[verified] fix: preserve tracker precision eligibility

.scratch/routing-compatibility-regression/PRD.md

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+# 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.