* fix(#1569): preserve explicit resolve_model_ids in non-Claude installs
The non-Claude finishInstall step keyed its resolve_model_ids:"omit" write on
!== "omit", so an explicit true opt-in (resolveModelInternal returns full model
IDs) was silently clobbered on every install/upgrade across all 14 non-Claude
runtimes, making generated agent manifests inherit the active chat model instead
of pinning the resolved model. Now only absent/falsy is defaulted to "omit"; an
explicit true (and an existing "omit") is preserved. Regression test
parameterizes across codex/opencode/gemini and covers the absent/false/idempotent/
claude/malformed boundaries.
* chore(#1569): backfill changeset pr ref to 1653
* fix(#1569): default non-canonical resolve_model_ids values to omit (codex review)
Adversarial review (codex, gpt-5.5/high) flagged that the original allowlist-by-
enumeration condition (undefined/null/false -> omit) preserved malformed values
(0, "", "yes", {}) instead of defaulting them to omit, letting them leak Claude
aliases a non-Claude runtime cannot resolve. Switch to an allowlist condition
(existing !== true && existing !== 'omit') so only an explicit canonical true
opt-in and an existing omit are preserved; everything else defaults to the safe
non-Claude omit. Adds a parameterized test over [0, "", "yes", {}].
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