Document the codebase thoroughly and tighten type safety

Docs: per-folder README.md for packages/ (family overview + one per
package: service, events, API, extension points, TODOs), examples/,
and examples/echo-agent/; folder-level AGENTS.md (+ CLAUDE.md
symlinks) for packages/ and vendor/; module-level doc comments in
every packages/*/src file; richer JSDoc on all exported API
(event side effects, disposal contracts, error behavior). Root
AGENTS.md gains a "Type Safety and Documentation" policy section:
the codebase aims to be very type-safe and well documented; type
gymnastics are acceptable in core packages when they improve
plugin-author DX; verbose docs are fine as long as they stay strictly
in sync with the code.

Type safety: removed the upstream-inherited "noImplicitAny": false
from tsconfig.base.json — packages/* now compile under full strict
mode; vendor/loader and vendor/include set it locally (vendor/cordis
already did). Eliminated every `: any` / `as any` from packages and
examples (catch clauses use unknown + a CodedError narrowing type;
event data access uses discriminated-union narrowing).

Typed tool schemas: new @deepseek-ai/dsh-tools schema DSL —
SchemaSpec with per-property `required: true` booleans, type-level
InferArgs<S>, a runtime SchemaSpec → JSON Schema converter, and
defineTool() so first-party tools get typed execute(args) with zero
casts (raw JSON Schema still accepted for MCP interop; chosen over
schemastery because it targets JSON Schema generation directly).
echo-tool and all test tools migrated; +7 tests.

packages/system-prompt/src/index.ts

@@ -1,3 +1,11 @@
+/**
+ * System prompt assembly registry. Plugins contribute ordered text sections and
+ * tool schema providers; `assemble()` collates them through a waterfall that
+ * runs once per step.
+ *
+ * @module @deepseek-ai/dsh-system-prompt
+ */
+
 import { Context, Service } from 'cordis'
 import type { ToolSchema } from '@deepseek-ai/dsh-llm'
 
@@ -59,7 +67,11 @@ export class SystemPrompt extends Service {
     super(ctx, 'systemPrompt')
   }
 
-  /** Contribute a section. Disposed with the calling fiber. */
+  /**
+   * Contribute a text section to the system prompt. Order is determined by
+   * `section.order` (ascending). The section is removed when the calling
+   * fiber is disposed. Emits `system-prompt/change` on register/unregister.
+   */
   section(section: PromptSection): () => void {
     return this.ctx.effect(() => {
       this.sections.push(section)
@@ -72,7 +84,11 @@ export class SystemPrompt extends Service {
     }, 'systemPrompt.section()')
   }
 
-  /** Contribute tool schemas (evaluated at each assembly). Disposed with the fiber. */
+  /**
+   * Contribute a tool-schema provider that is evaluated at each assembly
+   * call (so it can reflect the live registry state). The provider is
+   * removed when the calling fiber is disposed. Emits `system-prompt/change`.
+   */
   tools(provider: () => ToolSchema[]): () => void {
     return this.ctx.effect(() => {
       this.toolProviders.push(provider)
@@ -85,7 +101,13 @@ export class SystemPrompt extends Service {
     }, 'systemPrompt.tools()')
   }
 
-  /** Assemble the current prompt (sections sorted, tools collected). */
+  /**
+   * Assemble the current prompt (sections sorted by order, tools collected
+   * from all providers). Runs through the `system-prompt/assemble` waterfall,
+   * giving listeners the opportunity to mutate or replace the assembly before
+   * it reaches the model. Await the result before reading the assembly values —
+   * waterfall listeners may be async.
+   */
   assemble(): Promise<PromptAssembly> {
     const assembly: PromptAssembly = {
       sections: [...this.sections].sort((a, b) => a.order - b.order),