feat(llm): add default context window fallback

.agents/notes/implemented/architecture/2026-07-20-routed-model-context-and-compaction-policy.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-2026-07-20-routed-model-context-and-compaction-policy.md: f0b9288d3d864bfcc2964862b1ff294406daa345
-2026-07-20-routed-model-context-and-compaction-policy.zh.md: cda740a5671a3ef8a5bb415e5cc45ca8397c1c59
+2026-07-20-routed-model-context-and-compaction-policy.md: b637ba24d4ba5fc25c8cdd515a821ee97883a326
+2026-07-20-routed-model-context-and-compaction-policy.zh.md: 084e762ec29ddc0aecb0bf422c147b9d3122726b

.agents/notes/implemented/architecture/2026-07-20-routed-model-context-and-compaction-policy.md

@@ -16,7 +16,7 @@ Neither obvious configuration owner is sufficient. Compact-basic is optional and
 
 `LlmAdapter.resolveModelContext(provider, model)` optionally returns `LlmModelContext` for one exact route. `LlmService.resolveModelContext()` selects the registered route owner, validates a positive integer `contextWindow`, and returns a detached value. The query is independent of `listModels()`: an unlisted dynamic model may have capacity metadata, and `undefined` means only that the adapter cannot describe capacity.
 
-The hand-rolled DeepSeek adapter accepts optional `contextWindow` on each configured model. Its two default model entries publish 128,000 tokens; an explicit entry without capacity and an unlisted pass-through id return `undefined`. The pi-ai adapter resolves capacity from the same catalog descriptor that authoritatively resolves the request model.
+The hand-rolled DeepSeek adapter accepts optional `contextWindow` on each configured model plus an adapter-wide `defaultContextWindow`. Exact model capacity wins; an entry without capacity and an unlisted pass-through id inherit the adapter default, or return `undefined` when it is absent. The two built-in model entries each publish an exact 128,000-token capacity. The pi-ai adapter resolves capacity from the same catalog descriptor that authoritatively resolves the request model.
 
 ### Token measurement remains model-agnostic
 
@@ -36,7 +36,7 @@ An adapter that lacks capacity metadata remains a valid LLM route. Manual proact
 
 ## Testing
 
-Service tests cover detached context metadata, invalid adapter output, catalog independence, and default absence. Adapter tests cover DeepSeek configured/default/unlisted behavior and pi-ai exact descriptor resolution. Compact tests cover ratio scaling, exact provider/model overrides, load-time rejection of invalid merged ratios, runtime absolute-budget validation, same-model-id provider switches, target-specific warning suppression, and capacity-independent overflow recovery. Loader fixtures reject the removed token-meter capacity setting, and examples configure capacity on adapters.
+Service tests cover detached context metadata, invalid adapter output, catalog independence, and default absence. Adapter tests cover DeepSeek exact/default/unlisted resolution, invalid capacities, and pi-ai exact descriptor resolution. Compact tests cover ratio scaling, exact provider/model overrides, load-time rejection of invalid merged ratios, runtime absolute-budget validation, same-model-id provider switches, target-specific warning suppression, and capacity-independent overflow recovery. Loader fixtures reject the removed token-meter capacity setting, and examples configure capacity on adapters.
 
 ## Alternatives considered
 
@@ -51,7 +51,7 @@ Service tests cover detached context metadata, invalid adapter output, catalog i
 - Capacity has one authoritative owner at the provider seam, while compaction policy stays in the optional consuming plugin.
 - The same compact-basic instance safely handles different windows, provider switches, and identical model ids under different providers without consulting discovery metadata.
 - LLM-only and meter-only compositions remain valid; loading compact-basic adds no reverse dependency from adapters.
-- Deployments using explicit DeepSeek model lists must provide `contextWindow` for proactive pressure on those entries. Missing metadata is visible instead of silently applying a wrong global fallback.
+- DeepSeek deployments may set exact per-model capacities, or use `defaultContextWindow` for entries without capacity and unlisted pass-through ids.
 - Ratio defaults scale naturally across models, while exact-target absolute retention remains available for deployment-specific behavior.
 
