[Bug / patch available] Third-party plugins can rewrite the deployment default through session.selectModel (dsh-im case)

[yingyu4451]

Summary

session.selectModel applies the accepted ModelSelection to the addressed session and calls saveDefaultModelSelection() for the shared Agent default (see .agents/notes/archived/feature/2026-08-07-default-model-follows-the-picker.md). For the Web picker this is intended: the picker is the editor of the deployment default.

The same Remote is also the only way for integrations to apply a model to a session they created. So a third-party plugin that sets "the model this bot should use" silently rewrites the deployment default for every session created afterwards, in every workspace, including sessions the plugin has nothing to do with. The design note's justification — the picker and the future-session default are one user preference — does not hold for that caller: the user never touched the picker.

Concrete effect: a Feishu bot model card set to deepseek-flash / High flipped the GUI default for new conversations from Max to High; for the next ~28 hours every new conversation in my workspaces started at High. I hit the same thing earlier through the QQ bot card.

Environment

• DSH 0.2.1-rc.2 (dsh-v0.2.1-rc.2), web profile, Windows 11
• Plugin: @xmanrui/dsh-im 5.4.0 (community IM bridge; applies its bot model setting through session.selectModel)
• Affected setting: ~/.dsh/profiles/web/cordis.patch.yml → agent-default-model.reasoningEffort

Reproduction (from session logs, +08:00)

1. 2026-10-23 18:55:21 — Feishu bot model card set to deepseek-flash / high. dsh-im only writes ~/.dsh/integrations/dsh-feishu/workspaces.json; the DSH profile is untouched at this point.
2. 18:56:01.716 — dsh-im creates a new Feishu session (session-f077d147).
3. 18:56:01.759 — model/selection {provider: deepseek-official, model: deepseek-flash, reasoningEffort: high} recorded in that session: the bot card applied through session.selectModel.
4. 18:56:02 — agent-default-model.reasoningEffort in cordis.patch.yml becomes high.
5. Every session created after that instant starts at High: its first request/header carries reasoningEffort: high even though nobody opened the picker. Sessions that already logged a request keep their own selection (as designed).

Expected

A programmatic caller should be able to apply a model to the session it owns without moving the deployment default, while the GUI picker keeps being that default's editor.

Patch available

SessionSelectModelRequest gets an optional saveDefault?: boolean; the background saveSelection() runs only when it is true. packages/client/ui-model-selection/src/client/directory.ts passes saveDefault: true for both entry points (composer control and /model popup), so the picker behavior and the design note stay intact; integrations that omit the flag become session-local.

• Fork branch: https://github.com/yingyu4451/deepseek-harness/tree/fix/session-model-selection-save-default
• Commit: 805a2c54d9 — "fix(session): keep model switches Session-local unless requested"
• Compare: https://github.com/deepseek-ai/deepseek-harness/compare/master...yingyu4451:fix/session-model-selection-save-default?expand=1
• Files: packages/api/session-controller/src/{types,commands,index}.ts, packages/client/ui-model-selection/src/client/directory.ts
• Tests: session-models.host.spec.ts — the two existing default-save specs now pass saveDefault: true; a new spec proves an omitted flag leaves agent-default-model untouched while the selection still applies to the session.
• Docs: session-controller README (en/zh), ui-model-selection README (en/zh), regenerated docs/subsystems/session.md and Cordis catalog, upgrade guide docs/upgrade-guide/v0.2.1-rc.2/session-model-selection-local-by-default/.
• Verification: vitest run packages/api/session-controller/tests packages/client/ui-model-selection → 46 files / 1070 passed / 1 skipped; pnpm run typecheck → 5 gates passed; verify-cordis-catalog, verify-md-links, verify-upgrade-guides green.

Tradeoff

This changes the Remote contract for callers that relied on the implicit default save: they must pass saveDefault: true. Session format, credentials and permissions are unchanged; the GUI behavior is unchanged.

Related: #10316 (the same coupling reached through the picker), #10597 (community patch format).

Maintainers are welcome to review or cherry-pick it.

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中文摘要

session.selectModel 在把选择应用到目标会话的同时，还会把它写成部署默认（agent-default-model）。对 Web 选择器而言这是设计意图（选择器就是默认值的编辑器），但第三方插件也通过这个 RPC 给会话设模型：飞书机器人卡片设为 High 后，新建 IM 会话的那一次 selectModel 把部署默认一并改成 High，此后所有新对话都从 High 起步（约 28 小时）。补丁给请求加可选 saveDefault：仅在 true 时后台保存默认；GUI 两个入口传 true，插件不传即只影响本会话、不改动其他对话。维护者可 review / cherry-pick。