` outcomes still take precedence). `rejected` is a zero-step turn whose entire prompt batch was blocked by an `agent/prompt-submit` hook (the turn still opens and closes balanced; the ACP bridge maps it to `cancelled`). `interrupted` is synthesized by a persistence backend closing a crash-orphaned turn on reload. This lets a consumer distinguish a clean stop from a truncated/blocked one (the ACP bridge maps `max-tokens` to the `max_tokens` stop reason). `TurnEndReason` is merge-extensible; `refusal` and `max_turn_requests` are the next variants to add when an adapter/loop first emits them.
A failure that happens once the turn is already closed has no in-turn position for a turn-end error reason (the turn already ended). So a rejecting `session/flush` (the post-`turn/end` durability checkpoint) and a throwing `agent/turn-end` listener are reported via `agent/error` + the logger only, NOT as a session event; the turn stays balanced and the persistence backend keeps its buffered events for the next flush.
@@ -189,7 +198,7 @@ Every MVP feature (including the TODO-marked ones), with the mechanism that impl
| MVP feature | Plugin mechanism |
|---|---|
| Hook system (user + project level) | listeners on `agent/request`, `agent/step-result`, `tools/execute`, `agent/turn-continuation`; a hooks plugin bridges config files to shell commands |
| Hook system (user + project level) | listeners on `agent/session-start`, `agent/prompt-submit`, `agent/request`, `agent/step-result`, `tools/pre-execute`, `tools/post-execute`, `agent/turn-continuation` (each interception waterfall returns a typed Decision); a hooks bridge plugin maps config files / shell commands onto those seams, a native hook plugin uses them directly |
| `/goal` | force-continue via `agent/turn-continuation` + `steer()` reminders |
| `/loop` | on `agent/turn-end`, `send()` the next iteration; or force-continue |
| Dynamic workflow | orchestrator plugin on `agent/turn-end` (or the `step/end` session event) driving `send`/`steer` (+ sub-agents later) |
@@ -200,9 +209,9 @@ Every MVP feature (including the TODO-marked ones), with the mechanism that impl
| AGENTS.md (subdir, on-touch) + file-change notices | `agent.inject()` from a watcher / tool-result listener |
| Built-in tools (Read/Write/Edit/Bash/…) | `ctx.tools.register()`; schemas flow into the assembly automatically. **Bash: implemented**`dsh-bash` (seam) + `dsh-bash-local` (subprocesses) + `dsh-tool-bash` (`bash`/`bash_output`/`bash_kill`, incl. background tasks). **`todo_write`: implemented** — `dsh-tool-todo` writes the whole task list to the session log (`todo/write`), rendered as a stdio checklist / ACP `plan` |
| ToolSearch / progressive disclosure | wrap `agent/request`, filter `req.tools` |
| Tool sandbox (landlock / sandbox-exec) | wrap `tools/execute`, or implement a sandboxing `BashExecutor` (the dsh-bash seam) |
| Permission system / AskUserQuestion | wrap `tools/execute` (veto or ask); register an ask tool |
| Plan mode | wrap `tools/execute` (deny writes) + `agent/request` (inject mode prompt) |
| Tool sandbox (landlock / sandbox-exec) | `tools/pre-execute` (deny), or implement a sandboxing `BashExecutor` (the dsh-bash seam) |
| Permission system / AskUserQuestion | `tools/pre-execute` (deny/ask); register an ask tool |
| Plan mode | `tools/pre-execute` (deny writes) + `agent/request` (inject mode prompt) |
| Sub-agents (spawn / fork / steer) | TODO seam on `AgentLoop.create()`; fork = seed Session with parent events; `steer()` on the child handle |
| MCP | one plugin per server: discover tools → `ctx.tools.register()` |
| Skills | section + tool registration; `inject()` skill content on invocation |

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@@ -8,24 +8,20 @@ A tool registers on `ctx.tools`. The annotated `defineTool` example (typed `exec
## A hook plugin (permission gate)
A hook wraps the `tools/execute` waterfall to veto or rewrite a call — the seam where sandbox, permission, and plan-mode plugins live.
A hook returns a typed decision from the `tools/pre-execute` gate to allow or deny a call — the seam where sandbox, permission, and plan-mode plugins live. (A "native hook" is just this: an ordinary cordis plugin on the interception seams, returning typed decisions — no external protocol needed.)