 This note supersedes the global-capacity and no-model-policy parts of the [replay token meter service Agent Note](2026-07-15-replay-token-meter-service.md). Its single-fold measurement decision remains unchanged.

.agents/notes/implemented/architecture/2026-07-20-routed-model-context-and-compaction-policy.zh.md

@@ -16,7 +16,7 @@ Status: implemented
 
 `LlmAdapter.resolveModelContext(provider, model)` 可以为一条精确路由返回 `LlmModelContext`。`LlmService.resolveModelContext()` 选择已注册的路由所属方，验证 `contextWindow` 为正整数，并返回分离值。该查询独立于 `listModels()`：不在目录中的动态模型也可以拥有容量元数据，而 `undefined` 只表示适配器无法描述容量。
 
-手写 DeepSeek 适配器允许每个已配置模型提供可选 `contextWindow`。两个默认模型项都公开 128,000 token；未提供容量的显式模型项与未列出的透传 id 返回 `undefined`。pi-ai 适配器从同一个目录描述符解析容量，该描述符也用于权威解析请求模型。
+手写 DeepSeek 适配器允许每个已配置模型提供可选 `contextWindow`，并支持适配器级 `defaultContextWindow`。精确模型容量优先；未提供容量的模型项与未列出的透传 id 会继承适配器默认值，若默认值也不存在则返回 `undefined`。两个内置模型项都公开精确的 128,000 token 容量。pi-ai 适配器从同一个目录描述符解析容量，该描述符也用于权威解析请求模型。
 
 ### Token 计量保持模型无关
 
@@ -36,7 +36,7 @@ Compact-basic 拥有消费方策略。顶层字段定义默认值；`modelPolici
 
 ## 测试
 
-服务测试覆盖分离上下文元数据、无效适配器输出、目录独立性与默认缺失行为。适配器测试覆盖 DeepSeek 的配置值、默认值与未列出行为，以及 pi-ai 的精确描述符解析。压缩测试覆盖比例缩放、精确提供方/模型覆盖、加载期拒绝无效合并比例、运行时校验绝对预算、相同模型 id 的提供方切换、目标专用警告抑制与不依赖容量的溢出恢复。Loader fixture 会拒绝已经移除的 token-meter 容量设置，示例则在适配器上配置容量。
+服务测试覆盖分离上下文元数据、无效适配器输出、目录独立性与默认缺失行为。适配器测试覆盖 DeepSeek 的精确容量、默认容量、未列出模型解析及无效容量，以及 pi-ai 的精确描述符解析。压缩测试覆盖比例缩放、精确提供方/模型覆盖、加载期拒绝无效合并比例、运行时校验绝对预算、相同模型 id 的提供方切换、目标专用警告抑制与不依赖容量的溢出恢复。Loader fixture 会拒绝已经移除的 token-meter 容量设置，示例则在适配器上配置容量。
 
 ## 考虑过的替代方案
 
@@ -51,7 +51,7 @@ Compact-basic 拥有消费方策略。顶层字段定义默认值；`modelPolici
 - 容量在提供方 seam 上拥有唯一权威归属方，而压缩策略留在可选消费插件中。
 - 同一个 compact-basic 实例无需查询发现元数据，就能安全处理不同窗口、提供方切换，以及不同提供方下的相同模型 id。
 - 仅 LLM 与仅 meter 的组合仍然有效；加载 compact-basic 不会让适配器产生反向依赖。
-- 使用显式 DeepSeek 模型列表的部署必须为需要主动压力检查的条目提供 `contextWindow`。系统会暴露缺失元数据，而不是静默应用错误的全局回退值。
+- DeepSeek 部署可以设置精确的逐模型容量，也可以让未提供容量的模型项与未列出的透传 id 使用 `defaultContextWindow`。
 - 比例默认值会随模型自然缩放，同时仍可按精确目标使用绝对保留值，以满足部署专用行为。
 
 本记录取代[回放式 token 计量服务 Agent Note](2026-07-15-replay-token-meter-service.md) 中的全局容量与无模型策略部分，单折叠计量决策保持不变。