#20122: Fix sonnet alias resolving to opus in OpenCode Zen model aliases

## Problem The `sonnet` and `sonnet-4` aliases in `OPENCODE_ZEN_MODEL_ALIASES` incorrectly resolve to `claude-opus-4-6` instead of `claude-sonnet-4-6`. Users typing `sonnet` expecting the cheaper/faster Sonnet model silently get Opus instead — wrong model, higher cost, no warning. ## Fix - `sonnet` → `claude-sonnet-4-6` - `sonnet-4` → `claude-sonnet-4-6` - Added `sonnet-4.6` alias - `haiku`/`haiku-3.5` legacy aliases now point to Sonnet (closer match than Opus) <!-- greptile_comment --> <h3>Greptile Summary</h3> Fixes the `sonnet` and `sonnet-4` aliases in `OPENCODE_ZEN_MODEL_ALIASES` to correctly resolve to `claude-sonnet-4-6` instead of `claude-opus-4-6`, preventing users from being silently billed at Opus rates when requesting Sonnet. Also adds a `sonnet-4.6` alias and updates legacy `haiku`/`haiku-3.5` aliases to point to Sonnet instead of Opus. - **Bug found**: The `OPENCODE_ZEN_MODEL_ALIASES` test block (lines 99-101) was not updated — it still asserts `sonnet` and `haiku` map to `claude-opus-4-6`, which will cause test failures. - The source code changes in `opencode-zen-models.ts` are correct and consistent with the rest of the codebase (e.g., `model-selection.ts` and `live-model-filter.ts` already reference `claude-sonnet-4-6`). <h3>Confidence Score: 2/5</h3> - The source code fix is correct, but the test file has stale assertions that will fail — this PR should not be merged until the test is updated. - The alias corrections in the source file are valid and address a real billing/correctness issue. However, the test file contains two assertions (lines 100-101) that contradict the source changes and will fail, indicating the PR was not fully validated before submission. - `src/agents/opencode-zen-models.e2e.test.ts` — lines 99-101 have stale assertions that need updating to match the new alias mappings. _{Last reviewed commit: 2c2e2e4} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->