```ts
import type { Context } from 'cordis'
import type { ToolExecution } from '@deepseek-ai/dsh-tools'
import type { PreToolDecision, ToolExecution } from '@deepseek-ai/dsh-tools'
declare function isAllowed(exec: ToolExecution): Promise<boolean>
export const name = 'permission-gate'
export function apply(ctx: Context) {
ctx.on('tools/execute', async (exec, next) => {
ctx.on('tools/pre-execute', async (exec, next): Promise<PreToolDecision> => {
if (!(await isAllowed(exec))) {
return {
callId: exec.callId,
content: [{ type: 'text', text: 'Denied by policy.' }],
isError: true,
}
return { kind: 'deny', reason: 'Denied by policy.' }
}
return next()
})

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@@ -25,7 +25,7 @@ An agent was registered in the AgentRegistry and is ready to receive messages.
Types: [Agent](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:165`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:228`](../../packages/core/agent/src/types.ts)
#### `agent/disposed` — emit
@@ -37,7 +37,7 @@ An agent was disposed and removed from the registry; its fiber and any in-flight
Types: [Agent](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:171`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:234`](../../packages/core/agent/src/types.ts)
#### `agent/error` — emit
@@ -49,7 +49,19 @@ A step or turn errored. The loop reports a failure here (plus the logger) even w
Types: [Agent](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:245`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:334`](../../packages/core/agent/src/types.ts)
#### `agent/prompt-submit` — waterfall
Waterfall: decide what happens to ONE drained queued message before it becomes a `user/message` — allow (optionally rewriting the prompt bytes or attaching `additionalContext`) or block it. Fires inside the already-open turn, per drained message. Maps onto Claude Code's `UserPromptSubmit` hook. Call `next()` to delegate to the default (allow unchanged), or return a PromptDecision without calling `next()` to short-circuit.
```ts cordis-catalog
'agent/prompt-submit'(agent: Agent, content: ContentBlock[], source: MessageSource, next: () => Promise<PromptDecision>): Promise<PromptDecision>
```
Types: [Agent](../core-data-structures/core.md) · [ContentBlock](../core-data-structures/core.md) · [MessageSource](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:293`](../../packages/core/agent/src/types.ts)
#### `agent/queued` — emit
@@ -61,7 +73,7 @@ A message entered the agent's inbox (queued or steering). `source` is the resolv
Types: [Agent](../core-data-structures/core.md) · [ContentBlock](../core-data-structures/core.md) · [MessageSource](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:184`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:247`](../../packages/core/agent/src/types.ts)
#### `agent/request` — waterfall
@@ -73,7 +85,19 @@ Waterfall: mutate the fully-assembled GenerateOptions before the model call (hoo
Types: [Agent](../core-data-structures/core.md) · [GenerateOptions](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:214`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:300`](../../packages/core/agent/src/types.ts)
#### `agent/session-start` — emit
The agent's session lifecycle began, fired once before its first turn. `source` says why (SessionStartSource: fresh startup, a resumed persisted session, …). A pure NOTIFICATION (emit, not waterfall): it carries no veto — a session-start listener that wants to seed context does so via `agent.inject()` (a `context/message` the first request sees), not by returning a decision. Cannot block the session from starting; that gap is deliberate (a bridge logs/injects, it does not gate startup).
```ts cordis-catalog
'agent/session-start'(agent: Agent, source: SessionStartSource): void
```
Types: [Agent](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:260`](../../packages/core/agent/src/types.ts)
#### `agent/status` — emit
@@ -85,7 +109,7 @@ Agent status changed (`idle` ⇄ `running`, or → `disposed`). Drive lifecycle
Types: [Agent](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:178`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:241`](../../packages/core/agent/src/types.ts)
#### `agent/steering` — emit
@@ -97,7 +121,7 @@ Steering content was injected into a running turn.
Types: [Agent](../core-data-structures/core.md) · [ContentBlock](../core-data-structures/core.md) · [MessageSource](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:239`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:328`](../../packages/core/agent/src/types.ts)
#### `agent/step-result` — waterfall
@@ -109,7 +133,7 @@ Waterfall: post-process the assembled assistant Message before tool dispatch (va
Types: [Agent](../core-data-structures/core.md) · [Message](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:220`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:306`](../../packages/core/agent/src/types.ts)
#### `agent/stream-chunk` — emit
@@ -121,19 +145,19 @@ A raw StreamChunk arrived from the model (token-level UI/log feed).
