fix(agent-loop): always close a started turn and any open step on error (P1-5)

After turn/start was appended, nothing guaranteed a matching turn/end: a throw
from a boundary emit (agent/turn-start, agent/step-start, the normal-path
agent/turn-end) escaped runTurn, and the outer runLoop backstop logged an
error but never appended turn/end — leaving an unbalanced turn that replay,
telemetry, and the invariants plugin all assume is impossible.

runTurn is restructured around idempotent finalizers that satisfy the four
traps a naive finally would hit:
- closeStep()/closeTurn(emit) are guarded (stepOpen/turnEnded) so they run at
  most once; the agent/step-end and agent/error emits are contained so a
  throwing listener can't strand the turn open.
- failTurn() records the single error event + reason and emits agent/error
  exactly once (errorReported guard) — no double-logging when the outer catch
  also runs (e.g. a step error followed by a throwing turn-end listener).
- the catch closes an open step BEFORE turn/end (invariants reject turn/end
  while a step is open), and rethrows ONLY pre-turn throws (turnStarted false),
  where no turn/end is owed, so the backstop still nets them.
- disposal precedence: reason stays disposed only when disposed AND no error
  was reported; otherwise the error reason wins.

Tests (with the invariants plugin loaded as a balance oracle): throwing
turn-start (one error, one turn/end, no step), throwing step-start (step/end
before turn/end), throwing agent/error on a step-error path (balanced, loop
survives), disposal mid-turn (reason disposed, no error event), a pre-turn
turn/start-append throw (rethrown to the backstop, no turn/end owed), and a
step error + throwing turn-end listener (error logged exactly once). Verified
all six fail against a simulated finalizer bypass. dsh-invariants added as an
agent-loop devDependency (test-only oracle; no package cycle).
This commit is contained in:
Tianyi Cui
2026-06-15 01:06:13 +08:00
parent 9d5b3ab832
commit 22e9152d8b
4 changed files with 401 additions and 79 deletions
+1
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@@ -32,6 +32,7 @@
},
"devDependencies": {
"@deepseek-ai/dsh-agent": "^0.0.1",
"@deepseek-ai/dsh-invariants": "^0.0.1",
"@deepseek-ai/dsh-llm": "^0.0.1",
"@deepseek-ai/dsh-session": "^0.0.1",
"@deepseek-ai/dsh-system-prompt": "^0.0.1",
+150 -78
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@@ -151,7 +151,9 @@ export async function runLoop(ctx: Context, agent: LoopAgent, handle: LoopHandle
async function runTurn(ctx: Context, agent: LoopAgent, handle: LoopHandle, turn: number): Promise<void> {
const { session } = agent
// Drain queued messages into the session — they trigger this turn.
// --- Pre-turn. A throw here (the invariant guard or a user-message append)
// is owed NO turn/end — turn/start has not been appended — so it propagates
// to runLoop's backstop untouched.
const queued = agent.inbox.drainQueued()
const first = queued[0]
/* v8 ignore next 3 -- invariant guard: runLoop only calls runTurn when hasQueued */
@@ -161,91 +163,161 @@ async function runTurn(ctx: Context, agent: LoopAgent, handle: LoopHandle, turn:
session.append('user/message', { content: message.content, source: message.source })
}
session.append('turn/start', { turn, trigger })
ctx.emit('agent/turn-start', agent, turn)
let reason: TurnEndReason = { kind: 'completed' }
let step = 0
let turnStarted = false
let turnEnded = false
let stepOpen = false
let errorReported = false
while (true) {
step += 1
// Steering from the previous round's step-end/continuation listeners
// (or turn-start listeners on the first step) joins before the request.
drainSteering(ctx, agent, turn)
session.append('step/start', { turn, step })
ctx.emit('agent/step-start', agent, turn, step)
const abort = new AbortController()
handle.setAbort(abort)
let stepOutcome: { hadToolCalls: boolean } | { error: Error }
try {
stepOutcome = await runStep(ctx, agent, turn, step, abort.signal)
} catch (error: unknown) {
stepOutcome = { error: toError(error) }
} finally {
handle.setAbort(undefined)
}
if ('error' in stepOutcome) {
// Steering that arrived during the failed step stays in the inbox —
// runLoop re-enqueues it as a queued message, so an abort-then-steer
// starts a fresh turn instead of being silently consumed.
