fix: resolve 1M context for opencode-free and muse-spark family

[Steve-prog001]

Summary

• Map opencode-free to the opencode-go models.dev catalog. The opencode /models endpoint omits context metadata for all 66 models and opencode-free had no models.dev alias, so every model on that route survived only via the hardcoded catalog and muse-spark fell through to the 256K fallback.
• Add muse-spark=1048576 to DEFAULT_CONTEXT_LENGTHS (Meta docs: Standard and Contributor tiers share the 1,048,576-token window; verified 2026-09-03; missing from models.dev under every provider id and opencode exposes no metadata to probe).
• Route commandcode/commandcode-anthropic through the live /models endpoint, which reports authoritative context_length (e.g. 1048576) but was skipped as a known provider.

Test plan

• get_model_context_length now returns 1048576 for muse-spark-1.3-contributor-free / muse-spark-1.2 on opencode-free and meta/muse-spark-1.3-contributor on commandcode (was 256000); spot-checked qwen/deepseek/claude/gpt on opencode-free unchanged (provider-catalog values).
• tests/agent/test_model_metadata.py, test_models_dev.py, test_models_dev_meta_mapping.py: 185 passed.
• New tests/agent/test_opencode_free_mapping.py: 3 passed (with meta-mapping test file).

Note

• qwen3.6-plus on opencode-free now resolves via the provider catalog (1000000) instead of the DashScope hardcoded value (1048576); provider-specific catalog wins by design (safe direction).

[teknium1]

Closing in favor of #101949 (commit 0b96eaf), which landed the same muse-spark context entry (credited to @GTHell's earlier #98745) and your commandcode routing from #101588. Your models.dev-alias idea for opencode-free is in there too, credited to you — but mapped to opencode rather than opencode-go: the free tier is Zen-hosted (see opencode_model_api_mode, 'opencode-free is Zen-hosted'), and models.dev's opencode provider is where muse-spark-1.3-contributor-free lives. Thanks @Steve-prog001!

[Steve-prog001]

Hi @teknium1 — thanks for salvaging this into #101949 and for the clear explanation of why opencode-free maps to the Zen opencode catalog rather than opencode-go; that makes sense.

Same small follow-up as on #101588: since the merge was a rebase-merge, my commits don't surface in the repo's contributor aggregation (known GitHub gap for rebased commits). Could you add my mapping under contributors/emails/, like sosxradar@gmail.com -> GTHell?

290940015+Steve-prog001@users.noreply.github.com -> Steve-prog001

That would complete the attribution in the repo's own records. Thanks again!