Types: [Agent](../core-data-structures/core.md) · [StreamChunk](../core-data-structures/llm-streaming.md)
Source: [`packages/core/agent/src/types.ts:234`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:323`](../../packages/core/agent/src/types.ts)
#### `agent/turn-continuation` — waterfall
Waterfall: override the turn-continuation decision. The default (computed by the loop) is `hadToolCalls || steeringInjected`. Listeners can force-continue (/goal, /loop) or force-stop (budget guards).
Waterfall: override the turn-continuation decision via a typed ContinuationDecision. The loop's `defaultDecision` is `continue` when the step had tool calls or steering was injected, else `stop`. Listeners force-continue (`/goal`, `/loop` — optionally attaching a `reason` recorded as next-step steering) or force-stop (budget guards). Call `next()` to delegate to the default, or return a decision to override.
```ts cordis-catalog
'agent/turn-continuation'(agent: Agent, turn: number, defaultDecision: boolean, next: () => Promise<boolean>): Promise<boolean>
'agent/turn-continuation'(agent: Agent, turn: number, defaultDecision: ContinuationDecision, next: () => Promise<ContinuationDecision>): Promise<ContinuationDecision>
```
Types: [Agent](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:227`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:316`](../../packages/core/agent/src/types.ts)
#### `agent/turn-end` — emit
@@ -145,7 +169,7 @@ A turn ended. `reason` distinguishes a clean stop from a truncated, aborted, fai
Types: [Agent](../core-data-structures/core.md) · [TurnEndReason](../core-data-structures/session.md)
Source: [`packages/core/agent/src/types.ts:205`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:281`](../../packages/core/agent/src/types.ts)
#### `agent/turn-start` — emit
@@ -157,7 +181,7 @@ A turn began. `turn` is the 1-based turn number within the session.
Types: [Agent](../core-data-structures/core.md)
Source: [`packages/core/agent/src/types.ts:197`](../../packages/core/agent/src/types.ts)
Source: [`packages/core/agent/src/types.ts:273`](../../packages/core/agent/src/types.ts)
### `llm/*`
@@ -261,19 +285,31 @@ A tool was registered or unregistered (the available tool set changed).
'tools/change'(): void
```
Source: [`packages/core/tools/src/index.ts:48`](../../packages/core/tools/src/index.ts)
Source: [`packages/core/tools/src/index.ts:66`](../../packages/core/tools/src/index.ts)
#### `tools/execute` — waterfall
#### `tools/post-execute` — waterfall
Waterfall around every tool execution — the single seam where sandbox, permission, hook, and plan-mode plugins wrap or veto a call. Listeners receive `(exec, next)`: call `next()` to proceed (possibly around your own logic), or return a ToolExecutionResult without calling `next()` to short-circuit (veto).
Waterfall AFTER a tool runs — where hook plugins inspect the result and accept it (optionally REPLACING the model-facing content, and/or attaching `additionalContext` for the next request) or block it with corrective `feedback` (Claude Code's `PostToolUse`). Listeners receive `(exec, result, next)`: call `next()` to delegate to the default (accept unchanged), or return a PostToolDecision to override. The core tool dispatch sits between the two waterfalls as plain code, all inside `execute`'s outer try/catch (and the tool body keeps its own inner try/catch, so a thrown tool still reaches `post-execute` as an `isError` result).
```ts cordis-catalog
'tools/execute'(this: ToolRegistry, exec: ToolExecution, next: () => Promise<ToolExecutionResult>): Promise<ToolExecutionResult>
'tools/post-execute'(this: ToolRegistry, exec: ToolExecution, result: ToolExecutionResult, next: () => Promise<PostToolDecision>): Promise<PostToolDecision>
```
Types: [ToolExecution](../core-data-structures/tools.md) · [ToolExecutionResult](../core-data-structures/tools.md)
Source: [`packages/core/tools/src/index.ts:43`](../../packages/core/tools/src/index.ts)
Source: [`packages/core/tools/src/index.ts:61`](../../packages/core/tools/src/index.ts)
#### `tools/pre-execute` — waterfall
Waterfall BEFORE a tool runs — the gate where sandbox, permission, and hook plugins allow or deny a call (Claude Code's `PreToolUse`). Listeners receive `(exec, next)`: call `next()` to delegate to the default (allow), or return a PreToolDecision without calling `next()` to short-circuit. A `deny` skips dispatch and yields an `isError` result; the tool body never runs. Input rewrite is deliberately NOT offered here (see PreToolDecision); `ask` degrades to deny until the permission system lands (`FIXME(permissions)`).