session.append('step/end', { turn, step })
ctx.emit('agent/step-end', agent, turn, step)
const { error } = stepOutcome
if (handle.isDisposed()) {
reason = { kind: 'disposed' }
} else if (abort.signal.aborted) {
/* v8 ignore next -- abort.signal.reason always set by agent.abort() which provides a default */
reason = { kind: 'aborted', reason: String(abort.signal.reason ?? 'aborted') }
} else {
const coded = error as CodedError
session.append('error', { turn, step, ...errorData(coded) })
ctx.emit('agent/error', agent, turn, step, error)
reason = { kind: 'error', ...errorData(coded) }
}
break
}
// Steering that arrived during streaming/tool execution.
const steered = drainSteering(ctx, agent, turn)
// Close the open step exactly once (idempotent via stepOpen). The
// agent/step-end emit is contained: a throwing step-end listener must not
// abort finalization and strand the turn open (turn/end balance > notifying
// one bad listener). Appended before the emit (ADR 0003 append-before-emit).
const closeStep = (): void => {
if (!stepOpen) return
stepOpen = false
session.append('step/end', { turn, step })
ctx.emit('agent/step-end', agent, turn, step)
const defaultDecision = stepOutcome.hadToolCalls || steered
let shouldContinue: boolean
try {
shouldContinue = await ctx.waterfall(
'agent/turn-continuation', agent, turn, defaultDecision,
() => Promise.resolve(defaultDecision),
)
} catch (error: unknown) {
// A broken continuation plugin ends the turn, not the loop.
const err = toError(error)
session.append('error', { turn, step, ...errorData(err) })
ctx.emit('agent/error', agent, turn, step, err)
reason = { kind: 'error', ...errorData(err) }
break
}
// Steering from step-end/continuation listeners (the /goal pattern)
// demands the model see it — it overrides a negative decision; the
// next iteration's drain records it.
if (!shouldContinue && agent.inbox.hasSteering) shouldContinue = true
if (!shouldContinue || handle.isDisposed()) {
/* v8 ignore next -- disposal during continuation-decision window is a narrow race; error-path disposal is covered elsewhere */
if (handle.isDisposed()) reason = { kind: 'disposed' }
break
ctx.emit('agent/step-end', agent, turn, step)
} catch {
// contained: step/end is already recorded, so balance holds; a throwing
// step-end listener is the listener's bug, not the loop's.
}
}
session.append('turn/end', { turn, reason })
ctx.emit('agent/turn-end', agent, turn, reason)
// Record a step/turn failure exactly once: append the single `error` event,
// set the error reason, and emit agent/error (contained — trap: a throwing
// agent/error listener must not re-escape and strand the turn). Disposal and
// abort set `reason` directly without calling this (no `error` event for
// those — they are not failures).
const failTurn = (err: CodedError): void => {
if (errorReported) return
errorReported = true
session.append('error', { turn, step, ...errorData(err) })
reason = { kind: 'error', ...errorData(err) }
try {
ctx.emit('agent/error', agent, turn, step, err)
} catch {
// contained: the error is already logged; a throwing agent/error
// listener must not prevent the turn from closing.
}
}
// Close the turn exactly once (idempotent via turnEnded). `emit` is false on
// the error path (the failure was already surfaced via agent/error) and true
// on the normal/inline-error path. A throwing agent/turn-end listener on the
// normal path escapes to the outer catch, which surfaces it via failTurn —
// turn/end is already appended, so balance holds either way.
const closeTurn = (emit: boolean): void => {
if (turnEnded) return
turnEnded = true
session.append('turn/end', { turn, reason })
if (emit) ctx.emit('agent/turn-end', agent, turn, reason)
}
try {
// --- Turn boundary. Once turn/start is appended, a turn/end is owed no
// matter what throws below; the catch + closeTurn guarantee it.
session.append('turn/start', { turn, trigger })
turnStarted = true
ctx.emit('agent/turn-start', agent, turn)
while (true) {
step += 1
// Steering from the previous round's step-end/continuation listeners
// (or turn-start listeners on the first step) joins before the request.
