#17604: fix(context): use getAvailable() to prevent cross-provider model ID collision in MODEL_CACHE

## Summary `lookupContextTokens()` in `src/agents/context.ts` uses `modelRegistry.getAll()` which returns models from **all** built-in providers — including unconfigured ones. When multiple providers define the same model ID (e.g. `claude-sonnet-4-5`) with different `contextWindow` values, the last provider iterated overwrites the correct value in `MODEL_CACHE`. ## Fix Switch from `getAll()` to `getAvailable()`, which filters to only providers with configured authentication. This prevents unconfigured providers from polluting the cache with incorrect context window values. ## Impact - `/status` now shows correct context window - Token budget calculations use accurate context size - Session `contextTokens` field persisted correctly ## Testing - Existing `context.test.ts` passes (2/2 tests) - Build passes cleanly Fixes #17586 <!-- greptile_comment --> <h3>Greptile Summary</h3> Fixes a cross-provider model ID collision in `MODEL_CACHE` by switching from `modelRegistry.getAll()` to `modelRegistry.getAvailable()` in `src/agents/context.ts`. When multiple providers define the same model ID (e.g. `claude-sonnet-4-5`) with different `contextWindow` values, `getAll()` would let unconfigured providers overwrite the correct value. Using `getAvailable()` filters to only providers with configured authentication, ensuring accurate context window values. - Minimal one-line change that aligns with how `list.registry.ts` already distinguishes between "all models" (for display) and "available models" (for functional use) - Both `getAll()` and `getAvailable()` return `Model<Api>[]`, so the existing type cast and downstream iteration logic remain correct - Existing `context.test.ts` tests cover `applyConfiguredContextWindows` (which runs after the cache is populated) but not the cache population itself — this is acceptable since the fix is a straightforward API swap with the same return type <h3>Confidence Score: 5/5</h3> - This PR is safe to merge — it's a minimal, well-targeted one-line fix that uses the correct API for filtering to configured providers. - The change is a single method call swap from getAll() to getAvailable(), both of which return the same type. The fix directly addresses the documented bug (cross-provider model ID collision) and is consistent with how the rest of the codebase uses getAvailable() for functional/operational purposes. No new code paths, no behavioral changes for correctly-configured providers, and the surrounding error handling remains intact. - No files require special attention. _{Last reviewed commit: d2eed6e} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->