```ts cordis-catalog
'tools/pre-execute'(this: ToolRegistry, exec: ToolExecution, next: () => Promise<PreToolDecision>): Promise<PreToolDecision>
```
Types: [ToolExecution](../core-data-structures/tools.md)
Source: [`packages/core/tools/src/index.ts:47`](../../packages/core/tools/src/index.ts)
## Services
@@ -446,7 +482,7 @@ async execute(exec: ToolExecution): Promise<ToolExecutionResult>
Types: [ToolDefinition](../core-data-structures/tools.md) · [ToolExecution](../core-data-structures/tools.md) · [ToolExecutionResult](../core-data-structures/tools.md)
Source: [`packages/core/tools/src/index.ts:277`](../../packages/core/tools/src/index.ts)
Source: [`packages/core/tools/src/index.ts:341`](../../packages/core/tools/src/index.ts)
## Inherited tier (cordis core + loader/hmr/timer)

View File

@@ -306,7 +306,42 @@ interface Agent {
}
```
`AgentStatus` is `'idle' | 'running' | 'disposed'`. `AgentId` is a branded string. `AgentOptions` (`model?`, `systemPrompt?`) is merge-extensible — plugins add creation options by declaration merging. The `agent/*` event taxonomy (lifecycle, turn/step boundaries, the `agent/request`/`agent/step-result`/`agent/turn-continuation` waterfalls) is in [architecture.md § Event taxonomy](../architecture.md#event-taxonomy).
`AgentStatus` is `'idle' | 'running' | 'disposed'`. `AgentId` is a branded string. `AgentOptions` (`model?`, `systemPrompt?`) is merge-extensible — plugins add creation options by declaration merging. The `agent/*` event taxonomy (lifecycle, turn/step boundaries, the `agent/prompt-submit`/`agent/request`/`agent/step-result`/`agent/turn-continuation` waterfalls) is in [architecture.md § Event taxonomy](../architecture.md#event-taxonomy).
## Interception decisions
Each `agent/*` interception waterfall returns a small, seam-specific typed union — the unified Decision idiom (the tool seams' `PreToolDecision`/`PostToolDecision` in [tools.md](tools.md) follow the same shape). A CC/Codex hook bridge maps its `permissionDecision`/`decision`/`continue`/`additionalContext` fields onto these; a native plugin returns them directly. They share one envelope for model-facing context, `HookContext`, which is `inject()`ed as a `context/message` and so carries a REQUIRED `source` (a missing source would default to `{kind:'user'}` and mislabel plugin context as a user prompt).
Source: [`packages/core/agent/src/types.ts`](../../packages/core/agent/src/types.ts)
```ts type-equiv
interface HookContext {
content: ContentBlock[]
source: MessageSource
}
```
`agent/prompt-submit` returns a `PromptDecision` (allow a drained queued message — optionally rewriting its `content` or attaching `additionalContext` — or block it; a batch whose every prompt is blocked opens a zero-step turn that ends `rejected`):
```ts type-equiv
type PromptDecision =
| { kind: 'allow'; content?: ContentBlock[]; additionalContext?: HookContext }
| { kind: 'block'; reason: string }
```
`agent/turn-continuation` returns a `ContinuationDecision` (the loop's default is `continue` when the step had tool calls or steering was injected, else `stop`; a `continue` `reason` is recorded as next-step steering in the same turn — the typed `/goal` pattern):
```ts type-equiv
type ContinuationDecision =
| { action: 'stop' }
| { action: 'continue'; reason?: HookContext }
```
`agent/session-start` carries a `SessionStartSource` (why the session lifecycle began; a bridge keys its SessionStart matcher on it):
```ts type-equiv
type SessionStartSource = 'startup' | 'resume' | 'clear' | 'compact'
```
## `ToolDefinition`

View File

@@ -181,6 +181,16 @@ interface TurnEndReasonMap {
error: { kind: 'error'; step: number; message: string; code?: string }
disposed: { kind: 'disposed' }
'max-tokens': { kind: 'max-tokens' }
/**
* The turn's entire prompt batch was BLOCKED before any step ran — every
* drained queued message was vetoed by an `agent/prompt-submit` listener (a
* hook). The turn still opened (so the boundary stays balanced and the block
* is a durable in-turn fact), but ran zero steps. `reason` carries the block
* message from the vetoing decision. Distinct from `aborted` (a user-driven
* cancel) and `error` (a failure): the prompt was rejected by policy, not
* interrupted or broken. A UI renders it as "prompt blocked by hook".