drainSteering(ctx, agent, turn)
session.append('step/start', { turn, step })
stepOpen = true
ctx.emit('agent/step-start', agent, turn, step)
const abort = new AbortController()
handle.setAbort(abort)
let stepOutcome: { hadToolCalls: boolean } | { error: Error }
try {
stepOutcome = await runStep(ctx, agent, turn, step, abort.signal)
} catch (error: unknown) {
stepOutcome = { error: toError(error) }
} finally {
handle.setAbort(undefined)
}
if ('error' in stepOutcome) {
// Steering that arrived during the failed step stays in the inbox —
// runLoop re-enqueues it as a queued message, so an abort-then-steer
// starts a fresh turn instead of being silently consumed.
closeStep()
const { error } = stepOutcome
if (handle.isDisposed()) {
reason = { kind: 'disposed' }
} else if (abort.signal.aborted) {
/* v8 ignore next -- abort.signal.reason always set by agent.abort() which provides a default */
reason = { kind: 'aborted', reason: String(abort.signal.reason ?? 'aborted') }
} else {
failTurn(error)
}
break
}
// Steering that arrived during streaming/tool execution.
const steered = drainSteering(ctx, agent, turn)
closeStep()
const defaultDecision = stepOutcome.hadToolCalls || steered
let shouldContinue: boolean
try {
shouldContinue = await ctx.waterfall(
'agent/turn-continuation', agent, turn, defaultDecision,
() => Promise.resolve(defaultDecision),
)
} catch (error: unknown) {
// A broken continuation plugin ends the turn, not the loop.
failTurn(toError(error))
break
}
// Steering from step-end/continuation listeners (the /goal pattern)
// demands the model see it — it overrides a negative decision; the
// next iteration's drain records it.
if (!shouldContinue && agent.inbox.hasSteering) shouldContinue = true
if (!shouldContinue || handle.isDisposed()) {
/* v8 ignore next -- disposal during continuation-decision window is a narrow race; error-path disposal is covered elsewhere */
if (handle.isDisposed()) reason = { kind: 'disposed' }
break
}
}
// Normal / inline-error loop exit: close the turn and notify.
closeTurn(true)
} catch (error: unknown) {
// A pre-turn throw (turn/start append) is owed no turn/end — rethrow to
// the backstop. Otherwise a boundary emit (turn-start, step-start, the
// normal-path turn-end) or other unhandled throw escaped: close any open
// step, choose the reason (disposal wins only if no error was reported),
// record the error, and close the turn WITHOUT re-emitting agent/turn-end.
if (!turnStarted) throw error
closeStep()
// Choose the close reason. Disposal wins only if no error was already
// reported: a turn disposed mid-step sets reason=disposed in the step-error
// branch (without reporting an error), and if closeTurn(true)'s turn-end
// emit then throws, we land here and must PRESERVE disposed rather than
// overwrite it with the listener's throw. Otherwise a boundary-emit throw
// on a live agent is a real failure → failTurn. (errorReported is mutated
// only inside the failTurn closure, which the analyzer can't follow, hence
// the inline lint-disable.)
if (handle.isDisposed() && !errorReported) { // eslint-disable-line @typescript-eslint/no-unnecessary-condition
reason = { kind: 'disposed' }
} else {
failTurn(toError(error))
}
closeTurn(false)
}
// Durability checkpoint: persistence plugins drain write-behind buffers.
// A failing persistence plugin is reported but doesn't kill the agent.
@@ -6,6 +6,7 @@ import SystemPrompt from '@deepseek-ai/dsh-system-prompt'
import ToolRegistry, { defineTool } from '@deepseek-ai/dsh-tools'
import AgentRegistry, { AgentId } from '@deepseek-ai/dsh-agent'
import AgentLoop, { LoopAgent } from '@deepseek-ai/dsh-agent-loop'
import * as Invariants from '@deepseek-ai/dsh-invariants'
import { MockAdapter, textResponse, toolCallResponse } from './mock-adapter.ts'
/**
@@ -639,3 +640,250 @@ describe('P1-6: step/start is appended before agent/step-start is emitted', () =
expect(observed[0]).toMatchObject({ turn: 1, step: 1, lastEventType: 'step/start', sawStepStart: true })
})
})
describe('P1-5: a started turn (and any open step) is always closed on a boundary throw', () => {
// Harness with the invariants plugin loaded as an oracle: it throws on
// append if the log goes unbalanced (turn/end while a step is open,
// turn/start while a turn is open, etc.), so a regression surfaces as an
// InvariantError on the NEXT turn's append rather than a silent imbalance.
