fix(compat): merge partial model spec overrides

[javargasm]

Summary

Follow-up to merged #30 for regressions found by the post-merge blind audit and maintainer review:

• merge partial exact and substring modelSpecs overrides over the effective dynamic, static, or family defaults
• preserve operator precedence for fields that are provided while inheriting omitted output, thinking, minimum-budget, and context metadata
• keep required numeric model fields finite and align the TypeScript config contract with the runtime validator's partial-override behavior
• preserve partial modelSpecs through shared configuration normalization and persisted save/load paths
• make Antigravity context-window resolution honor the same exact and substring operator overrides used by effective model specs
• publish inherited dynamic context metadata without changing bundled catalog context-window behavior

Regressions

A partial substring override such as { "gemini-3.8": { "maxOutputTokens": 1000, "isThinking": true } } previously replaced the complete bundled spec. The omitted thinkingBudget reached thinking normalization as undefined, became NaN, and serialized to thinkingBudget: null.

Shared configuration normalization also rebuilt the configuration without modelSpecs, so validated API and persisted configurations silently lost those overrides. Separately, /v1/models reflected a valid contextWindow override while getAntigravityContextWindow() continued returning the bundled value.

Strict TDD evidence

• RED: the original partial exact/substring override regressions failed before the effective-spec merge fix
• RED: three maintainer regressions failed with normalized modelSpecs missing and exact/substring context helpers returning 1,000,000 instead of 222,222/333,333
• GREEN: all focused regressions pass, including persisted partial specs, unknown top-level field filtering, JSON serialization without null thinking budgets, valid zero budgets, and exact/substring context overrides

Verification

• focused compatibility/catalog/validator suite: 104/104 passed
• focused configuration/context-window files: 41/41 passed
• npm run check: 730/730 tests passed
• source and test typechecks passed
• lint passed with 15 pre-existing warnings and no errors
• git diff --check

[tuxevil]

Thanks for the follow-up work. I found one blocking issue that needs to be addressed before merge:

[P1] Preserve modelSpecs through configuration normalization

applyConfigDefaults() rebuilds the configuration object but does not copy config.modelSpecs. Both getCachedConfig() and setCachedConfig() call this function, so a modelSpecs section loaded from accounts.json or submitted through the config API is silently dropped before index.ts calls setModelSpecsOverride(). As a result, the partial-override fix works in direct unit tests but is not usable through the normal persisted configuration path. Please preserve modelSpecs in applyConfigDefaults() and add a regression test covering the validated/normalized configuration path (ideally load/save as well).

I also noticed that the newly accepted contextWindow override is reflected in /v1/models, but getAntigravityContextWindow() still returns the static/dynamic value and ignores the operator override. Please either wire that helper into the same effective-spec resolution or clarify/document that it is intentionally not overrideable.

The current tests and CI checks are green, but I recommend addressing the P1 before merging.

[tuxevil]

Thank you for the follow-up work and for addressing the review findings. The configuration persistence and context-window handling are now covered, and the PR has been merged. Your contribution is appreciated!