*/
rejected: { kind: 'rejected'; reason: string }
/**
* The turn never ended on its own: the process crashed mid-turn and a
* persistence backend later closed the orphaned (open) turn on reload so the
@@ -195,7 +205,7 @@ interface TurnEndReasonMap {
}
```
`max-tokens` mirrors the model-call `FinishReason` of the same name: any `max-tokens` step in a turn makes the whole turn end `max-tokens` (the cut-short fact wins over a later continuation), so a consumer can tell a clean stop from a truncated one. `interrupted` is the one reason no loop emits — it is synthesized by crash recovery (see [persistence.md](persistence.md)). Both maps are merge-extensible.
`max-tokens` mirrors the model-call `FinishReason` of the same name: any `max-tokens` step in a turn makes the whole turn end `max-tokens` (the cut-short fact wins over a later continuation), so a consumer can tell a clean stop from a truncated one. `rejected` is a zero-step turn whose whole prompt batch an `agent/prompt-submit` hook blocked (the ACP bridge maps it to `cancelled`). `interrupted` is the one reason no loop emits — it is synthesized by crash recovery (see [persistence.md](persistence.md)). Both maps are merge-extensible.
## The turn-enclosure invariant

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@@ -73,7 +73,7 @@ type InferArgs<S extends SchemaSpec> = Simplify<
## Execution: the `tools/execute` waterfall shapes
`ctx.tools.execute()` runs each call through the `tools/execute` waterfall — the single seam where sandbox, permission, hook, and plan-mode plugins wrap or veto. The pending call is a `ToolExecution`; the outcome is a `ToolExecutionResult`.
`ctx.tools.execute()` runs each call through a two-waterfall pipeline — `tools/pre-execute` (the allow/deny/ask gate) → core dispatch → `tools/post-execute` (inspect/replace the result, attach context) — the seams where sandbox, permission, hook, and plan-mode plugins gate or transform a call. The pending call is a `ToolExecution`; the outcome is a `ToolExecutionResult`.
```ts type-equiv
interface ToolExecution {
@@ -98,10 +98,36 @@ interface ToolExecutionResult {
* text in `content` is always present; this is extra structure for code.
*/
error?: ToolErrorInfo
/**
* Extra model-facing context a `tools/post-execute` listener attached for the
* NEXT request (Claude Code's PostToolUse `additionalContext`). It is NOT part
* of this call's `content` — `content`/`feedback` shape the tool RESULT, but
* `additionalContext` is a SEPARATE `context/message`. A step can carry
* multiple tool calls, so the loop BUFFERS every call's `additionalContext`
* and appends them only AFTER all `tool/result`s for the step, keeping
* tool-call/result adjacency intact. Carried on the result purely to ferry it
* from `execute()` up to the loop's per-step buffer.
*/
additionalContext?: HookContext
}
```
A waterfall listener receives `(exec, next)`: call `next()` to proceed (possibly around your own logic), or return a `ToolExecutionResult` without calling `next()` to veto. An unregistered tool routes through the same catch as a tool-thrown error, so both failure classes get a structured `{ name, code }` (`ToolNotFoundError` → `UNKNOWN_TOOL`) — the loop records a failed tool call instead of failing the whole turn.