async function balancedHarness(adapter: MockAdapter) {
const ctx = new Context()
await ctx.plugin(LlmService)
await ctx.plugin(SessionStore)
await ctx.plugin(SystemPrompt)
await ctx.plugin(ToolRegistry)
await ctx.plugin(AgentRegistry)
await ctx.plugin(AgentLoop, { agents: [] })
await ctx.plugin(Invariants, { freeze: false })
ctx.llm.registerAdapter(['mock'], adapter)
return ctx
}
/** Count turn/step boundary events for balance assertions. */
function boundaryCounts(agent: LoopAgent) {
const e = [...agent.session.events]
return {
turnStart: e.filter(x => x.type === 'turn/start').length,
turnEnd: e.filter(x => x.type === 'turn/end').length,
stepStart: e.filter(x => x.type === 'step/start').length,
stepEnd: e.filter(x => x.type === 'step/end').length,
errors: e.filter(x => x.type === 'error').length,
lastTurnEnd: e.findLast(x => x.type === 'turn/end'),
}
}
it('a throwing agent/turn-start listener still closes the turn with exactly one error and one turn/end, no step', async () => {
const adapter = new MockAdapter([textResponse('never reached')])
const ctx = await balancedHarness(adapter)
const agent = ctx.agentLoop.create('a-turnstart', { model: 'mock' })
let threw = false
ctx.on('agent/turn-start', () => { if (!threw) { threw = true; throw new Error('boom turn-start') } })
const errors: Error[] = []
ctx.on('agent/error', (_a, _t, _s, error) => void errors.push(error))
send(agent, 'go')
await waitForIdle(ctx, agent)
const c = boundaryCounts(agent)
// turn opened and closed; no step ran; exactly one error logged + emitted.
expect(c).toMatchObject({ turnStart: 1, turnEnd: 1, stepStart: 0, stepEnd: 0, errors: 1 })
expect(errors.map(e => e.message)).toEqual(['boom turn-start'])
expect(c.lastTurnEnd?.type === 'turn/end' && c.lastTurnEnd.data.reason).toEqual({ kind: 'error', message: 'boom turn-start' })
// model was never called (we threw before the step's request).
expect(adapter.requests).toHaveLength(0)
})
it('a throwing agent/step-start listener closes the open step then the turn (step/end before turn/end)', async () => {
const adapter = new MockAdapter([textResponse('never reached')])
const ctx = await balancedHarness(adapter)
const agent = ctx.agentLoop.create('a-stepstart', { model: 'mock' })
let threw = false
ctx.on('agent/step-start', () => { if (!threw) { threw = true; throw new Error('boom step-start') } })
const errors: Error[] = []
ctx.on('agent/error', (_a, _t, _s, error) => void errors.push(error))
send(agent, 'go')
await waitForIdle(ctx, agent)
const e = [...agent.session.events]
const c = boundaryCounts(agent)
expect(c).toMatchObject({ turnStart: 1, turnEnd: 1, stepStart: 1, stepEnd: 1, errors: 1 })
expect(errors.map(x => x.message)).toEqual(['boom step-start'])
// step/end must precede turn/end (the invariants oracle would reject
// turn/end-while-step-open, but assert the order explicitly too).
const stepEndIdx = e.findIndex(x => x.type === 'step/end')
const turnEndIdx = e.findIndex(x => x.type === 'turn/end')
expect(stepEndIdx).toBeGreaterThanOrEqual(0)
expect(stepEndIdx).toBeLessThan(turnEndIdx)
})
it('a throwing agent/error listener during a step-error path still balances the turn, loop survives', async () => {
// First turn: model stream ends with a finish-error → step error path →
// failTurn emits agent/error, whose listener throws. The turn must still
// close balanced. Second turn proves the loop survived.
const errorStream: StreamChunk[] = [{ type: 'finish', reason: { kind: 'error', message: 'provider 500' } }]
const adapter = new MockAdapter([errorStream, textResponse('turn 2 ok')])
const ctx = await balancedHarness(adapter)
const agent = ctx.agentLoop.create('a-errorlistener', { model: 'mock' })
let threw = false
ctx.on('agent/error', () => { if (!threw) { threw = true; throw new Error('boom error-listener') } })
send(agent, 'go')
await waitForIdle(ctx, agent)
const c = boundaryCounts(agent)
// turn 1 balanced despite the throwing agent/error listener.
