Backend Change Builder

---
name: backend-change-builder
description: "Use `task-agent` for bounded backend service, API, worker, and native/firmware runtime changes. Skip frontend-only and read-only work."
---

# backend-change-builder

## Role

Support `task-agent` in preserving invariants across bounded backend changes.

## When To Use

- backend behavior change
- service or worker change
- local native or firmware runtime implementation; device knowledge is a modifier and release remains with delivery

## Do Not Use

- frontend only
- source inspection only

## Required Inputs

- domain invariants
- authorization and failure-contract evidence
- transaction, delivery, and recovery constraints

## Professional Decision Rules

- Trace the affected invariant through authorization, mutation, side effects, repetition, and failure using only the triggered named References.
- Preserve compatible error contracts when failure behavior changes.
- Select redacted observability from current API and platform policy.

## High-Value Gotchas

- Late authorization, pre-commit effects, or unbounded repetition can violate the invariant.

## Execution Checklist

1. Select controls from the accepted invariant and reachable failure paths.
2. Implement the bounded change with compatible errors and redacted diagnostics.
3. Stop when a triggered invariant lacks negative-path or recovery evidence.

## Stop / Escalation Conditions

- Stop when behavior, ownership, validation, or a triggered invariant remains implicit.
- Stop new structure until placement, ownership, dependency direction, and the simpler local option are evaluated.
- Stop sensitive or external actions without authority, redaction, recovery, and fresh evidence.

## Output Contract

- changed backend invariants and boundaries
- authorization, consistency, delivery, and recovery decisions
- negative-path and recovery proof limits
- residual operational risk

For targeted implementation fields and gates, load `references/backend-output-and-gates.md`.

## Targeted References

| Path | Type | Load when | Do not load when | Required by | Required output |
|---|---|---|---|---|---|
| [backend output and gates](references/backend-output-and-gates.md) | targeted | extended fields apply when implementation closure depends on edit-to-validation ordering or repair proof | The root contract is sufficient for bounded implementation | task-agent | gate-decision, residual-risk |
| [checklist](references/checklist.md) | decision-checklist | A bounded implementation needs quick checks for its triggered backend risks | The root contract is enough or extended proof fields are needed | task-agent | checklist-result, residual-risk |
| [index](references/index.md) | index | competing backend change builder references require dependency, conflict, or output-fragment selection | the backend change builder root or a task-named reference already resolves selection | task-agent | reference-selection |
| [proactive triggers](references/proactive-triggers.md) | targeted | Authorization, tenancy, retries, async, public contracts, transactions, irreversible mutation, or AI-generated backend code are material | No hidden backend escalator is present | task-agent | boundary-decision, residual-risk |
| [professional modes](references/professional-modes.md) | mode-contract | implementation or accepted-finding repair needs mode-specific proof and ownership limits | The root contract determines implementation evidence or the task is still diagnosis/independent review | task-agent | mode-result, proof-limit |
| [solution optimality](references/solution-optimality.md) | targeted | An accepted implementation chooses a material algorithm, query pattern, cache, batch/stream boundary, concurrency control, pool, queue, or other resource-sensitive design | No runtime/resource tradeoff is material or current system evidence already fixes the mechanism | task-agent | selected-approach, residual-risk |