Each interception waterfall returns a typed **Decision** (the idiom shared with the `agent/*` seams). `tools/pre-execute` listeners receive `(exec, next)` and return a `PreToolDecision`; `tools/post-execute` listeners receive `(exec, result, next)` and return a `PostToolDecision`:
```ts type-equiv
type PreToolDecision =
| { kind: 'allow' }
| { kind: 'deny'; reason: string }
| { kind: 'ask'; reason?: string }
```
```ts type-equiv
type PostToolDecision =
| { kind: 'accept'; content?: ContentBlock[]; additionalContext?: HookContext }
| { kind: 'block'; feedback: ContentBlock[]; additionalContext?: HookContext }
```
Call `next()` to delegate to the default (allow / accept-unchanged), or return a decision to short-circuit. A `pre-execute` `deny` (or `ask`, which degrades to deny until the permission system lands) skips dispatch and yields an `isError` result; input rewrite is deliberately NOT offered on `PreToolDecision` (it would desync the pre-execution audit/history/UI from what ran — its own proposed RFC). A `post-execute` `accept` may replace the model-facing `content` (clean, because `tool/result` is logged after `execute()` returns); a `block` turns the call into an `isError` whose content is the corrective `feedback`. Core dispatch sits between the waterfalls as plain code; the tool body keeps its own try/catch so a thrown tool still reaches `post-execute` as an `isError`. An unregistered tool routes through the same catch as a tool-thrown error, so both failure classes get a structured `{ name, code }` (`ToolNotFoundError` → `UNKNOWN_TOOL`) — the loop records a failed tool call instead of failing the whole turn.
## Tool-presentation UI vocabulary

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@@ -45,6 +45,7 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
| [Multiplex concurrent ACP sessions over one connection](proposed/feature/2026-06-14-acp-multi-session.md) | 2026-06-14 |
| [Optional Code Mode — model writes TypeScript against an SDK of all tools](proposed/feature/2026-06-15-optional-code-mode.md) | 2026-06-15 |
| [Compaction as a capability seam (abstract contract + basic backend)](proposed/feature/2026-06-18-compaction-capability-seam.md) | 2026-06-18 |
| [Pre-tool input rewrite — a consistent design](proposed/feature/2026-06-30-pre-tool-input-rewrite.md) | 2026-06-30 |
### Simplification
@@ -86,6 +87,7 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
| [Subagent capability seam](implemented/feature/2026-06-21-subagent-capability-seam.md) | 2026-06-21 |
| [ACP subagent backend (out-of-process delegation)](implemented/feature/2026-06-22-acp-subagent-backend.md) | 2026-06-22 |
| [The `todo_write` tool — model task list as event-sourced session state](implemented/feature/2026-06-29-todo-write-tool.md) | 2026-06-29 |
| [Interception seams — the typed-Decision surface a hook programs against](implemented/feature/2026-06-30-interception-seams.md) | 2026-06-30 |
### Simplification

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@@ -0,0 +1,45 @@
# RFC: Interception seams — the typed-Decision surface a hook programs against
Status: implemented (accepted 2026-06-30)
<!-- XXX: legacy ADR/RFC body format, not yet normalized to a unified RFC template. -->
## Context
The harness needs a hooks subsystem: users extend or gate the agent at lifecycle points the way Claude Code (CC) and Codex do. The key reframe driving this design is that **"native hooks" are not a package** — a native hook is just an ordinary Cordis plugin subscribing to the canonical lifecycle events. So the real product is a *powerful, well-typed canonical event surface*; the CC/Codex bridges (a later stack PR) are merely translators that map an external shell-hook protocol onto that same surface. Anything a bridge can do, a plain plugin can do directly — more powerfully (no serialization boundary, full `ctx`, typed returns).
Before this change the interception surface was incomplete and inconsistent for that goal: there was no per-prompt seam (CC's `UserPromptSubmit`), no session-start signal (CC's `SessionStart`), the single `tools/execute` waterfall conflated the pre-gate and post-inspect phases (CC splits `PreToolUse`/`PostToolUse`), and `agent/turn-continuation` returned a bare `boolean` with no room for a force-continue *reason*. The [event-domain-semantics RFC](../architecture/2026-06-30-event-domain-semantics.md) (the stack's first change) pinned down the three-domain rule and the typed-Decision idiom as the interception convention; this RFC builds the actual seams on top of it.
## Decision
Add/reshape the interception seams so every one returns a small, seam-specific **typed Decision union**, and the set covers the hook points in scope (`session-start`, `prompt-submit`, `pre-tool`, `post-tool`, `stop`-via-continuation).
**New `agent/*` events** (`dsh-agent`):
- `agent/session-start(agent, source)` — emit, once before turn 1, carrying a `SessionStartSource` (`startup` for a fresh/forked create, `resume` for a reloaded persisted session; `clear`/`compact` reserved). A pure notification — it CANNOT block startup (a deliberate gap: a bridge logs/injects, it does not gate startup). A listener seeds context via `agent.inject()`.
- `agent/prompt-submit(agent, content, source, next) → PromptDecision` — waterfall, fired per drained queued message inside the open turn, before the `user/message` append. `allow` (optionally rewriting the prompt `content` or attaching `additionalContext`) or `block`.