expect(c.turnStart).toBe(1)
expect(c.turnEnd).toBe(1)
expect(c.stepStart).toBe(c.stepEnd)
expect(c.lastTurnEnd?.type === 'turn/end' && c.lastTurnEnd.data.reason).toMatchObject({ kind: 'error', message: 'provider 500' })
// loop survives: a second turn runs to completion (invariants oracle would
// throw on its turn/start if turn 1 had been left open).
send(agent, 'again')
await waitForIdle(ctx, agent)
const c2 = boundaryCounts(agent)
expect(c2.turnStart).toBe(2)
expect(c2.turnEnd).toBe(2)
expect(c2.stepStart).toBe(c2.stepEnd)
})
it('disposal during a running turn ends the turn with reason disposed (balanced)', async () => {
// The 'hang' adapter blocks in stream() until the signal aborts; disposing
// the agent's fiber mid-turn aborts the in-flight step. The turn must close
// balanced with reason disposed (no error event for a disposal).
const adapter = new MockAdapter(['hang'])
const ctx = await balancedHarness(adapter)
let agent!: LoopAgent
const fiber = await ctx.plugin(Object.assign((inner: Context) => {
agent = inner.agentLoop.create('a-dispose', { model: 'mock' })
}, { inject: ['agentLoop'] }))
const reasons: TurnEndReason[] = []
ctx.on('agent/turn-end', (_a, _t, reason) => void reasons.push(reason))
send(agent, 'go')
await new Promise(r => setTimeout(r, 30))
await fiber.dispose() // dispose during the hanging step
await agent.done
const e = [...agent.session.events]
const turnStarts = e.filter(x => x.type === 'turn/start').length
const turnEnds = e.filter(x => x.type === 'turn/end').length
expect(turnStarts).toBe(1)
expect(turnEnds).toBe(1) // balanced — the turn was closed despite disposal
expect(reasons).toEqual([{ kind: 'disposed' }])
// no error event: disposal is not a failure.
expect(e.some(x => x.type === 'error')).toBe(false)
})
it('preserves reason disposed when the turn-end emit throws during disposal (outer-catch disposed branch)', async () => {
// Dispose mid-step → the step-error branch sets reason=disposed (no error
// reported). closeTurn(true) then emits agent/turn-end, whose listener
// throws → control reaches the outer catch with isDisposed() && !errorReported,
// which must PRESERVE disposed rather than overwrite it with the listener's
// throw. This is the only path that exercises that catch sub-branch.
const adapter = new MockAdapter(['hang'])
const ctx = await balancedHarness(adapter)
let agent!: LoopAgent
const fiber = await ctx.plugin(Object.assign((inner: Context) => {
agent = inner.agentLoop.create('a-dispose-emit-throw', { model: 'mock' })
}, { inject: ['agentLoop'] }))
// The FIRST agent/turn-end emit throws (the disposal-driven turn end).
let threw = false
ctx.on('agent/turn-end', () => { if (!threw) { threw = true; throw new Error('boom turn-end during disposal') } })
// Collect agent/error emissions to prove none is surfaced through that
// channel either (the listener throw must be fully contained).
const errorEmits: Error[] = []
ctx.on('agent/error', (_a, _t, _s, error) => void errorEmits.push(error))
send(agent, 'go')
await new Promise(r => setTimeout(r, 30))
await fiber.dispose() // dispose during the hanging step
await agent.done
// The throwing turn-end listener actually fired — proving the outer-catch
// path was exercised, not skipped.
expect(threw).toBe(true)
const e = [...agent.session.events]
// Exactly one turn/start and one turn/end (balanced); the turn/end carries
// the disposed reason, NOT an error reason from the throwing listener.
expect(e.filter(x => x.type === 'turn/start')).toHaveLength(1)
const turnEnd = e.findLast(x => x.type === 'turn/end')
expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason).toEqual({ kind: 'disposed' })
// The throwing turn-end listener is contained: no error event is logged and
// no agent/error is emitted (disposal is not a failure; the throw is swallowed).
expect(e.some(x => x.type === 'error')).toBe(false)
expect(errorEmits).toHaveLength(0)
})
it('a throw at the turn/start append (before turnStarted) is rethrown to the runLoop backstop', async () => {
// A session/event listener that throws specifically on the turn/start
// event makes session.append('turn/start') throw while turnStarted is
// still false. runTurn must NOT try to close a turn it never opened — it
// rethrows, and the runLoop backstop records the error and survives.
