Per-instance cache keyed by (id(adj), start, goal). All 4 adj dicts
(_adj, _adj_all, _adj_local, _adj_mcpu_dma) are built in __init__ and
never mutated (topology is static per ADR-0006 / SPEC §0.1), so id(adj)
is stable for the router's lifetime. Cache is populated on the
successful-return paths; RoutingError paths intentionally re-run each
call (rare, keeps error semantics unchanged).
Motivation: cProfile of Case 4 decode at S_kv=8K showed 1,142
_run_dijkstra_with_dist calls consuming ~1.95s tottime. Paths depend
only on (adj, src, dst) so ~99% of those calls are recomputing the same
result.
Verified:
- tests/attention/test_milestone_gqa_decode_long_ctx_4cases.py: 18/18 pass
- 128K decode wall: 237.28s -> 233.71s (-1.5%)
- Modeled kernel latency: 461.13us (byte-identical before/after)
- op_log_len: 3057 (unchanged)
Small win but no risk: memoization returns byte-identical results and
paths cannot change during a sim run. Larger event-count reductions
require touching the per-hop hot path (zero-latency chain collapse
etc.).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
mukesh
f9d0077472