**Reshaped** `agent/turn-continuation` from `(…, defaultDecision: boolean) → boolean` to `(…, defaultDecision: ContinuationDecision) → ContinuationDecision`. A `{action:'continue', reason?}` may carry model-facing context recorded as next-step steering in the same turn — the typed twin of the existing `/goal` step-end-steer pattern.
**Split** the single `tools/execute` waterfall into `tools/pre-execute` (→ `PreToolDecision` allow/deny/ask gate) and `tools/post-execute` (→ `PostToolDecision` accept/block, optionally replacing content or attaching `additionalContext`). Core dispatch sits between them as plain code inside `ToolRegistry.execute`'s outer try/catch, and the tool body keeps its own inner try/catch so a thrown tool still becomes an `isError` result that `post-execute` listeners can inspect.
**New `TurnEndReason` variant** `rejected` (`dsh-session`): a turn whose entire prompt batch was blocked by `prompt-submit`.
### Three load-bearing loop decisions
1. **Always open the turn first; a fully-blocked batch is a zero-step `rejected` turn.** `prompt-submit` fires AFTER `turn/start`, per message. A batch whose every prompt is blocked does NOT skip the turn — it opens a zero-step turn that closes with `rejected`. This one move resolves three problems at once: (1) turn-enclosure holds (every event has an open turn to live in); (2) `agent/turn-end` fires and the ACP bridge settles normally (mapping `rejected``cancelled`) instead of hanging; (3) the block reason is a durable in-turn fact. An `allow`'s `additionalContext` is `inject()`ed into this now-open turn.
2. **Post-tool `additionalContext` is buffered and appended AFTER all `tool/result`s.** `content`/`feedback` shape the result `execute()` returns, but `additionalContext` is a SEPARATE `context/message`, and a single step can carry multiple tool calls. Appending context right after each result would interleave `result(c1) → context → result(c2)` and break tool-call/result adjacency. So `execute()` surfaces `additionalContext` on its `ToolExecutionResult`, and the loop buffers every per-call context for the step and appends them as `context/message`(s) only after every `tool/result` is appended.
3. **A forced `continue` `reason` is enqueued through the steering channel**, so the next step's top-of-loop drain records it as steering for the continued turn — next-*step* steering within the SAME turn, not a next-*turn* prompt (matching the existing `hasSteering` force-continue override).
### Pre-tool INPUT rewrite is DEFERRED (the over-reach signal)
`PreToolDecision` is allow/deny/ask only — **no `arguments` rewrite**. Output replacement (`PostToolDecision.accept.content`) is safe because `tool/result` is logged AFTER execution (one source of truth). Input rewrite is NOT safe today: `assistant/message` (the model-history source) and `tool/call` (the audit record) are both logged BEFORE execution, and live consumers READ `tool/call.arguments` for presentation (the ACP bridge remembers them for `presentResult`; `dsh-tool-bash` derives the title/cwd/terminal-vs-background from them). A rewrite that changed only execution would make the UI show one command while another RAN. Designing that consistently (rewriting the audit + history + presentation as one unit) is a real consistency-design problem CC itself warns is racy — so it gets its own [proposed RFC](../../proposed/feature/2026-06-30-pre-tool-input-rewrite.md), and `TODO(pre-tool-input-rewrite)` anchors it at the loop's pre-execute call site. This does not regress any production consumer (no production `tools/execute` listener mutated `exec.arguments`). The low-level capability to mutate `exec` in a `pre-execute` listener still exists (unadvertised — a test shim uses it to thread a generated id), but it is not a first-class advertised contract.
### What this PR does NOT do
It does **not** declare `hook/*` SessionEvents (the durable hook-invocation log) — those belong to the `dsh-hook-protocol` library (a later stack PR), because a native plugin can already use the typed Decisions without a durable hook log. A worked native-plugin example/test in this PR (`packages/core/agent-loop/tests/interception.spec.ts`) proves all the seams compose end-to-end through the REAL loop with NO `hook/*` involved — the concrete proof that "native hooks are just a plugin". Compaction (`PreCompact`/`PostCompact`), the Notification hook, Codex `PermissionRequest`, the permission/`ask` system, and the Stop loop-guard remain deferred (`FIXME(permissions)` marks the `ask`→deny degrade).
