refactor(agent): persist model selection in session state

python/development.md

@@ -38,7 +38,7 @@ uv run --project python/sdk python scripts/smoke-python-runtime.py \
   --scenario sdk-minimal --exe dist-exe/deepseek-harness-sdk-runtime-macos-arm64
 ```
 
-SDK scenarios compare committed expected output under `scripts/snapshots/python-sdk-single-exe/`. `minimal/model-visible.json` pins the Linux/macOS `sdk-minimal` profile's assembled system prompts, advertised tool schemas, and model-visible messages; `minimal/win-x64/model-visible.json` pins its PowerShell counterpart. `authoring/model-visible.json` pins the Linux/macOS Office authoring catalog and dependency result; `authoring/win-x64/model-visible.json` pins the Windows catalog, including the ACL diagnostic skill. A plugin that contributes an unintended system section or user message therefore fails the job, and every message the profile emits is compared. `advanced/` pins one complex process's SDK result and parent/child session logs across every target. `restart/` launches two complete SDK runtime processes against one persistence root and snapshots their isolated model histories, high-level results, and separate durable logs across every target. `sdk-minimal-in-history` reuses the persistent-shell and editor scenario with a section that changes after the first successful shell call. `minimal-in-history/prompt-history.json` pins both prompt versions, the unchanged leading prompt in later requests, appended SDK system-message events, and `request/context.systemPromptUpdate`; tool schemas stay fixed and the editor file is checked independently. `sdk-dynamic-tools` pins native tool additions and removals in `dynamic-tools/tool-history.json`, including historical header references and agreement between Python SDK results, notifications, and persisted events. Rerun the owning scenario with `--update-snapshots` and review that diff before committing it.
+SDK scenarios compare committed expected output under `scripts/snapshots/python-sdk-single-exe/`. `minimal/model-visible.json` pins the Linux/macOS `sdk-minimal` profile's assembled system prompts, advertised tool schemas, and model-visible messages; `minimal/win-x64/model-visible.json` pins its PowerShell counterpart. `authoring/model-visible.json` pins the Linux/macOS Office authoring catalog and dependency result; `authoring/win-x64/model-visible.json` pins the Windows catalog, including the ACL diagnostic skill. A plugin that contributes an unintended system section or user message therefore fails the job, and every message the profile emits is compared. `advanced/` pins one complex process's SDK result and parent/child session logs across every target. `restart/` launches two complete SDK runtime processes against one persistence root and snapshots their isolated model histories, high-level results, and separate durable logs across every target. Its resumed turn initializes a different model and pins the persisted selection, request route, and SDK event sequence. `sdk-minimal-in-history` reuses the persistent-shell and editor scenario with a section that changes after the first successful shell call. `minimal-in-history/prompt-history.json` pins both prompt versions, the unchanged leading prompt in later requests, appended SDK system-message events, and `request/context.systemPromptUpdate`; tool schemas stay fixed and the editor file is checked independently. `sdk-dynamic-tools` pins native tool additions and removals in `dynamic-tools/tool-history.json`, including historical header references and agreement between Python SDK results, notifications, and persisted events. Rerun the owning scenario with `--update-snapshots` and review that diff before committing it.
 
 `scheduler-recovery/` records a failed tool turn and a subsequent completed turn. It preserves the original `UNKNOWN` turn error, the first tool's completed result, and `TOOL_OUTCOME_UNKNOWN` / `TOOL_NOT_STARTED` results for the remaining calls. `sdk-snapshot` and `all` include this case; `--scenario sdk-recovery` runs it alone.