fix: unlock 1M-token context for Sonnet 4.5 and GPT-5 in pi

[dgokeeffe]

Summary

Fixes long-context metadata for Claude and GPT gateway models, with GPT handling scoped to Pi.

• Claude Code: add [1m] to Sonnet 4.5+ and Opus 4.6+ aliases.
• Pi: emit explicit Claude contextWindow, maxTokens, reasoning, image, and adaptive-thinking metadata instead of accepting Pi's custom-model defaults.
• Pi: emit model-specific GPT limits; GPT-5.6 Sol/Terra/Luna use the opt-in 1,050,000-token window rather than treating every GPT-5 model as 1M.
• Handle dotted, system.ai.*, databricks-*, and provider-qualified model IDs.

Closes databricks#222.

Root cause and reproducible proof

Pi 0.80.6 documents these defaults for custom models when fields are omitted:

contextWindow: 128000
maxTokens: 4096

ucode previously emitted Claude models as only {"id": ...}, so Pi displayed and compacted Opus 4.8 as a 128K model even though the gateway model is long-context.

The installed Pi catalog independently declares Claude Opus 4.8 as:

contextWindow: 1000000
maxTokens: 128000

Pi's model override docs also explicitly show GPT-5.6 Sol can opt into:

{"gpt-5.6-sol": {"contextWindow": 1050000}}

After this patch, rendering a ucode Pi overlay produces:

{
  "id": "databricks-claude-opus-4-8",
  "reasoning": true,
  "input": ["text", "image"],
  "contextWindow": 1000000,
  "maxTokens": 128000,
  "compat": {"forceAdaptiveThinking": true}
}

and:

{
  "id": "databricks-gpt-5-6-sol",
  "contextWindow": 1050000,
  "maxTokens": 128000,
  "reasoning": true,
  "input": ["text", "image"]
}

Claude Code 2.1.214 bundle inspection also confirms that [1m] selects context-1m-2025-08-07 independently of CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS. Therefore beta suppression was not the root cause of Pi's 128K display; the omitted Pi custom-model metadata was.

Validation

uv run pytest tests/test_agent_pi.py tests/test_databricks.py tests/test_agent_claude.py tests/test_lint.py -q
272 passed in 5.53s

uv run ruff check .
All checks passed!

A full local run reached 913 passed, 36 skipped; its only behavioral failure was the managed-environment Claude binary timing out before reaching the test capture server. The other failure was formatting, subsequently fixed and covered by the passing tests/test_lint.py run above.

Stacking

This PR is stacked on dgokeeffe:feat/pi-oss-provider-v2 / databricks#217. Retarget to databricks/ucode:main after databricks#217 merges.

[dgokeeffe]

Superseded by upstream PR: databricks#223