FA-100581 / Mixture of experts dispatch / Open access

Shared expert output is lost when routed experts are empty · case 01

Shared expert output is lost when routed experts are empty.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The combine step only visits conditional routes.

THE FAILURE

The combine step only visits conditional routes.

Unsuccessful approach: Adding the shared expert only when at least one conditional route survives still drops it on overflow.

Case contract

Given a shared scalar and routed (expert,weight,value) routes, return shared plus weighted route values.

Why this case matters

A deterministic toy router makes this dispatch decision independently inspectable.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(shared,routes):
    return sum(w*v for e,w,v in routes)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
rows=[('a',0.5,N),('b',0.5,2*N)]
check('shared and routes',solve(N,rows),N+1.5*N)
check('no routes',solve(N,[]),N)
check('one route',solve(2*N,[('x',1,N)]),3*N)
check('zero shared',solve(0,rows),1.5*N)
check('zero weights',solve(N,[('x',0,9)]),N)
check('empty and zero',solve(0,[]),0)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
shared and routes	`1.5`	`2.5`	Failed
no routes	`0`	`1`	Failed
one route	`1`	`3`	Failed
zero shared	`1.5`	`1.5`	Passed
zero weights	`0`	`1`	Failed
empty and zero	`0`	`0`	Passed

SHA-256 / 48aeeefb2c3b1b74eb3ad4270fc8e410e540760dc7e3488ef5a8fcbcd17747af

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(shared,routes):
    return shared+sum(w*v for e,w,v in routes) if routes else 0
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
rows=[('a',0.5,N),('b',0.5,2*N)]
check('shared and routes',solve(N,rows),N+1.5*N)
check('no routes',solve(N,[]),N)
check('one route',solve(2*N,[('x',1,N)]),3*N)
check('zero shared',solve(0,rows),1.5*N)
check('zero weights',solve(N,[('x',0,9)]),N)
check('empty and zero',solve(0,[]),0)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
shared and routes	`2.5`	`2.5`	Passed
no routes	`0`	`1`	Failed
one route	`3`	`3`	Passed
zero shared	`1.5`	`1.5`	Passed
zero weights	`1`	`1`	Passed
empty and zero	`0`	`0`	Passed

SHA-256 / 35d09e99f0874f26aafae448fbda6aaa891623fdbb4714a339e9bc275c46d024

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 6 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

Inputs are finite toy scores and routes; the contract does not model a production model, accelerator, or learned routing quality. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-30T16:48:37.194461+00:00.

Case digest / 5ba233384284dea988989180da200acee8e73d1f366d798f44aa02cbf3abde4f