## Consequences
The canonical interception surface is now complete and uniformly typed: a native plugin returns typed decisions directly, and a CC/Codex bridge maps its protocol fields onto the same unions. The loop gained four firing points (session-start emit, prompt-submit waterfall, the post-tool context buffer, the continuation reshape) and the `dsh-tools` registry runs a two-waterfall pipeline; both are documented in [architecture.md](../../../architecture.md) and the package READMEs, and the decision types in [core-data-structures](../../../core-data-structures/core.md#interception-decisions) + [tools.md](../../../core-data-structures/tools.md). All existing `tools/execute` and `turn-continuation` listeners (tests, docs) migrated to the new seams. The ACP bridge maps the new `rejected` reason to `cancelled` (its codec). A pure internal change with no editor-visible transcript shift for the existing scenarios — the new behavior only fires when a hook is registered — so the snapshot goldens are unchanged; a hook-driven snapshot scenario lands with the bridges (the PR that makes a hook observable end-to-end through ACP).

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@@ -0,0 +1,39 @@
# RFC: Pre-tool input rewrite — a consistent design (proposed)
Status: proposed (2026-06-30)
<!-- XXX: legacy ADR/RFC body format, not yet normalized to a unified RFC template. -->
## Context
The [interception-seams RFC](../../implemented/feature/2026-06-30-interception-seams.md) added `tools/pre-execute` returning a `PreToolDecision` (allow/deny/ask) — but deliberately NOT input rewrite (a hook changing a tool call's `arguments` before it runs). Claude Code's `PreToolUse` hook offers an `updatedInput`, so a faithful CC bridge wants the same. This RFC designs that, separately, because doing it consistently is a real problem — not a field to bolt onto the allow decision.
## The problem: three readers of pre-execution arguments
In the loop, a tool call's arguments are committed to the log and read by live consumers BEFORE the tool executes:
1. **`assistant/message`** is appended before tool dispatch — it is the model-history source `deriveMessages()` replays, so it carries the tool-call arguments the model itself emitted.
2. **`tool/call`** is the durable AUDIT record, appended before `ctx.tools.execute()`.
3. **Live presentation reads `tool/call.arguments`**: the ACP bridge remembers them and passes them to `presentResult`; `dsh-tool-bash` derives the card title, the rawInput, the cwd, and the terminal-vs-background treatment from them.
So an "input rewrite" that changes ONLY what executes would make the UI show one command while another RAN, and render result state against the wrong arguments — a real inconsistency, not a documentable gap. (The existing low-level capability to mutate `exec.arguments` in a listener has exactly this latent inconsistency; it is unadvertised precisely because of this.)
## Proposed design (sketch — to validate against the code when built)
Treat input rewrite as a consistency unit: when a `pre-execute` hook supplies `updatedInput`, the rewrite must be reflected in ALL three readers, atomically, before execution:
- The `tool/call` audit event records the REWRITTEN arguments (with the original retained in a sidecar field for the audit trail — a hook changed the call, and both the original and the effective arguments are facts worth keeping).
- The `assistant/message` in derived history must agree with what executed — options to evaluate: rewrite the assistant message's tool-call block in place (changes what the model "sees it said"), or record a separate correction the next request carries. The CC model is that the model sees the rewrite took effect.
- Presentation (`presentCall`/`presentResult`) reads the rewritten arguments, so the UI shows what actually ran.
The shape would extend `PreToolDecision` with an allow-variant `arguments` (or a dedicated `{kind:'rewrite', arguments}`), and the loop would thread the rewrite through the three readers above rather than only into `ctx.tools.execute()`.
## Why not now
The interception-seams RFC notes input rewrite "fought the code across two review rounds" — the signal AGENTS.md names for an over-reaching change. Shipping allow/deny/ask first keeps the seam honest (no advertised contract that silently desyncs the UI), and a CC/Codex bridge that receives an `updatedInput` logs it and surfaces a faithful-but-degraded warning (like `ask`→deny) until this lands. This RFC is the home for the consistent design; `TODO(pre-tool-input-rewrite)` in the loop's pre-execute call site anchors it.
## Open questions
- Does rewriting the `assistant/message` tool-call block corrupt any provider's expectation on replay, or is a separate correction safer?
- Should the original arguments be preserved on the `tool/call` event (audit) and, if so, under what field?
- How does this interact with a future permission `ask` flow (a user approving a rewritten call)?