Implements P-1 through P-6 of the prefer-routing-policy plan.
Adds a config knob that biases routing toward local arms, cloud
arms, or leaves selection unchanged. Default "auto" is
byte-identical to pre-change behavior (the new armTier path with
PreferAuto returns the same value as the old single-arg function).
Mechanism diverged from the plan after empirical testing:
The plan called for a score multiplier applied in bestScored.
Tests revealed the existing cost-floor math (scoreArm divides by
weighted cost which collapses to ~0.001 for free local arms) gives
local arms a ~280x raw-score advantage that a 0.3-0.5 multiplier
can't overcome. A tier-shift in armTier turned out cleaner:
PreferLocal: cloud arms (true API, IsLocal=false && !IsCLIAgent)
get +2 tier shift, landing behind locals.
PreferCloud: IsLocal arms get +2 tier shift, landing behind
cloud. SLM tier-0 arms shift to tier 2 — still
below cloud's tier 3 — so the SLM-protection
semantic (small stuff stays on the small model)
survives PreferCloud. This matches the open
question in the plan, now resolved as: yes, SLMs
keep winning under PreferCloud by design.
The policyMultiplier was kept in bestScored as a within-tier
nudge (mostly cosmetic in practice given the cost-floor dynamics
described above; could matter when costs are calibrated). Worth
revisiting once router-wide cost calibration lands.
Strengths cross-tier promotion is unaffected: the promoted-set
path in selectBest bypasses armTier entirely, so a strongly-tagged
cloud arm still wins SecurityReview tasks under PreferLocal
(validated by TestPreferPolicy_StrengthsBeatsMultiplier).
CLI-agent subprocess arms count as "local" for PreferLocal
purposes — they proxy to cloud but the user-visible behavior is
local. Users who want to exclude them can use --provider X.
Forced arms (--provider X) and incognito take priority over the
policy: forced arm test pins this, incognito-still-wins test pins
the LocalOnly hard filter dominating PreferCloud.
Test coverage (prefer_test.go): ParsePreferPolicy / String round
trips; policyMultiplier table; acceptance scenarios across all
three policies with adjacent-tier arms; SLM-still-wins under
PreferCloud; Strengths beats multiplier; forced-arm bypass;
incognito beats prefer; lone cloud arm wins when no local feasible.
Refs: docs/superpowers/plans/2026-05-23-prefer-routing-policy.md
vikingowl
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