# PRD: Legacy routing compatibility regression

## Overview

The tracker’s new request-precision gate rejects legacy node registrations that omit `quantization`. This conflicts with the explicit `capability_policy=compat` rollout: an older node without a capability report remains routable, but an older node without a quantization field is silently excluded from proxy, pinned-route, benchmark, billing, and latency paths.

## Goal

Restore backward-compatible routing for legacy registrations while preserving fail-closed behavior for explicitly declared invalid/unsupported quantization values.

## Quality gates

- Run targeted routing, billing, benchmark, pricing, validation, and latency tests.
- Run `python -m pytest -q` before completion and record any unrelated failures exactly.
- Preserve the admission-policy invariant: invalid capability reports remain non-routable; absent reports route only under `compat`.

## User story

### RCR-001: Legacy registration precision fallback

As an operator upgrading a mixed fleet, I need nodes that predate the `quantization` registration field to serve default-precision requests under `compat`, so the tracker rollout does not make otherwise healthy legacy nodes dark.

## Non-goals

- Do not weaken `enforce` capability policy.
- Do not treat explicitly malformed or unsupported quantization values as valid.
- Do not change requested-precision semantics for nodes that declare a supported precision.