// (Uses the plain harness — NOT the invariants oracle — because the
// throwing listener is itself a session/event subscriber.)
const adapter = new MockAdapter([textResponse('turn 2')])
const ctx = await harness(adapter)
const agent = ctx.agentLoop.create('a-preturn', { model: 'mock' })
let threw = false
ctx.on('session/event', (_session, event) => {
if (!threw && event.type === 'turn/start') { threw = true; throw new Error('boom turn/start append') }
})
const errors: Error[] = []
ctx.on('agent/error', (_a, _t, _s, error) => void errors.push(error))
send(agent, 'go')
await waitForIdle(ctx, agent)
// The backstop logged exactly one error for the failed pre-turn append.
expect(errors.map(e => e.message)).toEqual(['boom turn/start append'])
// No turn/end was appended (none is owed — the turn never opened).
expect([...agent.session.events].some(e => e.type === 'turn/end')).toBe(false)
// loop survives: a second turn runs normally.
send(agent, 'second')
await waitForIdle(ctx, agent)
expect(adapter.requests).toHaveLength(1)
})
it('a step error followed by a throwing turn-end listener logs the error exactly once (no double-report)', async () => {
// The step fails (finish-error) → failTurn records ONE error and sets the
// error reason. closeTurn(true) then appends turn/end and emits
// agent/turn-end, whose listener throws → the outer catch calls failTurn
// again, but its errorReported guard makes it a no-op. Trap #1: exactly one
// error, the turn stays balanced.
const errorStream: StreamChunk[] = [{ type: 'finish', reason: { kind: 'error', message: 'provider down' } }]
const adapter = new MockAdapter([errorStream, textResponse('turn 2 ok')])
const ctx = await balancedHarness(adapter)
const agent = ctx.agentLoop.create('a-double', { model: 'mock' })
let threw = false
ctx.on('agent/turn-end', () => { if (!threw) { threw = true; throw new Error('boom turn-end') } })
const errors: Error[] = []
ctx.on('agent/error', (_a, _t, _s, error) => void errors.push(error))
send(agent, 'go')
await waitForIdle(ctx, agent)
const c = boundaryCounts(agent)
// exactly one error event + one agent/error emit, despite two failTurn calls.
expect(c.errors).toBe(1)
expect(errors.map(e => e.message)).toEqual(['provider down'])
expect(c.turnStart).toBe(1)
expect(c.turnEnd).toBe(1) // single turn/end, balanced
expect(c.lastTurnEnd?.type === 'turn/end' && c.lastTurnEnd.data.reason).toMatchObject({ kind: 'error', message: 'provider down' })
// loop survives the compound failure.
send(agent, 'again')
await waitForIdle(ctx, agent)
expect(boundaryCounts(agent).turnEnd).toBe(2)
})
})
+2 -1
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@@ -558,6 +558,7 @@ __metadata:
resolution: "@deepseek-ai/dsh-agent-loop@workspace:packages/agent-loop"
dependencies:
"@deepseek-ai/dsh-agent": "npm:^0.0.1"
"@deepseek-ai/dsh-invariants": "npm:^0.0.1"
"@deepseek-ai/dsh-llm": "npm:^0.0.1"
"@deepseek-ai/dsh-session": "npm:^0.0.1"
"@deepseek-ai/dsh-system-prompt": "npm:^0.0.1"
@@ -611,7 +612,7 @@ __metadata:
languageName: unknown
linkType: soft
"@deepseek-ai/dsh-invariants@workspace:packages/invariants":
"@deepseek-ai/dsh-invariants@npm:^0.0.1, @deepseek-ai/dsh-invariants@workspace:packages/invariants":
version: 0.0.0-use.local
resolution: "@deepseek-ai/dsh-invariants@workspace:packages/invariants"
dependencies: