Drop speculative future-providers reference from CHANGELOG

The "future Anthropic / Gemini providers will follow the §8.X
template" framing references unproposed spec work. Out-of-scope
items belong in PR descriptions scoped to this PR; speculative
future capabilities and proposal numbers don't belong in the
release-notes record.

Author: chris-colinsky

CHANGELOG.md

@@ -20,7 +20,7 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/). The
 
 ### Changed
 
-- **`Provider.complete()` signature** extended with an optional `tool_choice: ToolChoice | None = None` parameter (per proposal 0025 v0.20.0). Backward-compatible: callers that omit the new argument see no wire-shape change. Third-party `Provider` implementations that don't add the parameter still structurally satisfy the `Provider` Protocol; their wire path silently drops `tool_choice`. The OpenAI mapping is in `OpenAIProvider`; future Anthropic / Gemini providers will follow the §8.X template (proposal 0026) and ship their own `tool_choice` wire mapping.
+- **`Provider.complete()` signature** extended with an optional `tool_choice: ToolChoice | None = None` parameter (per proposal 0025 v0.20.0). Backward-compatible: callers that omit the new argument see no wire-shape change. Third-party `Provider` implementations that don't add the parameter still structurally satisfy the `Provider` Protocol; their wire path silently drops `tool_choice`. The `OpenAIProvider` wire mapping is implemented per §8.1.1.
 - **`CompiledGraph.drain()` return type** changed from `None` to `DrainSummary` (pre-1.0; per proposal 0010 v0.19.0 contract). Callers that ignored the return are unaffected — `await graph.drain()` discards the returned dataclass exactly as before. Callers that explicitly typed the return as `None` will need to update their annotation.
 - **Fan-out resume behavior** flipped from atomic restart (0008's v1 contract) to per-instance resume. A crash mid-fan-out used to re-run the entire fan-out on resume; now only the instances that did not complete-and-record their contribution re-run. The economics matter for large fan-outs of expensive work (LLM calls, long extractions): an 80% complete fan-out crash now restores 80% of its results rather than discarding them.
 - **`SQLiteCheckpointer` schema** picks up a new `fan_out_progress_blob` column (added via `ALTER TABLE` for backward compatibility with pre-0009 databases). Pre-0009 rows back-fill as NULL on load and round-trip as the empty-tuple default. Both `pickle` and `json` serialization modes round-trip the new field.