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get_variants handed out a deep copy on every call so one caller's
mutation could not reach the next. services_overrides_for_round asks
for the map once per round, and a sweep resolves hundreds of rounds, so
the matrix planner paid that copy 460 times: 78 million deepcopy calls,
and get_variants alone accounting for 82 of the 163 seconds a profiled
build took.
The copy is now opt-out for that one caller. It reads the map and never
writes to it, resolve_pins takes it as a Mapping and has no mutation
site, and _deep_merge deep-copies both of its arguments, so nothing the
round produces keeps a reference into the cache. Fifteen other callers
keep the copy untouched.
Measured end to end on cli.meta.ci.playwright_coverage: 33.7s to 24.6s.
Equivalence is measured against the copying path for two fixed rounds,
291 roles each, rather than against a sweep -- two identical planner
runs assign different modes to some rows, so a plan diff cannot carry
that proof.
The test asserts identity rather than runtime, as the comparable
optimization in 0cb8bae88d did: a wall-clock bound on this machine is
the same flakiness the sweep already shows.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>